I think this guy is wrong. There would be No wind over the wings, If the conveyor belt moved at the exact same speed as the wheels. The plane Has to move forward, in relation to the ground, to get lift. As long as the plane is On it’s wheels, the conveyor belt would negate its forward motion. If not, why do planes even need runways? Could just build a large dynamometer, and planes could take off without moving forward.
@@stevehackett2678 it's more the case that a plane will act as if the conveyor isn't there. when you drive a car the engine moves the wheels along the road. when you fly a plane it move the air through the jet or propeller. you have to imagine that the air is the planes' road and the mode of propulsion is the wheels equivalent .If say instead of wheels a plane had skis and a flat icy surface, it'd move forward and eventually take off as normal.
@@stevehackett2678 The plane is not "fixed" to the wheels due to the bearings. The wheels are not the driving force. No matter how fast you spin the wheels, the engines will still see the air as standing still and thus create thrust. If you have thrust, you have forward motion. It's a plane, not a car...
@@stevehackett2678 You’ve basically just restated the problem. But the conveyer belt moving backwards (and the wheels spinning backwards) has no effect on the plane’s forward motion, as the forward thrust is provided by the engines and not by the wheels.
@@stevehackett2678 The plane does NOT have to move forward in relation to the ground in order to get lift, it has to move forward in relation to the AIR. So regardless of what it's wheels are doing it will still move forwards and gain lift - just as it normally would. It will travel the same distance forwards, and it will rotate at the same point it normally would. The ONLY difference is it's wheels would be spinning faster than they usually would, that is all.
The riddle is that you can't in reality make a treadmill that matches the speed of an airplane wheels. The wheels don't propel the plane, they just respond to the relative motion of the plane with the ground. Which means if you move the ground (i.e. treadmill), the plane or it's wheels don't know the difference. The plane will just move forward through the air not caring what the wheels or ground are doing.
My thoughts exactly. The wheels are not what's propelling the plane forward. They are just free-wheeling. As the plane picks up speed, the wheels would spin faster than the plane's forward movement would indicate, but other than that they would not in any way influence the plane's acceleration. Maybe a few tires would blow because they are spinning much faster than their designed limits, but it would not prevent the plane from taking off.
A easier to think about situation that is equivalent is placing a trailer on the same treadmill and pulling it off with a car in front. It moves (or the tires explode if the treadmill can go that fast). Now replace the trailer with a glider being pulled with a cable. It starts moving and takes off. And finally an airplane being pulled (or pushed) by it's prop or jets. In all those cases, the thing being moved is being moved by a force applied not though the wheels, so they are basically the same, so the airplane will move as well.
@@robertwatson818 The engines push the plane forward through the air (regardless of what the wheels are doing). The wheels on a plane are simply free-spinning bearings to allow the plane to "roll" on the ground, they have nothing to do with propulsion.
@@robertwatson818 but there will be because the airplane WILL move forward. The THRUST propelling the aircraft forward does not care that the conveyor is moving backwards. The wheels are free spinning. Make the conveyor move as fast as you want, the wheels will simply spin faster until the bearings or tires explode. The plane WILL move forward because the force propelling it will be exerted on the AIR, not transmitted through the tires to the roadway as will a car. Only if the combined friction of the free-spinning wheels overcomes the force of thrust would the aircraft not move forward and again, at that point you would have blown up your landing gear.
Wheels are not free spinning, they have friction, if the plane is not already flying, the friction will create drag, that's where the first part leads to (however you won't have infinite friction since the pressure downward is constant, is that enough to prevent the plane from take off we simply don't know, because the threadmill would overheat before it can reach that)
Joe, I’m pretty sure the wheels in scenario 1 would spin up exponentially and presumably explode but don’t think it would have a significant effect on airspeed any more than scenario 2.
Scenario 1 is an impossible (and absurd) theoretical/mathematical scenario; v(ground) needs to be >0 to create airspeed, but for that to happen v(wheels)>v(belt) which the text says is impossible (they're alway the same)... both conveyor and wheels will reach infinite speed in t=0 (infinite acceleration) and break the equations.
@@paolodalbono Agreed, but assuming the answer to the riddle is meant to be "Yes." or "No." rather than "Exploding infinity tires." - and keeping in the spirit of the problem - even if you adjust the conveyor belt to something reasonable, you still have what the Mythbusters already did in small and full scale. Even if you say the conveyor belt gets to accelerate twice as fast and to twice the take-off speed, right to just before the tires fail - which is presumably double the parameters of what this riddle is asking, the plane still takes off pretty effortlessly.
I mean it really is basic mechanics. Velocity in one direction with an equal and opposition direction in the other. You're net velocity would be zero. You can't achieve lift if you have no forward momentum.
@@cshoffie6593 it's the problem with the interpretation of the question. Captain Joe already explained both interpretations in this video. Mythbusters simply followed the 2nd scenario, while most people think the 1st.
Planes without wheels take off, as do VTOL aircraft, as can a aircraft with sufficient headwind without moving forward - a good pilot knows that takeoff and flying has nothing to do with ground speed
@@davidioanhedges I understand that, but the riddle isn’t about VTOL aircraft or a headwind sufficient for lift. It’s a hypothetical scenario of the wheels being cancelled out by the conveyor belt. Wheels obviously affect the movement of the aircraft while on the ground. If you have your brakes on, it’s going to be very difficult if not impossible for the aircraft to move to generate lift. So, considering you’re not in a VTOL aircraft and you have zero headwind, and if the wheel speed is being matched by a conveyor belt in the opposite direction, without delay, the aircraft cannot move. The confusion about this is a result of people adding variables to the riddle that shouldn’t be there.
@@cshoffie6593 Yes, but the brakes *aren't* on when the airplane is trying to take off. Given the lack of brakes, the only affect the wheels have on the plane's horizontal movement is a slight friction effect. So, yes, the conveyor belt will *slightly* slow the plane, but not enough to keep the plane from taking off.
The real question to answer here is "how does the airplane stay flying once the wheels are off the ground?" Once you know the answer to that, its easy to work the problem out.
The plane is pulled forward by the engines. Once you reach a high enough ground speed, the plane lifts off. Independent of underground and wheel speed. Although the wheels would in this case explode.
Simple thermodynamics, my friend. :) All mechanical systems boil down to energy in = energy out. In this case: thrust = friction. At infinite speed, the friction of the wheels will remove infinite energy from the mechanical system. Also, the conveyor is defined as matching the speed of the wheels. Any forward movement of the airplane with respect to the ground violates this definition.
@@c182SkylaneRG incorrect, if your going to try to pull that crap then you failed. Under no point in the question did it state the rotational speed of the wheels. Therefore the only logical assumption is that it is match the forward motion of the wheel itself. Your trying to selectively add things into the question. If I asked you the speed of a tire that broke lose from a moving vehicle noone would give you its rotational speed. This is a common issue with technically educated people and commonly worded questions. You destroy the spirit of the question by adding in stuff not present into the question. I mean why would you add in that if the pilot would apply a little bit of steering then you'd have wheels moving at different RPMs and the belt would therefore enter into a paradoxical state where it would need to be moving at multiple speeds at the same time. Basically this is equivalent to the mathematician that argued 2+2=5 could be true because it theoretically could be 2a+2b=5c or maybe some other hidden or non presenting variables or perhaps a variant numerical system.
@@nicolivoldkif9096 The term "wheel speed", lacking any other description, means the speed of the wheels across the ground, which is taken at the hub/axle. In this scenario, that would be the speed of the wheels relative to the conveyor belt. Their rotational speed is translated to a linear speed based on their diameter, which can only be in reference to the surface they're rolling on (the conveyor). Any good pilot starts on the center line of the runway, and stays on the center line of the runway. No self-respecting pilot takes off cock-eyed with respect to the runway centerline. Be realistic. :D
I think this question was thought up to highlight the difference between how a car is propelled down the runway and how an airplane is propelled down the runway. As such it is a thought problem and would work better (less confusion) if it was explicitly idealized. My suggestion is to include in the problem statement something like "consider the wheels themselves to have no friction in their bearings, no rotational inertia, no rolling friction, and no residual drag in the brakes when they are released." (visualize them to be something like a bicycle's spoked wheels with zero mass, and no brakes at all." LOL (also utterly indestructible). The question seems to me to be, then, "how can this conveyer belt runway PULL on this idealized airplane?" My answer is "it can't" - run the conveyor belt as fast as you want, all that will happen is the wheels will spin. The inertia of the airplane (tendency to resist changes in velocity) will keep it sitting there, until the throttles are advanced. With 4 big engines attached firmly to the body of the airplane it would accelerate down the runway with no trouble at all and take off when its airspeed reached the value to start rotation. However, if the wheels are given mass, and the conveyor belt runway is given access to unlimited energy and power, then pulling on the bottom of the wheels will actually transmit some force onto the body of the airplane (as well as give the tire rotational kinetic energy) and with infinite energy and power the conveyor belt would win.
Even if the wheels have only just enough friction from the ground to prevent slipping, the energy it takes to rotate them is coming from the engines. You can't just disregard the wheels because they are stealing all the energy you need to move the whole aircraft forward.
Yes, if the movement of the wheels is initiated by thrust, then the plane would take off. The thrust is not related to the wheels. The jet engine is not pushing against the ground. The travel distance before rotation airspeed/Vr would be similar to a normal takeoff. In this scenario the tires would be turning faster but the plane would still be moving forward through the air opposite of the thrust, thus generating lift. The wheels only contribution during takeoff is to mitigate friction between the aircraft and ground. They do not propel the aircraft during takeoff. Maybe this will help: if I hold a non powered toy car on a treadmill with my hand while the treadmill is running I can still make the car move forwards and backwards even if the treadmill were to instantly speed up/slow down as I moved the car forwards/backwards. In this case I am the jet engine and the wheels aren’t the source of power.
See, it's the qualifier of the conveyor belt exactly matching the speed of the tires with no delay. For this to be true, to take your car example, if I tried pushing the car forward, I would see (and probably hear) the tires and treadmill speed up proportional to how hard I push, but the car would never move forward - that would require the tires to move faster than the conveyor belt. It would be like an invisible, equal, and opposite force, pushing against me. I could even pull on the car until the treadmill and tires are at rest, I could pull even more and make them rotate the other way, but the car would never actually move. To actually move its position relative to the treadmill would be to break the requirements of the scenario with regard to the treadmill. It's not possible, but given the premise of the conveyor, the rest of physics would need to accommodate it. The aircraft will never produce enough thrust, regardless of means, to gain any relative airspeed (or true, or ground, or any motion period for that matter), for it would break the rule of the conveyor. The only way I see a possible takeoff is with headwind equal to or greater than rotational airspeed, or if the engines produced enough of a vertical thrust component to separate the aircraft from the conveyor, or if a hypothetical aircraft is constructed in such a way that the exhaust airflow is sufficient and positioned in a way to impart effectiveness on the control surfaces/wings, which sounds really goofy to me but maybe somebody can tell me if that's even possible or not.
@@dogboy0912 "It would be like an invisible, EQUAL (emphasis mine), and opposite force ,pushing against me". What force? Why equal? In the toy car example, the wheels would have to overcome a marginal amount of friction as they turn around the axel and where they make contact with the treadmill. Are you suggesting that I could not push the car forward as a treadmill was speeding up, even if instantly? Other than the weight of the car (not even the full weight because of the wheels) and a small amount of friction, what force would I have to overcome? Let's say I push the car forward with 50 pounds of force from my arm which I could easily do. What force is going to push back against me at 50 pounds?
Yes. The bearings in the landing gear will break their rolling elements if the wheels spin too fast. The centrifugal effect causes the rolling elements to load the contact force between the outer race and the rolling elements, and when that contact force exceeds the limiting strength of the materials, the rolling elements and outer race will rupture.
Something that’s not clear is where the lift is coming from, are the engines sending air under the wings or are they pushing the plane forward which makes air rush over them to create lift?
the wheels and treadmill are a red herring in this scenario, it doesn't affect the thrust produced by the engines which determine the airflow and thus lift. That is why Air Speed is important in flight, and not ground speed
You are just wrong. No one is saying the conveyor belt affects the thrust produced, but the basic geometric fact at the centre of this issue is that if the contact patch of the wheel is moving backwards at exactly the wheel speed then the net velocity of the wheel MUST be 0, literally just google "velocities on a wheel". You'll see that in every single case where the bottom of the wheel is moving backwards at the wheel speed that the centre of rotation has a velocity of 0. 0 velocity means no air speed beyond that of the wind, and wind isn't gonna make a 747 take off
@@szilveszterszalai230 if the wheel speed and treadmill speed ate identical literally by definition the plane can't be moving forward, if the plane is going forward then wheel speed is exceeding treadmill speed and you've completely ignored the question, set up your own different question, and claimed the correct answer to the original question is wrong 🤦♂️ that is the level of stupidity you are at, someone said 2+2=4 and your answer was "nO oNe PlUs OnE iS tWo"
You completely misunderstand, the wheels definitely do matter. If they didn't then breaks wouldn't work to slow the aircraft down. With the runway spinning faster and faster to match the speed of the wheels and with no slipping the aircraft isn't going anywhere.
It’s amazing that someone can be so confidently wrong. As the wheels spin freely and independently of the plane, the jet thrust will move the plane forward and the wheel/conveyor speed with increase as the plane moves along to take off velocity. Because the wheels of the plane spin freely, they can essentially be ignored.
The plane has to rest on the ground when the engine is getting up to speed. The conveyor belt will influence its movement. As the plane creeps forward, the belt pulls it back, so it never gets a chance to accelerate to a speed to generate lift. This is different from a frictionless surface, where wheels do no matter. The wheels can spin freely and the plane can still take off. This is where the ground actively pulls you back when you try to creep forward, hence u will never gather enough speed to lift off
@@parrotbrand2782Just how does the ground pull the plane back? The ground/belt and the airframe have no fixed connection in the direction of travel. In fact, a reverse-running belt will spin the plane's wheels FORWARD!
@@jrunsvold7150 Right, friction is the key. I'm really frustrated that neither those arguments nor those counter arguments is taking friction into account, which is the only way to make things clear. But to cancel the thrust of the engine, we need the same amount of friction, which I don't know if is actually possible (something tells me this is not going to happen in real life. I would still call this theoretically possible though.)
@@jrunsvold7150 ever seen a travelator at an airport? Think you could push a trolley along it in the opposite direction? Of course you could. It just needs enough power.
@@Xiaotian_Guan problem is the plane has wheels, and in an ideal situation (which is fair to assume since we have a conveyor belt the size of a big ol plane) the wheels are frictionless so the movement of the wheels exerts no force on the plane itself, it just spins the wheels. The wheels can't exert a force on the plane, so therefore it doesn't hold it back at all
The speed of the vehicle is only due to rolling. The explicit constraint of this exercise is that rolling speed is exactly neutralized by the magical adaptive nature of the conveyor. That’s why he gave the follow-up example if the conveyor had a steady speed which could be overcome by an acceleration (thrust or increase automobile speed). He explained it correctly.
@@MrDefreese That's my prediction not a counter, also if rolling resistance is greater than the thrust the wheels don't turn, the conveyor would thus be still and plane goes nowhere. Its like trying to take off with the park brake on.
@@MrDefreesethe speed of the vehicle is not due to rolling of wheels. The thrust of engines is pushing the plane forward. How would the belt create a counterforce to that if wheels are rolling freely?
@@psychosis7325 not correct. The wheels just roll along on the surface. The wheels don’t seize in place. He shows this in his first animation of the scenario.
@@Jashtvorak the vehicle only moves forward by rolling on the surface. You are given the express condition that the surface is moving at the same speed as the wheel which is exactly the vehicle speed. They are one and the same. For extra thought projects, we could resolve the force involved for such a conveyor. It is obviously impractical and out of the bounds of normal engineering design.
The issue is the interpretation of 'matching'. The sane interpretation is that 'matching' happens no matter what speed the wheels go, because 'matching' is a functional result of the mechanical contact between the wheels and the conveyor belt. In other words 'matching' means 'synchronizing to' not 'going as fast as'. But, since the rule demands compliance from the conveyor belt, not from the wheels, the interpretation doesn't even matter. If the conveyor belt runs afoul of physics, that is its problem, not the airplane's problem or the wheels' problem, thus the plane will happily ignore the logic explosions consuming the treadmill and take off regardless.
The 747 can only take off if the airflow over the wings is sufficient to provide enough lift. So the 747 must move forward at takeoff airspeed, regardless of the surface being a runway or a conveyor belt.
👍@stmounts You have put your finger on the pulse when you state that relative movement of air over wing surfaces causes lift. The conveyor belt and engines are not the elements which generate lift. Only the foreward motion of plane (with the help of the engines, etc) generates a pressure differential on 'curved' surfaces to create lift. How else does
@@waddup2336 Your understanding of how lift works vs thrust is not even close to how it actually works, if the plane moves the throttles forward and the wheels start to move from the ground speed of the plane starting to move, but then the conveyor then perfectly matches the speed of those tires for ground speed, so no the plane in no longer moving forward or backwards, how to the planes wings which have to have airspeed flowing around them to produce lift, produce lift if the plane is not moving at all on the ground so no lift is being produced by the wings? When the engines produce the thrust to get the plane moving on the ground to speed the plane up so the air around the plane is producing lift on the wings, the ground speed is then completely stopped by this conveyor that now puts the planes ground speed to 0 which then means there is no airspeed being produced for the wings to create lift. Just because the engines of a plane done care what happens on the ground does not mean that the wings can produce the lift from having no airspeed to then convert to lift as the plane that is on the ground has to have forwards movement to create the airspeed required for the wings to get the lift needed, but if the forward movement is 0 because the conveyor is now keeping the plane still, which makes the airspeed 0 over the wings, which means 0 lift is now being produced to have the plane take off.
There is nothing I enjoy more than pilots that don't know how airplanes work. If the plane isn't moving forward then the wheel speed is 0. Treadmill speed is zero. What is countering the thrust of the engine. The wheels only rotate if the plane moves forward.
IKR? When the 747 starts moving at 1 kts from the engine thrust, the conveyor moves backwards at 1 kts, so the wheels are spinning 2 kts. So 80 kts forward speed from the engine, 80 kts backward from belt, wheels spinning at 160 kts. At 160 kts from the engines forward, the 747 can rotate to take off. The belt is going backwards at 160 kts and the wheels are spinning at 320 kts. The wheels don't drive the 747 forward, the engines do, which even this pilot messed up.
I think the aircraft would take off in the first scenario as well. Both wheels and conveyor belt would reach speed of light and acts as a brakes but the conveyor belt would also create a headwind strong enough to lift the plane.
But nothing with mass can reach the speed if light, because it would require infinite energy. I'm pretty sure that the bearings would give up first, or the tires would explode
No one said the engines were on. Also, substitute skis for wheels, is there any difference? The simple answer is there needs to be enough airflow across the wings to create lift.
The wheel speed matching the conveyor is the key to solve this. The plane is sitting on the conveyor neither the wheel or the conveyor is moving. Now start the jet move 1 rev of the wheel now the plane has moved forward and 1 rev of conveyor is now behind the wheel. The real question is how fast the conveyor is moving. The answer is it is not and never will. That is the trick of this question.
But it doesn't matter . What matters is the TAS. And if the aircraft has a GS of 0 it means that there is no wind flow over the wing for them to be effective . So a plane on a conveyor belt would be the same as if it applied full throttle and applIed the brakes it just won't take off .
@@mojojojo3852 the engines and only the engines provide the forward thrust, even it was a plane on ski's, on floats, on 'wheels on a conveyor belt', it doesn't matter as long as it does not prevent the aircraft from moving (=attaching it to chains or putting large concrete blocks in front of the wheels - normal chocks won't do the job). If the conveyor belt was moving forward with the same speed, the wheels would not rotate and the aircraft would take of as normal. With the belt running backwards, the wheels will spin twice a fast (only marginally increasing wheel/axle friction) but the aircraft will 'thunder' along the runway thrusted forward by the engines. Maybe the tires will deflate because rotational speed is well above it's max. rating of somewhere around 220+ knots (but that is a different discussion).
@@DIBOYOU not really comparable with ski's or floats. If you stop the engines, the plane will go backwards due to friction belt/tire, because the plane has a weight that pushes down on the belt. So a part of thrust will be consumed just to make the plane still compared to ground. You will never be able to reach take off speed, because you'll always have this conveyor speed to compensate. What you say works if the plane weight is equal to zero.
@@pik2005 Not true, there is an accident investigation of a DC8 (I think) which had it's wheels frozen and on the slippery runway the aircraft started it's take off movement almost as normal. but given the enormous friction, it failed to take off. In this conveyor example, the wheels will only have minimal increase of friction in it's axles. The take off roll and speed will increase slightly, but as long as the axles don't seize completely due to overspeed, the aircraft will get airborne. If the conveyor belt turns in the other direction, the take off run will be marginally shorter, but the airplane won't lift of like a helicopter even with it's wheel not rotating at all. So yes it is comparable with ski's, floats, etc. all have different gradients of friction, but absolutely far less than the (jet) engine thrust
That is simply false, the net velocity of the plane while grounded is always going to be Vplane = Vwheel + Vconveyor, and since in scenario 1 Vconveyor = -Vwheel then Vplane = Vwheel - Vwheel == 0, i.e. the plane cannot ever move if the conveyor perfectly matches the wheel speed continuously as it cannot get any air speed. To make it clear that the equation for the planes velocity is as I have stated simply consider the scenario when Vwheel = 0, and the plane just moves along with the conveyor at the same speed, then consider the case when Vconveyor = 0, as the wheels roll freely they will match the planes speed perfectly
@@ClikcerProductions Is not the wheels turning what's moving the plane forwards while on the ground, it's the push from the jet engines or propeler, so what may happens is the wheels and the conveyor belt may continue accelerating, but the plane will move forward.
@@omargj1 If the plane moves forward the wheel speed is greater than the conveyor speed, so no, given we are literally told that the conveyor speed always matches the wheel speed it doesn't move forward, it has nothing to do with how the plane is driven, since the forward force from the jets is being matched perfectly by the backward force imparted by the accelerating conveyor belt. This is literally how the thought experiment is defined, if you disagree you are just ignoring the experiment and doing your own unrelated BS
@@ClikcerProductions The wheels have nothing to do with moving the plane forward beside having something to make it easy to move reducing friction with the ground, the plane moves by pushing air backwards, not by making it wheels turn, even the conveyor belt can be moving backwards at 3000, 5000 mph, or kph or any speed you want, the plane still would be able to move forward.
@@omargj1 If the plane is moving forward then wheel speed is exceeding conveyor speed, directly contradicting the stated conditions given, congratulations, you failed
It’s simple physics. The answer is in the riddle itself. Wheel speed the same as the belt. A plane will NEVER take off with that variable. It will ONLY take off if the wheel speed is greater than the belt (aka forward thrust pushing it along) It’s a question that gives you the answer by giving you an illogical physics problem
With this logic on the conveyor belt, it doesn't mean anything as you could ramp the conveyor up to 10x the speed of the plane in the opposite direction and yet the plane would still move forwards
Yes, however... he explains this in the second half of the video. The belt they used was meant to match the ground speed of the plane. And ... given the technology... they could not match the wheel speed *instantly and exactly.* The problem is more.with semantics than anything.
@@gitbse Yeah, but in that case the answer to the riddle should be that such theoretical conveyor belt would instantly generate friction on the wheels equal to thrust. Only that would prevent the plane from moving. It's a pretty pointless riddle.
@@eliass.4743 This whole “plane on a treadmill” thing dates back to the early 2000’s and was one of the first viral internet events. It spawned many a virulent argument that totally consumed message boards at the time.
I still think that this explanation is wrong. The plane will move throught the air. The wheels just spin at both speeds (air + conveyor belt) and the will move until is plane airspeed and lift
▓▒░ I paused this video and thought about it for -an hou- a few minutes. If the conveyor belt is moving in the *opposite* direction at the same speed as the wheels are, this means that the aircraft isn't moving toward the wind. In other words, it's standing still. It would be a miracle if it does take-off. ` Today is Saturday, the sixty-fifth day of the year two thousand and twenty-one. ░▒▓ `
How does a float plane take off against a current? Does the water direction pushing backwards stop you from taking off? The answer is no. Your ability to take off is only governed by the your airspeed. The plane pushes on the air not the water.
If the ground is moving, it is possible of course for the plane to move even if the wheels aren’t spinning or are even spinning backwards. The plane can push against the air directly, so it makes no difference which way the wheels are spinning. The only reason the wheels spin is the difference in speed between the axle and the ground beneath them, the freely spinning whee has no significant effect on the speed of the axle or the ground beneath it.
A little scary the pilot in this says first scenario wouldn't take off since wheel spin is only a reflection of airplane movement. The plane will always take off as the wheel has nothing to do in this scenario with thrust or plane speed.
If I'm on a treadmill on roller skates holding a rope my wheels will match the speed exactly, but if i pull on the rope I move forward. The engines are pulling the plane forward, the belt will not stop the plane from moving forward, the plane always takes off
you're assuming the treadmill's speed is always the same. the riddle's premise is that as you pull on the rope, the speed of the treadmill will also increase
@@jbt816but that won’t change anything, if the treadmill is going 20mph and you pull yourself forward at 1mph and some increases the speed of the treadmill at the same time you will still pull yourself forward at 1mph. The speed of the wheels and treadmill is completely irrelevant.
@@jagheterbananyou will pull your torso forward, but the conveyor adapts to the increased wheel speed and still results in the ‘wheel axle’ remaining static. That’s the whole point of the unintuitive example of the conveyor speed matching rolling speed. You would essentially tip over forward.
@@MrDefreese The wheels are attached to the roller skates with bearings essentially disconnecting them from you so no you wouldn’t tip over you would just increase the speed by which the wheels are turning. This of course brakes the premise that the wheels and treadmill are supposed to be going at the same speed, the only way to keep that premise is to not move i.e. not pull the rope. If you translate that to the airplane it would mean you can’t increase the thrust, so yeah an airplane that you’re not applying thrust to won’t takeoff but it’s not really because the conveyor belt is stopping you.
@@jagheterbanan the wheels and treadmill moving at the same speed means the position of the wheel never changes. The force applied by pulling the rope does mean that part of the body moves. We could do fun body deformation experiments with that - rigid body, flexibility at the waist, etc.
No because there is no windspeed. There is groundspeed but the windspeed is none. I don’t know why you said yes because you understand the concept but I assume you already watched the video.
@@AndreasRSD Nope, there's nothing the conveyor belt can do to stop the plane moving forwards, all it will do is cause the wheels to be rotating faster than they normally would at the point it takes off. I watched the vid, and I also watched the mythbusters vid, where they actually tested it with a real plane, and it took off with no problem.
@@AndreasRSD He's playing on the wording of proposition. If there is a strong enough wind that goes on the opposite direction that has enough force to generate lift and the engines can use it push enough thrust, so Yes it can. There are bush planes that can take off with as little 3 feet of ground because of the strong wind in the wildeness. Though the conveyor belt runway is useless and didn't contribute anything to the take-off. As Captain Joe pointed out, the question is tricky.
@@LeoH3L1 They used a small bush plane for that experiment, not a 747. Even a empty 747 will require a certain forward speed or a certain airspeed to generate lift. If the 747 cannot generate enough forward thrust to counteract the trend mill and cannot move forward, it will not take off. I love how people cite myth busters as some sort of gospel. Adam sucks. Long live Jamie.
Yes it will move forward and take off! But only due to thrust from the engines... The conveyor belt's velocity is completely irrelevant, since the wheels are not powered!
@@moebekdache3756 Yes it is. How does an airplane is supposed to fly once in the air? Once the wheels aren't touching the ground anymore? Engines push the plane forward, regardless what happens to the wheels
@@stevenfpv2345 So are you saying, that if 2 forklifts lifted the plane either side by the wing, let engine hit full power, then back the forklifts away, the plane will then go?? Correct me if I'm mistaken
ChatGPT: Airplanes take off by accelerating to a speed that provides enough lift from their wings to overcome gravity. The speed of the wheels on the runway is not directly relevant to the plane's ability to take off. If the plane's engines are producing enough thrust to move it forward, and the wings are generating sufficient lift, the plane can take off. In the case of the conveyor belt moving in the opposite direction to the plane's wheels, it won't prevent the plane from taking off. The conveyor belt might make it more challenging for the plane to start rolling, but once the plane's engines provide enough thrust, and the wings generate sufficient lift, it will take off as usual. The key point is that the thrust from the engines and the lift from the wings are what enable an airplane to take off, not the speed of the wheels relative to the ground.
The speed of the conveyor will always match the speed of the plane (in the opposite direction) if the conveyor is meant to exactly match the speed of the wheels. He tries to draw a distinction between the hypotheticals “conveyor belt matching the wheel speed” and “conveyor belt matching plane speed” when there is none. As long as the wheels aren’t sliding for some reason (friction/ breaks), they’ll be in contact with the conveyor which means they’d be matching its speed. So, saying the conveyor belt matching the wheel speed is the same as saying it’s matching the plane’s speed. Think about it as the top of the wheels moving it the direction plane is moving (at that speed) and the bottom, in the direction the conveyor is moving (at the conveyors speed). Those speeds added together equal the rotation speed of the wheels. So the conveyor matching the speed of the wheels spinning would mean it’s also matching the speed of the plane. This is how circles works. The only good point here is the mention of the max wheel speed. If the wheels couldn’t spin fast enough (they’d only have to spin twice as fast as they would on a static runway since the runway in this case is moving backwards at the same speed the wheels and plane are moving forward) then yes, that friction would prevent the plane from gaining enough speed to provide lift (air flowing over the wings fast enough).
I am pretty sure third law of Newton is at play here, eg, the engines push air backwards so the plane must move forward. The speed and direction of the conveyor belt is moot. But perhaps the riddle might indicate the the engines of the plane are not at full trust if you read the riddle in some way?? . At least I would expect full trust in the riddle, wouldn’t you not? Or is perhaps the riddle not complete?
@@bibaso12 if the plane takes off then the wheel speed is not matching the conveyor belt speed so you are talking about a different problem than the one in the original question.
Engines provide a force of thrust which is matched by the rolling friction and air friction of rotating wheels. If a plane move forward you are no longer satisfying the conditions in the question - the wheel and conveyor speeds are not matching.
@@tomaz2007 Which is why that isn't the spirit of the myth, is a deterministically dumb way to argue it because it presents a rule that violates physics to achieve a desired outcome, and is thus about as meaningful as arguing whether or not my imaginary superhero can beat your imaginary supervillain. The original intent of the question was "Can a plane can takeoff on a treadmill going equally as fast in the opposite direction." Mythbusters effectively demonstrated the concept which was bounded within reality. Plane is stationary relative to ground under the treadmill: Plane Vground = 0mph Vtreadmill = 0mph Vwheel = 0mph Plane starts throttling the engine: Plane Vground = 1mph Vtreadmill = -1mph Vwheel = 2mph Plane is now barreling down the runway about to takeoff: Plane Vground = 100mph Vtreadmill = -100mph Vwheel = 200mph
“The airplane has to move forward relative to the ground”. Do you think that you had a headwind equal to Vr you couldn’t take off? That ground speed, rather than TAS or IAS is what governs flight dynamics? Really? If the engine is generating thrust, Newton tells us the plane moves forward. If not, where is the equal and opposite reaction? All the conveyor belt is doing is spinning the wheels up at double speed. I am confounded that this experiment has been done and it was proven the plane takes off, but some people ignore experimental evidence because it conflicts with their (faulty) understanding.
Discaimer: I understand in practice (speed of belt = ground speed of plane, or any other higher reasonable speed the wheels can handle) the plane would take off no problems since the engines of a plane are not dependent on the wheel speed. The main issue in this ridle is as you wrote: "All the conveyor belt is doing is spinning the wheels up at double speed." Since the ridle says that belt matches the speed of the wheeels exactly it is now mooving at double speed also. So the wheels are moving at triple speed now. Belt matches and wheels are at 4x speed. Belt matches and so on. This has only 2 solutions: Wheel Speed = 0 - plane not moving so it does not take of. Wheel Speed = infinity - Wheels explode, plane on fire due to friction, black hole forms when speed reaches speed of light, either way plane propably not taking off... The riddle as witten just messes with math a little. From physics we know speedOFwheels = speedOFbelt + airplanegroundspeed. But since the ridle says speedOFbelt = speedOFwheels that is only possible if airplanegroundspeed = 0.
I'm with you! I'm embarrassed to admit that I, incorrectly, thought the plane wouldn't be able to takeoff when the Mythbusters conducted their test. I'm a lifelong aviation enthusiast and huge fan of Capt. Joe but disappointed that he got this wrong.
I disagree on your first answer that it will not move forward and take off. Ideal scenario: the free wheel should be considered as a roller with no friction. If you draw the free body diagram, the only force acting on the body is going down which is force due to weight. Even if the ground is moving in whatever direction in whatever speed in whatever moment in time, the body should stay stationary with respect to its initial location in space. Non ideal scenario (except that the impossible conveyor belt exist): The friction on the wheels (rolling friction, mechanical efficiencies, etc.) will create a force opposite to the force of the direction of the thrust. However with enough thrust, it will overcome the force due to friction, thus induce a motion forward - w.r.t. its initial location in space and according to the direction of thrust - and generate lift.
That does not matter a damn bit! If the belt matches the speed of the wheels then all forward thrust of the plane is being used to not be sent backwards!
@@thedausthed even if the wheels and the belt are made of sand paper, there’s only so much friction going on between the axels of the wheels and the landing legs which can easily be overpowered by the engines
@@thedausthed The belt can transmit a lot of spin to the wheels. But the wheels cannot transmit very much backward force to the airplane, because of their bearings. There will indeed be a slight backwards force due to internal friction, but regardless of the wheel speed the engines will have more than enough power to move the plane forward. If spinning wheels caused huge backwards forces, we also wouldn't be able to coast on roller skates without quickly coming to a stop.
@@joshualengers7743 The wheels are free-wheeling. The plane is effectively on roller skates. If I put you on roller skates and push you forward at 5mph on a conveyor belt, you still move at 5mph but the wheels on your skates move faster than they would normally.
@@maafg4435 that shouldn't matter, imagine the jets are 2 guys at either side of the plane pushing the wings while not standing on the treadmill. it'll move forward because the treadmill has no effect on the speed these guys push.
I think this is essentially a modern rehash of Zeno’s paradox. (Achilles races a tortoise. Tortoise has a head start. Race starts. Achilles covers the distance to where the tortoise is, but in the time that took, the tortoise has moved. Then he has to cover that distance, but the tortoise moves again. This, for infinity. ‘Achilles can’t overtake the tortoise’) In reality, that’s not how a race works. Similarly, this scenario tells you a thing is happening that can’t really happen. So of course it breaks a few brains. (I also think even though the ‘runway sized treadmill’ is often explained in the wording, this question is almost always accompanied by a diagram that makes it look like the treadmill is only the length of the plane, which straightaway primes the readers mind to imagine the question is saying ‘can the plane take off vertically on this treadmill by getting the treadmill up to the planes take off speed.’)
@@tomaz2007 Wheels will have to start skidding (so we achieve forward movement relative to the treadmill and airplane can take off) when the trust exceedes the friction
@@Siatkowkarzadzi exactly, it would just move forward relative to the ground. The wheels don't have to skid, their radial velocity would just be greater than the conveyor speed. But this breaks the condition of the question.
Captain Jo, I’m sorry, you’re wrong. The only opposite reaction would be friction on the wheel bearings which wouldn’t be enough to overcome the engine thrust. In this impossible scenario, the wheels would instantly speed up to infinity. The wheel bearings spinning would not provide an equal and opposite reaction to the engine thrust. Even if the friction was infinite, it wouldn’t be in the opposite direction of the engine thrust! Edit: The more I read the comments, it seems like people are thinking if the plane is standing still it won’t take off. Which is correct. However no conveyor belt, EVEN THE ONE IN SCENARIO 1 would keep the plane standing still no matter how the conveyor belt was setup even if it could match the plane’s wheel speed.
people seem to have a basic failure in understanding how airplanes work. the simplest explanation i can think of is just telling these people that planes propel themselves forward using their jets and/or propellers in the air - the wheels on the ground, which have zero propulsion, are thusly completely irrelevant to moving the plane - they're just there to keep the fuselage from dragging on the ground, just like wheels on a wagon. the jets are still going to move the plane forward regardless of what the wheels are doing, just like if you had a wagon on a conveyor belt you could still stand next to that conveyor belt and walk forward by using the wagon's handle to pull the wagon, and the wagon would still move forward, the exact same way a plane's jet engines tug it through the air. the ground plays zero role in a plane's forward movement.
@@kris003 yeah I don't get people... I mean it's even been physically proven that it will takeoff lol. Now technically the tires may blow if the belt is above a certain speed because they aren't rated for speeds above XYZ knots, but that's not the question. The question is "CAN an airplane takeoff on a conveyor belt?" It's like tying a string to a model plane on a treadmill... you can put the treadmill to the max speed and still pull the model plane to the front of the treadmill (simulating thrust).
@@ActuallySanFrancisco If the plane has forward progress on the belt, then the wheels spun faster than the belt by definition breaking the parameters of the myth, True or not true?
Sorry. Joe is right and you are wrong. But his diagram is not clear and so I can see the confusion. In the first example the conveyor is matching the engine thrust, so the aircraft will always be stationary and because - as you say - it is airflow that counts, the plane will not take off. But! In the second example the conveyor does not match the aircraft power. It is set to a fixed speed. So once the engine is pushing harder than the conveyor, the aircraft will start to accelerate along the conveyor, gaining airflow and taking off. Joe’s diagram is silly because it shows a short conveyor. The real conveyor would need to be as long as the real runway! But the real point is that a car puts power down through the wheels. To move faster than a conveyor you have to first push the engine to match its speed, and then push it even harder. But an aircraft doesn’t put its power through the wheels. So once you have matched the conveyor speed, you would just accelerate normally, with normal engine power. ie if a car’s top speed were 200mph, and you put it in a conveyor going 100mph in the opposite direction, the car would be able to go no faster than 100mph compared to the ground. But if an aircraft’s top speed were 200mph, it would be able to reach that. The conveyor is backwards momentum but it can be overcome.
This riddle was actually tested by mithbusters, with a small aircraft (i think was a cessna 150 or a piper) taking iff a convayer belt. It took off with no problem.
Yes, but the Mythbusters tested it wrong because the speed of the conveyor belt did not match the speed of the wheels, which you can clearly see because the plane is able to accelerate to takeoff speed.
You are obviously correct about scenario 2, however I’m not convinced about scenario 1. How can the plane be stationary on the conveyor belt? If the plane’s jet engines are spinning, it is pushing a lot of air behind it. Where is all that energy going? How does your explanation for scenario 1 fit with Newton’s third law?
I realize I’m way late here, but any absolute forward speed from the aircraft necessitates infinite speed in the wheels and conveyor belt, which would presumably explode the world. Example: say the plane has nearly reached takeoff speed, at 150 mph. This means the wheels are going at least 150, right? But that means the conveyor belt is going 150 rearward, which means the wheels are actually going 300, which means the belt is going 300, which means the wheels are actually going 450, which means the belt is going 450, which means the wheels are going 600… ad infinitum.
indeed, the forward motion of the airplane is provided by the engines only, as long as the wheels don't provide enormous friction (which is not the case on the conveyor belt) the aircraft will have enough forward motion (=lift) to take off
@@DIBOYOU well isn't the idea of this conveyor belt that it in some magical way cancels out the forward motion of the airplane while keeping the wheels spinning? if it is just a regular conveyor belt then i get your point, the wheels would just spin a lot faster than they normally would and the plane gets the forward motion relative to the air around it it needs to lift off.
@@kristian4559 No, it doesn't say that the conveyor stops the forward motion, only that it spins -exactly- the speed of the tires in the opposite direction. That this would cause the plane not to move is a fallacy, one most people fall into because we're used to vehicles which are driven by exerting force against a road.
Plane takes off in both scenarios. Conveyor belt has no effect apart from the wheels friction, but as the wheels spin freely, the aircraft engines would push the plane to proper airspeed and let it take off.
Bush planes definitely need sufficient airflow over the lifting elements and they take advantage of strong headwinds wherever possible. They still have to roll on the ground (and capitalize on clever design) in order to minimize takeoff speed and distance.
1:00 Take-off shouldn't be a problem: Planes gain speed by generating thrust with the engines mounted to their wings. Are there even any motors rotating the wheels? I don't think so. 🤔
No motors in aircraft wheels (except some experiments with 'electric taxiing') that are assisting the take-off. Only the engines are providing the forward thrust, which is totally not connected to any conveyor belt type of runway (it will only impact the rotational speed of the wheels, not the airplanes forward movement)
It will be a problem. If the belt and the plain are moving in the exact same speed in the opposite direction. the plain needs a forward motion in order to get the air under it's wings. If the belt is moving at the same time the same speed the other way. the plain in total would have a movement of 0, (zero) it is motionless only the. in this case the positive force and the negative force cancel the other. however real life dictates that this is impossible ether the aircraft is reacting to the belt or the belt is reacting to the aircraft. even a delay of 0,0000000000000000000000000001 would mean that motion has been made.
Think of it another way... Replace thrust with a rope. If the rope is reeled in, it doesn't matter how fast the wheels or conveyor are moving, the plane WILL move forward because the mode of locomotion is disconnected from the wheels.
@@Coren999 Hilarious mate. The thrust is on the plane and cares not one jot about what the wheels are doing. You didn't even watch Captain Joe at a guess (not that he's right, I address his error in a comment here).
@@donaldfegley6127 Nonsense. If you set a constraint on a system that constraint is not broken. The thrust propels the plane forwards. It cares not one jot WTF is happening at the wheels as long as, and this is a limiting issue is considered, any drag they exert that works against the thrust. You have not watched the video clearly nor read my explanatory comment in which I explain how Captain Joe errs, because if you had, you would have a full assessment already of the issue of what happens to the speed of the wheels and conveyor. But the thrust cares not one hour about that unless it causes drag, and propels the plane forwards.
@@BerndWechner So explain this to me then, if the plane moves the throttles forward and the wheels start to move from the ground speed of the plane starting to move, but then the conveyor then perfectly matches the speed of those tires for ground speed, so no the plane in no longer moving forward or backwards, how to the planes wings which have to have airspeed flowing around them to produce lift, produce lift if the plane is not moving at all on the ground so no lift is being produced by the wings? When the engines produce the thrust to get the plane moving on the ground to speed the plane up so the air around the plane is producing lift on the wings, the ground speed is then completely stopped by this conveyor that now puts the planes ground speed to 0 which then means there is no airspeed being produced for the wings to create lift. Just because the engines of a plane done care what happens on the ground does not mean that the wings can produce the lift from having no airspeed to then convert to lift as the plane that is on the ground has to have forwards movement to create the airspeed required for the wings to get the lift needed, but if the forward movement is 0 because the conveyor is now keeping the plane still, which makes the airspeed 0 over the wings, which means 0 lift is now being produced to have the plane take off.
I'm going with yes. The thrust of the plain will make it move forward. The wheel will just spin faster and the belt will spin faster too keep up with them. The thrust of the engine will still mover the plane forward creating air movement and then lift.
The plane would have to move faster than the wheels can keep up. Because the plane has mass, the wheels touching the ground, for the plane to move, the wheels would have to drag on the ground. Think a plane trying to take off with no wheels. That's what your saying.
ok, there are a few questions hidden in this thought experiment, and all are a problem of the relative motion of three objects, the air, the ground, and the plane: 1. will a plane take off if it is held in place by a conveyor belt keeping it from moving forward by exerting enough force on the wheels that the wheels exert enough force on the plane to prevent forward movement? if the plane can move the air past itself fast enough, it will take off. if the plane can't do that, it won't take off. if the air moves enough, the position of the plane relative to the ground doesn't matter. the plane can take off without moving forward, as the air moves fast enough to lift the plane 2. will a plane take off on a conveyor belt designed to keep the airplane in the same position relative to the air? if the air and plane aren't moving relative to each other, it doesn't matter how fast the plane moves relative to the ground, it won't take off.
My problem with the riddle is that it's not _quite_ defined well enough. Specifically, what _exactly_ does "designed to move at precisely the speed of the wheels in the opposite direction" mean? I see two main, and somewhat ambiguous, interpretations: 1. If it means that the conveyor's velocity is always equal and opposite to the average velocity of the wheels, i.e. the velocity of the central hub (which is the same as the velocity of the plane itself), then yes, it can probably take off. This would effectively simply double the radial velocity of the wheels, and as long as that is something that's within the tolerances of the tires and hubs to not explode and overheat, respectively (which I suspect it is, since a no-flaps landing in a tailwind could come pretty close to that ground speed), then there should be no problem taking off, since the plane doesn't rely on ground friction for its thrust and acceleration. Yes, there'd be a little more friction from the hubs and rolling resistance of the tires, due to the increased apparent wheel speed, but compared to the power of a passenger jet's engines, my head-napkin math says that should be negligible. 2. If it means that the conveyor's absolute velocity relative to an inertial observer is equal and opposite to the tangential velocity of the tires as they spin, then... probably not, but it still might be possible. This definition is recursive, so the wheels' speed and the conveyor's speed, which are each defined by each other, would create a positive feedback loop that would exponentially ramp the speed up toward infinity. Of course, you could never actually build an infinitely fast conveyor belt, so it would depend on whether the conveyor can go fast enough to over-speed the wheel assemblies before the plane has enough lift to take off. Edit: Cool, that's pretty much exactly the conclusion you came to. If you ever _do_ find yourself taking off on a conveyor belt in either scenario, I recommend the most extreme possible short-take-off setup... brakes on full as long as possible until engines spool up as fully as possible, for starters. I might even consider starting in a clean configuration for the initial acceleration, then dump flaps/slats approximately one cycle time before rotation speed (the earliest rotation speed possible given the load parameters, with engines running at absolute max power). Could you even spool up most of the way with reverse thrust selected, so that the reversers would be closing just as thrust passed maybe the 60% mark, and finish the transition just as the thrust pushed the mechanical limits of the hydraulics? In any case, since you'd be doing so in real reality instead of spherical cow thought experiment land, I think you could put your faith in the safety factor the engineers of the tires and wheels designed into them, over the bizarre possibility of an infinite-velocity, infinite-acceleration conveyor belt. That is, assuming the take-off is super-important, like to escape the massive volcano island on the verge of erupting that the supervillain who built the conveyor belt anti-takeoff system triggered, or something. If it's just, like, to go to another city for business, I'd just ... Actually, scratch that. If you ever find yourself facing a conveyor runway, just take off on the longest taxiway instead.
you are not going to believe this, but for the first time in a long time, I just used the phrase, "outside the box thinking" to describe another take. Then I read your comment and you used it. Crazy coincidences like that are what life was made for. Anyway. I think the whole thing comes down to the external force of the engine thrust acting on what is considered to be a closed system. The conveyor moves at the speed of the wheels, right? Well, in order for the wheel to turn in the first place, there must be forward movement. The engines will inch the aircraft forward just a bit, and the wheels will begin to roll. Nothing the conveyor can do, even magically can reverse that first movement. It then becomes a game of cat and mouse with the conveyor instantly (but with some imperceptible delay) matching the speed of the wheels. This acceleration will also be added to the speed of the wheels. All the while, the external thrust will continue to add to the gap between the speeds until the plane reaches takeoff speed. As for the whole breakdowns thing. Why does nobody consider the treadmill to be breakable? Everybody wants to talk about the wheels failing, but not a multi KM long treadmill with a motor, a belt system and tens of thousands of rollers with their own bearings that could heat up under all this stress.
The way I understand this, is that if the conveyor is matching the groundspeed, the wheels basically double in speed. If the propeller makes the plane begin to move, the conveyor will start as well. So if the plane crawls along slowly at 5km/h, the wheels will do the same 5km, which is matched by the conveyor. But because the wheels spin freely, and the plane is still able to move forward at 5km/h the wheels add on that extra ground speed, and will spin at 10km/h. So matching the groundspeed will simply double the speed of the wheel spin. The test could be done by putting a small model of a plane, attach it to something stationary, then turn the power to full. If you release it, it wouldn't automatically shoot up into the air. It would still need to reach takeoff speed to do it.
The conveyor isn't matching the ground speed, it's matching the wheel speed. If it is matching the wheel speed then ground speed is always 0 and the plane cannot ever take off
@@ClikcerProductions Wrong. The wheels can not hold back the plane if the engines are pushing it forwards. Oh, and the wheels are stuck to the plane, right? So they too move forwards relative to the ground. That movement determines how fast the belt is going backwards.
@@paldyvik7915 A force can be applied through free spinning wheels, this is something extremely obvious if you just hold a toy car on a running treadmill, you need to apply a force to keep it in place, if you remove that force the car is pushed backwards through it's free spinning wheels, the same thing can be done with the plane. If you think the plane moves forwards you are either allowing the wheels to slip (which is just super boring) or you do not understand very basic geometry, the only good argument for the plane being able to take off is that the treadmill would reach speeds high enough to produce winds fast enough to reach take off velocity while in place on the conveyor
@@ClikcerProductions I'm not stating that there is NO increased force from the conveyor belt moving the opposite direction. What many people don't realize is that these are WHEELS. Wheels are touching the surface below, and normally not slipping much (assuming friction exists). This contact point is however not what determines the speed of the wheel. The speed is measured at the CENTRE of the wheel, which may be moving relatively freely forwards and backwards, disregarding how fast the surface below is moving or not. The wheels are stuck to the plane, and when the engines start pushing the plane forwards, the wheels of course follow. as soon as the plane reaches 1 knot towards the left, the belt has responded and moves at 1 knot to the right. That causes the wheels to ROTATE at an RPM corresponding to 2 knots, but they are MOVING at a speed of 1 knot. The same continues as the plane accelerates and MOVES to the left, and at the moment take off speed has been reached, the belt is going to the right, also at "take off speed". Any argument have seen that the plane will stay stationary are false. Mostly, people assume that the extra rotation induced by the belt are able to magically cancel the push from the engine. Now figure this: 1. Imagine you are in your car, driving at 100 km/h. You probably realize that your wheels are moving at the same speed, right? If not, hand in your license. 2. Imagine a toy car, pointing to the left, with a red string attched to the front. Now pull that string to the left at a constant speed. Do you see the car moving? 3. Imagine the car is standing on a green paper sheet. Pull at that green paper sheet below the car, towards the right and at the same speed as the red string, but in the opposite direction. (You may want to practice with empty hands first, to build confidence in yourself as a researcher.) 4. Repeat step 3, while carefully observing whether or not the car is moving to the left. Repeat one or more iterations until the shock settles. Also observe the rotation of the wheels compared to in step 2. (Hint: The car IS actually moving to the left!) 5. The car is the 747. Pulling on the red string represents the push from the jet engines. Pulling on the green sheet represents the conveyor belt responding to the movement of the plane and its wheels. (Remember step 1?) The fact that the belt moving to the right does not prevent the plane from moving to the left at the exact same speed, as stated in the riddle, proves that the plane will be able to accelerate and its wings gain lift. Riddle solved: Take off OK!
@@paldyvik7915 The speed of the wheels is not the speed of the center of the wheels, that makes it a completely pointless thought experiment, if you want to interpret it that way you can, but that interpretation is so impressively lacking in any level of nuance or intrigue that I would expect a more interesting intellectual conversation from a 5 year old. The wheel speed is very clearly meant to refer to the speed of the surface of the wheel relative to it's center of rotation, I want to be very clear here that YOU are choosing to interpret the though experiment in a way which makes it pathetically dull. Please only reply if you have any interest in discussing the thought experiment the video is actually covering
Here is a trick. Imagine the plane has a hovercraft base. It is lofted above the ground by a cushion of air. Can it take off ? Of course it can ! The plane is moved forward by the the forward reaction of the plane to the movement of air moving backwards. As a result of this forward motion, surrounding air moves past the wings, such that, because of the curvature of the wings, there is less pressure above the wing than below. This results in lift and the plane rises. This means that, regardless of what is happening under the aircraft...wheels, opposite magnetic fields, a cushion of air, a conveyor belt...the plane will move forward and fly when it has enough lift provided by the wings. If one wanted to watch a plane "levitate" i.e. appear to fly vertically without upward thrust, one could use the same undercarriages as above, but provide a fan or other wind generator to move air past the wings, and use a propulsion device (prop/jet) to provide an equal and opposite force to wind, pushing or pulling the aircraft. Hopefully this description provides enough abstract elements for the imagination to conceptualize how this worked. The video editing of the execution of this experiment did not really show that the plane still moved forward sufficiently to provide lift and fly... while, at the same time, the "conveyor belt" was simply spinning the wheels underneath as they simply held the plane up as it moved.
But it isn’t; there is a mechanical connection between the wheels and the plane, and the wheels are practically connected to the ground. Unless the wheels slip there is no motion
Someone shared that on 9gag, and that was my explaination: - A plane is lifted by an airflow above and (most importantly) under the wings. - That plane on the imaginary conveyor belt is simply immobile relatively to the air surrounding wings. It doesn't matter how you twist it: turning the engines on, buying 24 elephants to pull the plane with ropes, pouring nitro into the engines... It's irrelevant: every thrust you can generate is nullified by the conveyor belt. So relatively to the air, it's an immobile plane. - You don't have an airflow under your wings. - The plane cannot possibly take off.
This is true ONLY as long as pulling/pushing force is less or equal to the friction between the wheels and the belt. In our case if thrust will exceed the friction, the aircraft will start moving (tires will start slipping/skidding on the belt)
This is true. The best way to explain the phenomenon is that you're just trying to get the engines going fast enough, that's it. Once the engines are at full speed, you achieve lift, whether or not your wheels are spinning. You can't just spin your engines up to full speed while you're sitting still though, that's why it's crucial that the treadmill be able to accelerate and match the speed of the plane. If the treadmill was stuck below some speed which would accommodate the engines reaching sufficient power for lift, there'd be no lift.
@@A38 you only achieve lift by having airflow and in this case, the vehicle motion is in equilibrium with this stupid conveyor. The resulting speed of vehicle is nil…while it is on the ground trying to roll. Another way to simplify this even more is this - remove the wheels; make it a big block with a force applied to it while on a conveyor. We know the formula for pushing a block with sliding using kinetic friction coefficient. That gives us acceleration/velocity, We know this stupid conveyor is designed to exactly match that speed. It’s doable, but it’s a stupid textbook problem.
@@Siatkowkarzadzi No, force of the belt is multiplying to lubricated bearings in the wheel friction, which is for theoretical experiment is equal to zero !! So backward force is zero, forward force - regular force from propeller
Maybe this is covered better later in the video, but ground speed doesn’t matter at all when it comes to flight. What matters is the air moving over the wings
True, but the problem here is that people focus on the wheels and extrapolate from cars. However, airplanes use propellers/turbines/etc. to push themselves off the surrounding air, with the wheels not being powered at all.
The aircraft thrust will move the aircraft forward, not turn the wheels to move the aircraft. So, the acft moves forward which causes the wheels to spin. Not even instant acceleration of the treadmill can undo that motion. So the wheels must even momentarily move faster than the treadmill. In this case, the treadmill must now catch up, but it's acceleration will be added to the acceleration of wheels. The forward thrust of the engines, which is not dependent on the wheels will constantly add to the gap until takeoff speed is reached. This is physics. It's like if you put a car on a dyno, but you put the non-drive wheels on it. When you hit the gas, the car will move forward no matter how fast the dyno can spin. That's because the forward thrust is not attached to the dyno. Just like the thrust is not attached to the treadmill through the free spinning wheels.
You're breaking the premise of the conveyor though. It can do the impossible. Imagine putting an rc car on a Dyno, but then pushing it with your hand (let's say your hand produces way more force than the car or dyno are capable of). In real life, the extra thrust from your hand would push it off the dyno. If this dyno worked like the magic conveyor, the car wouldn't move. You would see and hear the tires and Dyno spin even faster to keep up with the increased thrust proportional to how hard you push. You can pick up the car just fine, but as long as the tires and dyno are in contact, the rule applies and the rest of reality will bend to accommodate. All of your force is instantly counteracted by the dyno because it needs to match the tires, and any relative movement forward or backward would break that rule.
@@dogboy0912 ah, but at some point in my pushing, my force would be more than the car weighs and would simply force it off of the dyno. We are not talking about a wall here, just a small surface contact point. If the wheels were the source of the momentum, all this would be true, but because it's an outside force, it will be overcome. Some have mentioned I might be right if the plane "skipped" or slipped. Perhaps that is how it manifests, but the rule of the belt itself cannot be allowed to contravene all other forces. I mean, we already have to throw out breakage and any form of speed limit as a part of the question, but assuming that the conveyor is holding the tires down is a bridge too far for me. The body of the plane wants to move forward, it will.
I think this depends on the friction between the wheels and the conveyor belt. If the belt was low friction, you can put the park brake on, so the conveyor belt does not move and just take of as if you had skis.
You are 100% correct. When the plane starts to move, the conveyor belt has to move the same speed as wheels, but moving the belt spins the wheels faster. So if there is any friction involving the wheels, the belt and wheels will speed at infinite speed almost instantaneously. The only way to spin them at the same speed is to have the energy from the thrust of the engine be matched by the frictional energy lost by the wheels on the belt. So unless the wheels skid as you say, the given conditions are impossible. Same speed needs to be defined better.
@@Ryan50c actually, it's a brilliant, out of the box, solution to the problem. The belt doesn't move because the wheels are locked. The engine thrust then pushes the plane forward, belt and all. The only potential drawback is if you say the belt will only move under its own power and opposite the direction of the aircraft. But the principle is pretty hoopy thinking.
If you turn scenario 1 around. Start at the end of the runway and move the aircraft backwards with the conveyor. With no thrust it moves backwards. But in order to remain stationary it only needs to produce enough thrust to compensate for the friction in the wheel bearings. Thus in either Scenario this is the only backwards force acting on the aircraft. The only way it won’t take off is if the conveyor is moving so fast that the bearing friction matches the thrust which is absurd. In both cases the aircraft takes off with its wheels spinning faster.
The conveyor is essentially adaptive to wheel speed. He explains it in not so great fashion because it’s a subtle difference. In his second example, he provides the explanation of a conveyor with a constant speed which would of course allow takeoff. A conveyor that always exactly matches (rolling) speed, there is no velocity change.
@@MrDefreese Scenario 1 - aircraft will not move ONLY as long as thrust force is less or equal to the friction between the wheels and the belt. If thrust will exceed the friction, the aircraft will start moving (tires will start slipping/skidding on the belt)
@@Siatkowkarzadzi correct. Implicit in this example is that the wheels roll (freely) and excludes add-on items like busted bearings, absurd headwinds, etc. boiling it down, this is a basic cart and wheel physics problem where we are given unity for linear speed of the conveyor and the rotational speed of the wheels.
@@MrDefreeseonly if the wheels eventually fail. But if we’re assuming the conveyor is magic and can sustain infinite speeds, and we assume the wheels can sustain infinite speeds, they neutralise and the thrust still pushes the plane forward.
I think the flaw might be thinking that the wind speed equals the conveyor belt speed. At full thrust the wind speed moving over the wings would be greater than the tire rotation speed. This is how you can lift off into an extreme headwind with very little forward ground speed. Right?
Why would the B747 lift off once the wheel speed relative to the conveyor belt reaches 320 knots?? The wings would surely, still be stationary, relative to the ground...?
You can’t claim an imaginary runway and also not give me an equal set of imaginary strong wheels that won’t explode. The question sets the stage for me to assume some liberties as well. The plane takes off.
Planes don't get their propulsion from their wheels. So yes they can. If the belt moves at the speed required to takeoff, it won't make a difference. Now if the belt moved at the speed of the wheels, the belt would infinitely increase speed and do serious damage to the plane.
Forgive an old fool but how exactly does the conveyor belt matching the speed of the wheels cancel out the thrust of the engines? This is the bit I really struggle with, the wheels play no part in propelling the aircraft forward. Air is sucked in, forced out and the conveyor's speed doesn't alter the thrust produced.
@@ChrisFranklin.2260 hes not. If the conveyor belt was able to completely match the speed of the wheels, it would have no forward motion in reference to the air it is trying to use to take off. This is completely impossible in real scenarios due to a number of factors, but the baseline assumptions of the first example would mean that the plane would not be able to make forward progress and move through the air which it needs to take off
@@Professor-fc7vc I'm still not convinced. His arguments for the first case did not seem well fleshed out to me. There's still nothing to cancel out the hundreds of thousands of pounds of thrust on the body of the aircraft. Doesn't matter what the wheels are doing, or what the speed controller for the belt is basing its output on.
My answer before watching the video: yes, it can still take off, regardless of the speed of the wheels that engine is pulling on the surrounding air and those wheel bearing will probably give way and break the wheels off and the plane will still proceed forward with no wheels (theoretically)
we werent given that info. remember this is a magic conveyor which can move at infinite speed, so i assume these magic wheels can survive magically high speeds without failing.
Capten sorry but your plane will lift off in any case. Matching or even double the speed of the belt backwards it (if the weels can hold the spin) you will take off! If your consider is about if the weels can hold on the frictions ect it is another riddle
Something not considered in the airplane airplane scenario, the conveyor getting faster and faster might have an effect on the surrounding air to the advantage of the plane taking off.
You could use wind turbines, when they're not blowing aircraft into the air they can carry on their normal function of generating power. Or why not use a catapult? That would be brilliant for short take-offs from ships, then catch them with a very strong elastic band when they land. Once the plane has stopped, the elastic band will pull it back to the start of the runway ready for the next takeoff.
@@rogerbarton497 better yet remove engines from the aircraft entirely for short haul flights and just use big gliders and glorified slingshots. If you’re an adrenaline junkies we can just put you in a padded ball and launch you up to 60 miles away into a net, and hope the wind doesn’t change enough to cause you to...miss
@@grantkendrick277 It's strange how the simplest ideas are the best. I'm sure we could engage the services of top snooker and billiards players to solve the problem about getting the balls in the correct net.
For case 1,it is necessary to have at least one of the following conditions: - The wheel has non-zero inertia. - The bearings have non-zero friction. If none of this conditions is met, it could actually take off.
Nitpciky engineering "Well, actually" in regards to the car on the conveyer belt: You don't need the same power provided by the engine to go 150 km/h on the belt as you would need to go 300 km/h on the road. The cars groundspeed might need to be 300 km/h, its final "airspeed" on the belt is just 150 km/h, so you save a lot of power that you would otherwise need to overcome the difference in air resistance between 150 km/h and 300 km/h "airspeed" on the road. Anyways, nice video, thanks for the insightfull content Captain;).
Next Riddle: How will the plane land on the Conveyor belt
Ask a Navy Aviator
It think it just like landing in a moving ship/aircraft carrier
I don't think so. It would bounce too much.
That kinda ez I guess if it going opposite
Hmm
“ the only 747 that can do that is the captain’s joe 747“
I liked that part 🤣
You’ve become a good commercialiser
It’s the wind going over the wings that causes lift, irrespective of the wheel speed.
I think this guy is wrong.
There would be No wind over the wings, If the conveyor belt moved at the exact same speed as the wheels.
The plane Has to move forward, in relation to the ground, to get lift. As long as the plane is On it’s wheels, the conveyor belt would negate its forward motion.
If not, why do planes even need runways? Could just build a large dynamometer, and planes could take off without moving forward.
@@stevehackett2678 it's more the case that a plane will act as if the conveyor isn't there. when you drive a car the engine moves the wheels along the road. when you fly a plane it move the air through the jet or propeller. you have to imagine that the air is the planes' road and the mode of propulsion is the wheels equivalent .If say instead of wheels a plane had skis and a flat icy surface, it'd move forward and eventually take off as normal.
@@stevehackett2678 The plane is not "fixed" to the wheels due to the bearings. The wheels are not the driving force. No matter how fast you spin the wheels, the engines will still see the air as standing still and thus create thrust. If you have thrust, you have forward motion. It's a plane, not a car...
@@stevehackett2678 You’ve basically just restated the problem. But the conveyer belt moving backwards (and the wheels spinning backwards) has no effect on the plane’s forward motion, as the forward thrust is provided by the engines and not by the wheels.
@@stevehackett2678 The plane does NOT have to move forward in relation to the ground in order to get lift, it has to move forward in relation to the AIR. So regardless of what it's wheels are doing it will still move forwards and gain lift - just as it normally would. It will travel the same distance forwards, and it will rotate at the same point it normally would. The ONLY difference is it's wheels would be spinning faster than they usually would, that is all.
The riddle is that you can't in reality make a treadmill that matches the speed of an airplane wheels. The wheels don't propel the plane, they just respond to the relative motion of the plane with the ground. Which means if you move the ground (i.e. treadmill), the plane or it's wheels don't know the difference. The plane will just move forward through the air not caring what the wheels or ground are doing.
My thoughts exactly.
The wheels are not what's propelling the plane forward. They are just free-wheeling.
As the plane picks up speed, the wheels would spin faster than the plane's forward movement would indicate, but other than that they would not in any way influence the plane's acceleration.
Maybe a few tires would blow because they are spinning much faster than their designed limits, but it would not prevent the plane from taking off.
A easier to think about situation that is equivalent is placing a trailer on the same treadmill and pulling it off with a car in front. It moves (or the tires explode if the treadmill can go that fast). Now replace the trailer with a glider being pulled with a cable. It starts moving and takes off. And finally an airplane being pulled (or pushed) by it's prop or jets. In all those cases, the thing being moved is being moved by a force applied not though the wheels, so they are basically the same, so the airplane will move as well.
@@robertwatson818 The engines push the plane forward through the air (regardless of what the wheels are doing). The wheels on a plane are simply free-spinning bearings to allow the plane to "roll" on the ground, they have nothing to do with propulsion.
@@robertwatson818 but there will be because the airplane WILL move forward. The THRUST propelling the aircraft forward does not care that the conveyor is moving backwards. The wheels are free spinning. Make the conveyor move as fast as you want, the wheels will simply spin faster until the bearings or tires explode. The plane WILL move forward because the force propelling it will be exerted on the AIR, not transmitted through the tires to the roadway as will a car. Only if the combined friction of the free-spinning wheels overcomes the force of thrust would the aircraft not move forward and again, at that point you would have blown up your landing gear.
Wheels are not free spinning, they have friction, if the plane is not already flying, the friction will create drag, that's where the first part leads to (however you won't have infinite friction since the pressure downward is constant, is that enough to prevent the plane from take off we simply don't know, because the threadmill would overheat before it can reach that)
3:01
Captain Joe: rocket science, math, aviation
Me: oooo yellow black
*insert Wiz Khalifa - Black And Yellow here
Joe, I’m pretty sure the wheels in scenario 1 would spin up exponentially and presumably explode but don’t think it would have a significant effect on airspeed any more than scenario 2.
Correct!
Exactly
Scenario 1 is an impossible (and absurd) theoretical/mathematical scenario; v(ground) needs to be >0 to create airspeed, but for that to happen v(wheels)>v(belt) which the text says is impossible (they're alway the same)... both conveyor and wheels will reach infinite speed in t=0 (infinite acceleration) and break the equations.
@@nloko I agree! Scenario 1 cannot be performed in real world (infinite is not an option in real world), so has no meaning.
@@paolodalbono Agreed, but assuming the answer to the riddle is meant to be "Yes." or "No." rather than "Exploding infinity tires." - and keeping in the spirit of the problem - even if you adjust the conveyor belt to something reasonable, you still have what the Mythbusters already did in small and full scale. Even if you say the conveyor belt gets to accelerate twice as fast and to twice the take-off speed, right to just before the tires fail - which is presumably double the parameters of what this riddle is asking, the plane still takes off pretty effortlessly.
I mean it really is basic mechanics. Velocity in one direction with an equal and opposition direction in the other. You're net velocity would be zero. You can't achieve lift if you have no forward momentum.
The pilot who flew the plane on Mythbusters also thought he would not take off.
Mythbusters’ experiment didn’t match the speed of the wheels, which is the biggest misconception with this riddle. Their experiment was flawed.
@@cshoffie6593 it's the problem with the interpretation of the question. Captain Joe already explained both interpretations in this video. Mythbusters simply followed the 2nd scenario, while most people think the 1st.
Planes without wheels take off, as do VTOL aircraft, as can a aircraft with sufficient headwind without moving forward - a good pilot knows that takeoff and flying has nothing to do with ground speed
@@davidioanhedges I understand that, but the riddle isn’t about VTOL aircraft or a headwind sufficient for lift. It’s a hypothetical scenario of the wheels being cancelled out by the conveyor belt. Wheels obviously affect the movement of the aircraft while on the ground. If you have your brakes on, it’s going to be very difficult if not impossible for the aircraft to move to generate lift. So, considering you’re not in a VTOL aircraft and you have zero headwind, and if the wheel speed is being matched by a conveyor belt in the opposite direction, without delay, the aircraft cannot move.
The confusion about this is a result of people adding variables to the riddle that shouldn’t be there.
@@cshoffie6593 Yes, but the brakes *aren't* on when the airplane is trying to take off. Given the lack of brakes, the only affect the wheels have on the plane's horizontal movement is a slight friction effect. So, yes, the conveyor belt will *slightly* slow the plane, but not enough to keep the plane from taking off.
The real question to answer here is "how does the airplane stay flying once the wheels are off the ground?" Once you know the answer to that, its easy to work the problem out.
The plane is pulled forward by the engines. Once you reach a high enough ground speed, the plane lifts off. Independent of underground and wheel speed. Although the wheels would in this case explode.
The real question is something you'll never understand, because you couldn't read it in the first place.
Simple thermodynamics, my friend. :) All mechanical systems boil down to energy in = energy out. In this case: thrust = friction. At infinite speed, the friction of the wheels will remove infinite energy from the mechanical system. Also, the conveyor is defined as matching the speed of the wheels. Any forward movement of the airplane with respect to the ground violates this definition.
@@c182SkylaneRG incorrect, if your going to try to pull that crap then you failed. Under no point in the question did it state the rotational speed of the wheels. Therefore the only logical assumption is that it is match the forward motion of the wheel itself. Your trying to selectively add things into the question. If I asked you the speed of a tire that broke lose from a moving vehicle noone would give you its rotational speed.
This is a common issue with technically educated people and commonly worded questions. You destroy the spirit of the question by adding in stuff not present into the question. I mean why would you add in that if the pilot would apply a little bit of steering then you'd have wheels moving at different RPMs and the belt would therefore enter into a paradoxical state where it would need to be moving at multiple speeds at the same time.
Basically this is equivalent to the mathematician that argued 2+2=5 could be true because it theoretically could be 2a+2b=5c or maybe some other hidden or non presenting variables or perhaps a variant numerical system.
@@nicolivoldkif9096 The term "wheel speed", lacking any other description, means the speed of the wheels across the ground, which is taken at the hub/axle. In this scenario, that would be the speed of the wheels relative to the conveyor belt. Their rotational speed is translated to a linear speed based on their diameter, which can only be in reference to the surface they're rolling on (the conveyor).
Any good pilot starts on the center line of the runway, and stays on the center line of the runway. No self-respecting pilot takes off cock-eyed with respect to the runway centerline. Be realistic. :D
That’s one big conveyer belt.
It's made from my belt cause of my lockdown belly.
@@techmantra4521
😂😜 funny stuff kiddo !!
The earth is one big conveyer belt ;-)
@@brantwedel 🤯
It did take off BUT if you watch it closely the plane started moving forward before it rotated
I think this question was thought up to highlight the difference between how a car is propelled down the runway and how an airplane is propelled down the runway. As such it is a thought problem and would work better (less confusion) if it was explicitly idealized. My suggestion is to include in the problem statement something like "consider the wheels themselves to have no friction in their bearings, no rotational inertia, no rolling friction, and no residual drag in the brakes when they are released." (visualize them to be something like a bicycle's spoked wheels with zero mass, and no brakes at all." LOL (also utterly indestructible). The question seems to me to be, then, "how can this conveyer belt runway PULL on this idealized airplane?" My answer is "it can't" - run the conveyor belt as fast as you want, all that will happen is the wheels will spin. The inertia of the airplane (tendency to resist changes in velocity) will keep it sitting there, until the throttles are advanced. With 4 big engines attached firmly to the body of the airplane it would accelerate down the runway with no trouble at all and take off when its airspeed reached the value to start rotation. However, if the wheels are given mass, and the conveyor belt runway is given access to unlimited energy and power, then pulling on the bottom of the wheels will actually transmit some force onto the body of the airplane (as well as give the tire rotational kinetic energy) and with infinite energy and power the conveyor belt would win.
for fair experiment lets take force of the conveyor equal for the force of plane engine. In that case plane take off easily always
Even if the wheels have only just enough friction from the ground to prevent slipping, the energy it takes to rotate them is coming from the engines. You can't just disregard the wheels because they are stealing all the energy you need to move the whole aircraft forward.
Yes, if the movement of the wheels is initiated by thrust, then the plane would take off. The thrust is not related to the wheels. The jet engine is not pushing against the ground. The travel distance before rotation airspeed/Vr would be similar to a normal takeoff. In this scenario the tires would be turning faster but the plane would still be moving forward through the air opposite of the thrust, thus generating lift. The wheels only contribution during takeoff is to mitigate friction between the aircraft and ground. They do not propel the aircraft during takeoff. Maybe this will help: if I hold a non powered toy car on a treadmill with my hand while the treadmill is running I can still make the car move forwards and backwards even if the treadmill were to instantly speed up/slow down as I moved the car forwards/backwards. In this case I am the jet engine and the wheels aren’t the source of power.
See, it's the qualifier of the conveyor belt exactly matching the speed of the tires with no delay. For this to be true, to take your car example, if I tried pushing the car forward, I would see (and probably hear) the tires and treadmill speed up proportional to how hard I push, but the car would never move forward - that would require the tires to move faster than the conveyor belt. It would be like an invisible, equal, and opposite force, pushing against me. I could even pull on the car until the treadmill and tires are at rest, I could pull even more and make them rotate the other way, but the car would never actually move. To actually move its position relative to the treadmill would be to break the requirements of the scenario with regard to the treadmill.
It's not possible, but given the premise of the conveyor, the rest of physics would need to accommodate it. The aircraft will never produce enough thrust, regardless of means, to gain any relative airspeed (or true, or ground, or any motion period for that matter), for it would break the rule of the conveyor. The only way I see a possible takeoff is with headwind equal to or greater than rotational airspeed, or if the engines produced enough of a vertical thrust component to separate the aircraft from the conveyor, or if a hypothetical aircraft is constructed in such a way that the exhaust airflow is sufficient and positioned in a way to impart effectiveness on the control surfaces/wings, which sounds really goofy to me but maybe somebody can tell me if that's even possible or not.
@@dogboy0912 "It would be like an invisible, EQUAL (emphasis mine), and opposite force ,pushing against me". What force? Why equal? In the toy car example, the wheels would have to overcome a marginal amount of friction as they turn around the axel and where they make contact with the treadmill. Are you suggesting that I could not push the car forward as a treadmill was speeding up, even if instantly? Other than the weight of the car (not even the full weight because of the wheels) and a small amount of friction, what force would I have to overcome? Let's say I push the car forward with 50 pounds of force from my arm which I could easily do. What force is going to push back against me at 50 pounds?
Alternate title: Can plane on conveyor belt destroy landing gear of the plane?
Alternate ALTERNATE title: can you find a conveyor belt big enough to fit a plane?
Yes, it can.
Who cares. We're talking about a 747 on a treadmill. Just imagine the wheels can take the forces.
Yes. The bearings in the landing gear will break their rolling elements if the wheels spin too fast. The centrifugal effect causes the rolling elements to load the contact force between the outer race and the rolling elements, and when that contact force exceeds the limiting strength of the materials, the rolling elements and outer race will rupture.
The answer is in airflow over the wings, wich generates LIFT. Flying has NOTHING to do with wheels.
Actually it’s the airflow under the wings - Newton’s 2nd law. That’s what gives it lift.
@@ntsecrets agreed, but in any normal GA plane, how Mitch does it account?
Something that’s not clear is where the lift is coming from, are the engines sending air under the wings or are they pushing the plane forward which makes air rush over them to create lift?
@@ntsecrets I heard otherwise.
@@ntsecrets Not really. Most lift comes from the negative pressure over the wing. Bernoulli's theorem applies, not Newton's Second Law.
the wheels and treadmill are a red herring in this scenario, it doesn't affect the thrust produced by the engines which determine the airflow and thus lift. That is why Air Speed is important in flight, and not ground speed
You are just wrong. No one is saying the conveyor belt affects the thrust produced, but the basic geometric fact at the centre of this issue is that if the contact patch of the wheel is moving backwards at exactly the wheel speed then the net velocity of the wheel MUST be 0, literally just google "velocities on a wheel". You'll see that in every single case where the bottom of the wheel is moving backwards at the wheel speed that the centre of rotation has a velocity of 0. 0 velocity means no air speed beyond that of the wind, and wind isn't gonna make a 747 take off
@@ClikcerProductions good thing the velocity of the wheel has nothing to do with the forward velocity of the aircraft. The plane would take off.
@@ClikcerProductions starting by “you are just wrong” and then being wrong is a whole new level.
@@szilveszterszalai230 if the wheel speed and treadmill speed ate identical literally by definition the plane can't be moving forward, if the plane is going forward then wheel speed is exceeding treadmill speed and you've completely ignored the question, set up your own different question, and claimed the correct answer to the original question is wrong 🤦♂️ that is the level of stupidity you are at, someone said 2+2=4 and your answer was "nO oNe PlUs OnE iS tWo"
You completely misunderstand, the wheels definitely do matter. If they didn't then breaks wouldn't work to slow the aircraft down. With the runway spinning faster and faster to match the speed of the wheels and with no slipping the aircraft isn't going anywhere.
It’s amazing that someone can be so confidently wrong. As the wheels spin freely and independently of the plane, the jet thrust will move the plane forward and the wheel/conveyor speed with increase as the plane moves along to take off velocity. Because the wheels of the plane spin freely, they can essentially be ignored.
The plane has to rest on the ground when the engine is getting up to speed. The conveyor belt will influence its movement. As the plane creeps forward, the belt pulls it back, so it never gets a chance to accelerate to a speed to generate lift.
This is different from a frictionless surface, where wheels do no matter. The wheels can spin freely and the plane can still take off.
This is where the ground actively pulls you back when you try to creep forward, hence u will never gather enough speed to lift off
@@parrotbrand2782Just how does the ground pull the plane back? The ground/belt and the airframe have no fixed connection in the direction of travel. In fact, a reverse-running belt will spin the plane's wheels FORWARD!
If jet engines are pushing left, the conveyer pushing right, the wheels are just bearings and play no affect.
Ever heard of friction? As soon as you try to move forward the conveyor counters it so you would never move
@@jrunsvold7150 Right, friction is the key. I'm really frustrated that neither those arguments nor those counter arguments is taking friction into account, which is the only way to make things clear. But to cancel the thrust of the engine, we need the same amount of friction, which I don't know if is actually possible (something tells me this is not going to happen in real life. I would still call this theoretically possible though.)
@@jrunsvold7150 ever seen a travelator at an airport? Think you could push a trolley along it in the opposite direction? Of course you could. It just needs enough power.
@@Xiaotian_Guan problem is the plane has wheels, and in an ideal situation (which is fair to assume since we have a conveyor belt the size of a big ol plane) the wheels are frictionless so the movement of the wheels exerts no force on the plane itself, it just spins the wheels. The wheels can't exert a force on the plane, so therefore it doesn't hold it back at all
Nothing can be frictionless. Otherwise nothing would exist at all
Thrust
Not before you touch up with Manscaped!
@@kingkenny97 haha
thrust
Only if it's VTOL, lol
@Buddy Austin The wheel bearings prevent the conveyor from imparting backwards force on the plane, but the engines still accelerate the plane forward.
Wheel speed does not matter unless rolling resistance is greater than thrust of engines so it should take off.
The speed of the vehicle is only due to rolling. The explicit constraint of this exercise is that rolling speed is exactly neutralized by the magical adaptive nature of the conveyor.
That’s why he gave the follow-up example if the conveyor had a steady speed which could be overcome by an acceleration (thrust or increase automobile speed).
He explained it correctly.
@@MrDefreese That's my prediction not a counter, also if rolling resistance is greater than the thrust the wheels don't turn, the conveyor would thus be still and plane goes nowhere. Its like trying to take off with the park brake on.
@@MrDefreesethe speed of the vehicle is not due to rolling of wheels. The thrust of engines is pushing the plane forward. How would the belt create a counterforce to that if wheels are rolling freely?
@@psychosis7325 not correct. The wheels just roll along on the surface. The wheels don’t seize in place. He shows this in his first animation of the scenario.
@@Jashtvorak the vehicle only moves forward by rolling on the surface. You are given the express condition that the surface is moving at the same speed as the wheel which is exactly the vehicle speed. They are one and the same. For extra thought projects, we could resolve the force involved for such a conveyor. It is obviously impractical and out of the bounds of normal engineering design.
The issue is the interpretation of 'matching'. The sane interpretation is that 'matching' happens no matter what speed the wheels go, because 'matching' is a functional result of the mechanical contact between the wheels and the conveyor belt. In other words 'matching' means 'synchronizing to' not 'going as fast as'. But, since the rule demands compliance from the conveyor belt, not from the wheels, the interpretation doesn't even matter. If the conveyor belt runs afoul of physics, that is its problem, not the airplane's problem or the wheels' problem, thus the plane will happily ignore the logic explosions consuming the treadmill and take off regardless.
The 747 can only take off if the airflow over the wings is sufficient to provide enough lift.
So the 747 must move forward at takeoff airspeed, regardless of the surface being a runway or a conveyor belt.
Because the plane gets enough AIR-speed to take-off. The jet engines propel the AIR to move forward just like jet fighters.
👍@stmounts
You have put your finger on the pulse when you state that relative movement of air over wing surfaces causes lift.
The conveyor belt and engines are not the elements which generate lift. Only the foreward motion of plane (with the help of the engines, etc) generates a pressure differential on 'curved' surfaces to create lift.
How else does
a glider stay aloft ?
And Why do aircraft carriers use catapults to get off the deck?
@@yjk2202its so enough air to pass through the wings to generate lift.
@@waddup2336 Your understanding of how lift works vs thrust is not even close to how it actually works, if the plane moves the throttles forward and the wheels start to move from the ground speed of the plane starting to move, but then the conveyor then perfectly matches the speed of those tires for ground speed, so no the plane in no longer moving forward or backwards, how to the planes wings which have to have airspeed flowing around them to produce lift, produce lift if the plane is not moving at all on the ground so no lift is being produced by the wings? When the engines produce the thrust to get the plane moving on the ground to speed the plane up so the air around the plane is producing lift on the wings, the ground speed is then completely stopped by this conveyor that now puts the planes ground speed to 0 which then means there is no airspeed being produced for the wings to create lift. Just because the engines of a plane done care what happens on the ground does not mean that the wings can produce the lift from having no airspeed to then convert to lift as the plane that is on the ground has to have forwards movement to create the airspeed required for the wings to get the lift needed, but if the forward movement is 0 because the conveyor is now keeping the plane still, which makes the airspeed 0 over the wings, which means 0 lift is now being produced to have the plane take off.
Isn't it amazing to know that no one anywhere in the world has finished watching this video at this time?
Well, Joe has 👀
The editor has
There is nothing I enjoy more than pilots that don't know how airplanes work. If the plane isn't moving forward then the wheel speed is 0. Treadmill speed is zero. What is countering the thrust of the engine. The wheels only rotate if the plane moves forward.
IKR? When the 747 starts moving at 1 kts from the engine thrust, the conveyor moves backwards at 1 kts, so the wheels are spinning 2 kts. So 80 kts forward speed from the engine, 80 kts backward from belt, wheels spinning at 160 kts. At 160 kts from the engines forward, the 747 can rotate to take off. The belt is going backwards at 160 kts and the wheels are spinning at 320 kts. The wheels don't drive the 747 forward, the engines do, which even this pilot messed up.
I think the aircraft would take off in the first scenario as well. Both wheels and conveyor belt would reach speed of light and acts as a brakes but the conveyor belt would also create a headwind strong enough to lift the plane.
But nothing with mass can reach the speed if light, because it would require infinite energy. I'm pretty sure that the bearings would give up first, or the tires would explode
With cars, this conveyer belt would be called a dynamometer. :)
Creating lift by moving the wheels, Genius.
Magnus effect
Making comments without listening to the video, Genius.
@@grummhd3020 Plane would spin around wheel axis, since magnus effect is exponential.
No one said the engines were on. Also, substitute skis for wheels, is there any difference?
The simple answer is there needs to be enough airflow across the wings to create lift.
The wheel speed matching the conveyor is the key to solve this. The plane is sitting on the conveyor neither the wheel or the conveyor is moving. Now start the jet move 1 rev of the wheel now the plane has moved forward and 1 rev of conveyor is now behind the wheel. The real question is how fast the conveyor is moving. The answer is it is not and never will. That is the trick of this question.
Yes it can. Speed of the wheel have nothing to do with airplane speed relative to the ground.
But it doesn't matter . What matters is the TAS. And if the aircraft has a GS of 0 it means that there is no wind flow over the wing for them to be effective . So a plane on a conveyor belt would be the same as if it applied full throttle and applIed the brakes it just won't take off .
@@mojojojo3852 the engines and only the engines provide the forward thrust, even it was a plane on ski's, on floats, on 'wheels on a conveyor belt', it doesn't matter as long as it does not prevent the aircraft from moving (=attaching it to chains or putting large concrete blocks in front of the wheels - normal chocks won't do the job). If the conveyor belt was moving forward with the same speed, the wheels would not rotate and the aircraft would take of as normal. With the belt running backwards, the wheels will spin twice a fast (only marginally increasing wheel/axle friction) but the aircraft will 'thunder' along the runway thrusted forward by the engines. Maybe the tires will deflate because rotational speed is well above it's max. rating of somewhere around 220+ knots (but that is a different discussion).
@@DIBOYOU not really comparable with ski's or floats. If you stop the engines, the plane will go backwards due to friction belt/tire, because the plane has a weight that pushes down on the belt. So a part of thrust will be consumed just to make the plane still compared to ground. You will never be able to reach take off speed, because you'll always have this conveyor speed to compensate.
What you say works if the plane weight is equal to zero.
@@pik2005 Not true, there is an accident investigation of a DC8 (I think) which had it's wheels frozen and on the slippery runway the aircraft started it's take off movement almost as normal. but given the enormous friction, it failed to take off. In this conveyor example, the wheels will only have minimal increase of friction in it's axles. The take off roll and speed will increase slightly, but as long as the axles don't seize completely due to overspeed, the aircraft will get airborne. If the conveyor belt turns in the other direction, the take off run will be marginally shorter, but the airplane won't lift of like a helicopter even with it's wheel not rotating at all. So yes it is comparable with ski's, floats, etc. all have different gradients of friction, but absolutely far less than the (jet) engine thrust
Lol what about the wind that gives the lift? How high do you fly off the treadmill in the gym?
Since the plane doesnt use its wheels to propel itself on takeoff the conveyor is a moot point and doesnt do anything for takeoff
That is simply false, the net velocity of the plane while grounded is always going to be Vplane = Vwheel + Vconveyor, and since in scenario 1 Vconveyor = -Vwheel then Vplane = Vwheel - Vwheel == 0, i.e. the plane cannot ever move if the conveyor perfectly matches the wheel speed continuously as it cannot get any air speed. To make it clear that the equation for the planes velocity is as I have stated simply consider the scenario when Vwheel = 0, and the plane just moves along with the conveyor at the same speed, then consider the case when Vconveyor = 0, as the wheels roll freely they will match the planes speed perfectly
@@ClikcerProductions Is not the wheels turning what's moving the plane forwards while on the ground, it's the push from the jet engines or propeler, so what may happens is the wheels and the conveyor belt may continue accelerating, but the plane will move forward.
@@omargj1 If the plane moves forward the wheel speed is greater than the conveyor speed, so no, given we are literally told that the conveyor speed always matches the wheel speed it doesn't move forward, it has nothing to do with how the plane is driven, since the forward force from the jets is being matched perfectly by the backward force imparted by the accelerating conveyor belt. This is literally how the thought experiment is defined, if you disagree you are just ignoring the experiment and doing your own unrelated BS
@@ClikcerProductions The wheels have nothing to do with moving the plane forward beside having something to make it easy to move reducing friction with the ground, the plane moves by pushing air backwards, not by making it wheels turn, even the conveyor belt can be moving backwards at 3000, 5000 mph, or kph or any speed you want, the plane still would be able to move forward.
@@omargj1 If the plane is moving forward then wheel speed is exceeding conveyor speed, directly contradicting the stated conditions given, congratulations, you failed
It’s simple physics. The answer is in the riddle itself. Wheel speed the same as the belt. A plane will NEVER take off with that variable. It will ONLY take off if the wheel speed is greater than the belt (aka forward thrust pushing it along)
It’s a question that gives you the answer by giving you an illogical physics problem
With this logic on the conveyor belt, it doesn't mean anything as you could ramp the conveyor up to 10x the speed of the plane in the opposite direction and yet the plane would still move forwards
Myth busters did a great live demo with an actual airplane (ultra light) but still fun to see
And it did take off in case anyone is still wondering.
@@ricksharpe6895 There's a short 2min clip of that myth here on yt. It should answer your question.
Yes I saw the Mythbusters ep showing a plane taking off on a conveyor belt.
Yes, however... he explains this in the second half of the video. The belt they used was meant to match the ground speed of the plane. And ... given the technology... they could not match the wheel speed *instantly and exactly.* The problem is more.with semantics than anything.
@@gitbse Yeah, but in that case the answer to the riddle should be that such theoretical conveyor belt would instantly generate friction on the wheels equal to thrust. Only that would prevent the plane from moving. It's a pretty pointless riddle.
Oh come on man, just when some of us were able to put this train wreck out of our memory you go and dredge it back up again. Have you no conscience?
This whole video is just so damn stupid.
@@pequalsnpsquared2852 nah, just a case of very unrealistic things coming together
Which Train Wreck?
@@eliass.4743 This whole “plane on a treadmill” thing dates back to the early 2000’s and was one of the first viral internet events. It spawned many a virulent argument that totally consumed message boards at the time.
@@unclerojelio6320 Wow, people are dumb.
I still think that this explanation is wrong.
The plane will move throught the air. The wheels just spin at both speeds (air + conveyor belt) and the will move until is plane airspeed and lift
Your wrong of course. The thrust is in the air not on the wheels. The wheels are irrelevant to forward momentum.
The rotation of the wheels have no effect on the speed of the plane. The plane uses thrust from the engine not from the wheels
Well. I was gonna say that but I'm late to the show
I've now watched the video and this is stupid
But how will the plane take off if there is little relative wind around the airfoil and wings . Think
@@mojojojo3852 the plane will still move forward there no way for the belt to counter act the trust from the engines.
The dudes a 747 pilot, he would know more than you
▓▒░ I paused this video and thought about it
for -an hou- a few minutes.
If the conveyor belt is moving in the *opposite*
direction at the same speed as the wheels are,
this means that the aircraft isn't moving toward
the wind.
In other words, it's standing still.
It would be a miracle
if it does take-off.
`
Today is Saturday,
the sixty-fifth day of the year
two thousand and twenty-one. ░▒▓
`
How does a float plane take off against a current? Does the water direction pushing backwards stop you from taking off? The answer is no. Your ability to take off is only governed by the your airspeed. The plane pushes on the air not the water.
If the ground is moving, it is possible of course for the plane to move even if the wheels aren’t spinning or are even spinning backwards. The plane can push against the air directly, so it makes no difference which way the wheels are spinning. The only reason the wheels spin is the difference in speed between the axle and the ground beneath them, the freely spinning whee has no significant effect on the speed of the axle or the ground beneath it.
A little scary the pilot in this says first scenario wouldn't take off since wheel spin is only a reflection of airplane movement. The plane will always take off as the wheel has nothing to do in this scenario with thrust or plane speed.
If I'm on a treadmill on roller skates holding a rope my wheels will match the speed exactly, but if i pull on the rope I move forward. The engines are pulling the plane forward, the belt will not stop the plane from moving forward, the plane always takes off
you're assuming the treadmill's speed is always the same. the riddle's premise is that as you pull on the rope, the speed of the treadmill will also increase
@@jbt816but that won’t change anything, if the treadmill is going 20mph and you pull yourself forward at 1mph and some increases the speed of the treadmill at the same time you will still pull yourself forward at 1mph. The speed of the wheels and treadmill is completely irrelevant.
@@jagheterbananyou will pull your torso forward, but the conveyor adapts to the increased wheel speed and still results in the ‘wheel axle’ remaining static. That’s the whole point of the unintuitive example of the conveyor speed matching rolling speed.
You would essentially tip over forward.
@@MrDefreese The wheels are attached to the roller skates with bearings essentially disconnecting them from you so no you wouldn’t tip over you would just increase the speed by which the wheels are turning. This of course brakes the premise that the wheels and treadmill are supposed to be going at the same speed, the only way to keep that premise is to not move i.e. not pull the rope.
If you translate that to the airplane it would mean you can’t increase the thrust, so yeah an airplane that you’re not applying thrust to won’t takeoff but it’s not really because the conveyor belt is stopping you.
@@jagheterbanan the wheels and treadmill moving at the same speed means the position of the wheel never changes. The force applied by pulling the rope does mean that part of the body moves. We could do fun body deformation experiments with that - rigid body, flexibility at the waist, etc.
Yes because it doesn't matter what the wheels do on an airplane, airplanes rely on airspeed not groundspeed.
No because there is no windspeed. There is groundspeed but the windspeed is none. I don’t know why you said yes because you understand the concept but I assume you already watched the video.
@@AndreasRSD Nope, there's nothing the conveyor belt can do to stop the plane moving forwards, all it will do is cause the wheels to be rotating faster than they normally would at the point it takes off.
I watched the vid, and I also watched the mythbusters vid, where they actually tested it with a real plane, and it took off with no problem.
@@AndreasRSD He's playing on the wording of proposition. If there is a strong enough wind that goes on the opposite direction that has enough force to generate lift and the engines can use it push enough thrust, so Yes it can. There are bush planes that can take off with as little 3 feet of ground because of the strong wind in the wildeness. Though the conveyor belt runway is useless and didn't contribute anything to the take-off. As Captain Joe pointed out, the question is tricky.
Yes groundspeed no wheel speed.
@@LeoH3L1 They used a small bush plane for that experiment, not a 747. Even a empty 747 will require a certain forward speed or a certain airspeed to generate lift.
If the 747 cannot generate enough forward thrust to counteract the trend mill and cannot move forward, it will not take off.
I love how people cite myth busters as some sort of gospel. Adam sucks. Long live Jamie.
Yes it will move forward and take off! But only due to thrust from the engines... The conveyor belt's velocity is completely irrelevant, since the wheels are not powered!
How does thrust from the engine allow a plane to take off??? It doesn’t. You need airflow under the wings to create lift.
@@tracruz Yes it does.Thrust from the engine push the plane forward, gaining velocity thus airspeed
@@stevenfpv2345 But the plane isn't moving forward at all... The power of the engine is irrelevant, it's not a helicopter
@@moebekdache3756 Yes it is. How does an airplane is supposed to fly once in the air? Once the wheels aren't touching the ground anymore? Engines push the plane forward, regardless what happens to the wheels
@@stevenfpv2345 So are you saying, that if 2 forklifts lifted the plane either side by the wing, let engine hit full power, then back the forklifts away, the plane will then go?? Correct me if I'm mistaken
ChatGPT:
Airplanes take off by accelerating to a speed that provides enough lift from their wings to overcome gravity. The speed of the wheels on the runway is not directly relevant to the plane's ability to take off. If the plane's engines are producing enough thrust to move it forward, and the wings are generating sufficient lift, the plane can take off.
In the case of the conveyor belt moving in the opposite direction to the plane's wheels, it won't prevent the plane from taking off. The conveyor belt might make it more challenging for the plane to start rolling, but once the plane's engines provide enough thrust, and the wings generate sufficient lift, it will take off as usual.
The key point is that the thrust from the engines and the lift from the wings are what enable an airplane to take off, not the speed of the wheels relative to the ground.
Cool!
The speed of the conveyor will always match the speed of the plane (in the opposite direction) if the conveyor is meant to exactly match the speed of the wheels. He tries to draw a distinction between the hypotheticals “conveyor belt matching the wheel speed” and “conveyor belt matching plane speed” when there is none. As long as the wheels aren’t sliding for some reason (friction/ breaks), they’ll be in contact with the conveyor which means they’d be matching its speed. So, saying the conveyor belt matching the wheel speed is the same as saying it’s matching the plane’s speed. Think about it as the top of the wheels moving it the direction plane is moving (at that speed) and the bottom, in the direction the conveyor is moving (at the conveyors speed). Those speeds added together equal the rotation speed of the wheels. So the conveyor matching the speed of the wheels spinning would mean it’s also matching the speed of the plane. This is how circles works. The only good point here is the mention of the max wheel speed. If the wheels couldn’t spin fast enough (they’d only have to spin twice as fast as they would on a static runway since the runway in this case is moving backwards at the same speed the wheels and plane are moving forward) then yes, that friction would prevent the plane from gaining enough speed to provide lift (air flowing over the wings fast enough).
i like how u explain everything super clearly
I am pretty sure third law of Newton is at play here, eg, the engines push air backwards so the plane must move forward. The speed and direction of the conveyor belt is moot.
But perhaps the riddle might indicate the the engines of the plane are not at full trust if you read the riddle in some way?? . At least I would expect full trust in the riddle, wouldn’t you not?
Or is perhaps the riddle not complete?
The bottom line is that the wheels are irrelevant, as the plane isn't driven
by the wheels.
That's the logical error that people make.
Mythbusters tested it irl. The plane will take off
@@bibaso12 if the plane takes off then the wheel speed is not matching the conveyor belt speed so you are talking about a different problem than the one in the original question.
Engines provide a force of thrust which is matched by the rolling friction and air friction of rotating wheels. If a plane move forward you are no longer satisfying the conditions in the question - the wheel and conveyor speeds are not matching.
@@tomaz2007 Which is why that isn't the spirit of the myth, is a deterministically dumb way to argue it because it presents a rule that violates physics to achieve a desired outcome, and is thus about as meaningful as arguing whether or not my imaginary superhero can beat your imaginary supervillain.
The original intent of the question was "Can a plane can takeoff on a treadmill going equally as fast in the opposite direction." Mythbusters effectively demonstrated the concept which was bounded within reality.
Plane is stationary relative to ground under the treadmill:
Plane Vground = 0mph Vtreadmill = 0mph Vwheel = 0mph
Plane starts throttling the engine:
Plane Vground = 1mph Vtreadmill = -1mph Vwheel = 2mph
Plane is now barreling down the runway about to takeoff:
Plane Vground = 100mph Vtreadmill = -100mph Vwheel = 200mph
“The airplane has to move forward relative to the ground”. Do you think that you had a headwind equal to Vr you couldn’t take off? That ground speed, rather than TAS or IAS is what governs flight dynamics? Really? If the engine is generating thrust, Newton tells us the plane moves forward. If not, where is the equal and opposite reaction? All the conveyor belt is doing is spinning the wheels up at double speed. I am confounded that this experiment has been done and it was proven the plane takes off, but some people ignore experimental evidence because it conflicts with their (faulty) understanding.
Discaimer: I understand in practice (speed of belt = ground speed of plane, or any other higher reasonable speed the wheels can handle) the plane would take off no problems since the engines of a plane are not dependent on the wheel speed.
The main issue in this ridle is as you wrote: "All the conveyor belt is doing is spinning the wheels up at double speed." Since the ridle says that belt matches the speed of the wheeels exactly it is now mooving at double speed also. So the wheels are moving at triple speed now. Belt matches and wheels are at 4x speed. Belt matches and so on. This has only 2 solutions:
Wheel Speed = 0 - plane not moving so it does not take of.
Wheel Speed = infinity - Wheels explode, plane on fire due to friction, black hole forms when speed reaches speed of light, either way plane propably not taking off...
The riddle as witten just messes with math a little. From physics we know speedOFwheels = speedOFbelt + airplanegroundspeed. But since the ridle says speedOFbelt = speedOFwheels that is only possible if airplanegroundspeed = 0.
I'm with you! I'm embarrassed to admit that I, incorrectly, thought the plane wouldn't be able to takeoff when the Mythbusters conducted their test. I'm a lifelong aviation enthusiast and huge fan of Capt. Joe but disappointed that he got this wrong.
I disagree on your first answer that it will not move forward and take off.
Ideal scenario: the free wheel should be considered as a roller with no friction. If you draw the free body diagram, the only force acting on the body is going down which is force due to weight. Even if the ground is moving in whatever direction in whatever speed in whatever moment in time, the body should stay stationary with respect to its initial location in space.
Non ideal scenario (except that the impossible conveyor belt exist): The friction on the wheels (rolling friction, mechanical efficiencies, etc.) will create a force opposite to the force of the direction of the thrust. However with enough thrust, it will overcome the force due to friction, thus induce a motion forward - w.r.t. its initial location in space and according to the direction of thrust - and generate lift.
Of course it can it doesn’t use wheels to provide power
Exactly
That does not matter a damn bit!
If the belt matches the speed of the wheels then all forward thrust of the plane is being used to not be sent backwards!
@@thedausthed even if the wheels and the belt are made of sand paper, there’s only so much friction going on between the axels of the wheels and the landing legs which can easily be overpowered by the engines
@@thedausthed The belt can transmit a lot of spin to the wheels. But the wheels cannot transmit very much backward force to the airplane, because of their bearings. There will indeed be a slight backwards force due to internal friction, but regardless of the wheel speed the engines will have more than enough power to move the plane forward. If spinning wheels caused huge backwards forces, we also wouldn't be able to coast on roller skates without quickly coming to a stop.
Every time this does its rounds. It turns into a battle between pilots and engineers
I hope pilots and engineers are on the same side. I am an engineer and I say it will take off in all cases.
@@jphilb then you are not a good engineer
@@joshualengers7743 Put a rocket on the conveyor belt. Bet it will move.
@@joshualengers7743 lift comes from the air passing over the wings. Why do you think the belt should be able to hold back the plane?
@@joshualengers7743 The wheels are free-wheeling. The plane is effectively on roller skates. If I put you on roller skates and push you forward at 5mph on a conveyor belt, you still move at 5mph but the wheels on your skates move faster than they would normally.
Hey Joe, at 2:45 you say the plane has to move forward relative to the ground....but isn't it the plane moving through the air that creates lift?
@@maafg4435 that shouldn't matter, imagine the jets are 2 guys at either side of the plane pushing the wings while not standing on the treadmill. it'll move forward because the treadmill has no effect on the speed these guys push.
I think this is essentially a modern rehash of Zeno’s paradox. (Achilles races a tortoise. Tortoise has a head start. Race starts. Achilles covers the distance to where the tortoise is, but in the time that took, the tortoise has moved. Then he has to cover that distance, but the tortoise moves again. This, for infinity. ‘Achilles can’t overtake the tortoise’)
In reality, that’s not how a race works. Similarly, this scenario tells you a thing is happening that can’t really happen. So of course it breaks a few brains.
(I also think even though the ‘runway sized treadmill’ is often explained in the wording, this question is almost always accompanied by a diagram that makes it look like the treadmill is only the length of the plane, which straightaway primes the readers mind to imagine the question is saying ‘can the plane take off vertically on this treadmill by getting the treadmill up to the planes take off speed.’)
I think yes it can take off, its just the wheels will spin faster but the thrust will still move the plane forward relative to the air
If the plane moves forward you are breaking the condition in the question - wheel speed is not matching the conveyor belt speed.
@@tomaz2007 Wheels will have to start skidding (so we achieve forward movement relative to the treadmill and airplane can take off) when the trust exceedes the friction
@@Siatkowkarzadzi why would they have to? They'd just spin faster.
@@tomaz2007 They have to due to 2nd Newton's law. Aircraft has to move when forces acting on it are imbalanced (thrust > friction)
@@Siatkowkarzadzi exactly, it would just move forward relative to the ground. The wheels don't have to skid, their radial velocity would just be greater than the conveyor speed. But this breaks the condition of the question.
I really Love your Videos, there are so interesting and i am learning more than in school 😉
Captain Jo, I’m sorry, you’re wrong. The only opposite reaction would be friction on the wheel bearings which wouldn’t be enough to overcome the engine thrust. In this impossible scenario, the wheels would instantly speed up to infinity. The wheel bearings spinning would not provide an equal and opposite reaction to the engine thrust. Even if the friction was infinite, it wouldn’t be in the opposite direction of the engine thrust!
Edit: The more I read the comments, it seems like people are thinking if the plane is standing still it won’t take off. Which is correct. However no conveyor belt, EVEN THE ONE IN SCENARIO 1 would keep the plane standing still no matter how the conveyor belt was setup even if it could match the plane’s wheel speed.
people seem to have a basic failure in understanding how airplanes work. the simplest explanation i can think of is just telling these people that planes propel themselves forward using their jets and/or propellers in the air - the wheels on the ground, which have zero propulsion, are thusly completely irrelevant to moving the plane - they're just there to keep the fuselage from dragging on the ground, just like wheels on a wagon. the jets are still going to move the plane forward regardless of what the wheels are doing, just like if you had a wagon on a conveyor belt you could still stand next to that conveyor belt and walk forward by using the wagon's handle to pull the wagon, and the wagon would still move forward, the exact same way a plane's jet engines tug it through the air. the ground plays zero role in a plane's forward movement.
i dont understand why people... even cpt joe don't understand
@@kris003 yes. it's impressive. lol
@@kris003 yeah I don't get people... I mean it's even been physically proven that it will takeoff lol. Now technically the tires may blow if the belt is above a certain speed because they aren't rated for speeds above XYZ knots, but that's not the question. The question is "CAN an airplane takeoff on a conveyor belt?" It's like tying a string to a model plane on a treadmill... you can put the treadmill to the max speed and still pull the model plane to the front of the treadmill (simulating thrust).
@@ActuallySanFrancisco If the plane has forward progress on the belt, then the wheels spun faster than the belt by definition breaking the parameters of the myth, True or not true?
Great explanation. What really gets some people going is the dreaded down wind turn :-)
Joe, it is the wind over the wings. If the that determines lift...wheels have nothing to do with flying. I think your 2nd answer is nonsense.
Was just going to say this. I was a little disappointed in his erroneous answer
I agree.
Sorry. Joe is right and you are wrong. But his diagram is not clear and so I can see the confusion. In the first example the conveyor is matching the engine thrust, so the aircraft will always be stationary and because - as you say - it is airflow that counts, the plane will not take off.
But! In the second example the conveyor does not match the aircraft power. It is set to a fixed speed. So once the engine is pushing harder than the conveyor, the aircraft will start to accelerate along the conveyor, gaining airflow and taking off. Joe’s diagram is silly because it shows a short conveyor. The real conveyor would need to be as long as the real runway!
But the real point is that a car puts power down through the wheels. To move faster than a conveyor you have to first push the engine to match its speed, and then push it even harder. But an aircraft doesn’t put its power through the wheels. So once you have matched the conveyor speed, you would just accelerate normally, with normal engine power.
ie if a car’s top speed were 200mph, and you put it in a conveyor going 100mph in the opposite direction, the car would be able to go no faster than 100mph compared to the ground. But if an aircraft’s top speed were 200mph, it would be able to reach that. The conveyor is backwards momentum but it can be overcome.
This riddle was actually tested by mithbusters, with a small aircraft (i think was a cessna 150 or a piper) taking iff a convayer belt. It took off with no problem.
Yes, but the Mythbusters tested it wrong because the speed of the conveyor belt did not match the speed of the wheels, which you can clearly see because the plane is able to accelerate to takeoff speed.
You are obviously correct about scenario 2, however I’m not convinced about scenario 1. How can the plane be stationary on the conveyor belt? If the plane’s jet engines are spinning, it is pushing a lot of air behind it. Where is all that energy going? How does your explanation for scenario 1 fit with Newton’s third law?
I realize I’m way late here, but any absolute forward speed from the aircraft necessitates infinite speed in the wheels and conveyor belt, which would presumably explode the world.
Example: say the plane has nearly reached takeoff speed, at 150 mph. This means the wheels are going at least 150, right? But that means the conveyor belt is going 150 rearward, which means the wheels are actually going 300, which means the belt is going 300, which means the wheels are actually going 450, which means the belt is going 450, which means the wheels are going 600… ad infinitum.
Sir , is it possible to slow down(stop) an aircraft by providing a conveyor system at the end of short runways( like table top)
The plane could take off, if the tires dont explode. you Accelerate by pushing air the ground didnt matter..
if the plane isn't moving air isn't flowing over the wings and no lift will be generated
indeed, the forward motion of the airplane is provided by the engines only, as long as the wheels don't provide enormous friction (which is not the case on the conveyor belt) the aircraft will have enough forward motion (=lift) to take off
@@DIBOYOU well isn't the idea of this conveyor belt that it in some magical way cancels out the forward motion of the airplane while keeping the wheels spinning? if it is just a regular conveyor belt then i get your point, the wheels would just spin a lot faster than they normally would and the plane gets the forward motion relative to the air around it it needs to lift off.
@@kristian4559 No, it doesn't say that the conveyor stops the forward motion, only that it spins -exactly- the speed of the tires in the opposite direction. That this would cause the plane not to move is a fallacy, one most people fall into because we're used to vehicles which are driven by exerting force against a road.
The only way this doesn't take off is if the plane and the conveyor belt are in a vacuum chamber.
Lift?
@@limitedkanji no, I’ll use the stairs thanks
@@jasonlee3247 lol
If it doesn’t have air, how do the tires move?
@@guessmyhandle Read my post again, CAREFULLY.
Plane takes off in both scenarios. Conveyor belt has no effect apart from the wheels friction, but as the wheels spin freely, the aircraft engines would push the plane to proper airspeed and let it take off.
That's what he explained accurately.
@@Maniacguy2777 no, he said the first scenario was impossible, it is not.
@@fyrtiotva he said if both in equal speed the conveyor belt and the plane in equal speed is possible to take-off
What about BushPlanes? They don’t need runway at all and still can take off. Wheels don’t power plane. Engines do.
Bush planes definitely need sufficient airflow over the lifting elements and they take advantage of strong headwinds wherever possible. They still have to roll on the ground (and capitalize on clever design) in order to minimize takeoff speed and distance.
1:00 Take-off shouldn't be a problem: Planes gain speed by generating thrust with the engines mounted to their wings. Are there even any motors rotating the wheels? I don't think so. 🤔
No motors in aircraft wheels (except some experiments with 'electric taxiing') that are assisting the take-off. Only the engines are providing the forward thrust, which is totally not connected to any conveyor belt type of runway (it will only impact the rotational speed of the wheels, not the airplanes forward movement)
It will be a problem. If the belt and the plain are moving in the exact same speed in the opposite direction.
the plain needs a forward motion in order to get the air under it's wings. If the belt is moving at the same time the same speed the other way. the plain in total would have a movement of 0, (zero) it is motionless only the. in this case the positive force and the negative force cancel the other.
however real life dictates that this is impossible ether the aircraft is reacting to the belt or the belt is reacting to the aircraft. even a delay of 0,0000000000000000000000000001 would mean that motion has been made.
@@sirBrouwer it's not speed it forces.
Its always a good day when Captain Joe uploads
Think of it another way... Replace thrust with a rope. If the rope is reeled in, it doesn't matter how fast the wheels or conveyor are moving, the plane WILL move forward because the mode of locomotion is disconnected from the wheels.
There is no rope. All energy of the thrust is converted to belt speed
@@Coren999 Hilarious mate. The thrust is on the plane and cares not one jot about what the wheels are doing. You didn't even watch Captain Joe at a guess (not that he's right, I address his error in a comment here).
The thrust causes the tires to move faster than the conveyor belt
@@donaldfegley6127 Nonsense. If you set a constraint on a system that constraint is not broken. The thrust propels the plane forwards. It cares not one jot WTF is happening at the wheels as long as, and this is a limiting issue is considered, any drag they exert that works against the thrust.
You have not watched the video clearly nor read my explanatory comment in which I explain how Captain Joe errs, because if you had, you would have a full assessment already of the issue of what happens to the speed of the wheels and conveyor. But the thrust cares not one hour about that unless it causes drag, and propels the plane forwards.
@@BerndWechner So explain this to me then, if the plane moves the throttles forward and the wheels start to move from the ground speed of the plane starting to move, but then the conveyor then perfectly matches the speed of those tires for ground speed, so no the plane in no longer moving forward or backwards, how to the planes wings which have to have airspeed flowing around them to produce lift, produce lift if the plane is not moving at all on the ground so no lift is being produced by the wings? When the engines produce the thrust to get the plane moving on the ground to speed the plane up so the air around the plane is producing lift on the wings, the ground speed is then completely stopped by this conveyor that now puts the planes ground speed to 0 which then means there is no airspeed being produced for the wings to create lift. Just because the engines of a plane done care what happens on the ground does not mean that the wings can produce the lift from having no airspeed to then convert to lift as the plane that is on the ground has to have forwards movement to create the airspeed required for the wings to get the lift needed, but if the forward movement is 0 because the conveyor is now keeping the plane still, which makes the airspeed 0 over the wings, which means 0 lift is now being produced to have the plane take off.
How can it takeoff without airflow bouncing flaps or lifting the wings and fuselage?
I'm going with yes. The thrust of the plain will make it move forward. The wheel will just spin faster and the belt will spin faster too keep up with them. The thrust of the engine will still mover the plane forward creating air movement and then lift.
The plane would have to move faster than the wheels can keep up. Because the plane has mass, the wheels touching the ground, for the plane to move, the wheels would have to drag on the ground. Think a plane trying to take off with no wheels. That's what your saying.
A video on a start up from cold and dark would be super interesting
Wheel speed matters not one bit. Ever wonder why you’d want to put your small prop plane inside if there’s a windstorm?
The problem here is people can differentiate between the wheel ground speed and the aircraft’s airspeed being independent of each other .
Mentour Pilot has positive attitute, Captain Joe's riddle has positive feedback :)
I love when you say it in German 5:44
Because he's German...
@@jimday666 what's with the "..." ?
@@treeinafield5022 *sigh*. He's German
ok, there are a few questions hidden in this thought experiment, and all are a problem of the relative motion of three objects, the air, the ground, and the plane:
1. will a plane take off if it is held in place by a conveyor belt keeping it from moving forward by exerting enough force on the wheels that the wheels exert enough force on the plane to prevent forward movement?
if the plane can move the air past itself fast enough, it will take off. if the plane can't do that, it won't take off.
if the air moves enough, the position of the plane relative to the ground doesn't matter. the plane can take off without moving forward, as the air moves fast enough to lift the plane
2. will a plane take off on a conveyor belt designed to keep the airplane in the same position relative to the air?
if the air and plane aren't moving relative to each other, it doesn't matter how fast the plane moves relative to the ground, it won't take off.
My problem with the riddle is that it's not _quite_ defined well enough. Specifically, what _exactly_ does "designed to move at precisely the speed of the wheels in the opposite direction" mean?
I see two main, and somewhat ambiguous, interpretations:
1. If it means that the conveyor's velocity is always equal and opposite to the average velocity of the wheels, i.e. the velocity of the central hub (which is the same as the velocity of the plane itself), then yes, it can probably take off. This would effectively simply double the radial velocity of the wheels, and as long as that is something that's within the tolerances of the tires and hubs to not explode and overheat, respectively (which I suspect it is, since a no-flaps landing in a tailwind could come pretty close to that ground speed), then there should be no problem taking off, since the plane doesn't rely on ground friction for its thrust and acceleration. Yes, there'd be a little more friction from the hubs and rolling resistance of the tires, due to the increased apparent wheel speed, but compared to the power of a passenger jet's engines, my head-napkin math says that should be negligible.
2. If it means that the conveyor's absolute velocity relative to an inertial observer is equal and opposite to the tangential velocity of the tires as they spin, then... probably not, but it still might be possible. This definition is recursive, so the wheels' speed and the conveyor's speed, which are each defined by each other, would create a positive feedback loop that would exponentially ramp the speed up toward infinity. Of course, you could never actually build an infinitely fast conveyor belt, so it would depend on whether the conveyor can go fast enough to over-speed the wheel assemblies before the plane has enough lift to take off.
Edit: Cool, that's pretty much exactly the conclusion you came to.
If you ever _do_ find yourself taking off on a conveyor belt in either scenario, I recommend the most extreme possible short-take-off setup... brakes on full as long as possible until engines spool up as fully as possible, for starters. I might even consider starting in a clean configuration for the initial acceleration, then dump flaps/slats approximately one cycle time before rotation speed (the earliest rotation speed possible given the load parameters, with engines running at absolute max power). Could you even spool up most of the way with reverse thrust selected, so that the reversers would be closing just as thrust passed maybe the 60% mark, and finish the transition just as the thrust pushed the mechanical limits of the hydraulics?
In any case, since you'd be doing so in real reality instead of spherical cow thought experiment land, I think you could put your faith in the safety factor the engineers of the tires and wheels designed into them, over the bizarre possibility of an infinite-velocity, infinite-acceleration conveyor belt. That is, assuming the take-off is super-important, like to escape the massive volcano island on the verge of erupting that the supervillain who built the conveyor belt anti-takeoff system triggered, or something. If it's just, like, to go to another city for business, I'd just ...
Actually, scratch that. If you ever find yourself facing a conveyor runway, just take off on the longest taxiway instead.
you are not going to believe this, but for the first time in a long time, I just used the phrase, "outside the box thinking" to describe another take. Then I read your comment and you used it. Crazy coincidences like that are what life was made for.
Anyway. I think the whole thing comes down to the external force of the engine thrust acting on what is considered to be a closed system.
The conveyor moves at the speed of the wheels, right? Well, in order for the wheel to turn in the first place, there must be forward movement. The engines will inch the aircraft forward just a bit, and the wheels will begin to roll. Nothing the conveyor can do, even magically can reverse that first movement. It then becomes a game of cat and mouse with the conveyor instantly (but with some imperceptible delay) matching the speed of the wheels. This acceleration will also be added to the speed of the wheels. All the while, the external thrust will continue to add to the gap between the speeds until the plane reaches takeoff speed.
As for the whole breakdowns thing. Why does nobody consider the treadmill to be breakable? Everybody wants to talk about the wheels failing, but not a multi KM long treadmill with a motor, a belt system and tens of thousands of rollers with their own bearings that could heat up under all this stress.
Hey, Captain Joe... How about mounting a catapult, carrier style, on the runway?
I would pay double for that experience
The way I understand this, is that if the conveyor is matching the groundspeed, the wheels basically double in speed.
If the propeller makes the plane begin to move, the conveyor will start as well. So if the plane crawls along slowly at 5km/h, the wheels will do the same 5km, which is matched by the conveyor. But because the wheels spin freely, and the plane is still able to move forward at 5km/h the wheels add on that extra ground speed, and will spin at 10km/h.
So matching the groundspeed will simply double the speed of the wheel spin.
The test could be done by putting a small model of a plane, attach it to something stationary, then turn the power to full. If you release it, it wouldn't automatically shoot up into the air. It would still need to reach takeoff speed to do it.
The conveyor isn't matching the ground speed, it's matching the wheel speed. If it is matching the wheel speed then ground speed is always 0 and the plane cannot ever take off
@@ClikcerProductions Wrong. The wheels can not hold back the plane if the engines are pushing it forwards. Oh, and the wheels are stuck to the plane, right? So they too move forwards relative to the ground. That movement determines how fast the belt is going backwards.
@@paldyvik7915 A force can be applied through free spinning wheels, this is something extremely obvious if you just hold a toy car on a running treadmill, you need to apply a force to keep it in place, if you remove that force the car is pushed backwards through it's free spinning wheels, the same thing can be done with the plane. If you think the plane moves forwards you are either allowing the wheels to slip (which is just super boring) or you do not understand very basic geometry, the only good argument for the plane being able to take off is that the treadmill would reach speeds high enough to produce winds fast enough to reach take off velocity while in place on the conveyor
@@ClikcerProductions I'm not stating that there is NO increased force from the conveyor belt moving the opposite direction. What many people don't realize is that these are WHEELS. Wheels are touching the surface below, and normally not slipping much (assuming friction exists). This contact point is however not what determines the speed of the wheel. The speed is measured at the CENTRE of the wheel, which may be moving relatively freely forwards and backwards, disregarding how fast the surface below is moving or not.
The wheels are stuck to the plane, and when the engines start pushing the plane forwards, the wheels of course follow. as soon as the plane reaches 1 knot towards the left, the belt has responded and moves at 1 knot to the right. That causes the wheels to ROTATE at an RPM corresponding to 2 knots, but they are MOVING at a speed of 1 knot. The same continues as the plane accelerates and MOVES to the left, and at the moment take off speed has been reached, the belt is going to the right, also at "take off speed".
Any argument have seen that the plane will stay stationary are false. Mostly, people assume that the extra rotation induced by the belt are able to magically cancel the push from the engine.
Now figure this:
1. Imagine you are in your car, driving at 100 km/h. You probably realize that your wheels are moving at the same speed, right? If not, hand in your license.
2. Imagine a toy car, pointing to the left, with a red string attched to the front. Now pull that string to the left at a constant speed. Do you see the car moving?
3. Imagine the car is standing on a green paper sheet. Pull at that green paper sheet below the car, towards the right and at the same speed as the red string, but in the opposite direction. (You may want to practice with empty hands first, to build confidence in yourself as a researcher.)
4. Repeat step 3, while carefully observing whether or not the car is moving to the left. Repeat one or more iterations until the shock settles. Also observe the rotation of the wheels compared to in step 2. (Hint: The car IS actually moving to the left!)
5. The car is the 747. Pulling on the red string represents the push from the jet engines. Pulling on the green sheet represents the conveyor belt responding to the movement of the plane and its wheels. (Remember step 1?)
The fact that the belt moving to the right does not prevent the plane from moving to the left at the exact same speed, as stated in the riddle, proves that the plane will be able to accelerate and its wings gain lift.
Riddle solved: Take off OK!
@@paldyvik7915 The speed of the wheels is not the speed of the center of the wheels, that makes it a completely pointless thought experiment, if you want to interpret it that way you can, but that interpretation is so impressively lacking in any level of nuance or intrigue that I would expect a more interesting intellectual conversation from a 5 year old. The wheel speed is very clearly meant to refer to the speed of the surface of the wheel relative to it's center of rotation, I want to be very clear here that YOU are choosing to interpret the though experiment in a way which makes it pathetically dull. Please only reply if you have any interest in discussing the thought experiment the video is actually covering
Here is a trick. Imagine the plane has a hovercraft base. It is lofted above the ground by a cushion of air. Can it take off ?
Of course it can ! The plane is moved forward by the the forward reaction of the plane to the movement of air moving backwards. As a result of this forward motion, surrounding air moves past the wings, such that, because of the curvature of the wings, there is less pressure above the wing than below. This results in lift and the plane rises.
This means that, regardless of what is happening under the aircraft...wheels, opposite magnetic fields, a cushion of air, a conveyor belt...the plane will move forward and fly when it has enough lift provided by the wings. If one wanted to watch a plane "levitate" i.e. appear to fly vertically without upward thrust, one could use the same undercarriages as above, but provide a fan or other wind generator to move air past the wings, and use a propulsion device (prop/jet) to provide an equal and opposite force to wind, pushing or pulling the aircraft.
Hopefully this description provides enough abstract elements for the imagination to conceptualize how this worked.
The video editing of the execution of this experiment did not really show that the plane still moved forward sufficiently to provide lift and fly... while, at the same time, the "conveyor belt" was simply spinning the wheels underneath as they simply held the plane up as it moved.
But it isn’t; there is a mechanical connection between the wheels and the plane, and the wheels are practically connected to the ground. Unless the wheels slip there is no motion
No airspeed = no takeoff.
Someone shared that on 9gag, and that was my explaination:
- A plane is lifted by an airflow above and (most importantly) under the wings.
- That plane on the imaginary conveyor belt is simply immobile relatively to the air surrounding wings. It doesn't matter how you twist it: turning the engines on, buying 24 elephants to pull the plane with ropes, pouring nitro into the engines... It's irrelevant: every thrust you can generate is nullified by the conveyor belt. So relatively to the air, it's an immobile plane.
- You don't have an airflow under your wings.
- The plane cannot possibly take off.
Correct. The change in speed is always zero because of the adaptive conveyor behavior.
This is true ONLY as long as pulling/pushing force is less or equal to the friction between the wheels and the belt. In our case if thrust will exceed the friction, the aircraft will start moving (tires will start slipping/skidding on the belt)
This is true. The best way to explain the phenomenon is that you're just trying to get the engines going fast enough, that's it. Once the engines are at full speed, you achieve lift, whether or not your wheels are spinning. You can't just spin your engines up to full speed while you're sitting still though, that's why it's crucial that the treadmill be able to accelerate and match the speed of the plane. If the treadmill was stuck below some speed which would accommodate the engines reaching sufficient power for lift, there'd be no lift.
@@A38 you only achieve lift by having airflow and in this case, the vehicle motion is in equilibrium with this stupid conveyor.
The resulting speed of vehicle is nil…while it is on the ground trying to roll.
Another way to simplify this even more is this - remove the wheels; make it a big block with a force applied to it while on a conveyor.
We know the formula for pushing a block with sliding using kinetic friction coefficient. That gives us acceleration/velocity,
We know this stupid conveyor is designed to exactly match that speed. It’s doable, but it’s a stupid textbook problem.
@@Siatkowkarzadzi No, force of the belt is multiplying to lubricated bearings in the wheel friction, which is for theoretical experiment is equal to zero !! So backward force is zero, forward force - regular force from propeller
Maybe this is covered better later in the video, but ground speed doesn’t matter at all when it comes to flight. What matters is the air moving over the wings
True, but the problem here is that people focus on the wheels and extrapolate from cars. However, airplanes use propellers/turbines/etc. to push themselves off the surrounding air, with the wheels not being powered at all.
@@germansnowman you're rigth. Planes don't need to have wheels to take off. So they're not part of the equation
The aircraft thrust will move the aircraft forward, not turn the wheels to move the aircraft. So, the acft moves forward which causes the wheels to spin. Not even instant acceleration of the treadmill can undo that motion. So the wheels must even momentarily move faster than the treadmill. In this case, the treadmill must now catch up, but it's acceleration will be added to the acceleration of wheels. The forward thrust of the engines, which is not dependent on the wheels will constantly add to the gap until takeoff speed is reached.
This is physics. It's like if you put a car on a dyno, but you put the non-drive wheels on it. When you hit the gas, the car will move forward no matter how fast the dyno can spin. That's because the forward thrust is not attached to the dyno. Just like the thrust is not attached to the treadmill through the free spinning wheels.
You're breaking the premise of the conveyor though. It can do the impossible. Imagine putting an rc car on a Dyno, but then pushing it with your hand (let's say your hand produces way more force than the car or dyno are capable of). In real life, the extra thrust from your hand would push it off the dyno. If this dyno worked like the magic conveyor, the car wouldn't move. You would see and hear the tires and Dyno spin even faster to keep up with the increased thrust proportional to how hard you push. You can pick up the car just fine, but as long as the tires and dyno are in contact, the rule applies and the rest of reality will bend to accommodate. All of your force is instantly counteracted by the dyno because it needs to match the tires, and any relative movement forward or backward would break that rule.
@@dogboy0912 ah, but at some point in my pushing, my force would be more than the car weighs and would simply force it off of the dyno. We are not talking about a wall here, just a small surface contact point. If the wheels were the source of the momentum, all this would be true, but because it's an outside force, it will be overcome.
Some have mentioned I might be right if the plane "skipped" or slipped. Perhaps that is how it manifests, but the rule of the belt itself cannot be allowed to contravene all other forces. I mean, we already have to throw out breakage and any form of speed limit as a part of the question, but assuming that the conveyor is holding the tires down is a bridge too far for me. The body of the plane wants to move forward, it will.
Hey Cap the link for 747 model is not working.It is showing incorrect URL.
Please fix this issue.Thank you.
I think this depends on the friction between the wheels and the conveyor belt. If the belt was low friction, you can put the park brake on, so the conveyor belt does not move and just take of as if you had skis.
You are 100% correct. When the plane starts to move, the conveyor belt has to move the same speed as wheels, but moving the belt spins the wheels faster. So if there is any friction involving the wheels, the belt and wheels will speed at infinite speed almost instantaneously. The only way to spin them at the same speed is to have the energy from the thrust of the engine be matched by the frictional energy lost by the wheels on the belt. So unless the wheels skid as you say, the given conditions are impossible. Same speed needs to be defined better.
Not how that works at all, and not the point of the question
@@Ryan50c actually, it's a brilliant, out of the box, solution to the problem. The belt doesn't move because the wheels are locked. The engine thrust then pushes the plane forward, belt and all. The only potential drawback is if you say the belt will only move under its own power and opposite the direction of the aircraft. But the principle is pretty hoopy thinking.
If you turn scenario 1 around. Start at the end of the runway and move the aircraft backwards with the conveyor. With no thrust it moves backwards. But in order to remain stationary it only needs to produce enough thrust to compensate for the friction in the wheel bearings. Thus in either Scenario this is the only backwards force acting on the aircraft.
The only way it won’t take off is if the conveyor is moving so fast that the bearing friction matches the thrust which is absurd.
In both cases the aircraft takes off with its wheels spinning faster.
The conveyor is essentially adaptive to wheel speed. He explains it in not so great fashion because it’s a subtle difference. In his second example, he provides the explanation of a conveyor with a constant speed which would of course allow takeoff.
A conveyor that always exactly matches (rolling) speed, there is no velocity change.
@@MrDefreese Scenario 1 - aircraft will not move ONLY as long as thrust force is less or equal to the friction between the wheels and the belt. If thrust will exceed the friction, the aircraft will start moving (tires will start slipping/skidding on the belt)
@@Siatkowkarzadzi correct. Implicit in this example is that the wheels roll (freely) and excludes add-on items like busted bearings, absurd headwinds, etc. boiling it down, this is a basic cart and wheel physics problem where we are given unity for linear speed of the conveyor and the rotational speed of the wheels.
@@MrDefreeseonly if the wheels eventually fail. But if we’re assuming the conveyor is magic and can sustain infinite speeds, and we assume the wheels can sustain infinite speeds, they neutralise and the thrust still pushes the plane forward.
I think the flaw might be thinking that the wind speed equals the conveyor belt speed. At full thrust the wind speed moving over the wings would be greater than the tire rotation speed. This is how you can lift off into an extreme headwind with very little forward ground speed. Right?
Why would the B747 lift off once the wheel speed relative to the conveyor belt reaches 320 knots?? The wings would surely, still be stationary, relative to the ground...?
A plane can take off without wheels, so I think they are pretty irrelevant if they are on a conveyor or not.
🤣I am curious about your statement...how will a plane take off without wheels plz elaborate!
@@AtharvaSathaye Seaplane
You can’t claim an imaginary runway and also not give me an equal set of imaginary strong wheels that won’t explode. The question sets the stage for me to assume some liberties as well. The plane takes off.
Planes don't get their propulsion from their wheels. So yes they can. If the belt moves at the speed required to takeoff, it won't make a difference.
Now if the belt moved at the speed of the wheels, the belt would infinitely increase speed and do serious damage to the plane.
Forgive an old fool but how exactly does the conveyor belt matching the speed of the wheels cancel out the thrust of the engines? This is the bit I really struggle with, the wheels play no part in propelling the aircraft forward. Air is sucked in, forced out and the conveyor's speed doesn't alter the thrust produced.
He’s wrong on the first case. It would still take off. He’s thinking of it like a car.
@@ChrisFranklin.2260 hes not. If the conveyor belt was able to completely match the speed of the wheels, it would have no forward motion in reference to the air it is trying to use to take off. This is completely impossible in real scenarios due to a number of factors, but the baseline assumptions of the first example would mean that the plane would not be able to make forward progress and move through the air which it needs to take off
@@Professor-fc7vc I'm still not convinced. His arguments for the first case did not seem well fleshed out to me. There's still nothing to cancel out the hundreds of thousands of pounds of thrust on the body of the aircraft. Doesn't matter what the wheels are doing, or what the speed controller for the belt is basing its output on.
My answer before watching the video: yes, it can still take off, regardless of the speed of the wheels that engine is pulling on the surrounding air and those wheel bearing will probably give way and break the wheels off and the plane will still proceed forward with no wheels (theoretically)
we werent given that info. remember this is a magic conveyor which can move at infinite speed, so i assume these magic wheels can survive magically high speeds without failing.
@@sizone yea terrible question forming. Trick question.
Plane needs to generate lift first and foremost before any magic can happen.
@@sizone Then the wheels are getting dragged off the conveyor because regardless of what the wheels are doing, that plane is moving forward.
Capten sorry but your plane will lift off in any case. Matching or even double the speed of the belt backwards it (if the weels can hold the spin) you will take off! If your consider is about if the weels can hold on the frictions ect it is another riddle
Something not considered in the airplane airplane scenario, the conveyor getting faster and faster might have an effect on the surrounding air to the advantage of the plane taking off.
Straps CRJ 200 behind a really big fan
Me: “guys I made an expensive kite”
You could use wind turbines, when they're not blowing aircraft into the air they can carry on their normal function of generating power.
Or why not use a catapult? That would be brilliant for short take-offs from ships, then catch them with a very strong elastic band when they land. Once the plane has stopped, the elastic band will pull it back to the start of the runway ready for the next takeoff.
@@rogerbarton497 better yet remove engines from the aircraft entirely for short haul flights and just use big gliders and glorified slingshots.
If you’re an adrenaline junkies we can just put you in a padded ball and launch you up to 60 miles away into a net, and hope the wind doesn’t change enough to cause you to...miss
@@grantkendrick277 It's strange how the simplest ideas are the best. I'm sure we could engage the services of top snooker and billiards players to solve the problem about getting the balls in the correct net.
For case 1,it is necessary to have at least one of the following conditions:
- The wheel has non-zero inertia.
- The bearings have non-zero friction.
If none of this conditions is met, it could actually take off.
Nitpciky engineering "Well, actually" in regards to the car on the conveyer belt: You don't need the same power provided by the engine to go 150 km/h on the belt as you would need to go 300 km/h on the road. The cars groundspeed might need to be 300 km/h, its final "airspeed" on the belt is just 150 km/h, so you save a lot of power that you would otherwise need to overcome the difference in air resistance between 150 km/h and 300 km/h "airspeed" on the road.
Anyways, nice video, thanks for the insightfull content Captain;).
Good thing Cpt differentiated between "exactly" and "takeoff speed"...that is where the controversy lay.
Yes, during 150knots head winds