PLEASE READ. I noticed some viewers get hung-up on the "equal transit theory" at 2:21. I mostly ignored it at first since for me it's really besides the point and not what is to be taken out of that explanation. But now I have to address it. So to course-correct here's three things: 1. If it's understood that the accelerated air over the top of the airfoil causes lower pressure than below the airfoil, and this displaces air downwards and the reactionary force is lift/thrust then you understand the necessary. 2. My wording is admittedly poor and I never attempted to describe the "equal transit theory", but poorly attempted to describe what causes acceleration i.e. different distances to be covered (over the top and below), same amount of time causes acceleration. Air doesn't have to arrive at EXACTLY the same time and frankly in my opinion is completely irrelevant in lift creation, because of point 1 (it's the pressure differential that creates lift, not whether transit is equal or not). 3. I've come to the realization that just because I've never cared if the air over the top arrives at the same time, before or after the air below - and still don't - doesn't mean others don't care and it's not for me to decide if you should find it irrelevant or not. I hope that clarifies it and that the remainder of the video is enjoyable and informative.
The remainder of the video is spot on and is a good starting point for anyone interested in why propellers are so varied between aircraft as well as their principles and operations. For the sidewalk and blade pitch analogy, it might have been better to simply explain geometric/effective pitch and build on that. Maybe something to add in part 2. I would suggest not even mentioning the Bernoulli principle or the outdated idea that the upper curve of the airfoil creates low pressure or the associated equal transit theory, it just mucks up the underlying concept because none of it has a demonstrable effect and is often contradictory to itself relating to lift in fluid dynamics. Airfoils make lift purely by deflection (AOA, or pitch in the viewpoint of a blade), whereas the shape of the airfoil determines how efficient it is at making and defining that lift...the airfoil shape itself doesn't create lift simply because it exists as such. Flat airfoils and symmetrical airfoils will still make lift without any of the Bernoulli/equal transit nonsense involved (even space capsules without an airfoil traveling at hypersonic speeds negating the premise of those theories still make lift, via deflection), whereas a proper textbook airfoil shape won't produce any lift at all if it has no AOA/pitch. That's the simple explanation backed by fluid dynamics; deflection creates lift, airfoil shape defines lift characteristics. I don't know who was responsible for the first reference between Bernoulli and lift, but whoever it was did a great disservice to the world of aviation. It's taught in primary school and is still prevalent everywhere in aviation, so everyone's first and most important introduction to aerodynamics is based on a false premise, and that's why so many people are getting hung up on it.
@@Skinflaps_Meatslapper OK so I also caught that mistake (quoting that old-fashioned Bernoulli Equal Transit-Time Theory of Lift), and as someone who has designed and manufactured wind turbine blades, and know a few of the top guys in that field, I've had a lot of time to slowly gain an understanding of lift. Not to mention sailing and hang-gliding. Hang gliding really helps you understand lift. Not to mention, stalls. At some point the lightbulb goes off, and you think, "Wow, it's actually pretty simple!" (I never believed the Bernoulli Explanation, even as a kid.) By the way, I just saw a documentary with David Attenborough "explaining" how a flying dinosaur reptile's wings worked. Of course, like all the rest of the people still repeating the same old wrong explanation after so many decades, he said it was because the air went faster over the upper wing surface - what else? Rumors die hard! Only HE explained it with a crisp British accent, so like most science documentaries, it makes it sound like the narrator knows what the hell they're talking about. But half the time they don't. Anyway, yes it IS the TOP surface of the airfoil that produces most of the lift, which is why the top surface is where the sheet metal pulls up and away from the ribs, causing loose rivets on old airplanes, and why all the engines and weaponry are hung from the bottom surface of the wing, because they don't ruin the lift down there. The plane sucks itself into the sky. The vacuum on the top surface allows the ambient air pressure on all of the bottom surfaces, even the engines and weaponry, to push upward more than the lower pressure air on top pushes downward. And yes, the air actually goes MUCH faster over the top surface than even equal transit time would require! (watch a video of airfoils in wind tunnels and they show you) BUT, mere SPEED of the air over the top surface is NOT where MOST of the lift comes from. Some lift, yes, but not most of it. The amount of lower pressure from the mere faster speed of the air over the top surface of the wing is not sufficient to provide the amount of lift we actually get. They figured that out mathematically many decades ago. And I'm not going to say here what IS the reason we get such low pressure on the top surface. I'm saving that info. But it is funny to read articles in Magazines such as "Scientific American" where they admit that there is no universally-accepted theory of lift to this day, and experts could not agree, even if they HAD an explanation, which most of them don't. All they know is which airfoil makes how much lift under what conditions, but they don't know why, really. And they can write code to emulate airflow, and predict which airfoils will do what pretty accurately, but they are still scratching their heads over exactly why it all actually works - they can model it, they can design with it, but as far as "official science" is concerned, they can't understand it, or put it into words. Of course, "official science" also once insisted that stones could not fall from the sky! As is so often the case, the primitive people of the countryside knew more than the scientists sometimes. I like to watch STOL competitions. I'll bet some of those guys have also, like me making wind turbine blades, figured out how "lift" really works. Anyway, I think I have the explanation, and it's actually easier to understand than Bernoulli etc. Anyway, maybe I'll publicize it at some point. The world needs to know.
@@dougselsam5393 It's actually quite simple to understand intuitively; the primary reason why it's difficult to scientifically quantify is because like anything in fluid dynamics, you can't simply attribute it to one single thing and modeling it to proof a theory is difficult. The top of the airfoil experiencing low pressure on its own isn't enough to create the lift being generated, lift is the result of the entire air mass that the airfoil interacts with, both above and below the airfoil. If it were nothing more than low pressure, then a helicopter rotor wouldn't have downwash, there would just be a low pressure lens above the rotor holding the craft airborne. But we know that accelerating that mass of air downward is the action that creates the reaction of lift. Same goes for a propeller, it takes a certain mass of air and accelerates it rearward, as opposed to creating low pressure in front of the prop disk. Both are no different than a wing, which takes a certain amount of air and accelerates it downward. The low pressure is part of the equation, but moving that air mass downward is the action that creates the reaction (lift). You can imagine an airfoil splitting that air mass in half, the bottom physically pushing the air down, and the top pulling the air down. The more curve the top of an airfoil has, the more effective it is at high AOA, and thus is better suited for slower aircraft such as STOL, ag planes, aerobatics, etc. at the expense of drag. When you reduce that curve and make the airfoil flatter, it creates less drag at the expense of being less efficient at higher AOA. The reason for this is because that curve gives the air a surface to "stick" to without separating. A flatter airfoil causes a more abrupt change in direction at higher AOA, the air has a harder time suddenly changing directions and the air has a harder time sticking to the wing, separating into a turbulent mess instead. Flaps and slats and VG's and all those other gadgets are simply ways to help that air stay connected to the top of the airfoil, because if you can't bring that upper air mass down, the lower air mass is going to fill the vacuum created by the turbulent mess above it rather than continuing downward as it should. Deflection of the airfoil is what causes lift, and the shape of the airfoil is what defines what kind of lift is being created when that happens. The air mass on both sides of the airfoil have to be on the same page before lift is generated, you can't attribute lift to one or the other, as it's a singular action. I've had an instructor tell me that a jet moves forward by the suction from the engine, and while that force does contribute to thrust, it's primarily the acceleration of that air mass going out the nozzle that's responsible for thrust by a large margin. Modeling the cross sectional area of a jet intake and then calculating how much force could be generated by putting a hard vacuum on that area results in a fraction of the actual thrust of a jet. Same goes for a wing and the small amount of vacuum on top that it creates in high alpha (that's why you often see the vapor forming on top of fighter jets, that's low pressure forming). Attributing it to one side of the equation would be like saying the road pushing against a tire is what propels a car forward rather than the tires pushing against the road, when it's the interaction of both that propels a car forward.
@@Skinflaps_Meatslapper Well, you don't quite have the full picture. You said lift is NOT generated by suction on the top surface of the wing, and a propeller does NOT function due to suction on the front (suction) side of the airfoil. That is wrong. If there is one thing aero people agree upon, it is that suction on the top surface is what causes lift. The "mystery" is exactly what causes such extreme suction, since the windspeed alone cannot explain it. What you are attempting to do is apply the SECOND MOST COMMON MISSTATEMENT of what "causes" lift, which you confuse with the mere "result", that air is deflected downward. This is a very common, but insufficient, "explanation" for a "cause" of the lift. No, the air deflection is a RESULT of the same phenomenon that CAUSES the lift. When you stop to think about it, if the wing produces lift, then of course, there "HAS to be" a downwash, right? So that is not the cause, it is just one more result of a well-functioning airfoil. You had also stated that an airfoil with zero angle of attack will not provide lift. Guess again. Most airfoils DO produce lift, even at a zero angle of attack. Not as much lift, but they do still provide lift at zero angle. And you also cited helicopter blades and symmetircal airfoils as evidence that lift is NOT caused by suction on the top side - wrong again: these airfoils produce lift only when oriented at an angle of attack to the airflow, and when producing lift, of course they also produce a downwash. which is a result, not a cause, of lift. When people ask to understand the cause of the lift, they want to know what is physically "holding the airplane up", or in the case of the propeller, pulling the airplane forward. In either case, it is suction on (drumroll please...) the SUCTION side of the airfoil. There is a reason it is called "the suction side", because that is where the suction occurs, and suction is the key to "lift", just as suction is responsible for the function of a drinking straw. Would you say a drinking straw works BECAUSE of the liquid moving up inside the straw? NO, that is a RESULT of the suction, NOT the cause. And as I explained, that is why, when rebuilding an old airplane with a sheet metal wing surface, the rivets on the TOP surface (NOT the bottom surface) are what come loose and need attention (repair). And that is why the engines and armaments are always mounted on the pressure-side (lower side) because it hardly matters what happens down there, other than the drag all that stuff causes, but they put up with the drag. Really smart outsiders to it all, even with engineering degrees, often try to use the downwash as an "explanation" for the lift. That's like saying your exhaust coming out of the tailpipe is what powers your piston engine. Of course it has to have exhaust, but the exhaust is not the "reason" the car rolls down the road, it's more just another result of the process of the engine running. It;s also like saying your empty bank account is why you lost all your money in Las Vegas. No, your bak account is empty because of the specific gambling activity that gave away the money, not BECAUSE your bank account was emptied. See the difference? So, in the end, of course, a wing produces a downwash, but the downwash is a RESULT, not the cause, of the "lift". Saying the downwash CAUSES the lift is just an easy out for people who don't know HOW the wing is physically lifted. It's a way to take a true statement (that there is a downwash) and pretend it describes HOW that downwash is generated. Downwash is not a CAUSE, but just one more RESULT, of the phenomenon of lift.
I chose to not address this wives tale about airflow trying to meet at the trailing edge . An Air Force Captain in 69 explained it well. "A jet engine sucks a hole in the air and falls into it.... And a propeller does too.... LOL".
A part 2 would be beautiful, please. I’m very interested in toroidal propellers, particularly seeing the advantage Sharrow propellers offer the boating industry. Thank you. 🙏
Back in the '90's I had a propeller program from Hartzell that contained every profile available and all factors could be altered and the resulting efficiency curves displayed. Very fun to play with and a couple things really became obvious: a propeller is inefficient until it is spun to near it's maximum tip speed...much like a turbocharger compressor it needs the speed to work. And forward velocity adds to tip speeds so on a high performance aircraft that flies very fast maximum rpm as the tips are reaching the Mach must be reduced. So this really is a problem for reaching high speeds and much of what drove the change to jet propulsion as it doesn't matter how much power you make...the propeller has to keep slowing down the faster you go which just makes it consume more and more power for little velocity increase. On a variable pitch propeller the takeoff power available and the rpm needed for that has to be balanced with anticipated cruise speed and desired rpm when choosing the propeller size, blade profile and number. These factors also play a part in a turbo-fan engine's fan design but many of the modern ones actually do exceed the Mach and operate in a containing shroud so different physics are involved that don't work with exposed blades on normal aircraft. Really fascinating subject with lots of depth that most of us never think about...good video!!
I’m ready for part 2. I have a 3-blade ground adjustable carbon fiber propeller. It gives me amazing performance, but I’ve never really known why it is so good. Looking forward to your follow up video!
Another point on the blade length of properties vs the blade length of helicopter rotors: It is not *only* the speed of the propeller tip that has to remain under Mach 1, it's the combined air speed plus the propeller speed that has to remain subsonic. For helicopters this is even more of a problem because the rotors spin in the same plane as the direction of travel. Thus you have not only the rotor tip speed, but the fact that the side of the rotor that is turning into the direction of travel will encounter faster moving air than the side rotating away from the direction of travel. This means as the rotor approaches the transonic regime, it will lose lift unequally, which will roll the helicopter to the side, rather than keeping it in the air. The net result of all of this is that the fastest helicopters are dramatically slower than the fastest prop planes, as helicopters are fundamentally speed limited by the speed of sound. Same is true of jet turbines, incidentally, and if they aren't buried inside the plane, they are also limited to less than the speed of sound. On fighter jets, the air intakes have to be shaped in such a way that supersonic air is slowed to subsonic, and the tips of the turbine blades, just like props, also have to stay below the speed of sound. This happens to put a hard speed limit of turbines as well, because once you're moving at ~Mach 3, the air intakes themselves compress the air so much that we can't build a turbine that can compress it any more. (This is where the upper speed limit on the SR-71 comes from; the only reason it can go faster than Mach 3 is because it has a sophisticated cooling system that allows for dumping even more fuel into the afterburner.)
Watching this video I was taken back to my high school days in the mid/late 60s. This was when Youngsfield (Ottery,/Wetton Cape Town) was still a South African Air Force base - mostly conducting advanced training with Harvards. In Standards 9 and 10, our history, English and class master had served in the SAAF, culminating in flying Sabres in the Korean War. Our classroom was on the first floor (second in US parlance) and one side faced towards Youngsfield. More than once our teacher would watch and listen to a Harvard taking off and mutter, "Change to coarse pitch!" Another spin off from his service was being taken up twice in SAAF Dakotas (still with radial power then), from Ysterplaat air base. Great times! Grateful thanks, Mr Ross.
Another force that propellers need to contend with, although not by design, is vibration. Some would argue this is also the most difficult force to design for.
Heck yeah, I would like to see part 2. This was very informative. You took a complicated topic and broke it down for us into manageable pieces. Well done!
One way I've always thought of propeller pitch is similar to the gears in a car, what I mean is in a variable pitch propeller fine pitch is similar to a low gear faster acceleration where a course pitch is more like a higher gear it's more suited to flying faster similar to travelling faster in a car, the same applies to fixed pitch props a large diameter fine pitch is similar to low gear where a smaller diameter course pitch prop is like a higher gear, a fine large diameter prop movers more air slowly but a lot of it where a smaller courser pitch prop mores air faster but less of it, I know this is a simplistic way of looking at it, but it's simple, easy to understand and works for all intents and purposes.
This is s good start but there is so much more like pitch distribution, slip, tip shape, airfoil differences, minimum induced loss, etc.. Another video is definitely warranted.
The title of your video is very ambitious. But, in the end, yes, agreed. Thank you very much for this comprehensive and well presented information. I learned a lot.
The thrust direction is forwards, drag force is rearwards. The propeller blade bends forwards under the action of the thrust (lift from the aerodynamic pressure difference). Great video.
This is a really good breakdown of propeller mechanics. I would love to see a part 2 and in that cover how the angle of attack for the plane effects differing thrust across the ‘rotor disc’ as the RC Heli guys like to put it. I saw a video a while back explaining how a plane coming at a high angle of attack will mean a higher angle of attack for the blades crossing the bottom of the rotation and a lower angle of attack for the blades at the top of the rotation. They also mentioned how prop turbulence can wrap around the fuselage and push on the vertical stabiliser, but I’m having trouble keeping it all together. On RC planes, their small size and weight makes them very sensitive to torque roll and so a common trick is to angle the yaw of the propeller a few degrees off to one side, depending on which way your prop rotates. This helps the torque roll but seems to produce other effects that influence the steering, but I can’t quite figure out what’s going on exactly.
Air travelling over the top takes the same amount of time to travel across the chord as air underneath? What are the physics behind that? I do not believe that two adjacent air molecues need to be adjacent again after being divided by the propellar. This is a popular myth in flight schools talking about Wings too.
Yeah, Bernoulli only somewhat applies. The air over the top is accelerated additionally, however because it has a greater vertical motion (visualized as a wing) therefore it exerts less pressure. It’s funny that backward acceleration by the prop is recognized by flight instructors but downward acceleration by the wing is ignored.
Yeah a can of worms I honestly don't care very much about. Most important is the lower pressure caused by accelerated air over the top compared to higher pressure below, and the pressure differential displaces air downwards (which lifts the wing).
@@LetsGoAviateif you are attempting to pass on information you should care. The equal transit time myth has been thoroughly disproven several times over but sadly still persists in the industry. Some fight instructors still teach it even though it is wrong.
There are some wind smoke trace videos online into which die is injected in bursts above and below the wing. They clearly show that the die bursts start off together a the leading edge and DO NOT converge at the trailing edge. Equal transit time is a complete myth.
Dude “some” would be an improvement most single engine fci still stick with the completely wrong Bernoulli theory even when symmetrical wings kinda null all that out…
Formula for kinetic energy is: E = ½mv^2. Increasing velocity requires exponential energy, but increasing the mass doesn't. Formula for force is: F = ma. If this determines our thrust force, mass and acceleration contribute equally. If we want maximum thrust with the limited power our engine has, it is best to maximize the mass of air the propeller can accelerate, rather than to accelerate a small air-mass to a very high speed as that would require way more energy for the same thrust force produced. However, accelerating air to higher speeds allows for higher top speed as you cannot fly faster than the speed to which air was accelerated.
@@arturoeugster7228 e^x is known as the exponential function. Let's not confuse it with the mere implication of the existence of an exponent (2) in this context.
Very nice video. I am learning to understand a different accent too! However, one small correction: If you halve the diameter of a set of propellers, the reduced propeller will need to spin at four times as fast to generate the same thrust as the original propeller. That, in-spite of the reduced dia, gets the tips to the same speed as the tips of the original props.
This is by far the best and most detailed explanation while at the same time easy to understand. Especially that last section with prop pitch, and the drag in both vertical and horizontal profiles if you will. Great animations make it incredibly easy to visualize. My one suggestion would be to slow down the talking pace a bit, again in that last, very critical section of the video. Would also love to see a part 2 as others have suggested.
I am arts student and I am living in India so I couldn't understand anything due to language pronunciation problem but I am trying continue. And second problem with me I am an Hindi midem student and this is English language. But your pronunciation has good then other. So when I will watch your videos many times so it will help me for understanding proper theory and formula.
Thanks. I have also been adding closed captions (subtitles) to all latest videos manually, which creates a transcript for each video. You can copy/paste the text transcript into an online translater. It's a manual task, but hope that helps.
In reference to what is important in fluid dynamics' effect on wing lift: The vacuum metric is but a condition to allow the wing to better advance through the air. The vacuum does not contribute much directly, just as a jet engine doesn't 'suck' its way into a hole - that sucking is a very small contributor. It's the *push* that does the work; that push being of course the air pushing on the other side of the wing. To be sure, when you depend on action by pulling apart molecules, you aren't going to get anywhere much. When you *push* against molecules, this is where the work is done. For example, when one tries to pull on a hydraulic fluid, at first there is a possibility of movement, but shortly thereafter the bubbles are going to form and the pulling action amount levels off sharply. Same with air. An aside - the vacuum isn't caused by the differential of speed of the air going over the air foil. Air speed is only a *symptom* of the presence of the mechanics of fluid flow dynamics. That is all. To focus on increased air speed is akin to telling someone that the flu causes an elevated body temperature. No, a fever is a symptom of the flu. The fever is only an indicator of what the body is trying to do - to burn off the virus (which is why you mustn’t take aspirin!). Yes, the molecules "go faster", but stay with me and don't think about that right now... No, what is happening is that because the air has longer to travel over the air foil on the top, this necessitates that the molecules of the air are pulled apart. That is, the air becomes rarified. This rarefication is air that is "out of the way" on the top of the wing, so the wing can more easily travel upward (yay! upward... good!) into that rarefication. But the rarefication doesn't "suck" the wing up there. Rarefication is really a hole. This lets the real lifting force - the air on the bottom of the foil - the real working force - to be more efficient, because it does not have to push on the air above the wing (a hole is now there, remember) and instead more push energy is available to move the wing upwards. Rarefication of air molecules above the wing increases efficiency. I am unclear as to why there are so many questions and perceived mystery around why a wing is so effective. All one must do is to know how stubborn air molecules are, or any molecule for that matter. When air is at a certain temperature, the molecules are measured to be so far apart. Any force that tries to alter this distance will be met with INCREDIBLY frisky resistance from the air. It will not want to conform. This characteristic is responsible for the incredible force that air can impart on anything. If it weren’t a fluid, we would not even be able to move at all, even though "it's ONLY AIR". So, in summary: Pull on stuff - good, but very limited. Push on stuff - now THAT's what I'm talking about... To put this into perspective - to put why the rarefication of the air above the wing is only an efficiency-increasing characteristic and is only a small part of the lift of a wing - into perspective, is to look at a single surface hang glider wing. This is the most crappy air foil profile that can possibly be built, but we are still blessed with such a terrible thing working very well. The only reason this is possible is because, like any other wing, this wing depends on an angle of attack which is the single best way to enlist the air molecules on the bottom of the wing to push against the surface in the desired direction. This force is enormous, enough so that it can fight with the air on the top of the wing and still do wingy things and allow flight. Sure, there may be a slight bit of rarefication caused by air swooping up over the leading edge and causing a small rarefication there - this is important - but boy is the air 'noisy' there. No, the force on the bottom of this marginal wing is the major contributor. But can one use rarefication to fly without any angle of attack or wing being forced through air stuff? Sure! But now you know why balloons are so darn huge. I'll leave it to others to discuss the benefits of air accelerating past the trailing edge. All I'll comment on this is that any force one is talking about must be imparted onto the wing itself to do any "airplane good". These forces are both perpendicular (surface) and hydrodynamic. For lift, the perpendicular one is by far the most important. As such, the trailing edge thing in my view has more to do with making the air behave well and getting rid of some noise. Remember that the acceleration of air past this trailing edge is air that is, yes, forced downward, so that must be imparting some oppositional force on the wing to enhance lift, right? Well, yes, indirectly. The air forced down is actually pulling against the rarified air at the trailing edge but not past it - this rarefication imparting some efficiency (some may even say 'pulling' but this isn't really correct), and the accelerated air does this pulling by the inertia of the air molecules J-hooking downward slightly (change of direction) past the trailing edge. It really is more of a rarification maintainer for the back third of the wing more than a force imparted on the wing. In summary: Efficient airfoil = good. Efficient airfoil = controlled air. Controlled air = compressive force on one side, and rarified air on the other with little noise before and aft the foil. Crappy wings still work if underside upward force is enough and drag isn't objectionable.
very excellent and educational, thank you! Maybe clarify that the feathered blade only creates more drag with power applied, otherwise a feathered prop is used for engine out emergencies because it causes minimal drag.
Your explanation of how the blades create thrust is not complete. You explained the Venturi effect where the air speeds up when flowing above the curved wing and air molecules separated by the wing have no need to arrive at the same time at the trailing edge, that will never happen. Bernoulli explains why the pressure is lower above the wing compared to below (where its at ambient pressure). Next Newtons third law comes into play when the propeller moves air aft and opposite reaction occurs moving the plane forward.
Ditto! Yes, otherwise you couldn't fly a plane upsidedown, which is clearly possible. Most of the lift is generated from the air hitting the underside of the wing and being deflected slightly downwards. The reaction force pushes the plane upwards by an equal amount. So as long as the angle of attack is right, a plane can fly upsidedown.
Could you please explain why some propellers have squared tips as in massive C-130’s & others have rounded tips as on Douglas DC-7s or Constellations? What are their advantages & disadvantages? Thanking you in advance,
Great video, i learned a lot! but I also noticed a technical error during your description of airfoils. Air does not take the same time to cover the distance above and below the airfoil (in fact; you’ll see in wind tunnels the air above is quicker to reach the trailing end) but works instead by deflecting air on the underside and accelerating on the upper side by means of the kiwanda effect
Thanks. Yes I've received a few comments about it and finally decided to address it in a pinned comment. I don't even remember if I was taught the equal transit theory in flight school, it was long ago, but I highly doubt it. I've never cared if the air going over the top arrived behind the airfoil at the same time, slightly before or slightly after the air going below, as I've always found it completely irrelevant to lift creation. Lift is created by pressure differential (or the push/pull you described which is still air pressure), not by the exact timing of the top vs bottom air. But I appreciate now that just because I find irrelevant, others might care about it. So you are correct, and thanks for the comment, see that pinned comment for full explanation.
Assume that for a particular radius, the propeller is a wing section, which travels the length of one associated circumference and advanced forward a particular distance ( pitch) through a helical path. For any other radius, the associated " wing section " will travel a different circumferential distance but needs to travel forward the same distance for all radii, a forward distance , called pitch. The fact that at different radii the forward motion is the same, means that the blades appear to be twisted. The diameter of the propeller is related to engine power, while the pitch is related to the maximum speed of the aircraft. There are many arguments on how a wing aerofoil section operate, but since I was very young, 80 years ago, I always looked upon the lift of a wing section was due to the "acceleration" of the air masses above and below the wing or propeller. The most important issue here, is that acceleration is a VECTOR , and it has to be treated as such, considering its magnitude and direction, and the forces generated through these vector accelerations and decelerations, of the air particles in question, I do not care two hoots about Bernoulli equation, nor the equal distance theory, nor the circulation theory . Let us stick to basics. Two stationary air mass particles in line with the stagnant point at oncoming leading edge of the moving wing, one will hit the slight incline to go up, and the other hits the slight incline to go down . These two actions are no different from two moving golf club hitting two stationary golf balls containing mass, The upper air mass particle will be accelerated up, causing a force reaction on the leading edge, which contributes to drag, but as the air mass particle accelerates up it tend to leave the surface of the leading edge causing a partial vacuum, by the fact that air is a fluid and the air particles have "sticktion" between them to make them act as an impermeable blanket being pulled away from the upper surface of the leading edge, This impermeable sheet of air being pulled away up from the leading edge will cause a partial vacuum underneath the " air sheet" which will pull back the air sheet mass towards the leading edge, thus decelerating its upward movement after the leading edge had accelerated it. While the air particles sheet above the wing will try to return to the upper surface, this retracts down to keep the partial vacuum below it, and a good wing section will keep the air sheet from touching the upper wing surface till it dumps the whole air particle sheet being the trailing edge, One must not consider the air particles as individual mass particles, but more of a flexible sheet of little masses somewhat like impermeable diaphragm of an pump which sucks, as it is pulled away from some surface. Note all this is due to Force = mass . acceleration, where the acceleration/deceleration forces that generated, are vectors, contributing to lift by a suction on the upper surface. The air particle that hits below the stagnant point also try to reflect off the leading edge, causing a drag reaction, but due to the angle of attack other mass air particles lower down will REFLECT on the under surface of the wing and this Vector acceleration needs high pressure under the wing. which will add a slight forward velocity to the stationary air particle. Hence while the vacuum on the upper surface causes the associated air particles to gain a slight velocity backwards, the lower mass particles under the wing subjected to a pressure zone will gain a little forward velocity. Thus the air particles above and below the wing DO NOT MEET AT THE TRAILING EDGE, It is the acceleration/ deceleration of air particle above the wing due to the partial vacuum and the acceleration/ refection below the wing due to high pressure that lifts the wing up. The same happens in the profile section of a propeller. It is to be noted that at start, with the aircraft stationary, the inner 1/3 of the propeller is more like a paddle wheel, due to the high angle of attack, which normally stalls, while the drive is obtained from the outer 2/3 of the blade of a propeller, This settles down as the aircraft gains forward velocity. At the wing tips of wings and propellers, the best tip designs are those which imitate the wing tips of bird wing, and the flukes of a fish, dolphin, orca, whale tail, where both the leading edge and the trailing edge at the tips, ARE RAKED BACKWARDS.. For a propeller to keep pulling and biting, it needs to slip, where the forward distance covered is not the theoretical forward movement, of pitch multiplied by the revolutions of the propeller. There is more on propeller, especially when the tip velocity will reach that of the velocity of sound, also when the propeller face is not moving exactly perpendicular to the line of motion, where the pitch of the up going blade is different from that of the down going blade, causing vibration, Propellers are not too difficult to understand, if one forgets the Historic names associated with anything that causes lift, and simple use the basic fact, that when a mass particle needs to be accelerated or decelerated, it will do so by the creation and reaction of a force. A wing, or a propeller is no different from a running chisel/surface wood plane, continuously cutting or pushing away at the impervious block of mass air particles by, continuously slicing two mass sheets, one above and one below the wing and ACCELERATING AND DECELERATING them in a required direction, in locations above or below the wing surfaces, and the tips, then continually dumping it all DOWN behind the trailing edge and with many other complexities and circulations around the wing or blade tips Note that vortex circulation whose axis is parallel to the line of travel of the wing, do not do much harm, but vortex circulation parallel and occurring above or below the leading or the trailing edge are very dangerous indeed .
I mean, yeah, you completely forgot about Bernoulli's principle in your description of lift, but otherwise I have to give you a massive congratulations - this video is a really excellent description of propeller design principles and objectives in easy-to-understand language. Thanks, and I'd definitely be keen for a part 2.
It’s amazing to me that constant speed propellers are able to withstand the gyroscopic forces involved when changing direction. Especially when doing violent aerobatic maneuvers I would expect the blades to separate from the hub.
Unfortunately many pilots do not appreciate the high level responsibility of an engineer who needs to design structures to buffer all the forces that are continuously working to kill a pilot. A pilot is not killed because even in a normal landing the vertical momentum is totally absorbed by the undercarriage and the fuselage needs to flex to delay the absorbing time . In a crash the structure needs to buffer all unwanted forces and, as in a car, a collapsible structure will delay the deceleration to one which a human body can withstand. A human body cannot witstand much and in a piloted aircraft which is of the " come back home type" over 95 % of the structure is designed to bring the pilot back home and it is much cheaper to now design an autonomous missile which need not come back as that alone will double the range of the fuel on board. I am grateful to you for understanding the extra forces on the propeller when the aircraft changes direction, It does no break because the engineers are responsible people and in their dilemma to make an economic aircraft then need to introduce in a small cockpit in which the pilot is caged, enough devices which can help the pilot save his own life. Saving his own life is the priority responsibility of any pilot even if he is flying on his own taking an old aircraft to the boneyard. Testing and retesting and modifications and writing the right checklists for pilots is what keep flying as safe as it is, Thank you for appreciating.
Nice explanation particularly with the blade angle diagrams of the propeller cross section. I didn't find the people-mover analogy particularly illuminating but that's just me. Like I said overall great video
@@arturoeugster7228 I'm sorry, I thought the subject was aerodynamics, not electrodynamics! In electrodynamics, conservation of circulation works as it operates only in a the presence of a conservative force. Prandtl was responsible for the madness of trying to shoehorn Thompson's principle of conservation of circulation into fluid dynamics. Thompson's a paper explicitly states the law of conservation of circulation for a barotropic, ideal fluid with conservative body forces. Note: "conservative". The aerodynamic forces on a foil are NOT conservative. The only conservative forces in nature are electro magnetic and the "force" of gravity. It's poppycock, but is firmly entrenched in fluid dynamics.
@@arturoeugster7228 To "shoehorn" something (figuratively) means to force it into a place where it doesn't naturally fit, i.e. the principle of conservation of circulation "doesn't fit" into fluid dynamics because the aerodynamic force is not a conservative force. "Primitive non-technical expressions"? Examples please. Before referencing "conservative", look it up in in Feynman Vol1 14-3 where he uses the force of gravity as an example.
I just installed a Sensenich ground adjustable carbon fiber prop on my my plane. The blade shape is totally different from the old metal prop. The biggest difference I have noticed so far is there is no vibration! It feels like I'm flying a jet at a 100mph!
There's always a big debate about how an airfoil actually generates lift/thrust. The reason for this is that each side of the debate believes that they are correct, and humans generally _want_ to be correct. Normally one would just conduct an experiment to verify who really is correct, but in this case, there are several arguments that _all_ have evidence showing them to be correct. This is because in reality, an airfoil generates lift in several different ways simultaneously! So they all really are correct to some degree, with each source of lift adding to the whole (pressure differential/equal transit, incompressible Newtonian deflection, compressible fluid dynamics, and even some more nuanced aspects that don't generally get a major 'side' in the debate). To make it even more complex, all of those sources of lift account for different percentages of the total performance differently in different flight regimes, including AoA, laminar vs turbulent flow, separated vs attached boundary layer, mach number, the existence, absence, or location of vortices, and more. The truth is, aerodynamics is an _extraordinarily_ complicated topic that isn't yet completely understood. Or... perhaps more precisely, it is a topic in which the sorts of fine-detail complexities that _most_ dynamics tend to involve, get amplified to the level of not just being important, but being _critical._ Add in that humans have very poor intuition when it comes to wave physics, and yeah... you get lots of very passionate people passionately declaring everyone else to be wrong, all correctly. xD (For an idea of your level of intuition of wave mechanics, can you explain why large commercial ships have big bulbous noses that look about as streamlined as a brick wall?) Still, good job on the video! It was... quite a lot more basic than I'd hoped for, but that's not a new situation for me. Science and engineering communication is rarely aimed at people seeking to go from intermediate levels of technical understanding and proficiency to advanced levels. In particular, I'd love to see some more focus on _exactly_ how adding more blades changes things between efficiency and potential power usage, as my understanding is that each blade really acts in a way sort of hybridized between its actual physical shape, and its swept area, depending on operating regime. I feel like I have a reasonably okay understanding of that, but it isn't a particularly _intuitive_ understanding, more like one of those things you just come to accept as true as you do maths for homework problems. My journey of understanding across all sorts of fields of science and engineering tends to be to go from some degree of misconception from the "lies to children" oversimplifications we use in education (especially here in the US, but to some extent, everywhere), to an analytical mathematical understanding (which tend to involve myriad simplifying assumptions, a la 'spherical cows in vacuum'), then to a level of true comprehension that includes intuition. From there it goes to deep and specialized understanding that includes all of the nuance that we currently understand as a species, but people tend to only gain that level of expertise in one or two very specific topics in their lifetimes. Of course in some topics, _nobody_ has that final level, and in others, like quantum mechanics, it became so stigmatized to even try for the third level of intuitive comprehension that most working physicists just skip over it entirely and brute force their way from the simplified analytical understanding to the detailed simulation/experimental understanding.
Propeller Speed Reduction Unit (PSRU, or gearbox) Torque Multiplication Explained : ua-cam.com/video/LDsUTJ0f0tU/v-deo.html The Theory Behind Short Takeoffs Fully Explained : ua-cam.com/video/aJd1xEmbWOU/v-deo.html
What an overall excellent presentation and explanation of propellers. You earned a new subscriber here! I think your channel will grow quickly. Keep up the fine work! Thanks!
Good video. On my electric radio-controlled model planes, I chose the pitch first since electric motors turn a certain number of rpm per volt applied to them. I then calculate the diameter of the prop needed to load the motor to the proper rpm, current, and watts. I try to keep the diameter-to-pitch ratio (D:P) between 1.5:1 and 2:1. The larger the diameter, the harder the motor will have to work to spin the propeller blades thru the air instead of pushing air to the rear.
Great video! I was just wondering, why you summed up the chord length with "the same reason glider wings are long and thin". I searched for it, and it has to do something with laminar flow and the transition point, but that's it. Is this explained in more detail in another of your videos? A longer explanation would be better.
Long and thin wings (high aspect ratio) like that of a glider are more efficient than short span and wide wings (low aspect ratio) like that of a Piper Cub for example. Meaning the lift to drag ratio is better. Specifically it's the induced drag that is lower, partly because the wingtip is smaller (which is also the reason for winglets). The same applies for propellers. If you do an internet search for "induced drag coefficient" you will get the formula to calculate it. If you want to know why that is, you'll have to dig deep, it's not simple answers. Basically you need as much wing as possible exposed to airflow (longer span) but as low as possible surface area because surface area is drag. The aspect ratio is part of the formula, and the higher the aspect ratio tue lower drag coefficient. In theory the most efficient wing is infinitely long and infinitely thin, which of course isn't structurally possible. Hope this leads you to some more in-depth answers.
Great video. Part 2 would be welcome. Having made a few props for homebuilt airplanes the question I was asked by my mentor many years ago was: and how do you measure pitch ? is it the aerodynamic pitch or the bottom surface of the prop? I have tried some experiments with blade shape, ie; scimitar shape for example, in an attempt to see if aerodynamic twist works. My test platform is my plane. I usually do a full power tied down run-up to see if it turns fast enough. i'm looking for more than 2100 rpm with my o-200. the next observation is climb rpm and lastly I set throttle for manifold pressure of 22 inches and see what airspeed i get. There is also some difference with the wood species used I have heard. no pun intended ... I usually laminate maple, birch and cherry, as I like the look of the cherry on top. The prop on the SE5a in Singapore is one I made. Cheers.🍺
Recently I had a close up museum view of a mk16 Spitfire, with a Rotol 4 blade propeller. And decals on the forward face of the blade roots had different settings. The angle numbers recorded on the blades were around 34 to 38 degrees BUT each blade was marked with a different value. Why? And what for? How is it important?
Great video! Please address how the propeller RPM should be set during a prolonged high speed descent. Say, a descent from 15,000 feet to a sea level airport over a distance of 40 to 60 nautical miles.
Wow! Great content. Am grey haired (I blame being a GR III flight instructor for that) Seeing Rand, Ermelo? Nelson and a Jabi that had a prop strike. I dated a Portuguese girl in the 80's and your accent is too hybrid to be such. Half Boer half Italian? I still give technical briefs at a major airline, however my age has relegated myself to inspector status (I detest it and have erotic dreams about whiteboards, markets and toolboxes). Time moves on and I wish I could master PowerPoint in the same way that you presented this. Wings level and ball in the middle dude!
True helical pitch has been felt to be more efficient for model use as is contant reynalds number through making for hide root chord. Look at the props on the Supermarine Scneider cup winners.
What an amazing video. Thank you! But after listening to all of that, I still do not know if the fine or the course is the high or the lower pitch :D Which one is also called high and which one is called low pitch? Thank you!
Thanks. Not sure I've heard it called high or low pitch, but high pitch would be a high angle on the blade, i.e. course pitch, and low would be fine pitch.
Explained in this video ua-cam.com/video/WnJxrHmtT_c/v-deo.htmlsi=cOl-8pGvZavwkvek It's because the oncoming air doesn't hit the propeller blades perpendicularly. Imagine looking on from the side, airplane at high angle of attack, the downgoing blade moves towards the oncoming air from top to bottom. The upgoing blade moves front to rear, bottom to top and actually moves slightly rearwards. Comparing the AoA of the blades at midway up and down shows the difference. It's called P-factor or assymetric blade effect and is most pronounced for taildraggers on takeoff with all 3 wheels on the ground, but will affect all propeller aircraft at high AoA.
A very good description of prop operation. One add may be useful…… Maximizing thrust, particularly at takeoff is done with a large diameter prop because the larger diameter accelerates a large volume (mass) of at lower speed than would a smaller prop pushing a smaller mass at higher speed. Thus the larger prop gets a “firmer” grip on the air. That is to say that the larger prop is not trying to push air that is slipping away….sorta like trying to walk uphill on a shifting layer of sand. The slipping absorbs energy that is just wasted. So tug boat props are big and slow. Takeoff contest winners use biggest prop they can. Physicists call this impedance matching. For example, if you want to move an elephant, you bop it with something as heavy as possible, maybe another elephant. Hitting an elephant with a high speed baseball may annoy the elephant, or even kill it, but doesn’t much move it. Hitting a squirrel with an elephant is similarly inefficient.
This is well put and very informative. I make similar video tutorials on various aircraft system and I appreciate the time and effort you put to make this piece. keep it up.
@@LetsGoAviate It took me ages to work out what was on the wall of a Military social club I once visited. Too big for a propeller, too thin for a wing. Turned out to be the rotor blade from a Chinook! Now they are massive :)
@@jeffnorwood-brown8407 It can drive one mad lol. I still don't know exactly what this blade is from. Thought it was from a Continental R-670 powered plane, like a Stearman, but the shape is different. Looks more like that of a T-6 Texan, even though it seems too small.
⚓️ Thanks LGA 😎 ok??? What’s controllable pitch? Since defining varying pitch thru the length of a blade … then describing variable pitch as a control feature… LGA is confusing or combining two features with one description…. Which is it?? Controllable? Or Variable?
I don't 100% understand what you are saying. The AoA that changes along the span of the blade I called blade twist. And blade twist is necessary to compensate for faster turning speed at blade tip than at the blade hub. Blade twist is "baked in" at the factory and cannot be changed. Variable pitch propellers I called just that, the pitch that can be controlled (blue knob in the plane). And it's to get optimim blade AoA at all airplane airspeeds (vs a fixed pitch which would only by optimum at one airspeed, i.e. takeoff of cruise). Variable pitch changes the pitch (AoA) of the whole blade, and can be done in flight on varibale pitch or constant speed propellers. I'm not confused or combining anything that shouldn't be 🙂
17:50 Good video but wrong explanation of lift. The air over the camber does exit at the same time as the air flowing on the flat section of the blade.
It doesn't have to meet at the trailing edge. The faster moving air over the top might arrive at the trailing edge more or less the same time as the slower air below, but it might even arrive before the air from below. It would depend on factors like the shape of the wing, angle of attack etc.
I have always thought that the propeller sort of "scoops" itself forward in the air and pulls the airplane behind it. Is this a wrong way of thinking ?
Yes airplane propellers with winglets are called Q-tip propellers. Became pretty popular during the 80s and 90s. They were marketed more for being quieter propellers. That's where the Q in Q-Tip comes from
I had an APC propeller on my RC plane that had little winglets. One day a poor landing snapped the propeller and all I could find at the local hobby shop was a black propeller. Only when I fitted the black propeller did I notice that the APC propeller was much quieter and much faster. It appears the folks at APC really know their stuff when it comes to propellers.
PLEASE READ. I noticed some viewers get hung-up on the "equal transit theory" at 2:21. I mostly ignored it at first since for me it's really besides the point and not what is to be taken out of that explanation. But now I have to address it. So to course-correct here's three things:
1. If it's understood that the accelerated air over the top of the airfoil causes lower pressure than below the airfoil, and this displaces air downwards and the reactionary force is lift/thrust then you understand the necessary.
2. My wording is admittedly poor and I never attempted to describe the "equal transit theory", but poorly attempted to describe what causes acceleration i.e. different distances to be covered (over the top and below), same amount of time causes acceleration. Air doesn't have to arrive at EXACTLY the same time and frankly in my opinion is completely irrelevant in lift creation, because of point 1 (it's the pressure differential that creates lift, not whether transit is equal or not).
3. I've come to the realization that just because I've never cared if the air over the top arrives at the same time, before or after the air below - and still don't - doesn't mean others don't care and it's not for me to decide if you should find it irrelevant or not.
I hope that clarifies it and that the remainder of the video is enjoyable and informative.
The remainder of the video is spot on and is a good starting point for anyone interested in why propellers are so varied between aircraft as well as their principles and operations. For the sidewalk and blade pitch analogy, it might have been better to simply explain geometric/effective pitch and build on that. Maybe something to add in part 2.
I would suggest not even mentioning the Bernoulli principle or the outdated idea that the upper curve of the airfoil creates low pressure or the associated equal transit theory, it just mucks up the underlying concept because none of it has a demonstrable effect and is often contradictory to itself relating to lift in fluid dynamics. Airfoils make lift purely by deflection (AOA, or pitch in the viewpoint of a blade), whereas the shape of the airfoil determines how efficient it is at making and defining that lift...the airfoil shape itself doesn't create lift simply because it exists as such. Flat airfoils and symmetrical airfoils will still make lift without any of the Bernoulli/equal transit nonsense involved (even space capsules without an airfoil traveling at hypersonic speeds negating the premise of those theories still make lift, via deflection), whereas a proper textbook airfoil shape won't produce any lift at all if it has no AOA/pitch. That's the simple explanation backed by fluid dynamics; deflection creates lift, airfoil shape defines lift characteristics. I don't know who was responsible for the first reference between Bernoulli and lift, but whoever it was did a great disservice to the world of aviation. It's taught in primary school and is still prevalent everywhere in aviation, so everyone's first and most important introduction to aerodynamics is based on a false premise, and that's why so many people are getting hung up on it.
@@Skinflaps_Meatslapper OK so I also caught that mistake (quoting that old-fashioned Bernoulli Equal Transit-Time Theory of Lift), and as someone who has designed and manufactured wind turbine blades, and know a few of the top guys in that field, I've had a lot of time to slowly gain an understanding of lift. Not to mention sailing and hang-gliding. Hang gliding really helps you understand lift. Not to mention, stalls. At some point the lightbulb goes off, and you think, "Wow, it's actually pretty simple!" (I never believed the Bernoulli Explanation, even as a kid.) By the way, I just saw a documentary with David Attenborough "explaining" how a flying dinosaur reptile's wings worked. Of course, like all the rest of the people still repeating the same old wrong explanation after so many decades, he said it was because the air went faster over the upper wing surface - what else? Rumors die hard! Only HE explained it with a crisp British accent, so like most science documentaries, it makes it sound like the narrator knows what the hell they're talking about. But half the time they don't. Anyway, yes it IS the TOP surface of the airfoil that produces most of the lift, which is why the top surface is where the sheet metal pulls up and away from the ribs, causing loose rivets on old airplanes, and why all the engines and weaponry are hung from the bottom surface of the wing, because they don't ruin the lift down there. The plane sucks itself into the sky. The vacuum on the top surface allows the ambient air pressure on all of the bottom surfaces, even the engines and weaponry, to push upward more than the lower pressure air on top pushes downward. And yes, the air actually goes MUCH faster over the top surface than even equal transit time would require! (watch a video of airfoils in wind tunnels and they show you) BUT, mere SPEED of the air over the top surface is NOT where MOST of the lift comes from. Some lift, yes, but not most of it. The amount of lower pressure from the mere faster speed of the air over the top surface of the wing is not sufficient to provide the amount of lift we actually get. They figured that out mathematically many decades ago. And I'm not going to say here what IS the reason we get such low pressure on the top surface. I'm saving that info. But it is funny to read articles in Magazines such as "Scientific American" where they admit that there is no universally-accepted theory of lift to this day, and experts could not agree, even if they HAD an explanation, which most of them don't. All they know is which airfoil makes how much lift under what conditions, but they don't know why, really. And they can write code to emulate airflow, and predict which airfoils will do what pretty accurately, but they are still scratching their heads over exactly why it all actually works - they can model it, they can design with it, but as far as "official science" is concerned, they can't understand it, or put it into words. Of course, "official science" also once insisted that stones could not fall from the sky! As is so often the case, the primitive people of the countryside knew more than the scientists sometimes. I like to watch STOL competitions. I'll bet some of those guys have also, like me making wind turbine blades, figured out how "lift" really works. Anyway, I think I have the explanation, and it's actually easier to understand than Bernoulli etc. Anyway, maybe I'll publicize it at some point. The world needs to know.
@@dougselsam5393 It's actually quite simple to understand intuitively; the primary reason why it's difficult to scientifically quantify is because like anything in fluid dynamics, you can't simply attribute it to one single thing and modeling it to proof a theory is difficult.
The top of the airfoil experiencing low pressure on its own isn't enough to create the lift being generated, lift is the result of the entire air mass that the airfoil interacts with, both above and below the airfoil. If it were nothing more than low pressure, then a helicopter rotor wouldn't have downwash, there would just be a low pressure lens above the rotor holding the craft airborne. But we know that accelerating that mass of air downward is the action that creates the reaction of lift. Same goes for a propeller, it takes a certain mass of air and accelerates it rearward, as opposed to creating low pressure in front of the prop disk. Both are no different than a wing, which takes a certain amount of air and accelerates it downward. The low pressure is part of the equation, but moving that air mass downward is the action that creates the reaction (lift). You can imagine an airfoil splitting that air mass in half, the bottom physically pushing the air down, and the top pulling the air down. The more curve the top of an airfoil has, the more effective it is at high AOA, and thus is better suited for slower aircraft such as STOL, ag planes, aerobatics, etc. at the expense of drag. When you reduce that curve and make the airfoil flatter, it creates less drag at the expense of being less efficient at higher AOA. The reason for this is because that curve gives the air a surface to "stick" to without separating. A flatter airfoil causes a more abrupt change in direction at higher AOA, the air has a harder time suddenly changing directions and the air has a harder time sticking to the wing, separating into a turbulent mess instead. Flaps and slats and VG's and all those other gadgets are simply ways to help that air stay connected to the top of the airfoil, because if you can't bring that upper air mass down, the lower air mass is going to fill the vacuum created by the turbulent mess above it rather than continuing downward as it should. Deflection of the airfoil is what causes lift, and the shape of the airfoil is what defines what kind of lift is being created when that happens. The air mass on both sides of the airfoil have to be on the same page before lift is generated, you can't attribute lift to one or the other, as it's a singular action. I've had an instructor tell me that a jet moves forward by the suction from the engine, and while that force does contribute to thrust, it's primarily the acceleration of that air mass going out the nozzle that's responsible for thrust by a large margin. Modeling the cross sectional area of a jet intake and then calculating how much force could be generated by putting a hard vacuum on that area results in a fraction of the actual thrust of a jet. Same goes for a wing and the small amount of vacuum on top that it creates in high alpha (that's why you often see the vapor forming on top of fighter jets, that's low pressure forming). Attributing it to one side of the equation would be like saying the road pushing against a tire is what propels a car forward rather than the tires pushing against the road, when it's the interaction of both that propels a car forward.
@@Skinflaps_Meatslapper Well, you don't quite have the full picture. You said lift is NOT generated by suction on the top surface of the wing, and a propeller does NOT function due to suction on the front (suction) side of the airfoil. That is wrong. If there is one thing aero people agree upon, it is that suction on the top surface is what causes lift. The "mystery" is exactly what causes such extreme suction, since the windspeed alone cannot explain it. What you are attempting to do is apply the SECOND MOST COMMON MISSTATEMENT of what "causes" lift, which you confuse with the mere "result", that air is deflected downward. This is a very common, but insufficient, "explanation" for a "cause" of the lift. No, the air deflection is a RESULT of the same phenomenon that CAUSES the lift. When you stop to think about it, if the wing produces lift, then of course, there "HAS to be" a downwash, right? So that is not the cause, it is just one more result of a well-functioning airfoil. You had also stated that an airfoil with zero angle of attack will not provide lift. Guess again. Most airfoils DO produce lift, even at a zero angle of attack. Not as much lift, but they do still provide lift at zero angle. And you also cited helicopter blades and symmetircal airfoils as evidence that lift is NOT caused by suction on the top side - wrong again: these airfoils produce lift only when oriented at an angle of attack to the airflow, and when producing lift, of course they also produce a downwash. which is a result, not a cause, of lift. When people ask to understand the cause of the lift, they want to know what is physically "holding the airplane up", or in the case of the propeller, pulling the airplane forward. In either case, it is suction on (drumroll please...) the SUCTION side of the airfoil. There is a reason it is called "the suction side", because that is where the suction occurs, and suction is the key to "lift", just as suction is responsible for the function of a drinking straw. Would you say a drinking straw works BECAUSE of the liquid moving up inside the straw? NO, that is a RESULT of the suction, NOT the cause. And as I explained, that is why, when rebuilding an old airplane with a sheet metal wing surface, the rivets on the TOP surface (NOT the bottom surface) are what come loose and need attention (repair). And that is why the engines and armaments are always mounted on the pressure-side (lower side) because it hardly matters what happens down there, other than the drag all that stuff causes, but they put up with the drag. Really smart outsiders to it all, even with engineering degrees, often try to use the downwash as an "explanation" for the lift. That's like saying your exhaust coming out of the tailpipe is what powers your piston engine. Of course it has to have exhaust, but the exhaust is not the "reason" the car rolls down the road, it's more just another result of the process of the engine running. It;s also like saying your empty bank account is why you lost all your money in Las Vegas. No, your bak account is empty because of the specific gambling activity that gave away the money, not BECAUSE your bank account was emptied. See the difference? So, in the end, of course, a wing produces a downwash, but the downwash is a RESULT, not the cause, of the "lift". Saying the downwash CAUSES the lift is just an easy out for people who don't know HOW the wing is physically lifted. It's a way to take a true statement (that there is a downwash) and pretend it describes HOW that downwash is generated. Downwash is not a CAUSE, but just one more RESULT, of the phenomenon of lift.
I chose to not address this wives tale about airflow trying to meet at the trailing edge .
An Air Force Captain in 69 explained it well.
"A jet engine sucks a hole in the air and falls into it.... And a propeller does too.... LOL".
A part 2 would be beautiful, please. I’m very interested in toroidal propellers, particularly seeing the advantage Sharrow propellers offer the boating industry. Thank you. 🙏
Back in the '90's I had a propeller program from Hartzell that contained every profile available and all factors could be altered and the resulting efficiency curves displayed. Very fun to play with and a couple things really became obvious: a propeller is inefficient until it is spun to near it's maximum tip speed...much like a turbocharger compressor it needs the speed to work. And forward velocity adds to tip speeds so on a high performance aircraft that flies very fast maximum rpm as the tips are reaching the Mach must be reduced. So this really is a problem for reaching high speeds and much of what drove the change to jet propulsion as it doesn't matter how much power you make...the propeller has to keep slowing down the faster you go which just makes it consume more and more power for little velocity increase.
On a variable pitch propeller the takeoff power available and the rpm needed for that has to be balanced with anticipated cruise speed and desired rpm when choosing the propeller size, blade profile and number. These factors also play a part in a turbo-fan engine's fan design but many of the modern ones actually do exceed the Mach and operate in a containing shroud so different physics are involved that don't work with exposed blades on normal aircraft. Really fascinating subject with lots of depth that most of us never think about...good video!!
Yes, please do a part 2! Would be great if turbine fan blades could be discussed as well.
I’m ready for part 2. I have a 3-blade ground adjustable carbon fiber propeller. It gives me amazing performance, but I’ve never really known why it is so good. Looking forward to your follow up video!
Another point on the blade length of properties vs the blade length of helicopter rotors:
It is not *only* the speed of the propeller tip that has to remain under Mach 1, it's the combined air speed plus the propeller speed that has to remain subsonic. For helicopters this is even more of a problem because the rotors spin in the same plane as the direction of travel. Thus you have not only the rotor tip speed, but the fact that the side of the rotor that is turning into the direction of travel will encounter faster moving air than the side rotating away from the direction of travel. This means as the rotor approaches the transonic regime, it will lose lift unequally, which will roll the helicopter to the side, rather than keeping it in the air.
The net result of all of this is that the fastest helicopters are dramatically slower than the fastest prop planes, as helicopters are fundamentally speed limited by the speed of sound.
Same is true of jet turbines, incidentally, and if they aren't buried inside the plane, they are also limited to less than the speed of sound. On fighter jets, the air intakes have to be shaped in such a way that supersonic air is slowed to subsonic, and the tips of the turbine blades, just like props, also have to stay below the speed of sound. This happens to put a hard speed limit of turbines as well, because once you're moving at ~Mach 3, the air intakes themselves compress the air so much that we can't build a turbine that can compress it any more. (This is where the upper speed limit on the SR-71 comes from; the only reason it can go faster than Mach 3 is because it has a sophisticated cooling system that allows for dumping even more fuel into the afterburner.)
Very valid points, thanks!
Wow! Thanks
Watching this video I was taken back to my high school days in the mid/late 60s. This was when Youngsfield (Ottery,/Wetton Cape Town) was still a South African Air Force base - mostly conducting advanced training with Harvards. In Standards 9 and 10, our history, English and class master had served in the SAAF, culminating in flying Sabres in the Korean War. Our classroom was on the first floor (second in US parlance) and one side faced towards Youngsfield. More than once our teacher would watch and listen to a Harvard taking off and mutter, "Change to coarse pitch!" Another spin off from his service was being taken up twice in SAAF Dakotas (still with radial power then), from Ysterplaat air base. Great times! Grateful thanks, Mr Ross.
Another force that propellers need to contend with, although not by design, is vibration. Some would argue this is also the most difficult force to design for.
Great explanation. Please make part 2!
Heck yeah, I would like to see part 2. This was very informative. You took a complicated topic and broke it down for us into manageable pieces. Well done!
Fantastic video! Please do part 2. All of your videos are super well done - Thanks!
One way I've always thought of propeller pitch is similar to the gears in a car, what I mean is in a variable pitch propeller fine pitch is similar to a low gear faster acceleration where a course pitch is more like a higher gear it's more suited to flying faster similar to travelling faster in a car, the same applies to fixed pitch props a large diameter fine pitch is similar to low gear where a smaller diameter course pitch prop is like a higher gear, a fine large diameter prop movers more air slowly but a lot of it where a smaller courser pitch prop mores air faster but less of it, I know this is a simplistic way of looking at it, but it's simple, easy to understand and works for all intents and purposes.
Definitely interested in a part 2 with the more advanced stuff.
This is s good start but there is so much more like pitch distribution, slip, tip shape, airfoil differences, minimum induced loss, etc.. Another video is definitely warranted.
The title of your video is very ambitious. But, in the end, yes, agreed. Thank you very much for this comprehensive and well presented information. I learned a lot.
The thrust direction is forwards, drag force is rearwards. The propeller blade bends forwards under the action of the thrust (lift from the aerodynamic pressure difference). Great video.
Amazing lesson, huge thanks!
GREAT! Part 2 please!
This is a really good breakdown of propeller mechanics. I would love to see a part 2 and in that cover how the angle of attack for the plane effects differing thrust across the ‘rotor disc’ as the RC Heli guys like to put it.
I saw a video a while back explaining how a plane coming at a high angle of attack will mean a higher angle of attack for the blades crossing the bottom of the rotation and a lower angle of attack for the blades at the top of the rotation. They also mentioned how prop turbulence can wrap around the fuselage and push on the vertical stabiliser, but I’m having trouble keeping it all together.
On RC planes, their small size and weight makes them very sensitive to torque roll and so a common trick is to angle the yaw of the propeller a few degrees off to one side, depending on which way your prop rotates. This helps the torque roll but seems to produce other effects that influence the steering, but I can’t quite figure out what’s going on exactly.
I loved your video! It's really really helpful and easy to understand, can't wait to see part 2 🎉🙏
Air travelling over the top takes the same amount of time to travel across the chord as air underneath? What are the physics behind that? I do not believe that two adjacent air molecues need to be adjacent again after being divided by the propellar. This is a popular myth in flight schools talking about Wings too.
Yeah, Bernoulli only somewhat applies. The air over the top is accelerated additionally, however because it has a greater vertical motion (visualized as a wing) therefore it exerts less pressure.
It’s funny that backward acceleration by the prop is recognized by flight instructors but downward acceleration by the wing is ignored.
Yeah a can of worms I honestly don't care very much about. Most important is the lower pressure caused by accelerated air over the top compared to higher pressure below, and the pressure differential displaces air downwards (which lifts the wing).
@@LetsGoAviateif you are attempting to pass on information you should care. The equal transit time myth has been thoroughly disproven several times over but sadly still persists in the industry. Some fight instructors still teach it even though it is wrong.
There are some wind smoke trace videos online into which die is injected in bursts above and below the wing. They clearly show that the die bursts start off together a the leading edge and DO NOT converge at the trailing edge. Equal transit time is a complete myth.
Dude “some” would be an improvement most single engine fci still stick with the completely wrong Bernoulli theory even when symmetrical wings kinda null all that out…
Excellent video. I learned a lot of relevant information. Yes please on a part 2 video.
Formula for kinetic energy is: E = ½mv^2. Increasing velocity requires exponential energy, but increasing the mass doesn't. Formula for force is: F = ma. If this determines our thrust force, mass and acceleration contribute equally. If we want maximum thrust with the limited power our engine has, it is best to maximize the mass of air the propeller can accelerate, rather than to accelerate a small air-mass to a very high speed as that would require way more energy for the same thrust force produced. However, accelerating air to higher speeds allows for higher top speed as you cannot fly faster than the speed to which air was accelerated.
@@arturoeugster7228 e^x is known as the exponential function. Let's not confuse it with the mere implication of the existence of an exponent (2) in this context.
Great and clear explanation.
Very nice video. I am learning to understand a different accent too!
However, one small correction: If you halve the diameter of a set of propellers, the reduced propeller will need to spin at four times as fast to generate the same thrust as the original propeller. That, in-spite of the reduced dia, gets the tips to the same speed as the tips of the original props.
This is by far the best and most detailed explanation while at the same time easy to understand. Especially that last section with prop pitch, and the drag in both vertical and horizontal profiles if you will. Great animations make it incredibly easy to visualize. My one suggestion would be to slow down the talking pace a bit, again in that last, very critical section of the video. Would also love to see a part 2 as others have suggested.
Thank you, and noted regarding the talking speed.
I am arts student and I am living in India so I couldn't understand anything due to language pronunciation problem but I am trying continue.
And second problem with me I am an Hindi midem student and this is English language.
But your pronunciation has good then other. So when I will watch your videos many times so it will help me for understanding proper theory and formula.
Thanks. I have also been adding closed captions (subtitles) to all latest videos manually, which creates a transcript for each video. You can copy/paste the text transcript into an online translater. It's a manual task, but hope that helps.
In reference to what is important in fluid dynamics' effect on wing lift:
The vacuum metric is but a condition to allow the wing to better advance through the air. The vacuum does not contribute much directly, just as a jet engine doesn't 'suck' its way into a hole - that sucking is a very small contributor. It's the *push* that does the work; that push being of course the air pushing on the other side of the wing. To be sure, when you depend on action by pulling apart molecules, you aren't going to get anywhere much. When you *push* against molecules, this is where the work is done.
For example, when one tries to pull on a hydraulic fluid, at first there is a possibility of movement, but shortly thereafter the bubbles are going to form and the pulling action amount levels off sharply. Same with air.
An aside - the vacuum isn't caused by the differential of speed of the air going over the air foil. Air speed is only a *symptom* of the presence of the mechanics of fluid flow dynamics. That is all. To focus on increased air speed is akin to telling someone that the flu causes an elevated body temperature. No, a fever is a symptom of the flu. The fever is only an indicator of what the body is trying to do - to burn off the virus (which is why you mustn’t take aspirin!).
Yes, the molecules "go faster", but stay with me and don't think about that right now... No, what is happening is that because the air has longer to travel over the air foil on the top, this necessitates that the molecules of the air are pulled apart. That is, the air becomes rarified. This rarefication is air that is "out of the way" on the top of the wing, so the wing can more easily travel upward (yay! upward... good!) into that rarefication. But the rarefication doesn't "suck" the wing up there. Rarefication is really a hole. This lets the real lifting force - the air on the bottom of the foil - the real working force - to be more efficient, because it does not have to push on the air above the wing (a hole is now there, remember) and instead more push energy is available to move the wing upwards. Rarefication of air molecules above the wing increases efficiency.
I am unclear as to why there are so many questions and perceived mystery around why a wing is so effective. All one must do is to know how stubborn air molecules are, or any molecule for that matter. When air is at a certain temperature, the molecules are measured to be so far apart. Any force that tries to alter this distance will be met with INCREDIBLY frisky resistance from the air. It will not want to conform. This characteristic is responsible for the incredible force that air can impart on anything. If it weren’t a fluid, we would not even be able to move at all, even though "it's ONLY AIR". So, in summary: Pull on stuff - good, but very limited. Push on stuff - now THAT's what I'm talking about...
To put this into perspective - to put why the rarefication of the air above the wing is only an efficiency-increasing characteristic and is only a small part of the lift of a wing - into perspective, is to look at a single surface hang glider wing. This is the most crappy air foil profile that can possibly be built, but we are still blessed with such a terrible thing working very well. The only reason this is possible is because, like any other wing, this wing depends on an angle of attack which is the single best way to enlist the air molecules on the bottom of the wing to push against the surface in the desired direction. This force is enormous, enough so that it can fight with the air on the top of the wing and still do wingy things and allow flight. Sure, there may be a slight bit of rarefication caused by air swooping up over the leading edge and causing a small rarefication there - this is important - but boy is the air 'noisy' there. No, the force on the bottom of this marginal wing is the major contributor. But can one use rarefication to fly without any angle of attack or wing being forced through air stuff? Sure! But now you know why balloons are so darn huge.
I'll leave it to others to discuss the benefits of air accelerating past the trailing edge. All I'll comment on this is that any force one is talking about must be imparted onto the wing itself to do any "airplane good". These forces are both perpendicular (surface) and hydrodynamic. For lift, the perpendicular one is by far the most important. As such, the trailing edge thing in my view has more to do with making the air behave well and getting rid of some noise. Remember that the acceleration of air past this trailing edge is air that is, yes, forced downward, so that must be imparting some oppositional force on the wing to enhance lift, right? Well, yes, indirectly. The air forced down is actually pulling against the rarified air at the trailing edge but not past it - this rarefication imparting some efficiency (some may even say 'pulling' but this isn't really correct), and the accelerated air does this pulling by the inertia of the air molecules J-hooking downward slightly (change of direction) past the trailing edge. It really is more of a rarification maintainer for the back third of the wing more than a force imparted on the wing.
In summary: Efficient airfoil = good. Efficient airfoil = controlled air. Controlled air = compressive force on one side, and rarified air on the other with little noise before and aft the foil. Crappy wings still work if underside upward force is enough and drag isn't objectionable.
Ek wou sê jou aksent klink South African. Toe ek die eerste ZS sien op n vliegtuig toe weet ek. Nice video
This is very beautiful. I never knew propeller design was this important to airplane performance
very excellent and educational, thank you! Maybe clarify that the feathered blade only creates more drag with power applied, otherwise a feathered prop is used for engine out emergencies because it causes minimal drag.
Your explanation of how the blades create thrust is not complete. You explained the Venturi effect where the air speeds up when flowing above the curved wing and air molecules separated by the wing have no need to arrive at the same time at the trailing edge, that will never happen. Bernoulli explains why the pressure is lower above the wing compared to below (where its at ambient pressure). Next Newtons third law comes into play when the propeller moves air aft and opposite reaction occurs moving the plane forward.
Agreed. Differential pressure plays a small role. Flat plates would create similar thrust, albeit with a reduction in efficiency
Ditto! Yes, otherwise you couldn't fly a plane upsidedown, which is clearly possible. Most of the lift is generated from the air hitting the underside of the wing and being deflected slightly downwards. The reaction force pushes the plane upwards by an equal amount. So as long as the angle of attack is right, a plane can fly upsidedown.
He’s European- of course he knows what he is taking about.
But seriously-for this college educated Yankee - I found this very informative.
Any recommendation? Where can I get almost complete knowledge on this topic?
Thanks!
Could you please explain why some propellers have squared tips as in massive C-130’s & others have rounded tips as on Douglas DC-7s or Constellations? What are their advantages & disadvantages?
Thanking you in advance,
Yes, please create a part 2! Part 1 was fantastic!
Great video, i learned a lot!
but I also noticed a technical error during your description of airfoils. Air does not take the same time to cover the distance above and below the airfoil (in fact; you’ll see in wind tunnels the air above is quicker to reach the trailing end) but works instead by deflecting air on the underside and accelerating on the upper side by means of the kiwanda effect
Thanks. Yes I've received a few comments about it and finally decided to address it in a pinned comment.
I don't even remember if I was taught the equal transit theory in flight school, it was long ago, but I highly doubt it. I've never cared if the air going over the top arrived behind the airfoil at the same time, slightly before or slightly after the air going below, as I've always found it completely irrelevant to lift creation. Lift is created by pressure differential (or the push/pull you described which is still air pressure), not by the exact timing of the top vs bottom air. But I appreciate now that just because I find irrelevant, others might care about it. So you are correct, and thanks for the comment, see that pinned comment for full explanation.
great and very instructive video. Thanks!!!
Assume that for a particular radius, the propeller is a wing section, which travels the length of one associated circumference and advanced forward a particular distance ( pitch) through a helical path. For any other radius, the associated " wing section " will travel a different circumferential distance but needs to travel forward the same distance for all radii, a forward distance , called pitch. The fact that at different radii the forward motion is the same, means that the blades appear to be twisted.
The diameter of the propeller is related to engine power, while the pitch is related to the maximum speed of the aircraft.
There are many arguments on how a wing aerofoil section operate, but since I was very young, 80 years ago, I always looked upon the lift of a wing section was due to the "acceleration" of the air masses above and below the wing or propeller. The most important issue here, is that acceleration is a VECTOR , and it has to be treated as such, considering its magnitude and direction, and the forces generated through these vector accelerations and decelerations, of the air particles in question, I do not care two hoots about Bernoulli equation, nor the equal distance theory, nor the circulation theory . Let us stick to basics.
Two stationary air mass particles in line with the stagnant point at oncoming leading edge of the moving wing, one will hit the slight incline to go up, and the other hits the slight incline to go down . These two actions are no different from two moving golf club hitting two stationary golf balls containing mass,
The upper air mass particle will be accelerated up, causing a force reaction on the leading edge, which contributes to drag, but as the air mass particle accelerates up it tend to leave the surface of the leading edge causing a partial vacuum, by the fact that air is a fluid and the air particles have "sticktion" between them to make them act as an impermeable blanket being pulled away from the upper surface of the leading edge, This impermeable sheet of air being pulled away up from the leading edge will cause a partial vacuum underneath the " air sheet" which will pull back the air sheet mass towards the leading edge, thus decelerating its upward movement after the leading edge had accelerated it. While the air particles sheet above the wing will try to return to the upper surface, this retracts down to keep the partial vacuum below it, and a good wing section will keep the air sheet from touching the upper wing surface till it dumps the whole air particle sheet being the trailing edge, One must not consider the air particles as individual mass particles, but more of a flexible sheet of little masses somewhat like impermeable diaphragm of an pump which sucks, as it is pulled away from some surface. Note all this is due to Force = mass . acceleration, where the acceleration/deceleration forces that generated, are vectors, contributing to lift by a suction on the upper surface.
The air particle that hits below the stagnant point also try to reflect off the leading edge, causing a drag reaction, but due to the angle of attack other mass air particles lower down will REFLECT on the under surface of the wing and this Vector acceleration needs high pressure under the wing. which will add a slight forward velocity to the stationary air particle. Hence while the vacuum on the upper surface causes the associated air particles to gain a slight velocity backwards, the lower mass particles under the wing subjected to a pressure zone will gain a little forward velocity. Thus the air particles above and below the wing DO NOT MEET AT THE TRAILING EDGE,
It is the acceleration/ deceleration of air particle above the wing due to the partial vacuum and the acceleration/ refection below the wing due to high pressure that lifts the wing up. The same happens in the profile section of a propeller.
It is to be noted that at start, with the aircraft stationary, the inner 1/3 of the propeller is more like a paddle wheel, due to the high angle of attack, which normally stalls, while the drive is obtained from the outer 2/3 of the blade of a propeller, This settles down as the aircraft gains forward velocity.
At the wing tips of wings and propellers, the best tip designs are those which imitate the wing tips of bird wing, and the flukes of a fish, dolphin, orca, whale tail, where both the leading edge and the trailing edge at the tips, ARE RAKED BACKWARDS..
For a propeller to keep pulling and biting, it needs to slip, where the forward distance covered is not the theoretical forward movement, of pitch multiplied by the revolutions of the propeller. There is more on propeller, especially when the tip velocity will reach that of the velocity of sound, also when the propeller face is not moving exactly perpendicular to the line of motion, where the pitch of the up going blade is different from that of the down going blade, causing vibration, Propellers are not too difficult to understand, if one forgets the Historic names associated with anything that causes lift, and simple use the basic fact, that when a mass particle needs to be accelerated or decelerated, it will do so by the creation and reaction of a force. A wing, or a propeller is no different from a running chisel/surface wood plane, continuously cutting or pushing away at the impervious block of mass air particles by, continuously slicing two mass sheets, one above and one below the wing and ACCELERATING AND DECELERATING them in a required direction, in locations above or below the wing surfaces, and the tips, then continually dumping it all DOWN behind the trailing edge and with many other complexities and circulations around the wing or blade tips
Note that vortex circulation whose axis is parallel to the line of travel of the wing, do not do much harm, but vortex circulation parallel and occurring above or below the leading or the trailing edge are very dangerous indeed .
Great stuff, professor, nicely explained!! Do one on toroidal and advanced issues/features please.
I mean, yeah, you completely forgot about Bernoulli's principle in your description of lift, but otherwise I have to give you a massive congratulations - this video is a really excellent description of propeller design principles and objectives in easy-to-understand language. Thanks, and I'd definitely be keen for a part 2.
It’s amazing to me that constant speed propellers are able to withstand the gyroscopic forces involved when changing direction. Especially when doing violent aerobatic maneuvers I would expect the blades to separate from the hub.
Unfortunately many pilots do not appreciate the high level responsibility of an engineer who needs to design structures to buffer all the forces that are continuously working to kill a pilot. A pilot is not killed because even in a normal landing the vertical momentum is totally absorbed by the undercarriage and the fuselage needs to flex to delay the absorbing time . In a crash the structure needs to buffer all unwanted forces and, as in a car, a collapsible structure will delay the deceleration to one which a human body can withstand. A human body cannot witstand much and in a piloted aircraft which is of the " come back home type" over 95 % of the structure is designed to bring the pilot back home and it is much cheaper to now design an autonomous missile which need not come back as that alone will double the range of the fuel on board.
I am grateful to you for understanding the extra forces on the propeller when the aircraft changes direction, It does no break because the engineers are responsible people and in their dilemma to make an economic aircraft then need to introduce in a small cockpit in which the pilot is caged, enough devices which can help the pilot save his own life. Saving his own life is the priority responsibility of any pilot even if he is flying on his own taking an old aircraft to the boneyard. Testing and retesting and modifications and writing the right checklists for pilots is what keep flying as safe as it is, Thank you for appreciating.
Nice explanation particularly with the blade angle diagrams of the propeller cross section. I didn't find the people-mover analogy particularly illuminating but that's just me. Like I said overall great video
Great description- thank you.
Awesome video! Thanks for the information, I really understand different aircraft propellers alot more😁
That's awesome, thanks!
Good information, thank you. 🙂
Very good explanation .
Great overview. Please part 2.
Dragging Bernoulli in was unnecessary and the equal travel times a mistake - forgiven.
@@arturoeugster7228 Including circulation theory!
@@arturoeugster7228 I'm sorry, I thought the subject was aerodynamics, not electrodynamics! In electrodynamics, conservation of circulation works as it operates only in a the presence of a conservative force.
Prandtl was responsible for the madness of trying to shoehorn Thompson's principle of conservation of circulation into fluid dynamics. Thompson's a paper explicitly states the law of conservation of circulation for a barotropic, ideal fluid with conservative body forces. Note: "conservative". The aerodynamic forces on a foil are NOT conservative. The only conservative forces in nature are electro magnetic and the "force" of gravity. It's poppycock, but is firmly entrenched in fluid dynamics.
@@arturoeugster7228 Yes, I know. That's why I wrote force as "force"!
Which particular aerodynamics textbook are you quoting?
@@arturoeugster7228 To "shoehorn" something (figuratively) means to force it into a place where it doesn't naturally fit, i.e. the principle of conservation of circulation "doesn't fit" into fluid dynamics because the aerodynamic force is not a conservative force.
"Primitive non-technical expressions"? Examples please. Before referencing "conservative", look it up in in Feynman Vol1 14-3 where he uses the force of gravity as an example.
I just installed a Sensenich ground adjustable carbon fiber prop on my my plane. The blade shape is totally different from the old metal prop. The biggest difference I have noticed so far is there is no vibration! It feels like I'm flying a jet at a 100mph!
So … how did old guys do this with wooden handmade propellers and balance them …?
Amazing - Absolutely amazing ! Craftsmanship Very impressive !
There's always a big debate about how an airfoil actually generates lift/thrust. The reason for this is that each side of the debate believes that they are correct, and humans generally _want_ to be correct. Normally one would just conduct an experiment to verify who really is correct, but in this case, there are several arguments that _all_ have evidence showing them to be correct.
This is because in reality, an airfoil generates lift in several different ways simultaneously! So they all really are correct to some degree, with each source of lift adding to the whole (pressure differential/equal transit, incompressible Newtonian deflection, compressible fluid dynamics, and even some more nuanced aspects that don't generally get a major 'side' in the debate).
To make it even more complex, all of those sources of lift account for different percentages of the total performance differently in different flight regimes, including AoA, laminar vs turbulent flow, separated vs attached boundary layer, mach number, the existence, absence, or location of vortices, and more.
The truth is, aerodynamics is an _extraordinarily_ complicated topic that isn't yet completely understood. Or... perhaps more precisely, it is a topic in which the sorts of fine-detail complexities that _most_ dynamics tend to involve, get amplified to the level of not just being important, but being _critical._
Add in that humans have very poor intuition when it comes to wave physics, and yeah... you get lots of very passionate people passionately declaring everyone else to be wrong, all correctly. xD (For an idea of your level of intuition of wave mechanics, can you explain why large commercial ships have big bulbous noses that look about as streamlined as a brick wall?)
Still, good job on the video! It was... quite a lot more basic than I'd hoped for, but that's not a new situation for me. Science and engineering communication is rarely aimed at people seeking to go from intermediate levels of technical understanding and proficiency to advanced levels.
In particular, I'd love to see some more focus on _exactly_ how adding more blades changes things between efficiency and potential power usage, as my understanding is that each blade really acts in a way sort of hybridized between its actual physical shape, and its swept area, depending on operating regime. I feel like I have a reasonably okay understanding of that, but it isn't a particularly _intuitive_ understanding, more like one of those things you just come to accept as true as you do maths for homework problems.
My journey of understanding across all sorts of fields of science and engineering tends to be to go from some degree of misconception from the "lies to children" oversimplifications we use in education (especially here in the US, but to some extent, everywhere), to an analytical mathematical understanding (which tend to involve myriad simplifying assumptions, a la 'spherical cows in vacuum'), then to a level of true comprehension that includes intuition. From there it goes to deep and specialized understanding that includes all of the nuance that we currently understand as a species, but people tend to only gain that level of expertise in one or two very specific topics in their lifetimes. Of course in some topics, _nobody_ has that final level, and in others, like quantum mechanics, it became so stigmatized to even try for the third level of intuitive comprehension that most working physicists just skip over it entirely and brute force their way from the simplified analytical understanding to the detailed simulation/experimental understanding.
Thank you, I enjoyed the video
Love the info! Super interesting thanks! Looking forward to part #2
Thank you sir I love this video and your explanation
Very nice explanation! Waiting for the next video on propellers!
Propeller Speed Reduction Unit (PSRU, or gearbox) Torque Multiplication Explained : ua-cam.com/video/LDsUTJ0f0tU/v-deo.html
The Theory Behind Short Takeoffs Fully Explained : ua-cam.com/video/aJd1xEmbWOU/v-deo.html
I wouldn't want a plane with an automotive engine and a PSRU. Either one could fail and leave you without power..
What an overall excellent presentation and explanation of propellers. You earned a new subscriber here! I think your channel will grow quickly. Keep up the fine work! Thanks!
Very good video. Well done.
Really great job explaining Propellers. Part II should be super interesting, so please give us more.
Good video. On my electric radio-controlled model planes, I chose the pitch first since electric motors turn a certain number of rpm per volt applied to them. I then calculate the diameter of the prop needed to load the motor to the proper rpm, current, and watts. I try to keep the diameter-to-pitch ratio (D:P) between 1.5:1 and 2:1. The larger the diameter, the harder the motor will have to work to spin the propeller blades thru the air instead of pushing air to the rear.
GREAT! Part 2 please! 17:50
Great video! I was just wondering, why you summed up the chord length with "the same reason glider wings are long and thin". I searched for it, and it has to do something with laminar flow and the transition point, but that's it. Is this explained in more detail in another of your videos? A longer explanation would be better.
Long and thin wings (high aspect ratio) like that of a glider are more efficient than short span and wide wings (low aspect ratio) like that of a Piper Cub for example. Meaning the lift to drag ratio is better. Specifically it's the induced drag that is lower, partly because the wingtip is smaller (which is also the reason for winglets). The same applies for propellers.
If you do an internet search for "induced drag coefficient" you will get the formula to calculate it.
If you want to know why that is, you'll have to dig deep, it's not simple answers.
Basically you need as much wing as possible exposed to airflow (longer span) but as low as possible surface area because surface area is drag. The aspect ratio is part of the formula, and the higher the aspect ratio tue lower drag coefficient. In theory the most efficient wing is infinitely long and infinitely thin, which of course isn't structurally possible.
Hope this leads you to some more in-depth answers.
@@LetsGoAviate Thanks for the explanation :)
RC Planes - Now I'm the field expert...props to you xD
Watched from Old Harour Jamaica and can't wait for part 2.
thanks for the education. much appreciated
Great video. Part 2 would be welcome. Having made a few props for homebuilt airplanes the question I was asked by my mentor many years ago was: and how do you measure pitch ? is it the aerodynamic pitch or the bottom surface of the prop? I have tried some experiments with blade shape, ie; scimitar shape for example, in an attempt to see if aerodynamic twist works. My test platform is my plane. I usually do a full power tied down run-up to see if it turns fast enough. i'm looking for more than 2100 rpm with my o-200. the next observation is climb rpm and lastly I set throttle for manifold pressure of 22 inches and see what airspeed i get. There is also some difference with the wood species used I have heard. no pun intended ... I usually laminate maple, birch and cherry, as I like the look of the cherry on top. The prop on the SE5a in Singapore is one I made. Cheers.🍺
Recently I had a close up museum view of a mk16 Spitfire, with a Rotol 4 blade propeller. And decals on the forward face of the blade roots had different settings. The angle numbers recorded on the blades were around 34 to 38 degrees BUT each blade was marked with a different value.
Why?
And what for?
How is it important?
🔔😎🇺🇸
Excellent !!
Awaiting part 2 👍
Great video! Please address how the propeller RPM should be set during a prolonged high speed descent. Say, a descent from 15,000 feet to a sea level airport over a distance of 40 to 60 nautical miles.
Wow! Great content.
Am grey haired (I blame being a GR III flight instructor for that)
Seeing Rand, Ermelo? Nelson and a Jabi that had a prop strike.
I dated a Portuguese girl in the 80's and your accent is too hybrid to be such. Half Boer half Italian?
I still give technical briefs at a major airline, however my age has relegated myself to inspector status (I detest it and have erotic dreams about whiteboards, markets and toolboxes).
Time moves on and I wish I could master PowerPoint in the same way that you presented this.
Wings level and ball in the middle dude!
Markers! Not markets. That is why I miss markers.
You have control predictiive! (Flares at 80 feet and executed a go around).
True helical pitch has been felt to be more efficient for model use as is contant reynalds number through making for hide root chord. Look at the props on the Supermarine Scneider cup winners.
Cool.. love this maan!. Reminds me of mechanical engineering classes..
jirre chop I is liking the south african panes in the clip,I miss that here in New Zealand
Fantasties gedoen. Dankie
Excellent ❤Excellent ..Excellent..Thank you very much.
What an amazing video. Thank you! But after listening to all of that, I still do not know if the fine or the course is the high or the lower pitch :D Which one is also called high and which one is called low pitch? Thank you!
Thanks. Not sure I've heard it called high or low pitch, but high pitch would be a high angle on the blade, i.e. course pitch, and low would be fine pitch.
Great video Jaco, thank you for your time and dedication
Could you fi a video on the Corsair F4U and it's issues with losing control.
can you tell why angle of attack for downgoing propeller is more then upgoing propeller during climb ?
Explained in this video ua-cam.com/video/WnJxrHmtT_c/v-deo.htmlsi=cOl-8pGvZavwkvek
It's because the oncoming air doesn't hit the propeller blades perpendicularly. Imagine looking on from the side, airplane at high angle of attack, the downgoing blade moves towards the oncoming air from top to bottom. The upgoing blade moves front to rear, bottom to top and actually moves slightly rearwards. Comparing the AoA of the blades at midway up and down shows the difference. It's called P-factor or assymetric blade effect and is most pronounced for taildraggers on takeoff with all 3 wheels on the ground, but will affect all propeller aircraft at high AoA.
Nice video 🇿🇦 regular prop strikes is a problem with my foaMWARi model
A very good description of prop operation. One add may be useful…… Maximizing thrust, particularly at takeoff is done with a large diameter prop because the larger diameter accelerates a large volume (mass) of at lower speed than would a smaller prop pushing a smaller mass at higher speed. Thus the larger prop gets a “firmer” grip on the air. That is to say that the larger prop is not trying to push air that is slipping away….sorta like trying to walk uphill on a shifting layer of sand. The slipping absorbs energy that is just wasted.
So tug boat props are big and slow. Takeoff contest winners use biggest prop they can.
Physicists call this impedance matching. For example, if you want to move an elephant, you bop it with something as heavy as possible, maybe another elephant. Hitting an elephant with a high speed baseball may annoy the elephant, or even kill it, but doesn’t much move it. Hitting a squirrel with an elephant is similarly inefficient.
This is well put and very informative. I make similar video tutorials on various aircraft system and I appreciate the time and effort you put to make this piece. keep it up.
Have you got a propeller on your front room wall? Excellent video by the way.
Yeah it's an old propeller blade. Thanks!
@@LetsGoAviate It took me ages to work out what was on the wall of a Military social club I once visited. Too big for a propeller, too thin for a wing. Turned out to be the rotor blade from a Chinook! Now they are massive :)
@@jeffnorwood-brown8407 It can drive one mad lol. I still don't know exactly what this blade is from. Thought it was from a Continental R-670 powered plane, like a Stearman, but the shape is different. Looks more like that of a T-6 Texan, even though it seems too small.
⚓️ Thanks LGA 😎 ok??? What’s controllable pitch? Since defining varying pitch thru the length of a blade … then describing variable pitch as a control feature… LGA is confusing or combining two features with one description…. Which is it?? Controllable? Or Variable?
I don't 100% understand what you are saying. The AoA that changes along the span of the blade I called blade twist. And blade twist is necessary to compensate for faster turning speed at blade tip than at the blade hub. Blade twist is "baked in" at the factory and cannot be changed.
Variable pitch propellers I called just that, the pitch that can be controlled (blue knob in the plane). And it's to get optimim blade AoA at all airplane airspeeds (vs a fixed pitch which would only by optimum at one airspeed, i.e. takeoff of cruise).
Variable pitch changes the pitch (AoA) of the whole blade, and can be done in flight on varibale pitch or constant speed propellers.
I'm not confused or combining anything that shouldn't be 🙂
@@LetsGoAviate I guess you’re not open to specific descriptions… nomenclature using similar terms terms to define separate features is not consistent.
@@pierheadjump Not sure what inconsistencies you're referring to but I'll leave it there 🙂
Have you read Jack Norris book on propeller theory?
So much was explained. Part two please.
17:50 Good video but wrong explanation of lift. The air over the camber does exit at the same time as the air flowing on the flat section of the blade.
Very clear
Rubber powered free flight propellers are an interesting problem related to torque curve of rubber. Similar to CO2 or compressed air in this regard.
P factor would be interesting to hear about..
part 2 video please
Amazing video! More please 😊😊
What is the theory behind your statement about the airflow over and under the blade having to meet each other on the traling edge?
It doesn't have to meet at the trailing edge. The faster moving air over the top might arrive at the trailing edge more or less the same time as the slower air below, but it might even arrive before the air from below. It would depend on factors like the shape of the wing, angle of attack etc.
this is berry good love from a berrry blue fellow! 💙
I have always thought that the propeller sort of "scoops" itself forward in the air and pulls the airplane behind it. Is this a wrong way of thinking ?
Will part two cover counter- and contra-rotating propellers?
That's the plan
Uitstekende video. Baie dankie
Thank you!
Great video.
Most interesting - thanks.
Are there propellers out there with winglets?
Would that improve efficiency like on wings?
Yes airplane propellers with winglets are called Q-tip propellers. Became pretty popular during the 80s and 90s. They were marketed more for being quieter propellers. That's where the Q in Q-Tip comes from
I had an APC propeller on my RC plane that had little winglets. One day a poor landing snapped the propeller and all I could find at the local hobby shop was a black propeller. Only when I fitted the black propeller did I notice that the APC propeller was much quieter and much faster.
It appears the folks at APC really know their stuff when it comes to propellers.
Tip plares on blades should increase efficiency by reducing tip loss.
Yeah, but "plares" STILL have to be invented before we can use them!