Serenity is one of the most elegant and beautiful airframes I have seen in a long while, the way it flies in the way it moves in reaction to wind and input from your end is astonishing. Especially with different motor configurations it looks way better than more than half of the RC model planes out there it is so smooth and responsive and just amazing I love it’s design.
Hi there, if you are using washout to trim the airplane instead of for example a reflexed camber airfoil, the wing of course will have a more bell-shaped lift distribution. The literature on tip-mounted propeller efficiency gains uses elliptical lift distribution wings, with a conventional tail to balance the pitching moment. With a bell-shaped lifting distribution, the center of the trailing vortices is actually located about 70 percent of the span. Al Bowers, a scientist at NASA and probably one of the world's top experts on bell shaped lift distribution wings, told me directly 5 years ago that there would not be much benefit with a vortex imbedded propeller on a bell shaped lift distribution wing, at least not like there would be on a standard wing. You could try putting the propellers at 70 percent span to line up with the vortex center, but again, according to Al Bowers, it wont have the same gains as elliptic loaded wing, i.e. one with a conventional tail to counter the pitching moment.
I'm still looking for the math to draw the cord. The nomenclature for defining the re-flexed airfoil for a flying wings is mentioned, but not the math to plot it.
"After 360km of miles on the airframe..." Ha! Great experiment BTW I wonder if the first round was (partly) more efficient due to motor/component wear after 180km of miles on the airframe
@@ILLEagle_1 how hard were the eg: the motors pushed? Whats the time life on the bearings? What is the quality of the motors - cheap or high end? What about the batteries?
Thanks for the comment shout-out, took me a little by surprise. I think the differential thrust issue was expertly highlighted by that lovely flat spin when the ESC failed. As was the fallability of any form of propulsion. But what I really want to see right now is the WIG water toy video 😖🥰🥰 I've been thinking hard about the physics of tip propulsion and I'm struggling with it. It's not intuitive and I'm also looking forward to more content about it. I love feeling confused and finding resolution. Keep it up, loving the channel right now!
This would be an almost insurmountable objection to using this configuration for manned flight. An engine out would mean that you could only glide. Conventional placement will allow one engine flight, or at least a very great extension in glide.
I love that plane. I love your work man. I come from an aero club full of boomers and armchair engineers. Seeing science in practice in model aviation it incredible. Your my hero man :D
In his book Understanding Aerodynamics, Doug McLean makes a good case mathematically for why wingtip-mounted propellers do not have the intended effect on induced drag. He also talks about it in this time-stamped video: m.ua-cam.com/video/QKCK4lJLQHU/v-deo.html I suspect there are still some higher-order subtleties that can be exploited with the wake interaction, but from a fundamental level I think they would have to be relatively minor. Either way, the plane you have built here is one of the sleekest I’ve ever seen and I really enjoyed the video!
Yes, i instantly think of Doug McLean whenever wingtip devices are brought up. my guess is that the motor mounts are simply acting like winglets, AND the propellor pitch theory discussed by ThinkFlight
@@thinkflight while wing tip motors don't make it more officiant they allow a air craft to have a lower aspect ratio which makes weird looking planes look up Vought V-173 Flying Pancake
I am glad you brought up McLean. One of a few who is correct. Following up I like to point out that there is a conceptial difference between induced drag FORCE Di and the induced drag COEFFICIENT Cdi (just a number) Cdi = Di /(Area × q) q = dynamic pressure = rho×V²/2 rho = density V = speed Cl = Lift /(Area × q) lift coeff. Cdi = Cl² / (pi AR) pi=3.141592.. Clearly this number, an artifact is dependent on the aspect ratio AR = b²/ Area = b/ mean chord b = wing span But the induced DRAG force is (1:28) NOT dependent on the aspect ratio ! despite the narrative. Di = (Lift/b)² × 1/( pi × q ) The induced Drag FORCE is proportional to the square of the span loading Lift/b and inversely proportional to the Velocity² and density. Not in the least dependent on the wing chord c !! verify by substituting in Di = [ Cl² × 1/(pi × (b²÷A)) ] ×(A×q) Cl = Lift / (A×q) A cancels out and b² is in the denominator The induced drag force is independent of the wing area, hence chord. This in contrast to the parasite drag, where the wing Area dominates D parasite = Cdp × Area × q = Cdp× (b × chord) × q The effect of the chord affects only the parasitic drag, not the induced drag force The confusion created by the artificial meaningless induced drag COEFFICIENT is remarkable. If you derive the expression for the Lift to total Drag ratio by substitutions: The simple form results: L/D = b/2 × sqrt( pi /(Cdp × Area) ) Strong function of span b, weak function of parasite Drag Coeff. not a function of the aspect ratio b/c, but b×c instead. All the derivations above are valid for a wing with elliptic lift distribution, other wise a correction must be made with the Oswald efficiency factor.
My new hypothesis is that the props at the edge simply gets more clean unobstructed air. In addition to giving the thrust no obstruction. Making more efficient. My simple guess. Cant wait to see the next video!
I wonder if anyone mentioned the Vought V-173 aircraft in the previous videos. That was a unique set up that historically used wing tipped place airscrews to both improve the efficiency of the wing and keep the boundary layer attached on a high performance low aspect ratio wing. It made use of a lot of interesting tricks in its day, even interconnected engines so that if one engine failed both screws would still be turned by the transmission, kinda like on V-22’s today.
Career Unmanned System guy here... I am a new subscriber. I love how you narrate and show FPV and onboard video shots. The smoke trails really assist in viewing aircraft reactions etc. Wish I knew you when I was pushing military concepts etc. What you are doing is for the most part how myself and others like the Scan Eagle designers were doing in garages on their own dime. Scan eagle concept was eventually bought out by Boeing Insitu for about 300 Milion. Keep on what you are doing! your projects are before their time as were mine and it can be tough getting people to support you when you are a true innovator. Keep it up man, this is great stuff!
Serenity is one of the most elegant and beautiful airframes I have seen in a long while, the way it flies in the way it moves in reaction to wind and input from your end is astonishing. Especially with different motor configurations it looks way better than more than half of the RC model planes out there it is so smooth and responsive
10:00 were you able to measure a difference in motor current? Given the same motors and the same approximate pitch / diameter that would be an interesting measurement of total load on the motor.
I think what stands out to me anyway as pure BEV flight is now clearly very mature is how quickly everyone has ditched wings *period* which from these flights and thoughts upon them one can see why as there is no vertical stabilization here. In theory one could launch your wing nose up/blades down so as to test mission critical pitch and yaw with another option being similar to what the US Navy does with their Submarines namely create a housing around your blades then add some vertical "grid fins" in front of same said mechanism to provide at least some friction to add lateral stability upon such an austere platform. Point being what are trying to test is how your design works *IN LEVEL FLIGHT* and not just as an efficiency theory that happens to fly. Once you achieve "on the level" then a testable hypothesis can be made and indeed anything is possible "in the wild" (box wings, front facing control surfaces, landing skids, you name it.) A good UA-cam channel to check in on is BPS Space if you really want to crazy insane with the data science.
Sorry if they've been mentioned before. Two aircraft for your perusal/flight information are the Ho-229 "Flying wing' and how the Horten brothers resolved their stability issues with such a plan-form and the Vought XF5U. A machine specifically designed around wingtip mounted propellers. Even if the wing in that machine's case was virtually a frisbee. 👍
from what i can remember from my incompressible aero class induced drag increases greatly with speed. so at these low speeds the effect will be very hard to measure. Second the AR of these wings is reducing the effect of the wingtip props reducing induced drag. the props only extent a couple inches past the wing tip, and at this scale that is only a tiny increase in AR. If you look at the V-173 and XF5U the propellers increase the effective wingspan by a significant amount. (on the V-173 wingspan was 23 ft 4 in and the prop diameter was 16 ft 6 in).
Props on the tips. Depending on rotation the Wing Tip Vortex is taken into the mix. Wing Tp Vortex eliminators delay the Wing tip vortex to be farther from the wing it's self, thus delaying drag. So, putting the props on the tips solves this drag problem.
Much excellent content in this video, with great references. The aerial videos are most awesome. Great cinematography. After initially watching the video, I returned to the jet segment (from 1:03) ... watching repeatedly. Examining the vortexes frame by frame, a few things stand out. The most obvious vortex does not initiate at the wingtip, but instead appears to form at ~2/3 of a wing. (?) Also, the air about 1/2 a wingspan distance above the wing is clearly effected immediately as the wing passes by, as is air 1/2 span further out from the tip. It's like there are multiple scales and complexity to the vortex. (multiple cores) Distribution of lift, and pressure across the span is clearly not constant along a span, and extends beyond the span. This creates a pressure gradient and shearing forces that extends well beyond the wingtip. The flap generated vortexes (at 1:17) are dancing, clearly being influenced. I suspect this an interaction with the wingtip vortexes, which are not visible. The high angle of attach of the deployed flaps is creating a much greater wing loading on that surface (much higher pressure differential) vs the main wing. Thus wing loading and angle of attach are major factors to amount of energy going into a vortex. Reducing the pressure differential (between top/bottom of wing) towards the tips would be beneficial to reducing induced drag. As would be reducing the wing loading towards the tips. Think you may be seeing some of this in the Serenity design, as there is built in washout to the flying wing. (lower angle of attack at the tips) This likely why the results fell within the margin of error for Serenity 1. Also from Serenity 1, you noted the complexity of the vortexes at 7:45 (in Part 1, previous video); where vortexes initially rotated outward, then merged into a larger vortex rotating inward downstream. This can be seen in this video (9:45) as the vortex with red smoke wiggles and transitions. The RESULTS (5:43) of reversing propeller direction are pretty telling IMO. The 7.2% difference implies an efficiency change of just +/- 3.6%. This assuming one direction being an efficiency gain, the other a loss. Can see why now testing inward motors as explore further. BTW: I don't think the tractor motors (vs pushers) would have changed the results. (ie: would fall within the same margin of error) To the final question (9:35), I think the efficiency gains are the result of countering the larger 1/2 span inward rotating vortex, not just the smaller outward rotating tip vortex. Having access to a fog machine like Daniel (RCtestFlight) might give a better overall view of what's happening along the full wing and beyond the wing, vs a smoke pipe at the tip showing airflow across only a couple inches. (ie: more data is needed) In future it may be interesting to explore different wingtip designs to see the impact on efficiency. For example how the shape (square vs a tapered), and how tip wing loading (angle of attack, or washout) of the outer segment of span effects efficiency. The tip design at 0:48 is pretty rad. Note: testing tips designs on a flying wing will present a degree of challenge as pitch stability typically maintained by having washout towards the tip.
Your aircraft is awesome and your skill is amazing, however it's very difficult to predict what is going on due to the sweep angle, the blended fuselage and the moving ailerons altering the vortices shed from the wing. For the sake of your experiment I suggest you use a conventional wing - tail configuration, with no sweep, twist nor dihedral and better even with no ailerons on the wings (you can use differential thrust anyway) and with minimal wing-fuselage interface.
Great work.I made two models use tip props and they were flying well . I think you need a wind tunnel to make this more accurate. May be here is a possible reason: Propeller rotating at outer direction,needs less torque, because of the wingtip vortex,and rotating inner needs more torque. Maybe there is a slightly difference in efficiency of props, but motor efficiency changes.Some high kv motors may have higher efficiency in less torque,and this matches your flight test result.The only way to find this out is to add a torque sensor on wing tip, use rpm and torque to measure the real axial power,and this the real aerodynamically power you need.
I have two FPV planes the same span, one is a wing, the other is a balsa home built with a conventional wing and a twin boom to a tail. They both run all the same gear and have pusher motors. The Wing is lighter in foam at about 270grams , the balsa framed with covering is heavier at over 430 grams. The Balsa plane is more efficient by at least 20+ percent, even though it is heavier. I put this down to the wing has to use reflex and is swept in order to fly, where as the balsa own design does not, and now having seen this video also the tip vortices are opposite, and is affecting the efficiency of the wing type. Thankyou so much for doing this research it is MUCH appreciated!!, I was at the stage of trying wing tip motors. Also I figure that a tip splitter (winglets) is worth a try as these are used horizontally on race cars to split the air ahead of the bumper. I feel these can do this on the flat wingtip, to minimise bleed around from top to bottom of my balsa planes wing. Matt Western Australia
Good Stuff! I noticed a few times the elevons where trimmed up for level flight, this in my experience is a nose heavy plane and can be messing with your results. Thanks for sharing.
Hi, I'm an aeronautical engineering graduate. If you intend to mount the propeller at the wing tips the wing should be SWEPT FORWARD not swept back. The props should be rotating at opposite direction. But for real aircraft (not rc model) you have to choose between vortex or structural load at the wing root due to propeller torque. For me I think the best solution for your experiment is to use a counter rotating propellers like the DZP30. Enjoy.
An excellent point about drones having double the points of failure. Drones also have quadruple the dependencies, while in a plane a motor can quit and it can continue, or both quit and it glides down. With a drone every motor needs to operate, and also operate at the correct rpm
No it's not... "points of failure" here is a misnomer. You could still fly a drone with three props. Two props would be opposed so they would be the lifting props as they don't contribute an unbalanced force, and the third could be used for attitude (it would have to spin forward or backward, and have to reduce the amount since it's not working against an opposing rotor anymore, but that's just software. Geometrically and physically it's stable). You can't fly a flying wing plane with wingtip motors when one goes out because attempting to thrust would just yaw the plane the harder you push. The quad has more points of REDUNDANCY, not dependency, until it loses more motors, and then it depends on which one you lose. If one motor goes out on the quad, do the others stop working or work against the center of gravity with leverage? not necessarily, so it's not a mutual dependency. With one motor lost on the plane, it's just a glider because due to the position of the motor, you've essentially lost two.
@@enotdetcelfer you can’t do that with a drone, all four need to spin with opposites balancing opposites otherwise you get yaw issues. You clearly don’t understand drones and so I’m not going to bother explaining it because it’s something that you’d understand better from your own learning.
@@ryanm.191 - There are several videos here on UA-cam of experiments of quadrotor control after a motor failure. ua-cam.com/video/CzM8Cvcif6g/v-deo.html
This is really a moot point since most commentators were probably thinking more of a full scale scenario. A quadrotor will never be certified for people to fly in commercially without the proper redundancies in place.
@@gpaull2 exactly, commercial drones would need additional redundancies, but that would mean more redundancies required. Each power plant would need one redundancy meaning 4 power plants and 4 redundant power plants, which is additional weight. Compared to planes where the redundancy is just flying down. Additionally without very difficult to create systems and advanced training, a large commercial drone wouldn’t be able to autorotate as it would develop a yaw drift as well as pitch and roll instability which just wouldn’t pass flight certification requirements.
Oh, neat! Having my question highlighted like that only to *not* be answered (yet) is quite the cliffhanger. Wicked side-slip that thing was pulling. Can't wait for the conclusion! As the theory-crafters predicted and the 2nd experiment suggests, a swept-wing might not be ideal for observing vortex-related effects of wingtip motors, due to the apparent reversal of the vortex mid-span.
Also don't let anyone tell you what may or may not work. None of that matters. What does matter is that you are trying something different and learning along the way. And who knows. Maybe you'll discover something truly revolutionary!! And then I'll steal it 😜. Jk. Too lazy to even try.
In the case of a wingtip motor failure, the yaw would be tremendous and unrecoverable. To be practical this would require a common transmission between props, so that in the case of a motor failure, the remining motor could power both props. It would make sense to mount the actual powerplants inboard as well, to reduce their roll moment.
yeah i didn't like how he sort of hand waved that issue in the video. the comparison with quad rotor drones is apples to oranges, as the factor of safety for the design of a small unmanned drone vs the design of a fixed wing aircraft large enough to transport people is, obviously, vastly different.
No hand waving, this is an unmanned test bed whose sole purpose is to learn about wingtip motors. It is never suggested or recommended as a final configuration for manned aircraft, just as a quadcopter also is not recommended as a manned configuration.
Quick tip for managing controls and monitors and devices outdoors. Fill sandwich bags with dried beans, and use these waterproof beans-bags to prop up your gear.
Nasa did a rc experiment with a wing called a "Prandtl Wing", based on the complete equation, rather than the main lifting zone, basically the wing tip architecture is redirecting lift pressure about 30% before the tip from under to over the top to the tip, causing the vortex to appear at the 30% mark opposed to the tip causing drag and converting it to yaw stability which has a positive effect in banking turns.
Pressure mediation: Resonance tuning rotation to pulse tip vortex will amplify local pressure in a controllable way and increase lift efficiency generally. vortex is a source of coupling between energetic containers so to so to speak and all containers can be pressure accessed via resonance.
It's possible the reason the tractor wingtip configuration was giving the flying wing some massive sideslip was due to the propeller's vortex column thwarting the self stabilizing properties of the wing twist, where as the pusher configuration doesn't interrupt those properties at all
One way I visualize why the wingtip vortexs rotate outwards, is thinking about the airflow under the aircraft. The compressed air under the wind slips off as it reaches the trailing edge. Because the wings are swept back the first bit of air able to curl up, is gonna come from the center of the airframe. Since while this air is free to go to low preasure it can curl up and go outward, since the air further out on the wind is still stuck under the wings. I'd imaging this phenomenon changes with the swept back angle. With a straight wing, all the air exits at the same time (except the air near the tips which is free to curl inwards) At certain angle this flow reverses (not sure what that is)
Alice aviation also gave up on wingtip motors, and placed their nacelles alongside the fuselage like the mad dog. The reduction in vibration alone and the associated drag reduction is probably worth it. It still would be interesting to see the twin tip tractor configuration on a wing with elliptical lift distribution.
I have no idea why the increase in performance was so large. But I do know that is one very sexy aircraft. Such a cool video series keep up the great work.
Great video! Not sure about there being a inward rotating vortex and outward rotating vortex on the same wing. Wouldn’t that be less efficient than a wing with single vortex? If I remember correctly, the lift distribution curve is smooth transitioning from inboard to outboard and and slightly negative at tip. So I would wager no inboard rotating vortex. Since the pressure gradient is smooth.
the outer rotating configuration is inline with the fact that the differential rotor torque reaction helps during roll and banking movement in a flight. while in a inward rotating configuration, the outward motor torque reaction on a banking maneuver work against the required roll movement provided by flaperon. This could be one of the factors resulting in inefficiency seen in inward rotating configuration.
As an ultralight flying wing builder flyer I have found your experiments very intriguing. Fuel efficiency is the driver in new airliner design, 7% is a significant gain, you may well be on to the shape of the future.
have you tried forward facing large props (a bit like the Vought V-173) on a forward swept wing? the forward swept wings give slightly improved lift and the large props push the extra air down the wing giving even more lift making the plane super efficient
How difficult is it to build or rent something as a wind tunnel? Being able to set a specific and consistent wind/air speed might be really helpful instead of hoping for similar enough conditions outside. This was very cool and I look forward to more.
To compare wingtip devices you have to consider why span is limited in the first place. Airliners have to fit inside a gate, racing planes need a quick roll rate, other planes have structure constraints. Why is your plane span-limited? How can you work around this to use less energy throughout the flight? I think it would be interesting to compare tip motors to a span extension equal to the radius of the prop.
This is an amazing video as I am very interested in the effects of air movement and drag and its effect on efficiency. Any chance that you could get your models into a Wind Tunnel?
True, a quadcopter with 4 rotors would be unstable with a single motor failure - but that's why drones with uses that place a high premium on safety use 5+ motors. Same principle as so-called "office safety chairs", loss of one leg affects its stability, but not total loss of it. A better testbed could be removable wingtip motors as supplements to motors closer to the fuselage - then you can do a direct with/without comparison.
I think the issue of this theoratically very efficient configuration is not only the case of the failure of one motor. In fact, the power of the wing tip motors will have major effects on the lift of each wing and on all the axis of the plane. This means that all the control axis of the plane will be strongly coupled which is not considered a "good" and "safe" configuration. The stability of the plane will be highly dependant of the algorithm, the sensors and the controlers of the motors and will necessarily leads to a higher failure chance because of the dependancy of many part.This can be acceptable for a non habitable plane only.
If you think about how winglets work on an airplane is to remove the flow of air to the top of the wing due to high pressure on the bottom of the wing making its way to the top of the wing killing the lift on a portion of the wing. The propeller rotation outward I believe is doing the same thing pushing that airflow from the top far enough away from the wing to prevent it from reaching the bottom part of the wing killing the high pressure on a portion of the wing.
I'm curious to know what kind of simulation you ran (at about 8:15). Did you do any sort of higher-fidelity sims? The structure of wingtip vortices can be finicky to pin down. I'd be happy to run a RANS sim on the model if you're interested...
Reminds me of the XF5U, the "flying flapjack". It had an aspect ratio of less than 1, and depended on the tip mounted props to cancel the huge tip vortices expected at high AOA.
The reversed wingtip vortices are probably a result of the swept flying wing configuration utilizing the outboard portion of the wing as "horizontal stabilizer", in which case they are producing negative lift to counter the nose-down moment of the inboard lifting section in an aerodynamically stable configuration. Negative lift = negative circulation = reversed wingtip vortex
Some fascinating aspects of flight,the electric aviation channel from India is also very educational in relation to the physics of flight in electric aviation,well narrated documentary ,thanks
The problem with wingtip motors is that in the event that one motor/engine dies the plane becomes uncontrollable due to the fact the the yaw factor is much greater then the conventional design. On planes that have 2 engines the engines are located as close as possible to help minimize the yaw effect of one engine dies. They also make SOME propellers counter rotate to also help minimize this effect. The piper seminole is just one example
Thank you for sharing these experiments, very inspiring! One data point I haven't seen discussed is wing loading? The lower the WL the lower the induced drag as we all know, and seeing as how light our typical models planes are wingtip vortices constitute a (comparatively to full scale aviation) small part of total drag, which would throw the results in this case? If you plan to revisit this experiment there are other flying wing planforms such as deltas don't require as much reflex, and with a lower aspect ratio would generate more wingtip vortices, which in light of the experiment is a good thing, no?
Wing loading is relative, the cruising AOA is comparable to the cruising AOA of a larger aircraft and thus I would assume the induced drag component is also comparable. Specifically I'm trying to see if there is a benefit to wingtip motors on a plane with good efficiency already, rather than just trying to help out very inefficient aircraft.
pouncer the induced drag force is proportional to the spanloading square, NOT to the wing loading For an ellptically loaded wing: Dind = (L/span)² / (3.1415...×q) q=dynamic pressure and is the result of the downwards forward inclination of the downwash behind the center wing. Nothing to do with the energy of the tip vortices, which is taken from the very low pressure energy² inside the vortices. 2) the pressure follows the Bernoully energy conservation equation. p1 - p = density × ½(V² - V1²) If you put a pressure probe inside the vortex you can verify this. And the tip vorteces, downstream do carry angular momentum, imparted by the wing tip. Clock wise behind the left wing, when the wing tip is not acting as a pitch up surface, as is the case with the flying wing here.
If you were worried enough about engine failure (for a passenger model), you could always put a glide motor in the center of the rear, with enough power for emergency landings. AI could recognise a failure and immediately brake the wingtip motors.
I'm an F-15C pilot. I have two separate points to raise 1. Electric cell storage is bad for aircraft currently because the energy density is still not near the density of liquid fuels and unlike a liquid fuel aircraft, an electric aircraft never sheds weight as it flies through the process of combustion. This results in batteries being just dead weight, reducing efficiently the moment you rotate and leave the runway. Also, liquid fuels don't self-immolate spontaneously like current LIPO technologies seemingly with no warning. 2. Wingtip engines are a nightmare scenario to a combat pilot. I'd usually never advocate for less than 2 engines on an aircraft, but a ducted turbine with outlets at the wingtips would actually be safer, because if you lose one engine, you lose output to both wingtips. Lose an engine with two engines on wingtips and the aircraft instantly turns into a frisbee, and you have to recover from a spin before you can be a glider. On the ducts, you can control yaw with variable nozzles open/close. Also sometimes vortices are good, and jets sometimes have dogteeth that create them to increase pressure on certain control surfaces and reduce flutter, such as the horizontal stab on the F-15. Interestingly, AMRAAMs on F-16 wing tips also reduce flutter, but I am not sure if it's weight related or aero related. Maybe both.
I think most of the efficiency gain comes from the propellers' vortex cancelling the wingtip vortex. This would not work for jets. Some use ducts to the wingtip for VTOL and to augment thrust vectoring.
Have you tried to use ducted wing tip motors for this? would also make those crash landings easier on the components, I would personally use PVC pipe make a field goal with a soft net and fly into that for landing.
Excellent design, test methodology, and execution!! As always, you're scratch-built planes show you really have your build techniques down! I wonder if you would see larger efficiency differences with testing a similar motor placement change on a conventional tail & wing aircraft. However, it won't have the elegance of a flying wing. I am also curious about the efficiency differences between downward, upward, and both downward and upward-pointing winglets. Great series!
Thanks for the update. Looking forward to see the manned vehicle. I assume at some point you'll mix the tip motor and ground effect vehicle? A compact design, relying a lot on the ram / works like a hovercraft, with outward rotating motors... I think the prop vortex can really seal in the pressure! I'm gonna leave some of what I said on the last tip-motor video: "I'm not saying you didn't lower the induced drag, in this experiment you can't tell if it was that , or, a propeller working more efficiently. Maybe both? (Also, for flight time, totally irrelevant ;-) [...] I think putting them in front would work slightly better. But in this design you'd need a big pod to not have the noise from the prop being close to the frame. So I get putting them in the back."
Do you think the reason that the vortex did not move in board as it does with the traditional aircraft might be caused by the lack of tail structure? The mass of that tail structure would displaced a lot of air creating a vacuum behind it and then pulling in the smoke from the wingtips. The absence of such structure would not create the vacuum.
Try to test what motor configuration is best. Both spinning outboard, or inboard. Both spinning the same direction has always been normal for flight, but I'm sure wingtip vortices would benefit from contra rotation. Throw the air outboard or inboard?
What about using the wingtip motors for skidsteer-esque thrust vectoring? For ultra-long distance, or very long circular loitering missions it might more efficient than using control surfaces, assuming control surfaces disrupt aerodynamic efficiency in any significant manner.
I can see two issues. 1) asymmetric thrust when one engine fails. 2) the extra structure (weight and thickness) that would be needed throughout the wing in a commercial aircraft to support the engine weight.
Even though the props are rear mounted, the pressure field will propagate upstream and will have an effect on the airflows above and below the wing. My educated guess: Outwards turning props are more efficient, because they redirect some of the airflow on topside of the wing over the sides of the wing, effectively leading to more airflow over the leading edge of the wing and thus generating more lift. In the same way, the props push air under the wing, effectively slowing down the airflow under the wing, which is increasing the air pressure and again generating additional lift.
Just a quick suggestion regarding an engine out asymmetric truss problem. Considering the extreme lightness of these new electric motors, two of them could be used in tandem. Possibly with the prop shaft of the rear engine going through the prop shaft of the front engine. If the main front-engine fail for any reason, it would be immediately picked up by the rear engine. Just a thought.
Very cool! I am looking forward to the tractor test. The Vought XF5U is my favorite aircraft as it was designed around this idea. I am totally unsure what will be better tractor or pusher.
More elegant way to reduce wing tip, vertices can be achieved by changing the lift distribution from an elliptical lift distribution to be curved lift distribution. NASA test it some years ago with the project PRANDTL!
Serenity is one of the most elegant and beautiful airframes I have seen in a long while, the way it flies in the way it moves in reaction to wind and input from your end is astonishing. Especially with different motor configurations it looks way better than more than half of the RC model planes out there it is so smooth and responsive and just amazing I love it’s design.
Serenity flies like a leaf on the wind!
You either get it if don’t lol
Did Boeing not figure it out with millions in RAD? Durp
Hi there, if you are using washout to trim the airplane instead of for example a reflexed camber airfoil, the wing of course will have a more bell-shaped lift distribution. The literature on tip-mounted propeller efficiency gains uses elliptical lift distribution wings, with a conventional tail to balance the pitching moment. With a bell-shaped lifting distribution, the center of the trailing vortices is actually located about 70 percent of the span. Al Bowers, a scientist at NASA and probably one of the world's top experts on bell shaped lift distribution wings, told me directly 5 years ago that there would not be much benefit with a vortex imbedded propeller on a bell shaped lift distribution wing, at least not like there would be on a standard wing. You could try putting the propellers at 70 percent span to line up with the vortex center, but again, according to Al Bowers, it wont have the same gains as elliptic loaded wing, i.e. one with a conventional tail to counter the pitching moment.
Exactly. And central undercarriage - gilette spur
Wow
I'm still looking for the math to draw the cord. The nomenclature for defining the re-flexed airfoil for a flying wings is mentioned, but not the math to plot it.
Well pointed
"After 360km of miles on the airframe..."
Ha!
Great experiment BTW
I wonder if the first round was (partly) more efficient due to motor/component wear after 180km of miles on the airframe
Great point!
I was hoping for ten thousand of this comment.
In the grand scheme of things that’s not that much time. That’s only like 12 hours
@@ILLEagle_1 how hard were the eg: the motors pushed? Whats the time life on the bearings? What is the quality of the motors - cheap or high end? What about the batteries?
Are we the only ones noticed, or only ones that cared?
Thanks for the comment shout-out, took me a little by surprise. I think the differential thrust issue was expertly highlighted by that lovely flat spin when the ESC failed. As was the fallability of any form of propulsion.
But what I really want to see right now is the WIG water toy video 😖🥰🥰
I've been thinking hard about the physics of tip propulsion and I'm struggling with it. It's not intuitive and I'm also looking forward to more content about it. I love feeling confused and finding resolution.
Keep it up, loving the channel right now!
This would be an almost insurmountable objection to using this configuration for manned flight. An engine out would mean that you could only glide. Conventional placement will allow one engine flight, or at least a very great extension in glide.
I love that plane. I love your work man. I come from an aero club full of boomers and armchair engineers. Seeing science in practice in model aviation it incredible. Your my hero man :D
OK Boomer
@@thesnitch7 I do not see what you mean, ‘joined in 2009’ I was 4 years old when you made your account. Your the boomer :)
@@Robot_Child_Productions sure thing, Boomer
@@thesnitch7 ok grandpa
@@Robot_Child_Productions im 23 and i made my accound around 2011 i think. I will have to check. UA-cam has been around since 05
In his book Understanding Aerodynamics, Doug McLean makes a good case mathematically for why wingtip-mounted propellers do not have the intended effect on induced drag. He also talks about it in this time-stamped video:
m.ua-cam.com/video/QKCK4lJLQHU/v-deo.html
I suspect there are still some higher-order subtleties that can be exploited with the wake interaction, but from a fundamental level I think they would have to be relatively minor. Either way, the plane you have built here is one of the sleekest I’ve ever seen and I really enjoyed the video!
Yes, i instantly think of Doug McLean whenever wingtip devices are brought up. my guess is that the motor mounts are simply acting like winglets, AND the propellor pitch theory discussed by ThinkFlight
This video keeps coming up and I never get around to watching it. Thats it dammit, its time!
@@thinkflight while wing tip motors don't make it more officiant they allow a air craft to have a lower aspect ratio which makes weird looking planes look up Vought V-173 Flying Pancake
I am glad you brought up McLean.
One of a few who is correct.
Following up I like to point out that there is a conceptial difference between induced drag FORCE Di and the induced drag COEFFICIENT Cdi (just a number)
Cdi = Di /(Area × q)
q = dynamic pressure = rho×V²/2
rho = density V = speed
Cl = Lift /(Area × q) lift coeff.
Cdi = Cl² / (pi AR) pi=3.141592..
Clearly this number, an artifact is dependent on the aspect ratio AR = b²/ Area = b/ mean chord
b = wing span
But the induced DRAG force is (1:28) NOT dependent on the aspect ratio ! despite the narrative.
Di = (Lift/b)² × 1/( pi × q )
The induced Drag FORCE is proportional to the square of the span loading Lift/b and inversely proportional to the Velocity² and density. Not in the least dependent on the wing chord c !!
verify by substituting in
Di = [ Cl² × 1/(pi × (b²÷A)) ] ×(A×q)
Cl = Lift / (A×q)
A cancels out and b² is in the denominator
The induced drag force is independent of the wing area, hence chord.
This in contrast to the parasite drag, where the wing Area dominates
D parasite = Cdp × Area × q
= Cdp× (b × chord) × q
The effect of the chord affects only the parasitic drag, not the induced drag force
The confusion created by the artificial meaningless induced drag COEFFICIENT is remarkable.
If you derive the expression for the Lift to total Drag ratio by substitutions: The simple form results:
L/D = b/2 × sqrt( pi /(Cdp × Area) )
Strong function of span b, weak function of parasite Drag Coeff.
not a function of the aspect ratio
b/c, but b×c instead.
All the derivations above are valid for a wing with elliptic lift distribution, other wise a correction must be made with the Oswald efficiency factor.
@@thinkflight It's one of my favorite when it comes to explaining what goes on during flight!
My new hypothesis is that the props at the edge simply gets more clean unobstructed air. In addition to giving the thrust no obstruction. Making more efficient. My simple guess. Cant wait to see the next video!
The drone shots of the flying wing are just mesmerizing :) What a gorgeous aircraft. Absolutely love this dissemination of the underlying questions.
I wonder if anyone mentioned the Vought V-173 aircraft in the previous videos. That was a unique set up that historically used wing tipped place airscrews to both improve the efficiency of the wing and keep the boundary layer attached on a high performance low aspect ratio wing. It made use of a lot of interesting tricks in its day, even interconnected engines so that if one engine failed both screws would still be turned by the transmission, kinda like on V-22’s today.
Career Unmanned System guy here...
I am a new subscriber.
I love how you narrate and show FPV and onboard video shots. The smoke trails really assist in viewing aircraft reactions etc. Wish I knew you when I was pushing military concepts etc. What you are doing is for the most part how myself and others like the Scan Eagle designers were doing in garages on their own dime. Scan eagle concept was eventually bought out by Boeing Insitu for about 300 Milion. Keep on what you are doing! your projects are before their time as were mine and it can be tough getting people to support you when you are a true innovator. Keep it up man, this is great stuff!
Thank you for taking the time to leave this comment!
Serenity is one of the most elegant and beautiful airframes I have seen in a long while, the way it flies in the way it moves in reaction to wind and input from your end is astonishing. Especially with different motor configurations it looks way better than more than half of the RC model planes out there it is so smooth and responsive
10:00 were you able to measure a difference in motor current? Given the same motors and the same approximate pitch / diameter that would be an interesting measurement of total load on the motor.
everything else needs to be equal in order to make that assumption
much respect for pointing out the fact a quad had twice the failure points to some of your dimmer vewiers.... that is very funny... well said
I think what stands out to me anyway as pure BEV flight is now clearly very mature is how quickly everyone has ditched wings *period* which from these flights and thoughts upon them one can see why as there is no vertical stabilization here. In theory one could launch your wing nose up/blades down so as to test mission critical pitch and yaw with another option being similar to what the US Navy does with their Submarines namely create a housing around your blades then add some vertical "grid fins" in front of same said mechanism to provide at least some friction to add lateral stability upon such an austere platform.
Point being what are trying to test is how your design works *IN LEVEL FLIGHT* and not just as an efficiency theory that happens to fly.
Once you achieve "on the level" then a testable hypothesis can be made and indeed anything is possible "in the wild" (box wings, front facing control surfaces, landing skids, you name it.)
A good UA-cam channel to check in on is BPS Space if you really want to crazy insane with the data science.
So not only is this entertaining and informative, but he's just so wholesome when on camera talking. This is 10/10
It took UA-cam this long to recommend a channel that actually is of interest to me. Nice content, thanks for sharing.
Thank you for this update. I was wondering about the wingtip prop concept.
Sorry if they've been mentioned before. Two aircraft for your perusal/flight information are the Ho-229 "Flying wing' and how the Horten brothers resolved their stability issues with such a plan-form and the Vought XF5U. A machine specifically designed around wingtip mounted propellers. Even if the wing in that machine's case was virtually a frisbee. 👍
I'm not sure you explained how they fixed the stability issue, other than 'special machine fixes stability'
What a way to start the weekend. Bless you!
Thanks for all of the time and effort you put into this! Can't wait to try some of your experiments 😎🤙
that wing tip configuration is a thing of beauty. Maybe I need to get in to flying model planes.
Omg I'm IN LOVE WITH THIS CHANNEL, how did I just find this channel today? Welp I have a whole bunch of watching to enjoy!!!!
from what i can remember from my incompressible aero class induced drag increases greatly with speed. so at these low speeds the effect will be very hard to measure. Second the AR of these wings is reducing the effect of the wingtip props reducing induced drag. the props only extent a couple inches past the wing tip, and at this scale that is only a tiny increase in AR. If you look at the V-173 and XF5U the propellers increase the effective wingspan by a significant amount. (on the V-173 wingspan was 23 ft 4 in and the prop diameter was 16 ft 6 in).
Induced drag goes down with speed and parasitic drag takes over.
Yes! I've been waiting for this video to come out for ages!
Thank you fir sending the time to do this setup. So it works with pusher style. I have had the yaw issues with wingtip tractors and gave up
Props on the tips. Depending on rotation the Wing Tip Vortex is taken into the mix. Wing Tp Vortex eliminators delay the Wing tip vortex to be farther from the wing it's self, thus delaying drag. So, putting the props on the tips solves this drag problem.
Much excellent content in this video, with great references. The aerial videos are most awesome. Great cinematography.
After initially watching the video, I returned to the jet segment (from 1:03) ... watching repeatedly. Examining the vortexes frame by frame, a few things stand out. The most obvious vortex does not initiate at the wingtip, but instead appears to form at ~2/3 of a wing. (?) Also, the air about 1/2 a wingspan distance above the wing is clearly effected immediately as the wing passes by, as is air 1/2 span further out from the tip. It's like there are multiple scales and complexity to the vortex. (multiple cores) Distribution of lift, and pressure across the span is clearly not constant along a span, and extends beyond the span. This creates a pressure gradient and shearing forces that extends well beyond the wingtip.
The flap generated vortexes (at 1:17) are dancing, clearly being influenced. I suspect this an interaction with the wingtip vortexes, which are not visible. The high angle of attach of the deployed flaps is creating a much greater wing loading on that surface (much higher pressure differential) vs the main wing. Thus wing loading and angle of attach are major factors to amount of energy going into a vortex.
Reducing the pressure differential (between top/bottom of wing) towards the tips would be beneficial to reducing induced drag. As would be reducing the wing loading towards the tips. Think you may be seeing some of this in the Serenity design, as there is built in washout to the flying wing. (lower angle of attack at the tips) This likely why the results fell within the margin of error for Serenity 1. Also from Serenity 1, you noted the complexity of the vortexes at 7:45 (in Part 1, previous video); where vortexes initially rotated outward, then merged into a larger vortex rotating inward downstream. This can be seen in this video (9:45) as the vortex with red smoke wiggles and transitions.
The RESULTS (5:43) of reversing propeller direction are pretty telling IMO. The 7.2% difference implies an efficiency change of just +/- 3.6%. This assuming one direction being an efficiency gain, the other a loss.
Can see why now testing inward motors as explore further.
BTW: I don't think the tractor motors (vs pushers) would have changed the results. (ie: would fall within the same margin of error)
To the final question (9:35), I think the efficiency gains are the result of countering the larger 1/2 span inward rotating vortex, not just the smaller outward rotating tip vortex. Having access to a fog machine like Daniel (RCtestFlight) might give a better overall view of what's happening along the full wing and beyond the wing, vs a smoke pipe at the tip showing airflow across only a couple inches. (ie: more data is needed)
In future it may be interesting to explore different wingtip designs to see the impact on efficiency. For example how the shape (square vs a tapered), and how tip wing loading (angle of attack, or washout) of the outer segment of span effects efficiency. The tip design at 0:48 is pretty rad.
Note: testing tips designs on a flying wing will present a degree of challenge as pitch stability typically maintained by having washout towards the tip.
Your aircraft is awesome and your skill is amazing, however it's very difficult to predict what is going on due to the sweep angle, the blended fuselage and the moving ailerons altering the vortices shed from the wing. For the sake of your experiment I suggest you use a conventional wing - tail configuration, with no sweep, twist nor dihedral and better even with no ailerons on the wings (you can use differential thrust anyway) and with minimal wing-fuselage interface.
Great work.I made two models use tip props and they were flying well .
I think you need a wind tunnel to make this more accurate.
May be here is a possible reason:
Propeller rotating at outer direction,needs less torque, because of the wingtip vortex,and rotating inner needs more torque. Maybe there is a slightly difference in efficiency of props, but motor efficiency changes.Some high kv motors may have higher efficiency in less torque,and this matches your flight test result.The only way to find this out is to add a torque sensor on wing tip, use rpm and torque to measure the real axial power,and this the real aerodynamically power you need.
Awesome! Glad I discovered this channel today! What about ducted fans at the wing tips? Would love to this as part of your iterative test process.
That build is SWEET! It looks so slick .
I have two FPV planes the same span, one is a wing, the other is a balsa home built with a conventional wing and a twin boom to a tail. They both run all the same gear and have pusher motors.
The Wing is lighter in foam at about 270grams , the balsa framed with covering is heavier at over 430 grams. The Balsa plane is more efficient by at least 20+ percent, even though it is heavier.
I put this down to the wing has to use reflex and is swept in order to fly, where as the balsa own design does not, and now having seen this video also the tip vortices are opposite, and is affecting the efficiency of the wing type. Thankyou so much for doing this research it is MUCH appreciated!!, I was at the stage of trying wing tip motors. Also I figure that a tip splitter (winglets) is worth a try as these are used horizontally on race cars to split the air ahead of the bumper. I feel these can do this on the flat wingtip, to minimise bleed around from top to bottom of my balsa planes wing. Matt Western Australia
Good Stuff! I noticed a few times the elevons where trimmed up for level flight, this in my experience is a nose heavy plane and can be messing with your results. Thanks for sharing.
You can overcome any outboard motor failures by simply putting a centerline motor to recover! 😁👍✌
Very true!
@@thinkflight Or use thrust vectoring.
@@toolbaggers nope if an outboard motor goes out, .... she's goin down baby! 🤣😱
@@TinyHouseHomestead or fly in a small circle till it runs out of power then crashes..
@@altrusianwolfdog2564 well, .... yeah, but the idea is NOT to crash! 🤣😁👍✌
Hi,
I'm an aeronautical engineering graduate.
If you intend to mount the propeller at the wing tips the wing should be SWEPT FORWARD not swept back.
The props should be rotating at opposite direction.
But for real aircraft (not rc model) you have to choose between vortex or structural load at the wing root due to propeller torque.
For me I think the best solution for your experiment is to use a counter rotating propellers like the DZP30.
Enjoy.
An excellent point about drones having double the points of failure.
Drones also have quadruple the dependencies, while in a plane a motor can quit and it can continue, or both quit and it glides down. With a drone every motor needs to operate, and also operate at the correct rpm
No it's not... "points of failure" here is a misnomer. You could still fly a drone with three props. Two props would be opposed so they would be the lifting props as they don't contribute an unbalanced force, and the third could be used for attitude (it would have to spin forward or backward, and have to reduce the amount since it's not working against an opposing rotor anymore, but that's just software. Geometrically and physically it's stable). You can't fly a flying wing plane with wingtip motors when one goes out because attempting to thrust would just yaw the plane the harder you push. The quad has more points of REDUNDANCY, not dependency, until it loses more motors, and then it depends on which one you lose. If one motor goes out on the quad, do the others stop working or work against the center of gravity with leverage? not necessarily, so it's not a mutual dependency. With one motor lost on the plane, it's just a glider because due to the position of the motor, you've essentially lost two.
@@enotdetcelfer you can’t do that with a drone, all four need to spin with opposites balancing opposites otherwise you get yaw issues. You clearly don’t understand drones and so I’m not going to bother explaining it because it’s something that you’d understand better from your own learning.
@@ryanm.191 - There are several videos here on UA-cam of experiments of quadrotor control after a motor failure. ua-cam.com/video/CzM8Cvcif6g/v-deo.html
This is really a moot point since most commentators were probably thinking more of a full scale scenario. A quadrotor will never be certified for people to fly in commercially without the proper redundancies in place.
@@gpaull2 exactly, commercial drones would need additional redundancies, but that would mean more redundancies required. Each power plant would need one redundancy meaning 4 power plants and 4 redundant power plants, which is additional weight. Compared to planes where the redundancy is just flying down. Additionally without very difficult to create systems and advanced training, a large commercial drone wouldn’t be able to autorotate as it would develop a yaw drift as well as pitch and roll instability which just wouldn’t pass flight certification requirements.
3:26 as if that has never happened on any multi engine flyer.
Nothing like innovation and experimentation. Keep at it my man !
Oh, neat! Having my question highlighted like that only to *not* be answered (yet) is quite the cliffhanger. Wicked side-slip that thing was pulling. Can't wait for the conclusion!
As the theory-crafters predicted and the 2nd experiment suggests, a swept-wing might not be ideal for observing vortex-related effects of wingtip motors, due to the apparent reversal of the vortex mid-span.
Yup, didn't think about that getting into this based on computer predictions and will find out if this is indeed the case.
Such an awesome project series! Thank you!
So fascinating!
Which direction was more noisy?
Inward rotation
I'll comment and just say that I am absolutely loving this project of yours. Keep it up 😁
Also don't let anyone tell you what may or may not work. None of that matters. What does matter is that you are trying something different and learning along the way. And who knows. Maybe you'll discover something truly revolutionary!! And then I'll steal it 😜. Jk. Too lazy to even try.
Such an incredible video. The design is beautiful.
In the case of a wingtip motor failure, the yaw would be tremendous and unrecoverable. To be practical this would require a common transmission between props, so that in the case of a motor failure, the remining motor could power both props. It would make sense to mount the actual powerplants inboard as well, to reduce their roll moment.
yeah i didn't like how he sort of hand waved that issue in the video. the comparison with quad rotor drones is apples to oranges, as the factor of safety for the design of a small unmanned drone vs the design of a fixed wing aircraft large enough to transport people is, obviously, vastly different.
No hand waving, this is an unmanned test bed whose sole purpose is to learn about wingtip motors. It is never suggested or recommended as a final configuration for manned aircraft, just as a quadcopter also is not recommended as a manned configuration.
Quick tip for managing controls and monitors and devices outdoors. Fill sandwich bags with dried beans, and use these waterproof beans-bags to prop up your gear.
Nasa did a rc experiment with a wing called a "Prandtl Wing", based on the complete equation, rather than the main lifting zone, basically the wing tip architecture is redirecting lift pressure about 30% before the tip from under to over the top to the tip, causing the vortex to appear at the 30% mark opposed to the tip causing drag and converting it to yaw stability which has a positive effect in banking turns.
Pressure mediation: Resonance tuning rotation to pulse tip vortex will amplify local pressure in a controllable way and increase lift efficiency generally. vortex is a source of coupling between energetic containers so to so to speak and all containers can be pressure accessed via resonance.
It's possible the reason the tractor wingtip configuration was giving the flying wing some massive sideslip was due to the propeller's vortex column thwarting the self stabilizing properties of the wing twist, where as the pusher configuration doesn't interrupt those properties at all
One way I visualize why the wingtip vortexs rotate outwards, is thinking about the airflow under the aircraft.
The compressed air under the wind slips off as it reaches the trailing edge. Because the wings are swept back the first bit of air able to curl up, is gonna come from the center of the airframe. Since while this air is free to go to low preasure it can curl up and go outward, since the air further out on the wind is still stuck under the wings.
I'd imaging this phenomenon changes with the swept back angle.
With a straight wing, all the air exits at the same time (except the air near the tips which is free to curl inwards)
At certain angle this flow reverses (not sure what that is)
Lovely footage and excellent explanations man, looking forward to the next video.
Alice aviation also gave up on wingtip motors, and placed their nacelles alongside the fuselage like the mad dog. The reduction in vibration alone and the associated drag reduction is probably worth it. It still would be interesting to see the twin tip tractor configuration on a wing with elliptical lift distribution.
Really fascinating stuff man, looking forward to part 3!!
I have no idea why the increase in performance was so large. But I do know that is one very sexy aircraft. Such a cool video series keep up the great work.
Great video! Not sure about there being a inward rotating vortex and outward rotating vortex on the same wing. Wouldn’t that be less efficient than a wing with single vortex?
If I remember correctly, the lift distribution curve is smooth transitioning from inboard to outboard and and slightly negative at tip. So I would wager no inboard rotating vortex. Since the pressure gradient is smooth.
the outer rotating configuration is inline with the fact that the differential rotor torque reaction helps during roll and banking movement in a flight. while in a inward rotating configuration, the outward motor torque reaction on a banking maneuver work against the required roll movement provided by flaperon. This could be one of the factors resulting in inefficiency seen in inward rotating configuration.
As an ultralight flying wing builder flyer I have found your experiments very intriguing. Fuel efficiency is the driver in new airliner design, 7% is a significant gain, you may well be on to the shape of the future.
If that gain comes from where he thinks then it's not important since you could gain that back with a more optimal propeller angle for that rotation
@@joey_f4ke238 Variable pitch props could be useful in further tests.
have you tried forward facing large props (a bit like the Vought V-173) on a forward swept wing? the forward swept wings give slightly improved lift and the large props push the extra air down the wing giving even more lift making the plane super efficient
also, your plane is the best looking ive seen in years
I have not
Well, get on it! Just kidding. I agree, that is a gracefully flying design! Thank you for sharing your results! 😜
YO, BEST flight music. Idon't know what it is but it was so good.
How difficult is it to build or rent something as a wind tunnel? Being able to set a specific and consistent wind/air speed might be really helpful instead of hoping for similar enough conditions outside. This was very cool and I look forward to more.
You can DIY a wind tunnel pretty cheaply. The real issue is just real estate
beautiful footage and i can't wait for the next steps in this epic adventure!
To compare wingtip devices you have to consider why span is limited in the first place. Airliners have to fit inside a gate, racing planes need a quick roll rate, other planes have structure constraints.
Why is your plane span-limited? How can you work around this to use less energy throughout the flight?
I think it would be interesting to compare tip motors to a span extension equal to the radius of the prop.
This is an amazing video as I am very interested in the effects of air movement and drag and its effect on efficiency.
Any chance that you could get your models into a Wind Tunnel?
I did try but its pretty expensive, real world testing will have to do for now.
True, a quadcopter with 4 rotors would be unstable with a single motor failure - but that's why drones with uses that place a high premium on safety use 5+ motors. Same principle as so-called "office safety chairs", loss of one leg affects its stability, but not total loss of it. A better testbed could be removable wingtip motors as supplements to motors closer to the fuselage - then you can do a direct with/without comparison.
I think the issue of this theoratically very efficient configuration is not only the case of the failure of one motor. In fact, the power of the wing tip motors will have major effects on the lift of each wing and on all the axis of the plane. This means that all the control axis of the plane will be strongly coupled which is not considered a "good" and "safe" configuration. The stability of the plane will be highly dependant of the algorithm, the sensors and the controlers of the motors and will necessarily leads to a higher failure chance because of the dependancy of many part.This can be acceptable for a non habitable plane only.
If you think about how winglets work on an airplane is to remove the flow of air to the top of the wing due to high pressure on the bottom of the wing making its way to the top of the wing killing the lift on a portion of the wing. The propeller rotation outward I believe is doing the same thing pushing that airflow from the top far enough away from the wing to prevent it from reaching the bottom part of the wing killing the high pressure on a portion of the wing.
I'm curious to know what kind of simulation you ran (at about 8:15). Did you do any sort of higher-fidelity sims? The structure of wingtip vortices can be finicky to pin down. I'd be happy to run a RANS sim on the model if you're interested...
Reminds me of the XF5U, the "flying flapjack". It had an aspect ratio of less than 1, and depended on the tip mounted props to cancel the huge tip vortices expected at high AOA.
The reversed wingtip vortices are probably a result of the swept flying wing configuration utilizing the outboard portion of the wing as "horizontal stabilizer", in which case they are producing negative lift to counter the nose-down moment of the inboard lifting section in an aerodynamically stable configuration. Negative lift = negative circulation = reversed wingtip vortex
I've been waiting for this episode!! Hype!!
Awesome, I’ve been waiting for video 2. For video three and more data do a test with the more centerline motors with and without winglets
The plane looks amazing!
May I ask what program you are using to calculate the behaviour of your airfoils?
Flow5
Awesome! I'd love to see it with the Biggest Chonkin Props you could feasibly use on there. (Not thick, just really long skinny blades)
Great point about the quadrotor! :) There could be a potential collaboration on this if you are interested in wind tunnel testing!
I call dibs on shooting a video on this if a colab pans out!!
Very interested, my email is in the About section if you are serious!
Some fascinating aspects of flight,the electric aviation channel from India is also very educational in relation to the physics of flight in electric aviation,well narrated documentary ,thanks
Great video! I live the scientific approach. Keep at it dude!
The problem with wingtip motors is that in the event that one motor/engine dies the plane becomes uncontrollable due to the fact the the yaw factor is much greater then the conventional design.
On planes that have 2 engines the engines are located as close as possible to help minimize the yaw effect of one engine dies.
They also make SOME propellers counter rotate to also help minimize this effect. The piper seminole is just one example
If you're really worried about wing tip motor failure, you could drop a motor or two in the middle to kick in should one side lose power
Thank you for sharing these experiments, very inspiring!
One data point I haven't seen discussed is wing loading? The lower the WL the lower the induced drag as we all know, and seeing as how light our typical models planes are wingtip vortices constitute a (comparatively to full scale aviation) small part of total drag, which would throw the results in this case?
If you plan to revisit this experiment there are other flying wing planforms such as deltas don't require as much reflex, and with a lower aspect ratio would generate more wingtip vortices, which in light of the experiment is a good thing, no?
Wing loading is relative, the cruising AOA is comparable to the cruising AOA of a larger aircraft and thus I would assume the induced drag component is also comparable. Specifically I'm trying to see if there is a benefit to wingtip motors on a plane with good efficiency already, rather than just trying to help out very inefficient aircraft.
?!?!!? do you always ramble OFF THE TOPIC, like this.?!?
pouncer
the induced drag force is proportional to the spanloading square, NOT to the wing loading
For an ellptically loaded wing:
Dind = (L/span)² / (3.1415...×q)
q=dynamic pressure
and is the result of the downwards forward inclination of the downwash behind the center wing.
Nothing to do with the energy of the tip vortices, which is taken from the very low pressure energy² inside the vortices.
2) the pressure follows the Bernoully energy conservation equation.
p1 - p = density × ½(V² - V1²)
If you put a pressure probe inside the vortex you can verify this.
And the tip vorteces, downstream do carry angular momentum, imparted by the wing tip. Clock wise behind the left wing, when the wing tip is not acting as a pitch up surface, as is the case with the flying wing here.
If you were worried enough about engine failure (for a passenger model), you could always put a glide motor in the center of the rear, with enough power for emergency landings.
AI could recognise a failure and immediately brake the wingtip motors.
Not even "AI", simple sensors. Could probably make it all analog 60's/70's tech if you really wanted.
Yes, I think something like this would work well.
Can someone tell me what the type of airplane this is?
Very interesting. I hope you keep working on it.
Really interesting results, this is a cool experiment
I'm an F-15C pilot. I have two separate points to raise 1. Electric cell storage is bad for aircraft currently because the energy density is still not near the density of liquid fuels and unlike a liquid fuel aircraft, an electric aircraft never sheds weight as it flies through the process of combustion. This results in batteries being just dead weight, reducing efficiently the moment you rotate and leave the runway. Also, liquid fuels don't self-immolate spontaneously like current LIPO technologies seemingly with no warning. 2. Wingtip engines are a nightmare scenario to a combat pilot. I'd usually never advocate for less than 2 engines on an aircraft, but a ducted turbine with outlets at the wingtips would actually be safer, because if you lose one engine, you lose output to both wingtips. Lose an engine with two engines on wingtips and the aircraft instantly turns into a frisbee, and you have to recover from a spin before you can be a glider. On the ducts, you can control yaw with variable nozzles open/close. Also sometimes vortices are good, and jets sometimes have dogteeth that create them to increase pressure on certain control surfaces and reduce flutter, such as the horizontal stab on the F-15. Interestingly, AMRAAMs on F-16 wing tips also reduce flutter, but I am not sure if it's weight related or aero related. Maybe both.
I think most of the efficiency gain comes from the propellers' vortex cancelling the wingtip vortex. This would not work for jets. Some use ducts to the wingtip for VTOL and to augment thrust vectoring.
You have my dream job my friend.
Really awesome, you did a great job!
I love the videos keep it up man
Have you tried to use ducted wing tip motors for this? would also make those crash landings easier on the components, I would personally use PVC pipe make a field goal with a soft net and fly into that for landing.
Love this channel. Great work on the questions we all have re; vortices.
Thank you!
Would it make sense to make the wing tip thin & tiny? “Taper it out to nothing”? I’m enjoying your experiments 👍🏼👍🏼👍🏼. Great attitude. Great channel.
Depends on what you are after. If you haven't seen a Prandtl wing, check it out.
Excellent design, test methodology, and execution!! As always, you're scratch-built planes show you really have your build techniques down! I wonder if you would see larger efficiency differences with testing a similar motor placement change on a conventional tail & wing aircraft. However, it won't have the elegance of a flying wing. I am also curious about the efficiency differences between downward, upward, and both downward and upward-pointing winglets. Great series!
I think the efficiency gain probably is much greater with a conventional wing aircraft, or if a wing, a plank.
Thanks for the update. Looking forward to see the manned vehicle.
I assume at some point you'll mix the tip motor and ground effect vehicle?
A compact design, relying a lot on the ram / works like a hovercraft, with outward rotating motors... I think the prop vortex can really seal in the pressure!
I'm gonna leave some of what I said on the last tip-motor video:
"I'm not saying you didn't lower the induced drag, in this experiment you can't tell if it was that , or, a propeller working more efficiently. Maybe both? (Also, for flight time, totally irrelevant ;-)
[...] I think putting them in front would work slightly better.
But in this design you'd need a big pod to not have the noise from the prop being close to the frame. So I get putting them in the back."
Do you think the reason that the vortex did not move in board as it does with the traditional aircraft might be caused by the lack of tail structure? The mass of that tail structure would displaced a lot of air creating a vacuum behind it and then pulling in the smoke from the wingtips. The absence of such structure would not create the vacuum.
Try to test what motor configuration is best. Both spinning outboard, or inboard. Both spinning the same direction has always been normal for flight, but I'm sure wingtip vortices would benefit from contra rotation. Throw the air outboard or inboard?
What about using the wingtip motors for skidsteer-esque thrust vectoring? For ultra-long distance, or very long circular loitering missions it might more efficient than using control surfaces, assuming control surfaces disrupt aerodynamic efficiency in any significant manner.
Looking forward to further videos.
I can see two issues.
1) asymmetric thrust when one engine fails.
2) the extra structure (weight and thickness) that would be needed throughout the wing in a commercial aircraft to support the engine weight.
Even though the props are rear mounted, the pressure field will propagate upstream and will have an effect on the airflows above and below the wing. My educated guess:
Outwards turning props are more efficient, because they redirect some of the airflow on topside of the wing over the sides of the wing, effectively leading to more airflow over the leading edge of the wing and thus generating more lift.
In the same way, the props push air under the wing, effectively slowing down the airflow under the wing, which is increasing the air pressure and again generating additional lift.
Just a quick suggestion regarding an engine out asymmetric truss problem. Considering the extreme lightness of these new electric motors, two of them could be used in tandem. Possibly with the prop shaft of the rear engine going through the prop shaft of the front engine. If the main front-engine fail for any reason, it would be immediately picked up by the rear engine. Just a thought.
I'm sure something could be worked out without too much fuss.
3:16 true.
3:58 Lenovo Legion FTW!
Can't wait to see the next video!
Very cool! I am looking forward to the tractor test. The Vought XF5U is my favorite aircraft as it was designed around this idea. I am totally unsure what will be better tractor or pusher.
Unreal footage great video
The maiden looked like it was trying to replicate one of my recent builds 😉
hahahaha indeed
More elegant way to reduce wing tip, vertices can be achieved by changing the lift distribution from an elliptical lift distribution to be curved lift distribution.
NASA test it some years ago with the project PRANDTL!