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.

"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

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.

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!

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.kzfaq.info/get/bejne/h7Fzfpedr7K1eIk.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!

The drone shots of the flying wing are just mesmerizing :) What a gorgeous aircraft. Absolutely love this dissemination of the underlying questions.

Thanks for all of the time and effort you put into this! Can't wait to try some of your experiments 😎🤙

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

Really fascinating stuff man, looking forward to part 3!!

Thank you for this update. I was wondering about the wingtip prop concept.

Lovely footage and excellent explanations man, looking forward to 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.

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!

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.

It took KZfaq this long to recommend a channel that actually is of interest to me. Nice content, thanks for sharing.

beautiful footage and i can't wait for the next steps in this epic adventure!

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

Yes! I've been waiting for this video to come out for ages!

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!!!!

So not only is this entertaining and informative, but he's just so wholesome when on camera talking. This is 10/10

What a way to start the weekend. Bless you!

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!

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 KZfaq channel to check in on is BPS Space if you really want to crazy insane with the data science.

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.

Great video! I live the scientific approach. Keep at it dude!

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.

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.

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

Very interesting! Surprising results with the vortex.

Very interesting. I hope you keep working on it.

that wing tip configuration is a thing of beauty. Maybe I need to get in to flying model planes.

Such an incredible video. The design is beautiful.

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.

Really awesome, you did a great job!

I'll comment and just say that I am absolutely loving this project of yours. Keep it up 😁

Such an awesome project series! Thank you! So fascinating! Which direction was more noisy?

That build is SWEET! It looks so slick .

You can overcome any outboard motor failures by simply putting a centerline motor to recover! 😁👍✌

I've been waiting for this episode!! Hype!!

Really interesting results, this is a cool experiment

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.

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).

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."

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.

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

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!

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.

Looking forward to further videos.

Love this channel. Great work on the questions we all have re; vortices.

3:26 as if that has never happened on any multi engine flyer. Nothing like innovation and experimentation. Keep at it my man !

YO, BEST flight music. Idon't know what it is but it was so good.

I love the videos keep it up man

The wing tip motor configuration looked very stable and responsive. Have you compared it against an inward/center motor setup? Great video 👍

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)

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

Unreal footage great video

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.

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?

really interesting video and channel btw. Subscribed!!

Thanks for the incredible effort you put into these videos! This is some thorough building and testing. I'm impressed with your consistent morning flights. Where are you located, by the way?

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.

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

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

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.

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.

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.

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.

Can't wait for part 3

Reading about the Chance Vaught XF5U the sweeping down under props at the wing tip should supposedly makes quite a bit more lift but that aircraft was sorta designed to capitalize on this more than a more conventional design I think.

But I dont want to wait for another video! Now! Haha. Love the content man.

The plane looks amazing! May I ask what program you are using to calculate the behaviour of your airfoils?

amazing work

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.

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.

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)

Just found your channel. YT probably recommended it because I sub to RCTestflight. I figure you live in the IE but can't pinpoint 😂 . I run a channel for a flight school in Chino so I like to try to figure out landmarks from the sky. Love your content!

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.

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.

Good work.. thanks

Seems like a great idea from an efficiency perspective but now the center of thrust is now as far as possible from the longitudinal axis, especially when you factor in the P factor of the outwardly rotating propellers. What could be a solution for engine failures and Vmc roll tendencies?

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.

Cool video !

I decided to build a manned tail sitter and your work is being very helpful. I'm studying to figure it out how to have 4 motors for redundancy. Am I crazy? 🤪Many thanks!

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.

Do you think ducted fans would be a way to isolate the wing vortexes from the air intake? Or do you think you would need to product a wing which reversed the wing vortexes to prove conclusively that using motors to reverse to flow is advantageous? Could you put the nose correcting angle of attack inward on the wing such that the tips could be angled to produce the desired direction of rotation?

What a gorgeous airframe.

be kinda cool to see an osprey like config, where the motors are on gimbals and could transform from vertical takeof to horizontal flight, and or assist in turning etc

It looks like a very happy and content little airplane :D

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.

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.

if you changed to a conventional plane design ( main wing with tail stabilizer) would you see the vortices on the wingtips of the main wing behave more like how they do on airlines as the main wing trailing edge is still producting lift? then you could also get vortex visualization on the tips of the horizontal stabilizers. could wingtip motor efficiency just depend on the average lift of the component it is mounted onto?

Very nice shots and nice aircraft. You need to fix the audio levels in this video though, some parts are really hard to hear.

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.

Great point about the quadrotor! :) There could be a potential collaboration on this if you are interested in wind tunnel testing!

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...

ooooh cant wait for the next videoooooo

What would happen if you mounted motors in both a push pull configuration (total of 4 motors), with props spinning in opposite directions?

Lovely BWB deisgn. VEry stable flight. impressed