Proving Prandtl- With A Twist!

www.nasa.gov/ce...
A group of college aerospace engineering students in the 2012-2013 Aeronautics Academy at NASA's Dryden Flight Research Center have proven German aerodynamicist Ludwig Prandtl's theory on how to overcome one of the thorny problems of flight -- adverse yaw due to induced drag -- without relying on rudders or complicated computerized flight controls to accomplish it. This student-produced video details the students' research, using a student-built subscale flying-wing sailplane that proved that proverse yaw can be achieved just as birds achieve it -- through wingtip aerodynamics alone.
Music: Deadmau5 - Strobe (Evan Duffy Piano Cover)

[@nihil1]

This video is entirely a hidden jewel in youtube, it deserves much more attention than what it has had until now. It is both educational and inspirational!

[@flyingark173]

This video is amazing. It encapsulates an hour lecture into 8 minutes. The drawings are beautiful and crucial to this type of learning and I for one am very impressed. I believe in the flying wing as our future in air travel and I am very excited to live in this time of discovery. I encourage those intrigued about this subject to look for the lecture at the AMA conference which explains more of the history involved in the understanding of this technology/physics

[@mikekelsey6777]

When I started flying hang gliders in 1973, it was the standard Rogallo. I had an interest in seeing if I could make a small scale model to experiment with variations on the Rogallo design. The materials I was using made it expensive and very time consuming, and flight, although successful usually resulted in some damage as it was simply free flight. I turned to simple paper and Scotch Tape to create design modifications. Cheaper and I soon began to greatly improve the design to the point that it was now a very nice flying wing. It was around 1975 that I visited Bill Bennet Delta Wing Kites and Gliders manufacturer and showed him my paper airplane (Glider), which I call the OmniWing. He wanted to see it fly, so we went out to the parking lot and he grabbed it by one of the wing tips and tossed it into the air like a boomerang. Bill was from Australia, so I guess he did a bit of boomerang tossing. So the OmniWing went up into the air spinning out of of control, but it recover and went into stable flight and flew across the highway. I recovered the wing and he asked if I would leave it with him so that others could see the wing fly. Some months later he produces a hang glider that looked very much like my OmniWing planform. So I bought one. Now, almost all hang gliders look like my OmniWing design. Same aspect ratio, same nose angle, same sweep, and same twist and washout. Each manufacture has small variations, but all are very similar. Check out a flight of one of my OmniWings off of Mount Nebo, in Arkansas. Was an exceptional flight. Video shows a fast build of the wing and then one of my best flights. kzbin.info/www/bejne/iaO9YpWnisSaatE

[@FinbarSheehy]

It's a clever, non-obvious idea, using the washout to eliminate adverse yaw. However, without being sure, I imagine that the washout that eliminates adverse yaw will not simultaneously deliver the optimal low-drag lift distribution for straight flight. Thus, you eliminate the drag of the vertical tail, but accept the drag of the non-optimal lift distribution - not clear if that's a "free lunch", but maybe it is! Intuitively, if loading up the wing increases its L/D, that loading condition should be used on both wings in straight flight for greater efficiency (sacrificing the no-adverse-yaw feature). Also, the optimal washout for eliminating adverse yaw probably varies with speed (alpha). Certainly,as Eriksson Tord points out, birds routinely use their tails for yaw control. They generate lift with their tails, and tilt their tails to angle the lift to the side, providing a yaw force; they're not relying solely (if at all) on washout. I would be (very) surprised if soaring birds continuously operate away from the optimal L/D condition, just to provide automatic yaw control, but they may twist a wingtip for yaw control as needed. Hang gliders look similar to the model in the video - swept wings with neither vertical nor horizontal tails (although they have lower aspect ratio than that model). Whether weight-shift or aerodynamically controlled, hang gliders display a moderate amount of adverse yaw, and hang glider pilots just get used to it.

[@FinbarSheehy]

+Finbar Sheehy Having had a chance to think about this, I think we're looking at an interesting coincidence, here. There are three distinct parts to this, which I'll call A, B and C. Part A: The usual question about "minimum drag" says, "given a maximum wingspan, what is the lift distribution that gives the highest L/D ratio?" The answer to this is, "elliptical lift distribution", and that's not wrong. Prandtl, though, changed the question, and asked, given a maximum lift/bending moment, what is the lift distribution that gives the highest L/D ratio?" In this second question, wingspan is not constrained. So, here's a thought experiment: take a wing - any wing - and then add two sections to each wingtip, one lifting up and the other, outboard of it, lifting down by exactly the same amount. The net lift hasn't changed, but the bending moment at the wing root is lower, because the additional downward force is outboard of the additional upward force. And what about drag? Well, on the one hand, there's more wetted surface, but on the other hand there's more span, so it's not intuitively obvious what has happened to L/D. What Prandtl found was that the L/D will have gone up, and he went on to find the distribution that gives optimum L/D if the span is not constrained but the maximum bending moment is. That's all - notice that it has nothing to do with swept wings, and isn't about preventing tip stalling (the purpose of washout). Part B: This is the coincidence part. What happens when you put ailerons on an un-swept Prandlt wing? If the aileron is all on the outboard section, where the lift force is downward, then when you deflect the aileron downward you reduce the local (downward) lift force, and reduce the local drag. And vice versa on the other side. This is the opposite of the normal effect of adverse yaw on ailerons: it's proverse yaw. But, it only works if the ailerons are out at the tip, in the downforce region. If you have large-span ailerons, it won't work. Also, as the wing actually starts to roll, you'll still see a reduction in the "proverse yaw" and it may even reverse. Why? Suppose you roll right. You deflect the right aileron upward on a tip that is generating downforce. This increases the drag at the tip, and tends to yaw the aircraft to the right. But, as the roll starts, the (negative) angle of attack on the outboard tip will be reduced by the rolling motion, reducing the "proverse yaw" effect. It's conceivable to me - I haven't tried to prove it - that you could choose the aileron length so that you could get proverse yaw at the start of the roll (creating a skid), and some adverse yaw as you stop the rolling motion, so that the nose would stay close to - but not exactly - where it would point if there were a good glider pilot at the controls. Close enough to not really require a rudder for normal turns. But, because a straight wing is not yaw stable, you still need a vertical stabilizer for yaw stability in straight flight. Part C: A swept wing is yaw-stable in straight flight, without a vertical stabilizer. Normally, swept wings - like hang gliders - are yaw stable but have problems with adverse yaw during roll inputs unless you fit them with a vertical tail and rudder. With a swept Prandtl wing you can get yaw stability during straight flight and approximately zero yaw error during roll inputs. As long as the residual yaw deviations are acceptable, you can dispense with the vertical stabilizer and rudder. Of course, the properties of swept wings mean that, to achieve the Prandtl lift distribution, you'll need more geometric washout than you would have needed with straight wings, and this will narrow the speed range (or angle of attack range) where the arrangement will be optimal. Now for an observation. We're talking about a wing with quite a lot of twist (you can do some of it with airfoil selection, but the local zero-lift-coefficient incidence angle will have a lot of twist in it), and as you move away from the design airspeed (change the AoA) the lift distribution will move away from optimal - all the more so if the wing is swept. As you speed up there will be too much downforce at the tips, too much upforce in the center, and too much drag from both. As you slow down, you will lose the proverse yaw benefits. So there's a trade-off here: you do get to remove the vertical stabilizer, with its associated drag, but you narrow the efficient speed range of the aircraft. Sailplanes actually need wide speed ranges, so despite eliminating the drag of the vertical stabilizer, I doubt that this is going to be a winner in a sailplane application, even in the Open class (unlimited span).

[@pylon500]

+Finbar Sheehy Well put! I missed the 'extra' replies under some of the arguments above, not realising someone had more or less already explained some of the (misconceptions is a bit harsh but) confusion about performance from winglets versus 'flat winglets'. Seems to me they have accidentally discovered the benefits of aspect ratio !! As you say, we are not likely to see flying wing sailplanes any more as they have reached their limits (Horten IV was something like 40:1 in 1938), normal layout gliders far exceed that today.

[@jazldazl9193]

@@FinbarSheehy Thanks for your learned comments. What is the problem with a v tail mixed with ailerons?

[@FinbarSheehy]

@@jazldazl9193 There is no real problem at all with that approach - or with using a conventional tail. The video is simply discussing the interesting property that the wing can be designed in such a way that the V tail is (approximately) unnecessary.

[@thinkflight]

@@FinbarSheehy This may be the best breakdown I've ever come across on Prandtl wings.

[@mblaber2000]

Might want to also consider sailboats. They have a separate centerboard and rudder. Won’t sail controllably if either is absent. Centerboard resists side slip, and rudder provides yaw moment. The vertical tail in a plane characteristically comprises the vertical stabilizer (immovable) and rudder (movable). Thus, the airplane tail has two distinct and unique structural elements with different yet essential functions.

[@ErikssonTord_2]

All birds use their tails for both yaw and pitch control, as the video so eminently shows. Professor Prandtl was old when he designed his tail-less flying wing, so he probably had forgotten how a bird really flies, but teaching students that birds don't have a tail like aircraft is silly (the do lack a fin, but use the tail as a replacement surface), as the video so well shows. Modellers sometimes add a V-tail to birdlike models, to get some control in yaw, but I am not aware of any living bird with a V-tail! Thousands of videos have been taken by now showing how birds move their tails in detail, and some birds even use their webbed feet, and necks, to control pitch. And big beaks affect yaw, of course. They move their tails up and down, twist them (for roll control), and also move their tails from side to side, plus use complex combinations of these basic movements, thus there isn't any passive use of tails on birds ever. Hawks spreads their tails for soaring, and closes them for power dives, and I've studied extremely complex movements of the tails of crows and jackdaws, from very close distance. As an ex-glider pilot it is interesting to note that there are no, as far as I can see, control surfaces on bird wings, so ailerons and spoilers for roll control are man's inventions, not the birds. Airfoil camber can be controlled, and they have feathers that functions similar to flaps. But essentially their wings are rigid, with adjustable camber and span. Some bending occurs during flapping, but this is about gliding birds, as Prandtl's design wasn't designed for flapping, was it?! Doves change course by using more power on one wing than the other, and battle with their wings as well, never using their feet, or beaks, to harm the opponent, unlike some other birds. Much like boxing, they first try to stare the opponent so submission, and then stand with their torsos vertically, and deliver heavy body blows - great fun to watch!

[@RockinRobbins13]

Eriksson Tord Actually, he had not forgotten anything. There are two types of birds, land birds and maritime birds, which use two different methods of controlling flight. For land birds you are right, they use their tails as control surfaces. However sea birds, take the albatross as an example, do not use their tail surfaces for attitude control. The albatross is the bird Prandtl studied.

[@krampdrucker1753]

+Eriksson Tord I have watched hummingbirds in close quarters, when the hummingbirds allow. They appear to change the angle of every part of their bodies, including wings, to yield the forces necessary to cause orientation change, especially when *fighting* (which is nearly constant around my feeders).

[@ivicamilosavljevic4706]

You are right! I have similar conclusions, and because of that, I am reading this stuff... something does not go in the correct direction. All birds use tails (even Albatros have one)... not vertical surfaces, but they are shifting it ...

[@JeffCurtisIflyHG]

Hang gliders have wing tip twist or washout and have had for decades. Training gliders have the most and have almost no adverse yaw. Gliders for intermediate and advanced pilots have less washout (among other things) to improve glide performance, especially at higher speeds, with the result that there is more initial adverse yaw before roll forces and pilot induced pitch up coordinate the turn. There is no free lunch, washout reduces the glide performance of a wing when flying straight and generates more drag at higher speed. Washout also is part of the pitch stability system, the tips are behind the root and since they have a lower angle of attack, the root stalls first, the tips still provide lift and a pitch down moment that causes the glider to dive if the pilot stalls the wing. Hang glider pilots have limited ability to actively modify washout and are not able to modify washout asymmetrically. I don't know what control birds have on washout but if they can modify washout then they could keep the twist low for gliding flight, especially at high speed, and then twist one wing tip to generate proverse yaw as part of a turn. I am glad the students are learning but unless I missed a subtle detail everything they described has been in use for years by every hang glider manufacturer.

[@FinbarSheehy]

Hi Jeff! Hang glider pilots can and do actively modify the washout - especially asymmetrically: it's how they roll the gliders. The design change to the floating crosstube, in the 1980s, was the key. When the pilot shifts weight to the right (for example), the actual control input is to pull the control bar to the left (there's also something of a twisting action but that's not relevant here). The control bar is attached to the sidewire, which is attached to the outer end of the right crosstube (or the leading edge near it), and pulls that to the left. At the same time, the pilot's hang strap is attached to the keel, and when the pilot's body moves to the right, the hang strap pulls the keel to the right. With the sidewire pulling the crosstube to the left, and the hang strap pulling the keel to the right, and no physical connection between the crosstube and the keel, the distance between the right wingtip and the back of the keel shortens, allowing more washout on that side (and of course less washout on the left side, where the distance increases). The effect on the washout is quite large. This, and not the weight shift itself, is the primary source of roll control on modern hang gliders.

[@abidfarooqui-sla3301]

+Jeff Curtis . You are right trikes and HG use similar concept but the designers are doing this from intuition more than controlled sense and data to be very honest. Its not optimized. Plus its a flexwing that looses a lot of the efficiency. Some designers like Dr. Bill Brooks have tried to optimize trike wings for lift distribution making large gains from previous generation wings using Prandl's work and careful measurements.

[@awuma]

+Finbar Sheehy Fascinating! The "text books" on hang gliding don't talk about this at all (at least Pagen's beginner/intermediate Traing Manual doesn't).

[@FinbarSheehy]

+awuma Mine does :-)

[@mikekelsey6777]

When I started flying hang gliders in 1973, it was the standard Rogallo. I had an interest in seeing if I could make a small scale model to experiment with variations on the Rogallo design. The materials I was using made it expensive and very time consuming, and flight, although successful usually resulted in some damage as it was simply free flight. I turned to simple paper and Scotch Tape to create design modifications. Cheaper and I soon began to greatly improve the design to the point that it was now a very nice flying wing. It was around 1975 that I visited Bill Bennet Delta Wing Kites and Gliders manufacturer and showed him my paper airplane (Glider), which I call the OmniWing. He wanted to see it fly, so we went out to the parking lot and he grabbed it by one of the wing tips and tossed it into the air like a boomerang. Bill was from Australia, so I guess he did a bit of boomerang tossing. So the OmniWing went up into the air spinning out of of control, but it recover and went into stable flight and flew across the highway. I recovered the wing and he asked if I would leave it with him so that others could see the wing fly. Some months later he produces a hang glider that looked very much like my OmniWing planform. So I bought one. Now, almost all hang gliders look like my OmniWing design. Same aspect ratio, same nose angle, same sweep, and same twist and washout. Each manufacture has small variations, but all are very similar. Check out a flight of one of my OmniWings off of Mount Nebo, in Arkansas. Was an exceptional flight. Video shows a fast build of the wing and then one of my best flights. kzbin.info/www/bejne/iaO9YpWnisSaatE

[@fanBladeOne]

Prandtl and Deadmau5? This is what KZbin is all about! Very clear explanation of drag types and influence on aircraft handling. Recreating Horten's wondrous effects and demonstrating efficiencies to be gained. Loved this video! You will all lead prosperous aerospace carreers! Bless you all :)

[@prabhakarkmv4135]

Very knowledgeable video! 👍In early days one of my friends was in Air India.His job was called "Navigator" Once I asked him out of curiosity about this.He said his job was to help the plane take a turn&change its direction by operating rudder ! I don't think this system exists anymore.Now I think everything operated by the pilot (commander) himself from the cockpit ! Right!? High Tech age maan! Nice video! 👍👌👍

[@osmick15]

Great video! Also, song is Strobe by Deadmau5

[@akkudakkupl]

A neat way to steer the model would be to torque the wing by the tips - the twist would be distributed along the wing with most of it near the tips (because that party has least rigidity) - so perfect to get proverse jaw. Servos could be installed in the fuselage and would connect through beams to the wing tip (could run inside tubular wing spars maybe).

[@peterbecker8907]

The wing tips seem to be what we called "Balanced" control surfaces, common on 1930's light aircraft like Piper Cubs, and surviving in model aircraft to this day ( RADIAN sailplane and Olympic 650 sailplane. The area forward of the hingeline can exert a very strong force on the wing, much like the pinion feathers on a birds wingtip...

[@willkaporis7958]

This is amazing, hope this starts getting implemented into everyday aircraft from here on in!

[@europaeuropa3673]

10 years later in 2023 and I ain't seeing much.

[@ByDesignation]

Thank you guys for your work. This will truly be the next passenger aircraft. It is kind of hard to mentally conceptualize the twisted wing and how the vortexes would vector the thrust opposite to the induced drag at the wingtip.

[@captarmour]

Looking forward to see a powered version!

[@kenwebster5053]

Lift, weight, thrust, drag, pitching moment, yaw moment & roll moment.

[@pylon500]

Lots of odd ideas being suggested here, many not being used 'in comparison' to the claims being made... As the Horten's, and Lippisch before them found, a swept flying wing is stable when lots of washout used and is apparently efficient when compared to a similar sized wing. However, the L/D efficiency came from not having to drag a fuselage and tail around the place, BUT, did take a wing of greater area, the added percentage of which is used to create the stabilising effect against the pitching moment of the wing section. More than having the lift curve drop to 'the bell shape' towards the tip, the lift actually becomes negative at the tip. A whole load of variables can be played with to lessen the negative lift (drag) of the tip such as low pitching sections (less overall lift), more sweep (more structural problems and weight) or rearranged CofG (less stability). By comparison, a straight flying wing relying on a reflexed wing section, is not very efficient at all, these type of craft survive through low weight, but not well. As for basic control dynamics of flying wings, rearward swept wings use elevons, which while in straight and level flight, and with a rearward CofG, can be at a fairly neutral angle thereby creating very low drag, if possibly a little unstable. But as soon as you try to turn, even before you have to start adding a pitch correction, the act of applying the aileron input will have the inboard elevon go up and create a marked negative AofA, and actually create a tip vortex (in reverse) generating drag on the inboard wing (proverse yaw). The outboard elevon will initially go down and create no drag, and maybe add to the overall lift being generated by the outboard wing, hence a turn is initiated. Having rolled in, the flying wing will begin to lose lift so both elevons are held back (up) while in a reasonably balanced turn. Unfortunately, now it gets messy as you try to roll OUT of the turn. Typically, most flying machines need MORE aileron to roll out of a turn than they did to get into it, fortunately the swept flying wing is the least effected at this point although with no rudder, the yawing motion will require more outboard drag (up elevon) to stop the yaw, but as we are still 'pitching up' to maintain height in the turn, this becomes a problem. If we begin rolling out of the turn AND pitch forward, we lose the proverse yaw of the outboard elevon and the machine begins to slip into the still existing bank. Slipping a swept wing has the same effect as dihedral, giving a rolling reaction away from the slip. The interplay here has a LOT of variables, all making flying wings just that little bit harder to fly coordinated. Upshot is; flying wings a great when flying straight and level, will sit in a stable turn very efficiently, but can be messy if trying to maneuver, probably being the reason you don't see many swept flying wing gliders (full size) as constant maneuvering is a pre-requisite of flying a glider. I'm not an Aerodynamicist, but I have flown models, hang gliders and sailplanes, and am a flying instructor, and have to explain to students the reasons that flying machines do the things they do.

[@krampdrucker1753]

+pylon500 That was a wonderful explanation. I have a mechanical engineering degree, and am a student sailplane pilot, and you have very clearly filled in what is missing from my understanding of PRANDT-L. I have been suspicious of the claims made by the program, and you have shined an illuminating light into it. I would like to read your thoughts on the use of upper wing spoilers, such as on the A-I-R ATOS rigid wing gliders, to bank without adverse yaw.

[@pylon500]

+Kramp Drucker, G'Day kramp. There are a few aircraft that use 'Spoilerons' as their primary roll control, but as a glider pilot it initially seems abhorrent to deliberately induce drag for any reason. However, they can be a more simplified way of obtaining roll without complex differential linkage systems. From an aerodynamic design point, they just need to be placed at the optimum position to create the most lift loss, for the least amount of drag. When dealing with the lower speed end of flying (like the Atos) the spoilerons tend to need to be a fair size and are an unfortunate compromise, but ailerons would be far to complex and heavy in that situation. Remember, when you get really slow (para-sails, Gossamer Condor etc) there is a tendency to actually use 'reverse' ailerons and turn flat purely on adverse yaw! High speed, heavy aircraft using spoilerons can run into a problem, induced by the pilots when trying to maintain level in strong turbulence (usually on approach) where multiple inputs in both directions basically result in a net loss of lift and a shortfall on the approach.

[@krampdrucker1753]

pylon500 G'Day and thank you. That makes clear sense to me.

[@itsnotallrainbowsandunicor1505]

"all making flying wings just that little bit harder to fly coordinated. Upshot is; flying wings a great when flying straight and level, will sit in a stable turn very efficiently, but can be messy if trying to maneuver, probably being the reason you don't see many swept flying wing gliders " There you have folks in a nutshell. I admire what the students were doing for their internship/coop/study/whatever, but the issue I find with many students or fresh graduates is they don't post ALL the facts. They like to present the information as a new discoverer, or that they rediscovered a forgotten concept. The flying wing was looked at back in early the 1930s by the Horten brothers. The flying wing did not make it's debut until 1943. The request was for a faster and efficient German bomber. The trade off was less control. The Americans built the Northrop YB-49 with first flight occurring in October 1947. The concept didn't go very far. Then came the YB-35 and YB-49. Issues with the YB-49 required very long bomb runs to dampen out directional oscillations. The oscillations were not severe, but posed a problem with degraded bombing accuracy. (If you think back in the Vietnam war and how we bombed the crap out of the Hồ Chí Minh trail partly due bombs lacking guidance compared to today where one placed guided munition can do the trick). It wan't until fly-by-wire and computer aid that the issue with control became less of a factor.

[@NickelCityPixels]

Uh, that's great, but... how exactly is a "flat winglet" distinguishable from a plain ol' flat wing tip? And how can I apply this new knowledge to my RC plane designs?

[@Chipchap-xu6pk]

Not an aeronautical engineer, but I think it's the negative lift at the end of the bell lift distribution. The elliptical distribution went to zero at the wingtip, with this design it went zero slightly inboard. I guess that induces the vortex inboard as well. So the bit of wing beyond it is acting like a wingtip.

[@fiftystate1388]

This clip is cafeteria engineering: pick the items they like and ignore the rest. The 3:12 meat and 4:25 potatoes look great, but I'm not sure I'd buy 5:03 the winglet's creamed spinach, it's hard to get a dish like that just right. First: Yeah, what you say. (The winglet/flat winglet) Second: Induced drag, this isn't electromagnetism, at this level of physics there's drag and reduced drag. Third: Winglet "induced thrust" 5:01 yes, there's a lowest pressure area where the arrow is rooted, and immediately toward the leading edge is a highest highest pressure area (in competition with the trailing edge region of an airfoil.) *_Sounds good_* and you learned a lot, and I'll bet the students featured would partially approve this clip too. The yaw-to-increased-drag section, before and after is very important. Doesn't the vortex coming off the leading tip interfere, "spoil." the airflow over the tip and affect the lift?

[@klausbrinck2137]

Generally, wings with winglets have the main characteristics for bell-shaped-spanload, cause they are triangular, not rectangular. If u twist the leading egde (from root to tip in a non-linear fashion, such that twist is noticable only between 45-90% of the length) , or bend the triangular tip upwards (often leading to a similarly twisted leading edge thereby), the results are similar , and the wing is longer at the end (if this extra-length is bent-up or flatten-out). But simply making a winglet flat isn´t as good as aiming for a bell-spanload from the ground up. That´s a bit of what I understand. Non-linear-twist: 0 is the wing-root, 20 is 100% of the wing´s length, the tip, the other numbers are radial degrees. "On Wings of the Minimum Induced Drag: Spanload Implications for Aircraft and Birds" 0 8.3274° 11 7.2592 1 8.5524° 12 6.6634 2 8.7259° 13 5.9579 3 8.8441 14 5.1362 4 8.9030 15 4.1927 5 8.8984 16 3.1253 6 8.8257 17 1.9394 7 8.6801 18 0.6589 8 8.4565 19 -0.6417 9 8.1492 20 -1.6726 10 7.7522

[@Flyingwigs]

i am almost certain that the narrator is the same guy who does minute physics!

[@kevinmoore4887]

It would be nice to do close up shots of the wing and point out how it differs from a conventional wing. Aspect ratio, built in twist, are the ailerons conventional or wing warping. I have watched a couple videos and they either show a conventional aircraft being drawn or show the math. Either point at the features in the model up close or draw two wings, one with and one without these changes.

[@nevillecreativitymentor]

LOVELY video ... well explained ...

[@mountains_beaches98]

thank you for explaining this concept, best one out there.

[@RoscketTasartir]

Well done!

[@jetpowered1]

Nice job guys!

[@mithunmahato309]

at 5:10 how could one get a forward driving force from the design of the winglet that prevents the tip vortices (the air vehicle is colliding with the static air particles in the flight path. )?

[@jazldazl9193]

If u made a really big winglet you could toss the motor

[@wordreet]

So at it's most basic, a wing will be ideal when it produces sufficient lift and no tip vortices can affect it. There may be no strength at the tip if it comes to a perfect point, but almost no forces are acting on it at the tip. I like it. My next experimental project. :¬)

[@wordreet]

Don't worry, I build foam RC planes.

[@klausbrinck2137]

That what the chief of the group always stresses, how "unloaded" the wingtips of big birds look during flight. Everyone knows, that these wingtip-feathers are preeeeetty soft, yet, they don´t seem to bend under the load. That´s explained with a bell-spanload, but not with the elliptical spanload, so, birds´ wings function differently than state-of-the-art human-built-ones.

[@wordreet]

@@klausbrinck2137 Yep, probably in part because birds do use the tip feathers in various way. They are "joined" at times in some species, but definitely spread out during landing or tight maneuvers. Almost impossible to manufacture and operate something so complex.

[@theHDRflightdeck]

what about all those other flying wing models that dont use prandtl principles. They still yaw the correct way. What's the difference?

[@okhwatnoornoor8893]

In "on wings of minimum induced drag" it is given that symmetric airfoil is used at tip of the wing . If airfoil is at negative angle of attack , why symmetric airfoil is used; it will not produce any lift at neg angle of attack . ?

[@kraboyii]

I still have a question, why the flat winglets don "become" the wing tips? What makes it different from each other?

[@zachansen8293]

Description of lift at 1:56 is wrong. Tons of videos about this.

[@RockinRobbins13]

The concept is even better described and the ideas supported in this video from the 2014 AMA Expo. kzbin.info/www/bejne/iKC3Y6imeceXi8k. You'll see all the negative comments below are totally rebutted. These wings have less drag in level flight plus the approximately 12% drag reduction from elimination of vertical stabilizer and rudder to produce a plane more efficient in all aspects including straight and level flight. You'll see that Prandtl didn't forget how birds flew, he studied maritime birds, which have different flight mechanisms than land birds. It's explained very satisfactorily. The surprising thing is that the tip isn't just reflexed to the point of zero lift. It is actually reflexed past that and the wingtips generate negative lift! That is the secret to the Prandtl wing and it's not something a modeler or hang glider would intuitively try and "of course" come up with the same idea for cheap. They didn't. None of their designs actually dared to try negative lift at the wingtips. This is truly revolutionary even though the principle was originated in 1933, but ignored because it makes no intuitive sense at all. But it works perfectly.

[@FinbarSheehy]

+RockinRobbins13 Great link! Thanks!

[@krampdrucker1753]

+RockinRobbins13 Birds can use body english and full span angle of attack adjustments. I find your argument specious.

[@RockinRobbins13]

+Kramp Drucker Fine. Present your contradictory research.

[@krampdrucker1753]

RockinRobbins13 I don't have to. I just have to force you to prove your theories. That's how science works. If you can't prove your propositions, then they are groundless. I don't see your data, and the guy in your video even claims he doesn't have all the data he needs, which is a classic trick to maintain funding on something that has no merit.

[@RockinRobbins13]

+Kramp Drucker You're playing games. This is a NASA project with leading scientists. Your extraordinary claims need extraordinary backup or you have nothing worthwhile. That's how science works.

[@briankoch7041]

Deadmau5 instrumental during the flight footage. :) Nerds can be cool.

[@buttole]

so a wing twist was used to make a load distribution bell curved, but why does this result in proverse yaw?

[@abidfarooqui-sla3301]

Because that basically acts almost like a winglet except could be even better. Looks at trikes (weight-shift-control) aircraft. They have been using similar ideas with no rudder required for a long time

[@tombouie]

Well-Done

[@eastdave2]

Great work, whats next?

[@SladkaPritomnost]

Could some one explain how winglet gets lift forward? Inward is due to airfoil (I guess) but what's behind forward force? Is it a vortex itself?

[@Traqr]

The thing to remember is that the apparent wind is coming in from the side due to the vortex rolling around the tip, so the resultant lift is angled forwards of the aircraft's direction. There're additional aerodynamic effects that would take more explanation, but that's the main one.

[@pylon500]

The concept of forward lift (thrust?) from winglets is a crock. People try to explain 'lift' from flow around an airfoil that has a high camber line, or is at an angle of attack. Either way, the initial airflow 'up' over the leading edge has a tendency to create a low pressure (lift) line that is forward from perpendicular 'to the direction of travel'. In theory, this looks like 'thrust', BUT, winglets rarely have much camber (which causes drag), and are not usually set with an angle of attack the the airflow (which causes drag). The idea of winglets is to actually STOP generating lift by the time you get to their tip, thereby cancelling the pressure differential between upper and lower (inner and outer) surfaces, which cancels any reason for a tip vortex to form. Basically, in level flight do very little, they add a little directional stability (on swept wings), they add a little roll stability (straight or swept), but the wetted area they have usually negates any thought of generating thrust. What they WILL do, that is not always obvious, is that as a wing increases angle of attack, thereby increasing the tendency to form a tip vortex, the winglet 'catches' the vortex, which then appears as lift or as an apparent increase in span. An analogy would be like extending a longer wingtip for flying slower, easy for birds, not for us...

[@SladkaPritomnost]

@savvas christoforou got it, thnx :)

[@klausbrinck2137]

Downwash is usually back&downwards in romal wings with an elliptical-spanload. This generates lift, directed up&backwards (a force 90° tuned-forwards, relative to the downwash). Up lift is desirable, and called simply "lift". Backwards lift is undesired, and thus called "lift induced drag". In a bell-shaped-spanload-wing, the AOA changes from +8,5° (root) to -1,5° (tip). Now, the last segment of the wing, that near the tip, produces very little aerodynamic force, but cause of the downwash now turned into an upwash, this force is directed up&forwards. Up lift is desirable, and called simply "lift". Forwards lift is also desirable, and and thus called "lift induced thrust". But such wings have to be longer than the ones above, with the elliptical-spanload, to make good for "parasitic drag" loses (remember: now one part of the wing produced much less "induced drag", but also less lift and "induced thrust". But "parasitic drag" remains the same. To compensate for that, such wings have to be longer, in order to profit under the line. Still, they are shorter, than if one would try to reduce "induced drag" by simply making a normal wing longer, thus increasing the aspect-ratio, which also reduces "induced drag")

[@tankalvin1444]

With induced thrust at the tips, does that mean a lower aspect ratio aircraft could be considered?

[@geesehoward700]

flat winglets? as in a normal wing?

[@jeffcauhape6880]

Thank you. This is the first clear explanation I've seen on how and > WHY < this works!

[@halnineooo136]

What about side wind at landing ? More specifically unpowered emergency landing. Can you do without a rudder ?

[@pauljames1682]

Elervons can be V flaps to add drag on one side reducing low speed yaw.

[@davidgermain]

a lot of the test flights are been done with a glider, on a salt bed lake. so side winds and unpowered are factored in.

[@SkybowKite]

Yaw, Das is Goudt!

[@m0IrbkF8bHxs]

Great Job!

[@wisedupearly3998]

Is there any evidence that the downwash vortexes actually impact the wing surfaces? Or is it merely flow separation on the upper surface towards the end of the wing? The assumption seems to be that the air "leaks" from under the wing to low pressure above with sufficient rapidity to overcome or offset the forward flight speed.

[@ManjitSingh-kr6mi]

This video is awesome 🇺🇸👑💕💕

[@RoboTekno]

Haven't we known about the effects of wing tip wash-out for decades?

[@26mridul]

@Dan Nguyen the difference is using a trip to shed vortex at the place where wing ends at winglet starts.

[@richardyoung5429]

This design is the basis for an aircraft which is proposed for Mars according to the Washington Post. www.cnet.com/uk/news/this-could-be-the-first-airplane-on-mars/

[@ashutoshpradhan9262]

Strobe by deammau5. Awesome

[@tankalvin1444]

Is twisting the wing the only way to achieve bell shape lift distribution? With regards to sweep, taper ratio and the wing tips, are there recommended specifications?/range

[@mblaber2000]

Might want to consider motor torque. Birds don’t have to deal with that.

[@mohammadtaleghani5973]

Are you sure the engineer who invented the winglet, is Dick Whitcomb and not Richard Whitcomb?

[@wagner24314]

pro-verse yaw is produce by the swept wing at thats it! If the wing was a strait it would not be yaw stable and would require drag rudders under gyro control.

[@RockinRobbins13]

wagner24314 swept wings do not produce proverse yaw. All current flying wings have some system of differential drag that overcomes the natural adverse yaw by introducing more drag to counteract.

[@wagner24314]

RockinRobbins13 i have been flying rc wings for year and also hang gliders. i can tell you that you dont know what your talking about so i suggest you read about swept wings and yaw stability

[@RockinRobbins13]

wagner24314 Read very carefully and learn something. Swept wings work this way (pay attention). When a swept wing yaws there is a leading wing and a trailing wing. When the plane yaws right the left wing is the leading wing, the right wing the trailing wing. This is standard aerodynamic language so as an expert who knows everything you agree. Good. Now, the leading wing presents more frontal area to the wing, increasing the drag on that side. The trailing wing presents LESS frontal area to the wind, decreasing drag on that side. This yaws the plane back to straight line flight. There is an oscillation pattern which damps out after a hopefully small number of cycles to regain coordinated flight. This system is called differential DRAG, not proverse yaw, which is the system the Prandtl wing uses to actually produce forward THRUST, not DRAG to achieve coordinated flight. The trailing wing actually generates forward thrust, unyawing the airframe. Rudders and swept wings are drag mechanisms. The entire advantage of the Prandtl wing is the reduction of drag and the use of THRUST instead of drag to produce coordinated turns and eliminate adverse yaw. Of course, as a more learned person who has flown a hang glider you can defend your position with something better than a fallacy. So let's have it. Demonstrate your superior understanding of the principles of flight since you have such vast experience flying RC for a whole year and surviving a few hang gliders.

[@wagner24314]

for one thing i have about 800hours in flight in gliders. 2. you stated a swept wing is yaw stable. 3 if you take a swept wing lets use a zaggy if you mix the elevons so in roll you dont lift a wing only push it down you dont have adverse yaw. by the way your a troll.

[@RockinRobbins13]

You are the troll. You don't understand the concept of proverse yaw. And not understanding it, you dismissed it as nothing new. As two videos carefully explain, you are wrong. This is a new and important development. It uses THRUST to coordinate turns. All flying wings to this point except the Horten wings used differential drag. Eliminating drag is central to higher efficiency. That's not a troll, it's the truth. 

[@asaero92]

AMAZING

[@lesterhall90]

What did he say?

[@peterxyz3541]

Nice......but, “where’s my flying car”? No, seriously, I want to see this understanding in use: I need an airplane!!! 👍🏼👍🏼👍🏼❤️

[@Love2FlyKAP]

Reinventing the wheel that's all this is. Norten brothers are the inventor not NASA. Basic aircraft use differential ailerons to compensate for induced drag in yaw when banking. Look at a basic J3 Cub.

[@HaochuanNi]

Now look at the shape of the wings of the B-21. Rather uncanny similarities in principles. 😉

[@woeileongchan9552]

Flies well without a tail... So, why do birds need horizontal tail... hm...

[@BC3012]

1:45 Why is there no downwash? Newton is not amused.

[@raoulcruz4404]

Very interesting. Video presentation could stand on it's own without the piano music.

[@mouser485]

I wish I could ”scribble” like he does.

[@aifly1985]

强大

[@Sethorion99]

subscribed :)

[@bingobongo17]

Where can I buy one of em flying wings for rc use?

[@GrantBennett2013]

Isn't this just what was previously called 'washout?'

[@lilalaser]

no.

[@GrantBennett2013]

Ah, the young and less learned. Yes, it was. It was used to prevent stalling, and was a part od building all model gliders.

[@GrantBennett2013]

And I don't mean to disparage your work, as I do think it is significant, but we did do this to prevent stalling on model gliders. If this is significant to current aircraft, then great; but it's use, even for another use, did have another name.

[@christheother9088]

I've flown a lot of weight-shift controlled hang gliders ( swept, twisted flying wings ) since the 70's and for the most part adverse yaw was not an issue at all. The wings were yaw-roll coupled by nature of their geometry (when configured correctly). We didn't really need an on-board microprocessor to verify this.

[@FinbarSheehy]

+Chris Gonzales Yes, adverse yaw is a real issue on weight-shift-controlled hang gliders. They do work, but they have significant adverse yaw - especially the high-performance gliders with higher aspect ratio. Hang glider pilots just live with it.

[@Thatguythere-u7r]

horten brothers nothing new