NASA's Albion H. Bowers - "Why Birds Don't Have Vertical Tails" - AMA EXPO 2014

[@tocrank]

I feel very lucky to have run in to this gem of a lecture!

[@RTOVideos]

This is genius. Dr. Bowers is absolutely correct, and is correct in questioning some of the assumptions at the heart of aerodynamics!

[@JavierChiappa]

Oh wow, this was the most amazing talk ever on that problem.

[@OrenWasser]

I'm a fan of your work!. I've noticed that each and every single feather of a bird's wing has it's shape and lift properties as a standalone structure. So if you look closely on a feather that is not attached to a bird, you'll be able to know it's place and position on the wing!!

[@jibeneyto91]

This is an excellent presentation with lots of useful references! Also the questions from the audience are very good; I would have liked to see the "debate" on the Trefftz Plane at 35:46 further elaborated.

[@guytrimble8171]

I'm happy to be watching this again and worthy of comment.

[@mxcollin95]

Awesome talk! Reinforces how nature is smarter than we are... lol.

[@jazldazl9193]

tbf it has a couple of years on us

[@dominictarrsailing]

had just learnt about adverse yaw... wondered how do birds handle that? managed to find this video! amazing

[@roginutah]

Certainly right about starting with a clean slate.

[@robertpepper7061]

Going to look more into this, super Interesting stuff. I never thought I'd be so interested in hearing a seminar about birds lol

[@jameshickman5299]

Regarding Lilienthal's vertical tail. Disclaimer: I'm not an engineer, aerodynamicist, or Lilienthal expert. Dr. Bowers' reference is to the Wright's use of a movable rudder to achieve co-ordinated, turning flight. Examining photographs of Lilienthal's gliders, they do have a vertical tail surface, but it appears to be a covered portion of the fuselage. It is a fixed vertical stabilizer. It is not a movable rudder. Lilienthal used weight shift to control his machines. He did add a hinged horizontal surface to some machines, for pitch control. Dr. Bowers' statement is correct.

[@MotoMarios]

From what I get from the video, if a technology like this gets implemented, then the engineering compromise becomes how much wingspan you can get away with for a given overall aircraft weight.

[@WillN2Go1]

Thank you. Very cool. It all seems so obvious...now.

[@entropia666]

Great presentation! Thanks for sharing

[@ianmorgan889]

There is so much TALK about the PRANDTL wing but nowhere can I find any actual info on what makes it so special, why did you choose not to snow Albion H Bowers looking over the wing he had on stage and speaking about its characteristic shape?-Most frustrating! If any more videos are released about this wing, could you kindly show much more of the actual wing or let us see at least a diagram or two showing the structure in its entirety? Thanks.

[@Triple_J.1]

Now, connect this information with the use of thin airfoils having

[@awuma]

I think this is more subtle than the old washout-driven stability of flying wings (which we've known about forever). It shows how one can optimize the washout distribution and the functioning of the flaperons. Very interesting. Also, how much can drag be reduced by relying on gyro-stabilized fly-by-wire control rather than inherent static stability?

[@cherminatorDR]

Wasn't the whole point that a fly-by-wire aircraft like B2 needs to intentionally induce drag to maneuver, whereas this design would eliminate the need for that altogether?

[@rcwgs]

on my RC models, I usually include washout over the entire wing from fuselage to tip each side of course.

[@paulhope3401]

Very interesting. I guess at the time of this talk, morphing carbon fibre to wing warp was not yet really a developing technology. It is now... and at some scale must offer Bowers concept the potential of a far wider speed and performance envelope. I wonder where he is at with the project now in 2020 and if he has looked into incorporating it?

[@martincox4520]

The Horten brothers started as modellers!!

[@Fix-a-stall]

Interesting ideas for statically stable designs - personal aircraft. I still think you would want decoupling between axis for dynamic damping. Wish he talked more about the constant wing versus constant span concepts.

[@stuartsteele9984]

It would have been valuable to see the airfoil section used and the planform with the aileron and the airfoil section span-wise of the aileron if not consistent with the general planform.

[@Bourne246]

Im sure im not the only one who noticed the downward angled wing tips of the SR-71 and F-22..

[@liam3284]

@13:00 This has interesting implications for sail shape and trimming

[@BOKI797]

Albion; Watched your Video & it was Very Good ! Never new anything about it but it & sure was & Excellent Video ! Thanks

[@regdor8187]

"Why Birds Don't Have Vertical Tails".....Last time I watched a bird fly, I observed the rotation of their normally horizontal tail into a near 45 deg angle similar to the function of a Vee tail Bonanza.....

[@engnrpetev]

I think Albion Bowers' enthusiasm sometimes takes him out of his lane. I'm hopeful that his explanation of proverse yaw with bell shaped lift on span unconstrained wings with twist explains how an albatross flies efficiently without a vertical tail. In one lecture, however, he mentions that if your design IS span constrained, then the elliptical lift distribution is to be used. Well most birds are span constrained. I'm thinking of eagles, hawks, crows, waterfowl. Most of these have feathers that can splay out at the wingtips as what we might call winglets (but to my knowledge haven't been modeled successfully) and this is different than Bowers special case. I'm particularly impressed with the flight of swallows; they have 'lunate' shaped wings that end in points, but not a great aspect ratio. Another exception to 'proverse yaw'? So when Bowers informs us that a bird researcher is 'wrong' to explain bird formations flying with wingtips overlapping at the wingtip rather than at the ~ .7 wing station, I have to take exception to either generalization. I took a photo of pelicans in formation flying overhead last year and the overlap ranged from birds almost colliding to most often, birds separated by a portion of a wing length up to a wing length. I have to conclude there was some up wash well outboard of the wing tip, if they were doing this for a boost in efficiency. Certainly there might be a difference if the birds are flapping rather than just soaring. This should really be studied without preconception or hasty generalization on either side.

[@kennethhawley1063]

@@engnrpetev There is always upwash outboard of the wing tips. The BSLD moves the effective centre of the vortex inboard so that the upwash affects more of the outboard part of the wing. When flying in formation it is not necessary for wings to overlap to gain an advantage. Birds will manoevre themselves into the position requiring least effort, wherever that may be. As you say birds with low aspect ratios are likely to derive little or no benefit from proverse yaw when gliding and make great use of their tails to provide directional control. The lift distribution more than likely comes from the requirements of flapping, rather than gliding flight, but is used to good effect by high aspect ratio gliding birds. The real answer to why birds do not have vertical tails is because they they don’t need them. On an aircraft, the vertical tail is redundant if the aircraft is in stable straight and level flight, but creates drag all of the time. A bird only deploys it tail when it is needed, the rest of the time it is tucked away with no drag penalty.

[@carloslemos6919]

@@kennethhawley1063 The way you talk makes me think you know something about aerodynamics, given that, would you like to explain how does a hang glider could be stable without a vertical stabilizer? Thank you in advance.

[@niio111]

This is exactly what I have observed as well. I also believe birds use the effect Bowers describes as they are not mutually exclusive phenoma. Proverse yaw is more evident in sea birds where span is not constrained, but look at owls flying in forests to see heavy use of the tail motion you describe.

[@jimallen8186]

& I’ve just watched a Hummingbird slo-mo. Not exactly a soaring bird the hummingbird. Does get lift both forestroke and aft-stroke with some amazing shoulder flexibility. But the tips in both strokes looked flat. And the tail seemed to bobble up and down a little bit but all horizontal no vertical.

[@jimallen8186]

Very interesting. Would I still need a tail, however, to side slip and/or kick a crab out for crosswind landings? Seems crabbing then rolling straight when I would have kicked out would be a setup for a downwind wheel landing with the cross picking up the upwind wing. Could I get a different way to balance this? Adjusted alignment of the gear like the B-52 seems a bit complicated to build. Some other way for managing if not outright creating yaw? Separately, what about platforms that for some reason may desire to maintain zero roll in a turn? In this, birds have advantage in shoulder joints not just elbow and wrist. They can change the axis of wing through fuselage and maintain a more flat fuselage for that SAR mapping or other need to stay straight AOB function.

[@jimallen8186]

Similar concern RE turning tendencies with propellers?

[@kevinshen9391]

How would a sustained turn work? On a traditional aircraft once you banked you would use rudder and elevator to keep it turning, but here the ailerons control yaw. After the flying wing banks, there would be no more proverse yaw, right?

[@jimallen8186]

Shouldn’t both roll moments and yaw moments go away when neutralizing controls thus sustaining the established AOB?

[@greerengineering]

There is a construct used in model aircraft wing design called 'washout', which is essentially a twist in the wing resulting in reduced angle of incidence at the tip compared to the root. The effect is that the root of the wing stalls before the tip, hopefully making the aircraft more stable throughout more of the envelope. Is this essentially the same construct you describe in reference to stability with no vertical tail?

[@flyboy8814]

Yes washout is the described mechanism for altering the spanwise lift distribution.

[@jibeneyto91]

+Aaron Greer Hi Aaron; I believe that the twist you describe and the one described in the video are different things in "concept". The twist you mention has the purpose of making the aircraft more controllable in a stall, this twist is usually a linear curve from a positive AoA to a less positive AoA. The twist mentioned in the video has another purpose: moving the zero downwash point inboard (altering the lift distribution). Also, the twist function is not as the one you describe: from root to tip: the AoA rises first, reaches a maximum value, then starts decreasing, gets to zero at about 90% out and finally reaches a negative AoA in the tip. You can see this twist distribution on page 22 of the presentation: ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110003576.pdf

[@greerengineering]

+jibeneyto Thanks, that is some interesting clarification.

[@jibeneyto91]

You're welcome!

[@jimallen8186]

No. Washout is towards a symmetric or neutral wing airfoil. This would be going beyond that to an inverted chamber at and near the tip.

[@dawgtv]

I enjoyed this video.

[@terryboehler5752]

Watch a grackle fly. They form a vee tail with a little vertical underneath.

[@ivicamilosavljevic4706]

Is there any possibility for collaboration in the research, and descovery of new details? ...

[@praveenb9048]

33:07 There's a student/intern called Walter Horten in the third list (last line)

[@ironchicken7240]

Walter Horten was taken by the Americans after WW2

[@kennethhawley1063]

Birds don’t have vertical tails because they don’t need them. Birds have a number of ways of controlling yaw. Bell shaped lift distribution is but one of them, and this only really applies to larger seabirds. The apparent bell shaped lift distribution is a natural consequence of using flapping as a means of propulsion.

[@wingnutzster]

Any relation to Bowers of Fly Baby?

[@abdirahmaanahmed677]

Who can summerise this explanation?

[@PhilippeLarcher]

you ?

[@samuelhowe3465]

Ok, so how would this translate to private and commercial designs? With an aircraft shaped like this i cant imagine how large the wing span would have to be on a 747 or something similar to transport mail, cargo and passengers. With the private market I could see this being amazing for fuel efficiency and easy responsive controls. But how large would the wingspan be for things ranging from single seater with a minimal storage to a small passanger/cargo plane that fits maybe 10 people. I think the wing span would be excessive unless the wings are able to be taken apart and reassembled easily or fold. I really only see this as a great application for military planes and private industry. Im extremely new to this topic so please feel free to tell me where I am wrong. I just can't (in my head) figure out how we could apply this.

[@jazldazl9193]

Gains are made by increment

[@Plateaudweller]

So is he saying they have discovered how modern hanggliders work....25 years later ?! Next thing you know they will discover variable geometry.

[@Marmocet]

3:02 Ok, never knew that. Aeronautics engineers literally have boxes they climb inside when they want to do a little thinking.

[@jerryluis8119]

Because they got beaks

[@richardnagy665]

Wow, this is exactly, how Hang gliders fly. Am I right? (not rogallos, but high performance modern hang gliders)

[@jazldazl9193]

No

[@TORDesign]

Very informative thank you. In summary does this extend the design methods of Horten, or prove them?

[@regdor8187]

Al has done an excellent proof of the theory of pro verse yaw......I wounder how that idea works on aeroplanes seeking speeds much much faster than gliders....Seems to me that 12 deg or so washout would be a problem at say mach 0.7 and the down loads would need additional structure .....

[@tonyturiano2872]

Makes me wonder if gull-wing and/or inverted gull-wing aircraft such as the F4U, Piaggio 136 and Minimoa benefitted from end-plate effects?

[@jimallen8186]

F4U was gull shape to get the gear lower to accommodate a larger propeller radius; wings themselves were more elliptical and producing lift across the whole span; you still have tip vortices and downwash not upwash near the end of the wings. It also has fairly long ailerons hence refer back to the inboard vs outboard roll moment discussion.

[@tonyturiano2872]

I know but perhaps the outboard section enhances the efficiency of the inboard

[@MProper]

Wrong statement at 8:50! There are pictures of Otto Lilienthal in a self build glider from 1895! And of course, the glider has a vertical tail ... ;)

[@paulhope3401]

Shhh... we cant have a non Amercan lay claim to be the first man to fly. ;) Maybe he meant powered flight?

[@vlatkopopovski2685]

The authors have two wrong scientific approaches: researching the creation of Lift force and Low pressure at upper side of the wing, relative to the ground surface and Earth. I explain the aerodynamic cavitation and existence of Lee side aerocavern, and creation of Aerodynamic force.

[@65gtotrips]

Man can never outdo what God created, only mimic it.

[@flyboy8814]

Does anyone know of any more detailed descriptions of the prandtl bell curve? e.g. a bigger/more detailed graph or an analytic equation. I NEED to build a wing like this.

[@aeromodeller1]

+Colin Hamilton References at end: ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110003576.pdf

[@SladkaPritomnost]

+Colin Hamilton Just copy some Horten wing, most of them you can google out :)

[@aeromodeller1]

+Colin Hamilton Prandtl, Ludwig: "Uber Tragflugel kleinsten induzierten Wiederstands"; Zeitschrift fur Flugtechnik und Motorluftshiffahrt, 28 XII 1932; Munchen, Deutschland

[@amanieux]

biomimicry is great but why did you focus at albatros that have wings optimized by natural selection for optimal gliding (tip features remain straight because load is 0 at wing tip)and not at the bald eagle that have wings optimized for big payloads (they carry preys that are heavier than their own body weight) (tip feathers bends upwards because load is not 0 at wing tip) - in the end we want to optimize our wing design to fly a payload and not just fly for the beauty of flying.

[@benthurber5363]

For a given wing mass you get more efficiency and, therefor, payload. This approach, however, will result in more total wingspan for a given load, despite greater efficiency. That's his big caveat. If wingspan is not your constraint, use this. If it 'is' your constraint, like a hangar or an airport gate, use elliptical. It all comes down to what you want to design for.

[@charlesseymour1482]

Fly like an eagle

[@amanieux]

@@benthurber5363 for small wingspan to fit in a hangar but with good efficiency in gliding what about rotating wings : kzbin.info/www/bejne/Z3vWea2tlLqAb5Y or folding wings kzbin.info/www/bejne/mYupZnduadmtb80 ?

[@jimallen8186]

@@benthurber5363 what about implications for landing in crosswinds?

[@jimallen8186]

How about the hummingbird? Definitely not a soaring bird. Yet its tips don’t appear to bend up. Does appear to generate lift both fore and aft strokes however with incredible shoulder flexibility. As for the albatross, what is the wing mass versus body mass? It has payload in that it has to carry itself.

[@LONEWOLF-ss5dy]

1:1 he is right.

[@LONEWOLF-ss5dy]

I want this man in NK

[@frelix2milebolinha]

Just didn’t get why can’t he put a smaller scale half wing model on a wind tunnel, try to get the closest Re possible, and prove the damn proverse yaw..

[@kevinshen9391]

Wouldn't there be another vortex at the wingtip because of the upwash, like a reverse vortex?

[@licencetoswill]

yes but the two added together results in an overall smaller "wing" vortex instead of a huge one at the wingtip

[@kevinshen9391]

@@licencetoswill ah I see thanks

[@jimallen8186]

Yes, and it would also contribute to entropy, but… wouldn’t it push you up and forward hence why he talked about a little bit of wingtip thrust whereas your traditional vortex both takes your energy for entropy and pushed you down and sucks you back a touch? Visualize how such swirls hit your wing.

[@Jwmbike14]

There are always those few guys at the end that blatantly don't pay attention, and then comment and act as if they know better.....

[@jibeneyto91]

+Justin Martin If you're pointing at the guy who asked about the Trefftz plane, I don't think it was meant as you say. Bear in mind that this is a very complex topic, highly non-intuitive and non-trivial. People are "surprised" if what they always held as the "truth" turns out not to be so...

[@mysterygamer8682]

And people like you complain about what they are complaining!

[@SladkaPritomnost]

25:54 How's that the theory doesn't work scaled on small aircraft? Birds aren't larger than standard size models...

[@jibeneyto91]

+SladkaPritomnost What he meant is that in Aerodynamics scaling things up or down doesn't work as in a "printer" in which you just keep the aspect ratio constant. Aerodynamics depends on the Reynolds number which is smaller for smaller airplanes and thus the flow behaves as if it were more viscous.

[@himanshu.g345]

+jibeneyto so with change of airfoil will it work?

[@Appletank8]

HIMANSHU GIRDHAR Basically, the way fluids behave small scale do not scale up linearly. You need to know the Reynolds number in order to determine how your airfoil will behave.

[@kennethhawley1063]

Nobody told the birds about Reynolds numbers.

[@SladkaPritomnost]

@@kennethhawley1063 TOP comment :)

[@adrians5083]

I knew this when I was 9 years old this is over 35 years ago where are you heading ?

[@jurgenblick5491]

I like active wings