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Here's some food for thought for any higher math guys or aero dynamic guys on Tip Vortices

I found this fascinating Maybe a new paradigm for aviation 

 For nearly a century Ludwig Prandtl’s lifting-line theory initially points to the elliptical spanload as the most efficient wing choice, and it has become the standard in aviation. Research in bird flight has increasingly generated data in disagreement with the elliptical spanload. In 1933 Prandtl published a little-known paper presenting a superior spanload. We argue this second spanload is the correct model for bird flight data and we present a unifying theory for superior efficiency and coordinated control in a single solution. Specifically, Prandtl’s second spanload offers the only solution to three aspects of bird flight: how birds are able to turn without a vertical tail; why bird formations have wingtips overlapped; and why narrow wingtips do not wingtip stall. The latest research data from a Fiber Optic Shape Sensing system and a pressure measurement data system were used on the wing, results are shown. For more information on the Prandtl Wing project, please visit https://www.nasa.gov/centers/armstron...

 

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I’ve not watched the second one, but as a comment there is astonishingly little “new” aerodynamics at the sub sonic level, there are different ways of looking at the same data of course.

‘For what its worth the concept of washing a wing out so that at a normal cruise speed the wing tip is producing no lift with the idea of reducing induced drag has been done before, however the additional skin drag of the “extra” wing along with the extra structure weight required to support the otherwise useless wing cancels out the reduced induced drag.

However this seems to be mainly based on the weight reduction of the elimination of the vertical tail, and there may be something to that. 

‘My prediction is that the square cube ratio will “get” them and when scaled up to practical transport category sized aircraft the extra wings weight will cancel out any increase in efficiency.

 

The Gurney flap is the only real “new” aerodynamics I know of, and of course to look at it, it doesn’t look aerodynamic at all.

 

Edited by A64Pilot
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On 4/5/2021 at 11:05 PM, carusoam said:

Interesting tiny sensors being used...   trying to avoid Schrödinger’s cat in the trunk arguments... :)

Is this the same Prandtl?

https://en.wikipedia.org/wiki/Prandtl_number

I’ll be back... it got late on the East coast...

Best regards,

-a-

Same guy, he's all over fluid mechanics.   He designed the wind tunnels that were used by Germany, Japan, and the U.S. to design and test their WWII fighters.  Probably safe to say that nobody since has had such a large singular effect on aerodynamics.

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4 hours ago, A64Pilot said:

For what its worth the concept of washing a wing out so that at a normal cruise speed the wing tip is producing no lift with the idea of reducing induced drag has been done before, however the additional skin drag of the “extra” wing along with the extra structure weight required to support the otherwise useless wing cancels out the reduced induced drag.

I think what he is promoting is using the higher washout to produce a vector FWD so as to eliminate adverse yaw (especially in a flying wing).  His models have been instrumented for years and he has gathered data to indicate such an outcome. Eliminate the adverse yaw and tip drag panels are not needed (weight savings) and the entire tail is superfluous. 

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There is no free lunch, so a winglet shifts the lift vector forward and develops thrust, but not more thrust than there is drag, so it’s a reduction in drag, but the drag still exceeds the thrust, other wise it’s a perpetual motion machine :)

‘Of course a winglet works better at high angles of attack, so on a GA airplane like ours there is only added weight and drag as we don’t fly in cruise at high angles of attack.

‘I know we aren’t talking specifically about winglets, but in truth we are, as he said, take a winglet 1/3 wingspan and lay it flat.

‘To make his proposition most useful, you dump the fuselage, maybe have a blended body like a B-2, but no tubular fuselage like we are used to, and no rudder. he didn’t say no tail. but i’d suspect that’s the eventual end.

Who knows, maybe we will live to see one, and maybe we will live to see average people flying above Mach 1, it could happen, but I don't think so.

I’m surprised Gulfstream didn’t build a Supersonic “business” jet years ago, I know they were working on one, the lead Engineer died in a crash at Sun-N-Fun years ago, I know nothing about the crash though, just that it occurred.

On edit, easier to find than I thought.

https://www.wtoc.com/story/8160702/fl-plane-crash-kills-gulfstream-employee/

Edited by A64Pilot
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His models flown with data recording show a trust vector fwd INSTEAD of a drag vector from adverse yaw.

Granted no free lunch but it seems the "winglets" remove the adverse yaw and its intendant rudder drag.

His theory is that one can have a flying wing without adverse yaw in roll. maybe one "drag" polar replaces another but no adverse yaw is a move fwd in aerodynamics. He uses a lot of observational studies from birds in his research (overlapping wings in formation cruise to get the correct length of the outboard "winglets" etc.  I have read a lot of his studies Its very interesting stuff. 

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  • 2 weeks later...

Here's an English translation of the paper by Prandtl that the video presenter says motivated his thinking.   I'm pretty sure that Prandtl was an alien. This paper is super cool.  The simultaneous translation is really fun.  The translation "tapered wing" is assumed to come from "spitzendigen Flügel"

The trick here is that the outer bit (< 5%) the wing has 0 angle of attack (alpha) and therefore generates no lift.   It kills the tip vortex much more effectively than any winglet.  Of course running part of a wing at 0 alpha is muy peligroso.   If a rigid airfoil and designed for 0 alpha in cruise, it would develop negative alpha in a descent. :o  So, for any of this work, one needs a variable geometry wing, like a bird's wing.

I'm going to leave this up for only a while.  I could get my hand slapped for posting copyrighted material.  I'm just sharing with a few "colleagues" in this thread.  Enjoy.

Fred

 

Prandtl_Smallest_Induced_Drag_Via_Airfoil_1933(English).pdf

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HUH?   Well you got me buried about the second equation

Remember I'm trig and a little more it was my neighbor who had the math PhD :-)

I think I understand your thoughts on zero angle of attack but in the flying wing glider example the "0" or even negative angles were constrained to the out 1/3 IIRC to eliminate adverse yaw tendencies allowing no vertical surface or drag rudders

The study I was following was limited to flying wings IIRC again

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16 hours ago, 0TreeLemur said:

If a rigid airfoil and designed for 0 alpha in cruise, it would develop negative alpha in a descent. :o 

Why? In unaccelerated flight, Lift = Weight. If lift and airspeed are constant then alpha must be constant. Doesn't matter if you are climbing, descending or flying level.:)

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11 hours ago, PT20J said:

Why? In unaccelerated flight, Lift = Weight. If lift and airspeed are constant then alpha must be constant. Doesn't matter if you are climbing, descending or flying level.:)

Because lift is strongly a function of angle of attack, a transition to descent like a cruise descent (downward acceleration) can start with a decrease in alpha.  If alpha=0 and lift=0 near the end of this wing at cruise, then in a transition to a cruise descent the wing tip creates negative lift, and could set up flutter or other ugliness depending on the structural characteristics of the wing.

I could have been more specific.

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What the paper seems to say is that if you constrain the design to a specific weight and wingspan, then the elliptic lift distribution is optimal. If instead you relax the wingspan requirement taking into account that increasing spans have lower drag but more structural weight, there will be an optimum wingspan and it will have a lift distribution other than elliptical. It makes sense that birds would have evolved in such a manner.

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12 hours ago, 0TreeLemur said:

Because lift is strongly a function of angle of attack, a transition to descent like a cruise descent (downward acceleration) can start with a decrease in alpha.  If alpha=0 and lift=0 near the end of this wing at cruise, then in a transition to a cruise descent the wing tip creates negative lift, and could set up flutter or other ugliness depending on the structural characteristics of the wing.

I could have been more specific.

OK, now I better understand your point. But don't forget that a cambered airfoil generates lift at zero angle of attack.

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There are other ways to deal with adverse yaw other than a rudder, fries ailerons, spoilers, and simple drag devices like most flying wings, not sure if they should be called spilt ailerons or not.

Adverse yaw really isn’t much of a problem for an aircraft efficiency wise, because how much time does one spend turning? If it were I’d assume multi engine transport category aircraft would use asymmetric thrust as opposed to opposite rudder, and I don’t think they do?

But there is a lot more to a rudder than adverse yaw correction, try a crosswind landing without one for instance, or how good is yaw stability without one? Ask a Bonanza pilot how well an aircraft with less than optimum size of rudder flies in turbulence.

Plus an airfoil at zero lift still has drag, that rudder we seem to want to get rid of for instance.

‘It’s all interesting of course, back in the I guess it was early 70’s and I was young, if you had asked me I would have told you that within 10 years that Canards would become the dominant design, as. they were clearly more efficient, but other than the Beech Starship, what happened with Canards?

Beech got rid of the Starship for reasons other than it being a Canard I believe, not so sure I buy the avionics being it either.

You can take a standard aircraft and with aileron rigging wash out the end of the wing and likely get close to zero lift in cruise for the last few feet.

I know a crop duster with its ailerons deflected up a few degrees is lighter in roll and has a quicker response and faster roll rate, and if they are deflected down a few degrees the opposite is true.

 

So what I’m saying is this is interesting, I would expect to see it applied to ultra high performance sailplanes etc, but wouldn’t expect it to become mainstream

Edited by A64Pilot
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7 hours ago, PT20J said:

OK, now I better understand your point. But don't forget that a cambered airfoil generates lift at zero angle of attack.

Yes, very true.  The Prandtl optimal airfoil with minimum induced drag has no circulation at the tip, therefore ideally a symmetric airfoil that automagically maintains 0 AOA.  Hence the need for a variable geometry airfoil near the tip- like a bird.  A dynamic wing section.   They left that part off our Mooneys!

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There is no magic here, and this isn't really newly discovered information. Five minutes with Google turned up additional, later references. Attached is a NACA paper from 1950. Quoting from that paper, the key idea is:

"The foregoing calculations show, as was to be expected, that the elliptic loading yields a smaller drag than any of the others within a restricted span. However, if the restriction on the span is removed, still lower values of the induced drag can be obtained without any increase in the bending moment at the wing root. The lower values are obtained by permitting the span to increase and at the same time adopting a more tapered form of the loading curve." and further "It will be noted that a 15-percent reduction in induced drag below that for elliptical loading can be achieved with a 15-percent increase in span."

So, it is not simply altering the wing tips, but rather the combination of increasing span and changing the wing in such a way as to more rapidly decrease the lift toward the tips that results in the reduced drag.

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19760012005.pdf

 

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Nothing new here.  Al has been giving this talk for years (decades?) at the Western Soaring event in Tehachapi.   Adverse yaw is trivial in the grand scheme of drag.  I'm still looking for that rudderless, high thrust, multi-engine bird.  The Citation X wing is designed similarly (30 years ago).  It is very much a point designed airplane,  ... then they went and added a winglet (no comment).

@A64PilotCanards are terribly INEFFICIENT.  One needs to look further than the surface of one portion of the balance equation.  Yes, in a canard, both surfaces are lifting, but that is ignoring a lot of other downsides.  The downwash off the canard affects only the inboard section of the main wing ... and each flight condition produces a different downwash.  As a result, the main wing inboard section needs to be of variable incidence :)) ... while not changing the outboard section.  All takeoff and landing performance is based on stall speed.  Canards have higher stall speeds because the small wing (canard) is maximized at the expense of the main wing (which should not stall).  Inboard DOWNload on the main wing of the Starship is near 1000 lbs. in cruise.  CG loading is also much more difficult in a canard.

There are a good reasons why the King Air is still in production and the Starships have been destroyed.

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Ah, but when they were first introduced they were the cats meow.

Just like this, to implement this is going to require a much longer wingspan, which will require a much stronger wing, which will be way more expensive  and heavier, lots heavier 

Stsrship died for many reasons but chief among them was they were their own competition, and they were making more money from the King Air.

Starship paved the way for Certified composite airframes, the FAA was of course the biggest hurdle because they didn’t want to deal with it, look at the Lear Fan.

Did Beech have ODA then, and or do they now?

The funny thing about Starship is way more than normal it brings out way so much emotion in people, even what 40 years later?

Canards are in my opinion a lot like flying wings, if you ignore the downsides to the design, they seem to have enormous advantages.

That is why I said in the 70’s it seemed that most new designs would be canards, because in the beginning only the advantages were written about.

There is a reason why all transport category aircraft have the same design, and it’s not inertia.

‘Although I think we have pushed that design about as far as it can be, there will continue to be advances, but they will be small incremental ones

 

There is a lot that can be done with little airplanes, but the market is dead, and I can’t explain Cirrus because that shows there is still a market

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5 hours ago, A64Pilot said:

1. Ah, but when they were first introduced they were the cats meow.

2. Starship died for many reasons but chief among them was they were their own competition, and they were making more money from the King Air.  Starship paved the way for Certified composite airframes, the FAA was of course the biggest hurdle because they didn’t want to deal with it, look at the Lear Fan.

3. Did Beech have ODA then, and or do they now?

4. There is a lot that can be done with little airplanes, but the market is dead, and I can’t explain Cirrus because that shows there is still a market

1. When they were first introduced people listened to all the hype (one-sided ... not telling the whole story).  Yes, an 85% scale Starship (72% drag) will meet performance numbers when full size engines are ,used.

2. Although the Starship was originally intended to replace the King Air, it couldn't compete (for many, many reasons ... most of them performance related).  King Airs are just efficient flying machines.  There are good reasons that there aren't composite airplanes all over the place.  They are heavy and expensive.  Cirrus sells chute.  BTW, good OEMs outdate their own airplanes every 8 years or so.

3. Beech had ODA then, before they went bankrupt and now under Textron Aviation.  

4. There is no new airplane market because OEMs won't look for new cheese ... or at cost effective prices.  The 70s market was ... well ... 50 years ago.  Different times, different manufacturing cost structure and different labor costs.

There are new airplane markets.

1B. The same is true for the new $$BB Uber Elevate market.  Great idea, but no physics has been looked at.  A helicopter that takes 150 HP takes 150 HP to operate - gas powered, electric powered, hydrogen powered, etc.  Making the disc loading higher INCREASES noise and decreases efficiency.  Go figure :) 

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1 hour ago, Blue on Top said:

There are good reasons that there aren't composite airplanes all over the place.

Unless you count airliners and military aircraft, then they're all over the place and have been for a long time.   Fiberglass was pretty much developed for airborne radomes in WWII.

 

 

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I agree about the composites, there are huge issues with inspection and repair, metal is just so easy in comparison, to say nothing with UV resistance and high cycle fatigue, on and on.

You can literally crack an airframe or dimple it if it’s metal, bang it out and rivet a doubler in, composite not so much. Even something as simple as stripping to repaint may take on a whole new meaning 

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The weight penalties of composites have been showing for a while....

In other markets such as automotive...

1) Fiberglass cars... one: Corvette...  not known for being very light at all...

2) Composite cars... one family: Saturn... not known for being successful after 2008...

2.5) Anyone remember the Pontiac Fiero.... heavy, underpowered, composite covered, over steel structure...

3) They were only surfaces, supported by steel substructures...

4) Interesting materials being used lately.... Lots of aluminum being intricately formed for large Sport Ute parts... like Ford’s expedition (hood and tailgate) and the F150 got an aluminum bed....

 

So... aluminum shaping is getting much better... not quite as good as what composites can do... but much better than 1970.

Pp thoughts only...

Best regards,

-a-

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