Airbus aeroelastic(?) hinged wingtip

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bmcj

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OK, I’ll admit that I haven’t read any details about this yet, but the video says it has benefits such as gust load alleviation. My question is, if it is truly free hinged, how does it contribute any meaningful lift, and how does it alleviate gust loads any better than simply leaving the wingtips off completely?

 

Scheny

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It seems they use the same idea as for semi-rigid helicopter rotors which also have hinges to counteract the load differences experienced through the different speeds for advancing and retreating blade (resulting in different AoA as here by the gusts).

Speaking of the lift, there is the myth about elliptical lift distribution ("the bell"), as Prandtl stated this in his first work. A few years later he corrected this after researching long travelling birds, but the corrected version never got that famous. For the optimum you have to unload the tips, so vortices will move inboard. So, maybe this is following this approach and you have zero lift outside the hinge?
 

flyboy2160

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...if it is truly free hinged, how does it contribute any meaningful lift, and how does it alleviate gust loads any better than simply leaving the wingtips off completely?...
...A few years later he corrected this after researching long travelling birds, but the corrected version never got that famous. For the optimum you have to unload the tips, so vortices will move inboard. ...
I have some other references, but I can't find them now. I'll post them later.

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20160003578.pdf


 
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BBerson

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It seems they use the same idea as for semi-rigid helicopter rotors which also have hinges to counteract the load differences experienced through the different speeds for advancing and retreating blade (resulting in different AoA as here by the gusts).
But rotors use centrifugal force to keep the hinged blades from simply folding upward.
Looks like the floating tip ailerons tested about a century ago.
 
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flyboy2160

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One report online says these are only gust alleviating gadgets, so I'm not sure my 'new! improved!' Prandtl references are worth anything in regard to this.
 

Derswede

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Great...next time I fly commercial, now I will have to explain that the wing is NOT falling off, nor is it flapping...! Coming back from Vietnam a couple of months ago, the guy beside me with the window seat was CONVINCED that the wing was going to fail (we hit some turbulence). The funniest part is that he was a mechanical engineer. We were on a Boeing Dreamliner, he saw how much wing movement there was and got worried. He asked me if I ever worried about it, I just said that as long as I can see wings attached to the airplane, I am OK. Then I messed up and said, That is, as long as the engines are still there and running. Think he got a bit more nervous. Now, with flapping wingtips, half the passengers will be like that.

Derswede
 

Scheny

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Now I had time to watch it thoroughly. It is indeed a Prandtl wing, as he described in 1933. The wingtip vortex is located at the hinge. Prandtl said without a constraint of the span, you should instead make itt 22% longer and save 11% drag. In addition you get proverse yaw (opposite of adverse yaw).

So, the Airbus is really a hybrid between a Prandtl wing and a semi-rigid rotor head. During a gust, it will flex up, therefore lowering span and lift.
 

wsimpso1

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I suspect that these are not free-hinged, but are spring or actuator mounted, and perhaps a combination. There appears to be a spring engaging the last few feet at the hinge. If an actuator is providing the motion, the mechanism gets more complicated, relying upon power, sensors, and algorithms. The FMEA would have to be impressive because malfunctions would reduce aileron function and possibly produce big rolling moments.

There are a number of intended actions:
  • One way is to maintain nominal tip position when load is below some nominal load. As long as the load is below that nominal load, the tip simply adds span, and nominal spanwise lift distribution exists with its nominal shear, bending and torsion curves loading the wing structure and going up and down with g. When wing loading exceeds some limit, the tip lifts out of nominal position;
  • This first method could be designed to work with nothing more sophisticated than springs and a hinge or with sensors, software, and actuators. Smart work would require redundant sensors and a mechanical backup;
  • Another way is a simple spring and all load on the tip will deflect the tip in ratio to the load and spring rate. This would require testing and development, but would be automatic under all conditions;
  • I would have a bunch of concern for flutter contribution...
Depending upon exactly what the direction of the hinge line is, the deflected tip could behave as a winglet, which could keep the spanwise wing loading where it was, or it could unload the outer portion of the wing, reducing the rate at which g's increase the shear, bending moment, and torsion on the inner sections of the wing.

Since a number of folks have talked about this unloading the wing in gusts, I suspect that the hinge line angle is chosen to do the latter, reducing lift outboard of the hinge and making the wing behave more and more like one with a semi span only to the hinge.

Lots of possibilities and pitfalls here...

Billski
 
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flyboy2160

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Mr. Bowers mentions several times that the span is increased with this design. The increased span might cause an airport gate issue unless it's folded at the gate.
 

Sockmonkey

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If the hinges are angled outward slightly, then the tip flexing up would put it at a negative AOA relative to the direction of flight and push the tip back down. Done that way, structurally it acts like a shorter wing while aerodynamically acting like a longer wing.
 
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