How to build flex wing

[hardingfv32]

So exactly how do you build flex wings? Lets go beyond the normal "laminate orientation" answer.

First, let us assume that the bending is not linear or maybe has a knee in the curve just after test range.

Can a laminate design create non linear strength? Roughly how would this be accomplished?

Could there be something physical in the structure that could meet our goal? Some way to change the strength of a truss to be non-linear also repeatable?

Brian

[sm68]

I recently asked a top composites engineer at a F1 team (one that has won multiple world championships) just this question. He said he did not know how it could be done. He thought that it might be possible to arrange for a wing to buckle in a controlled fashion above some critical load but that it would be very difficult.

[hardingfv32]

I have thought about a truss/beam that buckles. How or why does it return to an un-buckled condition?

Brian

[marcush.]

I think you could build a spar and ribs wing up to the point where they apply the testload and just reduce or even omit the inside structure outwards of the test load point.this would effectively let the endplates and outer section of the wing bend down quite easily and through the connection of the flaps it would tension and bow the whole wing into an arc..On the slow motion footage you can see that most wings are still quite stiff at the leading edge and bend down more at the trailing edge..to me this reduces the AoA and any gain coming from getting the wing closer to the ground is eaten up by this loss.Only the RedBull wing seems to bend as a whole .

[marekk]

It's probably relatively easy to design and build wing flexing under static load, but aero forces are far from static, and the key IMO is to understand fully the interaction between aero and structural forces.
Not an easy task by any means, and if you add rotating tyres and ride height change to the eqaution it starts to become real brain braker.

[hardingfv32]

Ok, if it easier we will restate the problem as: How to build a flexing wing that has a non linear flex rate when acted upon by a linear increasing load. Make it a mechanical test. Purely a structural problem, no aero.

This is a narrow focused thread. There are other treads that discuss the other things that might be happening with the general subject of perceived wing flex.

Brian

[mep]

It's interesting that the wing doesn't start to oscillate. I really wonder how they prevent that.

[PhillipM]

I have thought about a truss/beam that buckles. How or why does it return to an un-buckled condition?

Brian

Make it like a diagphram spring, curved one way and preloaded to pass the tests, once on track and past a certain force the curved laminate springs go over centre and instead of lifting the wing attempt to force it down, effectively reducing the spring rate of the outer elements. You've also built a little hysterisis into the system then so it doesn't bounce like a pogo spring around the area where it flicks over centre.

[Richard]

Brian, so you are excluding a scenario where the test load is not in the same place as the aero load, and you are only considering vertical loads?

[hardingfv32]

Yes, no twisting, just a simple vertical load with no aero influences.

Brian

[hardingfv32]

Will a diaphragm spring return after it goes over center?

Brian

[shelly]

Good reference here:

http://www.mcajournal.org/volume6/vol6no1p67.pdf

shows that orthotropic beam behaves differently form isotropic beam when loaded with a distributed load

[hardingfv32]

This is well known. Now how do we get a non-linear response in a beam from a linear load application?

Brian

[Tim.Wright]

This was my suggestion from the flexi wings thread;

[Muulka]

You mentioned non-linear flexing. I'm pretty sure that that's impossible, if the wing is to return to its original shape- see Hooke's Law:

The extension of a body is directly proportional to the load applied, provided that the elastic limit has not been exceeded.

This applies to stretching, and flexing is stretching more on one side, surely...