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In some aircraft which have large wing deflection due to bending, do ailerons or flaps not get stuck or bent themselves? In the case where hinging axis is also bent how do ailerons operate?

enter image description here

Mridul
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    I know aircraft wings are flexible, but that's... Wow... – FreeMan Jan 17 '22 at 17:51
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    Part of the answer is visible in the photo-- – quiet flyer Jan 17 '22 at 18:17
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    Here's a few more wings, some bent much more than that. https://www.popularmechanics.com/flight/g2428/7-airplane-wing-stress-tests/ – Camille Goudeseune Jan 17 '22 at 21:02
  • Re above comment-- re the last example, "Boeing 787 Passes Incredible Wing Flex Test -- Boeing has completed one of the more spectacular tests of the 787 Dreamliner program. The airplane maker completed the “ultimate-load wing-up bending test” on Sunday using airframe ZY997, the test aircraft that is basically built to be tortured on the ground and never fly. During the test, the wings on the 787 were flexed upward […] "-- if it was never going to fly, why did they finish the fuselage in such detail? Could make for another ASE question-- – quiet flyer Jan 17 '22 at 21:32
  • And not sure any of these examples are "bent much more than" wings of glider in photo in this question-- – quiet flyer Jan 17 '22 at 21:35
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    @CamilleGoudeseune Those wings cheat - they use hydraulics and electric motors for aileron movement. Glider wings do it properly, with pushrods between aileron and stick. – Peter Kämpf Jan 17 '22 at 21:35
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    @quietflyer, the airframe is used for a whole lot of different tests, so it makes sense to build a complete one. – Mark Jan 18 '22 at 00:26

1 Answers1

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Flaps and ailerons are weak in bending and have multiple hinges along the span. Also, as you can see in the photo, the flaps are segmented which not only helps to optimize the deflection angle over span but also limits any sideways offset of the hinge points due to bending. Using only glassfiber or aramid fiber for the flaps makes them very flexible so they easily follow the bending of the wing.

Flexible flaps are also torsionally flexible. This necessitates to distribute the mass balance along the span which is normally achieved by glueing a brass rod to the forward edge of the flap which reaches into the flap cutout of the wing.

The control surfaces are connected with pushrods. Those are segmented as well and have ball joint swivel bearings between them to allow for some misalignment. The joint is held in place by a swiveling buckling support; in the sketch below (own work) it is attached with its hinge point at the lower wing skin; it could as well be placed horizontally in the wing and be supported at the spar web.

buckling supports for wing pushrods

If you follow the deformation of the wing, you will see that in this example the pushrods sit near the upper surface of the wing. This will make them relatively longer when the wing structure deforms in upward bending, and will create a negative aileron deflection (trailing edge up), which reduces lift on the outer wing and reduces bending. The linkage can, therefore, be used to limit loads and dampen the bending motion.

The design has to account for the maximum possible elastic deformation and for differences in thermal expansion between structure and linkage.

Peter Kämpf
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  • Thank you for answering and brilliant sketches sir. Another question I have now is when the hinge axis is curved does it cause problems? I think aileron travel should be affected when the whole wing is curved like that – Mridul Jan 19 '22 at 17:47
  • @Mridul I expanded the answer. – Peter Kämpf Jan 19 '22 at 17:57