Aileron Span

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GESchwarz

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Why is it that so many planes have aileron that do not extend all the way to the tip, rather, they stop where the full-chord fiberglass wingtip starts? Is it just cheaper and easier to make a one-piece, full-chord wingtip?
 

Norman

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There's a profile drag penalty for running the ailerons clear to the tip but there's an induced drag bonus so it's 6 of one and 1/2 a dozen of the other. Either way the aileron's affect on drag only happens during roll maneuvers. If you want fancy wing tips they might interfere with the hinge.
 

Topaz

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The last few inches of aileron, if it extended to the tip, would be entirely ineffective. You'd get nothing for the extra weight of hinge, etc. Any pressure differentials would simply spill over the tip.
 

BBerson

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An aileron at extreme tip will be damaged in a wing tip dragging event.
Some say a tip aileron is susceptible to flutter. I don't know why.
 

jeanray

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Ailerons at extreme tip will tend to induce "control inversion" if the wing is too flexible: lifting the left aileron (left bank) causes the wing to "flex" counterclockwise, making the leading edge higher... and causing the same effect as an aileron... going down, resulting in an unwanted right bank. Aircrafts with high aspect ratio (long and thin wings) are susceptible to that effect, even at relatively small airspeeds. This phenomenon was discovered during the first flights tests of jets, and was thought to only happen when passing the sound barrier, until manufacturers of large people carrier aircrafts developed thinner wings over large wingspans: the phenomenon can happen at pretty slow airspeeds. To counter that effect, large aircrafts (Boeing etc), have a "secondary" aileron, set between the flaps and the aircraft body (that is: where the wing does not twist!), and these secondary ailerons take priority (under the control of the on-board computer, of course).
 

Norman

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The last few inches of aileron, if it extended to the tip, would be entirely ineffective. You'd get nothing for the extra weight of hinge, etc. Any pressure differentials would simply spill over the tip.
The pressure differential starts to equalize at the end of the aileron so if it ends a foot from the wing tip a vortex starts in the gap and you do lose some span efficiency because of it. All the potential problems mentioned, except sticking the wing tip in the dirt, are design issues and not hard deal with.
 

Topaz

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The pressure differential starts to equalize at the end of the aileron so if it ends a foot from the wing tip a vortex starts in the gap and you do lose some span efficiency because of it. All the potential problems mentioned, except sticking the wing tip in the dirt, are design issues and not hard deal with.
Can't be too bad an effect, in the scheme of things. All modern competition sailplanes end the aileron inboard of the tip. It may well be an issue of preventing the "down" aileron from dragging in the dirt, however.
 

autoreply

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Can't be too bad an effect, in the scheme of things. All modern competition sailplanes end the aileron inboard of the tip. It may well be an issue of preventing the "down" aileron from dragging in the dirt, however.
Tip stall with an aileron to the tip can get pretty nasty. That's THE reason virtually no plane carries them on to the tip. Not an issue with winglets though.
 
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