chrome350

My Feedback: (66)

Hi Reza,
I have an 86" Yak that I have just started putting togther. I have noticed that both ailerons are warped upward at the wing tips. Someone had mentioned to me that the ailerons might be that way on purpose to create wash-out. I have never heard of that being done on an ARF. If they are not supposed to be that way, any suggestion on how to straighten them out?


Thanks,
Larry

dmccormick001

I'll give you the best explaination I can give you, but there are probably some guys here who can correct it or do much better.

Washout can't be created by the ailerons, it must be created by the wingtips. It is a function of the leading edge of a wing, not the trailing edge. Washout is a term used to describe the difference in the incidence of the tip of the wing as compared to the root of the wing, where the wing meets the fuselage. In case you are unfamiliar with the term, "incidence" is the angle at which the leading edge of a wing meets or "attacks" the air, as compared to that of the horizontal stabilizer. Most wings have either 0 degrees of incidence designed into them, or something between a fraction of a degree and a couple of degrees of positive incidence built into them. This helps the wing fly and create lift. If a wing has washout in it, then the wing tip will have slightly more positive incidence built into it than the root of the wing, and this is done to prevent the wing tip from stalling before the rest of the wing stalls. If the tip of a wing stalls before the rest of it does, and before the opposite wing stalls, then that wing tip (right or left) will suddenly stop flying, and the result will be that the plane suddenly rolls over (or "snaps" ) onto that side, sometimes rolling completely over onto it's top, and it's hard not to lose the plane completely if/when it does. That's the dreaded "tip stall". Of course a plane only stalls when it is flying slow, so that means tip stalls usually happen when you're setting up to land, and are low and slow, and so you have little or no time and no altitude in which to recover. I check every warbird I have, no matter if it's a kit built or an ARF, to make sure it has a little bit of washout in the wings. If a wing gets warped so that you have negative washout in the wings, it can be a monster to fly no matter how good you may be.

To check your plane, you'll need an incidence meter, and to correct a wing with negative washout, or to add some positive washout if you want to, you'll need a heat gun. Hold the wing secure in a rack, or get someone to help you hold it, and twist the wing in the direction it needs to go while heating the covering with the heat gun. Heat it on both sides, and as the covering cools off and shrinks back, it will hold the wing/wingtip in the corrected position. Move it a little at a time until you get it where you want it.

If your ailerons are just warped, do the same thing. Hold them on one end and twist the other end while you heat the covering. It will cool and hold them in the new position. You'll be surprised how much twist or warp you can remove from a wing just by heating the covering while you twist the frame into the right position.

Rezagh

My Feedback: (73)

That is exactly right! It is really easy to do as well. Thanks for taking time and helping out!