Flap twist

cnpeters · #1 08-04-2007, 08:47 PM

I noticed 3/16-4/16" of twist in my left RV-9A flap that is almost finished (TE to be riveted still). Is this considered acceptable or should I try and fix it? The plan would be to drill out the lower skin to spar rivets, flatten the flap, and reset them. I am not too keen on this as I may enlarge the holes a little from drilling out. Some are already oversized a little from the countersinking. Thoughts?
Thanks.

alpinelakespilot2000 · #2 08-04-2007, 10:27 PM

I asked Van's this question as well. One of mine has about 1/4" of twist. (My only control surface with any twist!

) Ken S. said that 1/4" over 8 foot of flap was probably nothing to worry about. He said only flight testing would determine if it might cause a heavy wing. The problem remains though that now my flap and aileron don't line up when the flap is all the way up. It bugs the heck out of me. Not sure whether I'll rebuild or try to fix it, but I'll probably at least take a stab and drilling out all the trailing edge rivets (and removing proseal) and giving it a shot. Please let me know if you hear anything from Van's or from elsewhere. Good luck.

yakdriver · #3 08-05-2007, 01:55 PM

If you want a fast airplane do everything you can to build it straight in the first place. Anytime you have to add a trim tab or adjust a control surface causes drag. Also you can only trim it for a certain speed mostly cruise. It will fly straight in cruise but not at other airspeeds. I fly a friend's 6A that has a trim tab under the left aileron and it flys level at cruise but rolls of to the right at lower speeds. It is quite a bit slower than another friend's 6A with the same engine and horsepower. It also has a pretty sharp wing drop at stall. Don

cnpeters · #4 08-05-2007, 08:08 PM

Thanks, guys. Interestingly, this twist was not locked in. I still had to rivet the TE, so I weighted the heck out of the flap (2X4's, 8 bricks, 2 cleco bins) to flatten it, riveted the TE, and now the twist is just a little less than 1/ 8". I'll accept that for an 8 foot flap!! As a bonus, the TE was dead straight. So, as a lesson, if someone hasn't riveted the TE yet, it is still possible to straighten this a bit.

alpinelakespilot2000 · #5 08-05-2007, 11:24 PM

Quote:

Originally Posted by cnpeters

Thanks, guys. Interestingly, this twist was not locked in. I still had to rivet the TE, so I weighted the heck out of the flap (2X4's, 8 bricks, 2 cleco bins) to flatten it, riveted the TE, and now the twist is just a little less than 1/ 8". I'll accept that for an 8 foot flap!! As a bonus, the TE was dead straight. So, as a lesson, if someone hasn't riveted the TE yet, it is still possible to straighten this a bit.

Carl-
Thanks for the update. Sounds like mine might be fixable if I can drill apart the trailing edge. When you weighted in down, did you weight it down flat or did you overcompensate and twist it a little bit opposite direction while you riveted?