When to check for wing twist...

aarvig · #1 12-17-2014, 02:09 PM

The instructions ask us to check the wing for twist after the fuel tank has been cleco'd to the spar and the T912 attach brackets have been drilled to the wing. I am curious...why do the instructions ask us to check for twist now? It seems strange.
The reason I ask is I have one wing that has 1/32nd of twist and the other wing has 3.5-4/32 of twist. No matter what I do, I am unable to work the twist out of the wing, short of pulling it out by the rear spar and clamping it down.
How tight does the measurement have to be and when is it critical to have it right on?

airguy · #2 12-17-2014, 02:14 PM

I remember this point - and I remember that the manual gives you absolutely zero idea about what to do about it, what might cause it, how you might fix it, or how much is too much.

Just check for it. That's all, just check...

cjhammes · #3 12-17-2014, 07:05 PM

1/32 and ~1/8....nice job. Now stop measuring and continue with the build.

bruceh · #4 12-17-2014, 11:16 PM

I recall measuring the wing with plumb bobs in about 10 different directions and could never get everything 100% perfect, but it was always a 1/32" off somewhere.

Build on! Just make it work (to quote Tim Gunn). You might still need an adjustment later with your ailerons or flaps to get it to fly straight.

aeroaddict · #5 12-18-2014, 08:10 AM

Little farther along but same here, I measured and clamped the bottom spar to get close to zero twist. Then riveted on the top skins. Then the instructions state that you can take the wing off of the rack and lay them flat (unsupported) to rivet on the bottom skins. Seemed odd that after all the pain to reduce twist, then you can just lay them down and finish the wing.

I have now installed the aileron and flaps and everything was square and straight upon install.

So I'm not sure why Van's has you check the twist since the bottom skins are installed without and control or restriction for twist. I would do the best you can and build on.

wirejock · #6 12-18-2014, 08:28 AM

Quote:

Originally Posted by aeroaddict

Little farther along but same here, I measured and clamped the bottom spar to get close to zero twist. Then riveted on the top skins. Then the instructions state that you can take the wing off of the rack and lay them flat (unsupported) to rivet on the bottom skins. Seemed odd that after all the pain to reduce twist, then you can just lay them down and finish the wing.

I have now installed the aileron and flaps and everything was square and straight upon install.

So I'm not sure why Van's has you check the twist since the bottom skins are installed without and control or restriction for twist. I would do the best you can and build on.

I left mine in the jigs and checked them every work day, correcting any twist until the bottom skins were riveted.

larrynew · #7 12-18-2014, 08:42 AM

Quote:

Originally Posted by wirejock

I left mine in the jigs and checked them every work day, correcting any twist until the bottom skins were riveted.

I did the same. I found that the order (left to right, top to bottom) you cleco things back together made a difference. I re-clecoed the skins several times until I removed all the twist I could measure.

AF_Alan · #8 12-18-2014, 04:26 PM

I checked for twist when I built the wing stand and again as stated in the instructions after fitting the tanks to the spar. If you don't confirm there is no twist now, it will be much harder to fix after riveting on the leading edge and main skins.

Believe the instructions say less than 3/32" is acceptable. Adjusting (or installing) clamp on rear spar to hold it in position with minimal twist worked for me. As someone else already stated, the order and direction of clecoing the skins (treat it like fabric on an ironing board) might be enough to correct the 1/4" twist.

Good Luck!

jrs14855 · #9 12-18-2014, 07:02 PM

Clecos by themselves do not properly line up rivet holes. For non dimpled holes temporary rivets can be used(not driven) to properly line up the holes while clecoing. For dimpled holes tapered punches(awls)will do a better job as the dimpling process results in a slightly oversize hole. Example: line up the first and third holes with punches, install a cleco in #2. Line up #4 and install cleco in #3.
From the John Thorp School of matched hole "tooling"