Paul Babcock on PA-18 Wing Ass'y

[James L. Smith]

I watched the wing assembly DVD from beginning to end--xlnt. Great points like using bungees to put on your false spar and LE, and getting pre-washout in the leading edge by putting a spacer under the rear spar near the tip. But it doesn't go into stringing the aileron cables. There must be more DVD's to come.

$45 incl shipping from Univair.

Now I'm in a quandary because he says you have to remove everything from the spars and start by marking them for trammeling. I have one wing with Dakota Cub's great ribs already pushed on and don't want to push them back off again. They are tight and I didn't want to press the bushings out of the wing attach fittings. Can't I trammel that wing without removing the ribs? Course, I'll remove them and start over rather than take a risk of doing it wrong.

Thanks from the novice here. But I have restored T-Craft wings.

 

[Steve Pierce]

Put a bolt in the wing attach fitting and mark the front and rear spars at the same location. Now use your trammel points to mark a point about in the center of the next compression strut. Mark the center of the spar at that point. Now do the same thing at each compression strut knowing that the front and rear spar marks are the same distance because you used the trmmel points at the same setting for front and rear. I have had to do this becaue I either forgot to mark the spars or I didn't disassemble the whole wing. Probably not clear but I can take some pictures to clearify.

 

[bob turner]

I thought tramming was done at the compression strut?

A very sharp engineer once asked me why I didn't stretch a string along the forward spar while tramming. Now I never tram without looking for a dead-straight forward spar. Theoretically, once you do one bay, you ought to be able to do the rest using only the string (or laser, if you are a fanatic). I think Piper shows tramming using the little spoke nuts on the wood-spar wing; I think the same thing works on the metal spar wings. Whatever you do, a dead-straight spar is stronger than one with any curve in it.

 

[Steve Pierce]

I use the wing attach bolt holes as a comon point to measure from because it is easier to measure from than the number 1 compression strut.