National Aeronca Association Bulletin Board

Am restoring a Chief. Even after careful shrinking of the wing fabric, I still managed to warp the root ribs between the trailing edge and rear spar. They really need some sort of brace there but it has to clear the aileron cables. Has anybody dealt with this and is it legal? Thanks, John

I never realized how much strength the fabric has when you're tightening it. The butt rib is pretty husky but I managed to distort it too. This is my first set of wings so I'm still 'winging it' . Guess I don't understand the rational as the STC holder (Superflite in my case but it could be anyone using the ceconite process) tells you to "take it up to the final temperature of 350 degrees or you'll have loose fabric when it's damp". So like a leming I do exactly what they say. Hopefully I'll be a lot smarter on the second wing and watch things closer (Am I missing something???).

MikeB

With unshrunk Dacron fabric (ceonite, polyfiber, superflight, airtex); you have to heat set the fabric to stabilize the weave. If you don't get ALL the fabric to 350*F, when the tempurature changes, so will the fabric.

If you have a known area of concern, like the butt rib, pinch a little extra fabric in the open span so it doesn't pull as hard when shrunk to 350*F.

Remember; Dacron shrinks 5% equally (north/south/east/west) at 250*F and 10% at 350*F.
example: 6' cord with a 16' span will shrink 6" in the direction of the Cord and 19" through the span.

nkh

Thanks for the responses. I think on my next wing I may try installing a diagonal brace to the spar, one on the top and one on the bottom of the rib. I just don't know if it is legal since one would have install screws in the spar. Another idea I had was to brace to brace the rib on the outside before the fabric shrinking and then remove it after shrinking. What are your thoughts?

John,
I think the outside support makes more sense (in my humble opiniion). Also, like Nathan says, I guess it's best to leave a little extra fabric (loose) in the root area. I probably had mine too tight to begin with. The question would be "how much??". Mine was compounded because I have a 5 gallon fuel tank in that area and as the root rib moved inward it also pushed against the plywood base which moved the second rib over about 1/4 inch (which didn't make me happy ).

MikeB

You might get Bill Pancake's thoughts on this. At his shop I saw a root rib with some reinforcing angles riveted in place in critical areas. Surely he'll have a presentation at Oshkosh and someone might ask him about this area. jrh

John, I do have an answer for you. But I don't have any documentation to prove it. My airplane(7AC-564), is an early one. These braces were on it from new. But, no blueprints or anything show them. Bill Pancake might have some info. I can measure them in a few days if you need. Hope this helps. David J.

Thank you! These braces are exactly what is needed but it doesn't show them on the wing drawing. I know you said they were original but I think they might be homemade. I have never seen them on any other wing. John

John, I do think the are factory made. Look at the ends next to the spars in the first photo. The second photo shows ends next to the spars that we made to repair damage. Look how square and mitered the top ends are. Just my opinion. Remember my production date is 1/11/46. Lots of changes made during the production run. We have found other things changed but not noted on the prints. Like 3/4" bushings changed to 7/8" bushings. David J.

David,
Looks like an answer but I don't believe you could put wing tanks in with those braces. Of course the early 7AC's didn't have wing tanks so the point is 'mote'.

MikeB
(who is sitting in a motel in Greybull, Wyoming and a long way from his L16 project)