National Aeronca Association Bulletin Board

I have a good friend who lives in Merritt Island, Florida. Matt is restoring his 7AC Champ. We were discussing how to attach the fabric over his wing ribs today. He prefers rib stitching over rivets or pk screws. I tend to be neutral here, but only have experience with Cubs. So, I told him I'd ask you guys your opinion. So guys, what do you like, and what works best for the long run?

Mike

I don't think it's legal to rib stich a champ. Besides, the cubs and other aircraft have beveled edges on the ribs to allow for stitching. The champs do not. Very sharp edges. It wouldn't take too long to start cutting the stitching where it goes around the flange. PK screws. It doesn't take that long. When you are ready to put the screws in, put a bright light under the wing and you can see the holes very well.

We've had this discussion a couple times but nothing definite (in my eye's ) has come to light. The 7AC manual only discusses PK screws, but I'm of the opinion you could stich if you protect the cord. Either smooth the edges of the rib or put a piece of anti-chafe tape on the capstrip folded over.

I got jumped in an earlier thread because I like the idea of Stiching. There's an L-16 getting restored at the next airport over and he stiched the wings. When it comes down to it, I bet none of the FAA locals would know the differemce. So you'd only have to fool the other Aeronca owners!

nkh

Jody Wittmeyer wrote:I don't think it's legal to rib stich a champ. Besides, the cubs and other aircraft have beveled edges on the ribs to allow for stitching. The champs do not. Very sharp edges. It wouldn't take too long to start cutting the stitching where it goes around the flange. PK screws. It doesn't take that long. When you are ready to put the screws in, put a bright light under the wing and you can see the holes very well.

How about the Martin clip wire, can it be used on a Champ?

Robert

I would have to do some checking. They were used on some pre wars.

I looked at a Champ from Minnesota at a local fly in once that was rib stitched. He said he had a form 337 on it although I never saw the actual paperwork . I agree with Jody though as the Champ ribs are pretty sharp. Nothing wrong with PK screw either other than they leave a little more 'hump". I'd want to be awful sure it was 'legal' before I stitched the wings as it would be a big job to correct should the "powers that be" so order.
Mike

How about wood ribs to go with wood spars like the prewar Chiefs? We were kicking it around the other day since we just finished rebuilding a prewar chief wing for a friend. Spars, ribs, wing tip bow--you name it.

Doug

I believe the Service manual calls out PK screws or Martin clip. The object is to secure the fabric to the ribs. If someone rib stitches the wing I wouldn't see a problem with it. If during the inspection I found broken stitches, than a repair would need to be made.
Paul

I used low profile alum. rivets, as does a very well informed aeronca gent in W. VA. does. I used a pnue. riveter I obtained from Harbor Freight at a reasonable price, I've rib stiched, and used PK screws before, but the rivets were the fast'st & easy'st for me, and they don't leave as big a bump as the PK's. Jack

I know a Champ owner who rib-stitched the wings 10 years and 400 hours ago. He still owns the plane and there have been zero problems or issues.
He protected sharp edges with anti-chafe tape. The pre-war Chiefs with wooden ribs were rib-stitched. Obviously, Aeronca went to the #4-40 screws to attach fabric to aluminum ribs for improved productivity . This is fine for initial assembly, but not so good when the holes strip thereafter. Also, with rib stitching, taping is easier and drag is reduced.

I'm confused . Help me out here. As much as I'd like to use pop rivets on the wings, mostly because a lot of the holes are 'wallowed' out, I thought rivets weren't approved because of the rib size on the old Champ ribs. Is there a STC or PMA to use a special (probably smaller) pop rivet? Pop rivets would beat the heck out of both rib stitching and/or PK screws.
I know the new ribs I got from Wag Aero are made for pop rivets but I don't want to replace all the ribs either and I'm not quite to assembling the wing yet but it doesn't hurt to look ahead either.


Mike Berg

Mike,
There is a STC for the rivets, SA4760NM calls for a Marson Klick-fast rivet.
I think the edge distance is the problem for using the Citabria rivets. While this is a poor practice and will cause rib damage in the future, I don't remember anything directly prohibiting it.
Paul

Use a ball peen hammer and bucking bar to go over the screw holes and it not only closes them up some, but the fabric won't catch on them when shrinking.

Disclaimer: might be an STC, but not that I have seen

Rib stitchng is not approved. I generally agree with the above; you should have a beveled edge for a stitch. Although with tough 'plastic' stings of today, it might not matter for 25+ years.

1/8" pops or any rivit that size is not approved on wings that used the PK screws before. If they are approved, they shouldn't be. You need either a bigger flange (which they did not change) or thicker material (which they went to .032 ribs). Othwerwise the attachment strength is significantly less than the PK screw was. Champion did the testing on this in the 60's when they wanted to transition.

I was looking at a 7GCBC that needed recovering last fall, because someone decided to rib stitch the wings. Over time the rib cord was cut by the ribs and fabric lifted from the wing enough to cause serious flying problems for the pilot on a low level flight in rough air. He landed and sold the plane.
If he had crashed, the Fed's would have had a field day.