Form 337's

MikeB · Post by **MikeB** » Fri Aug 07, 2009 15:16

I check Todd's site aeronca.com on a periodic basis and see that Travis Gregory and Fred Larson have submitted their 337's for the installation of the Sky-Tec starter and Odyssy battery. Well written 337's and may help someone else intending to use the Sky-Tech and Odyssy 'total loss' system. Also, just below that, is the 337 I submitted and was approved for installing fabric pop rivets on the .032 ribs (rather than PK screws).

May help someone else out intending to get approval in either case.

MikeB

flyingfool · Post by **flyingfool** » Fri Aug 07, 2009 16:54

Talking with the guys at Stewarts System covering at Oshkosh. They said that they sold an STC for 3/32 pop rivets (along with washers). If I recall correctly they said it was $75.

I do not know if that STC only applied to their system and the price only if you bought their product. But maybe this will help or be a source for people to use if they want to use the pop rivet method.

Between your 337 and the STC this should give people plenty of options.

Do you have any pictures of the finished pop rivet covering? I'd like to see how they look compared to the PK screws. They tell me by the time you get the washer on, there is not that much visuallyl diferent than PK's.

MikeB · Post by **MikeB** » Fri Aug 07, 2009 17:29

I have the wings ready to cover but going to wait until winter to cover them at this point. I'm using the AB42BSLF (large flange) rivets. Basically
the reason being I'm replacing all the ribs and the new ribs (.032) come with 1/8 holes already drilled in the ribs for the certified rivets rather than PK screws. I think the rivets described by Stewart are 3/32 for the lighter (.020 ribs) but I don't have anything against PK screws either.

Mike

DC Krog · Post by **DC Krog** » Sat Aug 08, 2009 07:42

I am curious to the objections to PK screws? I restored my 7AC ten years ago and used 1/4 SS PK screws and thought it was easier (and cheaper) than any other type of fastner for the Champs. I have to admit that removing the old Steel PK screws proved to be a challenge due to some of the screw heads were rusted. That's why I used SS screws to replace them.

The real question is was is the cost differental between 1 Pk screw and 1 pop-rivet in material and labor time.....then multiply by 500 (I can't remember the total amount of screws in both wings and vertical stab.

james gevay · Post by **james gevay** » Sat Aug 08, 2009 10:22

I don't have an issue with the PK screws either.
I didn't think it was difficult to remove them, other than a few rusted ones on the trailing edge. I haven't gotten to the point of recovering, so I'll see how easy it is to install them. There may some small time savings in using pop rivets over screws, but I'm in not that big a hurry.
There's a little over 900 PK screws in the airframe.
The factory way is good enough for me in this case.

Post by **joea** » Sat Aug 08, 2009 11:11

DC,

The other thing is that the ribs were not designed for rib stitching. One edge is sharp enough to cut rib stitching cord and has done so in several cases in the past, with the fabric then ballooning up and making the airplane very difficult to control.

PK screws were what the factory used and personally any airplane I fly will have them holding the fabric on the wing and tail. If someone wants to experiment, then do it on an experimental airplane.

Joe A

MikeB · Post by **MikeB** » Sat Aug 08, 2009 14:03

I think you're missing my point for using the pop rivets. I'm only using them because I wound up replacing all the ribs and the ribs now come at .032 with 1/8 holes for pop rivets (like the Citabria). A #4 screw won't hold in a 1/8 hole so it would be necessary to drill new holes in the ribs to match the #4 screws and you're back to having your new rib looking like swiss cheese unless you flush rivet a small plate under the 1/8 holes like Dave J. did on Lloyd's L16. If I was only replacing a couple of ribs that's probably the route I would have gone, however as long as I was replacing all I decided to bring them up the SL 85 standards. Especially since I was replacing all the spars, ribs, leading edge, new wing tanks, etc. It certainly would have been cheaper to use PK screws and I don't think the pop rivets would be a lot of fun to remove either (drill, drill). Otherwise, PK screws would have been just fine in my book and a lot less hassle trying to get the 337 approved even though it met the standards of SL85. I did look at a Champ the other day which had tip damage and the fabric on the replaced end ribs were held down with wide flange pop rivets for whatever it's worth.

Agree with Joe though, regarding rib stitching. I think the ribs are just too sharp for rib stitch cord, although I have seen it done (with approval).

Mike

james gevay · Post by **james gevay** » Sat Aug 08, 2009 17:39

I understand your reason for using them Mike, and it makes perfectly good sense. But over the years there's been a lot talk from others about rib stitching, Martin clips and pop rivets. I just don't have a problem taking the time to remove them, or install them either. I think it would be a lot easier to remove PK screws for the next owner than drilling out all those pop rivets, which I would hate to do.

I replaced 9 ribs in my left wing and 4 ribs in the right wing and I didn't want to have different bumps under the fabric. So I went ahead and drilled new holes about 3/8" back from the old holes, so I could stay with PK screws. Tedious maybe, but I didn't want to have a mix.
When I talked to Safe Air and Univair about ordering ribs, I asked about ordering ribs without the 1/8" holes, and was told it wasn't possible.

flyingfool · Post by **flyingfool** » Mon Aug 10, 2009 11:18

Wasn't possible?

I don't understand how it is impossible to get a rib undrilled. Expecially if you pay the same price. The manufactuerer would save a step and labor so they'd make more profit.

Not standard and special order maybe. But not possible?????

David Johnson · Post by **David Johnson** » Tue Aug 11, 2009 06:22

I too asked the same question several years ago. Something about the punch dies are already made with the large holes in there. Did not get anywhere either. David J.