Rib Stitching a Champ - Part 2

Jay · Post by **Jay** » Thu Jan 19, 2006 11:48

For those who followed the earlier thread - the definitive answer (at least from the Northwest Mountain Region) is in.

Rib stitching is NOT an approved method of attaching fabric to the wing of a 7AC. The factory approved methods include PK screws or pop-rivets, period. There is an STC allowing the use of the clips as well. There is no basis for approval of any other method at this time.

Should someone wish to persue rib stitching as an alternative method, the FSDO would require approval from the factory or a DER. One issue that would need to be addressed (with perhaps, some legitimacy) would be the issue of the rib stitching chafing against the stamped side of the cap strip. Most other aircraft that use rib stitching provided protection against chafing at the cap strip i.e.; Cub ribs however that protection was not provided by the stamped ribs used on the 7AC.

So there it is. I know that there are some rib stitched Champs out there and as long as they have an approved 337 they are OK untill the next time they get covered. Remember that what was OK last time is not necessarily acceptable the next time and a re-cover is one of those areas.

Post by **joea** » Thu Jan 19, 2006 18:46

Jay,

If someone has a 337 for rib stiching on their Champ/Chief (same wings on both birds) then why would they have to get a new 337 to replace the fabric in the same manner on the same wing on the same airplane?

When you have a 337 to put a wind generator, or tailwheel or larger generator on an airplane you do not have to get a completely new 337 to replace it with a new or overhauled unit of the same type on the same airplane.

Joe A

Paul Agaliotis · Post by **Paul Agaliotis** » Thu Jan 19, 2006 20:08

This just another example of a regulatory body out of control. Their mission statement is for continuious safety improvements. How does this improve safety?
The fabric on an airplane needs to be secured to the structure by an approved/acceptable means. If this is accomplished by whatever system is chosen how does it compromise safety? If ,in this case, the stiching gets abraded or severed by the rib edge the defect will need to be repaired prior to flight.
Many Aeronca,s are rib stiched. The evidence doesn,t favor the FAA,s position. They are simply regulating because they can!
The safest aircraft is the one that doesn,t fly.
Paul

MikeB · Post by **MikeB** » Fri Jan 20, 2006 08:56

I suppose this has been covered before (I seem to remember it). Is there a STC that allows the use of pop rivets instead of PK screws? I thought there was a problem with the width of the Champ/Chief ribs that wouldn't allow the use of pop rivets. It seems the rivets would have much less fabric protrusion on the wing surface, if they are legal. Certainly would be less time consuming than rib stitiching or even working with oversized PK screw holes. I may be covering another set of wings in the near future so it's worth investigating.

Thanks,
Mike Berg

Post by **joea** » Fri Jan 20, 2006 09:08

Mike,

Believe that there is an STC for this but you have to be using ribs of a certain thickness. Evidently the older ribs were thinner and when the newer Champion ribs came along they were thicker. Believe these are legal for pop rivets under this STC but not positive.

JoeA

Jay · Post by **Jay** » Fri Jan 20, 2006 09:43

joea - In answer to your question - because the 337 is not for rib stitching per se, it is for the major alteration (if using a new covering process than was previously on the airplane) or the major repair (if using the previously installed covering process) of the airframe. You don't get to use a prior 337 to document the new work, it requires a new 337 - on the wings for example, any recover that covers an area greater than 2 rib bays requires the submission of a 337 for the major repair. That's where they have you for a recover using the previously applied covering method - it quite obviously exceeds 2 rib bays so it becomes a major repair but not an alteration because it is conforming to the previously approved process.

The rib stitching (or whatever method is used) is the method you use during the covering process to hold the fabric to the wing and in completing the 337 you must document that procedure including what basis was used for determining that the method you used was an approved method. This is where we can get in trouble. Because a new 337 is required each time we recover the requirement for basis of approval must be met each time. Generally that will be in accordance with the STC but you will find that all of the STC's for fabric covering, while they allow rib stitching, also state that the method of attachment must be in accordance with the approved factory method or a field approval for the 337 must be obtained - and of course that just completed the circle and brought us back to the beginning of the thread.

Hope this answered your question - I know it's not what most folks want to hear, heck I don't even agree with all of it though I understand the reasoning. (I may be spending too much time hanging aroung beaurocrats!)

Just remember - I didn't make the decision, I'm just the messenger.

Dennis · Post by **Dennis** » Fri Jan 20, 2006 22:51

Mike,

Just purchased new ribs for my Champ from Wag. They were all pre-drilled for pop rivets.

Dennis

Nathan K. Hammond · Post by **Nathan K. Hammond** » Fri Jan 20, 2006 23:15

New Super-D ribs are .020 and pop rivited. Yikes!

nkh

Post by **joea** » Sat Jan 21, 2006 04:17

Dennis wrote:Mike,

Just purchased new ribs for my Champ from Wag. They were all pre-drilled for pop rivets.

Dennis

Dennis,

Are the holes small enough that you can also use PK screws or are you locked into using the pop-rivets?

Jay, thanks for the info.

Joe A

Ron Babos · Post by **Ron Babos** » Sat Jan 21, 2006 09:14

For what it's worth, my Champ has pop rivets in the ribs. They are the standard large head type specifically for that task. After reading some of the concerns with .020 ribs and pop rivet combinations, I have been pulling the covers and looking for any problems. I have not found any. I never did care for a screw in thin aluminum, certified or not. It takes a good feel for those things to not pull to the point of stripping the hole out . Now it's a bigger screw, close to rivet size? Rivets may be faster to install, but removal will take some time and care. The rivet should be held under the rib lip while the head is drilled or they can spin with the drill bit.
Ron

Dennis · Post by **Dennis** » Sun Jan 22, 2006 12:18

Jay,

The first thing I checked was the size of the hole because I wanted to use pk screws (which I had already purchased). Bottom line, the predrilled holes are much larger than the holes needed for pk screws but are the right size for pull rivets. So I guess I will be using rivets. I really don't want to drill holes in new ribs just to use screws.

Dennis

jerrymjr · Post by **jerrymjr** » Mon Jan 23, 2006 10:48

Nathan K. Hammond wrote:New Super-D ribs are .020 and pop rivited. Yikes!

nkh

Yeah, but they have a wider flange and 36% more ribs per wing.
Apples > Oranges

Derek Landstrom · Post by **Derek Landstrom** » Sat Jan 28, 2006 21:15

I had a set of the .032" ribs from Safe Air. They were drilled for the 1/8" fabric rivets. There is a Service Letter, I think it's #85, that allows the use of rivets in the .032" ribs, but did not specifically list the 7AC. In any event, I once saw a set of these used with the small PK screws. The owner just drilled a small hole offset about 1/4" from the 1/8" fabric rivet holes. It looked like it worked out real well.