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Assembly/Disassembly of PA-18 Wing

I don't believe that the Univar ribs are approved for the late model cubs. At least thats what they told me at Univar. Their Stc predates the last type certif. :crazyeyes: :crazyeyes:
:howdy T.J They should be SN# 1809001 thru 1809113 which should be 1988-93 or possibly 94 not really a lot of planes Ted
TJ additionally I believe the Dakota ribs are Ok to use (new Stc covering all SN) haven't seen the stc
Leading Edge Skins

When installing leading edge skins I use bunch of 1" ratchet straps. After installing the bottom flange of the skin I place one strap over each nose rib and around the rear spar, set it just off to one side of the nose rib to allow room for screwing the skin down. I start working all the straps a little at a time until the skin is laid down and tight aginst the nose ribs. Push the skin into the nose ribs to see if it is bubbled out away from the nose rib, it should lay down tight against each rib. Screw the skin down using the screw pattern as instructed by Dakota Cub or the Piper erection manual. Attach the upper flange to the spar cap. If the spar cap has had a previous leading edge, use a strap locator to locate the old screw holes, don't drill a bunch of new ones, that is woostery workmanship and weakens the spar cap. Crash
Do you have any engineering to support that statement? I drilled new holes. The old ones weren't up to my standards of spacing or staightness. I've never seen anything from Piper or the FAA that said to use old holes. Besides, who would ever know? Quality should be commended but this is beyond that. Besides, except when the plane's parked, the top spar cap is subjected to compression, rather than tension loading. I can't imagine the holes would affect it's ability to resist compression. (And my spar's lighter than yours!) And, if I ever fly out to some little bush strip and someone walks out of the trees, looks at my top spar screw spacing, and criticizes it, I'll just have to smile and think he must be a friend of yours. Oh heck, he'd never notice because he'd be trashing my VG's.
Spar Cap

Stewart: I made that statement because I've seen spar caps that looked like swiss cheese from all the different leading edge skins that had been installed with new screw holes for each one. You can't tell me that all those holes in the flange of basically an "I" beam dosn't weaken it. They are all a place for a hair line fracture to start from with all the flexing that occures in flight. I know you're pulling my leg. Between Mark and Dave riding my ass on every post, I think I'll just shut up and build Cubs. Crash
Correct on all accounts, including leg pulling. Picking on friends is easier than picking on strangers. I know the capabilities of my friends, both as plane builders and as pilots. Everyone else is unknown.
Don't use the stainless steel screws that Univair sells. They break off while tightening. The screws that Mark Erikson(Dakota Cub) has are better by far in my experience.
Morning Steve----good point----a lot of junk stainless out there. Nothing worse than having to remove a broke stainless in a new hole. Works pretty good to go in a new hole with standard steel screw then follow with your stainless. The spot that comes to mind is the interior wing root, fitting the panels to the steel gingerbread. Sounds like you have done some hair pulling over that junk also. The amount of time one junk screw can take up!!!

What? Stainless steel into aluminum? Now there's a recipe for trouble. My mechanic handed me a box of screws to attach the leading edges with. I assumed them to be conventional steel. Last year, when I handed him a Skybolt stainless fastener kit for my Cessna cowl, he handed them back to me, and said he wouldn't put them in. I'll have to ask what I used on the 12.
I just finished drilling apart a set of Luscombe wings. There was a small rise in the spar web underneath an Adel clamp held with a steel screw. Picked at it with an awl and it turned into a major explosion of inner granular corrosion. Granted there is AD on these spars due to inproper heat treatment. 3 out 4 spars were bad. I have rebuilt several Piper wings and only found a little rust but if I can get a better quaility stainless screw that would be my first choice. Don't know what your Mechanic has against S/S cowling screws. Been using them for years on cowlings and inspection panels.
I suspect it's my proximity to the ocean. I could hit an average 3-wood from my back yard and dunk a ball in salt water. Slightly further at Lake Hood. I learned to avoid the stainless/aluminum combination. I've seen what electrolosis can do to boats, even freshwater boats. I assumed that concern was universal. I did ask my mechanic what screws I used on my edges, and he said common steel.
Just some info that I was thinking about tonight. Make sure you read AC43.13-1B par 2-10a about the legality of substituting Rivets,PK screws, Marten fabric clips, Cessna fabric clips, or just plain old rib stitching from what was used Originally from the factory you might have some heartache coming up with some documentation for a Field Approval.

2-10. LACING.

a. Fabric should be attached to aircraft components to prevent ballooning due to aerodynamic forces, in the identical manner and locations as used by the original aircraft manufacturer. Any deviation from the original method(s) of attachment such as screws, rivets, wire clips, lacing cord, etc., are considered a major alteration and in conflict with the aircraft type design data. Obtain FAA approval on any deviation.

Some of you may not have the info so I did some cut and paste of what the paragraph says.

Now I have not read the STC for Univair's stamped ribs so the use of rivets may be covered by the STC.

AD42BSLF pop rivets. Doesn't mention clips. Does say "Sheet Metal Screw Attachment Of fabric Is Not Permitted."
Thanks Steve

What I don't understand is why you can't rib stitch in place of using screws,rivets,clips without it being a Major Alteration.

I guess cause there are so many different rib styles and rib stitching will hold the fabric down on all of them. Plus it is the method that has been around the longest. You know aviation is very resistant to change.
Installing Leading Edge Skins & False Spars

Here is a tip I had to learn the hard way. When Installing the inboard leading edge skin and false spar if you are using the Univair tank cover or any tank cover that is pre-drilled, you should screw the tank cover to the LE skin & false spar before attaching them to the wing. This will assure that the pre-drilled holes in the tank cover will line up with the nut plates installed on the skins. If you neglect this and the skins are miss-aligned even slightly you will wind up over sizing the holes in the tank cover after everything is covered and painted.