MainlandCub
Registered User
New Zealand
Thanks for the response Andrew. What you are saying is that the top and bottom of the "cutouts" (actually the original Piper ribs are not cut out as the spar attach points are just vertical angle pieces attached to the ribs) are clear of the spar caps by how far? In my stamped ribs (new but made in the 70's) I didn't receive any "clips" to join them together and the flanges have no predrilled mounting holes for the PK screws so I'm having to work out the mounting holes as to centering the spars, or 7/16 up from the bottom, or maybe 1/2" up from the bottom to provide a small amount of clearance to the spar cap (bottom of spar) or maybe some other distance? Hopefully someone will read this and figure out what I'm trying to ask. The answer probably lies in following the drilling directions for the spar and also the drilling directions for the rib mounting angles (transferring those dimensions to the built in flanges on my stamped ribs) and then screwing the rib to the spar in the pre drilled holes.
qsm,
On the original Piper ribs, the top and bottom of the "cutouts" are the cap strip which is continuous from the trailing edge on the bottom to the trailing edge on the top if no repairs have been carried out to the rib. The vertical angles rivet to the upper and lower cap strips. The clearance is of the order that Gordon mentions, but might be even less.
Really your ribs need to be equi-spaced above and below the spar. If you are using a vendor made leading edge (or even if you're making your own) the flanges are the same length and should sit on the top and bottom "spar cap flanges" equally. At the rear spar, you don't want your fabric touching the spar or even close.
I feel I'm getting into too much detail, but you need to figure out where they are going to be (we can't do that for you) and make a jig to hold the ribs in the correct location on the spar and then drill them off to the spar; eyeball or mark all your edge distances and get the holes in the spar in the correct place, or make a jig to drill the ribs on the bench so they are all the same and also probably a jig for the spar, and then assemble and screw like they were new parts from Univair or DCA.
I hope that helps some,
Andrew.