ETLB Squawk Forums — Archive

Greetings to all. I just finished my first spar layup less the plywood web. Before going to this next step I was checking a few things and noticed that my ribs do not match up to the front spar as expected. I built the ribs per the full fize template. The front spar per the drawing dimensions (6-7/8") (attached dwgs). But the rib does not match up to the dimension of the front spar (photo).

Has anyone else run into this?

I see two remedies ( I am not rebuilding all my ribs).

1.) Reduce the upper spar cap by this amount when I cut the 10" angle. or
2.) Rebuild this spar and all the others with the slight reduction in the verticles to make it fit.

Thoughts?

First, just as a general statement:  This is why working from so-called "full sized plans" is a very bad idea.  These prints shrink and swell a great deal and in some cases I've seen errors in printing the drawing to exactly the proper size.  Ribs can be made by figuring out how much the drawings have shrunk or swollen and adjusting the dimensions so you can loft corrected dimensions onto your jig base.  The other way is to buy one sample rib from Team and build your jig from that.  I've done both on designing my jig for "Epic Sport" ribs.  However to solve your problem. David tells me that when builders have sent in ribs they've built from the drawings none of them match the ones from the shop jig.

If we take as a given that you aren't going to build new ribs, the solution is not to cut down the spar below the required dimensions.  That's just too dangerous.  Few aircraft have large safety factors by the standards of structures which don't have the weight restrictions aircraft work under.  You can't fool with reducing these spars at all.

Your only solution will be to "pad" the top of the ribs with carefully tapered wood to make them fit.  If this is done carefully to either a drawing relofted as described above or to match a purchased rib, you will have a rib which matches the intended shape.  As long as you don't try to "eyeball" the shape you are going to be alright on the airflow.  However there will be a weight penalty.

I personally redraw all drawings which are supposedly "full size" to make sure they are compatible with the original intent.  I did this with my rib jig.

Tom

Thanks Tom,

It all makes sense and I can do as you suggest. Sounds like the best route will be for me to get a factory rib from Dave.  Thankfully I only live a few miles from him and might just make another visit and just take one of mine down and determine what to do.

Rocky

Full VW Hi-Max........  You've already got enough weight penalties. Just my .02c.