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Wing Rib Jig

Posted: Mon Jun 15, 2020 6:07 pm
by builderwannabe
Before asking my question, I would just like to thank the group here for the help that has been provided in the past. I do not want to think what I would have sitting in my basement without that help. I am embarking on the next phase of my build which will be the wing ribs, and like the previous endeavors has plenty of questions for which I am seeking answers. I reference West Coast Piet a lot to get ideas and to ensure that what I see in my mind is what I should be doing. Looking at the "wing rib' section of Chris Tracy's site he states that " I did not use the full size wing rib drawing supplied with the plans because it did not match the measurements from the plans (advice from a bunch of builders)". This unfortunately negates what I thought was a good idea(buying the full sized wing rib drawings to make getting the wing ribs correct easier). I noticed though that the pictures he posted seems to be of the his wing rib on top of the GN-1 wing rib schematic, and not the pietenpol ribs schematic.
My questions at this point are:

1. Does anyone have an opinion on the correctness of the full sized wing rib drawings from the official pietenpol website?

2. If those are not correct are there mistakes in the plans for the wing rib as I cannot make the numbers work and look like a wing rib. The problem in the
1.5 in height of the chordline followed by the increase to 2" height .5 inches later.

Any help is greatly appreciated.

Sean

Re: Wing Rib Jig

Posted: Mon Jun 15, 2020 11:36 pm
by taildrags
Sean; there are as many tweaked versions of the airfoil/rib as there are builders, almost. You've got to use the basic template as a starting point and hold the important characteristics... the overall chord, the dimensions of the spar pockets, and the general shape. Beyond that, a bit of smoothing and eyeballing are needed to fair in the curves and eliminate the little hiccups between the coordinates that are provided. There is obviously NOT a hump or jump in the wing surface or profile; some of the numbers were either incorrectly noted or the location where they are stationed was not correct.

I've attached a full-size PDF of the airfoil with stationing included. This drawing was created by Leo Ponton in 2001 but I don't know where he derived or created it from, and it's certainly not to be taken as The Perfect Piet Airfoil Drawing. However, it might be useful for you to print it out full-size if you have access to a plotter, or in 8.5x11 chunks that you can tape together for study and comparison with what you've got to see if maybe you can get to the bottom of the discrepancy that you're seeing.

Oscar Zuniga
Medford, OR
Air Camper NX41CC, A75 power

Re: Wing Rib Jig

Posted: Tue Jun 16, 2020 7:30 am
by builderwannabe
Oscar, thanks for the reply and the drawing this helps a lot. If there are lots of variations I will just use the full size template I purchased with the plans. I like to keep things simple.


Sean

Re: Wing Rib Jig

Posted: Sun Jun 28, 2020 2:37 pm
by builderwannabe
Oscar, thanks again for the reply. I am onto rib #5 today. I spent a few hours on the first rib getting the truss members exact and then used them as the templates to mark future truss members before cutting. I then use a shooting board marked with the exact angle i want for each cut. This has worked well so far and i can go from an empty jig to epoxy drying in 2.25-2.5 hours. with a little slop included for any clean up of the ribs I think maybe 90 hours of build time on ribs. not sure how that compares with other builders experience. I put this out there as a data point for those who build in the future.
Sean
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Re: Wing Rib Jig

Posted: Sun Jun 28, 2020 5:56 pm
by danoliver
Wow! I've never heard of a shooting board before, looks like the perfect tool for the job.