Question for Chewie---

[fairchild]

Just found your pic of your nose ribs with the little wavy spot at the top and bottom front edges. I am seeing that same little defect.
I also noticed that on some of them the radius seem a bit smaller than farther back. I am using a larger than specified radius
so I figured that wasnt a deal breaker. some of my ribs have it and some dont. I was worried about the artifact too so I took
one of them and magnifluxed it on both spots and saw no cracks. (thats good)

some of my nose ribs have it and some dont. I think I can see why now. I am using the ribber press method. And like you -
my backer block is cut back about 3/16 away from the form so I can get my little dead blow rubber hammer onto the edge.

When I started pressing- the rubber would bend the flange about 1/2 way or maybe a little less. then I would finish the bend with the hammer.
Now I went from 20 ton jack to a 30 ton. That now pushed the rubber way farther around the corner--- so now I get an about a 80
degree bend on the flange from the rubber.

I believe the big difference is that the defect area is in need of being compound bent--- and it has to stretch to do that. To stretch
it-- you have to "trap" the material to prevent it from taking the path of least resistance. (and causing the observed defect)
I think the rubber pad traps the material and forces the sheet to stretch instead of making the little loop of excess material.
I think that when you bend it less in the rubber and do more bend with the hammer-- the backer block cant trap the material
enough and the excess stress and excess material just moves down instead of stretching like you want it to.
I think that the more angle that can be bent by the rubber (while trapped) the less likely to get the little loop of excess material.

So I think you said that Bob thought it was OK and it wouldnt hurt anything ?
I was thinking that as a QC check---- I might cut a form from the mylar-- a piece of 1/4 MDF which matches the contour of the
top and bottom curves. It would be a complementary curve matching the nose rib-- so I could put it up against each rib to verify
that there are no lumps or discontinuities in the curve. Im pretty paranoid about the curve being perfect - since that part of the
wing's surface has the most to do with the stall behavior. If I have one thats off and I cant adjust it I will scrap it and make a replacement.
Not too worried about the other ribs as the curve being way less---they should put up much less resistance to being worked.

This is my first build and it seems like there are many little details of technique like this waiting to be figured out.

Tim

[Bdflies]

Just to clarify, you used dye penetrant chemicals, to inspect for cracks? Not magnetic particle inspection. Right?

Bill

[Chewie]

Tim -
Correct, Bob said the important thing was that the wing profile was maintained. The defect I had on mine were not on the plane of the flange so the wing skin would be unaffected. As to what caused it, my guess is as you said a path of least resistance. It might've been a combination of my backer being too undercut and the relief radius too far forward, but that's just a wag.

Why you gotta go and dig up my old sins, yo?

[fairchild]

Bill--- Yes - i used dye -penetrant test. (since magniflux is a brand name - I guess it could be either)
mark- tomorrow Im cutting out the MDF contour gauge. i will cut it about 1/32 (or attempt to) inch larger than the mylar to account
for the rib thickness. If it doesnt fit- I must aquit.....nooo.. that was something else..... :-)
My first couple ribs didnt have the little loop- confusing----
There WILL be sins..... even in factory built machines.....just how big and how many-----
Tim