Thursday, July 24, 2014

F-1202N-L&R Forward Skin Stiffeners Remade

Those readers following the DOG Aviation RV-12 know that it is being built utilizing flush blind rivets as opposed to low profile dome blind rivets. There have not really been any issues with dimpling the parts especially when the need for a smaller diameter 120 degree male dies was discovered very early on in the project. All of the parts have been successfully dimpled thus far with great results with the exception of the F-1202N-L&R forward skin stiffeners. Many months ago both F-1202N stiffeners were dimpled for flush rivets … they took on quite a bow which I was able to eliminate by fluting. The reason for this was the factory drilled holes in the stiffeners were close to the web to flange transition … this caused the small male dimple die to ride into the transition region of bend. The process of dimpling caused the angle to open a bit and also created a bow in the two stiffeners.

This is an interior part and the fluting will show. This has bothered me somewhat, so when making the angles for the baggage bulkhead modification, decided to fabricate a couple of additional angles so new F-1202N forward skin stiffeners can be fabricated.
The fluting necessary to straighten the F-1202N stiffeners can easily be seen on the left of this photo … the new yet to be drilled replacement angles are on the right.

The newly fabricated angles in the above photo have a 1/2" flange and the rivet holes will be centered at 1/4" in from the outer edge. This will allow just enough room so the male dimple die will clear the transition area and not bow the metal as the dimples are created. New F-1202N pieces were purchased to use as a template for the hole spacing when drilling the new angles.
Match drilling the replacement stiffener using a new F-1202N as a template.

Ran out of time so did not get the new stiffeners dimples but I do not expect any issues. If there are any dimpling issues, it will be duly noted here for those builders utilizing flush rivets in their RV-12.