Wed Jul 4 2007

Tank skin / baffle dimpling

Well I've been out of town for the past few days. Kerin and I drove over to Blacksburg, VA to visit her sister on the long weekend. Kind of a bummer that I had a 5 day weekend and didn't get to work on the plane except today.

Anyway, it struck me about 2:00am last night that when I dimpled the left tank skin that I inadvertently dimpled the two rows of holes for attaching the skin to the baffle. These are supposed to be countersunk instead. Well damn! I got to worry about that for the six hour ride home.

I had actually considered intentionally dimpling these holes anyway except for the few at the very inboard end of the tank. See, I believe the reason they have you countersink these is because there is very little clearance with the spar cap bars for the shop heads of the rivets. However, once you get past the inboard eight holes or so, the spar cap bars are machined down (thinner), so this isn't a problem. What I was thinking of doing is dimpling all but the inboardmost eight holes. Unfortunately when I was dimpling, I forgot all about this and just dimpled the entire rows (both top and bottom).

The next morning I went down to scope out the situation:

Here, I've set the baffle in place on the left wing. It looks like there won't be any issue with spar cap clearance for the row of holes on the bottom of the tank. The bottom spar cap is thinner than the top one.

I put a flush head rivet into the hole with the manufactured head on the inside so I could get an idea of how the shop head will look when it's all assembled. Looks good. So there's officailly no reason to worry about rivet clearance along the bottom of the tank.

But clearance is a lot tighter on top of the tank.

Here I fabricated a piece of .016 aluminum with a dimple in it to see how much clearance there is if I dimple this row of holes. It looks like it's gonna be close for the inboard most eight holes.

Got the "dimple simulator" clecoed on. I actually had to grind down the fingers of this cleco so they wouldn't hit the spar.

I actually think this is gonna be OK. By looking at the cleco fingers, it looks like there will be enough room for a rivet shop head. On top of that I won't have the .016 thickness of the test dimple, so I should have an extra .016 clearance.

Well after all that I was feeling pretty good...thinking this is gonna work out just fine...until I looked at dimpling the baffle. See, the baffle flange holes are so close to the bend radius that there's no room to get the dimple dies lined up with the holes. I went out to the Cleaveland Aircraft Tool site and found a small diameter female dimple die that looked like it would do the job. But wait...I dimpled the skin with the tank dies, so that means I need to dimple the baffle with tank dies also. But Cleaveland doesn't make a small diameter dimple die with the tank sized recess. So I sent an e-mail to Mike at Cleaveland asking him if he would make me a small diameter dimple die with the tank die sized recess instead of the regular 3/32 inch recess.

Mike remembered me from the time I worked with him on the modifications I made to The Main Squeeze squeezer. See Tue Apr 5 2005. He was thankful for that help and offered to make me one and send it to me at no charge! How's that for service?!!! Thanks, Mike.

Hopefully I'll get that die soon so I can try dimpling the baffle.