[Don Jones]

I have been working on the flaps lately trying to finish up the last of the control surfaces thank gawd. I was assembling the right flap and all was looking good until riveting the bottom skin/nose skins to the spar. I wasn't happy with the results I was getting. It seemed like the countersinks in the spar were too shallow and even though the rivets set nicely, you could push on the material between rivets and it would give. Looking at the junction from the inside it appeared there was a gap. Sooooo, I ripped it apart, but couldn't find anything wrong. Hmmmm, only now some of the holes in the spar have opened up enough from the rivet expanding in the extremely thin edge of the c/s holes that I am afraid to put it together again. Hello Vans, send me some parts.

The good news is the fuse kit is ordered with a last week of May delivery date. Need to get these wings finished off.

Has anyone dimpled the spars rather than counter sinking them? They are the same thickness material as the rear wing spar and that gets dimpled?

 

[SmittysRV]

Hi Don,

I had the same idea about dimpling the flap spars. As you have probably noticed, one flange is at a perfect 90 degree angle and the other is not. The rear spar on the wing is the same thickness as the flap spar and I didn't see why I couldn't use the same procedure on the flap spar as the wing spar, but with one exception. The bottom flange on the flap spar is not at a 90 degree angle, so dimpling this flange will bend the flange out because there is not enough room for the small diameter dimple die to sit flatly on the interior of the flange. The top flange is at a perfect 90 degree angle, so the small diameter dimple will work fine. So I countersunk the bottom flange and dimpled the top flange. This made me use longer rivets and I had to dimple one of the end flanges on each rib. Here's a drawing I made showing why I couldn't dimple the bottom flange of the spar.

The trick with the countersink on this spar is to make a dimpled "hole checker" out of piece of scrap aluminum the same thickness as the skin that is riveted into the countersink. Then place the scrap dimpled aluminum into the countersink to see if the outer edges of the scrap sit flatly on the surface of the spar flange, while the dimple sits inside the countersink hole. The gotcha' here is to not allow the countersink to go in so far that it makes the original hole in the spar bigger than it's original width. If that happens, your clecos won't hold the skins to the spar because the holes are too wide. Kind of like brain surgery. A very delicate and precise procedure.

Here's the final product:

 

[Don Jones]

Might give it a try!

Thanks Smitty, I might try the dimple thing. The countersinks were perfect before rivets(still are) only now after the rivet expanded in the holes they won't all hold cleco's any more. I may actually measure them
to see if they are within tolerance per the rivet chart. There are a couple that I know will require oops rivets which shouldn't be a problem as long as the rest will work. The left flap is going much better so far and I have the parts ordered for the right. So I have time to play with it.

 

[scard]

Dimple them if you can at all figure it out. I've been there, done that. If you really machine countersink the spar further than you already have (and didn't like the results), the hole is going to get too big with a knife edge, then you'll end up with oops rivets all the way down the row. Things begin to get real messy from there. Next time, I would work a lot harder on a way to dimple the difficult flange. How about a close quarters die only on the back side used with a squeezer with a thin no hole yoke?

 

[Mel]

I dimpled these holes with Avery's dimpling pliers. Very easy.
A pop rivet dimpler will work too.

 

[Don Jones]

Dimples

Don- I've got both of these if you want to borrow them.

I have vise grip dimplers, pop rivet dimplers, and small diameter dies. I will try the dimple thing. The counter sinks were perfect before having a rivet mashed in them. I had C/S them using a scrap .020 piece with the appropriate dimple and was careful to only go deep enough to get the dimple to set flush. This did not open up the hole too large for the rivet. I also was careful drilling out the rivets and only had to drive the last little bit of the rivet out of the spars, but the holes were now oversize

I was looking at it this morning and see absolutely no problem dimpling them with the small diameter die with my custom yoke that I ground the end down so that it does not extend beyond the diameter of the small diameter die so we will see how it goes.