Countersink or Dimple .032

[husabeast]

I'm sure this has been asked in the past, but I can't find a definitive answer anywhere. The RV-8 left elevator instructions say to countersink many holes on the various spars made from .032. Section 5.5 COUNTERSINKING AND DIMPLING states that for AD3 rivets, .032 thickness or less must be dimpled and .032-.040 should be dimpled but can be countersinked if necessary.
I am leaning toward dimpling since it does not require the removal of material. It is also easier and less likely to ruin a part. Any thoughts would be appreciated.

[Bavafa]

Sometimes dimpling will cause the piece to curve, this is particularly if the part is the flange of the piece.
While I am not familiar with the part that you are talking about but being a spar, I imagine it is the flange and in that case the countersinking might be the reason it says to do.

[Mel]

Originally Posted by Bavafa

Sometimes dimpling will cause the piece to curve, this is particularly if the part is the flange of the piece.
While I am not familiar with the part that you are talking about but being a spar, I imagine it is the flange and in that case the countersinking might be the reason it says to do.

When in doubt, dimple. Countersinking .032 for 3/32 rivets is marginal and not as strong as dimpling.

MHO!

[bjdecker]

Dimple — all the way up to and including .040”

[WingsOnWheels]

Originally Posted by bjdecker

Dimple — all the way up to and including .040”

+1, I even dimpled the 0.040 forward floor and countersunk the angle. A dimple is almost always better than a countersink. On 0.032 I would only countersink if there were no way to dimple.

[David Z]

The head height on a 3/32" rivet is .036", that's slightly deeper than .032" sheet. It's apparently acceptable, but definitely not preferred. There's a chart somewhere, but can't seem to recall where.

[Bavafa]

Has anyone tried to dimple a piano hinge to see what happens to it?

As a general rule, yes dimple is prefered over countersink but there are applications or types that VANS has you countersink despite the skin not being very thick. RV14 has multiple examples of that.

[bjdecker]

Originally Posted by Bavafa

Has anyone tried to dimple a piano hinge to see what happens to it?

As a general rule, yes dimple is prefered over countersink but there are applications or types that VANS has you countersink despite the skin not being very thick. RV14 has multiple examples of that.

Yes, I dimpled the MS20001 hinge that I used for the trim tab. It was hard, the material curved, etc. etc.

But, at the end of day, it worked out ok...

[wirejock]

Originally Posted by Bavafa

Has anyone tried to dimple a piano hinge to see what happens to it?

As a general rule, yes dimple is prefered over countersink but there are applications or types that VANS has you countersink despite the skin not being very thick. RV14 has multiple examples of that.

Yes, not on the airplane. It will bow.
I think most hinge we use is thicker than .032. Seems like it's .040. Easy to countersink.

[David Z]

Piano hinge is usually the bottom layer too, meaning it recieves the dimple from other layers. Doesn't much matter if it's a dimple in a dimple, or a dimple in a countersink in the last layer, the additional strength is still there. The shop head either sits on the dimple bottom, or the smooth back side of the material (hinge). I suppose it's lighter to countersink the last layer as the rivet will be shorter and removing material.

There's a couple spots in the RV8 where a countersink is specifically directed in the plans where it's way too deep and knife edges. #6 c/s screws in .040 sheet. 1/8" rivets in the same .040 sheet also knife edges slightly. Even the spar flanges where the fuel tanks attach goes way deeper than the thickness of the flange material. I called Van's support about it once and told to basically "follow the plans, it's fine, I'm over-thinking things". I suppose they're right. The designer decided this was the best way to do it. Of the thousands of RVs flying, they aren't falling out of the sky because people followed the plans.