RV-7/7a Plan Gottcha's

[idubrov]

Originally Posted by jls32

Dimple NOT countersink the forward face of the L/R Elevator spar E-702 for the 706/5 attachment. 702 is too thin to countersink and you'll end up with a hole larger than spec. THANKS VANS!!!! FIX YOUR **** INSTRUCTIONS!

FWIW, I asked them about this particular area. I suggested using NAS1097 instead, since they have a smaller head. I did not want to dimple as I wanted parts to sit completely flat (since there is this whole horn that mounts over them). I know some builders dimpled, though, and it worked fine.

The answer was to follow the plans, so I did countersink for AN426AD3, but I did it without a cage, manually, carefully controlling the depth. The E-702 is 0.032" and the "full" countersink depth for AN426AD3 is about that exact depth. So you do get a knife edge.

Either way, I don't think it matters much as this steel horn over these two parts won't let anything to move anyway.

[jls32]

Originally Posted by idubrov

FWIW, I asked them about this particular area. I suggested using NAS1097 instead, since they have a smaller head. I did not want to dimple as I wanted parts to sit completely flat (since there is this whole horn that mounts over them). I know some builders dimpled, though, and it worked fine.

The answer was to follow the plans, so I did countersink for AN426AD3, but I did it without a cage, manually, carefully controlling the depth. The E-702 is 0.032" and the "full" countersink depth for AN426AD3 is about that exact depth. So you do get a knife edge.

Either way, I don't think it matters much as this steel horn over these two parts won't let anything to move anyway.

You MUST take the cage off in order to fit against the fillets.

If you do the trig, the depth of the countersink works out to 0.037" deep which is greater than the E702 thickness of 0.032". That means the hole is enlarged (not just knife-edged) and it's beyond the mil-spec.

[idubrov]

Originally Posted by jls32

You MUST take the cage off in order to fit against the fillets.

Right. I have a small adapter that I can either chuck in a drill or spin between fingers to create a countersink.

Originally Posted by jls32

If you do the trig, the depth of the countersink works out to 0.037" deep which is greater than the E702 thickness of 0.032". That means the hole is enlarged (not just knife-edged) and it's beyond the mil-spec.

I used numbers (well, the head diameter primarily, but it matches the one I measure with the calipers) from https://www.univair.com/hardware/riv...tersunk-rivet/

The formula is tan(50 degree) = (B - C) / 2h, where h is the depth. h = (B - C) / 2 / tan(50), which is (11/64 - 3/32) / 2 / tan(50 degree) ~= 0.033. Which is a tad thicker than 0.032" material, but just one thou. And you can leave rivet sticking just a bit, per spec, if you really want to (but in this specific location, given the steel bracket on top of it, it probably shouldn't stick too much).

Which is consistent with Section 5, also:

For AD3 rivets, a total material thickness between .016 [.4 mm] and .032 [.8 mm]
must be dimpled. Material thickness between .032 [.8 mm] and .040 [1.0 mm],
should be dimpled, but a countersink may be used if necessary.

Either way, what I am saying is that I don't see much reason to stress over these specific holes. I don't like the way it is specified in the manual, but I assume that changing anything in the manual is a bigger risk for Vans than leaving as is. What they specify probably works.

Just a heads up, they will ask you to countersink E-606P as well, which is also a 0.032" spar.

[idubrov]

Not really a gotcha, more like something that made me chuckle.

I was trying to verify the 0 degree incidence angle on the horizontal stabilizer, and just couldn't get the fore and the aft tooling holes to align (which is what instructions tells you to check).

Then I looked at the other side, and realized that the aft tooling hole was indeed not centered on the rib.



I know, it is kind of obvious if you look at the lightening holes, but I had some sort of a tunnel vision seeing only the tooling holes

The fore hole seems to be centered, though.

I wonder, if it was a downstream effect of SB 14-01-31 integrated into the plans when they replaced HS-405 ribs (or whatever was there before in RV-7 plans) with the HS-00005 ribs?

[wirejock]

Originally Posted by idubrov

Not really a gotcha, more like something that made me chuckle.

I was trying to verify the 0 degree incidence angle on the horizontal stabilizer, and just couldn't get the fore and the aft tooling holes to align (which is what instructions tells you to check).

Then I looked at the other side, and realized that the aft tooling hole was indeed not centered on the rib.

Attachment 47079

I know, it is kind of obvious if you look at the lightening holes, but I had some sort of a tunnel vision seeing only the tooling holes

The fore hole seems to be centered, though.

I wonder, if it was a downstream effect of SB 14-01-31 integrated into the plans when they replaced HS-405 ribs (or whatever was there before in RV-7 plans) with the HS-00005 ribs?

Yep. I measued all day on that one. Finally realized the holes were not matching the manual. Legacy manual instructions I guess. In the end, I trusted the actual measurements and ignored the holes.