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Empennage tip rivet interference

RV8Bob

Member
I’m getting close to riveting on the tips for the rudder and elevator and have identified a possible issue. After riveting one side the aft most rivet will surely interfere with the opposite side. I would guess the head of the second rivet would initially be at least 1/8” above the skin. I have limited experience with pop rivets. Will the head pull down to the skin when set or am I missing something?
97609CA1-9186-4099-A937-18ABAC5198C0.jpg
 
Rivet

I’m getting close to riveting on the tips for the rudder and elevator and have identified a possible issue. After riveting one side the aft most rivet will surely interfere with the opposite side. I would guess the head of the second rivet would initially be at least 1/8” above the skin. I have limited experience with pop rivets. Will the head pull down to the skin when set or am I missing something?
View attachment 19621

The pop rivet wi squeeze quite a bit. Grab some scrap of simulated thjcknes and try it.
I don't recall a problem with mine but it's a 7A.
 
The pop rivet wi squeeze quite a bit. Grab some scrap of simulated thjcknes and try it.
I don't recall a problem with mine but it's a 7A.
Thanks for the suggestion. I did set up an experiment with limited space for the shop end of the blind rivet. The factory head initially raised off the skin approximately 1/8”. I found that the factory head will pull tight against the skin as long as adequate pressure is applied toward the surface while setting.
 
Bond too?

Do y'all also bond the tip to the skin too?
It seems the front plug ends up bonding the tip to the rudder anyway.
I was thinking the skin to tip transition would crack if not bonded. No?
 
Bonded

Do y'all also bond the tip to the skin too?
It seems the front plug ends up bonding the tip to the rudder anyway.
I was thinking the skin to tip transition would crack if not bonded. No?

I've seen both. Some builders plan for potential removal. Others bond and rivet. I used G-flex on the final install then pop riveted after it cured. The problem with no bond is the paint can crack. Less likely to crack with a good strong adhesive.
 
The pop rivet wi squeeze quite a bit. Grab some scrap of simulated thjcknes and try it.
I don't recall a problem with mine but it's a 7A.
My fear was affirmed today. I should have replicated the test again because as you can see in the picture the head of the trailing edge rivet was protruding over the 1/8” I guessed. Even with pressure toward the skin the rivet popped before the head made contact with the skin.
 

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If you don't have a shorter rivet, you can tap the mandrel out of the rivet, grind the rivet shorter, then put it back on the mandrel.
Stewart Willoughby, 6 final assembly
 
If you don't have a shorter rivet, you can tap the mandrel out of the rivet, grind the rivet shorter, then put it back on the mandrel.
Stewart Willoughby, 6 final assembly
They are the correct rivet, CS4-4. Unfortunately the kit doesn’t include shorter rivets. I went with your solution. Removed mandrel and shortened rivet. It worked great. Probably wouldn’t do that to a structural rivet but I’m sure it maintained nearly 100% of its strength. Unfortunately it appears to be impossible to find a CS4-3 rivet
 
If you don't have a shorter rivet, you can tap the mandrel out of the rivet, grind the rivet shorter, then put it back on the mandrel.
Stewart Willoughby, 6 final assembly

This is a good procedure when a pulled rivet is too long. Just make sure that the final length is sufficient to get a good "shop head".
 
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