D

David Z

Well Known Member
Long story short, I had two rudder horns. So I decided to find out how strong the little 3/32 rivets are. It was very unscientific and the method used to break the part created a stress point that's unrealistic of actual flight stresses.

One person held the rib while I pulled as hard as I could on the skin and this was the result.
p3210002x.jpg


The first one pulled through with quite a bit of difficulty, and the second one just ripped off. Both of them took quite a bit of force.
p3210004w.jpg


Looks like it got shot with a .22
p3210005.jpg


Looking at this sure gives me a lot of confidence in the strength of a dozen 3/32" rivets all in a line.
 
...and that was in the peel direction, the weakest direction.

If you had just pulled instead of lifting the end, and loaded the rivets in shear you would have needed a lot of power assist...:D
 
When I experienced wing flutter in my Moni Motorglider, the wing skin was ripped off very similar to your test. The rivets remained in tact. The wing skin was .020 2024-T3. The flutter was violent enough to break the ribs from the rear spar at the fuselage and tore the aileron almost in two.
 
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Fortunately I was close to the ground. I got the airplane slowed down about the time I got into "ground-effect" and the flutter stopped. I landed "on the runway" and taxied up to a very shocked crowd. They said they could see the wing-tip oscillating up and down at least 2 feet.
I actually have a letter from John Monnette in my file that claims the cause of the failure was because I used solid AN rivets instead of the SS pop rivets called out in the plans.
 
Mel said:
<snip>
I actually have a letter from John Monnette in my file that claims the cause of the failure was because I used solid AN rivets instead of the SS pop rivets called out in the plans.
Click to expand...

Ummm...yeahhhhh...riiiggghhhhttt. And if you believe that, I've got some ocean front property in Montana to sell you. :rolleyes:
 
His reasoning was that the AN rivet is not as strong as the SS pop-rivet in tension. This fact is true; However, the rivets did not fail. The skin tore from around the rivet heads.

Of course his main reasoning was, "You deviated from the plans!"
 
Scary

I'm sincerely hope I never see this on my RV8 once it's flying. My little experiment distroyed enough airplane parts for me. Interestingly, I could not tear the other side, no matter how hard I tried.
Scary to hear how distructive flutter is.
 
it would be interesting to do the test with a perfect rivet, cleated rivet, slanted, offset, and all the common mistakes we all make.
 
Thanks for posting those data from Bill Marvel. Very informative! I had heard that this was the case, but having some data to back it up is great.

cheers,
greg
 
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