Thorp Air Command - T18.net

OK... here's a strange question. Has anyone ever encountered what appears to be "weak rivets."

Tonight I removed a gear leg fairing for reasons I don't want to admit. On my airplane the fairings are pretty standard: one folded skin with a strip in between at the trailing edge, riveted with AN470-4 rivets. I like to start with a 3/32 bit when I remove rivets. On half of these rivets the heads snapped off just from the torque of the drill! The rest also came off much more easily than usual. Some of the fracture surfaces appear to be old (ie fatigue cracked).

I remember when I first started this exercise I found one headless rivet on an aileron bracket in one of the wing gaps, which I thought was quite odd.

On the up side, I have not encountered a single AN426 rivet that felt weak, and most of the rivets on the airplane are flush.

Anyway, should I be worried?

_________________
_________
In theory, theory and practice are the same. In practice, they are not.

Sad to say, but many T-18s were built using surplus rivets of dubious linage. They were age hardened before they were driven, hence all the early newsletter bits on annealing rivets. Worse than that, many folks used soft rivets (especially on the trailing edges) 'cause they were easier to drive with less distortion. These will show up rather quickly as they loosen in the prop wash areas. My advise: If you find a headless rivet, drill out the adjacent ones and replace them with rivets of known condition.

_________________
Bob Highley
N711SH
SN 835
KLAL

If I recall the structural rivets will have a dimple on the top and the "softer rivets" are "smooth." Standard political disclaimer..."To the best of my recollection..."

RB

RB said (in a new topic????) "If I recall the structural rivets will have a dimple on the top and the "softer rivets" are "smooth." Standard political disclaimer..."To the best of my recollection..." "

Indeed. Mine did have dimples. It was not like they were soft... it was more like brittle and crumbly. I even swear there was a little puff of dust when the head snapped off on some of them. Does anyone have a scanning electron microscope so I can go in for a closer look?

I wasn't planning to take the other fairing off, but I will do now just to see if I get the same result.

_________________
_________
In theory, theory and practice are the same. In practice, they are not.