wrote:


2) The main accepted shortcoming of "pop" rivets in the aircraft
structures community, is one of fatigue strength. The failure of pop
rivets in fatigue was brought to attention by the crash of a
helicopter into the East river in NYC a few years ago, that was
attributed to the structural failure of a tail rotor area repair done
using Cherrymax rivets. Bell helicopter did some fatigue research
concerning pop rivets following this. The results of the report are
proprietary, but available, and states the general rule that pop
rivets have only about 80% the fatigue life of bucked solid rivets.
(My personal take on this is the report did not consider all the
factors involved, such as hole dimensions or more specifically repair
"quality". The helicopter that crashed did not have the hole
dimensions available. If the drill holes for the pop rivets used in
the repair were elongated or "wallowed" out (since they were done by
hand), then that would explain the fatigue failure. Bucked rivets are
much more deformable than pop rivets, and are therefore more forgiving
of a less than perfect installation. This is only my opinion)


Yeah that's why even aircraft designed around pop rivets use solids for
the spars. In the other areas the loads are small enough to push the
fatigue curve way out there. These designs generally only do a couple
hundred cycles a year at the most, which almost makes lifetime fatigue
issues redundant in all but a few key stress points.


3) Many production aircraft use Cherrymax rivets in critical
structure, where bucked rivets are not practical. The Aerostar high
performance twin comes to mind. Many pop rivets are used in the wing,
straight from the factory.

4) As was stated by someone else, Cherrymax rivets are WAY more
expensive than bucked rivets. Need we say more?

5) There are also many blind or "pop" bolts out there! My Cessna just
had a repair kit (from Cessna) installed that used a NAS 1669 "Jo
Bolt" to repair the front wing spar attachment. Talk about critical
structure!

Regards,
Bud


My beef with the steel mandrel Avex rivets Zenith uses is the fact that
contrary to their claim that the fracture surface of the stem, which has
no zinc plate, won't rust, they do in fact rust as a look at any older
Zenith that's been parked outside will confirm. I would recommend
filling a syringe with epoxy zinc chromate and adding a drop to each
mandrel hole on all the top surface rivets.

John