On Apr 27, 8:14 am, Andrew wrote:
CC: Zenith Aircraft Company

I have an aeronautical engineer friend retired from McDonnell
Douglas who once was in charge of the Harrier project for the U.S.
team. I respect his opinion which is that pull type, "pop" rivets are
only used on aircraft where a bucked rivet could not possibly be used
or on non-critical, low stress applications.

It is my understanding that the bucked rivet, which has been
used over the years in aluminum aircraft, is stronger than the pull-
type pop rivet. In consideration of the Zenith Aircraft 601 and 701,
how is it that they are using a Textron Brand pull-type rivet? Has
there been some breakthrough in material or design in theses Textron
pop rivets making them comparable to the old style "bucked" rivets?

Thanks,
Andrew

You have recieved some good replies on this one. I would like to add
my 2 cents, since I have a fair amount of experience analyzing
aircraft structures. I will simply post the following facts that I
have collected over the years.

1) The STATIC strength of cherrymax and cherrylock or Avex rivets is
usually stronger than the static strength of bucked solid rivets. This
is due to the fact that the stem is usually made of stronger material
than the outside collar. Aircraft (NAS or MS spec) quality blind
rivets are used in many production aircraft, and strength
specifications for them are in every major aircraft manufacturing
structures manual that I have seen, and I have seen most of them. They
are approved by Boeing, Lockheed, etc., for installation in PRIMARY
structure.

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)

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