"Andrew" wrote in message
ups.com...
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


Chris Heintz designed his aircraft to use 6000 series aluminum and Avex pop
rivets. The aluminum he uses is not quite as strong at 2400 series aircraft
aluminum but it is not anywhere near as susceptible to various modes of
corrosion that eat airplanes.

When you design a riveted joint you have to consider both the shear strength
of the rivet and the shear strength of the metal being riveted. Most
airplanes are designed and the rivet number and spacing is determined for
2400 series aluminum with driven rivets. The shear strength of a driven
rivet is slightly greater than that of an Avex pop rivet. The Avex pop
rivet is far stronger than the hardware store aluminum pop rivet. If the
joint is designed for the lower shear strength rivet there will be a few
more rivets but the strength will be as good as you can expect to get with
any riveted joint.

Your engineer friend is correct though with working with existing designs.
If a joint was designed for an aircraft type driven rivet, replacing those
rivets with pop rivets without redesigning the joint to attain the original
strength will probably cause a catastrophic failure.

There is one type of "pop" rivet that develops a shear strength that is
comparable to the driven rivet. This is the "Cherry" rivet, which is a pull
set rivet that does not drop the inside out when it is set and develops the
same shear strength as a driven rivet. These rivets can be used to replace
driven rivets with no problems. However, they are generally used only where
a driven rivet cannot be used. That is because of the cost difference. A
typical driven rivet costs less than a penny. A "Cherry" pull set rivet
costs $.50 to $.60 each. With something like 15000 rivets in a small
airplane, that cost difference adds up. Even the weaker Avex rivets that
Heintz uses cost about a dime each, and you can save a lot of money by
driving rivets where you can do so. I have noticed that most of the
designs that are designed for Avex type rivets use driven rivets in their
factory assembled "quick build" kits. Saves many bucks. Of course, it
does take a little bit of practice to learn how to properly drive and buck
rivets. Nothing you can learn though. :-)

Highflyer
Highflight Aviation Services
Pinckneyville Airport ( PJY )