Zenith Aircraft and Pull Type Rivets

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

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

"J.Kahn" wrote in message news:U5JYh.120163

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.


I filled mine with structural epoxy before painting, levelled each hole and
it looks like solid rivets. It's not necessary but it looks nicer.

I have been using these rivets, with the modified gun nose, on a
homebuilt project of my own.

Just a simple Harbor Freight Air/Oil Gun, $24.

Rivets are about .04 to .06 cents each.

Very reasonable!

I did quite a bit of research on the process, as well some testing
before making that decision.

Personally, I'm very comfortable with the avex rivet procedure.

Colin
A&P I/A

http://www.jumprunenterprises.com

The question at hand has been well covered by the answers so far, you may be
interested in the 'reverse' of the pop vs. solid rivet question.
When I built my Zenith, CH200 from plans I decided, or maybe was talked into
doing the skins in solid flush rivets. In consulting with Chris, he said,
'use one dash smaller in solid rivets", therefore my skins are done in -3
and -4 solid rather than -4 and -5 Avex 'Pop' rivets. It doesn't make the
plane any stronger, or weaker, just different.
When I built the prototype CH801 I used all Avex Pop rivets everywhere
except the structure that called for solid rivets. All hand pulled by the
way and I never found hand pulling to be a particular chore. If the whole
plane was ready to rivet at once I can see where the power puller would be a
godsend but who has that many clecos?

Stew



"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

Richard Riley wrote:
On Sun, 29 Apr 2007 15:18:20 GMT, "Stew Hicks"
wrote:

The question at hand has been well covered by the answers so far, you may be
interested in the 'reverse' of the pop vs. solid rivet question.
When I built my Zenith, CH200 from plans I decided, or maybe was talked into
doing the skins in solid flush rivets. In consulting with Chris, he said,
'use one dash smaller in solid rivets", therefore my skins are done in -3
and -4 solid rather than -4 and -5 Avex 'Pop' rivets. It doesn't make the
plane any stronger, or weaker, just different.
When I built the prototype CH801 I used all Avex Pop rivets everywhere
except the structure that called for solid rivets. All hand pulled by the
way and I never found hand pulling to be a particular chore. If the whole
plane was ready to rivet at once I can see where the power puller would be a
godsend but who has that many clecos?

There's no such thing as too many clecos. My wife bought me 500 of
each color a few years ago for my birthday.

If she feels the need to make another such gift point her my way.
I'm not proud, I'll accept the gift.

Dan, U.S. Air Force, retired

"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 )