Zenith Aircraft and Pull Type Rivets

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

Earlier, Andrew wrote:

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?

This question comes up regularly. I'm starting to think we need an FAQ
page on it somewhere.

The short answer is, it depends.

The slightly longer answer is that not all pop rivets are created
equal.

For example, the Emhart MK- and MP-series Monel pop rivets and their
Cherry commercial MSC and MSP equivalents have shear strength values
on a par with equivalently sized MS20470AD and MS20426AD solid rivets.
They're also about a hundred times more expensive than the solid
rivets, but still only about 1/5 the price of CherryMax and CherryLock
aerospace rivets.

The aside to the slightly longer answer is that Chris Heintz was wrong
when he referred to Monel as a type of stainless steel. There is no
iron at all to it; Monel is an alloy of nickel and copper. It is more
galvanically neutral than stainless steel. Monel pop rivets have a
long and well-proven service history in several aircraft designs, of
which I'm most familiar with Dick Schreder's HP/RS series kit
sailplanes.

The somewhat longer answer is that, aside aside, Chris Heintz is a
smart guy and a capable designer and engineer, and that the Zenith
aircraft are specifically designed around the strength values
available from the specified rivets. They are also generally designed
around the lower strength values of 6061-T6 aluminum sheet instead of
the more expensive 2024-T3 aluminum more common in production
airplanes. There are some compromises required, but in general the
result is better economy in a perfectly servicable airplane.

I'm an amateur, don't try this at work.

Thanks, and best regards to all

Bob K.
http://www.hpaircraft.com/hp-24

Doug Hoffman wrote:
Andrew wrote:


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?

Apparently Zenith took into account the
strength of the Textron pull rivets when
designing the aircraft. Perhaps this meant
they used more pull rivets than solid bucked
rivets. Whatever. If the design accounts for the
strength of the fasteners then there is
no problem.

--
Doug via Treo handheld

That is correct, Doug. I think his basic formula is along the lines of( 4
pulled rivets = 3 bucked rivets = 1 AN bolt). That may not be exactly right
but you get the idea. It's been a long time since I read that part of my
build manual.

When I started and bought all my rivets Zenith was even specific on which
Avdel "Avex" rivets you used. The ones made in the UK were OK those made in
other places were not. The design shear strength is 110 & 180psi depending
on which size is used. The proper rivets are 130 and 220 psi.

After years of bilding I have little doubt that you could probably remove
every other rivet in the aircraft and it would still fly. Not that I'd try
it.



Andrew, the Zenith website has quite a bit on Chris' design theories.

Bob Kuykendall wrote:

(some snippage for ptactice)


The somewhat longer answer is that, aside aside, Chris Heintz is a
smart guy and a capable designer and engineer, and that the Zenith
aircraft are specifically designed around the strength values
available from the specified rivets. They are also generally designed
around the lower strength values of 6061-T6 aluminum sheet instead of
the more expensive 2024-T3 aluminum more common in production
airplanes. There are some compromises required, but in general the
result is better economy in a perfectly servicable airplane.

I'm an amateur, don't try this at work.

Thanks, and best regards to all

Bob K.
http://www.hpaircraft.com/hp-24


Chris also uses flat head flush rivets - but with specially
modified tool heads that deform the flat rivet head into a
round finished head.

This "work hardens" the rivet head.

And them things are a bear to drill out...

Richard

On 27 Apr 2007 08:14:59 -0700, 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
There are about 3 times as many rivets in a Zenith Aircraft than
would be required for strength alone - they are put closer together to
keep the edges smooth etc. The Textrons are a lot different than
hardware store POP rivets.

--
Posted via a free Usenet account from http://www.teranews.com

Andrew wrote:


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?

Apparently Zenith took into account the
strength of the Textron pull rivets when
designing the aircraft. Perhaps this meant
they used more pull rivets than solid bucked
rivets. Whatever. If the design accounts for the
strength of the fasteners then there is
no problem.

--
Doug via Treo handheld



--
Posted via a free Usenet account from http://www.teranews.com

"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.

That opinion is not shared by everyone. Now, you can't willy nilly replace
bucked rivets with pop rivets, but there are examples of aircraft designed
for pop rivets. The T-18 is an example. It would be hard to argue that John
Thorpe didn'd know what he was doing, eh?


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?

They designed it that way?

Has
there been some breakthrough in material or design in theses Textron
pop rivets making them comparable to the old style "bucked" rivets?

I doubt it.

John Thorpe specified Monel pop rivet from, IIRC, U.S. Shoe Manufacturing
(But don't quote me on the source - it's been 30 years since I worked on a
T-18)

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

On Apr 27, 9:14 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

The Zenith line of experimental aircraft are designed around the Avex
pulled rivets. Gigs statement about 4=3=1 is a good way to look at the
fastener concept. So far my Zenith 801 with the V-8 Ford in it has
shown no signs of failing at any joint. Yet. G I can tell ya it has
14,210 pulled rivets in it. :-)


Ben
N801BH

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