AirTalk.org Aviation discussions newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Zenith Aircraft and Pull Type Rivets Goto page 1, 2  Next          AirTalk.org Forum Index -> Aircraft Design & Building View previous topic :: View next topic   Author Message Andrew Guest Posted: Fri Apr 27, 2007 8:14 pm    Post subject: 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 Back to top Bob Kuykendall Guest Posted: Fri Apr 27, 2007 9:25 pm    Post subject: Re: Zenith Aircraft and Pull Type Rivets Earlier, Andrew <rga...@yahoo.com> wrote: Quote: 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 Back to top Gig 601XL Builder Guest Posted: Fri Apr 27, 2007 10:02 pm    Post subject: Re: Zenith Aircraft and Pull Type Rivets Doug Hoffman wrote: Quote: 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. Back to top cavelamb himself Guest Posted: Fri Apr 27, 2007 10:28 pm    Post subject: Re: Zenith Aircraft and Pull Type Rivets Bob Kuykendall wrote: Quote: (some snippage for ptactice) Quote: 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 Back to top Guest Posted: Sat Apr 28, 2007 12:41 am    Post subject: Re: Zenith Aircraft and Pull Type Rivets On 27 Apr 2007 08:14:59 -0700, Andrew <rganey (AT) yahoo (DOT) com> wrote: Quote: 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 Back to top Capt. Geoffrey Thorpe Guest Posted: Sat Apr 28, 2007 2:09 am    Post subject: Re: Zenith Aircraft and Pull Type Rivets "Andrew" <rganey (AT) yahoo (DOT) com> wrote in message news:1177686899.519619.72370 (AT) t39g2000prd (DOT) googlegroups.com... Quote: 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? Quote: 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? Quote: 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. Back to top stol Guest Posted: Sat Apr 28, 2007 5:35 am    Post subject: Re: Zenith Aircraft and Pull Type Rivets On Apr 27, 9:14 am, Andrew <rga...@yahoo.com> wrote: Quote: 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 Back to top Doug Hoffman Guest Posted: Sat Apr 28, 2007 6:11 am    Post subject: Re: Zenith Aircraft and Pull Type Rivets Andrew wrote: Quote: 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 Back to top Richard Riley Guest Posted: Sat Apr 28, 2007 6:11 am    Post subject: Re: Zenith Aircraft and Pull Type Rivets On 27 Apr 2007 17:35:33 -0700, stol <benford2 (AT) aol (DOT) com> wrote: Quote: 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. The best money I ever spent was $20 for a Harbor Freight air powered puller. It's done about 4000 rivets so far and shows no sign of failing. Back to top Guest Posted: Sat Apr 28, 2007 6:11 am    Post subject: Re: Zenith Aircraft and Pull Type Rivets On Apr 27, 8:14 am, Andrew <rga...@yahoo.com> wrote: Quote: 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 Back to top J.Kahn Guest Posted: Sat Apr 28, 2007 7:45 pm    Post subject: Re: Zenith Aircraft and Pull Type Rivets budcun (AT) msn (DOT) com wrote: Quote: 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. Quote: 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 Back to top Al Gunn Guest Posted: Sat Apr 28, 2007 8:31 pm    Post subject: Re: Zenith Aircraft and Pull Type Rivets "J.Kahn" <jdkahn (AT) REMOVEvideotron (DOT) ca> wrote in message news:U5JYh.120163 Quote: 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. Back to top Guest Posted: Sat Apr 28, 2007 10:04 pm    Post subject: Re: Zenith Aircraft and Pull Type Rivets 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 Back to top Peter Dohm Guest Posted: Sun Apr 29, 2007 2:56 am    Post subject: Re: Zenith Aircraft and Pull Type Rivets "Richard Riley" <Richard (AT) mylastname (DOT) net> wrote in message news:eta533le9v5rqfinb40hm60j55djqkblgj (AT) 4ax (DOT) com... Quote: On 27 Apr 2007 17:35:33 -0700, stol <benford2 (AT) aol (DOT) com> wrote: 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. :-) The best money I ever spent was $20 for a Harbor Freight air powered puller. It's done about 4000 rivets so far and shows no sign of failing. Compared to hand pulliing all those rivets, it would still be worth while at 10 times the price! Peter Back to top Richard Riley Guest Posted: Sun Apr 29, 2007 4:26 am    Post subject: Re: Zenith Aircraft and Pull Type Rivets On Sat, 28 Apr 2007 17:56:11 -0400, "Peter Dohm" <lefty133 (AT) bellsouth (DOT) net> wrote: Quote: The best money I ever spent was $20 for a Harbor Freight air powered puller. It's done about 4000 rivets so far and shows no sign of failing. Compared to hand pulliing all those rivets, it would still be worth while at 10 times the price! Absolutely. I have a couple of dozen 1/4" Stainless pull rivets in this project, and had to get a puller with arms about 3 feet long. It's like a bolt cutter. After I put those in I felt like I'd run for 2 miles. I remember when I was a kid and my dad wanted a pnumatic puller. He was never able to justify it, they were a weeks salary. The chinese stuff from HF may mostly be junk - but the pnumatic stuff seems to be a bargain. 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