John Mininger Posted July 13, 2021 Report Posted July 13, 2021 Has anyone actually found an A&P who would install these as an owner produced part? Mooney Landing Gear Shock Disk – AV Unlimited For what it's worth, here's a link to an article that Mike Busch wrote about ten years ago on owner produced parts: EAA_2011-08_owner-produced-parts.pdf (savvyaviation.com) Quote
MikeOH Posted July 14, 2021 Report Posted July 14, 2021 Hmm, regardless, I'm not sure I'd do biz with a company that would charge $20 shipping, per disk!!! I mean, come on, if you want $70 per disk, just say so...don't make a lame attempt to hide it by tacking on a ridiculous 'shipping' charge! 2 Quote
carusoam Posted July 14, 2021 Report Posted July 14, 2021 Our rubber donut producer is in South Africa… He gave insight around here regarding the various rubber qualities… If I were mechanically inclined…. Swapping donuts isn’t that hard…. Saving hundreds of dollars by getting identical rubber donuts from South Africa…. Wouldn’t take too much convincing… For additional insight… find @Gert… PP thoughts only, not a mechanic… Best regards, -a- Quote
Hank Posted July 14, 2021 Report Posted July 14, 2021 13 minutes ago, MikeOH said: Hmm, regardless, I'm not sure I'd do biz with a company that would charge $20 shipping, per disk!!! I mean, come on, if you want $70 per disk, just say so...don't make a lame attempt to hide it by tacking on a ridiculous 'shipping' charge! That can save money, as places like eBay, Amazon, etsy, etc., take a percentage of the sales price but not shipping costs. Quote
A64Pilot Posted July 14, 2021 Report Posted July 14, 2021 You willing to make the logbook entry that you produced or participated in its manufacture IAW the FAR? If the answer is yes, then I would consider it for a part that was either not available or really stupid expensive. But without a logbook entry saying you produced the part, no. Would I buy a airplane that had owner produced parts that are available from the factory? No. 1 Quote
EricJ Posted July 14, 2021 Report Posted July 14, 2021 3 hours ago, John Mininger said: Has anyone actually found an A&P who would install these as an owner produced part? Mooney Landing Gear Shock Disk – AV Unlimited For what it's worth, here's a link to an article that Mike Busch wrote about ten years ago on owner produced parts: EAA_2011-08_owner-produced-parts.pdf (savvyaviation.com) Search around, there is at least one other thread here including input from the company doing that and a lot of relevant discussion. It looks to me like a potentially reasonable option and appears to compare well to the same process used by many of us in the past to get parts from other manufacturers like McFarlane. 4 Quote
MikeOH Posted July 14, 2021 Report Posted July 14, 2021 20 hours ago, A64Pilot said: You willing to make the logbook entry that you produced or participated in its manufacture IAW the FAR? If the answer is yes, then I would consider it for a part that was either not available or really stupid expensive. But without a logbook entry saying you produced the part, no. Would I buy a airplane that had owner produced parts that are available from the factory? No. I'm pragmatic and would consider OPPs on a case by case basis. In this case: Yes, I consider the disks to be "stupid expensive" It wouldn't bother me one whit if a plane I was considering had these donuts. I would want their installation documented in the log. 1 Quote
RobertGary1 Posted July 15, 2021 Report Posted July 15, 2021 23 hours ago, A64Pilot said: You willing to make the logbook entry that you produced or participated in its manufacture IAW the FAR? If the answer is yes, then I would consider it for a part that was either not available or really stupid expensive. But without a logbook entry saying you produced the part, no. Would I buy a airplane that had owner produced parts that are available from the factory? No. I'd bet money that 99% of buyers would never notice that in the logs. -Robert 1 Quote
RobertGary1 Posted July 15, 2021 Report Posted July 15, 2021 23 hours ago, A64Pilot said: You willing to make the logbook entry that you produced or participated in its manufacture IAW the FAR? If the answer is yes, then I would consider it for a part that was either not available or really stupid expensive. But without a logbook entry saying you produced the part, no. Would I buy a airplane that had owner produced parts that are available from the factory? No. I guess it depends on how much participation you want. If you go to their website you have to fill out a form that includes all the required dimensions etc. They've been nice enough to prefill that for you though. -Robert Quote
A64Pilot Posted July 15, 2021 Report Posted July 15, 2021 (edited) 25 minutes ago, RobertGary1 said: I guess it depends on how much participation you want. If you go to their website you have to fill out a form that includes all the required dimensions etc. They've been nice enough to prefill that for you though. -Robert After some thought I’ve sort of come to the conclusion though that as an A&P my function is to determine airworthiness and properly install. ‘That’s why I would require the manufacturer of the part to attest to the fact that they made it and state so in the logbook, my opinion without some kind of evidence of how this part came into being, it’s an unapproved part, with the manufacturers log book entry, that legitimizes the part. If you attest to the fact you built it, I don’t believe it’s my responsibility to ensure you did. My responsibility is to determine its airworthiness and properly install it. My hesitancy is what if the part fails and causes an accident, I can see how I could be facing a lawsuit for not determining the airworthiness of the part correctly as that is my job, and it failed so it wasn’t airworthy, so I believe I could be found liable. But truthfully the bottom line is, I can see my exposure, but don’t see what the upside for me is. ‘I’m speaking to parts that are available from the aircraft manufacturer, which often isn’t the case, for my neighbors Stinson Reliant, he doesn’t have much choice so that is a different case. ‘Now these thoughts are just my opinion, other people are entitled to theirs as I am. It’s the determining the airworthiness of the part that is what I trip up on, how do you do that without the factory specs. The crop duster I built also has elastomeric biscuits, they are pulled together as opposed to being pushed together. We had them manufactured to our specs, and when we “bought” them in other than filing the “certs” we also of course measured the things and had a machine that determined their durometer or how hard they were and sometimes some failed. It was a simple thing similar to the one we used to determine Rockwell harness of heat treated metal. As an A&P I don’t have Mooney’s specs for how hard the elastomer is supposed to be, nor do I have a way of testing these. But if they came with paperwork attesting that Mooney’s specs were xx to xx durometer and these meet that spec, then that would make me feel a whole lot better. Then I can say it’s a legit part via the logbook entry and I have paperwork attesting to its airworthiness, in that it meets the aircraft manufacturers specs. Edited July 15, 2021 by A64Pilot Quote
A64Pilot Posted July 15, 2021 Report Posted July 15, 2021 32 minutes ago, RobertGary1 said: I'd bet money that 99% of buyers would never notice that in the logs. -Robert I would hope that whoever your paying to inspect the aircraft would though, assuming of course the records weren’t somehow destroyed, but to me undocumented maintenance and gaps and or missing records is reason enough to keep looking, others have different opinions. Quote
carusoam Posted July 15, 2021 Report Posted July 15, 2021 what PPIs are for…. Ferret out the un-AW issues that have occurred and see that the plane was put back into AW condition… properly… When deciding to go OPP parts…. There is some risk analysis to consider… How critical is the part if it fails? What is the chance it fails catastrophically without warning? If something didn’t work as expected? How expensive is it to fix? I don’t think we’re are going to see manufacturers ever pass out their product specs… Surely when we use a qualified supplier… they have the skills and technology to determine what the material specs are…. If they can’t, that is an indication that they are not qualified… Don’t select a rubber donut manufacturer the way Al Mooney did…. Find one that makes rubber donuts for the aviation world already… the QC process will already be in place… by people that understand what it needs to do… There wasn’t any high tech rubber donuts in the 60s… our rubber donuts haven’t changed since then… PP thoughts only, not a rubber engineer… Best regards, -a- 1 Quote
RobertGary1 Posted July 15, 2021 Report Posted July 15, 2021 1 hour ago, carusoam said: what PPIs are for…. Ferret out the un-AW issues that have occurred and see that the plane was put back into AW condition… properly… When deciding to go OPP parts…. There is some risk analysis to consider… How critical is the part if it fails? What is the chance it fails catastrophically without warning? If something didn’t work as expected? How expensive is it to fix? I don’t think we’re are going to see manufacturers ever pass out their product specs… Surely when we use a qualified supplier… they have the skills and technology to determine what the material specs are…. If they can’t, that is an indication that they are not qualified… Don’t select a rubber donut manufacturer the way Al Mooney did…. Find one that makes rubber donuts for the aviation world already… the QC process will already be in place… by people that understand what it needs to do… There wasn’t any high tech rubber donuts in the 60s… our rubber donuts haven’t changed since then… PP thoughts only, not a rubber engineer… Best regards, -a- I understand but I was speaking more to the specific pfd this company requires that includes those measurements and data. While many of the values are prefilled they are required in the order form the owner must sign. Quote
carusoam Posted July 15, 2021 Report Posted July 15, 2021 Some OPP data used around here has been… 1) Engine control cables…. send in the old, they pull a proper copy of it off their shelf…made by the same company Mooney buys their control cables from… 2) Gear down lock block… There is only one design. Dimensions were taken from an existing block, metallurgy was determined by a lab, enough paperwork was copied and signed to complete the legality issues… the parts manufacturer also manufactures certified airplane parts as a business. 3) For rubber donuts… back to one design again… really simplifies verifying the design issue… three dimensions to check… ID, OD, thickness… similar to aluminum alloy, the rubber compound needs to be matched… chemistry, fill content, fill materials, % X-linking… 4) Don’t forget the aluminum disks that go between the donuts… are they included or purchased separately? Oddly… Somebody reported changing out their donuts the other day… first time in 50+ years… wonder how much of the original qualities were still in tact… even % X-linking in rubber has a tendency shift over years and temps…. All old fuzzy memory… may not be right, or complete… Best regards, -a- Quote
A64Pilot Posted July 15, 2021 Report Posted July 15, 2021 9 hours ago, carusoam said: I don’t think we’re are going to see manufacturers ever pass out their product specs… It’s usually not that hard, it is in the drawings, so if you have those you have the material specs. Somehow though you have to determine materials to make a part, Aluminum composition can be determined by electrical conductivity for instance and level of heat treat by a simple machine that applies a measured amount of pressure and the depth of the dent is measured. ‘I believe durometer is the same, pretty simple to determine, a device pushes a measured amount of force and displacement is measured. Apparently even Amazon has durometer testers https://www.amazon.com/s?k=durometer+tester&crid=16Q15UVBYADUO&sprefix=durometer+%2Caps%2C226&ref=nb_sb_ss_ts-doa-p_5_10 It’s not tough or expensive to verify durometer, of course I’m sure you can spend a whole lot more, for much more accurate calibrated instrumentation too. ‘I toyed with but never did on Thrush biscuits what the mountain bike guys do with their suspensions, that is different durometer biscuits, a couple of softer ones should soak up the small bumps well like pavement frost heaves. ‘But changing the durometer is a major change and would require new landing gear drop tests, even tire pressure can cause one to fail drop tests and a Thrush’s landing weight is much less than it’s takeoff weight due to landing gear drop tests, there is no excess strength, so it was one of the many things I didn’t get to try 1 Quote
PilotX Posted July 15, 2021 Report Posted July 15, 2021 I wonder how this would be caught on a PPI or the logs, if it was logged. In my limited experience. I am no pro but I have found unlogged stuff in planes years later. Maybe if it was blue rubber, oooo @GeeBee can you do blue shock disks to match my Zerk fittings? 1 Quote
A64Pilot Posted July 15, 2021 Report Posted July 15, 2021 Properly done there shoud be two entries for the disks. ‘One to certify them as an OPP, and the second installing them. Being an OPP makes them legitimate as an aircraft part. Its in the Mike Bush article as it is in others. ‘This article is almost 20 years old, but explains it better than most https://www.aviationpros.com/home/article/10387511/owner-produced-parts-how-they-affect-maintenance Quote
N201MKTurbo Posted July 15, 2021 Report Posted July 15, 2021 I wonder why he doesn't apply for a PMA? Quote
EricJ Posted July 15, 2021 Report Posted July 15, 2021 53 minutes ago, N201MKTurbo said: I wonder why he doesn't apply for a PMA? He's on a different continent and said it wasn't practically possible. 1 hour ago, PilotX said: I wonder how this would be caught on a PPI or the logs, if it was logged. In my limited experience. I am no pro but I have found unlogged stuff in planes years later. Maybe if it was blue rubber, oooo @GeeBee can you do blue shock disks to match my Zerk fittings? They're easy to inspect, which during a PPI isn't a bad thing to check just to see how old they are, anyway, via the date code. That is one down side of these, that there's no visible date code or external marking. That's not that big of a deal since they're replaced on condition, anyway. And you're right about stuff not being represented in logbooks. I suspect very few airplanes are well represented by their historical logs. Since it is not required to keep records after a year, random records could legally have been disposed of any time along the way, assuming it was ever logged in the first place. Quote
N201MKTurbo Posted July 15, 2021 Report Posted July 15, 2021 (edited) 7 minutes ago, EricJ said: He's on a different continent and said it wasn't practically possible. They're easy to inspect, which during a PPI isn't a bad thing to check just to see how old they are, anyway, via the date code. That is one down side of these, that there's no visible date code or external marking. That's not that big of a deal since they're replaced on condition, anyway. And you're right about stuff not being represented in logbooks. I suspect very few airplanes are well represented by their historical logs. Since it is not required to keep records after a year, random records could legally have been disposed of any time along the way, assuming it was ever logged in the first place. h. Importing Modification and Replacement Parts. Under 14 CFR § 21.502, we allow foreign manufacturers to export modification and replacement parts to the United States if an applicable bilateral agreement exists. This agreement defines the scope and manner of the FAA’s acceptance. We expect foreign manufacturers to include documentation of airworthiness with these exported parts. Other acceptable replacement and modification parts from foreign countries with bilateral agreements include: 2 6/23/08 8110.42C (1) Parts produced by a foreign holder of an FAA type certificate (TC), STC, or letter of TSO design approval (LODA) on a foreign state of design product , or (2) Parts produced by a foreign manufacturer, holding a production approval from the bilateral partner Civil Aviation Authority (CAA), for U.S. State of Design products produced under a licensing agreement with the design approval holder. (3) Parts that have PMA from a foreign airworthiness authority and are recognized in a bilateral agreement with us. So, if he could get a South African PMA, and there is a bilateral agreement, he is good to go. He might need a special agreement with the Zulu warlords. Edited July 15, 2021 by N201MKTurbo Quote
RobertGary1 Posted July 15, 2021 Report Posted July 15, 2021 4 hours ago, A64Pilot said: It’s usually not that hard, it is in the drawings, so if you have those you have the material specs. Somehow though you have to determine materials to make a part, Aluminum composition can be determined by electrical conductivity for instance and level of heat treat by a simple machine that applies a measured amount of pressure and the depth of the dent is measured. ‘I believe durometer is the same, pretty simple to determine, a device pushes a measured amount of force and displacement is measured. Apparently even Amazon has durometer testers https://www.amazon.com/s?k=durometer+tester&crid=16Q15UVBYADUO&sprefix=durometer+%2Caps%2C226&ref=nb_sb_ss_ts-doa-p_5_10 It’s not tough or expensive to verify durometer, of course I’m sure you can spend a whole lot more, for much more accurate calibrated instrumentation too. ‘I toyed with but never did on Thrush biscuits what the mountain bike guys do with their suspensions, that is different durometer biscuits, a couple of softer ones should soak up the small bumps well like pavement frost heaves. ‘But changing the durometer is a major change and would require new landing gear drop tests, even tire pressure can cause one to fail drop tests and a Thrush’s landing weight is much less than it’s takeoff weight due to landing gear drop tests, there is no excess strength, so it was one of the many things I didn’t get to try You have to wonder how much the ride could be improved with a progressive hardness of the 4 donuts on each main. -robert Quote
A64Pilot Posted July 15, 2021 Report Posted July 15, 2021 59 minutes ago, RobertGary1 said: You have to wonder how much the ride could be improved with a progressive hardness of the 4 donuts on each main. -robert I think quite a lot, but how would it affect when something broke? There is a point when the biscuits squish just about all they can and then they pass on the forces of course. But the drop test is a very quick sudden huge impact, maybe some softer pucks could absorb more energy, maybe the impact is so fast that the pucks pass the energy through, or maybe they would make it worse? Prohressively wound springs are normal in auto suspensions and the mountain bike guys years ago discovered progressively hard elastomers give similar results I think computer modeling has matured so much now that you could probably determine the best durometer or mix of durometers and whether or not you have a valid stack without dropping an airframe, sure you would have to drop one to prove the computer, but your not dropping several. You can reuse an airframe for a drop test, but if it breaks did it break because it was weakened from previous drops? I assume that back in the day when Mooney designed the system, computer analysis wasn’t possible. Plus surely the same pucks for a C model if they are optimal for it, surely aren’t for a much larger heavier aircraft, but they have the same pucks? Unfortunately it all boils down to desire and money, I don’t believe the design has matured to where there is no room for improvement, just the money to improve the design just isn’t there. Quote
GeeBee Posted July 15, 2021 Report Posted July 15, 2021 There is a progressive polymer disk unit for Super Cub type aircraft called "AOSS" which amazingly is "ground adjustable". It works quite nicely if one day you are doing pave strips and the next day "rocks and props". His "doughnuts" are quite a bit more robust than the Mooney type. I wonder who he uses and what the difference. is in formulation. https://www.aoss.net 1 Quote
A64Pilot Posted July 15, 2021 Report Posted July 15, 2021 (edited) I wish I had a picture of the Thrush shock, the pucks aren’t flat, the middle two inches or so are, but the rest of it gets thinner at an angle, Looks like a discus Being shaped like that initially only the middle flat portion takes a load, but as they compress more and more of the puck makes contact bringing more and more elastomer into contact as the shock is compressed, this makes it very progressive. 1960’s design. ‘There has always been a lot of variation in batches too, some split early, but the ones that don’t last a long time. Crop Duster pilots are all Engineers, if you don’t believe me ask one, one of the field Engineering things I have seen are combine springs in place of the pucks, a steel spring has no dampening and in my opinion doesn’t work as well as the elastomer puck. Edited July 15, 2021 by A64Pilot Quote
Will.iam Posted July 15, 2021 Report Posted July 15, 2021 So I've read through this thread and what is the problem of installing the OPP donuts and when you finally put the aircraft up for sale replace the OPP donuts with ones that have a PMA or TSO part? I guess if I was selling my plane and a buyer was held up over an OPP part being on the plane 2.5 amu's should be able to correct that, or is putting an OPP part on a plane once in it's history like a gear up landing, it always devalues the price of the plane because it had at one time an OPP part? Quote
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