Fly Boomer Posted September 27, 2023 Report Posted September 27, 2023 1 minute ago, carusoam said: Note: these are old memories of a private pilot, that once had some additional knowledge of polymers, but not a lot… hoping that this is helpful… Best regards, You have to know this is coming from just about everyone on the forum: WELCOME BACK! 1 1
carusoam Posted September 27, 2023 Report Posted September 27, 2023 6 minutes ago, Fly Boomer said: You have to know this is coming from just about everyone on the forum: WELCOME BACK! Thank you! (To All) One of these days… I’ll spend some better controlled time on MS! There is nothing more enjoyable than being part of the Mooney family. Best regards, -a- 3
0TreeLemur Posted September 27, 2023 Report Posted September 27, 2023 14 minutes ago, carusoam said: Hey all! Welcome back Anthony! I missed your lists! 1 1
carusoam Posted September 29, 2023 Report Posted September 29, 2023 FAA invitation to a presentation regarding parts support…. Vintage Airplanes… = before 1980 You have asked us to notify you when a webinar is scheduled that meets your criteria. The following webinar may be of interest to you: "Vintage Aircraft Replacement and Modification Program VARMA" Topic: Scott Fohrman from the Chicago Aircraft Certification Branch will be doing a presentation on the VARMA Program On Tuesday, October 10, 2023 at 11:00 Eastern Daylight Time (08:00 PDT; 09:00 MDT; 10:00 CDT; 05:00 HST; 07:00 AKDT; 08:00 Arizona; 15:00 GMT) Select Number: EA17124379 Description: Scott Fohrman from the Chicago Aircraft Certification Branch will be doing a presentation on the Vintage Aircraft Replacement and Modification Program VARMA. This program is indented to help owners and operators of vintage aircraft (certificated before Jan 1, 1980, fixed wing, unpressurized, under 12,5000 lbs with a reciprocating engine) find and use replacement parts or processes, when the parts are no longer available, obsolete and out of production. To view further details and registration information for this webinar, click here. The sponsor for this seminar is: FAASTeam The following credit(s) are available for the WINGS/AMT Programs: Basic Knowledge 3 - 1 Credit AMT: 1.00 Click here to view the WINGS help page 2
tmo Posted September 30, 2023 Report Posted September 30, 2023 I'll add that as far as I understand "before 1980" means "Type Certificate issued before 1980" which covers everything up to M20K (approved in 1978) no matter when the plane was actually built. IOW it covers all the J and K serial numbers.
gummirat Posted November 23, 2023 Report Posted November 23, 2023 Happy Thanksgiving all, still hopeful. Mark 1
Kevin Harberg Posted November 23, 2023 Report Posted November 23, 2023 Happy Thanksgiving Mark, (and to all Mooney enthusiasts). Unfortunately not a positive result from Smithsonian M-18 Lower Shock Pad drawings (for scaling replacement donuts). The drawing received is for the thin metal plate that separates the pucks. Can't seem to find any drawings related directly to the rubber components.
Pinecone Posted January 5, 2024 Report Posted January 5, 2024 Probably because it was an off the shelf part from a vendor. Maybe contact who made the original shock discs and ask about drawings of that part. DO NOT MENTION IT IS FOR AIRCRAFT USE.
BenT Posted January 16, 2024 Report Posted January 16, 2024 Was a source found for these other than Lord? We may need material specs, formal drawings for a custom mfr to produce. Does anyone have these? There was a reference to Mack Truck motor mounts. Has anyone found a replacement product?
gummirat Posted January 16, 2024 Report Posted January 16, 2024 Hi All, Firestone made them. They are gone as of about 2000. Bridgestone didn't want to continue mechanical goods so molds, prints etc. are gone. I've been trying for 4yrs to get prints, measurements to make the mold. I have a rubber formula that should work well for this (a modified tank pad rubber). Was trying to get Clarence M-20 doc to get me the dimensions off the o.e.m. ones he had but they run him off. Kevin Harburg has been a huge help on this so far and hope he hasn't lost faith in getting this done as I am probably going to need more of his input. Going to try to do it thru the FAA Varma program Mark
R.May Posted December 28, 2025 Author Report Posted December 28, 2025 I have some time and money to make this happen. Give me the steps. Is there an original I can hand carry across the country if needed? Or take to a local shop for a scan? How about just making a polyurethane copy that has the durometer 78 mentioned above? I was thinking they were probably flat, not the concave as seen in the photo. That would allow for a more gentle compression as more material starts to resist as the compression goes up. This would be helpful if you have a rubber that is too hard...tech back then being what it was. Also mentioned above is that soft rubber will flow more easily so it would not be stable over the 6-12yr period needed for a place. So, just put a harder recipe in there and make the metal discs concave. Give me some steps and I will work on it. I am willing to fund it too. 1
Slick Nick Posted December 28, 2025 Report Posted December 28, 2025 I’ve thought for a long time that urethane replacements would be the way to go. We have urethane replacements for almost everything rubber in the automotive world, suspension bushings, motor mounts, etc. why can’t we use that technology in the aviation industry? 1
carusoam Posted yesterday at 07:09 AM Report Posted yesterday at 07:09 AM Just a note… current rubber donut technology for the M20s are cylindrical shaped discs when they are molded. The steel washers begin life perfectly flat… they take on the slight donut shape when weight is put on them. They extrude outwards over time, temperature cycles, and weight strain… the rubber may continue to cross-link over decades getting harder with age… one thing that won’t change… the weight and volume of the rubber part, unless… it has absorbed some grease and oil. when rubber absorbs grease or oil… it has a tendency to swell. rubber parts that swell… only swell in one direction. Outwards, in both thickness and radius… important to know… the inner diameter doesn’t try to compress against the metal tube. sooo…. If you have an old donut. And, it is still tight against the rubber tube. It is not indicating signs of swelling. if you decide to make ‘owner supplied parts’ in accordance with the FAA guidelines… it will be important to try to duplicate what you have as far as rubber chemistry goes. rubber chemistry is interesting… it also includes fillers and carbon black. Molecular weight and percent X-linking also help to define what is there. for a how-to guideline of how to make an owner supplied part for a certified airplane… there is a thread around here for making an aluminum part for gear up lock block, and gear down lock block. selecting a better rubber, or changing the ingredients in the rubber compound won’t comply with the owner supplied parts rules… if you have a reason to improve the donuts… that would use the STC process. Have a look at that process as well…. We have a few STC writers around here that have built new Mooney cowlings, and swapped out the old air bag servos for electric motor servos on the step… the entire rubber molding world was centered around Akron Ohio during the 1900s. chemical analysis of the original parts can be done by a company familiar with rubber chemistry. Expect to hear words like DSC, and TGA… differential scanning calorimetry and thermo gravimetric analysis. physical analysis also can give hints to what the rubber was designed to do… hardness and compression followed by recovery after compression… then compare your analysis with one from a brand new M20C donut…. You may find out the rubber requirements for Mooneys hasn’t changed much in decades… the old donuts will have terrible hardness, and compression data… all stuff that changed since the day they were molded… do some research… snoop around the Lords website… see what specifications they can give you regarding the rubber donuts they make… they produce both engine mounts, and landing gear donuts… and metal washers that get used in both applications… The hard parts… duplicating the chemistry is all about finding the best rubber formulating lab… somebody that understands your requirements. Get the testing done. duplicating the hardness and compression details… that rubber formulating lab will have these tools as well… duplicating the original dimensions comes from the best estimates you can get from what you have in hand… and possibly contacting the Mooney Mechanic in Canada for his assistance. He has a set and knows how to measure. there are examples around here of how donuts compress over time… with pictures showing stack height change between old vs. donuts… also around here is a rubber hose manufacturer… a guy that knows a lot about rubber. He makes mostly seals and rubber hoses for high end sports cars. But can help navigate getting donuts made. if I was in a bind… and needed to replace my donuts. And didn’t know where to start…. look for thick sheets of rubber… with the best match you can figure out… find somebody that has a die cutter, and makes the dies… (find that rubber hose / seal guy around here, he has this stuff) cut dozens of thick pieces of rubber, and stack them… testing your dimensions for ID, OD, and overall thickness… know that these will not be perfect replacements for molded donuts… but don’t be surprised how the compression function will be amazingly similar… of course, if you test the dimensions of a stack of sheets, and you have a stack height that works… next step would be to have a mold made to those dimensions… simulate donuts with premade rubber sheets, cut to the dimensions you determined earlier… Prove to yourself that you know the dimensions that you pre-determined earlier actually work… make donut molds that match the simulated donuts that you made… in the end… you can impress the FAA that you knew the original…. 1) dimensions of the existing donuts, when new… 2) chemistry of the existing donuts, when new… 3) relevant physical properties of the existing donuts, when new… 4) rubber manufacturing process of the existing donuts, back in the day… 5) make mold, make donuts, make paperwork… 6) review how to change the rubber donuts of your aircraft often… this may be easier on an M18. But, it may still need some specialized tools as well… compressing donuts, and setting gear rigging can be serious. PP thoughts only, not a rubber chemist or rubber formulator… or even a mechanic… best regards, -a- 1
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