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Thread: AEC Donuts - From the Horse's Mouth

  1. #11
    The Sierra MLG donuts are not interchangeable with any of the fixed gear locations. They will physically fit, but they have a different compression ratio (durometer) than the -7 fixed gear donuts. The Mooney donuts are identical to Sierra MLG donuts in physical dimensions but are significantly harder than the Sierra's.

    Rap McBurney
    N8786

  2. #12
    When you are talking to Lord, see if they will send you a drawing of each disc? Or at least tell you what the material / durometer is. You never know what you might get....and that would be awesome if someone wanted to OPP these discs.
    Dave Gribble
    Marion IA
    Flying the Restored Hangarmouse (Super III N3698Q)
    Building RV-9A N149DG


  3. #13
    Here is Rellihan's research. It's all I have, but there must have been more as AECi reverse engineered the donuts later.

    Rap
    Attached Files Attached Files

    Rap McBurney
    N8786

  4. #14
    I have been dealing with the same basic question ever since I bought my Sundowner. Rap was kind enough to send me an old donut to experiment with, and I've had some luck in restoring a bit of "life" to it. I ordered a small bottle of Wintergreen oil and simmered the donut in a mixture of the oil and water for a few hours a day for several days (don't do this in the house, the smell is overwhelming.) The beginning dimension was .940 and the ending dimension was 1.050, and it has held that dimension for about a month now. I have been told that a stack of 8 totals 9", or 1.250 per donut, so I am still .075 short. But it is measurably more pliable than before, and since my donuts are not too bad yet, I'm considering attempting a renewal instead of a replacement.

    Also, I recently met an engineer with extensive experience in rubber injection. He pulled out his durometer tester and the "refreshed" donut measured at 75. He is out of the country for a few months, but he has given me 2 other contacts that I will follow up with. He is in agreement that these are $10 parts.

    I am also attaching a link to an article that allows a person to calculate durometer based on shape, area, and known compressibility. Apparently a stack of 8 donuts should compress 1" when subject to a 3000 lb load. I did some quick back of the napkin math while on the road (without the exact diameter of the donuts) and 70-80 seems about right.

    https://moldeddimensions.com/urethan...ompression.php

    Free time is all that is keeping me from pursuing this further. I will keep the club updated with whatever I find out.

    Bruce

  5. #15
    Oops, public math strikes again! The correct thickness of a new donut should be 1.125, not 1.250. I'm still .075 short of new, though.

  6. #16

    Do this!

    Quote Originally Posted by Jurassic View Post
    Also, I recently met an engineer with extensive experience in rubber injection. He pulled out his durometer tester and the "refreshed" donut measured at 75. He is out of the country for a few months, but he has given me 2 other contacts that I will follow up with. He is in agreement that these are $10 parts.
    I think this is the proper approach. Get a drawing of the correct donut, with material identified (best case), or a brand new donut combined with the info in Rellihan's document above (second best case) - and pay someone to make these available. Then they are legit OPP parts, just like the trim actuator bushing that just happened.

    I bet there are enough of us here that would order a set of donuts (even if they aren't needed right now) - to cover the NRE.

    dave
    Dave Gribble
    Marion IA
    Flying the Restored Hangarmouse (Super III N3698Q)
    Building RV-9A N149DG


  7. #17
    Quote Originally Posted by Unclerap View Post
    Here is Rellihan's research. It's all I have, but there must have been more as AECi reverse engineered the donuts later.

    Rap
    I had a conversation with Lord about the problem with gel engine mounts, back in 2009.
    I mention this, because the contact (then) was Bernie Chan, and he was extremely helpful.
    He sent me written confirmation that leaking gel mounts were fully airworthy, which was something Mike Rellihan had been trying to establish with them for ages. He sounded like he was “old furniture” at Lord. Maybe he is still there?
    Mark
    In Oz


    Where I have landed a Beech

    (Plus, Australia, Canada, New Zealand, United Kingdom)

  8. #18
    I have several old, used -1 and -7 donuts if anyone wants a sample.

    Rap McBurney
    N8786

  9. #19
    And I have a new (current series) set of AECi -1 and -7 that I will offer for research.
    Mark
    In Oz


    Where I have landed a Beech

    (Plus, Australia, Canada, New Zealand, United Kingdom)

  10. #20
    I just read the Rellihan document. RAPCO is about two miles from me if there is anything I can do to restart this effort. I used to have a couple of contacts there, but unfortunately they are gone.
    Bob Schmidt, Founding Member
    Sundowner N282G has landed in:

    Also flew VH-WEI in Oz.

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