Flexadyne drive

Discussion in 'Firewall Forward / Props / Fuel system' started by BDD, Apr 24, 2005.

Help Support HomeBuiltAirplanes Forum by donating:

  1. Apr 24, 2005 #1

    BDD

    BDD

    BDD

    Well-Known Member

    Joined:
    Apr 2, 2005
    Messages:
    388
    Likes Received:
    3
    Location:
    WI
    Does anyone know what the flexadyne (spelling?) drive that Molt Taylor used to use weighs?

    Also, is there a lightweight version for ultralights? If so, what does it weigh?
     
  2. Aug 19, 2005 #2

    Topaz

    Topaz

    Topaz

    Super Moderator Staff Member

    Joined:
    Jul 30, 2005
    Messages:
    13,729
    Likes Received:
    5,407
    Location:
    Orange County, California
    I don't have the answer, but I know who does:

    http://www.mini-imp.com/

    These are the folks still selling the plans to Molt's designs. The Flexidyne is manufactured by Dodge (no relation to the auto manufacturer), but they refuse to sell to aircraft builders. You have to go through a reseller and say something like "I'm building an airboat." Seem like they think that if it has wings, they'll automatically get sued.

    Your biggest worry with a Flexidyne is not the weight. It's the price. Upwards of $1,100 (!) for one in the power ranges for aircraft.
     
  3. Aug 20, 2005 #3

    orion

    orion

    orion

    Well-Known Member

    Joined:
    Mar 3, 2003
    Messages:
    5,800
    Likes Received:
    135
    Location:
    Western Washington
    There's a couple of basic problems with the Flexadyne and the one near the top of my list is the price. I actually knew it was up there but over a grand? No thanks.

    The weight is pretty substantial at well over sixty pounds. There may be other suitable models of this coupling but the one that Molt used was a pretty hefty boat anchor.

    The other major problem though is that although it works, it does so at times only for a limited period. The coupling is basically a swash plate running in an enclosed volume that is filled with lead shot (and hence the weight). As the torque and rpm are increased, the lead shot are pressed outward through centrifugal loading and locked into place against the sinusoidally shaped swash plate.

    During occurances of potentially damaging torque peaks, such as are encountered when you encounter torsional feedback, the coupling has the ability to momentarily disengage and thus limit the torque peaks to below destructive levels. The coupling does not necessarily elimiate the feedback but it does keep it from building to a destructive level.

    But now here's the problem - this locking and unlocking action may happen at a relatively high frequencies. As such, the lead shot is under quite a bit of loading and friction, which eventually starts to wear on the little balls. The wear breaks them down into powder.

    If this situation goes on long enough, the volume fills with this lead powder, which then tends to firmly lock the assembly in place, thus eliminating the ability to break loose at high torque levels. At that point you might break the driveline just as if you had no coupling there at all since you have a rigid direct connection.
     
  4. Aug 21, 2005 #4

    Topaz

    Topaz

    Topaz

    Super Moderator Staff Member

    Joined:
    Jul 30, 2005
    Messages:
    13,729
    Likes Received:
    5,407
    Location:
    Orange County, California
    Yeah, the price is simply absurd, considering what it must actually cost to manufacture the thing in quantity. There are photos on the Mini-IMP website of a disassembled coupling: A cast outer housing with bearing seats, a stamped 'wavy plate' for the coupling, and a machined output shaft.

    Motion Industries lists the 9C coupling (currently recommended by the Mini-IMP plans dealer) at $1,757.40, which is up nearly $400 from the last time I checked about a year ago.

    Probably in exact regard to the problem you mention, Orion, the Flexidyne is now using steel shot (and even stainless is available) for the working 'fluid' now. I imagine that eliminates the problem.

    Still, it all starts to feel like it's more trouble than it's worth, especially when you realize that you're going to have custom-machine an adapter plate for the output shaft of your motor, plus a custom fitting for the driveshaft to the prop as well. I looked into one of these for an older version of my project, when it appeared that I might need some kind of drive shaft.

    I gave it up and found another way.
     

Share This Page

arrow_white