Paul,

    Years ago there were two brothers from Venezuela with a Cozy powered by
   two
    Suzuki Swift engines that were Siamesed together.  They didn't share the
    same prop, but instead used two counter-rotating props.  The prop shafts
    shared the same centerline.  In cruise, they could shut down one engine
   and
    greatly reduce the fuel burn.  I don't see why this idea couldn't be
    applied to the rotary using two 13b engines.  It would require the use
 of
    belt drives.  I believe Wankel GMBH developed one along these lines they
    called the Wankel Twin-pack.  (discussed in your YouTube video)  I
 always
    thought that would make a great package for a larger plane if someone
    wanted to spend the time and money to work out all the details.

    Mark


   I've been tossing this idea around in my head, and I really like it.
   (This is why I was asking about reverse rotation and 3d models a few
   days ago).  It seems so neat to be able to have an almost completely
   independent twin setup in a single engine sized package.  The only
   interlink really is the sharing of the engine mount and perhaps some
   bearings in the prop shafts.  Both of those can be designed to a very
   low failure rate.

   I've roughly sketched out a few things, and it seems to me that the
   best way to go about it would be to face one engine forward, and the
   other backwards.  The backwards engine would drive a countershaft off
   the similar to some supercharger setups except off the flywheel side,
   and the forward facing engine could drive the external co-axial shaft.
    I think Mark was right that a belt drive setup would be best.  This
   setup has a couple of benefits over facing both engines the same way.
   First is that you can have the plugs all facing inwards and the
   exhaust and intake facing outwards.  This will make mounting of coil
   packs a bit easier, and will prevent exhaust from one engine heating
   the other up.  The intakes could possibly share a common filter and/or
   plenum depending on how you set them up.  Depending on the mounting
   setup, you may be able to keep the engines a little closer together.
   The countershaft could also provide a great moment arm to resist the
   bending moment from the props

   If one did want to keep both engines pointing the same direction, a
   gearbox type setup with a reverse idler would certainly work.  I think
   it would be more expensive to do that way, and possibly a little
   heavier as well.  You'd have to worry with oiling too.

   Anyone have any thoughts?


   Josh


  Are you talking about twin engines driving a single prop, or a twin setup
  with independent engines, props, etc?

  Kevin Alderman



 I'm talking about twins driving separate contra-rotating props.
 Basically everything would be independent. It's all the advantages of
 a twin in with single engine drag, no yaw on engine out, and no torque
 steering on the ground... like the Cessna 337 except both engines and
 props are at the same location.

 Joshua Jacobs


The engineering has been done- find any Volvo boat outdrive from the last
20 to 25 years- they have been using counter rotating props on the same
shaft for decades.
The design is simple- the shafts are one inside the other. The main input
shaft has a single gear on it and the shaft drive gears mesh with this
drive gear. Since the drive gear is being tapped for power from both sides,
the shafts rotate opposite directions.

Lately Mercruiser/Cummins have partnered to make a diesel powered unit
similar to the original Volvo unit.

http://www.marinepartsexpress.com/vp_sch_fs.html

Kevin Alderman

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