Hi Paul,
          A couple of pics of the gearbox bits so far. I am going to see if the gearbox can be made so as to be able to change the ratio to 2.85 or 3.17 relatively easily.
                  Cheers Chris. in NZ


Looking good Chris. Good idea. Since the stock red line on the Mazda RX8 is 9000 RPM the
3.12 makes the most sense. At 1700 prop RPM that gives 8400 Engine RPM which is still below the 300 HP possible with a Mazda p-port at 9000 RPM. My guess is an easy 280 HP. That puts the Mazda rotary 100 pounds lighter than any piston aircraft engine of the same power and about the same weight as a turbo prop engine with half the fuel burn. With aluminum end housings it would be 50 pounds lighter still. Of course a turbo compound version would destroy the rest of the light aircraft engine industry and give more power at altitude than a turbo prop.

I wonder when they are going to wake up :)

Paul Lamar


Hi Paul,
         Here are a few more pics of gearbox parts, I am going to make it so it can be used for pusher or tractor configuration.
             Cheers Chris.

Beware those rubber doughnut couplings. They have about a 5000 RPM limit.
That could have been the demise of the Rotomax. The crash occurred because the engine disconnected from the prop. They are also a bit too stiff.

What brand is it?

Paul Lamar


It is a centaflex-A. The guys at Bravini in Auckland where I bought it reckon it should go higher. Note it is a four bolt one, size 22 as opposed to the three bolt one in your picture.
I'll give it a try and keep an eye on it. I'm going to make the engine cowlings like a car bonnet (hood) so that it will be real easy to open for each preflight.
        Cheers Chris.


Size 22 is too small.


200 foot pounds from the rotary is 271 newton meters.
That is average. Peek is twice that. For oscillating torque you must triple the rating.
That means you will need at least a number 30 and that max RPM is 4000.


Also the temperature must be taken into consideration.
The box runs up to 200F or 93 C. For 90C you must double
the torque factor. They are not made with high temperature
(500 F) silicon rubber.

On top of all that they are too stiff.

Frankly IMHO these joints are dangerous as they give no warning of total failure.

Billet  couplings or welded couplings are fail safe in that they go into a metal to metal state
if all the silicon rubber gets out of there some how so the prop keeps turning no matter what.

Paul Lamar

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