G'day Vic,

Despite the the theories given here the full size 337 performs better on just the rear engine than just the front!

Not by much, but it's measurable (single engine climb front 425'/minute vs 510. Single engine ceiling better on rear engine)

Pusher propellers are generally considered to be more efficient compared to tractor propellers. Bits of airplane in front of the prop create far less problems than bits behind. Propellers are reasonably tolerant of airflow interruptions ahead of them, while fuselages behind props will experience higher drag due to the faster air flow.

The turbulence of the front prop affecting the rear prop is a bit of a myth as well. Firstly props don't create much turbulence. They smoothly accelerate the air and give it a small spiral rotation (there are vortices from the tips similar to wing tip vortices).

Secondly, imagine that a given prop gives a 60 mph blast of air at full power on the ground with the airplane stopped. If you could measure the air just ahead of the prop it would be moving too, maybe 50 mph. Now imagine that that same plane flies at 50 mph, the blast behind the prop is still around 60 (let's throttle back a bit to allow for the prop unloading in this thought experiment). By the time that flow goes the length of the fuselage to the rear prop it will have slowed somewhat, maybe 55. So the rear prop sees air substantially the same as the front.

Obviously there will be more of a difference in a high power low speed climb, but my point is there isn't as much difference as most people think.

I think that if you double your thrust calculation you will be pretty close.

I would be very surprised if you found a noticeable difference having a higher pitch on the rear prop.

Like anything in this hobby the best bet is to make an intelligent guess for a start then adjust as required.

Nice model btw,

Dave H