Paul, At what RPM would you say a p ported one rotor would make more power
that a side ported engine with large side housing, like 3rd gen Rx7 or 20B
housings? Has anyone dyno tested to find out? What RPM are the 13b aircraft
engines at max take off power? Cruise?

Curious

Skip Gorman

With the proper length and diameter of intake pipes it could be as low
as 4000 RPM. However since HP and HP to weight ratio is a direct function
of RPM it would be very dumb not to tune for 7500 RPM max or more.

HP = RPM X TORQUE / 5252

My crude guess is max HP at 4000 would be 4000/7000 X 120 or 70 HP.
That is assuming the engine is geared and can swing an 85% efficient
large diameter prop. The net HP out of the prop will
then be 70 X .85 or 60 HP.

If not geared and running the largest diameter prop possible
at 4000 RPM the prop efficiency will drop off to 50 to 60% efficient.
Now the net HP out of the prop becomes .6 times 70 HP or 42 HP.
Not enough for just about any aircraft with a 200 pound lump in
the engine compartment.

If you are going to handicap the power to weight ratio of a one rotor why
bother with a rotary engine? Just install a 90 HP geared Rotax 912 or better
yet a 200 pound direct drive 100 HP O-200 Continental. A lot less work.

However if you want fundamental structural reliability and a good HP
to weight ratio with lower cost go with a 120 HP p-port all aluminum
rotary with a 2.85:1 gear box.

Paul Lamar