Paul,
   I am commited to using the P port configuration  and started looking at
   specs for props.  I do not think a 74" prop will fit on a pusher even
   though I have 48" from the ground to the thrustline.  I went to your
   website where you have two P Ports with different runner lengths.  Is
   there any advantage running the 2.85 PSRU over the 2.17?  The curve on
   the higher performance runner looks flat in the range from 6500 to
   7800.  I think I could swing a 68" prop.  Just trying to find the right
   combination.

   Joe Berki
   Limo
    EZ

   Yes. There definitely is a HP advantage. If you can not handle 74 inches think
   of a wider blade or 3 bladed prop that will absorb 240 HP of lower diameter.

   Just explain things to the prop builder and he will build a prop
   for 240 HP as little as 65 inches in diameter. Could be as many
   as four blades if he does not have a wide blade version.
   --
   Paul Lamar ...No rotor no motor.



I?m fairly new to the auto engine for aircraft concept and am looking
at the Rotary for my project. Can anyone explain the PSRU??s different
reduction ratios and how that relates to varying horse power from the
same Engine (my aircraft need around 200HP)? The way I understand it
is you?re basically trading RPM for Torque. Is this correct and can
someone expand on that? Should you expect much of a power difference
between using Tracyâ??s 2.85 to 1 PSRU or going to a 2.95 to 1 PSRU; is
there really that significant of a difference between the two ratios?

Thanks,

Rob Lutz

Airplanes fly on HP. Prop torque is mainly a function of the gear
ratio. A side intake port rotary has about 160 foot pounds of torque.
You can move this peak up and down the RPM range. The higher the RPM
of the peak torque is the more the HP.

This very simple formula well illustrates that relationship.

HP = Torque times RPM divided by 5252.

Since the rotary torque is a constant 160 foot pounds the higher
the RPM the higher the HP.

If you use a p-port the torque will go up to about 200 foot pounds.
If you use a 23 inch 2 inch OD diameter intakes pipes the peak torqure
will occure about 5500 RPM and HP will be 240 at 7400 RPM.

A 2.85:1 PSRU will give you the right prop RPM.