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 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.
   --
   Paul Lamar ...No rotor no motor.



Thanks for the explanation, it's helped clear the fog.

Rob Lutz


Paul Lamar ...No rotor no motor.

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