Richard Konnen wrote:

Paul,
  If understood correctly. With avariable length intake, as you get

shorter

to keep torque up at higher RPM, you loose volume efficiency. Is there a
happy medium to this or is there a particular combination that would be
needed.
Richard Konnen

Not necessarily. Depends also on pipe diameter. Shorter pipes less skin
friction drag. Higher RPM, more air, higher velocity in the intake... more
pipe skin friction drag. Drag is velocity squared. Bigger pipes less skin

friction

drag for a given amount of air. The amount of air actually getting in the
engine with a tuned intake system is also affected by the velocity in the

pipes

so at low RPM you want smaller pipes to keep the velocity up. That is

mainly

applicable to cars that need high HP throughout the RPM range.

Don't forget HP is torque times RPM so you are not necessarily losing
HP. The PP rotary breaths so well however HP is a straight line more or

less up to

the limit of the rotor bearings or somewhere around 10,000 RPM. Assuming

of course

you change pipe length and diameter :) That is what the RX8 intake system
does in incremental steps.

Airplanes fly on HP and not torque. The reason this is true is HP is also

drag

times velocity. Prop torque is whatever the gear box ratio is.

For a simplified pseudo math equations:

Engine RPM times engine torque = prop RPM times Prop torque = HP

Prop RPM X Prop Torque = Drag X Velocity = HP

There are a few constants here and there missing :)

The Le Mans engine had about two inch diameter pipes which are as about
as large as practical given the rotor width. With the right
length pipe it had a record amount of HP at 6000 RPM. Namely
240 HP for a two rotor version.

Paul Lamar

Did you mean 340? 240 sounds rather low.....

Thomas J. :)

240 for a two rotor normally aspirated at 6000 RPM is very very good.
480 at 6000 RPM for a four rotor.
Peak HP for the four rotor was 690 at 9000 RPM.

Remember we are not talking turbo charger here.

Power Sport had about 215 HP NA at 6000 RPM with a PP.

BTW the NA side port RX8 motor makes only about 180 HP at 6000 RPM. To get
250 you need to wind it to 8500 RPM.

This is why you need a 2.85:1 PSRU. Ken Welter mentioned he is
building a 3.12:1 PSRU based on the Ford six pinion planetary gear set
for his Coot. Amphibians need a lot of low speed thrust and that
can only be had by a large diameter prop. (Think of a helicopter) 
Since the prop tip speed is limited you need a lot of gear reduction to 
run the engine faster and obtain the HP.

Paul Lamar
 
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