Jerry Hey wrote:

Paul,  on your drawing of the pp modification you have the
instruction to "Port the Inner Part with a die grinder to square
it up,"   what are your referring to?  Does the port transition
from round on the  outside to square on the inside?

Yes. Here is a picture of a racing beat PP.
The drawing is of Ken Powell'e variable timing PP but
it shows the dimensions of the square. You should round off
the corners.

Can you provide a drawing showing the inner
shape?   Also, is there a throttle body available as you have
drawn it, or one  that can be modified?   Jerry

You will have to make that part. Two throttle bodies are used. One
for each rotor housing. Gives a better idle when the butterflies
are close to the rotor housing.

Paul Lamar

Paul and Jerry,
   I would love to see the variable PP design installed and tested.
   Jerry, would you
be interested in installing the variable PP intake valves that Paul
built?  I would be happy to send them to you if you are interested.
   It is thought by some that a PP motor with large amounts of
   overlap has
somewhat poor idle characteristics due to exhaust gas dilution of
the intake charge. In order to minimize this intake charge dilution
we decided to use the same technique that are used on 2-stroke
racing motorcycles, i.e., vary the port timing on the intake port.
A secondary benefit is that at small throttle settings the velocity
of the intake charge is accelerated while in the intake port,
further promoting fuel atomization.  Also note that the BSFC should
improve at cruise due to the more conservative port settings.
   A slower idle is important because even at 700 - 800 prop rpm a
   highly pitched
prop will generate lots of thrust.  Since the Fast Glass and the
RV's are difficult to slow down a slower prop speed is beneficial.
Note that a 1200 rpm idle (engine) when used with a 2.85 redrive
will result in a prop rpm of only 421 rpm, a substancial reduction
over a 1800 rpm idle and a 2.17 redrive wich results in a prop rpm
of 830 rpm.

Ken Powell

If you are good you can get a high sink rate by putting the airplane
on the back side of the power curve. Pull the nose up short of stall
and watch the vertical sink rate increase. Its called "dragging it
in". Also a slip will increase the sink rate.

Paul Lamar

Oh, I really hate the back side of the power curve.  I can't help but imagine that I will
be in deep **** if the motor dies.  Slips are good!

Ken P.

True. I always try to stay high and slip it in. Safer in case the engine
quits on short final. Tracy will confirm that I screw up occasionally.
I landed down wind at his place because I was too lazy to fly over and look
at the wind sock. I over ran that little road that crosses the North East end
of the runway near Tracy's house. There were no trees for another 100
yards but I can tell you it is pretty rough in that over run area.
Tracy was real kind and merely claimed I used all of the runway :-)

Paul Lamar
 
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