Rather than NACA, might consider a "speed mod" described in book "Speed with
Economy" by Kent Paser, Paser Publications, 5672 West Chesnut Ave,
Littleton, Colorado 80123 (1994), Chapter 3, Engine Intake System
Modifications, starting page 52, ". . . use of propellor pressure pulses to
augment the ram air flow into the cowl carb air scoop." . . . ". . .the
scoop was extended forward about 8 inches, and the scoop opening was
rounded-off with an inlet area reduced to about 1.5 times that required for
sufficient flow to the carburetor. . . the scoop clears the propellor by
only 5/8 of an inch, with an inlet area only 10% larger than the venturi
throat area of the carburetor. . . .The scoop inlet is . . .about a 10
degree angle into the advancing propellor blade. . .the sides of this inner
liner diverge at less than an 11 degree total angle.  Any larger . . .and
the scoop would go turbulent"

David Carter

----- Original Message ----- From: "Paul" <sqpilot@bellsouth.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Wednesday, February 16, 2005 5:26 PM
Subject: [FlyRotary] I found the power


Today I finished installing the firesleeve on the remaing fuel lines, made
some stand-offs so that the fuel lines would not be right up against the
engine, and finished hooking up and securing a few other items. With the top
cowling off,  I ran the pumps for a minute, then checked for leaks...none
found.  Then I started the engine and ran it for 20 or so seconds and shut
it down and reinspected for fuel leaks. None found.  I restarted and taxiied
away from the hangar a bit so as to not be as loud for others in and near
the hangar and did a full power runup.  I hit 5600 static rpm's. In the
past, the best I could hope for was 5200, most of the time settling for 5100
rpm's.  I taxiied back in and installed the top cowling....max rpm's 5100.
Took the top cowling back off....max rpm's 5600.  One more try....5100 with
the cowling back on.  It is beginning to become more clear to me, that one
of two things are affecting rpm's.  Option one is that with the top cowling
on the engine is ingesting heated air and just cannot develop the same power
as when it ingests outside unheated air.  Option two is the muffler bearing
may be worn.  I'm kinda leaning toward option one.
    I was thinking of installing two small NACA ducts on the bottom of my
cowling with two hoses coming up to feed air to my TWM throttlebody.  The
NACA ducts I purchased from Van's RV (made for cowling ventilation) already
have a male outlet already molded in the assembly, so you just slide a hose
over it and secure with a clamp. Very simple installation.(Works well for my
cabin ventillation) If I recall correctly, they are about the same size as
my throttle body bore. I wonder if I will loose much efficiency as the air
goes through the corregated hose, and if the Van's RV ventillation NACA
ducts will provide a sufficient volume of air. Of course while flying, I
would have the advantage of a little bit of ram effect as well as the
ability to suck in fresh outside air that has not been heated inside the
cowling during taxi/takeoff run.  Any opinions/suggestions would of course
be much appreciated.  I will discuss the vapor lock issue in the next post,
so as to not complicate responses, etc.  Thanks to all who reply.  Paul
Conner



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