Subject: BSFC and stuff
From: Rotary Engine
Date: 4/16/2008, 9:17 PM
To: AAA Put this in the To box


a constant speed prop can improve overall fuel efficiency in
2 ways. That lower engine RPM reduces net fuel consumption and increase in
pitch allows better engine loading reducing BSFC?
C. Smith

Absolutely and right on.  It is very noticeable in my C182. I can up the
pitch slow the engine lean, the carb and I am burning 11 gallons an hour with a 230
HP engine and getting 13.6 MPG with my real draggy C182 at 150 MPH.

This 215 HP P-port rotary powered Velocity with a constant speed prop ran
212 MPH and burned 14 gallons and hour in the 500 mile Dayton to OSH race last year
as I recall. 15 MPG.

-- 
Paul Lamar ...No rotor no motor.


Paul, this is exactly the same method we used operating our T182T. I picked
it up reading a book titled "Flying High Performance Singles and Twins"
written by John C. Eckalbar. My fuel burns were 12.4 GPH, 131 KTAS @2100 RPM
with a MP of 27/28 inHg: TITs were set to book of 1640 (IIRC) so lean of
peak operations could have saved even more fuel (though probably at a loss
of airspeed). I think when I finished the math from some long cross
countries my gas mileage was close to that of my Ford P/U 17-18 Mpg.

I would like to propose an effort to get constant speed/in flight variable
pitch props added to the permitted equipment list in all aircraft, including
UL and light sport based on the fuel efficiency gains. There is nothing in
my experience of operating a constant speed prop that makes this a giant
leap in cockpit workload, or pilot proficiency. The biggest problem is see
is some of the wives tales taught by flight instructors about "Squaring
manifold pressure to prop RPM". There is nothing adverse in operating over
square, as long as the engine manufacturer has not prohibited it. In fact,
over square operation increases engine efficiency, and emissions. Lets try
to get the regulators to help reduce the carbon footprint of GA, while it's
still politically correct to save fuel and have cleaner air!

C. Smith


The rotary does not care about over square :)

Paul Lamar

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