Re: Propellor "reverse thrust"

Date:         11 Sep 97 03:35:32 
From:         k_ish <>
Organization: Netcom
References:   1 2 3
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C. Marin Faure wrote:
> This and the rest of your post is basically correct but for a couple of
> points.  Fine (flat) pitch is used during takeoff and climb to maximize
> rpm and therefore horsepower, sort of like the first gear in your car.
> Coarse or high pitch is used during cruise to maximize thrust while
> minimizing rpm and therefore fuel consumption, similar to fourth or
> fifth gear in your car.

You are correct, got the pitch explanation backwards!  I agree with your
horsepower explanation.  But optimizing prop pitch for a given airspeed
( putting the airfoil section of the prop blades at an angle of attack
that delivers the best l/d) is also an important factor, especially at
cruise speeds.  My experience flying Mooney 201s and Cessna 172RGs is
that cruise airspeed increases with prop RPM to a point.  But beyond
that RPM, airspeed starts to decrease a bit.  This would not happen if
it were due to horsepower alone.

Just hypothesizing based on observation...any comments?

BTW, Peter Garrison published a letter written to him in a recent
(July?) issue of Flying.  The writer has a very interesting and
different explanation for P-factor, while showing that the accepted
explanation cannot be correct.  Did you read it?  Comments?

Ken Ishiguro