Re: Propellor "reverse thrust"

Date:         05 Sep 97 17:27:23 
From:         faurecm@halcyon.com (C. Marin Faure)
Organization: Northwest Nexus Inc.
References:   1 2
Followups:    1
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In article <airliners.1997.1971@ohare.Chicago.COM>, k_ish
<kenish@ix.netcom..com> wrote:

> showie@uo.guelph.ca wrote:
> > On the subject of reverse thrust, I took a flight on a Manx Airlines
> > Shorts 330 a few years back.
>
> Almost every high-performance piston or turprop aircraft has a variable
> pitch propellor.  A coarse (high) pitch is more efficient at low
> (climbout) airspeeds, a finer (low) blade pitch is efficient at cruise
> speeds.  On descent, a zero or almost zero pitch creates lots of drag to
> help control descent airspeed.  Most turboprop aircraft have a "beta" or
> reverse-pitch position which works exactly as you speculate.  Lastly,
> most multi-engine planes can "feather" their props (blades aligned with
> the airstream).  If an engine fails, its prop is feathered to minimize
> drag.

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.  The Beta range of a propeller actually includes that
portion of fine pitch that is flatter than the normal minimum pitch as
well as zero pitch and reverse pitch.

C. Marin Faure
  author, Flying A Floatplane