REFLECTOR: Slowing down - reduce power; add drag

[Scott Baker]

In constant speed, hydraulic controlled propeller operations in single 
engine aircraft, the propeller governor will attempt to maintain the 
selected RPM by adjusting pitch.  When power is reduced at moderate air 
speeds (such as in the landing pattern) there becomes a point where their 
just isn't enough power to maintain the selected RPM - and the RPM begins to 
drop regardless of the propeller control setting.  An example of this is 
seen during normal landing operations when power is reduced opposite the 
numbers to begin the approach to landing.

Air speed is a factor in this discussion.  For example: If the aircraft were 
placed in a high speed, power off dive, the propeller governor would 
continue to operate normally - changing the pitch of the propeller to 
maintain the selected RPM.  The propeller control can be set for High RPM 
for increased drag (Example: Engine fire - pull the mixture (no power) - 
select High RPM for maximum drag - and point the nose down to get down NOW). 
Or, the propeller can be set for Low RPM (Example: Engine power failure - 
select Low RPM for minimum drag - less drag, less sink rate - less sink 
rate, more time in the air - more time in the air, the further the glide - 
the further the glide, more landing field choices).

If the engine were not turning - oil would not be supplied to hydraulically 
controlled, constant speed propeller - at which point the propeller is 
designed (in most single engine aircraft) to move to the High RPM position. 
In twin engine aircraft, the propeller is designed to move to Low RPM in the 
event of engine power failure.

SB

>> For aircraft equipped with constant speed or variable pitch propellers,
>> changing the propeller setting to High RPM adds drag - and contributes to
>> a
>> higher sink rate.
>> Conversely, in emergency power off glide situations, changing the
>> propeller
>> setting to Low RPM reduces drag - and minimizes sink rate.
>> SB
>
> Does this apply to a situation in which the engine is still turning (but
> producing little or no power) or engine not turning?
>
> Sid
>
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