Page 140 - Understanding Flight

CH05_Anderson 7/25/01 8:58 AM Page 127

Airplane Propulsion 127

Angle of attack

Low Airplane speed
Wind due to rotation

Angle of attack

Wind due to
airplane speed
High Airplane speed Wind due to rotation

Pitch

Fig. 5.5. Angle of attack of a rotating propeller.

Envelope of Max Efficiency
45¡
30¡ 60¡
20¡
Propeller Efficiency 10¡

Airplane Speed
Fig.5.6. Efficiency of a propeller at a single rotation speed for various
pitch angles as a function of the speed of the airplane.

too high an rpm. Thus the fixed-pitch propeller is at best a
compromise.
A solution to this compromise is the constant-speed propeller. The
constant-speed propeller allows the pilot to control both rotation
speed and propeller pitch. A constant-speed propeller works