Figure 2-1. Hartzell Pitch Change Mechanism

Figure 2-2. Hartzell Constant-Speed Propellor

TM-1-1500-204-23-5 General Aircraft Maintenance Manual
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TM 1-1500-204-23-5 c. Feathering Propeller. A feathering propeller is a controllable propeller having a mechanism to change the pitch to an angle so that forward aircraft motion produces a minimum windmilling effect on a power-off propeller. Feathering propellers must be used on multiengine aircraft to reduce propeller drag to a minimum under engine failure conditions. d. Reverse-Pitch Propeller. The reverse-pitch propeller is a controllable propeller in which the blade angles can be changed to a negative value during operation. The purpose of the reversible-pitch feature is to produce a high negative thrust at low speed by using engine power. Although reverse-pitch may be used in flight for steep descents, it is used principally as an aerodynamic brake to reduce ground roll after landing. 2-5. Propeller Efficiency. A propeller is used with an engine to provide thrust. The engine supplies brake horsepower through a rotating shaft. The propeller absorbs the brake horsepower and converts it into thrust horsepower. Propeller efficiency is the ratio of thrust horsepower. Thrust horsepower usually constitutes approximately 80 percent of the brake horsepower. The other 20 percent is lost in friction and slippage. Controlling the blade angle of the propeller is the best method of obtaining maximum propeller efficiency for all conditions encountered in flight. 2-6. Engine Efficiency. Mechanical, thermal, and volumetric efficiency are explained in the following paragraphs. a. Mechanical Efficiency. The mechanical efficiency of an engine is measured by the ratio of the shaft output or brake horsepower to the indicated horsepower or power developed in the cylinders. It can be expressed by the following formula: Brake horsepower Mechanical efficiency = Indicated horsepower Figure 2-1. Hartzell Pitch Change Mechanism 2-4

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