fixed pitch propellers and variable pitch propellers.

Propellers are divided into two categories: fixed pitch and variable pitch propellers.

Fixed pitch propeller

    Wooden propellers are generally fixed pitch. Its pitch (or blade installation angle) is fixed.

    The blade installation angle suitable for low speed is too small at high speed; similarly, the installation angle suitable for high speed is too large at low speed. Therefore, the fixed-pitch propeller is more efficient only in the selected speed range, and is less efficient in other conditions. The fixed-pitch propeller has simple structure and light weight, and is widely used in light aircraft and ultralight aircraft with low power.

Variable pitch propeller

    In order to solve the contradiction between the high and low speed performance of fixed pitch propellers, variable pitch propellers appeared in flight. The propeller pitch changing mechanism is driven by hydraulic or electric power. The two-pitch propeller started. Use high pitch at high speeds and low pitch at low speeds (such as take-off and climb conditions). Later, the number of pitches will be gradually increased to adapt to more flight conditions. A more complete variable pitch propeller is a constant speed propeller with a speed regulator. The speed regulator is actually a device that can automatically adjust the pitch and maintain a constant speed. The driver can change the speed of the engine and the propeller by controlling the regulator and the throttle. On the one hand, it can adjust the propeller’s pulling force while keeping the propeller in a better working condition. In a multi-engine aircraft, when an engine fails and stops, the propeller rotates like a windmill under the action of oncoming airflow. On the one hand, it increases the flight resistance and causes a large unbalanced torque. In addition, it may further damage the engine. For this reason, the variable-pitch propeller can also automatically feather, that is, the blades turn to the basic downstream direction to make the propeller stand still to reduce resistance. The variable-pitch propeller can also reduce the pitch and generate negative pulling force to increase drag and shorten the landing roll distance. This state is called reverse propeller.

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