The propeller blade of a ship refers to a blade that can rotate in the water. It is a part of the device that converts the engine’s turning power into propulsive force. There may be two or more blades connected to the hub. A kind of marine propeller.
The change of the propeller blade’s pulling force with the rotation speed is as follows: As the engine output power increases, the propeller rotating speed (tangential speed) rapidly increases to a certain value, and the propeller pulling force increases. In the process of ship technology development, the research on the design of propeller blades has done more than any professional field. It has transitioned from empirical methods to digital design, and then applied computer technology to optimize the design of propeller blades. The blade angle of the propeller should gradually increase from the blade tip to the root
Propellers are divided into fixed-pitch and variable-pitch propellers. ① Fixed-pitch propeller Wooden propellers are generally fixed-pitch. Its pitch (or blade mounting angle) is fixed. The blade installation angle suitable for low speed is too small when flying at high speed; similarly, the installation angle suitable for high speed flying 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 states. The fixed-pitch propeller has a simple structure and light weight, and is widely used in light aircraft and ultralight aircraft with very small power.
② Variable pitch propeller In order to solve the contradiction between high-speed and low-speed performance of fixed-pitch propellers, variable-pitch propellers have appeared in flight. The propeller pitch changing mechanism is driven by hydraulic or electric power. The original use was a double-pitch propeller. Use high range at high speeds and low range at low speeds (such as take-off and climb), and then increase the number of pitches gradually to accommodate more flight conditions. The most 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 rotational speed of the engine and the propeller by controlling the regulator and the throttle. On the one hand, the drag of the propeller can be adjusted while the propeller is in the best working state. In a multi-engine aircraft, when one engine fails to stop, the propeller rotates like a windmill under the action of oncoming airflow, which increases flight resistance on the one hand, causes a large unbalanced torque, and may further damage the engine. To this end, the variable-pitch propeller can also be feathered automatically, that is, the blades are turned to the basic airflow direction to keep the propeller stationary to reduce the resistance. The variable-pitch propeller can also reduce the pitch and generate negative tension to increase resistance and shorten the landing run distance. This state is called reverse paddle.