Blade screw

Propeller) with variable pitch aircraft Hercules C.4 Royal Air Force in the plowed position

Blade screw - a device that rotates with the blades fixed perpendicular to the axis of rotation, designed to convert the movement of rotation of the screw into the translational movement of gases and liquids, and vice versa.

Application: aircraft and marine drive ( propeller , propeller ); the movement of gases, liquids, bulk and lumpy materials and the reverse transformation of the translational movement of gas or liquid to obtain rotational motion ( windmills , turbines of hydroelectric power stations , wind power stations ).

Blades of a wind farm

Submarine Propeller

Options:

• The diameter of the screw is the diameter of the circle described by the ends of the blades during rotation of the screw.
• Propeller tread - the actual distance that a propeller moving progressively moves in the medium in one full revolution (depends on the speed of the screw and speed of movement).
• The geometrical pitch of a screw is the distance that a screw moving progressively must travel in one full revolution if it moves in air as in a solid medium . The geometric pitch of the screw differs from the step of the screw by the amount of slip of the screw in the air.
• Propeller blade installation angle - the angle of inclination of the blade section to the plane of rotation of the screw. Since many screws have a twist of the blades, the installation angle is measured by the conditional section (usually 2/3 of the blade length).
• The edge of the blade that cuts through the air is called the leading edge , and the rear edge is called the trailing edge . The plane perpendicular to the axis of rotation of the screw is called the plane of rotation of the screw .
• The sections of the working part of the blade have wing profiles. The profile of the blade is characterized by: chord , relative thickness and relative curvature . For greater strength, blades with a variable thickness are used - a gradual thickening to the root. The chords of the sections do not lie in the same plane, since the blade is made twisted.

The screws are divided into screws with a constant pitch along the blade (all sections have the same pitch) and with a variable pitch (sections have a different pitch). For fixed pitch screws, the thrust increases as the rotation speed increases. Variable pitch propellers rotate at a constant speed, and their thrust changes with the speed-regulating angle at which the propeller blades run into air or water.