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The screw propeller geometryHere we will define the geometry and vocabulary to describe a screw propeller
- he X axis represents the axis of rotation or the propeller shaft.The direction and speed of the upstream fluid is parallel to the X axis
- The y-axis Represented the axis of the blade. For variable pitch propellers is the pitch change axis.
- P represents the plane of rotation of the propeller. The disc swept by the blades of the propeller, is located on the plane of rotation.
- W is the angular velocity of rotation. This speed can be given in radians / second (rad / sec) or revolutions per minute (Rpm or rev / min)
The propeller blade is described by profiles, which divide it into elements:
The elements of the blades are framed by profiles located at a distance R on the axis of blades:
To optimize the efficiency of the propeller blade profiles are usually aerodynamic or hydrodynamic shape. (Detailed profiles blades Description).
- The profile chord line connecting the leading edge to the trailing edge
- L = chord length
- A= leading edge(attack) of the profile
- B= trailing edge of the profile
- e= Maximum thickness profile
- d= distance leading edge and blade axis
The angle between the apparent direction of the fluid and the profile chord is the angle of incidence or attack angle:
The profiles can be arranged along the blade axis in a line which is called the generator profiles. this Generator profiles can be curved in the direction of rotation. This curvature generator is called "skew". The generator may also form an angle with the plane of rotation. This gives conicity angle to the propeller. This angle moves the blade tip back in the plane of rotation. This offset is called "Rake" .
interface generator in HELICIELThe curvature of the generatrix of the blade, coupled with twisting, causes a shift of the profiles to the rear. It therefore generates a conicity induced by the curvature of blade generator. This even if no cone angle is given to the generator.