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The screw propeller geometry
Here we will define the geometry and vocabulary to describe a screw propeller

screw propeller geometry

 

The propeller blade is described by profiles, which divide it into elements:

screw propeller geometry

Bootup screen software propellers and wings design HELICIEL

 

The elements of the blades are framed by profiles located at a distance R on the axis of blades:

screw propeller geometry

To optimize the efficiency of the propeller blade profiles are usually aerodynamic or hydrodynamic shape. (Detailed profiles blades Description).

screw propeller profile

The pitch of the propeller deserves a detailed description because it is necessary to distinguish the geometric pitch of the propeller, and the effective pich of the propeller:The combination of the rotational speed and the speed of the fluid generates a speed composed, which we will call Apparent speed.The angle between the fluid path and the plane of rotation is the apparent angle.

screw propeller attack angle incidence spedd

The angle between the apparent direction of the fluid and the profile chord is the angle of incidence or attack angle:

le calage des profils de la pale est réglé por que l'angle apparent et la corde donne une incidence optimum

 

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 HELICIELblade profile generator

The 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.