Air flow through each small section blade aerodynamic, resistance ΔD and lift ΔL, after synthesis The total aerodynamic ΔR.ΔR component for tension along the direction of flight ΔT, and screw propeller rotating in the opposite direction of force Δ P stop rotating propeller.The whole blade on the tensile strength of the small pieces together and stop rotating force, tension and to prevent the propeller of the propeller of a rotational torque.
Figure can be seen from the above two.Each section must make propeller working in lift-to-drag larger Angle of attack, to obtain larger tension, smaller drag torque, high efficiency.The propeller is working.Axial velocity does not change with the radius and the tangential velocity change with radius.Therefore, near the blade tip radius with strong flow Angle is small, the corresponding blade Angle should be smaller.And near the blade root, the radius of the small flow Angle is bigger, the corresponding blade Angle should be larger.Propeller blade Angle from the blade tip to the blade root should be gradually increase according to certain rule.So the propeller is a reversed wing is more exact.
Can be seen from the table, the flow Angle actually reflect the speed and the ratio of tangential velocity.A section of a screw profile Angle of attack changes over the ratio.Angle of attack change, pull and drag torque changed also.Use into torque than the "J" reflect the blade tip flow Angle, J = V/nD.Type of D - propeller diameter.Theory and experiment prove that: the tensile strength of the propeller (T), overcome the propeller torque required power (P) and efficiency (η) can use the following formula:
T=Ctρn2D4
P=Cpρn3D5
η=J·Ct/Cp
Type: Ct —— tension coefficient;Cp —— power coefficient;ρ —— air density;N —— propeller speed;D —— propeller diameter.The Ct and Cp depends on the geometrical parameters of the screw, its value changing with J for each propeller.Figure 1-1-21 called characteristic curve of screw propeller, it is obtained by theoretical calculation and test.Characteristic curve is given the propeller force coefficient, power factor and efficiency change with forward than relationships.Is the design of propeller and performance of plane calculation is one of the main basis.
