Contents
What are propeller coefficients?
A propeller creates a thrust force out of the supplied power. While an airfoil can be characterized by relations between angle of attack, lift coefficient and drag coefficient, a propeller can be described in terms of advance ratio, thrust coefficient, and power coefficient.
What does a bigger diameter prop do?
A prop with more diameter has more total blade area, which allows it to handle more power and create more thrust to move a heavy boat. More blade area gives the engine more “traction,” like a set of aggressive truck tires.
How to calculate the diameter of a new propeller?
This can be done by solving the following expression for the new diameter, Dnew, which is the diameter of the replacement prop: NBold, NBnew = number of blades on the old and new propellers, respectively S old, Snew = blade planform area of the old and new propeller, respectively, in ft 2 or m 2
How big is the pitch of a 2 bladed propeller?
Almost 2000 static (J = 0) function points were considered for 2-bladed propellers from different brands, diameters in the 8 – 30 inches range, Pitch/Diameter in 3 – 1 range and different RPM ranges.
Since power and torque are related through Equation (14-29), this implies that the torque generated by the new propeller cannot exceed that of the old prop. The following assumptions are made: The planform shape of the old and new propellers is the same. This means that the center of pressure of the blades occurs the same distance from the hub.
J we have as an input, Re and Ma can be written as functions of D and RPM, as for Beta, pitch is defined as how much would the propeller travel forward with one revolution, so we can argue that the P/D ratio is somewhat related to a “average angle of incidence” of the propeller.