Microlight » Aircraft Tech Knowledge » Propellers

The function of a propeller is to convert the power developed by the engine (brake horsepower) into thrust to propel the aircraft forward through the air.

Propeller blades are constructed using aerofoil sections to produce an aerodynamic force, in a similar manner to a wing.

The pitch of a fixed-pitch propeller is fixed from manufacture.  

The performance of your aircraft is determined on the day your propeller is fitted, and is going to be limited within the constraints of the propeller.

A good example is with a car and you had only one gear.

Because a propeller blade is most efficient at only one pitch angle, a fixed-pitch propeller is only efficient for one phase of flight and has a limited range of power and speed (it is usually set to be most efficient for the cruise phase of flight).

Therefore, during other stages of flight (climbing & descending) it is less efficient.

A variable-pitch propeller was designed to overcome this problem.