Page 758 - PPL-engelsk 2025

Aircraft general knowledge

8.11.2.1 Constant speed propeller

A special type of propeller - the constant speed propeller - can maintain a fixed

speed and vary the blade angle depending on the engine's performance.

The thrust delivered is determined by speed + manifold pressure (air intake).

A fixed pitch propeller operates at peak performance in only one phase of flight

- normal climb, cruise or something in between.

Choosing one over the other means less performance in the other phases.

Choosing a propeller type therefore has both advantages and disadvantages. If

you choose to have a climb propeller delivered with the aircraft, it is probably

because you need to take off from short runways and climb over obstacles.

You then lose something in terms of cruising performance, as the aircraft's

cruising speed will be lower than if your aircraft had been delivered with a cruise

propeller.

This problem has been solved with a constant speed propeller, which utilizes a

central hub that connects the individual propeller blades.

The constant speed propeller provides good efficiency at all speeds, because the
blade angle can be controlled.

The propeller is controlled via the propeller handle, which gives the pilot the

option of choosing fine or coarse pitch depending on the circumstances.

In a constant speed propeller, 3 forces are utilized:

- Centrifugal twisting forces

- Oil pressure from the engine (gives low blade angle)

- Oil pressure from the Governor (gives high blade angle)

Flyveteori PPL(A)(UL)/LAPL Henning Andersen, Midtjysk Flyveskole© 2025 758