In a constant speed propeller, constant speed unit maintains the selected RPM automatically.
In Variable pitch propeller pilot has to do tit manually by varying the blade angle using the propeller levers.
It consists of
- Fly weights
- Speeder spring.
- Pilot value
- Governor oil
- Pitch changing mechanism
- Reservoir
On speed condition RPM = Selected RPM
Centrifugal force = Tension
Under speed condition RPM< Selected RPM
Centrifugal force < Tension
Centrifugal force is less than Tension
Oil pressure decreases blade angle increases and RPM decreases.
Over speed condition RPM > Selected RPM
Centrifugal force > Tension
Centrifugal force is more than tension.
Oil pressure increases blade angle decreases and RPM increases.
Oil pressure changes pitch to decrease blade angle.
Speeder Spring causes pitch to increase blade angle.
Pilot value is a float valve a position of float value is governed by centrifugal of flyweights and tension of the speeder springs.
Forces on the flyweights are centrifugal and tension.
Centrifugal tends to pull them out and tension tends to push them inwards.
If oil pressure increases, it compresses the piston and blade angle decreases and rpm increases.
– If spring force increasing, oil pressure decreases, blade angle increases, rpm decreases.
On moving the propeller lever in the cockpit we actually change the tension of the speeder spring.
When we select a higher rpm, we increase the tension of the speeder spring and vice-versa.
EPR is ratio of pressure before entering combustion chamber to outlet of combust chamber (Before entry turbines.)
When propeller are put full forward to increasing rpm the speeder spring tension increases and oil pressure decreases angle and increases rpm