Originally Posted by
aerobat77
Do you have an example where pitch locks are installed in a free turbine design ?
The PW 100 series engine is a free turbine engine with pitchlock capability on the Hamilton-Standard propeller.
To quote from my notes...
"
Aerodynamic loads on the propeller tend to drive the blades toward low blade angles. Should the supply oil pressure be lost, a pitchlock feature engages to prevent aerodynamic loads from reducing the Blade Angle more than 1 degree and the propeller speed increasing more than 2% from the point of oil pressure loss. It then acts like a fixed pitch prop, increasing and decreasing speed with PL movement. The pilots could still feather the prop because the electrical feathering pump would pump oil from a cavity in the case (like a stand pipe). This is activated when the CL is placed in the feather position."
While the method to achieve pitchlock may be different, the effect is the same on the Allison engine that has a very different type of Ham Standard prop. Like the PW 100-Hamilton-Standard combination, a pitchlock leads to the equivalent of a fixed pitch propeller operation. There just seems to be more undesirable postential consequences on the Allison if rpm is not managed properly.