BAe146/Avro RJ Speedbrake Expending on Ground

I have noted from some YouTube streams of the JustFlight BAe146/Avro RJ that they were wondering why the Speedbrake extends on the ground when no hydraulic system is available. 

The reason for this is that the actuator that operates the Speedbrake petals is an unequal area piston type. Although the hydraulic system is not available,  there is pressure still applied to the actuator from the hydraulic reservoir. 

So the hydraulic reservoir pressure (50 psi) acting on the unequal area actuator generates sufficient force to overcome friction and the Speedbrake petals move open.

However, once Green hydraulic pressure is available,  the actuator retracts under the control system to close the Speedbrake petals.

Edited November 5, 20241 yr by Peterwk
Correct the title.