Virgin Galatic Spaceship Two down in the Mojave.

[pchapman]

Deptrai quoted: "Two main pneumatic 625-psi actuators with a 9.5-in bore and 31-in stroke, change the position of the feather ..."

625 psi (max?) over an area corresponding to 9.5" diameter gives a force of over 40,000 lb possible on each actuator. Quite a bit, which would seem to make it nearly irreversible, almost as good as a hydraulically operated screw jack on an airliner.

But is there pressure already applied to both sides of the piston before the Feather handle is actuated? From the results, maybe not.

Perhaps the feathering cylinders only receive pressure when the feathering handle is turned to open valves -- Rather than having both sides of the cylinder pressurized. That would be perhaps slightly more complex, more like some always-active hydraulic system. Rather than just "start adding a shot of air when needed to the Feather side". (Even then they would need to be able to let the pressure bleed down and pressurize the other side of the piston to defeather later.)

As for forces on the tail, the stabilizers themselves might well have a down force on them, especially as a typical airplane tends to have a mach tuck due to rearwards movement of the center of pressure in the transonic range (and loss of effectiveness of a conventional elevator, not a factor here).

However, the feathering mechanism also includes the aft end of the wings which will have some lift on them. While I'm a little surprised at it, the results suggest the net forces were to flip the tail up as soon as the locks were removed.

In conclusion, it sound like the feathering system may be set up assuming that there would be very little aerodynamic force once the locks were withdrawn, without the system being pressurized before selecting Unlock, and thus unable to oppose any significant aerodynamic forces.

That would suggest a design which, while entirely effective, lacked some safety redundancy that could have been added probably without too much trouble. Turn that one handle too soon and boom, you pitch up with massive up elevator and loss of lift from the aft end of the tail, you swap ends and disintegrate.

But one would like to know more about the feathering system to better understand whether this speculation is correct or not.
(Edit: And I don't know what kind of leverage the tail might have on the actuator around a pivot point, which also affects to what degree the tail can try to back drive the piston even if pressurized)