RichardC10
since the locks are not needed when the vehicle is slowing down through the same speeds after engine shut-down.
thcrozier
I'd be very interested to know the altitude at which it goes subsonic on descent.
It may well be that during the descent the aircraft is subsonic before the feather is lowered and gliding begins.
The idea of the feather is that the aircraft is both stable and has high drag. (I am almost sure that everyone will know this already but not quite:-)
SpaceShipOne Pilot Report
SS1 simulator ride
"As we approached apogee, as indicated by the rate of climb, Jim Siebold, one of the SCALED test pilots who had taken over coaching me, called for feather deployment. I pulled a large lever under my left arm up to unlock the feather, waited until the TONU told me it was unlocked, then pulled the feather lever.
...
In the SS1, once in feather, the airplane is so stable and self-aligning that the pilot doesn’t have a thing to do but wait until it’s down to around 60,000 feet, when he puts it back in glider mode and he starts worrying about finding the airport.
The foregoing is a brilliant concept. It removes the single most terrifying and critical part of space flight. The SS1 never sees indicated re-entry speeds higher than about 130 knots even though mach numbers are approaching 3.2 so it never gets hot."
So if an indicated airspeed of 130 was assumed someone could work out the altitude that the aircraft passed below mach one. That would set a lower bound to the altitude since the actual IAS might be lower.
I could root around for a while and get some numbers but there is likely someone here who knows what they are about and I propose to leave that to them.
Ah, coffin corner! Possibly an easy way to get some decent data.
According to the diagram on
Coffin corner (aerodynamics) - Wikipedia, the free encyclopedia the U2's "mach limit" (pretty sure this is under mach 1) is 125 KIAS at 65,000 ft and 145 KIAS at 60,000 ft. In the case of SS1 then 130 KIAS therefore seems comfortably subsonic at 60,000 ft when the feather is unfeathered. Does anyone have any idea what the stall speed might be? That is, is there any need to go faster again?
If it is the case that the stall speed at 60,000ft is above 145 KIAS then the transonic flight regime could be avoided entirely during the feather stowed portion of the gliding descent to the landing.