When, at what altitude and speed, did the pilots of SpaceShipOne and SpaceShipTwo lose all or most of aerodynamic control over their spaceplane when rising into space? The SS1 and SS2 conducted five spaceflights altogether (as yet). Both planes reach top speeds around Mach 3. Is there a certain defined limit in the SS1 and 2 mission profiles above which aerodynamic control is no longer possible?
The Virgin Galactic "Party Submission" to the NTSB report on the Spaceship 2 accident sheds some light on this. This picture shows the cockpit procedural cue card for the accident flight. (Emphasis mine)
It shows the reaction control system (RCS) being enabled at 135,000 feet on the upward leg of the flight and disabled around 60,000 feet (specifically at 40 knots equivalent airspeed) on the downward leg.
For maneuvering outside the atmosphere, SS2 is fitted with a cold-gas reaction control system, with nozzles in the nose for pitch and yaw, and in the wing tips for roll thrust.