Virgin Galactic's WhiteKnight Two prime contractor Scaled Composites is planning to fly above 50,000ft (15,250m), the altitude at which it will release its rocket-powered SpaceShip Two payload for its sub-orbital flights.

Scaled's high-altitude test announcement followed WK2's fourth test flight on 20 April, which saw the SpaceShip Two mothership experience a tail scrape.

Mojave air and spaceport based-Scaled has explained in a 23 April statement that a touch and go manoeuvre on the 20 April flight included a tail scrape and thrust asymmetry during take-off, causing a large left yaw. The asymmetry, says Scaled, was caused by an incorrect idle setting.

Scaled says that the yaw, which started to become a roll, was not due to the 15-20kt (28-37km/h) gusting crosswind reported by Mojave's aviation weather observation service that day.

Scaled also says that WK2 lacked stability augmentation and that means that changes had been necessary to the twin fuselage aircraft's rudders. Main landing gear wake vortices prompted some rudder modifications that included the addition of vortex generators to the vertical stabilisers. Rudder changes have been previously reported by Flight International. The company says it will not make any more rudder modifications.

"The basic stability of the WK2 about all three axes is strongly positive, and the aerodynamic design predictions match the flight test data very closely," says Scaled. "We will be flying to high altitudes [above 50,000ft] this summer."

Source: Flight International