Burt Rutan's Scaled Composites has conducted three glide flights of its SpaceShipOne suborbital vehicle, intended to test changes introduced to correct a pitch-up problem experienced on the third flight in September. On that flight, the first stall entry manoeuvre resulted in an uncommanded nose rise before reaching the wing stall angle-of-attack.
Scaled says its computational analysis was not enough to predict airflow separation on the outboard horizontal tails, which operate in the wingtip vortices.
Further ground testing resulted in the addition of a fixed strake bonded to the tail boom forward of the stabilator and a spanwise flow fence on the leading edge of each horizontal tail at mid-span. Following modification, no pitch-up tendency was noted on the 17 October fourth glide flight.
Subsequently, the horizontal tails were enlarged. Two flights with the larger tails have shown increased pitch and roll control authority, Scaled says. The flights demonstrated satisfactory handling at aft and emergency centre-of-gravity limits.
Source: Flight International