Virgin Galactic's SpaceShipTwo mothership faces rudder problem

By Rob Coppinger

Virgin Galactic's WhiteKnightTwo may need to have its rudder and yaw stability improved to counter issues such as the greater fishtail effect that would be expected with a twin fuselage aircraft.

Flight International has learned that WK2 prime contractor Scaled Composites' test pilot Peter Siebold was finding it hard to keep the aircraft on the runway during the 20 December high-speed taxi trials preceding its maiden flight the following day. This could be due to inadequate yaw damping.

On 20 December Siebold asked Scaled's WK2 chase car if there was anything unusual with the rudder's tufts. Tufts are strips of material taped on to a rudder to give a clear indication of airflow around it.

Witnesses to the 21 December maiden flight told Flight International that they noticed some yawing during take-off, indicating a rudder issue or a problem with the airframe's stability in yaw. Flight International also learned that on 21 December, Siebold was hesitant to attempt any sideslip manoeuvres because of "the rudder issue".

Virgin Galactic president Will Whitehorn told Flight International: "There are no issues we know of at all at this stage which will affect the programme or the overall design [of the WK2]. It is beyond ridiculous. I am afraid to comment on alleged take-off cockpit dialogue during a first flight which then went to 16,000ft [4,880m] and landed without a hitch."

Whitehorn told Flight on 21 December 2008 that the next flight would be "early in the new year". To resolve any issues, Scaled may have to redesign WK2's rudder or improve whatever stability augmentation is being used. Scaled declines to comment. "At this time Scaled is not releasing any information related to the flight testing of [WK2] other than the fact it has made its first flight," it says.

© Reed Business Information 2009

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