BACK IN ACTION

It's one of the strangest-looking aircraft in recent aeronautical history, but Scaled Composites' "White Knight" was the ideal vehicle for carrying SpaceShipOne (SSO) to high altitude. Dropped there, SSO ignited its rocket and flew into space and the record books in 2004--twice. Now, the one-of-a-kind White Knight is serving as an ideal testbed for large, heavy payloads.

The gangly, gull-winged White Knight hardly looks the part of a heavylifter, but its wide stance and long "legs" provide at least 7 ft. of ground clearance for test articles mounted on the centerline pylon. An approximately 82-ft.-long wing and two General Electric J85-GE-5 afterburning engines combine to deliver the testbed's high performance. The capability to carry large, heavy payloads to high altitudes at a reasonable operating cost has brought a number of customers to Scaled's door.

This Aviation Week & Space Technology editor flew on board the White Knight recently, doubling as a flight-test engineer during a 1.4-hr. data-gathering mission. Our payload was a FlexSys Inc. 50-in.-long "adaptive compliant wing" section with a 30-in. chord and a variable-camber trailing edge (see p. 72). It was mounted vertically on the White Knight centerline pylon, aligned with the direction of flight. The flexible trailing edge could be deformed +/- 10 deg., with a 1-deg. twist per foot of span.

Backed by U.S. Air Force Research Laboratory (AFRL) funding, the compliant wing model was tested in an AFRL high-speed wind tunnel in July, prior to a seven-flight series of tests on the White Knight. In essence, the aircraft was being used as "a wind tunnel in the sky" to acquire additional data under high-altitude flight conditions, notes Douglas B. Shane, Scaled Composites' vice president of business development and director of flight operations.

The White Knight's only purpose was to carry SpaceShipOne to high altitude, but it was designed also to mature many SSO systems and serve as a trainer for the spaceship's pilots (AW&ST Apr. 21, 2003, p. 64). "[The aircraft] was designed around helping SpaceShipOne's development," Shane explains. "It has the same cockpit, of course, but other benefits are huge. The main [landing] gear actuators are the same as the 'feather' system actuators on SSO. The horizontal stabilizer trim actuators are the same. The environmental control system (ECS), the electrical system, the avionics, the pilot's station, control stick--all the pilot-interface stuff--are absolutely as close to [those] in SpaceShipOne as we could make them. The only differences are throttles [in White Knight], instead of rocket-motor switches, and displays for the Knight's jet engines."

High-altitude White Knight flights led to critical modifications of both the SSO and its carrier aircraft. "When flying at 50,000 ft., [Knight systems] were cold-soaked very close to what the spaceship would see. That [matured] the environmental control system, and built our confidence to fly [SSO] into space without a pressure suit," Shane says.

The cabin is a closed environment, although engine bleed air and pneumatic bottles can be manually activated periodically to replace air that leaks. Dual-pane, porthole-like windows, dual seals throughout the cabin and dual-redundant pressurization sources can maintain as much as a 14.5-psi. differential pressure (delta-p).

Crewmembers wear oxygen masks having an extra hose that diverts exhaled air through carbon-dioxide-scrubber cartridges. Although cabin humidity is controlled, enough moisture routinely condenses inside to cause window fogging and icing, a problem that plagued both vehicles for some time.

"We learned a lot about CO2 scrubbing and humidity control. An [SSO] pilot's worst fear was having those little portholes get iced or fogged over to where he couldn't see to land," Shane says. "We had a lot of that in the White Knight early on. It was a [great] testbed to refine the ECS, so we didn't worry about those things on the spaceship."