First Engine Start For Stratolaunch

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Stratolaunch, the massive airplane that is being built by Scaled Composites to deliver satellites to low Earth orbit, successfully ran all six of its Pratt & Whitney turbofan engines for the first time this week, the company has announced. The PW4056 engines, which previously powered a Boeing 747, support a payload capacity of more than 150,000 pounds and an operational range of about 2,000 nautical miles. At 385 feet from wingtip to wingtip, Stratolaunch is the largest airplane, by wingspan, ever built. It’s also the first aircraft to fly with six 747 engines. It’s under construction at the Mojave Air & Space Port, in California. The company, which is funded by Microsoft co-founder Paul Allen, says the airplane will be fully operational by 2020.

The engine tests consisted of three phases, the company said. The first test was as a “dry motor,” using an auxiliary power unit to charge the engine. Next was a “wet motor” test, using fuel. Finally, each engine was started, one at a time, and allowed to idle. In these initial tests, each of the six engines operated as expected, the company said. A number of failure-mode conditions also were tested. The team also completed fuel testing. Each of the six fuel tanks was filled independently to ensure proper operations of fuel mechanisms and to validate the tanks were properly sealed.

Prerequisite testing of the electrical, pneumatic and fire detection systems also were completed successfully. Tests also have begun on the flight control system. So far, the company said, they have exercised the full limits of motion and rate of deflection of control surfaces on the wing and stabilizers. “Follow-up testing this fall will exercise the unique avionics, hydraulics, electrical and fuel systems,” said Joe Ruddy, director of the Stratolaunch project. “This will advance the aircraft one step closer to taxi testing – one of the final test series prior to flight.”

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