[texas booster]

Over the next few days, each of the plane’s six fuel tanks will be filled independently to make sure that the tanks are properly sealed and that the fueling mechanisms work, Stratolaunch said.

Then the tanks will be drained, and the aircraft will be returned to its hangar for weight and balance testing. Over the months ahead, the plane’s systems will undergo further checks in preparation for taxi tests, flight operations and airworthiness testing....

The plane, built in partnership with Mojave-based Scaled Composites, is mostly made of carbon composite. Key elements of the craft, including its six engines and eight sets of landing gear, were taken from Boeing 747 jets.

The Stratolaunch plane’s 385-foot wingspan makes it the world’s widest airplane.

Reusing parts from the 747 makes sense, but I am a bit surprised that they are using the 747 engines. I thought that they were not efficient enough for modern planes.

[Enchante]

Fuel efficiency would not be the main consideration for this kind of aircraft.

[Moonman62]

Reusing parts from the 747 makes sense, but I am a bit surprised that they are using the 747 engines. I thought that they were not efficient enough for modern planes.

...

If they are the same as the 747-8 they would be very modern engines.

[Secret Agent Man]

The 747s have received multiple engine upgrades over time, they are probably using the latest and best versions.

[Cboldt]

The engines are cheap and reliable, and "so what" about efficiency, given the use of this aircraft. Not like commercial flight ... Average Daily Flying Time - Airliners.net ... across thousands of planes, the fuel savings add up.