Rejected takeoff the most dangerous test 787 faces

The 787 is getting down to the serious business of flight testing. Rejected takeoff is the most dangerous that the test pilots face.
Written by John Dodge, Contributor

Can you guess which will be the most dangerous trick the 787 Dreamliner will have to perform during the next 10-12 months of flight testing? Here's a hint: it does not happen in the air. It will give you an idea of the dangers test pilots face.

Judging from testing of the 787 Dreamliner's predecessor, the 777, it is the Rejected Takeoff Test.  Passengers know it as an aborted takeoff for one reason or another - an obstacle in the way or a last grounded moment mechanical malfunction. The video below shows a 777 performing a rejected takeoff. Click "Watch on Youtube."

In short, the pilot jams on the brakes as hard as possible to the tune of 9.7 million foot pounds (if you've ever used a torque wrench, you know that's a lot).

Why is this so dangerous? Well, watch the video as the carbon brakes - worn down at the start to minimum thickness - catch fire as test pilot Cashman slams on the brakes at maximum speed and thrust. The plane, loaded to its maximum weight of 280 tons, travels another 4,000 feet with its jammed brakes heating up to 3,000 degrees centigrade.

Then comes the most dangerous part. The plane has to stand or taxi for another five minutes without "catching fire." That's the time it would take firetrucks to reach it. During that time, the pilots are sitting on "a potential time bomb." The pilot reports back that after braking the wheels are "still rolling" as he slowly taxis toward the fire trucks.

Each tire has fuse plug that melts so the tires safely deflate instead of exploding. They all go flat after the critical five minutes - $750,000 worth of tires down the drain.

Now it's the 787's turn. The brake test will be particulalry interesting because its brakes are electric, and as such, simpler and comprehensively monitored. Before the 787, brakes were basically like the ones in your car - hydraulic.

Overall, the 787 will undergo 5,000 hours of flight testing versus 600 hours for Boeing's first passenger jetliner, the 707.  Now you understand why flying is so safe at least from a mechanical and structural standpoints. Boeing's company magazine Frontiers has a cover story on the 787 and 747-8 test programs.

It's busy times for Boeing's 45 test pilots. The Boeing 747-8, the 15th version of the original jumbo-jet 747-100, is rumored to be scheduled to take its first flight on Jan. 14. The last time Boeing conducted two simultaneous test flight programs was a quarter century ago with the advent of the 757 and 767.

Flightblogger Jon Ostrower has a detailed rundown of 787 systems, electrical, control, stability and route testing as the craft edges closer to commercial airworthiness and FAA certification.

If rejected takeoff is the most dangerous test, guess the most extreme. That's pushing to wings to the physical breaking limits of a stationery test plane in a steel frame. The 787 has already been pushed to 150 per cent of the forces it is projected to ever encounter in flight. The dramatic video below is the 777 getting its wings clipped 15 years ago so to speak. It hit 154 per cent of load before both wings snapped - simultaneously and in the same location.

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This post was originally published on Smartplanet.com

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