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787-9 Gear Doors

Mon Sep 23, 2013 6:39 am

Boeing is giving away little about a curious aspect of the new 787-9 observed as the aircraft departed on its maiden flight.

The aircraft’s main landing-gear doors opened as the aircraft rotated from runway 34L at Paine Field, and were clearly seen to be deployed as the aircraft climbed away.

This was despite the gear being left extended, as is normal for a first flight, following the take-off on 17 September.

Boeing says the landing-gear doors “functioned as designed”.

“That’s part of an enhancement we’ve made on the 787-9,” says the airframer, but adds that it is not discussing the reasoning behind the feature.

Looks like a system where by the gear doors open during rotation so when the gear is selected up the gear can begin retraction immediately.

Interesting if that's the design.

Will have to watch for future -9 flights where they retract the gear normally after takeoff rather than leaving it extended for the first part of "first flight".

[Edited 2013-09-22 23:45:41]
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RE: 787-9 Gear Doors

Mon Sep 23, 2013 7:39 am

That's a strange feature, if it is actually one.

I can't see why they would feel the need to have the doors open during rotation, as that creates extra drag during a critical part of an engine-out takeoff (though it could help with directional stability).

It would allow for a faster gear retraction, thus helping slightly with the second and subsequent segments, but it seems a rather peculiar thing to do unless the a/c was performance limited in the second segment.
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RE: 787-9 Gear Doors

Mon Sep 23, 2013 10:52 am

They left them open on takeoff, but that doesn't mean that's the purpose. They could be doing some measurements with the idea of leaving them open on landing, where extra drag might be desirable.
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RE: 787-9 Gear Doors

Mon Sep 23, 2013 11:40 am

I did notice this on footage of the first flight and thought it was unusual since the nose gear doors didn't open along with the mains
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RE: 787-9 Gear Doors

Mon Sep 23, 2013 2:08 pm

Quoting dan23 (Reply 3):
I did notice this on footage of the first flight and thought it was unusual since the nose gear doors didn't open along with the mains

the nose gear doors might be mechanically connected to the NLG and be directly controlled by the gear itself

I don't think this is a feature of the -9. there are several reasons for leaving the gear down after rotation. I don't think you wouldn't want the extra drag of the open doors in these cases.
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RE: 787-9 Gear Doors

Sat Sep 28, 2013 7:30 pm

Perhaps opening the main gear doors at a significant angle of attack involves countering significant pressure from onrushing air and spikes the current draw; the 787 being a heavily monitored electric beast, someone probably noticed and then wondered how to avoid that spike. Opening them while on the runway (before rotation) would eliminate this hypothetical spike (door's straight generating line -- speaking geometrically -- in line with airflow). Anyway, that was my first reaction to seeing them open early.

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