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CCA
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787-9 Gear Door. Updates?

Sun Dec 01, 2013 3:11 pm

Anyone got any further information on the 787-9 gear doors?

http://www.flightglobal.com/news/art...cement-to-787-9-gear-doors-390730/

Quote:

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.

Boeing has secured orders for 388 of the -9 twinjets, the first of which is to be delivered to Air New Zealand in mid-2014.
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wingscrubber
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RE: 787-9 Gear Door. Updates?

Sat Dec 14, 2013 5:09 pm

Just a theory but, if they had attempted to retract the gear with locking pins in, that would explain why the doors opened without the gear coming up. Did the NLG doors open too?

Not sure why you would want to separately command the MLG doors to open on their own; this would only be possible if the landing gear controller is designed with that capability. Maybe for gear bay ventilation reasons, but unlikely.

I strongly suspect they tried to retract the gear with the locking pins in. Has happened before on other types, is sure to happen again.
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BravoOne
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RE: 787-9 Gear Door. Updates?

Sat Dec 14, 2013 5:47 pm

Not sure about this event, but originally the -8 had an auto gear retraction function to enable 2nd segment climb perf. Perhaps this has reappeared on the the -9? It was found to be unnecessary in the final -8 cert.
 
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CCA
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RE: 787-9 Gear Door. Updates?

Sun Dec 15, 2013 3:04 am

Quoting wingscrubber (Reply 1):
Just a theory but, if they had attempted to retract the gear with locking pins in, that would explain why the doors opened without the gear coming up. Did the NLG doors open too?

Not sure why you would want to separately command the MLG doors to open on their own; this would only be possible if the landing gear controller is designed with that capability. Maybe for gear bay ventilation reasons, but unlikely.

Only the main gear doors open and videos/pics still show that it's happening it wasn't only unique to the first flight.
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AirlineCritic
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RE: 787-9 Gear Door. Updates?

Sun Dec 15, 2013 11:07 am

Aerodynamics? Somehow sensible in that phase of lift-off?
 
hivue
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RE: 787-9 Gear Door. Updates?

Mon Dec 16, 2013 12:30 am

Quoting wingscrubber (Reply 1):
if they had attempted to retract the gear with locking pins in

I would think leaving the pins in would be a big mistake even on a routine flight, let alone a first flight.

Quoting CCA (Reply 3):
videos/pics still show that it's happening it wasn't only unique to the first flight

They're still not retracting the gear after take off?

Quoting BravoOne (Reply 2):
Not sure about this event, but originally the -8 had an auto gear retraction function to enable 2nd segment climb perf. Perhaps this has reappeared on the the -9?

Maybe they just disabled (in the software) the auto-retraction of the gear itself and left the rest of the process as-is.
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CCA
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RE: 787-9 Gear Door. Updates?

Mon Dec 16, 2013 1:28 pm

Quoting hivue (Reply 5):
They're still not retracting the gear after take off?

The main gear doors open just after lift off, the gear is retracted normally but this is only evident by the opening of the nose gear doors.

I think it's just a new idea to save time/fuel retracting the gear, as once the gear is selected up the main gear can begin retracting immediately rather than wait the 3 sec for the gear doors to open.

Auto gear retract sounds interesting.
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hivue
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RE: 787-9 Gear Door. Updates?

Mon Dec 16, 2013 2:20 pm

Quoting CCA (Reply 6):
I think it's just a new idea to save time/fuel retracting the gear, as once the gear is selected up the main gear can begin retracting immediately rather than wait the 3 sec for the gear doors to open.

Interesting. So could such a feature be helpful in case of an engine failure between V1 and Vr? Would the aircraft get cleaner faster?
"You're sitting. In a chair. In the SKY!!" ~ Louis C.K.
 
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RE: 787-9 Gear Door. Updates?

Mon Dec 16, 2013 8:50 pm

Quoting CCA (Reply 6):
I think it's just a new idea to save time/fuel retracting the gear, as once the gear is selected up the main gear can begin retracting immediately rather than wait the 3 sec for the gear doors to open.

But opening them prematurely would just increase the overall drag, no? And how much of a difference in fuel consumption is that three second interval really going to make? I mean, to make this small change there must have been many hours of meetings, testing, coding, certifying, blah blah blah. I'm just having trouble figuring out what about it is so important.
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hivue
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RE: 787-9 Gear Door. Updates?

Tue Dec 17, 2013 12:10 am

Quoting DocLightning (Reply 8):
I'm just having trouble figuring out what about it is so important.

Right. What would be the advantage of using a half gallon less fuel on a 8500 mile flight? That's why I'm guessing it's related to engine failure at takeoff.
"You're sitting. In a chair. In the SKY!!" ~ Louis C.K.
 
Sgarr
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RE: 787-9 Gear Door. Updates?

Tue Dec 17, 2013 1:45 am

Could it be as simple as alleviating some aerodynamic load that the doors might be exposed to in the closed position at high angles of attack with the gear extended? Intuitively it seems like that configuration could cause relatively high pressure inside the closed portion of the gear well.
 
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CCA
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RE: 787-9 Gear Door. Updates?

Tue Dec 17, 2013 10:40 am

I'd say getting the gear up as quickly as possible is the goal and it would obviously have many advantages, I agree the fuel advantage is going to be very small but over the life's time of the aircraft it'll add up, plus the performance improvement may lead to a two fold fuel gain or increase the load carried by flights limited by second segment performance as stated above. Trust me on this, airlines are very conscious about fuel savings and if every takeoff gains XXkg fuel savings they will want it.

Perhaps what we are seeing is Boeing going through the motions of a possible performance improvement, if it turns out the early door opening negates the benefit of the quicker gear retraction maybe it'll never happen. I guess time will tell.

[Edited 2013-12-17 02:43:24]
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