B787-9 LDG gear retraction

[flyby797]

Hi,
Can somebody shed some info on how performance are improved by the early door function on the -9 when LDG gear is retracted? Thanks
FCOM extracts:« To improve performance, an early doors function automatically pre-opens the main landing gear doors one second after lift-off and prior to the pilot moving the gear lever to the UP position. »

[Fursty Ferret]

If the doors are already open, the landing gear can be retracted faster in the event of an engine failure because you don't have to wait for the doors to open before the gear starts moving.

[flyby797]

Thanks!

[dixi188]

What about the extra drag with the doors open if the startle factor of the engine failure causes the crew to forget to retract the gear?
I've seen this in the sim.

[LOWI]

What about the extra drag with the doors open if the startle factor of the engine failure causes the crew to forget to retract the gear?
I've seen this in the sim.

If you're flying a 787, chances of experiencing startle factor is non-existent. These guys have major experience.

[Fursty Ferret]

What about the extra drag with the doors open if the startle factor of the engine failure causes the crew to forget to retract the gear?
I've seen this in the sim.

They will close again after 30 seconds. Having said that the engine-out performance of the 787 is so marginal that I suspect you’d know pretty quickly that you’d forgotten the gear.

[Commander Taco]

If you're flying a 787, chances of experiencing startle factor is non-existent. These guys have major experience.
Wanna bet?

[BFSGrad]

Watching some 787 departures, am I correct in observing that this is also a feature of the -10 but not the -8?

[stilton]

They will close again after 30 seconds. Having said that the engine-out performance of the 787 is so marginal that I suspect you’d know pretty quickly that you’d forgotten the gear.


Never flown the 787, the 757 and 767 did very well on one engine so I’m surprised at this

[tdracer]

Never flown the 787, the 757 and 767 did very well on one engine so I’m surprised at this
The 787 has an interesting issue with engine out - at lower airspeeds they have to limit the thrust of the 'good' engine to insure there is adequate vertical tail/rudder authority to maintain directional control.

[Check Airman]

The 787 has an interesting issue with engine out - at lower airspeeds they have to limit the thrust of the 'good' engine to insure there is adequate vertical tail/rudder authority to maintain directional control.
How do they go about limiting the thrust?

[tdracer]

How do they go about limiting the thrust?
I don't know the details (never worked the 787), but an aircraft system (FMC?) sends a signal to the FADEC basically telling it the max thrust that can be used at those conditions before directional control is compromised. I think the problem is a bit worse on the -8 (shorter, so less tail authority) but that's just an assumption.

[Fursty Ferret]

I’m not sure it’s so much a directional control problem as a performance problem. Essentially you get better performance if TAMS is intervening and reducing thrust than if you have full thrust but significant rudder input and bank angle towards the good engine.

Having said that it would require spectacular mismanagement of an engine failure to end up here.

[stilton]

The 787 has an interesting issue with engine out - at lower airspeeds they have to limit the thrust of the 'good' engine to insure there is adequate vertical tail/rudder authority to maintain directional control.


Understand that having the smallest vertical tail is good for lower drag but this is quite a trade off

Not scientific at all but all you have to do is look at a 747s vertical fin to know it’s more than enough

The 777 and 787 fin always looked too small and out of proportion, the A350 even more so

[tdracer]

Not scientific at all but all you have to do is look at a 747s vertical fin to know it’s more than enough


Even on the 747, you can run out of tail. If you take a close look at the vertical tail on the 747SP, you'll notice there is a large 'extension' at the top compared to the regular 747s.
On the 747-400 - with the higher thrust options (and the 747-8), we had to limit go-around thrust because if you had two engines out on the same side, you could run out of tail doing a go-around with max thrust. However in the case of the 747, it wasn't foolproof - we simply modified the thrust target and how far the Autothrottle would push the levers - you could still override it by pushing the throttles fully forward.

[stilton]

Even on the 747, you can run out of tail. If you take a close look at the vertical tail on the 747SP, you'll notice there is a large 'extension' at the top compared to the regular 747s.
On the 747-400 - with the higher thrust options (and the 747-8), we had to limit go-around thrust because if you had two engines out on the same side, you could run out of tail doing a go-around with max thrust. However in the case of the 747, it wasn't foolproof - we simply modified the thrust target and how far the Autothrottle would push the levers - you could still override it by pushing the throttles fully forward.


Interesting, I’m guessing that was also the reason behind the double hinged rudder on the SP and the 747-8

[TURIN]

Interesting, I’m guessing that was also the reason behind the double hinged rudder on the SP and the 747-8
777 too.
​​​​​I think the DC10 also had a double actin rudder but mainly because the #2 engine was in the way.

[Cough]

Watching some 787 departures, am I correct in observing that this is also a feature of the -10 but not the -8?

Correct!

The 787 has an interesting issue with engine out - at lower airspeeds they have to limit the thrust of the 'good' engine to insure there is adequate vertical tail/rudder authority to maintain directional control.

True, but I think this is there for the abuse case rather than normal ops. Our QRH states in the event of the system failure for this we have to maintain flight above 130knots to remain in control in the event of an engine failure. Been on the 787 several years and I don’t think I’ve ever flown below that speed…

[FlyingH1gh]

I presume you are alluding to the fact that the 787 is certified for a double derate - this means both fixed and assumed temperature method (ATM). On the 787, the engines have been certified at 100%, 90% and 80%. Crews can then add an ATM on top of that. Whilst this saves engine wear, in the event of an engine failure if the crew were using a double derate then pressing TOGA would advance the thrust levers to 100% (or 50% on one engine) and risk having full power on one engine whilst flying at a speed below VMCA. Hopefully that makes sense...

Crews forgetting to retract the gear - whilst possible its not an assumption within Performance A.