777 Spoiler Panel

[Mariano]

Does anyone know why the second spoiler panel, outboard of the inboard aileron (flaperon?) extends a few degrees less than the others upon landing on the 777?

Regards,

Mariano

[boeing747430]

Just a guess:
Maybe to control the pitch-up momentum? The 777 does have a quite weird deployment schedule for the spoilers during landing for this reason.

On the 747-8, the innermost spoiler panels will only deploy further from about half at touchdown to full when there is a certain weight on the nose gear and below a certain airspeed. At least, that's what I was told. But it is difficult to find documentation about it. You can do nothing after main gear touchdown and the nose gear will come down quite gently on the 747-8, which is why I try to remember to get it down a bit more actively and sooner in order to get the full spoilers and better directional control. Still' nobody mentioned anything about it in training and most 747-8 pilots seem to be unaware of the behaviour of the inboard spoilers.

There are quite a few aircraft types around, where the spoilers differ in their extension values at all three functions, the flight spoiler (for roll), speed brake and ground spoiler.

[John H Watson]

Does anyone know why the second spoiler panel, outboard of the inboard aileron (flaperon?) extends a few degrees less than the others upon landing on the 777?

The books don't mention why, but for roll control, these spoilers aren't fly by wire. There are cables running from the control column to the hydraulic power units which operate these spoiler panels. Perhaps because of this, the mechanisms have to be designed differently/limited. They are, however, FBW for speedbrake.

[Hardy Heinlin]

Did the designers intentionally exclude these spoilers from the fly-by-wire system in order to have a pure hydro-mechanical backup for the roll control in case the fly-by-wire fails?

[IefCooreman]

Yes, FCOM mentions this is done for the remote case of a complete electrical failure. The manual control allows straight & level flight until the electrical system is restarted.

[Mariano]

Very interesting regarding both the 777 design and the -8 (different) extension schedule, thank you.

Best regards,

Mariano

[boeing747430]

Just saw another vid of a 777 wing during landing. The first mentioned spoiler does support the flaperon on the ground while extended. It moves to match the other spoilers at full up when the flaperon moves up. So that seems to solve the mystery.

[Mariano]

Thanks for input. The 777 ATA 27 chapter is next on my reading list.

I also noticed that the 787 flaperon moves up (from a down/takeoff, not neutral position) as the thrust increases on takeoff, and soon after it moves down to its previous position.

I am sure that someone will enlighten us with the logic behind this soon.

Best regards,

Mariano

[boeing747430]

Did you see this on a video? Or live?
777 is similar, I guess. Firstly, the flaperons go into ,,bypass". Hydraulic power is removed and they droop. Then, thrust and airspeed let them "fly" up. At some airspeed, I think above 50kts, hydraulics slowly come back and at around 100kts, everything goes back to normal. It´s a stress relief feature.

[Mariano]

Aha! That's exactly what I saw (in a video, yes).

Makes sense.

Thanks for the explanation.

Best regards,

Mariano