747-8 fly by wire roll channel

[Ilari Kousa 116]

Hi,

 

I've been looking for answers for a long time including the FCOM and several 747-8 pilots I know, but haven't received a clear answer: does the fact that the 747-8 has a fly-by-wire roll channel have any bearing on how the aircraft is flown? When I spent a few hours in the FFS, I didn't notice any control augmentation logic of note. It being FBW, would some elec/flight control computer failures degrade the controllability of the airplane in roll? More importantly, did PMDG somehow specifically model these FBW features?

[scandinavian13 5,192]

4 hours ago, Ilari Kousa said:

does the fact that the 747-8 has a fly-by-wire roll channel have any bearing on how the aircraft is flown?

Left for left, right for right. Why would it?

4 hours ago, Ilari Kousa said:

When I spent a few hours in the FFS, I didn't notice any control augmentation logic of note.

Why would you?

4 hours ago, Ilari Kousa said:

It being FBW, would some elec/flight control computer failures degrade the controllability of the airplane in roll?

If one lost the thing that controls those controls, why would one expect otherwise?

4 hours ago, Ilari Kousa said:

More importantly, did PMDG somehow specifically model these FBW features?

If we did in the 777, why would we suddenly drop a function of the aircraft when we modeled the 748?

[downscc 1,327]

If you look in the FCOM in the flight controls section you'll find that only the outboard ailerons are electronically controlled hydraulics.  In this sense the roll is hybrid at low speeds only.

[Jetlinker 13]

On 11/21/2018 at 3:51 AM, Ilari Kousa said:

It being FBW, would some elec/flight control computer failures degrade the controllability of the airplane in roll?

If there is a failure with the FBW it will trigger the “AILERON OUTBD” EICAS advisory and/or the “SPOILERS” EICAS advisory messages. These advisories are unique to the -8 and the FBW system (the 400 doesn’t have them). Essentially the QRH for both will state to plan for a reduced roll rate at slower speeds, and for the case of ailerons it adds a reduced crosswind component for landing. 

As downscc said the FBW is only for the outboard ailerons (which are only used at slower speeds) and for the spoilers. 

[kevinh 409]

Fly By Wire does not necessarily mean any control augmentation is involved. It may simply be the replacement of a mechanical linkage with an electrical one. In previous 747 versions the outboard ailerons had an electro-mechanical lockout mechanism to stop them moving at higher airspeeds. Replacing this with FBW probably saves weight and improves reliability. 

Edited November 26, 2018 by kevinh

[Ilari Kousa 116]

On 11/26/2018 at 2:53 PM, kevinh said:

Fly By Wire does not necessarily mean any control augmentation is involved. It may simply be the replacement of a mechanical linkage with an electrical one. In previous 747 versions the outboard ailerons had an electro-mechanical lockout mechanism to stop them moving at higher airspeeds. Replacing this with FBW probably saves weight and improves reliability. 

Yeah I'm aware of that. Thanks everybody for your interesting comments!