How does the Boeing 777's yoke of both the captain and the first officer have synchronized movement?
How does the Boeing 777's yoke of both the captain and the first officer have synchronized movement?
On Airbus planes, the side stick of both the captain and co-pilot are not synchronized in movement, meaning if you the captain moves the side stick, the co-pilot's side stick will not move together. If the co-pilot moves the side stick while the captain does, it will be a dual input.
However, on the Boeing 777 is also a fly-by-wire(FBW) design. But if you watch a 777 cockpit during flight, both of the captain and the co-pilot's yoke moves.
How is that done? Are both of the yokes connected by one mechanical system, and that mechanical system feeds the pilot input to the conputer? Or is it done electronically, with motors or other stuff?
2 Answers
2
From the FCOM v2 (9.20.1):
The primary flight control system uses conventional control wheel, column, and
pedal inputs from the pilot to electronically command the flight control surfaces.
The system provides conventional control feel and pitch responses to speed and
trim changes. The system electronic components provide enhanced handling
qualities and reduce pilot workload.
[...]
The columns and wheels are connected through jam override mechanisms. If a
jam occurs in a column or wheel, the pilots can maintain control by applying force
to the other column or wheel to overcome the jam.
The rudder pedals are rigidly connected between the two sides.
So yes, there is a direct mechanical link between the control columns, but it can be overridden.
Edit:
As John K pointed out in the comments, the technical term for the mechanical link is a torque tube with a breakout mechanism. The details are described in patent US5782436A:
When a sufficient amount of force is exerted on the un-jammed control, the connection of the swivel arm to one side of the torque tube will disconnect due to the force applied overcoming the force of the spring holding connection in place.
So basically the movement on the yoke is electronically created?
– lpydawa
Aug 22 at 11:13
No, they are linked mechanically, but the link can broken with adequate force thus allowing the free control wheel or column to control the aircraft.
– Bianfable
Aug 22 at 11:24
ohhh I see, do they designed it so it is linked, but if you apply force then the mechanical system (lets say its a locking / electromagnetic system) will automatically toggle off.
– lpydawa
Aug 22 at 11:46
@lpydawa To "jam" means to get stuck (this is a non-technical term).
– David Richerby
Aug 22 at 15:21
"both of the yokes connected by one mechanical system, and that mechanical system feeds the pilot input to the computer" - just like non-FBW airplanes.
So are you saying the 777 is not fbw?
– lpydawa
Aug 22 at 11:11
@lpydawa no its still FBW, but there is a mechanical linkage between the two yokes to mirror movements, beyond the cockpit it is electronic .
– James Trotter
Aug 22 at 13:07
The FBW system is more or less replacing the control cable runs and most of the bellcranks and quadrants with electronics. Being keeps the traditional controls and linkages in place "upstream" of where the cable runs would start, all to run the little electric transducers that tell the computers were the controls are, because Boeing's philosophy for FBW is to physically replicate the traditional config as much as possible, and give the crew more authority than the Airbus system does.
– John K
Aug 22 at 13:13
The columns will be interconnected by a torque tube that is split into left and right ends, with a breakout clutch device making them operate as a single tube until a certain amount of force is applied. With all the mechanical linkage in the cockpit, provision still has to be made for things like seized bearings and such, hence the anti-jam provisions that are similar to a non-FBW system.
– John K
Aug 22 at 13:18
@JohnK Please post that as an answer instead.
– Michael Kjörling
Aug 22 at 14:51
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What does it mean by "jam"
– lpydawa
Aug 22 at 11:11