Fly by wire aircraft.

[Waghi Warrior]

Questions,
Do you get any force feed back whilst flying these machines, the planes with a joystick in them (ie: A320's and planes like that), and what about fly by wire aircraft with the normal control yoke setup? (ie: do you get a fell for the aircraft as though you were flying a normal cable controlled aircraft?)

[halfpast3bus]

Can't speak for the 777 but the 330 side stick has no feed back. Just a constant centering spring pressure. :)

[John Farley]

WW

Not wishing to nitpick, but accuracy is everything.

With a normal cable controlled aircraft the feel you get is not for the aircraft (if only it was) it is just a measure of the hinge moments you are applying to the moveable surfaces.

The force feedback in a flyby wire aircraft (what you feel through moving the controller – whether that controller is a side stick, a centre stick or a yoke) is determined by what the design team think is best for that aircraft type. Simple spring centring (double the force for double the input deflection) is one commonly used arrangement. Others use a speed squared term (similar to what you get from a cable system) but anything is possible. It is just another design choice like high or low wings or whatever.

JF

[Genghis the Engineer]

Adding to what John said, Airbus don't believe in the need for force or control movement feedback - so far as am aware however Boeing do.

Designers will often "tweak" artifical feel - for example if there is a corner of the envelope to which you should not routinely go (the stall for example) but which must be reachable they may design a steep increase in control forces so that you can get there if you wish - but certainly won't do so by accident.

G

[Three-Twenty]

I was told that the artificial 'spring pressure' is actually rigged so that it 'feels' right eg. for RHS, you have more strength pushing the stick LEFT than right, so the resistance to you pushing it left is slightly higher. Very clever.

With no force feedback, there is no need for manual trim (no forces to trim out! Though the aeropplane would still trim for fuel efficiency) - just wondering, does 777 et al with artificial feel routinely use manual trim?

[Saint-Ex]

Genghis, you are right but one must appreciate that the philosophy adopted by the two Companies is totally different. Airbus do not need to increase feel force on approach to the stall as, in normal law, the aircraft is protected from getting there. It doesn`t matter which you support but obviously as the flying characteristics on the 777 are those presented by a computor, then a warning by a computorised feel programme must be fed in to warn the pilot of the impending stall.

[spanners]

The 777 has trim switches etc just like any other boeing you find, on the stick and a lever on the pedestal. The feel is created by feedback actuators under the flt deck floor.
The FBW has methods of trimming and deals with long term and short term trimming.
The short term is normal trim switches but if the control is held off for a long period, the FBW trims the stab to the new position.
unlike the Airbuses the 777 is quite good in that you can see all the controls move, and supply feel in the various flight regimes.

Just out of interest, the 777 does have bank angle protection as well, e.g over 30 bank and the wheel will right itself with the voice shouting 'bank angle'. this can be ovverriden.
Regds


[This message has been edited by spanners (edited 12 October 2000).]

[MasterGreen]

Just to set a couple of things straight on the B777.

It has a conventional yoke and column control with a "standard" Boeing trimmer in the offside grip. The feedback is provided by a unit under the floor.

Points of interest.

The feedback is very subtle and it "feels" just like the real thing. It's very sensitive though and you need a gentle pair of hands to keep it really smooth. The dear lady (now departed) who wrote the handling notes for many of the RAF's aircraft would have definately said that "the controls are light and well harmonised". (In joke - but many will know what I am saying)

There is a lot of power in the controls and it is all available to you all the way through the flight envelope. One of the nicer touches is that even with system degradation (hydraulic system loss for example) the same response is available for the same input. Very nice if you have it. The downside is that if you take the computers out and fly "raw" the thing is a total bitch by comparison.

The trim is "speed select". If you have trimmed for a speed then changing config or power does not phase it a tiny little bit. This takes a little getting used to. Say about 20 seconds. Then you wonder why everything else you have ever flown didn't work like this. Truely - it is lovely. Easy - don't ask !!

The bank angle protection is set at 35 degrees and as well as a Nagging Nanny "Bank Angle" warning the yoke hardens up to make life much harder to exceed the 35 degrees. It doesn't stop you exceeding, but you need to show considerable determination to make the exceedence continue. Works well - nice one Boeing. There is equally effective and similar protection in the pitch regime also. All these protections can be progressively removed if required, but the bottom line is that in normal operations they are quite transparent and the aircraft is only a delight to fly.

Best toy in the box apart from the Chippy.

MG

[CaptainSquelch]

Waghi,

It may surprise you but even the old fly-by-string B747-jurassic has no real feel at all. The only thing you moved when displacing the controls are hydraulic controlvalves, located dozens of meters behind the flightdeck. So all you feel are the combined frictions of the cable system and all the rollers. On top of this there is an artificial feel system for every control axis based on spring forces and adjusted for things like q and, for the elevator, the Cg. The design challenges in this respect do not differ much between Fly-by-string and Fly-by-wire.