Re: Airbus A320 flight controls

From: (Robert Dorsett)
Organization: Netcom Online Communications Services (408-241-9760 login: guest)
Date:         25 Jan 96 00:55:00 
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In article <airliners.1996.43@ohare.Chicago.COM> "P. Wezeman" <> writes:
>   In a recent exchange of postings in several people have
>mentioned conplaints of a lack of proper force feedback in the Airbus A320
>sidestick control. Could someone who is familiar with the system please
>describe it briefly? In particular, does it work by sensing force or by
>sensing movement? Roughly how much force does it take to operate it? If the
>stick moves, where is the pivot point in relation to the pilots hand and
>what is the range of movement and force gradient? I am also interested
>in any pros and cons of the device.

The A320 flight control system uses a load-demand control law, based on
something called "C*".  In effect, the position of the side stick commands
an aircraft loading.  Once commanded, the loading is preserved.  The side
stick can be viewed as commanding AOA.

In pitch, the maximum load is 10 daN, and can be rotated +- 16 degrees.
It is oriented 20 degrees forward, and has a sensing threshold of 0.5 daN.

In roll, its maximum load in is 3 daN, out 2 daN.  Its threshold is 0.4 daN
in both directions.  Maximum deflection is +-20 degrees, and it is oriented
12 degrees inboard.

The joystick is not coupled.  That means that the two joysticks are com-
pletely independent critters.  Their inputs are algebraically added.  If
one pilot pulls full-left and the other full-right, nothing will happen.

There is no backfeed. The joysticks do not reflect aerodynamic forces.

An override capability exists; it's a button in the grip.  When one pilot
has overriden another, an arrow pointing to the other pilot flashes in the
glareshield.  There is also an aural annunciator.  This override, in effect,
"turns off" the other stick, until the pilot tries to use it, again.

The pilot's arm rest can be adjusted for a more comfortable fit, but in
reality, most pilots have reported that the arm rest position doesn't sig-
nificantly affect control.

Robert Dorsett                         Moderator, sci.aeronautics.simulation