Re: Airbus A320 flight controls

From:         rdd@netcom.com (Robert Dorsett)
Organization: Netcom Online Communications Services (408-241-9760 login: guest)
Date:         25 Jan 96 00:55:01 
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In article <airliners.1996.43@ohare.Chicago.COM> "P. Wezeman" <pwezeman@blue.weeg.uiowa.edu> writes:
>   In a recent exchange of postings in rec.travel.air 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.

Oh, I forgot the pros and cons:

Pros: it's dirt-cheap.  No back-driving servos, no interlinks between the
two sticks.  Easy and cheap to maintain.  Probably saves a couple hundred
pounds (hey, they had to get the weight savings SOMEWHERE, to justify the
FBW experiment :-)).

Cons:

1.  The lack of interconnectivity makes non-verbal communication between
pilots somewhat questionable.  The "algebraic" addition of command forces
means that both pilots may end up reacting to a threat the wrong way.  It
is thus a "fuzzy" interface.

This observation usually results in a note that in a real airplane, the
strongest pilot wins.  Not really.  In a real airplane, the weakest dog
usually "rolls over" and defers to the pilot with the stronger personality.
In any event, the communication is clear: you can't move the stick.

2.  Similar constraints can also make training interesting for new pilots.
Since most airlines operating the A320 are ab initio airlines, and since
the A320 is an entry-level aircraft, I'm sure this can make life interesting.

3.  The lack of force feedback almost *begs* for protections.  The same
forces exist (provided by the nonlinear springs) whether the airplane is
on the ground or in flight.

4.  A few papers have shown force-less joysticks to generally be among the
weakest there are for most applications.  The most obvious other airplane
using one is the F-16, but it uses something rather different (it's a force-
joystick, not a positional joystick).

The factors 1-4 have been touched upon in the literature and this and other
newsgroups since 1986 or so.  All have been cited as justification for the
simulation of conventional control columns by Boeing in the 777.



--
Robert Dorsett                         Moderator, sci.aeronautics.simulation
rdd@netcom.com                         aero-simulation@wilbur.pr.erau.edu
                                       ftp://wilbur.pr.erau.edu/pub/av