Re: Airbus side stick

From:         bareynol@cca.rockwell.com (Brian A. Reynolds)
Organization: Rockwell Avionics - Collins, Cedar Rapids, IA
Date:         21 Jun 95 02:56:48 
References:   1 2 3 4
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Jean-Francois wrote:
-As well, perhaps the Airbus engineers decided that it was impossible to
-provide the complete feel to an electronic joystick and that another method
-would be best to give the pilot the feedback that is required.

-In other words, they may have decided that it would not be safe to give
-the pilot a false sense of feedback through the joystick when that sense
-could not represent all that was going on.
---

Adding 'load feel' to a side stick is possible at the cost of increased
complexity with attendent increases in certification risk, as well as the
recurring manufacturing costs and increased life-cycle costs.

For instance, adding one pound to the side-stick(for the feed back servos,
clutch, and gearing if required) would add two pounds to the airplane.
The airlines will tell you (as the designer) how much carrying that two
pounds around for the life of the airplane will cost.  The cost of spares
will increase, as the unit would be more complex.  Maintenance will
increase as the reliability of the unit will decrease (based on more parts
to fail).  So I would assume that Airbus performed such an economic
analysis and determined that it could not be cost justified.  However,
any economic analysis contains opportunities for bias (similar to lies,
damm lies, and statistics :).  IF the individual/group doing the analyis
FELT that feedback was not necessary, then they would come up with an
economic reason why it is; a)not required, b) cannot be cost justified,
c) etc. etc. etc.

I do not see how it could have been made a safety issue for NOT providing
tactile feedback.  IF the feedback is based (via a defined control law)
on the current position of the surface and the commanded displacement from
the current position, then I also would NOT classify this as a 'false
sense' of feedback.

However isn't this the role of the regulatory agencies to perform the
final evaluation of the suitability for use of any function provided?  Or
can the regulatory agencies (of whatever country) get caught up in national
interests and allow themselves to be 'pursuaded' that something is good
even though they might have reservations?

****
Opinions are mine - Rockwell has their own.  Oh, I don't work in flight
controls so I don't have any axe to grind.  The pilots that I've spoken
with like the Airbus sidestick like it is.  I don't understand that, but
accept it.  Just seems counter intuitive to me.
****

Brian