Re: FLY-BY-WIRE (AIRBUS vs. BOEING)

From:         rdd@netcom.com (Robert Dorsett)
Organization: Netcom Online Communications Services (408-241-9760 login: guest)
Date:         21 Jun 95 02:56:50 
References:   1
Followups:    1
Next article
View raw article
  or MIME structure

In article <airliners.1995.792@ohare.Chicago.COM> Jean-Francois Mezei <MEZEI_JF@Eisner.DECUS.Org> writes:
>
>Although the Airbus's FBW system makes actual flight decisions (eg: pilot
>trying to make a movement that is outside aircraft's capabilities)

The Airbus system makes no flight decisions.  It restricts the use of the
flight control system.  There is a difference.


>which can
>prevent stalling etc etc, I get the impression that Boeing's system is not as
>sophisticated and is really a glorified auto-pilot with a couple more warning
>buzzers. I get the impression that to Boeing, FBW means just that:

You are incorrect.  Perhaps you should read up on it.  There is a huge
amount of academic literature on the 777, currently; you can also find lay
articles in most recent issues of the popular flying magazines.


>Am I right in assuming that the Boeing system has less "smarts" built into
>it and that Boeing concentrated instead on providing mechanical feedback to
>those joysticks to replace the mechanical interfaces that existed between the
>pilot and co-pilot ?

If you view complexity as a good thing, I suppose you'd be reasssured by
the lack of a simple joystick, and, instead, a complex cockpit interface
which simulates a conventional aircraft.  I'd call this "smarter."  "Safer"
in terms of operator functionality (Boeing has, indeed, chosen a safer
approach), but hopefully the interface implementation itself doesn't have
any failure modes.

In-flight characteristics of the control laws are similar to the A320: a load-
demand system is used, which provides flight path augmentation.  One
difference is that the pilots are allowed to trim the airplane (since they
want to be able to do so), which lets them better feel what it is up to,
aerodynamically.  There should not be any of these low-speed, high-rate of
descent crashes.

The 777 system provides "stops" in the normal flight control mode.  What
would be a hard stop on an A320 is a "soft stop" on the 777.  The pilot,
therefore, has cues that he's nearing the edge of what would be considered
normal operating practices.  If he exerts some muscle, he can push back these
limits.

If there is control system failure, the normal control laws revert to a
direct mode.  There is not the bogus "alternate" mode of the A320, nor
the zillion switch-overs to consider.

The hierarchical layout of the flight control computers is also simpler,
representing current philosophies on safety-critical systems.  Instead
of five processors of two types, there are three of three types.  The
software in use in all three processors is identical, but has been compiled
by three different compilers for use on the three computers.  The FCS was
written in a highly restricted subset of Ada.

Oh, and Boeing is also proudly proclaiming this airplane has more computers
than any other airplane.  Something on the order of 150.  For those who
think this is a good thing, I guess Boeing is winning the chip war. :-)




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