Re: Quiet Airliners of the Future?

On Sat, 17 Sep 2005 03:41:46 GMT, "Capt.Doug" <Capt.Doug@xxxxxxxxxx>
wrote in <_fMWe.50609$qY1.40732@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>::

>>"Larry Dighera" wrote in message > In the event of an in flight electrical
>failure disabling the
>> electronic control augmentation, it could get "interesting." What
>> does Airbus use to overcome that issue?
>
>Airbus's first answer is that it has never happened.

That smacks of the argument used in assuring security against the
September 11, 2001 attacks. :-)

>If an engine generator drops offline, the other generator picks up the load.
>The APU generator can pick-up the load if the second engine generator drops
>offline. The ram air turbine powers a back-up generator if all 3 main
>generators crap out. Even if the RAT doesn't deploy, the batteries provide
>at least 25 minutes of electricity. The engines' FADEC units have their own
>independent generators.

At first glance, five levels of electrical power source redundancy
would seem safe in guarding against 'Complete electrical failure',
however there are other points of failure in electrically operated
systems. Each electrical circuit is fed through a circuit breaker.
How many circuit breakers are involved in the Airbus flight control
system? How many electrical buses?

>Augmentation may be the wrong word. It refers to the levels of protection
>afforded to the flight envelope. As long as you have a generator or a
>battery, you will have control. 'Complete electrical failure' is the wording
>I believe you wanted.

No, that is the phrase that describes the issue you addressed. I'm
more concerned about single points of failure.

If the circuit breaker (an electrical/mechanical device) feeding the
electrical bus supplying the flight control system were to
malfunction, regardless of power being available, the bus could be
de-energized, and no amount of available power would bring the flight
control system back into operation, unless you know of additional
redundancy designed in to the Airbus control system that you have not
yet discussed.

>Try flying a light twin without touching the yoke. You have throttles,
>rudder, and elevator trim, but no elevator, ailerons, flaps, or instruments.
>And the gear probably won't extend.

I've not had that experience, but in a light single engine aircraft
with exclusively mechanical controls, its occupants would probably
walk away from the "landing." In the event that a mechanical
malfunction in its control system, it would only affect the control of
a single axis (like the Alaska flight that went down off the Ventura,
California coast five years ago :-(), not the entire 3-axis flight
control system. But Airbus products do have mechanical elevator trim,
IIRC, so in the event of the electrical portion of the flight control
system failing, there would still be some control of one (important)
axis.

>The A-320 stalls like a C-172, lots of
>buffet and drops straight ahead. With calm winds and a long runway, you can
>make your dinner reservations at Nanno's.

So you're intimating that only the ailerons and elevator are
electrically operated?

>The real danger is if you lose all 3 hydraulic systems.

Are you saying there are three hydraulic actuators, one from each
hydraulic system, attached to each control surface?

.

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