Quiet Airliners of the Future?

On Wed, 14 Sep 2005 23:46:10 GMT, Chris Kennedy
wrote in ::

but the
issue is with uncommanded roll as a consequence of turbulence.

If the aircraft is not maneuvering (or even if it were), the
electronically augmented control system would detect an incipient wing
displacement before a human could detect it, and issue the appropriate
control input to counter it. These commands would occur so rapidly as
to be virtually undetectable by the occupants.

Think of the electronic suspension systems available on some of
today's automobiles*. They are capable of providing a smooth ride
over the roughest of roads by sensing body dip, and immediately
extending the suspension to prevent further excursions. These
corrections happen in milliseconds; it verges on magic.

If the roll
rate is brisk, there may be some increase in G felt by passengers in
the rising wing, and decrease in G felt by those in the descending
wing, but with today's computerized fly-by-wire control systems, all
these concerns could be largely eliminated in nearly all cases.

Unless you're suggesting that fly by wire could automatically limit the
roll rate to limit the acceleration felt by outboard passengers I'm
unclear how it would address the problem.

I'm confident that an electronic control system could dampen all but
the most severe turbulence induced excursions, in addition to seeing
that the commanded roll rate was strictly met.

There's also the roller coaster effect -- being on the high side and
looking down the width of the cabin at what seems like an exaggerated
angle -- but I suppose one could deal with that with dividers of some
sort.

Exactly. First class would be along the longitudinal axis with coach
toward the wing tips with obscure partitions separating them.

There's also the issue of just how one evacuates such an aircraft.

Umm... Crashworthyness would be an issue less amenable to resolution
than evacuation.

As I said, good for freight, but I'd take some convincing before I flew
in one.

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?

Of course I'm not too thrilled with the idea of riding in an
A380, either.

Right. In the event of a 800+ passenger stampede, one would likely be
trampled before he could clear the aircraft. :-)




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Larry Dighera wrote:

but the
issue is with uncommanded roll as a consequence of turbulence.


If the aircraft is not maneuvering (or even if it were), the
electronically augmented control system would detect an incipient wing
displacement before a human could detect it, and issue the appropriate
control input to counter it. These commands would occur so rapidly as
to be virtually undetectable by the occupants.

Most contemporary transport aircraft have gust alleviation systems (not
so much for ride comfort than to reduce structural loads); the B-2 has a
similar system. The systems have only limited ability to counter roll
but it's not for want of trying -- it's sort of entertaining looking out
and watching twitchy spoilers trying to keep the wings level -- or the
wingtips from trying to touch.

Actuator response times, interactions with the stability of the design
and the possibility that the roll rate induced by gust could exceed the
roll rate of the aircraft place limits on the magic that you can
perform. It's not to say that you can't come close.

Think of the electronic suspension systems available on some of
today's automobiles*. They are capable of providing a smooth ride
over the roughest of roads by sensing body dip, and immediately
extending the suspension to prevent further excursions. These
corrections happen in milliseconds; it verges on magic.

Yet more technology grafted on from Lotus. I was never quite understood
why they never commercialized that technology -- save for the fact that
it sucked power and had really bad failure modes.

Unless you're suggesting that fly by wire could automatically limit the
roll rate to limit the acceleration felt by outboard passengers I'm
unclear how it would address the problem.


I'm confident that an electronic control system could dampen all but
the most severe turbulence induced excursions, in addition to seeing
that the commanded roll rate was strictly met.

That's sort of my point. Unless you limit commanded roll rate to
something small you haven't done anything to address the problem of G
(un)loading for the outboard passengers, and setting the roll rate limit
low creates its own class of problems.

There's also the roller coaster effect -- being on the high side and
looking down the width of the cabin at what seems like an exaggerated
angle -- but I suppose one could deal with that with dividers of some
sort.


Exactly. First class would be along the longitudinal axis with coach
toward the wing tips with obscure partitions separating them.

Yeah, that's the notion I was after.

There's also the issue of just how one evacuates such an aircraft.


Umm... Crashworthyness would be an issue less amenable to resolution
than evacuation.

Both would be -um- problematic.

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?

They don't. Everything is inputs to the redundant autopilot system;
stick and throttle are suggestions, not really commands. Raise your
hand if you've had to sit on the ramp while they do a complete engine
shut down in order to reboot an A320 series aircraft prior to departure
(it's happened to me twice).

Of course I'm not too thrilled with the idea of riding in an
A380, either.


Right. In the event of a 800+ passenger stampede, one would likely be
trampled before he could clear the aircraft. :-)

That's assuming that you weren't in the middle of a refreshing mud bath
with cucumber slices on your eyes (if you believe for a moment the
claims of Airbus and Branson that A380s will have such amenities as
opposed to high density seating).

"Chris Kennedy" wrote in message
They don't. Everything is inputs to the redundant autopilot system;
stick and throttle are suggestions, not really commands.

This true when operating in normal law mode (99% of the time). However, when
degraded to direct law mode, the A-320 operates like a normal airplane. The
reboot is not because it can't fly, but because we like everything to work
so as to provide the safest flight we can (and we are lazy and don't want to
handfly a whole leg).

D. (it tunes it's own VORs)

"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.

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.

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.

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. 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.

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

D.

On Sat, 17 Sep 2005 03:41:46 GMT, "Capt.Doug"
wrote in ::

"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?

"Larry Dighera" wrote in message
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?

Airbus understood from inception that their company would live or die by the
integrity of their fly-by-wire design. There are 7 computers responsible for
the primary flight control surfaces. Three are ELACs (elevator-aileron).
They perform the same functions with slight differences. Each is
manufactured by a different vendor with different computer code so that if
one assembly line has a batch of bad parts or bad code, the other two are
not affected. The same goes for the 2 SECs (spoiler-elevator) and the 2 FACs
(rudder plus flight protections). One ELAC, one SEC, and one FAC are powered
by a DC essential bus which switches automatically to any of the power
sources mentioned (AC or DC). The sister computers are powered by other
busses which are normally powered by a seperate main bus. A failure of any
single computer results in nothing more than a message to the crew. A
failure of any 2 like computers results in some crosswind limitations for
landing.

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

Which was a concern of my sceptical way of viewing engineer's creations. I
couldn't find any single points of failure which would cause much concern.
However I have just begun to look.

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.

There is more than one bus feeding the flight control computers. The two
main busses have independent power supplies. The enormous amount of
redundancy explains why it takes 6 weeks of training to ultimately flip on
the autopilot at 100'AGL.

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

Electrically "controlled" and hydraulically "actuated", as are all the
flight control surfaces in normal operations. Each flight control surface
has multiple actuators receiving hydraulic power from seperate hydraulic
systems. For example, there are 3 spoilers on each wing used for roll
control (the forth is for speedbrake and the fifth is for ground spoiler).
Each spoiler has 2 actuators which are powered by different hydraulic
systems. A loss of any single hydraulic system won't affect control. A loss
of any 2 hydraulic systems will result in a loss of 1 of the 3 spoilers.

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

There are at least 2 actuators, each from a different hydraulic system. All
control surfaces are hydraulically "actuated". In the event that all 3
hydraulic systems are lost, none of the control surfaces will move. The
pilots would have only engine thrust for control, just like the United DC-10
that crashed at Sioux City.

In the event of complete electrical loss, there is still hydraulic pressure,
and the pilots can manually control the hydraulic actuators for the rudder
and the horizontal stabilizer in addition to controlling engine thrust.

Hope it's all clear now :-)

D.

On Mon, 19 Sep 2005 06:17:24 GMT, "Capt.Doug"
wrote in ::

Hope it's all clear now :-)

While we haven't thoroughly exhausted all possible failure modes of
the complex Airbus flight control systems, the information you have
provided has convinced me that minds trained in the disciplines
required to engineer these systems have spent significantly more time
analyzing their design than I am willing to commit. Thank you for
elucidating the arcana of Airbus' computerized electro-hydrolytic
flight control systems. It is enlightening indeed.

Larry Dighera wrote:

minds trained in the disciplines
required to engineer these systems have spent significantly more time
analyzing their design than I am willing to commit.

What a surprize! :-P

Stefan

"Larry Dighera" wrote in message
While we haven't thoroughly exhausted all possible failure modes of
the complex Airbus flight control systems, the information you have
provided has convinced me that minds trained in the disciplines
required to engineer these systems have spent significantly more time
analyzing their design than I am willing to commit. Thank you for
elucidating the arcana of Airbus' computerized electro-hydrolytic
flight control systems. It is enlightening indeed.

You're most welcome.
An interesting side note- During a sim session break, I strolled over to the
A330/340 sim and peeked inside. It looked almost exactly the same as the
A320 sim. The transition course is 4 days. The A380 and A350 transition
courses are expected be the same. To change the 330 sim into a 340 sim, a
sim tech changes the throttle quadrant and reboots. It takes about 5 minutes
total.

D.