Quiet Airliners of the Future?

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)