Re: A320 comments

From:         Rick Hughes <rmhughes@iinet.net.au>
Organization: iiNet Technologies
Date:         28 Sep 95 03:52:41 
References:   1 2
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In Article<airliners.1995.1497@ohare.Chicago.COM>, <tristar500@aol.com> wrote:

> >13.  Gust Load Aleviation:  They put in a gust load function.  I've heard
> >about the idea for 20 years but apparently no one ever actually put one
> >on an aricraft before the A-320.  It doesn't work......
>
> Would this be the same as Maneuvering DLC or the Active Control Surface
> system on the L/1011? Just wondering.

The principle is quite different.  In the Tristar DLC was designed more to
provide a more precise, direct and almost instantaneous addition/subtraction
of lift. It made very little difference to the actual structural loads on the
wing itself.

I haven't flown the A320, so can't comment on that directly; however, the
A330/340 has a system known as Manouevre Load Alleviation (MLA). It works
something like this:

"The purpose of MLA is to redistribute the lift over the wing to relieve
structural loads on the outer wing surfaces (bending moment).
The demanded load factor is maintained.
MLA utilises spoilers 4, 5, and 6 and the ailerons.
The MLA becomes active when side stick is pulled less than 8 degrees and load
factor is more than 2 g in which case:
- The ailerons are deflected symmetrically upwards:
  Maximum 11 degrees added to roll demand if any.
- The spoilers 4, 5, 6 are deflected symmetrically:
  Maximum 9 degrees added to roll demand if any.
- Deflection is proportional to load factor in excess of 2 g.
- An elevator demand is simultaneously applied to compensate for the pitching
  moment induced by spoilers and ailerons.
The load alleviation is only available when:
- aircraft speed is above 250 kts.
- FLAPS lever is in 0 position.
- in Normal or Alternate law flight mode.
The MLA has priority over Speedbrakes."

Perhaps closer to the Gust Load Alleviation on the A320 is the Turbulence
Damping Function on the A330/340. Its purpose is to damp the structural loads
induced by atmospheric turbulence. The PRIMS (Flight Control Primary
Computers) compute a turbulence damping command which is added to the Normal
Law command for the elevator and the yaw damper.

Like a lot of things in FBW aircraft, you don't notice them working for you,
but they are there nonetheless. IMHO ... the system works very well and the
previous correspondent may well feel differently about the A320 with more time
spent operating the system. I still felt uncomfortable at his point in the
conversion process with non-moving throttles, but have learnt to fully
appreciate the benefits of the system now that I've been operating the A340
for the past 12 months. Airbus put a lot of refinements into the A330/340 in
response to the perceived/actual shortcomings of the A320, and I believe most
would be pleasantly surprised.

Rick Hughes
Perth
Western Australia