"M" wrote:


I was sitting on a Northwest Airbus A-330 a few Sunday's ago at Tokyo
Narita airport waiting for everybody to board on the flight back to
Seattle, when I noticed something strange with the ailerons. Both
ailerons were at their full
downward deflection at about 30 degrees. Things like this can of
course never
happen in any light GA planes where the ailerons are mechanically
linked to
move in opposite directions. I have never seen that on any Boeing
planes
either. Knowing those airbus having flight by wire systems I assumed
that the
computers were just taking a hiatus when the galley was being loaded
and the
ailerons should straighten out once the engines are started.

I peeked out of the windows again as we lined up on the runway and
began the
takeoff roll. To my astonishment both sides of ailerons were still at
a
downward deflection at about 10 degrees. As we rumbled down the runway
I had
this strong urge to tell the flight attendents to check the ailerons.
Can you
say "flight control: free and correct" in the before take-off
checklist? Those
ailerons just plainly looked wrong to me. The big turkey finally
lifted off
the runway and it suddenly hit me: this bizarre behavior of the
ailerons was
actually a genius engineering feat by the nerds at Airbus!

It became obvious that the fly-by-wire computer actually uses the
independently
controlled ailerons to act as part of a full-span flap system. This
allows the
benefit of a full-span flap without having the drawback of a
traditional
full-span flap like the MU-2 (MU-2 has full-span flaps but it has no
room for
ailerons. It uses spoilers for roll axis control). By doing so Airbus
probably saves some weight in the main flap system which, in my wildest
un-scientific guess, reduces the fuel cost per-seat on my 4000nm trip
to
Seattle by maybe a dollar. I'm sure that's very important for the
airline bean
counters.

As the plane climbed out over Tokyo bay the ailerons returned to their
normal
position as the main flaps were retracted.

On our final approach to Seattle the main flaps were down to about 30
degrees
and those ailerons were down again at about 10 degrees. The weather
was CAVU
to 200 feet above the ground, and it was near zero visibility in fog at
the airport. The autopilot flew a fabulous category III ILS all the
way the
ground and the main gears landed very gentally. The pilot was in a
hurry to
derotate the nose down to the ground and the nosewheel hit really hard.
I
guess when you can't see a damn thing 30 feet in the air as the rear
end of
plane already on the runway, you want to get the nose down asap and
start
braking.

What goes around comes around? in the mid fifties the RCAF
acquired an ASW aircraft called the Argus...it was a much
modified Bristol Britannia and had 'floating controls'. They were
free floating and were controlled by 'tabs' on their trailing
edges. When at rest the ailerons hung down (both of them!) at
about 45 degrees and when the 'gust locks' were on they both
reared up about the same. The elevators both hung down 30 0r 40
degrees when unlocked and were straight back when locked, the
rudder was straight back when locked and was 'where-ever it
damned well wanted' when unlocked...quite weird...got many tower
controllers (and airline pilots) in a knot.
--

-Gord.
(use gordon in email)