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A-330 ailerons
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. |
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