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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. |
#2
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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. I don't know the specifics of the A-330, but many modern (i.e. fly by wire) jets use their control surfaces in all sorts of interesting ways which would not be possible on a cable-pully-and-bellcrank system like we've got in our spamcans. On many jets, roll is controlled (as you observed) with a mix of spoilers and ailerons, and both ailerons can move together to effectively act as flaps. |
#3
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I've seen 747 using both the ailerons and outboard spoilers for roll control. However I've never seen the aileron-as-flap thing until I saw it on the A-330. And I'm quite certain that B-737, 747, 757 and 767 don't do that. Nor do I think A-320 families do that either. I've been on a A-340 once but I didn't pay attention to the control services, it probably does it just like A-330. Never rode on a B777. |
#4
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M wrote:
ailerons to act as part of a full-span flap system. Such control surfaces are called flaperons. Nothing new. You find them on many aircraft, from gliders to military jets. The system does not rely on fly by wire, e.g. on gliders it's realised mechanically. Stefan |
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On Mon, 14 Mar 2005, Stefan wrote:
M wrote: ailerons to act as part of a full-span flap system. Such control surfaces are called flaperons. Nothing new. You find them on many aircraft, from gliders to military jets. The system does not rely on fly by wire, e.g. on gliders it's realised mechanically. Some of DeHavilland Canada's designs have/had them; I know the Twin Otter does - it's interesting watching them land in the harbour here with the entire trailing edge of the wing sagging! The Twin Otter is mechanical, of course. For real oddness, the F16 supposedly uses its elevators for roll control; they can move together (pitch) or differentially (roll). Brian www.warbard.ca/avgas/ |
#6
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"Brian Burger" wrote in message
ia.tc.ca... On Mon, 14 Mar 2005, Stefan wrote: M wrote: ailerons to act as part of a full-span flap system. Such control surfaces are called flaperons. Nothing new. You find them on many aircraft, from gliders to military jets. The system does not rely on fly by wire, e.g. on gliders it's realised mechanically. Some of DeHavilland Canada's designs have/had them; I know the Twin Otter does - it's interesting watching them land in the harbour here with the entire trailing edge of the wing sagging! The Twin Otter is mechanical, of course. For real oddness, the F16 supposedly uses its elevators for roll control; they can move together (pitch) or differentially (roll). Brian www.warbard.ca/avgas/ As does the F15, F14 and, I belive, the F/A18 as well. For additional "oddness", check out the A10: the ailerons function as speed brakes by splitting and deploying both up and down. I've often wondered if the amount of up/down is variable for roll control or if the amount of split remains constant and the entire assembly pivots up and down as ailerons normally do? Jay B |
#7
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snip Some of DeHavilland Canada's designs have/had them; I know the Twin Otter does - it's interesting watching them land in the harbour here with the entire trailing edge of the wing sagging! The Twin Otter is mechanical, of course. snip These are called drooping ailerons and were used (in a reportedly unreliable design prone to asymmetric deployment caused by freezing of cable actuating system) on the Noorduyn Norseman. Credit is usually given to Dick Hiscocks and Fred Buller for the excellent design of the mechanical (reliable rod actuated) drooping ailerons used on the DHC stol series that began with the DHC-2 Beaver and grew into the single (and later twin) Otter as well as the larger Buffalo and Caribou aircraft. These aircraft are legendary for their stol capabilities due mainly to the use of drooped ailerons (and big powerplants). I believe that the Robertson stol kits for the C-337 and others also feature modifications that cause the ailerons to droop with the application of flaps. Blue skies to all |
#8
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Correct. I flew a turbo 206 with the Robertson kit. It would droop the
ailerons 10 degrees with the first 15 degrees of flap. We regularly operated in and out of a 500 foot strip in Southern Oregon for 14 years. Al "private" wrote in message news:VdAZd.687525$8l.581495@pd7tw1no... snip Some of DeHavilland Canada's designs have/had them; I know the Twin Otter does - it's interesting watching them land in the harbour here with the entire trailing edge of the wing sagging! The Twin Otter is mechanical, of course. snip These are called drooping ailerons and were used (in a reportedly unreliable design prone to asymmetric deployment caused by freezing of cable actuating system) on the Noorduyn Norseman. Credit is usually given to Dick Hiscocks and Fred Buller for the excellent design of the mechanical (reliable rod actuated) drooping ailerons used on the DHC stol series that began with the DHC-2 Beaver and grew into the single (and later twin) Otter as well as the larger Buffalo and Caribou aircraft. These aircraft are legendary for their stol capabilities due mainly to the use of drooped ailerons (and big powerplants). I believe that the Robertson stol kits for the C-337 and others also feature modifications that cause the ailerons to droop with the application of flaps. Blue skies to all |
#9
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"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) |
#10
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Gord Beaman wrote:
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. Doesn't the DC-9 work this way too? I have a vague recollection of talking to a DC-9 pilot who explained the system to me -- mechanical interconnections to servo tabs, with the main surfaces floating free. Or is my memory faulty? |
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