Pyrex From Portugal, joined Aug 2005, 4213 posts, RR: 30 Posted (7 years 4 weeks 9 hours ago) and read 7792 times:
I just did a flight for the first time in a 767, a Delta -300(ER?) from ATL to GIG and, while landing, noticed on the wing what seemed to me a strange control surface. It was large, between the inboard and outboard flap on the trailing edge of the wing, took about 25% of the chord and had an awkward shape. At first I thought it was another spoiler but it didn't move in tandem with the spoilers. It did, however, move when the aircraft was turning.
I think it might be some kind of roll damper but I had never seen anything quite like that. If it is, in fact, a roll damper, it mustn't be very efficient to have such a large moving surface just for that. Can anybody help me identify this control surface?
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UAL747 From , joined Dec 1969, posts, RR:
Reply 6, posted (7 years 4 weeks 8 hours ago) and read 7717 times:
Quoting Pyrex (Reply 4): That is exactly it. Is it normal for widebodies to have these or is it just the 767 aileron's that have little roll authority?
This is the high speed aileron, or inboard aileron. It's common on Boeing widebody aircraft, although the 787 will feature only outboard ailerons. Modern Airbus widebodies do NOT have inboard ailerons.
The outboard ailerons lock after the flaps are fully retracted or at a certain speed and only the inboard ailerons are used in cruise. The theory is that at slower speeds, the outboard ailerons kick in because they will have the most effectiveness because they are farthest away from the center of gravity. They lock out at high speeds because the inboard ailerons are sufficient and give less loading on the wing when in action.
CptSpeaking From United States of America, joined Apr 2006, 639 posts, RR: 1
Reply 7, posted (7 years 4 weeks 7 hours ago) and read 7672 times:
Ok, I understand the theory behind limiting the twist of the wing at high speeds, but the effectiveness theory doesn't sound right to me...
Airplanes that have the most "effectiveness" rolling would have to be the T-38, the Pitts S-2, etc...but the common denominator here is SHORT wings and less distance from the flight controls to the CG. Seems to me that a control deflection 20 feet out on the wing gives you twice the roll rate of the same deflection at 40 feet out on the wing. If you watch videos of these high speed ailerons, you'll see that they're really moving around and working a lot at LOW speeds. Am I just way off on this?
The aircraft you mentioned also have ailerons that are relatively large compared to the wing they are on. The short span combined with the large ailerons help generate the dramatic roll rate.
As to your question on the deflection of the ailerons, all other things (air pressure, altitude, etc) being equal, a control surface will have to deflect further at a lower airspeed to generate the same result as a smaller deflection at a higher airspeed. This is why the outboard ailerons can be locked out at high speed with no penalty. If they fail to unlock during approach, then you do suffer penalties. The simplest way to visualize it is to imagine a boat and note the effectiveness of the rudder at 5,10, and 20 knots.
Jetlagged From United Kingdom, joined Jan 2005, 2602 posts, RR: 25
Reply 9, posted (7 years 4 weeks 4 hours ago) and read 7588 times:
Quoting CptSpeaking (Reply 7): Airplanes that have the most "effectiveness" rolling would have to be the T-38, the Pitts S-2, etc...but the common denominator here is SHORT wings and less distance from the flight controls to the CG. Seems to me that a control deflection 20 feet out on the wing gives you twice the roll rate of the same deflection at 40 feet out on the wing. If you watch videos of these high speed ailerons, you'll see that they're really moving around and working a lot at LOW speeds. Am I just way off on this?
They've been called high speed ailerons here. All speed aileron is more accurate. The inboard/all speed ailerons work at low speeds and high speeds. Outboard/low speed ailerons work at low speeds, not at high speeds. These are generalisations, there are a lot of detail differences between aircraft types.
As for roll rates, an aircraft with a short stubby wing can generate a high roll rate because the roll damping from the wing is small (centre of pressure of the wing close to the CG) compared to one with high aspect ratio wings. They also have lower inertia about the roll axis, too. Ailerons are less effective closer to the CG (their leverage is less in layman's terms). Larger aileron area can make up for less leverage. Hence high rate of roll in the T-38, Pitts S-2, etc.
Quoting UAL747 (Reply 6): Modern Airbus widebodies do NOT have inboard ailerons.
The A330 and A340 do have inboard and outboard ailerons but they are side by side, outboard of the flaps. In manual flight outboard ailerons only deflect at low speeds (< 190 kts) with flaps extended. In automatic flight and with certain failures they operate with the inboards up to 300 knots.
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UAL747 From , joined Dec 1969, posts, RR:
Reply 10, posted (7 years 4 weeks 4 hours ago) and read 7575 times:
Quoting Jetlagged (Reply 9): The A330 and A340 do have inboard and outboard ailerons but they are side by side, outboard of the flaps. In manual flight outboard ailerons only deflect at low speeds (< 190 kts) with flaps extended. In automatic flight and with certain failures they operate with the inboards up to 300 knots.
Ah, well, I learn something new everyday. However, I still consider those to be a "set" of outboard ailerons when compared to the distance of the inboard ailerons from the Boeing aircraft, but to each his own. I wonder then what they call all 3 of them on the A380? Outboard, Middle, Inboard Ailerons? BTW, speaking of the A380's ailerons, does anyone else think that their movements are really strange? It seems there is no method to the madness as they are ALL always moving, some down while others up.....strange...though I know that there is a reason for it, just can't explain it.
Lemmy From United States of America, joined Dec 2004, 260 posts, RR: 0
Reply 15, posted (7 years 4 weeks 1 hour ago) and read 7495 times:
I've heard stories about 747 test flights with the outboard aileron lockout deactivated. At high speeds, the pilot was able to quickly turn the wheel to full deflection and the plane stayed put. This is because the wing twisted in the opposite direction enough to counteract the aileron.
Quoting CptSpeaking (Reply 14): I'm pickin up what you're puttin down about the center of pressure, dampening, etc., but I'm still struggling with how ailerons closer to the CG are less effective...
I think they key has less to do with roll rate than with roll authority. Since they outboard ailerons are further from the CG, they've got far more leverage. This means they'll be more responsive at low speeds. Think of it this way: if you had to roll an airplane by grabbing the wing and pulling down, you'd have to apply much more force to get it started by holding the wing root. For the same amount of force, you'd get it started easier at the wing tip.
Happy-flier From Canada, joined Dec 1999, 299 posts, RR: 0
Reply 20, posted (7 years 3 weeks 6 days 2 hours ago) and read 7158 times:
Yup! A310 has no outboards.
Perhaps less known, but also true, is the fact that the Convair jets - the 880 and 990 - had no outboard ailerons, only inboards. Making it even more idiosyncratic, the CV990 had no inboard spoilers, just immediately inboard of the outer engines. This particularly good perspective of the NASA CV990 shows this peculiarity quite well.
May the wind be always at your back . . . except during takeoff & landing.
Mir From United States of America, joined Jan 2004, 22157 posts, RR: 55
Reply 21, posted (7 years 3 weeks 6 days 1 hour ago) and read 7129 times:
Quoting CptSpeaking (Reply 7): Seems to me that a control deflection 20 feet out on the wing gives you twice the roll rate of the same deflection at 40 feet out on the wing.
Actually, a control deflection 20 feet out on the wing would give you half the roll rate of the same deflection 40 feet out on the wing. This is just simple physics: force X arm = moment. If you're trying to turn a bolt with a wrench, you're going to have a much easier time if you hold the part of the wrench furthest from the bolt, because the additional arm will make your efforts much more effective.
Comparing the effectiveness of a 767's ailerons to those of a T-38 is comparing apples to oranges. Or, more accurately, apples to coffee tables - they're nothing alike.
Quoting CptSpeaking (Reply 7): If you watch videos of these high speed ailerons, you'll see that they're really moving around and working a lot at LOW speeds. Am I just way off on this?
Since they are less effective than the outboard ailerons, they do have to move around more to achieve a similar result.
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I think I'm starting to get it...my tiny little brain was thinking that if I push down on the wingtip 2 feet at a certain rate, the airplane will roll at x rate, and if I push down at half the distance for 2 feet at the same rate, I'll get twice the roll rate, and the wingtip will now be 4 feet down rather than 2 with the same force being applied, just in a different spot...what I wasn't considering was the difference in force required caused by the difference in arm/moment...got it now though, thanks
BAe146QT From United Kingdom, joined Sep 2006, 996 posts, RR: 0
Reply 24, posted (7 years 3 weeks 5 days 11 hours ago) and read 6991 times:
Quoting Mir (Reply 21): If you're trying to turn a bolt with a wrench, you're going to have a much easier time if you hold the part of the wrench furthest from the bolt, because the additional arm will make your efforts much more effective.
Lemmy's story suggests that you might also extend this analogy;
Imagine a seized bolt - one that resists turning. Gaining more leverage with an extension bar might get it undone, but it also might just shear the bolt - or bend the extension bar.
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: To Pyrex, Regarding the wing of the Boeing 767, you probably saw the high-speed aileron. Traditionally, the best place to put the ailerons on a wing a
: The amount of counter-torque caused by dragging the wings through the air as you roll. Thing of a rolling airplane as a paddle wheel with the wings a
: Damping is a force opposing motion, due to velocity. So roll damping is a rolling moment opposing the rolling motion due to roll rate. If you initiat
: Tdscanuck and Jetlagged, Thank you for the explanations Blackbird
: No exceptions. The further out the aileron is, the higher the roll rate will be (all other things equal). FxA=M doesn't lie. -Mir