Roll rate
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Roll rate
What is the maximum roll rate that can be achieved in a plane like a Boeing 757. I assume this is normally limited by the computer. Is the maximum roll rate affected by air speed? If there was no over-ride, what would be the maximum roll rate?
On the B757 there is no computer that limits roll rate, it's not a fly-by wire system, simply mechanical powered controls with both ailerons and spoilers for roll control. Max roll rate is not relevant in normal operations, one never needs more than a gentle wheel input to achieve what is needed. I can't remember using in the air more than perhaps 20 degrees of the available 90 degrees of wheel movement. On the ground, for takeoff and especially landing with strong x-wind, much more will be used.
That's perhaps a long way of saying I can't answer the question directly, but I can tell you it is speed-dependent, with higher roll rates at higher speeds. TAS or IAS? There's a question!
Incidentally, the flight manual gives no figures and no limits.
That's perhaps a long way of saying I can't answer the question directly, but I can tell you it is speed-dependent, with higher roll rates at higher speeds. TAS or IAS? There's a question!
Incidentally, the flight manual gives no figures and no limits.
Forgive me for offering what amounts to off-topic trivia, but during my BAC111-200 conversion, our flight-controls groundschool instructor - who had worked at BAC - claimed that the roll-rate could equal that of the EE (BAC) Lightning in certain circumstances. As I recall, you needed to have the spoilers slightly extended (i.e., as medium airbrake) to achieve the best roll rate. (The spoilers on the upgoing wing would, of course, then retract.) Whether the speed was the higher the better, and whether that would be IAS or TAS related, I don't know.
Chris
Chris
main_dog,
Regret I cannot assist in that area. (And listen, we're talking about roll RATES, not rolling!)
Unlike its big sister, the VC10, the One-Elevens all employ manual spring-servo-tab ailerons - not PCUs. Spoiler/Speedbrake surfaces are hydraulically powered, of course.
According to my hand-written course notes (in Doug Realff's lectures at the Bee Hive in 1977, re the 200 series): when speedbrakes (why don't we call them AIRbrakes?) are retracted, they do not lift as roll spoilers until 4deg of aileron, unlike the cruder system on the B707. This avoids spoilers cracking open in gentle turns or with aileron trim, and reduces initial roll rate. 4deg of aileron represents roughly 11 - 15deg of control-wheel movement.
However, with 10deg of speedbrake (half the maximum permitted in flight), the situation is slightly more volatile.
"...as soon as the (control wheel) is (fully) displaced, the spoilers will rise on the downgoing wing (to 43deg)......and the spoilers on the upgoing wing will retract. In this config, maximum roll rate is about 400deg per second."
Returning to the speed issue, the spoiler surfaces are designed to "blow back" at a certain air load. This would probably limit roll rate at high IAS, and presumably applies to all aircraft types. FBW types, no doubt, prevent that happening by limiting roll-rate (although blow-back of the surfaces can still occur in speedbrake mode).
Chris
Regret I cannot assist in that area. (And listen, we're talking about roll RATES, not rolling!)
Unlike its big sister, the VC10, the One-Elevens all employ manual spring-servo-tab ailerons - not PCUs. Spoiler/Speedbrake surfaces are hydraulically powered, of course.
According to my hand-written course notes (in Doug Realff's lectures at the Bee Hive in 1977, re the 200 series): when speedbrakes (why don't we call them AIRbrakes?) are retracted, they do not lift as roll spoilers until 4deg of aileron, unlike the cruder system on the B707. This avoids spoilers cracking open in gentle turns or with aileron trim, and reduces initial roll rate. 4deg of aileron represents roughly 11 - 15deg of control-wheel movement.
However, with 10deg of speedbrake (half the maximum permitted in flight), the situation is slightly more volatile.
"...as soon as the (control wheel) is (fully) displaced, the spoilers will rise on the downgoing wing (to 43deg)......and the spoilers on the upgoing wing will retract. In this config, maximum roll rate is about 400deg per second."
Returning to the speed issue, the spoiler surfaces are designed to "blow back" at a certain air load. This would probably limit roll rate at high IAS, and presumably applies to all aircraft types. FBW types, no doubt, prevent that happening by limiting roll-rate (although blow-back of the surfaces can still occur in speedbrake mode).
Chris
Last edited by Chris Scott; 19th Mar 2011 at 16:11. Reason: Minor clarifications
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Well, that is a range of responses. Let's make the question more specific.
Say a B 757 was approaching the circuit area, still at high speed, and the pilot had a short blackout. He woke up to discover he had pushed the throttles fully forward and the plane was doing 460 knots, banked at an angle of 80 degrees. Knowing that the plane will be dropping fast, and scared that there might be a plane just below him, the pilot wants to level the wings as fast as possible. Bearing in mind that spoilers will not be involved, how long will it take to get the wings level?
It seems this is not just a question of maximum roll rate that can be achieved; some inertia must be overcome getting the roll started.
Say a B 757 was approaching the circuit area, still at high speed, and the pilot had a short blackout. He woke up to discover he had pushed the throttles fully forward and the plane was doing 460 knots, banked at an angle of 80 degrees. Knowing that the plane will be dropping fast, and scared that there might be a plane just below him, the pilot wants to level the wings as fast as possible. Bearing in mind that spoilers will not be involved, how long will it take to get the wings level?
It seems this is not just a question of maximum roll rate that can be achieved; some inertia must be overcome getting the roll started.
Psychophysiological entity
... during my BAC111-200 conversion, our flight-controls groundschool instructor - who had worked at BAC - claimed that the roll-rate could equal that of the EE (BAC) Lightning in certain circumstances...
I just can't resist chipping in here, as nearly all my years on the 1-11 had me training on the real aircraft. We were also told the story of the roll rate from a man that had flown both types during testing. I was not sure if I believed it, but it gave a bit of street-cred.
At 20k feet or so, I was told to roll the aircraft this way and that - as hard as I liked. I think our speed would have been c 250k. It was quick, but unremarkable, the controls seeming rather heavy.
Several years went by.
I managed to get a very sick aircraft going in Seville, after desperate attempts by engineers had failed. We'd been stuck on the aircraft for 36 hours. When we came to leave, we had no crew oxygen, so headed back to the UK at low level. <10k. Plenty of fuel, 4 crew + 3 engineers.
Somewhere west of the French coast, and at cruising speed, I had a finger thrust under my nose, along with a loud cry of "Mind That!" My reaction must have been adrenalin fueled. Certainly, the ailerons were way past the angle needed to lift a spoiler, and the aircraft virtually snap-rolled. In disbelief, I stopped it with wings past the vertical, and rolled it back the long way. I know, total wimp.
It had rolled faster than anything I'd flown for aerobatics. Period.
(Fortunately, I'd spent quite a lot of time throwing small aircraft around, so managed to keep the huge toolbox stuck to the flightdeck floor during the recovery.)
I've often wondered about that tail. A lot of mass up there - hydraulic and electric motors and the like. A lot of stress in the roll.
Not a thing was ever mentioned about it, and come to think of it, I got no thanks for jerry-rigging the airplane.
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Wow. It seems some aircraft can roll fast.
I came across this at Aviation Week:
"Aircraft with very long wings, and in particular airplanes with engines distributed outboard along the wings, tend to have more formidable inertia than airplanes with engines located on the fuselage. The amount of fuel in the wings can also make a considerable difference in an aircraft's roll inertia, as an aircraft with fully loaded wings at the beginning of a long-range flight will have a much higher moment of inertia about the aircraft's longitudinal axis than when those tanks are empty. It takes a lot of force to begin rolling those transports. According to the FAA's Airplane Upset Recovery Training Aid, "This greater inertia must be overcome by the rolling moment to produce a roll acceleration and resulting roll angle, and the effect is a sluggish initial response."
So it seems there can be considerable variation. Specific questions:
Does the B757 deploy spoilers at high speed?
As its engines are some distance out from the body, would it be regarded as sluggish in initiating a roll?
Would the amount of fuel in the tanks make a perceptible difference to the initiation of roll?
I came across this at Aviation Week:
"Aircraft with very long wings, and in particular airplanes with engines distributed outboard along the wings, tend to have more formidable inertia than airplanes with engines located on the fuselage. The amount of fuel in the wings can also make a considerable difference in an aircraft's roll inertia, as an aircraft with fully loaded wings at the beginning of a long-range flight will have a much higher moment of inertia about the aircraft's longitudinal axis than when those tanks are empty. It takes a lot of force to begin rolling those transports. According to the FAA's Airplane Upset Recovery Training Aid, "This greater inertia must be overcome by the rolling moment to produce a roll acceleration and resulting roll angle, and the effect is a sluggish initial response."
So it seems there can be considerable variation. Specific questions:
Does the B757 deploy spoilers at high speed?
As its engines are some distance out from the body, would it be regarded as sluggish in initiating a roll?
Would the amount of fuel in the tanks make a perceptible difference to the initiation of roll?
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One of the fastest rolling aircraft around is the A-4 Skyhawk at up to 720 degrees/sec. Enough roll acceleration to bang your head off the canopy if you aren't the one flying (2 seat versions). Enough roll rate to over-pressurize the wing fuel tank from centrifugal force effects and damage the wing (I've investigated some of the resulting incidents). Max roll rate only allowed for one 360 degree roll before stopping it due to roll-pitch coupling.
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Acrobatic planes not of interest in this case
Can anybody give me a figure for how long it would take in a standard Boeing757 to go from an 80 degree bank to wings level at a high speed?
Strange that no 757 jockeys appear to have latched on to this thread. Never flew them myself.
But I am also curious to know why you are fixated with the 757, gravity32, and it seems I may not be the only one.
Fair question?
But I am also curious to know why you are fixated with the 757, gravity32, and it seems I may not be the only one.
Fair question?
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Why the interest in a Boeing 757?
I have been involved in arguments with people over some of the events of 9/11. They are arguing that the official account of the impact of AA77 on the Pentagon cannot be correct because they found a few witnesses who say the plane passed north of the former Citgo gas station. If it did, it could not line up with the damage trail, both outside and inside the Pentagon. They assert the damage was done using explosives, while the plane flew over the top of the Pentagon. No witnesses to the plane flying over the top have been found. These people do not seem to respond to the fact that far more people are on record that the plane hit the Pentagon.
We have radar data showing the plane aiming right at the impact damage at the Pentagon, but it does not go all the way as the plane gets too low for radar. I have done some calculations which show that if the plane curved round the Citgo gas station at the reported 530 mph, it would have to be steeply banked. It has to come out of the left bank then go into a right bank.
There is only one thing missing in my calculations: the time and distance it would take to switch bank from left to right, say 70 degrees each way, assuming maximum control wheel input was used?
We have radar data showing the plane aiming right at the impact damage at the Pentagon, but it does not go all the way as the plane gets too low for radar. I have done some calculations which show that if the plane curved round the Citgo gas station at the reported 530 mph, it would have to be steeply banked. It has to come out of the left bank then go into a right bank.
There is only one thing missing in my calculations: the time and distance it would take to switch bank from left to right, say 70 degrees each way, assuming maximum control wheel input was used?
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My guess is 3 or 4 seconds unless you wanted to rip up the wings but what difference does it make? I always knew I could right the 757 with no problem but probably wouldn't have hacked a stopwatch. I'm sure it would do a great aileron roll. I wish I had done one in the sim. My home flight simulator does it very well but it also does a split S to a landing. I've flown in level flight inverted in the 737 real sim over LAX. It has a very good roll rate so assume the 757 is about the same.
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G32, if you didn't care about tearing up the airplane a 70 left to right bank could be accomplished in around three seconds. Wonder where the airplane and all their passengers went after the event? AA587 and TWA800 investigations were both bogus in my opinion but not this one. Coverups are quite common throughout the world to get the public to believe certain things. Hiding a 757 with a bunch of passengers on board that disappeared after being in sight on descent heading for the pentagon at low altitude isn't. Blaming a copilot for aggressive rudder movements and center fuel tank explosions are easier to BS the public with. They were both BS but most of the public went along with it. Airbus and the US government were successful in pulling it off.
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Thanks B44. That is a good clear response. If 3 seconds is the quickest the roll could be done, this manoeuvre is out of the question as there are only about 4 seconds available for the whole thing, left turn, roll, right turn. With 3 seconds used up rolling, hardly any turn would occur.
Can anyone find a reason it could be done quicker?
Can anyone find a reason it could be done quicker?