Roll rate
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The quickest would be to deploy a bit of spoilers so you have differential spoilers helping the roll rate and using full aileron but you could cause some damage to the aircraft.
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I didn't think spoilers could be deployed at such high speed, 460 knots. I thought they would not be needed at high speed as the ailerons would have all the authority anyone would need. I also thought they might be at risk of damage at high speed. Perhaps I am wrong about these things.
If spoilers could be used, and were used, what would be your estimate of roll rate?
If spoilers could be used, and were used, what would be your estimate of roll rate?
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Probably around 100 degrees per second with full deflection. Good luck on everything hanging together. I would expect the ailerons to take a lot more stress than the speed brakes would with full deflection.
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gravity32:
The AA77 maneuvering problem is more basic than just roll rate. Why not chart the supposed course on a city map, using the greatest possible turn radii, then work it as a centrifugal force problem at 530 mph (kts I presume?). At 530 in a 2g turn, the nose just creeps around the horizon. Even if you totally neglect the time required to roll into/out of the required bank, I'll bet you need to make 4 or 5g turns to fly the required course.
The AA77 maneuvering problem is more basic than just roll rate. Why not chart the supposed course on a city map, using the greatest possible turn radii, then work it as a centrifugal force problem at 530 mph (kts I presume?). At 530 in a 2g turn, the nose just creeps around the horizon. Even if you totally neglect the time required to roll into/out of the required bank, I'll bet you need to make 4 or 5g turns to fly the required course.
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With half a second allowed for roll time the radius of turn is 1893 feet, the force is 9.97g, the bank angle 84.3 degrees.
It couldn't survive the g-force and if it did, nobody saw that bank!
It couldn't survive the g-force and if it did, nobody saw that bank!
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B757 Upgrade To B767 — Tech Ops Forum | Airliners.net
I couldn't find any official reference to this post 20 and 22 info.
I couldn't find any official reference to this post 20 and 22 info.
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Chris Scott
That's on par with some aerobatic aircraft...
Why would they have configured the control-system to produce such a heavy roll rate all the sudden at maximum control surface deflection? I thought the whole idea is so that it builds up in a predictable manner...
Loose Rivets
Impressive...
Machinbird
I didn't know a plane could roll fast enough to damage itself...
What's roll-pitch coupling?
"...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."
Why would they have configured the control-system to produce such a heavy roll rate all the sudden at maximum control surface deflection? I thought the whole idea is so that it builds up in a predictable manner...
Loose Rivets
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.
It had rolled faster than anything I'd flown for aerobatics. Period.
Machinbird
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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What's roll-pitch coupling?
The angle of attack displaces the nose above the roll axis and the tail below the roll axis. Centrifugal force from the roll tends to force these extremities away from the roll axis causing a potentially uncontrolled increase in angle of attack.
I didn't know a plane could roll fast enough to damage itself...
Each aircraft has different considerations, but under the right conditions you could overpressurize a wing or throw engines by generating a great enough roll rate.
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It seems to me I have asked the wrong question. The term "roll rate" appears to relate to a stabilized process in which the initial inertia has been overcome.
In a plane like a B757 the wings are long, the engines are outboard and the fuel tanks go well out along the wings, so there would be a lot of inertia.
The proper question is not roll rate, but time for a roll of a specific number of degrees. Since flying at 2g is within the permitted range, which has a bank of 60 degrees, does anyone have a figure for the time to go from wings level to 60 degrees, with maximum control wheel input, in a B757?
In a plane like a B757 the wings are long, the engines are outboard and the fuel tanks go well out along the wings, so there would be a lot of inertia.
The proper question is not roll rate, but time for a roll of a specific number of degrees. Since flying at 2g is within the permitted range, which has a bank of 60 degrees, does anyone have a figure for the time to go from wings level to 60 degrees, with maximum control wheel input, in a B757?
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Depending on speed probably less than a second to reach a 60 degree bank but nobody flies that way because the engines and pylons aren't built to take those forces so even test pilots don't do it. They may withstand it but nobody flies like that. Tell your conspiracy friends about the 9-11 Pentagon crash that it didn't make a 10G turn but vaporized. That is the only explanation for not seeing it depart at high speed. I wonder after the 10 G turn where they were going?
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There is of course no doubt the plane hit the Pentagon. There are many witnesses, including three of their star north-of-Citgo witnesses, Lagasse, Turcios and Brooks, who all said they saw the plane hit the Pentagon. Sean Boger from the Control tower at the Pentagon Heliport watched it all the way into the Pentagon. Albert Hemphill at the Navy Annex said it was to his right, and flew straight over the bridge into the Pentagon. There is not one witness to the plane flying over the Pentagon though there were hundreds of cars stuck in traffic around the area.
There is radar data from four installations all leading directly to the Pentagon impact site. Now there is also the FDR file, which has recently been fully decoded, showing the plane flying straight, at the same track angle as the radar, and descending. The last radio height is 4 feet. Add 6 feet for the offset and 16 feet for the height of the wings above the wheels and you get a height that matches the length of the chopped off light poles.
So all the evidence shows the plane hit the Pentagon. Its mass is sufficient to smash the wall. Most of it went inside. There is enough debris outside to account for the parts that were too light to penetrate. The claim the plane flew north-of-citgo is a claim based on no evidence other than a few who were mistaken about something that would not seem important to remember at the time.
You can read about this here:
The Science of 9/11| Pentagon
There is radar data from four installations all leading directly to the Pentagon impact site. Now there is also the FDR file, which has recently been fully decoded, showing the plane flying straight, at the same track angle as the radar, and descending. The last radio height is 4 feet. Add 6 feet for the offset and 16 feet for the height of the wings above the wheels and you get a height that matches the length of the chopped off light poles.
So all the evidence shows the plane hit the Pentagon. Its mass is sufficient to smash the wall. Most of it went inside. There is enough debris outside to account for the parts that were too light to penetrate. The claim the plane flew north-of-citgo is a claim based on no evidence other than a few who were mistaken about something that would not seem important to remember at the time.
You can read about this here:
The Science of 9/11| Pentagon
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So you get a corkscrewing action going?
gravity32
I wouldn't worry too much what a few borderline psychos have concocted. Reasoning, thinking, men can hear these stories and discard them. Those that embrace these strange theories have an emotional need. That is their problem. All you need to do is firmly state, "That is BullSh*t," to indicate you do not want to play their game.
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Machinbird
Okay... so as it would roll, centrifugal forces would rapidly drive up the AoA, which then arrests the roll and causes a gigantic sideslip?
Worse than that. The aircraft could go completely belly into the wind and convert its roll momentum into yaw momentum (worst case).
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Machinbird, these guys are not psychos. They are smart operators who have figured out that they can sell DVDs by creating controversey. They do harm and should be opposed.
My revised calculations show that the plane would have to be banked at 77degrees to perform the proposed ridiculous turn with a g-force of 4.4.
This leads to an interesting question. What is the maximum bank angle that a B757 could fly at and maintain height?
The maximum legal bank is arrived at from the maximum legal load, 2.5g, about 66 degrees, but we don't want to apply this restriction. The question is really about power. At maximum power, what bank angle could it get to and maintain height, assuming it did not break up?
I presume it could be worked out knowing the max power, and the drag at various AoA, given that the AoA and bank angle must be related in a level turn.
Any takers?
My revised calculations show that the plane would have to be banked at 77degrees to perform the proposed ridiculous turn with a g-force of 4.4.
This leads to an interesting question. What is the maximum bank angle that a B757 could fly at and maintain height?
The maximum legal bank is arrived at from the maximum legal load, 2.5g, about 66 degrees, but we don't want to apply this restriction. The question is really about power. At maximum power, what bank angle could it get to and maintain height, assuming it did not break up?
I presume it could be worked out knowing the max power, and the drag at various AoA, given that the AoA and bank angle must be related in a level turn.
Any takers?
Last edited by gravity32; 11th Apr 2011 at 16:24.
Quote from Jane-DoH:
"Quote from Chris Scott:
"...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."
"...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."
That's on par with some aerobatic aircraft...
Why would they have configured the control-system to produce such a heavy roll rate all the sudden at maximum control surface deflection? I thought the whole idea is so that it builds up in a predictable manner..."
Apologies, Jane: I completely missed your post. Did have some later misgivings re mine, though. Obviously, once the roll-spoilers on the upgoing wing have retracted, the situation is the same as if they had been retracted (as speedbrakes) in the first place.
However, I think the point my BAC 1-11 ground instructor was making may have been relating to the initial response. Due to the moment of inertia of a 30-ton aeroplane with a fairly large wingspan, the rate of increase of roll-rate is likely to be pedestrian in relation to lighter fast jets with small wingspans, like the contemporary English Electric (BAC) Lightning that he was comparing it with.
I think you have a point, except that it wouldn't happen all of a sudden on the One-Eleven. Mind you, the 200 series I first flew certainly was agile. If you look back to my post, you'll see reference to the roll-spoilers not "cracking" until a moderate amount of aileron displacement (unlike the B707). Being airline pilots, we tried not to pass that threshold if convenient, because of the slight aerodynamic rumble from the spoilers.
Regards,
Chris
"Quote from Chris Scott:
"...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."
"...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."
That's on par with some aerobatic aircraft...
Why would they have configured the control-system to produce such a heavy roll rate all the sudden at maximum control surface deflection? I thought the whole idea is so that it builds up in a predictable manner..."
Apologies, Jane: I completely missed your post. Did have some later misgivings re mine, though. Obviously, once the roll-spoilers on the upgoing wing have retracted, the situation is the same as if they had been retracted (as speedbrakes) in the first place.
However, I think the point my BAC 1-11 ground instructor was making may have been relating to the initial response. Due to the moment of inertia of a 30-ton aeroplane with a fairly large wingspan, the rate of increase of roll-rate is likely to be pedestrian in relation to lighter fast jets with small wingspans, like the contemporary English Electric (BAC) Lightning that he was comparing it with.
I think you have a point, except that it wouldn't happen all of a sudden on the One-Eleven. Mind you, the 200 series I first flew certainly was agile. If you look back to my post, you'll see reference to the roll-spoilers not "cracking" until a moderate amount of aileron displacement (unlike the B707). Being airline pilots, we tried not to pass that threshold if convenient, because of the slight aerodynamic rumble from the spoilers.
Regards,
Chris
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What is the maximum bank angle that a B757 could fly at and maintain height?
But the 757 didn't have to maintain height; it was undoubtedly using its potential energy in a shallow dive, aiding the specific excess power issue.
Nonetheless, good luck with the 4.4g.
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barit1, that is a very interesting article. Thanks.
It is clear that height and excess speed can provide power to maneuvre. Certainly the 757 had plenty of speed but very little height. The problem is it only had at the most 1 second to get its wings level from 77 degrees and pull out of the dive. It finished virtually level.
The FDR data shows it pulled up from a 5 degree descent to about 1 degree in 2 seconds and that the average force during these 2 seconds was 2g. If this absurd turn is to be believed, only 1 second would be available thus 4g lift would be required, all starting from a bank of 77 degrees. Could it do it?
It is clear that height and excess speed can provide power to maneuvre. Certainly the 757 had plenty of speed but very little height. The problem is it only had at the most 1 second to get its wings level from 77 degrees and pull out of the dive. It finished virtually level.
The FDR data shows it pulled up from a 5 degree descent to about 1 degree in 2 seconds and that the average force during these 2 seconds was 2g. If this absurd turn is to be believed, only 1 second would be available thus 4g lift would be required, all starting from a bank of 77 degrees. Could it do it?
Last edited by gravity32; 13th Apr 2011 at 11:42.