The Danger with Rapid Rotations
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The Danger with Rapid Rotations
Discussion came up over coffee about the rate of rotation used by some pilots. F/O said he was consistently amazed at the fast rate of rotation of one captain in his company flying 737NG variants and couldn't understand why there had not been a tail-strike so far. He felt that a comment would not be received gracefully so merely gritted his teeth.
Some years ago I transferred to another company flying the 737-200. The chief pilot criticised my rotation rate as being far too slow (in his opinion) and warned this could compromise obstacle clearance with engine failure. I was surprised at this as no one had criticised the rotation rate before because I had stuck strictly to the one potato - two potato up to 15 degrees.
Over the next few sectors I then observed carefully the rotation rate of the crusty old chief pilot of my new company and stopwatched him consistently on 2.5 seconds from Vr call to 15 degrees. As it was a -200 then wasn't much danger of tail strike but a high speed stall at that rate of rotation was a danger particularly at Flaps 1 take off.
The CP did not believe me when I said he had been timed at 2.5 seconds from Vr call to 15 degrees up and I realised he honestly thought he was doing the job at the FCTM ideal of 3 degrees per second.
So apart from the possibility of a tail strike, how dangerous are rapid rotations? In the early years of 737-200 operation, there were several documented instances of sudden pitch up and wing drop on Flap 1 rapid rotations especially if there was traces of frost or ice. This led to Boeing advice that if ice was around it was better to use greater flap settings or improved climb speeds to give a greater stall margin and also to ensure rotation rates were as per FCTM.
I believe that some pilots are quite unaware of their fast rotation rates aalthough one would think a diligent instructor would spot their bad habit during simulator training. For all the 737 variants there is a momentrary pitch force change around 10 dgrees body angle due to the tailplane encountering ground effect and it often results in a slight hesitation at 10 degrees before normal stick force returns. Some pilots will either unconsciously or deliberately force the rotation through that area and maintain this additional pull right through to the nominal 15-18 degrees. This results in a rapid rotation before the pilot is aware of it. A rapid rotator should be picked up in the simulator because it is a habit that is hard to crack. It begs the question should a pilot who is a rapid rotator be subject to a comment by the other pilot who may consider the manoeuvre potentially dangerous? Or do you play the shrug your shoulders game and keep quiet? Comments welcome.
Some years ago I transferred to another company flying the 737-200. The chief pilot criticised my rotation rate as being far too slow (in his opinion) and warned this could compromise obstacle clearance with engine failure. I was surprised at this as no one had criticised the rotation rate before because I had stuck strictly to the one potato - two potato up to 15 degrees.
Over the next few sectors I then observed carefully the rotation rate of the crusty old chief pilot of my new company and stopwatched him consistently on 2.5 seconds from Vr call to 15 degrees. As it was a -200 then wasn't much danger of tail strike but a high speed stall at that rate of rotation was a danger particularly at Flaps 1 take off.
The CP did not believe me when I said he had been timed at 2.5 seconds from Vr call to 15 degrees up and I realised he honestly thought he was doing the job at the FCTM ideal of 3 degrees per second.
So apart from the possibility of a tail strike, how dangerous are rapid rotations? In the early years of 737-200 operation, there were several documented instances of sudden pitch up and wing drop on Flap 1 rapid rotations especially if there was traces of frost or ice. This led to Boeing advice that if ice was around it was better to use greater flap settings or improved climb speeds to give a greater stall margin and also to ensure rotation rates were as per FCTM.
I believe that some pilots are quite unaware of their fast rotation rates aalthough one would think a diligent instructor would spot their bad habit during simulator training. For all the 737 variants there is a momentrary pitch force change around 10 dgrees body angle due to the tailplane encountering ground effect and it often results in a slight hesitation at 10 degrees before normal stick force returns. Some pilots will either unconsciously or deliberately force the rotation through that area and maintain this additional pull right through to the nominal 15-18 degrees. This results in a rapid rotation before the pilot is aware of it. A rapid rotator should be picked up in the simulator because it is a habit that is hard to crack. It begs the question should a pilot who is a rapid rotator be subject to a comment by the other pilot who may consider the manoeuvre potentially dangerous? Or do you play the shrug your shoulders game and keep quiet? Comments welcome.
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Currently a hot topic here in the WoT.
2 tail strikes last year (757 and 763)
All new pilots are VERY carefully monitored on rotation rates.
Very hot on it in the initial TR Sims and during line training where if you are rotating too quickly you will soon be told about it either verbally or with nudge of the column.
2 tail strikes last year (757 and 763)
All new pilots are VERY carefully monitored on rotation rates.
Very hot on it in the initial TR Sims and during line training where if you are rotating too quickly you will soon be told about it either verbally or with nudge of the column.
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hi 'g' ground stall if you really fool around
also rotation rate is affected by the actual aircraft perf. really heavy rotate slower, really light, faster, mid weight mid perf rotate @datum rate. don't want to do all that then rotate at the rate scheduled in the afm. i.e datum rate
also rotation rate is affected by the actual aircraft perf. really heavy rotate slower, really light, faster, mid weight mid perf rotate @datum rate. don't want to do all that then rotate at the rate scheduled in the afm. i.e datum rate
Last edited by rhovsquared; 29th Apr 2006 at 16:40.
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Well, I don't fly with crusty old Chief Pilots, but I have noticed a time or two where a new (sometimes not so new) First Officer will try to rotate too rapidly.
I have NO idea where they might get this idea, but I come from the old school, flying old 4-engine types early on, and if these were rotated too fast, especially at heavy weights, getting airborne would have been doubtful, at best.
In addition, a slightly slower rotation rate will enable the flying pilot to successfully handle an engine failure scenario, when and if that engine (especially an outboard one on a four engine type) fails at the most inopportune time during the takeoff...just prior to, or at rotation.
I watched one young guy in the sim rotate with such vigor, that during the wing engine failed just at rotation exercise, he found himself trying to climb at just under V2 at a heavy weight...and getting absolutely nowhere.
I have NO idea where they might get this idea, but I come from the old school, flying old 4-engine types early on, and if these were rotated too fast, especially at heavy weights, getting airborne would have been doubtful, at best.
In addition, a slightly slower rotation rate will enable the flying pilot to successfully handle an engine failure scenario, when and if that engine (especially an outboard one on a four engine type) fails at the most inopportune time during the takeoff...just prior to, or at rotation.
I watched one young guy in the sim rotate with such vigor, that during the wing engine failed just at rotation exercise, he found himself trying to climb at just under V2 at a heavy weight...and getting absolutely nowhere.
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Over the years I worked on several (at least a dozen) Tail Drags/Tail Strikes and I can't remember one that occured on takeoff, all were on landing. Does any one know the ratio takeoff to landing?
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Originally Posted by A37575
It begs the question should a pilot who is a rapid rotator be subject to a comment by the other pilot who may consider the manoeuvre potentially dangerous? Or do you play the shrug your shoulders game and keep quiet? Comments welcome.
I think that any time either pilot sees the other guy rotating like what has been described here, it would be not only a smart thing to do to bring it to his attention, it could be the best conversation of your career. It borders on being unsafe, and at the higher gross weights probably is unsafe. There would be nothing more sad than to have your friends mention the fact that you knew it was dangerous but you decided to keep it to yourself, and do so at your funeral. And, by the way, if the other guy tells you to "stuff it," I think a chat with the Chief Pilot might be in order. Sorry guys, but he asked.
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Rapid Rotations during High Performance Take-offs.
To be objective in examining the manoeuvres from rotation to initial climb away for aircraft having high excess thrust you should consider the two basic segments of the rotation and throw in the effects on the human occupants.
Segment 1 would be the tranistion from ground roll to lift off.
Segment 2 would be the requirement to change the vertical direction of the aircraft from horizontal at lift off to the initial climb away angle.
Ignoring smoothness/human effects the initial rotation could be almost instantaneous to rapidly increase the wing lift to fully support the aircraft weight but one should not overlook the total rotational momentum then generated which would inevitably cause some overshoot towards a potential tail strike before adequate development of the second segment.
Having lifted off at a defined safe margin above the 1g stall you now enter the next segment which is a 1g+ manoeuver to change vertical direction through to the initial climb angle during a period when continuing increasing air speed should be allowed thus maintaining an initial margin over the small increase in the 1g+ stall.
All of these factors including human effects will have been embraced in the flight tests to determine the best rotate V for weight by TPs who expect that most pilots are trained to operate flight controls in a positive and smooth manner with some emphasis on smoothness.
To be objective in examining the manoeuvres from rotation to initial climb away for aircraft having high excess thrust you should consider the two basic segments of the rotation and throw in the effects on the human occupants.
Segment 1 would be the tranistion from ground roll to lift off.
Segment 2 would be the requirement to change the vertical direction of the aircraft from horizontal at lift off to the initial climb away angle.
Ignoring smoothness/human effects the initial rotation could be almost instantaneous to rapidly increase the wing lift to fully support the aircraft weight but one should not overlook the total rotational momentum then generated which would inevitably cause some overshoot towards a potential tail strike before adequate development of the second segment.
Having lifted off at a defined safe margin above the 1g stall you now enter the next segment which is a 1g+ manoeuver to change vertical direction through to the initial climb angle during a period when continuing increasing air speed should be allowed thus maintaining an initial margin over the small increase in the 1g+ stall.
All of these factors including human effects will have been embraced in the flight tests to determine the best rotate V for weight by TPs who expect that most pilots are trained to operate flight controls in a positive and smooth manner with some emphasis on smoothness.
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also rotation rate is affected by the actual aircraft perf. really heavy rotate slower, really light, faster, mid weight mid perf rotate @datum rate. don't want to do all that then rotate at the rate scheduled in the afm. i.e datum rate
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Originally Posted by Milt
Ignoring smoothness/human effects the initial rotation could be almost instantaneous to rapidly increase the wing lift to fully support the aircraft weight but one should not overlook the total rotational momentum then generated which would inevitably cause some overshoot towards a potential tail strike before adequate development of the second segment.
Now, if you *know* what the lift-off attitude is you could perhaps argue that could be attained almost instantaneously with little direct adverse effect, though there would still be overrotation concerns.
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My first large jet training was on the MD80. Prior to that, I just yanked back on the turboprops I was flying and no one said anything.
The MD80 will be difficult to control on an engine failure prior to rotation if you haul it off the ground rapidly. I learned my lesson and would rather be criticised for rotating too slowly than have control issues for rotating too fast.TC
The MD80 will be difficult to control on an engine failure prior to rotation if you haul it off the ground rapidly. I learned my lesson and would rather be criticised for rotating too slowly than have control issues for rotating too fast.TC
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Likewise with the older models of the B707, AA717driver, and even with most models of the Lockheed TriStar, at very heavy weights.
Slower rotations (within reason) ARE better.
Slower rotations (within reason) ARE better.
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Apologies if someone else pointed it out before (if so I missed it during my scanning of the posts) .. quite apart from tailstrike considerations, performance data is based on the technique described in the flight manual so that technique should be the process routinely aimed for by the pilot ...
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Rapid rotation can cause other problems than tailstrike. If your aircraft is fitted with a stick pusher, too high a rate can provoke the alpha dot term to generate a push. Most modern Stall Protection Computers ramp in the alpha dot term a couple of seconds after liftoff for this very reason.
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Mad Scientist
I must take more care with the words!
No way was I proposing a technique for rapid rotation through about 15 degrees to the lift off alpha - just that it would be of little consequence if you did just that other than for a tendency to overshoot too early into the airborne segment. It would certainly startle those aboard but would get the wings doing their thing promptly.
Much better to aim for a constant rate of rotation through the transistion from ground to air borne knowing that when airborne you then start to pull some extra loading (1g+) to establish your initial climb angle whilst expertly flaring off the rotation to reach the initial climb attitude coincident with the initial climb IAS. Now that takes a bit of type experience and some 'stick and rudder' finesse to do it all smoothly, all of which tends to sort out the good pilots from the not so good!
Then there will be the hot day and a weighty heavy which will be reluctant to go flying. This is where experience can hone the instincts of the pilots in a determination of the optimum technique for rotation to lift off when the margins are small. For most types a slow rotation to lift off will often be consistent with progressively replacing rolling wheel drag with increasing wing drag throughout the rotation to achieve maximum acceleration. There will be precious little rotation to be concerned with after the lift off. Runway length will be a major factor and the lessons learned from rotations made too early are legendary.
I must take more care with the words!
No way was I proposing a technique for rapid rotation through about 15 degrees to the lift off alpha - just that it would be of little consequence if you did just that other than for a tendency to overshoot too early into the airborne segment. It would certainly startle those aboard but would get the wings doing their thing promptly.
Much better to aim for a constant rate of rotation through the transistion from ground to air borne knowing that when airborne you then start to pull some extra loading (1g+) to establish your initial climb angle whilst expertly flaring off the rotation to reach the initial climb attitude coincident with the initial climb IAS. Now that takes a bit of type experience and some 'stick and rudder' finesse to do it all smoothly, all of which tends to sort out the good pilots from the not so good!
Then there will be the hot day and a weighty heavy which will be reluctant to go flying. This is where experience can hone the instincts of the pilots in a determination of the optimum technique for rotation to lift off when the margins are small. For most types a slow rotation to lift off will often be consistent with progressively replacing rolling wheel drag with increasing wing drag throughout the rotation to achieve maximum acceleration. There will be precious little rotation to be concerned with after the lift off. Runway length will be a major factor and the lessons learned from rotations made too early are legendary.
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Originally Posted by A37575
I am not sure you are right Rhovsquared. Apart from the engine failure rotation the Boeing 737 FCTM advice on rotation rates does not differentiate between light weights and max gross. From observation I believe that with a light weight and thus a rapidly accelerating aircraft there is sometimes a tendency to hurry the rotation where the pilot perceives the airspeed is rapidly building up just after lift off before he is ready for it.
I definitely don't want to tell working line pilots what to do, but it could also be a Datum Rate meaning a Mid-perf test rate that protects against the stall or hi 'g' throughout the extrema of the performance (AEO and OEI) range with out comprimising distance.
To look at the raw physics of it (as well as that info being in a well known TP's book
If you ingore flight path momentum for a moment, as it is high in both cases i.e Mv or mV,. and bring it down to the fundemental forces F=MAsince A is changing the F= Lift is changing as V^2, because the plane is accelerating fron Vr to Vlof through the screen at V2 or V3 the rate of change of the lift force must be met with the appropriate rate of change in AoA(incidence).
My statement does assume there is no abuse in rotation attitude or speed; edited to add rate of change of AoA
I'm sure 411A rotates at the exact rate the performance calls for i.e if 2.6575 deg/sec was called for that's what he gives
Last edited by rhovsquared; 10th May 2006 at 00:23.
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In the two aircraft types I have flown, 727 and 737-200, the recommended rotation rate was 3° per second. The 727 had tailstrike potential but on the 737-200, it was much less likely.
I was reading an accident brief the other day(for a DC-9-10) and found this interesting quote...
"Normal DC-9 Series 10 operating procedures advocate an approximate 6° per second rotation rate. The 6° per second rate of rotation can result in higher than desirable angle of attack as the airplane becomes airborne. The Safety Board believes that a 3° per second rotation rate of the DC-9 Series 10 airplane should be specified when icing conditions exist. The same procedure was applied to Boeing 737 airplanes after a number of them experienced “wing roll-off”(partial stall) at liftoff in icing conditions."
I have never seen this mentioned anywhere else. Is it still a 6° rotation rate on the short DC-9's?
Anyone have old 737 manuals(on the net perhaps) that mentions the 6° rotation rate?
I looked at the Air Florida report but nothing is mentioned about it.
I was reading an accident brief the other day(for a DC-9-10) and found this interesting quote...
"Normal DC-9 Series 10 operating procedures advocate an approximate 6° per second rotation rate. The 6° per second rate of rotation can result in higher than desirable angle of attack as the airplane becomes airborne. The Safety Board believes that a 3° per second rotation rate of the DC-9 Series 10 airplane should be specified when icing conditions exist. The same procedure was applied to Boeing 737 airplanes after a number of them experienced “wing roll-off”(partial stall) at liftoff in icing conditions."
I have never seen this mentioned anywhere else. Is it still a 6° rotation rate on the short DC-9's?
Anyone have old 737 manuals(on the net perhaps) that mentions the 6° rotation rate?
I looked at the Air Florida report but nothing is mentioned about it.
6° per second? You have got to be joking. The 717 (shortish DC-9) FCOM recommends 2.5° per second and that feels too fast.
Understatement of the century. 
The 6° per second rate of rotation can result in higher than desirable angle of attack as the airplane becomes airborne.
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Even 3° per second is too much on a long 737 in gusty wind conditions, that tail gets very close to the ground.
From the 2011 737NG FCTM:
I flew with a Captain back when I started on the 737-800 first and he used a really fast rotation to about 8° then leave it settle for a second before launching it up again to 15°. He used to fly the -500 for another airline before but I used to cringe every time he'd rotate and wait for a thud
From the 2011 737NG FCTM:
rotation rates vary from 2° to 3° per second
with rates being lowest on longer airplanes. Liftoff attitude is achieved in
approximately 3 to 4 seconds depending on airplane weight and thrust setting.
with rates being lowest on longer airplanes. Liftoff attitude is achieved in
approximately 3 to 4 seconds depending on airplane weight and thrust setting.
I've never understood some people's obsession with trying to snatch the aircraft off the ground, all engines running. If you get an engine failure, you're going to be rotating a bit slower to a lower pitch attitude anyway, so it doesn't compromise performance noticeably. Yanking the thing into the air does make me squirm in the seat, though!