Better Perf during rolling takeoff?
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From: US
Simulator season. Five takeoffs and 5 aborts at V1+10.
Three takeoffs allowing autothrottles to advance the power resulted in all three a/c departing the runway about approx. 60 kts.
Two takeoffs manually advancing the power resulted in two aborts still on the pavement.
How quickly you get takeoff power matters. Most pilots doing rolling takeoffs are farther down the runway before takeoff power is set vs. a static takeoff.
Three takeoffs allowing autothrottles to advance the power resulted in all three a/c departing the runway about approx. 60 kts.
Two takeoffs manually advancing the power resulted in two aborts still on the pavement.
How quickly you get takeoff power matters. Most pilots doing rolling takeoffs are farther down the runway before takeoff power is set vs. a static takeoff.
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From: Australia
I think that a point that seems to have been missed, and perhaps what the original poster was alluding to is confusion with the "Roll-On" Takeoff (not Rolling). That is, a Takeoff where the aircraft enters the runway at the nominal Takeoff commencement point already rolling with residual speed from the taxy.
For a 90 degree or 180 degree turn to line-up, this is obviously not practical or safe, but there are many Runway entry points such as Brisbane 19 and the new Singapore 20C where significant taxy speed can safely be maintained up to the SOT (Start of Takeoff) point where Takeoff Thrust / Power is then applied whilst still rolling.
I recall working on one Douglas jet aircraft where the AFM stated that the Maximum Achievable Takeoff Weights were (1) Roll-On Takeoff, (2) Standing Start, and (3) Rolling Takeoff in that descending order. The AFM went on to explain that a properly executed Roll-On Takeoff was one where the aircraft had a minimum speed of 10 knots at the normal SOT. In these circumstances Standing Start Takeoff limiting weights were permissible, whilst better than Standing Start actual performance could be expected.
Regards,
Old Smokey
For a 90 degree or 180 degree turn to line-up, this is obviously not practical or safe, but there are many Runway entry points such as Brisbane 19 and the new Singapore 20C where significant taxy speed can safely be maintained up to the SOT (Start of Takeoff) point where Takeoff Thrust / Power is then applied whilst still rolling.
I recall working on one Douglas jet aircraft where the AFM stated that the Maximum Achievable Takeoff Weights were (1) Roll-On Takeoff, (2) Standing Start, and (3) Rolling Takeoff in that descending order. The AFM went on to explain that a properly executed Roll-On Takeoff was one where the aircraft had a minimum speed of 10 knots at the normal SOT. In these circumstances Standing Start Takeoff limiting weights were permissible, whilst better than Standing Start actual performance could be expected.
Regards,
Old Smokey
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From: US
stilton - "757 / 67 'Rotates lowly' and while they are good performers it is not exactly Bugatti Veyron acceleration.
Certainly not whiplash inducing
"
Hmm, 757 w/RR engines at Max Power is very impressive.
Especially if your weight is down around 180-190,000 lbs (85,000 Kg).(typical weight for a 2-3 hr flight).
Thrust to weight is almost down to .5, which is similar to fighter a/c 'dry' thrust to weight ratios.
Certainly not whiplash inducing
"Hmm, 757 w/RR engines at Max Power is very impressive.
Especially if your weight is down around 180-190,000 lbs (85,000 Kg).(typical weight for a 2-3 hr flight).
Thrust to weight is almost down to .5, which is similar to fighter a/c 'dry' thrust to weight ratios.
Last edited by misd-agin; 19th November 2008 at 21:01. Reason: added sentence
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From: Planet Earth
True, but if I was that light it is very unlikely I would be using full thrust for take off.
A good example would be departing Bristol in a 757 at max weight (closer to 250,000 pounds) for an 8 hour flight back to NY.
A good example would be departing Bristol in a 757 at max weight (closer to 250,000 pounds) for an 8 hour flight back to NY.
Fleet Manager
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From: various places .....
horses for courses ..
(a) standing start is useful for reference as it is the most easily repeatable set of data .. but it shakes the stuffing out of the aircraft so should be used only when it is sensibly appropriate.
(b) if the aircraft is heavy and we don't dilly dally with the levers, the power is set in a few turns of the wheels - near enough to standing start
(c) if the aircraft is light (and low Hp/OAT), the aircraft will be some distance down the roll prior to achieving takeoff settings. If the runway is short/limiting, this is probably not a sensible strategy, if long and definitely not limiting, it is more useful for the aircraft maintenance than a standing start (I acknowledge BelArg's concerns but they are related more to the limiting runway situation, with which I concur)
(d) roll on from a highspeed exit or displaced threshold - refer OS' words.
(e) autothrottle .. on the Boeing many of us used to override the autothrottle, pushing the levers up manually and then let the auththrottle fine tune the setting. Seemed to work real fine.
(a) standing start is useful for reference as it is the most easily repeatable set of data .. but it shakes the stuffing out of the aircraft so should be used only when it is sensibly appropriate.
(b) if the aircraft is heavy and we don't dilly dally with the levers, the power is set in a few turns of the wheels - near enough to standing start
(c) if the aircraft is light (and low Hp/OAT), the aircraft will be some distance down the roll prior to achieving takeoff settings. If the runway is short/limiting, this is probably not a sensible strategy, if long and definitely not limiting, it is more useful for the aircraft maintenance than a standing start (I acknowledge BelArg's concerns but they are related more to the limiting runway situation, with which I concur)
(d) roll on from a highspeed exit or displaced threshold - refer OS' words.
(e) autothrottle .. on the Boeing many of us used to override the autothrottle, pushing the levers up manually and then let the auththrottle fine tune the setting. Seemed to work real fine.
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From: Blighty (Nth. Downs)
Quote from stilton:
Whichever technique you decide to use choose one ! I have sat in the back on the runway as power is increased while the brakes are dragging with the aircraft in motion for hundreds of feet !
Not exactly sure what they were trying to do but that is definitely the worst of both worlds.
[Unquote]
Amen to that. Not sure about hundreds of feet, but any are too many. It seems to be the norm now on B737s (CFM) with at least one British airline. Does it result from an SOP, to cover some engine issue or other?
Whichever technique you decide to use choose one ! I have sat in the back on the runway as power is increased while the brakes are dragging with the aircraft in motion for hundreds of feet !
Not exactly sure what they were trying to do but that is definitely the worst of both worlds.
[Unquote]
Amen to that. Not sure about hundreds of feet, but any are too many. It seems to be the norm now on B737s (CFM) with at least one British airline. Does it result from an SOP, to cover some engine issue or other?
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From: dubai
misd-agin
"Simulator season. Five takeoffs and 5 aborts..........."
Interesting post.
If it is the 747 simulator, try this one. Full or as much power on the brakes, before you go skipping and get the sim instructor to fail an outboard engine and see if you keep it on the tarmac.
"Simulator season. Five takeoffs and 5 aborts..........."
Interesting post.
If it is the 747 simulator, try this one. Full or as much power on the brakes, before you go skipping and get the sim instructor to fail an outboard engine and see if you keep it on the tarmac.
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From: Australia
On a related matter. The 737 Classic and NG FCTM states thrust levers should be opened to approx 40 percent N1 and a slight delay not more than two seconds to check equal power, before pressing TOGA for the autothrottle.
My estimation from observing hundreds of take off's in the simulator is that most pilots open up the thrust levers to well beyond half way up the quadrant (the old stand 'em up policy required of the JTD8D engines) and then as the N1 passes rapidly through 40 percent, they hit TOGA. Certainly the engines are never allowed to stabilise momentarily at 40 percent N1. It is almost as if they are attempting to "hurry up" the acceleration with rapid thrust lever movement. I can never understand what they are attempting to achieve because certainly their technique is not the Boeing way. Maybe they are just impatient or perhaps they cannot be bothered to read the FCTM?
Different story on the 737-200 series where the JT8D engine requires a specific EPR setting before the throttles are full advanced to take off EPR. That specific initial EPR setting for stabilisation is 1.6 EPR or close enough and that requires a throttle setting half way up the quadrant. Hence the term "Stand them up."
My estimation from observing hundreds of take off's in the simulator is that most pilots open up the thrust levers to well beyond half way up the quadrant (the old stand 'em up policy required of the JTD8D engines) and then as the N1 passes rapidly through 40 percent, they hit TOGA. Certainly the engines are never allowed to stabilise momentarily at 40 percent N1. It is almost as if they are attempting to "hurry up" the acceleration with rapid thrust lever movement. I can never understand what they are attempting to achieve because certainly their technique is not the Boeing way. Maybe they are just impatient or perhaps they cannot be bothered to read the FCTM?
Different story on the 737-200 series where the JT8D engine requires a specific EPR setting before the throttles are full advanced to take off EPR. That specific initial EPR setting for stabilisation is 1.6 EPR or close enough and that requires a throttle setting half way up the quadrant. Hence the term "Stand them up."
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From: US
doubleu-anker - "misd-agin
"Simulator season. Five takeoffs and 5 aborts..........."
Interesting post.
If it is the 747 simulator, try this one. Full or as much power on the brakes, before you go skipping and get the sim instructor to fail an outboard engine and see if you keep it on the tarmac.
"
----------------------------------------------------------------------
I'm a fan of the skids marks at the brakes release point that swerve towards the side of the runway.
Tee emm is correct about folks pushing more and more throttle lever while the motors are lagging behind. If it's already lagging why do you think pushing the power lever forward will help? As doubleu-anker implies, good luck keeping it on the runway if you get a large power split.
The best skid mark to view that is Cancun (CUN) Rwy 12. Main gear skid marks come within feet of leaving the runway.
Another is MIA Rwy 08R. FO thought it was from someone turning onto the runway too fast but you can see where the nose tire skid marks start on the runway centerline stripe.
JFK 31L had a differential N1 skid mark, it faded over several months/years, so someone replaced it with a new one.
Never understood how the skids marks were produced until I saw it happen. Full left nose wheel while the a/c shudders and bounces to the right with smoke billowing from the nose tires!
FO and I were speechless.
"Simulator season. Five takeoffs and 5 aborts..........."
Interesting post.
If it is the 747 simulator, try this one. Full or as much power on the brakes, before you go skipping and get the sim instructor to fail an outboard engine and see if you keep it on the tarmac.
"----------------------------------------------------------------------
I'm a fan of the skids marks at the brakes release point that swerve towards the side of the runway.
Tee emm is correct about folks pushing more and more throttle lever while the motors are lagging behind. If it's already lagging why do you think pushing the power lever forward will help? As doubleu-anker implies, good luck keeping it on the runway if you get a large power split.
The best skid mark to view that is Cancun (CUN) Rwy 12. Main gear skid marks come within feet of leaving the runway.
Another is MIA Rwy 08R. FO thought it was from someone turning onto the runway too fast but you can see where the nose tire skid marks start on the runway centerline stripe.
JFK 31L had a differential N1 skid mark, it faded over several months/years, so someone replaced it with a new one.
Never understood how the skids marks were produced until I saw it happen. Full left nose wheel while the a/c shudders and bounces to the right with smoke billowing from the nose tires!
FO and I were speechless.
Last edited by misd-agin; 20th November 2008 at 13:57. Reason: spelling
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From: Gone Flying...
misd-agin
"Simulator season. Five takeoffs and 5 aborts..........."
Interesting post.
If it is the 747 simulator, try this one. Full or as much power on the brakes, before you go skipping and get the sim instructor to fail an outboard engine and see if you keep it on the tarmac
"Simulator season. Five takeoffs and 5 aborts..........."
Interesting post.
If it is the 747 simulator, try this one. Full or as much power on the brakes, before you go skipping and get the sim instructor to fail an outboard engine and see if you keep it on the tarmac
doubleu-anker,
That's my favorite engine-failure training on the 340! Early recognition and quick action will save your day
Fly Safe, what ever bird you fly!
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From: Blighty (Nth. Downs)
Stand-up for spool-up
Confusing that we've got rolling-T/O and full-length T/O discussion threads running in parallel, with so much potential overlap.
Tee Emm describes "standing up" the throttles on the JT8D (1.6 EPR), and we used to do precisely that on the JT3D-engined 707s (1.2 EPR, I think).
If we were joining the runway from a 90-degree angle, the PF would stand up the throttles (err: sorry captain, the thrust levvers) when we were about half way round the corner. They were then greedily grabbed by the F/E, and – after the airplane had accelerated round the corner – he would eventually announce something like "engines all stable". The PF would then call for "take-off"
power (not the only ambiguous call in those days).
I always feared we were vulnerable to an outboard failing to spool-up as we shot round the corner...
Quote from Tee Emm:
I can never understand what they are attempting to achieve because certainly their technique is not the Boeing way. Maybe they are just impatient...
[Unquote]
Possibly. As humble SLF, what grates me most about the current technique on some CFM/B737s is when, having lined up and still rolling forward at idle thrust, the pilot applies the brakes and simultaneously starts increasing the power for the procedure you describe.
Tee Emm describes "standing up" the throttles on the JT8D (1.6 EPR), and we used to do precisely that on the JT3D-engined 707s (1.2 EPR, I think).
If we were joining the runway from a 90-degree angle, the PF would stand up the throttles (err: sorry captain, the thrust levvers) when we were about half way round the corner. They were then greedily grabbed by the F/E, and – after the airplane had accelerated round the corner – he would eventually announce something like "engines all stable". The PF would then call for "take-off"
power (not the only ambiguous call in those days).I always feared we were vulnerable to an outboard failing to spool-up as we shot round the corner...
Quote from Tee Emm:
I can never understand what they are attempting to achieve because certainly their technique is not the Boeing way. Maybe they are just impatient...
[Unquote]
Possibly. As humble SLF, what grates me most about the current technique on some CFM/B737s is when, having lined up and still rolling forward at idle thrust, the pilot applies the brakes and simultaneously starts increasing the power for the procedure you describe.
Last edited by Chris Scott; 20th November 2008 at 15:46. Reason: Minor, plus 2 paragraphs added.
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From: Vancouver, Canada
misd-agin,
You write "Sims = training and events you can't, or shouldn't, do in the a/c. Yesterday 11:03
"Training" for rejected take-offs above V1 is trouble looking for a place to happen. It is called "negative training" and should be avoided at all costs.
Back to the thread now ... In the Lear 45XR that I now fly you must add 300 feet to the runway distance required if doing other than a brakes on take-off.
best regards,
Bruce Waddington
"fly the way you train and train the way you fly"
You write "Sims = training and events you can't, or shouldn't, do in the a/c. Yesterday 11:03
"Training" for rejected take-offs above V1 is trouble looking for a place to happen. It is called "negative training" and should be avoided at all costs.
Back to the thread now ... In the Lear 45XR that I now fly you must add 300 feet to the runway distance required if doing other than a brakes on take-off.
best regards,
Bruce Waddington
"fly the way you train and train the way you fly"
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From: US
We'll classify aborting past V1 as "events you shouldn't do in the a/c".
Balanced field V1 abort stays on the runway.
V1+10 abort should go off at approx. 60 kts.
Guys don't necessarily believe that a 10 kt difference makes a 60 kts difference at the end of the pavement.
The training event isn't to practive V1 aborts after V1. It's to show the results of that incorrect decision.
I don't think that's negative training.
Balanced field V1 abort stays on the runway.
V1+10 abort should go off at approx. 60 kts.
Guys don't necessarily believe that a 10 kt difference makes a 60 kts difference at the end of the pavement.
The training event isn't to practive V1 aborts after V1. It's to show the results of that incorrect decision.
I don't think that's negative training.
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From: Arizona USA
Power against brakes will always give better perf than rolling. With rolling you are using TODA before you have take off thrust.
B707-320B (advanced cowl) aircraft are a specific example, due to auxiliary inlet door design.
Maximum Achievable Takeoff Weights were (1) Roll-On Takeoff, (2) Standing Start, and (3) Rolling Takeoff in that descending order. The AFM went on to explain that a properly executed Roll-On Takeoff was one where the aircraft had a minimum speed of 10 knots at the normal SOT.
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From: Blighty (Nth. Downs)
Roll-on technique
Following 411A's remarks, here's a slightly bigger chunk of his quote from Old Smokey (post #23):
...the "Roll-On" Takeoff (not Rolling). That is, a Takeoff where the aircraft enters the runway at the nominal Takeoff commencement point already rolling with residual speed from the taxy.
For a 90 degree or 180 degree turn to line-up, this is obviously not practical or safe...
...I recall working on one Douglas jet aircraft where the AFM stated that the Maximum Achievable Takeoff Weights were (1) Roll-On Takeoff, (2) Standing Start, and (3) Rolling Takeoff in that descending order. The AFM went on to explain that a properly executed Roll-On Takeoff was one where the aircraft had a minimum speed of 10 knots at the normal SOT.
[Unquote]
This "roll-on" technique is precisely what I try to describe in post #33 – the Boeing-recommended technique I was taught (like 411A?) for the JT3D-powered B707-320B/C.
Whether Old Smokey is right to say that the 90-degree-turn case is not practical or safe, I'm not sure. Achieving a minimum 10kt demands a slightly less-sharp alignment, so the turn is not completed until a little bit further along the runway centreline. The main issues are probably: (1) integrity of nosewheel steering; (2) strain on L/G (B707 legs are short); (3) possible asymmetry of spool-up leading to loss of control.
As for the 180-degreee-turn case: it depends on the situation, the comfortable radius of turn the aircraft can achieve, and pavement width. If the runway has a very short spur just downwind of the most-downwind entry point, the take-off run can sometimes be maximised by entering the runway and turning the long way round (270 degrees or more). This works very well at a steady speed. On completion, a large aeroplane will have overshot the centreline, of course, but can be gently nursed back as it accelerates.
If, however, the thrust levers have been "stood up" before the aircraft is pointing in a safe direction, it becomes a fairly demanding and vulnerable manoeuvre.
...the "Roll-On" Takeoff (not Rolling). That is, a Takeoff where the aircraft enters the runway at the nominal Takeoff commencement point already rolling with residual speed from the taxy.
For a 90 degree or 180 degree turn to line-up, this is obviously not practical or safe...
...I recall working on one Douglas jet aircraft where the AFM stated that the Maximum Achievable Takeoff Weights were (1) Roll-On Takeoff, (2) Standing Start, and (3) Rolling Takeoff in that descending order. The AFM went on to explain that a properly executed Roll-On Takeoff was one where the aircraft had a minimum speed of 10 knots at the normal SOT.
[Unquote]
This "roll-on" technique is precisely what I try to describe in post #33 – the Boeing-recommended technique I was taught (like 411A?) for the JT3D-powered B707-320B/C.
Whether Old Smokey is right to say that the 90-degree-turn case is not practical or safe, I'm not sure. Achieving a minimum 10kt demands a slightly less-sharp alignment, so the turn is not completed until a little bit further along the runway centreline. The main issues are probably: (1) integrity of nosewheel steering; (2) strain on L/G (B707 legs are short); (3) possible asymmetry of spool-up leading to loss of control.
As for the 180-degreee-turn case: it depends on the situation, the comfortable radius of turn the aircraft can achieve, and pavement width. If the runway has a very short spur just downwind of the most-downwind entry point, the take-off run can sometimes be maximised by entering the runway and turning the long way round (270 degrees or more). This works very well at a steady speed. On completion, a large aeroplane will have overshot the centreline, of course, but can be gently nursed back as it accelerates.
If, however, the thrust levers have been "stood up" before the aircraft is pointing in a safe direction, it becomes a fairly demanding and vulnerable manoeuvre.
Last edited by Chris Scott; 22nd November 2008 at 11:10. Reason: Clarification in last sentence
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From: Australia
Just playing it safe and conservative Chris Scott, I'd hate the thought (particularly in a large geometry aircraft) of someone doing a 90 or 180 degree line-up whilst attempting to maintain 10 knots throughout the manoeuvre.
I have no problem with your suggested "slightly less sharp alignment", I do it too, but I've seen a good many trainees shooting for a nice 30 degree flare onto the centre-line, thus using 100 to 200 metres of runway in the process. Not so bad for a JAR certified aircraft which considers line-up allowance, but for a large geometry FAR25 aircraft (which makes no consideration of line-up allowance), you're behind the 8 ball, even if you do it correctly.
Regards,
Old Smokey
I have no problem with your suggested "slightly less sharp alignment", I do it too, but I've seen a good many trainees shooting for a nice 30 degree flare onto the centre-line, thus using 100 to 200 metres of runway in the process. Not so bad for a JAR certified aircraft which considers line-up allowance, but for a large geometry FAR25 aircraft (which makes no consideration of line-up allowance), you're behind the 8 ball, even if you do it correctly.
Regards,
Old Smokey
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From: Planet Earth
I must be missing something, on the Aircraft I fly 75 / 67 unless you are doing 8-10 knots in a 90 degree turn at heavy weight you will slowly come to a stop.
Around 8 knots will take you smoothly round a 90 degree turn onto the runway with no great stress (providing you are smooth) so there you are, not having wasted any runway with 10 knots already 'in hand' you can advance the power a little before alignment enough to be equally spooled then straight to take off power once lined up.
Best of both worlds, useful momentum in hand with take off power set and no runway wasted
Around 8 knots will take you smoothly round a 90 degree turn onto the runway with no great stress (providing you are smooth) so there you are, not having wasted any runway with 10 knots already 'in hand' you can advance the power a little before alignment enough to be equally spooled then straight to take off power once lined up.
Best of both worlds, useful momentum in hand with take off power set and no runway wasted
