Jet takeoff xwind technique
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I understand that airbus sidestick inputs command roll rate and not just aileron deflection?
When does this 'law' come into effect? I assume that as soon as the a/c becomes airborne the computers attempt to roll the a/c at a rate relevant to the amount of sidestick applied.
Is this correct? Does it completely alter the technique over conventional machines?
When does this 'law' come into effect? I assume that as soon as the a/c becomes airborne the computers attempt to roll the a/c at a rate relevant to the amount of sidestick applied.
Is this correct? Does it completely alter the technique over conventional machines?
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BOAC
Wouldn't disagree, but as always it is useful to have a datum to hang your hat on as a point from which to start, and it is much more critical on a highly swept wing like the B747 vs the B737.
Windsheer
My recollection of the A320 family (3 years since I last flew it), it that 'normal' law blends in at 100ft AGL on take off (at which point sidestick deflection becomes a roll command vs an aileron position demand / direct law / conventional aircraft) and that shortly after touchdown, the aircraft reverts to 'direct' law. I hope that makes sense. I can dig more into it, but am off for a curry!
In effect that means that you can hold into wind aileron on the take off roll and after landing it is beneficial to again put some into wind aileron in to stop the wing lifting.
Wouldn't disagree, but as always it is useful to have a datum to hang your hat on as a point from which to start, and it is much more critical on a highly swept wing like the B747 vs the B737.
Windsheer
My recollection of the A320 family (3 years since I last flew it), it that 'normal' law blends in at 100ft AGL on take off (at which point sidestick deflection becomes a roll command vs an aileron position demand / direct law / conventional aircraft) and that shortly after touchdown, the aircraft reverts to 'direct' law. I hope that makes sense. I can dig more into it, but am off for a curry!
In effect that means that you can hold into wind aileron on the take off roll and after landing it is beneficial to again put some into wind aileron in to stop the wing lifting.
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Gents,
Done correctly the X wind takeoff is a thing of rare beauty. Problem is I rarely see it done correctly and given that I fly ultra long haul ( so sector count is an issue) it ends up being a verbal discussion with the FO after the event. Some want to learn , others .....
I have flow the 757,767,747 classic and now the 744 and the technique is identical. Preset a small amount of aileron and fly the wing down the runway. Use rudder to keep straight. As a result of the swept wing design the into wind wing has a resultant less angle of sweep than the downwind wing and produces more lift for a given angle of attack so, during a SLOW rotation (MAX 3 deg/sec) , apply an increase in into wind aileron otherwise the wing will lift. When away from the ground slowly neutralise control forces and the aircraft will beautifully weathercock into wind and track on the extended runway centerline.
I will add that the 744 wing starts working at 60 kts hence the need to preset the aileron.
As to the debate of how much aileron, use what you need and forget about the spoiler deployment. You are going to look a meathead explaining to the Chief Pilot the pod strike on 1 or 4 because you were concerned you may have too much drag due spoiler deployment. To counter the loss of effeciency re the boards up use a slow rotation - simple huh?
Boeing releases Flight Operational Reviews which from memory detailed spoiler deployment on the 767 was at 2.4 units control wheel deflection and 744 I think was 2.2 units - critics be gentle with me on this as the grey matter is not what it was. At times when parked at the passenger terminal with those shiny windows get clearance from the your man on the ground, pressurise the hydraulics and let the FO displace the control wheel and note in the reflection from the windows when he detects spoiler pick up - works better than just telling him at what # of units it will happen.
Done correctly the X wind takeoff is a thing of rare beauty. Problem is I rarely see it done correctly and given that I fly ultra long haul ( so sector count is an issue) it ends up being a verbal discussion with the FO after the event. Some want to learn , others .....
I have flow the 757,767,747 classic and now the 744 and the technique is identical. Preset a small amount of aileron and fly the wing down the runway. Use rudder to keep straight. As a result of the swept wing design the into wind wing has a resultant less angle of sweep than the downwind wing and produces more lift for a given angle of attack so, during a SLOW rotation (MAX 3 deg/sec) , apply an increase in into wind aileron otherwise the wing will lift. When away from the ground slowly neutralise control forces and the aircraft will beautifully weathercock into wind and track on the extended runway centerline.
I will add that the 744 wing starts working at 60 kts hence the need to preset the aileron.
As to the debate of how much aileron, use what you need and forget about the spoiler deployment. You are going to look a meathead explaining to the Chief Pilot the pod strike on 1 or 4 because you were concerned you may have too much drag due spoiler deployment. To counter the loss of effeciency re the boards up use a slow rotation - simple huh?
Boeing releases Flight Operational Reviews which from memory detailed spoiler deployment on the 767 was at 2.4 units control wheel deflection and 744 I think was 2.2 units - critics be gentle with me on this as the grey matter is not what it was. At times when parked at the passenger terminal with those shiny windows get clearance from the your man on the ground, pressurise the hydraulics and let the FO displace the control wheel and note in the reflection from the windows when he detects spoiler pick up - works better than just telling him at what # of units it will happen.
Per Ardua ad Astraeus
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TB - as I said - it is for the individual 'comfort level' rather than a 'must do'. I have flown far higher wing sweeps than any airliner with far greater 'lifting' tendencies, and my PERSONAL technique has been to fly the a/c. The into-wind wing does not just start 'lifting' at rotate.
On the subject of 'comfort', I am not comfortable with 'it's 2.5 units for this wind and that's it' which I have seen develop into nasty rolls one way or the other when the rotation wind ain't the same - and sadly the thinking process isn't there either
.
This is all rather like 'how you must do a crosswind landing', isn't it?
On the subject of 'comfort', I am not comfortable with 'it's 2.5 units for this wind and that's it' which I have seen develop into nasty rolls one way or the other when the rotation wind ain't the same - and sadly the thinking process isn't there either
.This is all rather like 'how you must do a crosswind landing', isn't it?
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411A's takeoff technique...
...both B707 and L1011, with strong crosswinds (35 knots) at heavy weights.
Spool up engines evenly and release brakes..
Add aileron into wind as necessary to keep the upwind wing from lifting.
None of this 'preset' aileron business, ever.
At Vr, delay rotation by a few knots, thence commence a slow(er) rotation than normal, using whatever aileron is necessary to keep wings level.
Sometimes, full upwind aileron is needed.
Once airbourne, turn into the wind, to make good a straight runway track.
Note: With early models of the B707, slightly uneven thrust initially is desired...IE: lead with the upwind engines.
In no case, however, will I plan to become airbourne at less than V2, in either type.
Don't fly new(er) types, so can't comment about those.
NB. I was taught to fly the B707 by old time PanAmerican pilots, who first flew the type, in 1958.
Spool up engines evenly and release brakes..
Add aileron into wind as necessary to keep the upwind wing from lifting.
None of this 'preset' aileron business, ever.
At Vr, delay rotation by a few knots, thence commence a slow(er) rotation than normal, using whatever aileron is necessary to keep wings level.
Sometimes, full upwind aileron is needed.
Once airbourne, turn into the wind, to make good a straight runway track.
Note: With early models of the B707, slightly uneven thrust initially is desired...IE: lead with the upwind engines.
In no case, however, will I plan to become airbourne at less than V2, in either type.
Don't fly new(er) types, so can't comment about those.
NB. I was taught to fly the B707 by old time PanAmerican pilots, who first flew the type, in 1958.
Quote from WindSheer:
I understand that airbus sidestick inputs command roll rate and not just aileron deflection?
When does this 'law' come into effect? I assume that as soon as the a/c becomes airborne the computers attempt to roll the a/c at a rate relevant to the amount of sidestick applied.
Is this correct? Does it completely alter the technique over conventional machines?
[Unquote]
No, TopBunk is right. We had a discussion on A320 crosswind techniques in the Spring, remember? Here's a link to something I posted, with the help of other PPRuNers on the same thread:
http://www.pprune.org/tech-log/31609...ml#post3979423
Quote from the above:
CROSSWIND TAKE-OFF
A small amount of into-wind aileron can be selected before starting the T/O run, avoiding "cracking" the spoilers.* During rotation, the upwind wing tends to rise in the conventional manner, and can be countered by retaining into-wind aileron. As the main L/G lifts off, any downwind rudder will be eased off, yawing the aeroplane into wind. This will temporarily assist the aileron. Half a second after lift-off, however, Normal Law in roll is introduced (AND the white cross on the PFDs has disappeared). At that point, any remaining roll input needs to be released.
5 seconds after main L/G lift-off, Normal Law also becomes fully effective in pitch. Stick-to-elevator control is now removed, and pitch-attitude can be refined by small nudges of sidestick.
* Roll-spoiler deployment can be avoided by placing the PFD white-cross so that its inner edge is not noticeably to the side of the centre spot.
[Unquote]
I can't guarantee that the precise timing of stick-to-aileron removal is still correct, as I don't get the FCOM amendments these days.
So the standard technique still applies until properly airborne, and I'm with you, Rainboe and TopBunk on that. Most jets seem to offer a small amount of aileron without cracking the spoilers. The only one I flew that didn't was the B707. on the A320, pre-setting the maximum before starting the take-off run – using the white cross and/or the F/Ctl page on ECAM – enables you to concentrate on looking out and flying the aeroplane. Flying the aeroplane includes controlling roll, but that should not happen on a modern jet until you start to rotate (I don't regard the 707 as "modern").
In over 10 years doing line checks on the A320 (mainly from the jump seat), the most common handling error I saw was the upwind wing rising on rotation, countered by the belated use of sidestick. If the wing rises while stick-to-aileron is still in effect, Normal Law will not subsequently recover it for you. Despite the aerodynamics of the A320 being boringly conventional, the powers-that-be insisted that any into-wind aileron should be removed at rotation: i.e., BEFORE the mains had left the ground.
That's the point when you usually need it most...
411A,
Your technique – just what I was taught by AA on the B707 in 1975 – works well, and preset aileron is not a good idea on the 707 because any aileron cracks the spoilers. But it does mean using more runway, and we had little to spare coming out of LAX to LGW on a warm day with 189 punters. [Have you voted yet?]
I understand that airbus sidestick inputs command roll rate and not just aileron deflection?
When does this 'law' come into effect? I assume that as soon as the a/c becomes airborne the computers attempt to roll the a/c at a rate relevant to the amount of sidestick applied.
Is this correct? Does it completely alter the technique over conventional machines?
[Unquote]
No, TopBunk is right. We had a discussion on A320 crosswind techniques in the Spring, remember? Here's a link to something I posted, with the help of other PPRuNers on the same thread:
http://www.pprune.org/tech-log/31609...ml#post3979423
Quote from the above:
CROSSWIND TAKE-OFF
A small amount of into-wind aileron can be selected before starting the T/O run, avoiding "cracking" the spoilers.* During rotation, the upwind wing tends to rise in the conventional manner, and can be countered by retaining into-wind aileron. As the main L/G lifts off, any downwind rudder will be eased off, yawing the aeroplane into wind. This will temporarily assist the aileron. Half a second after lift-off, however, Normal Law in roll is introduced (AND the white cross on the PFDs has disappeared). At that point, any remaining roll input needs to be released.
5 seconds after main L/G lift-off, Normal Law also becomes fully effective in pitch. Stick-to-elevator control is now removed, and pitch-attitude can be refined by small nudges of sidestick.
* Roll-spoiler deployment can be avoided by placing the PFD white-cross so that its inner edge is not noticeably to the side of the centre spot.
[Unquote]
I can't guarantee that the precise timing of stick-to-aileron removal is still correct, as I don't get the FCOM amendments these days.
So the standard technique still applies until properly airborne, and I'm with you, Rainboe and TopBunk on that. Most jets seem to offer a small amount of aileron without cracking the spoilers. The only one I flew that didn't was the B707. on the A320, pre-setting the maximum before starting the take-off run – using the white cross and/or the F/Ctl page on ECAM – enables you to concentrate on looking out and flying the aeroplane. Flying the aeroplane includes controlling roll, but that should not happen on a modern jet until you start to rotate (I don't regard the 707 as "modern").
In over 10 years doing line checks on the A320 (mainly from the jump seat), the most common handling error I saw was the upwind wing rising on rotation, countered by the belated use of sidestick. If the wing rises while stick-to-aileron is still in effect, Normal Law will not subsequently recover it for you. Despite the aerodynamics of the A320 being boringly conventional, the powers-that-be insisted that any into-wind aileron should be removed at rotation: i.e., BEFORE the mains had left the ground.
That's the point when you usually need it most... 411A,
Your technique – just what I was taught by AA on the B707 in 1975 – works well, and preset aileron is not a good idea on the 707 because any aileron cracks the spoilers. But it does mean using more runway, and we had little to spare coming out of LAX to LGW on a warm day with 189 punters. [Have you voted yet?]
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747 crosswind takeoffs
I am much more concerned, in the 747, as to scrape an outboard engine after rotation when compensating with excessive bank into a crosswind situation. To drift away from initial alignment with runway flight path is not critical. I rather accept a (say) 5º drift to the left or right, after lift-off.
xxx
Same story with the 707 and DC8...
xxx
Outboard engine scraping incidents seem more related to crosswind situations, tailstrikes are not. Boeing does not provide any specific procedure in their 747 FCTM regarding crosswind. I have a kept an old 1982 edition FCTM for the 747, which contains much more data than newer editions, and I often find answers in the older manual than what is printed in the new edition. In example there is a graph "Aileron/Spoiler Deflection Vs. Aileron Trim" on the old manual page 05.40.08... Try to find this, in a new FCTM...
xxx
Training briefings and classroom discussions, in the subject of crosswind handling, do depend much of the experience each individual pilots. I do not preselect a certain amount of trim for aileron (or rudder) for crosswind. And further, do not come with "nosewheel steering compensation" as it is worthless at high speed. Nosewheels are "as effective for directional control, as a piece of wet kleenex tissue".
xxx
To avoid a tailstrike, in a 747, remain at 10º pitch nose up limit... and to avoid scraping an outboard engine, do not bank more than 5º on ground at Vr speed, and be careful on crosswind gusts. The primary aerodynamic control in crosswind takeoff and landings, remains the rudder.
xxx
Happy contrails
xxx
Same story with the 707 and DC8...
xxx
Outboard engine scraping incidents seem more related to crosswind situations, tailstrikes are not. Boeing does not provide any specific procedure in their 747 FCTM regarding crosswind. I have a kept an old 1982 edition FCTM for the 747, which contains much more data than newer editions, and I often find answers in the older manual than what is printed in the new edition. In example there is a graph "Aileron/Spoiler Deflection Vs. Aileron Trim" on the old manual page 05.40.08... Try to find this, in a new FCTM...
xxx
Training briefings and classroom discussions, in the subject of crosswind handling, do depend much of the experience each individual pilots. I do not preselect a certain amount of trim for aileron (or rudder) for crosswind. And further, do not come with "nosewheel steering compensation" as it is worthless at high speed. Nosewheels are "as effective for directional control, as a piece of wet kleenex tissue".
xxx
To avoid a tailstrike, in a 747, remain at 10º pitch nose up limit... and to avoid scraping an outboard engine, do not bank more than 5º on ground at Vr speed, and be careful on crosswind gusts. The primary aerodynamic control in crosswind takeoff and landings, remains the rudder.
xxx
Happy contrails
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BOAC
BOAC, I'm not saying we disagree, but what were the wingspans of the aircraft you flew with greater sweep angles?
I have flown far higher wing sweeps than any airliner with far greater 'lifting' tendencies, and my PERSONAL technique has been to fly the a/c. The into-wind wing does not just start 'lifting' at rotate.
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TB - the first point of my post was
As with many things in life, it is not how big yours is, it is what you do with it. Each to his/her own?
The into-wind wing does not just start 'lifting' at rotate.
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x-wind takeoff in B744
Hi Guys
A lot has been said about using aileron for x-wind T/O in a B744
Some guys who have never flown the type seem to have a pretty good idea how to do the trick.
Here some aspects you might consider for your own technique
1. You will need Aileron!
2. Preseting some Aileron into the wind before commencing T/O roll has zero effect on aircraft, because lack of speed But has a nice "mental" effect : you and your other crewmembers have to make some thoughts about where the wind may come down the road.
3. When the aircraft picks up speed, you will see how much is the correct amount and adjust accordingly. Gusts, increasing effectiveness of controls change the required input during the T/O roll constantly. But with a little aileron in your "mind" you dont get cought by suprise. Correcting too late and too much makes it harder than it is.
4. If you start the T/O roll with zero aileron, you will be suprised how easily such a big plane reacts on X-wind. Its a bit tough to recognize how much bank you get, because you sit high, all the windows have different angles and dont help much as a reference to ground and going on instruments doesnt help maintaining centerline either. Its just a wobbly feeling if you dont counteract the x-wind.
5. for liftoff you should have wings pretty much level, you had them during the take-off roll level so why not now? getting blown a bit away from the centerline is not as expensive as getting your plane scratched during rotation. Achieve a nice crab after liftoff.
6. forget all this talk about degrees, how much spoiler deployment you get, and therefore lack of performance, slow rotation. and so on. x-wind take off is not made by numbers, its flown by feeling. The time to react and usable reference is too limited to fly it by numbers. Look out of the window, you just need some aileron thats it, the rest remains the same. If you are interested when the spoilers open, just check CMC, flightcontols page and look on lower EICAS during flightcontrol check or taxi. You will never need such a control column input if you stay within the max x-wind limits for T/O.
Happy fuel flow
Lars
A lot has been said about using aileron for x-wind T/O in a B744
Some guys who have never flown the type seem to have a pretty good idea how to do the trick.
Here some aspects you might consider for your own technique
1. You will need Aileron!
2. Preseting some Aileron into the wind before commencing T/O roll has zero effect on aircraft, because lack of speed But has a nice "mental" effect : you and your other crewmembers have to make some thoughts about where the wind may come down the road.
3. When the aircraft picks up speed, you will see how much is the correct amount and adjust accordingly. Gusts, increasing effectiveness of controls change the required input during the T/O roll constantly. But with a little aileron in your "mind" you dont get cought by suprise. Correcting too late and too much makes it harder than it is.
4. If you start the T/O roll with zero aileron, you will be suprised how easily such a big plane reacts on X-wind. Its a bit tough to recognize how much bank you get, because you sit high, all the windows have different angles and dont help much as a reference to ground and going on instruments doesnt help maintaining centerline either. Its just a wobbly feeling if you dont counteract the x-wind.
5. for liftoff you should have wings pretty much level, you had them during the take-off roll level so why not now? getting blown a bit away from the centerline is not as expensive as getting your plane scratched during rotation. Achieve a nice crab after liftoff.
6. forget all this talk about degrees, how much spoiler deployment you get, and therefore lack of performance, slow rotation. and so on. x-wind take off is not made by numbers, its flown by feeling. The time to react and usable reference is too limited to fly it by numbers. Look out of the window, you just need some aileron thats it, the rest remains the same. If you are interested when the spoilers open, just check CMC, flightcontols page and look on lower EICAS during flightcontrol check or taxi. You will never need such a control column input if you stay within the max x-wind limits for T/O.
Happy fuel flow
Lars
When I did a (refresher) conversion onto the B737-800, a very experienced pilot instructor from SAS was of the opinion that in limiting crosswinds FULL aileron should be applied during rotate to keep the wings level
Very experienced pilots sometimes have a tendency to have their own personal gimmicks and swear by them.
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1. Boeing tests takeoff performance without spoilers or aileron deflected. If you're not on the drag profile they certified, especially on a balanced field, you're a test pilot and on your own.
2. They recommend aileron as necessary to keep the wings level.
3. A plane at rest needs no cross controls. At rotation it will need the same amount of cross controlling that it would have if you were landing.
4. Understand #3, observe the wing 'lifting', and gradually apply #2, not to exceed #3.
2. They recommend aileron as necessary to keep the wings level.
3. A plane at rest needs no cross controls. At rotation it will need the same amount of cross controlling that it would have if you were landing.
4. Understand #3, observe the wing 'lifting', and gradually apply #2, not to exceed #3.
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1. Boeing tests takeoff performance without spoilers or aileron deflected. If you're not on the drag profile they certified, especially on a balanced field, you're a test pilot and on your own.
2. They recommend aileron as necessary to keep the wings level.
3. A plane at rest needs no cross controls. At rotation it will need the same amount of cross controlling that it would have if you were landing.
4. Understand #3, observe the wing 'lifting', and gradually apply #2, not to exceed #3.
2. They recommend aileron as necessary to keep the wings level.
3. A plane at rest needs no cross controls. At rotation it will need the same amount of cross controlling that it would have if you were landing.
4. Understand #3, observe the wing 'lifting', and gradually apply #2, not to exceed #3.
Younger folks should read, and understand the above.
Especially important on older types, IE: B707, L1011 as well.
