A320 Sidestick Forward
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A320 Sidestick Forward
Why do we do it on the take-off roll?
There is no prop wash, so it has very little aerodynamic effect in holding the nose-wheel firmly on the ground until just about when we remove it at 80-100kts.
With a tailwind, if anything it has a negative effect for the first part of the acceleration yet we double the input. Why?
There is no prop wash, so it has very little aerodynamic effect in holding the nose-wheel firmly on the ground until just about when we remove it at 80-100kts.
With a tailwind, if anything it has a negative effect for the first part of the acceleration yet we double the input. Why?
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5LY
For the same reason that the rudder is ineffective, the elevator is ineffective.
There is initially very little airflow or even worse reverse airflow with a tailwind, and the rudder would be becoming usefully effective at about the same time as the elevator.
In the tailwind case, if I actually believed that the stab has any effect at low speed in the initial accel, which I don't, it would be the opposite of what is wanted! Until gnd speed at least equals tailwind, the negligible lift it is producing is working against holding the nosewheel down.
That's why I asked the question. Both rudder and elevator/horizontal stab require positive and significant airflow to have any effect. Try taxiing at 30kts and pull full back. Does the nose rise majestically??
I think not.
I will possibly accept that something usefully aerodynamic is starting to happen IAS >50kts, but that is also the case with a tailwind, obviously, so why the difference in procedures.
Is this left over from old prop-wash aircraft?!
So why do we do it?
For the same reason that the rudder is ineffective, the elevator is ineffective.
There is initially very little airflow or even worse reverse airflow with a tailwind, and the rudder would be becoming usefully effective at about the same time as the elevator.
In the tailwind case, if I actually believed that the stab has any effect at low speed in the initial accel, which I don't, it would be the opposite of what is wanted! Until gnd speed at least equals tailwind, the negligible lift it is producing is working against holding the nosewheel down.
That's why I asked the question. Both rudder and elevator/horizontal stab require positive and significant airflow to have any effect. Try taxiing at 30kts and pull full back. Does the nose rise majestically??
I think not.
I will possibly accept that something usefully aerodynamic is starting to happen IAS >50kts, but that is also the case with a tailwind, obviously, so why the difference in procedures.
Is this left over from old prop-wash aircraft?!
So why do we do it?
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Tourist...
Next time you see an Airbus depart at the holding point, have a look at the horizontal stab. Amazing the amount that it shakes when the engines wind up... I'm guessing it's not the wind doing that...
Next time you see an Airbus depart at the holding point, have a look at the horizontal stab. Amazing the amount that it shakes when the engines wind up... I'm guessing it's not the wind doing that...
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Loads of jets have the same effect of shaking the horizontal Stab early in the take off roll, perhaps the down elevators will catch some of the rising hot air from the engine efflux to provide some up force to stop the shake a bit?
Mind you, it could all just be some old fashioned airmanship that escaped the translation into French and back?
Mind you, it could all just be some old fashioned airmanship that escaped the translation into French and back?
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Hi Tourist,
By increasing the load on the nose wheel, you improve the nose steering capability with rudder bar deflection. Initially up to say 50kts, your ground speed is low and there is time to react before you run off the side of the runway after an engine failure. As you approach VMCG, the rudders will have sufficient control hence relax on the nose down bit.
With a tailwind, you'll need more even more elevator to provide the same nose wheel steering for the same ground speed.
I will possibly accept that something usefully aerodynamic is starting to happen IAS >50kts, but that is also the case with a tailwind, obviously, so why the difference in procedures.
With a tailwind, you'll need more even more elevator to provide the same nose wheel steering for the same ground speed.
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Rudderrat
You are not reading what I have written.
I would fully understand the procedure if in fact it had the effect of increasing pressure on the nose wheel.
I don't think it does for the reasons I have stated twice.
Particularly in the case of a tailwind, where if there is any effect of stick down it would be to release pressure on the nose wheel for the critical early stage of the acceleration. Think about what reverse flow over a wing does! If you push forward you are increasing the downward force it is producing until flow over the tail is in the correct sense.
Fortunately, I don't think this is a problem because the forces created over a wing at low speed are negligible hence relying on nose wheel steering until some decent air flow is produced by forward acceleration.
Cough
That would be a good justification if true. Do you reckon that there is actually some "blown" effect that high up?
You are not reading what I have written.
I would fully understand the procedure if in fact it had the effect of increasing pressure on the nose wheel.
I don't think it does for the reasons I have stated twice.
Particularly in the case of a tailwind, where if there is any effect of stick down it would be to release pressure on the nose wheel for the critical early stage of the acceleration. Think about what reverse flow over a wing does! If you push forward you are increasing the downward force it is producing until flow over the tail is in the correct sense.
Fortunately, I don't think this is a problem because the forces created over a wing at low speed are negligible hence relying on nose wheel steering until some decent air flow is produced by forward acceleration.
Cough
That would be a good justification if true. Do you reckon that there is actually some "blown" effect that high up?
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Hmm.
That pic only shows plan form and doesn't really show either way.
Cough, yes that does seem to suggest that there is some impingement, though flat items of pavement can behave oddly in airflow.
The tail-plane really is quite high, and the flaps work to direct the wash
downwards.
Ok, for the sake of argument, lets accept that the tailplane has some effect.
If that is the case, why extra nose down for tailwind?
You only have tailwind until you hit 10kts GS, after that it is just a normal take-off as if you started at nil wind. The apparent wind vector very quickly moves forward.
That pic only shows plan form and doesn't really show either way.
Cough, yes that does seem to suggest that there is some impingement, though flat items of pavement can behave oddly in airflow.
The tail-plane really is quite high, and the flaps work to direct the wash
downwards.
Ok, for the sake of argument, lets accept that the tailplane has some effect.
If that is the case, why extra nose down for tailwind?
You only have tailwind until you hit 10kts GS, after that it is just a normal take-off as if you started at nil wind. The apparent wind vector very quickly moves forward.
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Did anybody see a video with brave/stupid plane watchers blown away while trying to hold themself at the fence behind A320 (or may be 757) applying TOGA on take off at Princess Juliana?
Taken from the A320/21 FCTM:
On a normal takeoff, to counteract the pitch up moment during thrust application, the PF should apply half forward (full forward in cross wind case) sidestick at the start of the takeoff roll until reaching 80 kt. At this point, the input should be gradually reduced to be zero by 100 kt.
So I imagine Airbus have a different opinion on aerodynamic effects than you do.
On a normal takeoff, to counteract the pitch up moment during thrust application, the PF should apply half forward (full forward in cross wind case) sidestick at the start of the takeoff roll until reaching 80 kt. At this point, the input should be gradually reduced to be zero by 100 kt.
So I imagine Airbus have a different opinion on aerodynamic effects than you do.
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Well done Jonty, you can read a book.
I didn't ask what to do, I asked why.
We know that in normal flight there is negligible engine "blown" effect over the tail plane, otherwise stall recovery would not be such a concern with thrust induced pitch up having not enough elevator control to counteract it.
I didn't ask what to do, I asked why.
We know that in normal flight there is negligible engine "blown" effect over the tail plane, otherwise stall recovery would not be such a concern with thrust induced pitch up having not enough elevator control to counteract it.
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Tourist
I also always wondered about this. I guess the elevator is down and when the blast goes under them it causes some airflow to create pressure on them from underneath. It doesn't need air to go over the elevators.
I also always wondered about this. I guess the elevator is down and when the blast goes under them it causes some airflow to create pressure on them from underneath. It doesn't need air to go over the elevators.
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Ahh yes, the ever present misunderstanding of how an aircraft flies, rears its ugly head again.
Should you actually believe that the airfoil generates lift by the difference in pressures, ie Bernoullian physics, like this, then read no further
IF you believe in Newtonian physics, then you have a chance to understand why Airbus is much further ahead in airfoil design.
So, as the ac moves down the runway, the pressure wave underneath the wing builds as speed increases. Given the angle of the wing, the pressure wave will begin to build in front of the wing, causing the nose to lift, at the same time, the compressed air from the trailing edge, will be forced out at a rapid rate, causing cavitation which will tend to bring the tail down (a downwash suction).
While this illustration is closer, is does touch on the building of the pressure wave in front of the airfoil..think of that effect on takeoff.
Note the high pressure forward of the airfoil! (ps, high pressure means compressed air, ie, the air had to come from somewhere, hence the 'low pressure' zone above, but still missing a bunch of components)
As you can sortof visualize, the pressure wave building in front of the airfoil has a rotational effect. This rotation effect exceeds the lift component of the ac to lift from the ground, ie the ac will rotate the nose up, before it can lift it from the ground.
That is why you hold the nose down, it is beacuse of the function of a much more effective lift of the wings, and especially the centerwing. Steering feels light way before v1, well, it may not be lift. it is the bird trying to push away from the ground, just in a different way.
Much the same effect on landing, which is why the A380 crosses the threshold at 120kts. (if you do decide to stand under the flightpath, (or measure the winds), you will find that you get blown back, not from the engines, but from the compressed pressure wave, for lack of a better analogy, compressing the air in front of the wing, and shooting it out the back as it moves forward, or a funneling effect)
I am probably not expaining the mechanics very well, but hopefullly, one can visualize what I am trying to illustrate.
EDIT: interesting, that 'ground effects' are understood for flare on landing, but not on takeoff...
Should you actually believe that the airfoil generates lift by the difference in pressures, ie Bernoullian physics, like this, then read no further
IF you believe in Newtonian physics, then you have a chance to understand why Airbus is much further ahead in airfoil design.
So, as the ac moves down the runway, the pressure wave underneath the wing builds as speed increases. Given the angle of the wing, the pressure wave will begin to build in front of the wing, causing the nose to lift, at the same time, the compressed air from the trailing edge, will be forced out at a rapid rate, causing cavitation which will tend to bring the tail down (a downwash suction).
While this illustration is closer, is does touch on the building of the pressure wave in front of the airfoil..think of that effect on takeoff.
Note the high pressure forward of the airfoil! (ps, high pressure means compressed air, ie, the air had to come from somewhere, hence the 'low pressure' zone above, but still missing a bunch of components)
As you can sortof visualize, the pressure wave building in front of the airfoil has a rotational effect. This rotation effect exceeds the lift component of the ac to lift from the ground, ie the ac will rotate the nose up, before it can lift it from the ground.
That is why you hold the nose down, it is beacuse of the function of a much more effective lift of the wings, and especially the centerwing. Steering feels light way before v1, well, it may not be lift. it is the bird trying to push away from the ground, just in a different way.
Much the same effect on landing, which is why the A380 crosses the threshold at 120kts. (if you do decide to stand under the flightpath, (or measure the winds), you will find that you get blown back, not from the engines, but from the compressed pressure wave, for lack of a better analogy, compressing the air in front of the wing, and shooting it out the back as it moves forward, or a funneling effect)
I am probably not expaining the mechanics very well, but hopefullly, one can visualize what I am trying to illustrate.
EDIT: interesting, that 'ground effects' are understood for flare on landing, but not on takeoff...
Last edited by underfire; 8th Jan 2014 at 11:00.
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Hi Tourist,
How big a tail wind do you accept on take off?
We are limited to only 10 kts - and the effect on the nose wheel from stationary to 10 kts ground speed is not significant.
You're not reading mine either.
Particularly in the case of a tailwind, where if there is any effect of stick down it would be to release pressure on the nose wheel for the critical early stage of the acceleration. Think about what reverse flow over a wing does!
We are limited to only 10 kts - and the effect on the nose wheel from stationary to 10 kts ground speed is not significant.
You are not reading what I have written.
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underfire.
Yes, I understand Lift. From your post I have my doubts that you do....
In fact I have taught the subject to aviators.
"That is why you hold the nose down, it is beacuse of the function of a much more effective lift of the wings, and especially the centerwing. Steering feels light way before v1, well, it may not be lift. it is the bird trying to push away from the ground, just in a different way."
Are you trying to suggest that we are trying to hold the nose down because the main wings generate lift sooner than the tail-plane thus we have to hold the nose down to stop the nose rotating up until the tail-plane can take its share of the lifting load?
If so, then you need to do a bit more study about which way the tail-plane lift is acting.
Yes, I understand Lift. From your post I have my doubts that you do....
In fact I have taught the subject to aviators.
"That is why you hold the nose down, it is beacuse of the function of a much more effective lift of the wings, and especially the centerwing. Steering feels light way before v1, well, it may not be lift. it is the bird trying to push away from the ground, just in a different way."
Are you trying to suggest that we are trying to hold the nose down because the main wings generate lift sooner than the tail-plane thus we have to hold the nose down to stop the nose rotating up until the tail-plane can take its share of the lifting load?
If so, then you need to do a bit more study about which way the tail-plane lift is acting.
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Two thoughts, Tourist...
1. Jet efflux passes under the THS at more than 60kts.... this will entrain more air all over the THS at a speed high enough for the deflected elevator to produce an upward force.
2.Without the deflection a mis-set or mis-calculated THS might produce an undesirable downward force.
3. If FCOM said "from 50 to 100 knots apply half forward side-stick" it might need an extra call when PM should be concentrating elsewhere, and plenty of us would forget! Simpler to do it from the start of T/O roll, which also avoids a change in rudder pedal deflection as PF applies full forward in a crosswind...
1. Jet efflux passes under the THS at more than 60kts.... this will entrain more air all over the THS at a speed high enough for the deflected elevator to produce an upward force.
2.Without the deflection a mis-set or mis-calculated THS might produce an undesirable downward force.
3. If FCOM said "from 50 to 100 knots apply half forward side-stick" it might need an extra call when PM should be concentrating elsewhere, and plenty of us would forget! Simpler to do it from the start of T/O roll, which also avoids a change in rudder pedal deflection as PF applies full forward in a crosswind...