Flap 2 on A320
Thread Starter
Joined: Apr 2005
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From: England
Flap 2 on A320
It has always puzzled me, that on such a clever automated a/c as the A320 why the trim compensation does not kick in quick enough to stop the a/c ballooning with the selection from flap 1 to 2 on the approach.
Is there a technical reason why it behaves this way? It plays havoc with my Continuous descents, one minute a nice steady -700fpm to +300fpm when flap 2 is selected
Is there a technical reason why it behaves this way? It plays havoc with my Continuous descents, one minute a nice steady -700fpm to +300fpm when flap 2 is selected
Joined: Jan 2001
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From: home
"And why does it pitch up when selecting Flap 1 to Zero?"
I would hazard a guess it is to protect from overspeed especially on heavy aircraft. I know of an incident where a crew manually flying a departure followed the f/d and got an overspeed which led to an interesting few seconds of airbus logic defying logic!! One problem is that the VFE strip disappears as soon as the flaps are selected to 0, but there is still a danger of overspeed until the flap indicator indicates 0. Unfortunately I have seen that one happen myself.
I would hazard a guess it is to protect from overspeed especially on heavy aircraft. I know of an incident where a crew manually flying a departure followed the f/d and got an overspeed which led to an interesting few seconds of airbus logic defying logic!! One problem is that the VFE strip disappears as soon as the flaps are selected to 0, but there is still a danger of overspeed until the flap indicator indicates 0. Unfortunately I have seen that one happen myself.
Joined: Jul 2006
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From: On an aeroplane
Having flown both Boeing and Airbus, here is my observation.
Airbus have a simple flap selection naming process, in that the flap angle is really irrelevant when flying. Boeing have traditionally named their flaps corresponding with their angular position.
Flap 2 drives the slats out to their intermediate position with no obvious change in aircraft attitude, but as the trailing edge drives out from the fully retracted position to the intermediate position there is a signifiicant increase in the wing area and thus from first principles a significant increase in lift and change in the centre of pressure. Thus the balloon.
It has always been my belief that Boeing overcame the ballooning effect by have lots of intermediate flap settings to minimise the balloon effect.
Having flown Fokker 50, BAe146, 737 and A320 the 737 was the only one that didn't significantly balloon at intermediate flap. But then the B737 has flap 1, 2, 5, 10, 15, 25, 30 and 40.
The ying and yang of aviation.
Airbus have a simple flap selection naming process, in that the flap angle is really irrelevant when flying. Boeing have traditionally named their flaps corresponding with their angular position.
Flap 2 drives the slats out to their intermediate position with no obvious change in aircraft attitude, but as the trailing edge drives out from the fully retracted position to the intermediate position there is a signifiicant increase in the wing area and thus from first principles a significant increase in lift and change in the centre of pressure. Thus the balloon.
It has always been my belief that Boeing overcame the ballooning effect by have lots of intermediate flap settings to minimise the balloon effect.
Having flown Fokker 50, BAe146, 737 and A320 the 737 was the only one that didn't significantly balloon at intermediate flap. But then the B737 has flap 1, 2, 5, 10, 15, 25, 30 and 40.
The ying and yang of aviation.
Thread Starter
Joined: Apr 2005
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From: England
Craggenmore you may be talking about retracting but everyone else is answering the original question. Calm down.
Thanks for the answers but surely this is fixable with a tweak of the trim software. As fantom states it works fine at G/S* intercept why not at any other stage????????
Thanks for the answers but surely this is fixable with a tweak of the trim software. As fantom states it works fine at G/S* intercept why not at any other stage????????
Joined: Mar 2006
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From: Choroni, sometimes
Craggenmore you may be talking about retracting but everyone else is answering the original question. Calm down.
Thanks for the answers but surely this is fixable with a tweak of the trim software. As fantom states it works fine at G/S* intercept why not at any other stage????????
Thanks for the answers but surely this is fixable with a tweak of the trim software. As fantom states it works fine at G/S* intercept why not at any other stage????????
Joined: Aug 2002
Posts: 1,320
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From: Switzerland, Singapore
Ballooning, speed trends, pitch changes - this is just a normal characteristic of every jet airliner.
Airbus never intended to overcome these effects by the flight guidance. One of its golden rules (actually the first one) states that:
"Inspite of FBW, the aircraft can be flown like any other aircraft."
It is not advisable to take the pilot out of the loop by diminshing aerodynamic effects. So there will always be a ballooning, not only, but very pronounced, when selecting flaps 2 (the biggest change of lift on flap changes).
hth,
Dani
Airbus never intended to overcome these effects by the flight guidance. One of its golden rules (actually the first one) states that:
"Inspite of FBW, the aircraft can be flown like any other aircraft."
It is not advisable to take the pilot out of the loop by diminshing aerodynamic effects. So there will always be a ballooning, not only, but very pronounced, when selecting flaps 2 (the biggest change of lift on flap changes).
hth,
Dani
Joined: Sep 2005
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From: London
The true answer to the question is as simple as it is subtle.
The A320 balloons at the selection of Flap 2, WHEN THE AUTOPLIOT IS ENGAGED. The autopilot pitch authority is soft by design and will never pitch forward fast enough to prevent ballooning. Has nothing to do with trim software, trim is to relieve aerodynamic load, not change pitch.
When hand flying, the aircraft will not balloon because we as competant pilots ANTICIPATE and pitch forward to prevent the balloon.
Airbus have not been able to design software that can anticipate. In all situations computers are reactive only.
Why does the A320 not balloon at G/S*? Because by design the autopilot pitch authority is increased in G/S* and G/S modes. The increase is necessary to hunt the G/S acurately.
Why is the A320 less likely to overspeed or underspeed in EXP mode? For the same reason, by design autopilot pitch authority in increased in EXP CLB and EXP DES.
Where is any of this written? Nowhere do airbus devolve such secrets, but test it for yourself, you will find it to be true.
Cheers
The A320 balloons at the selection of Flap 2, WHEN THE AUTOPLIOT IS ENGAGED. The autopilot pitch authority is soft by design and will never pitch forward fast enough to prevent ballooning. Has nothing to do with trim software, trim is to relieve aerodynamic load, not change pitch.
When hand flying, the aircraft will not balloon because we as competant pilots ANTICIPATE and pitch forward to prevent the balloon.
Airbus have not been able to design software that can anticipate. In all situations computers are reactive only.
Why does the A320 not balloon at G/S*? Because by design the autopilot pitch authority is increased in G/S* and G/S modes. The increase is necessary to hunt the G/S acurately.
Why is the A320 less likely to overspeed or underspeed in EXP mode? For the same reason, by design autopilot pitch authority in increased in EXP CLB and EXP DES.
Where is any of this written? Nowhere do airbus devolve such secrets, but test it for yourself, you will find it to be true.
Cheers
Dog Tired
Joined: Oct 2001
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From: uk
Joined: Feb 2004
Posts: 34
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From: PARIS
I say it again
Like Dani said balooning effect is normal on any aicraft.
Now have you ever had a vertical upgust on an airbus fly by wire.
The aircraft (if AP on) flies at 0.1 g. It damps so smoothly that you can gain several hundreds feet if you do not disconnect the AP.
The same happens when you extend the flaps especially at F 2 because you have such an amount of lift.
Check your FCOM FCTM guys
Like Dani said balooning effect is normal on any aicraft.
Now have you ever had a vertical upgust on an airbus fly by wire.
The aircraft (if AP on) flies at 0.1 g. It damps so smoothly that you can gain several hundreds feet if you do not disconnect the AP.
The same happens when you extend the flaps especially at F 2 because you have such an amount of lift.
Check your FCOM FCTM guys
Joined: Jul 2006
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From: 'tween posts
Ok here is my observation on A320: 
when on approach assume AP on, and descending spd at green dot.
select flap one how does the a/c decelerate to S speed ?(remember power at idle): by increasing pitch attitude as in any a/c
Next you select flaps 2 now there is a huge change in target speed from about 185 to about 140,and with power at idle the a/c has no choice but to pitch up* to acheive Fspeed.agreed she doesnt do it smoothly enough
*except during G/S star because the priority for the A/P is to first capture G/S then to slow down to target speed
when on approach assume AP on, and descending spd at green dot.
select flap one how does the a/c decelerate to S speed ?(remember power at idle): by increasing pitch attitude as in any a/c
Next you select flaps 2 now there is a huge change in target speed from about 185 to about 140,and with power at idle the a/c has no choice but to pitch up* to acheive Fspeed.agreed she doesnt do it smoothly enough
*except during G/S star because the priority for the A/P is to first capture G/S then to slow down to target speed
Joined: Jul 2006
Posts: 451
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From: USA
A320 Flaps
Gentlemen,
Please reference Airbus FCOM 1.27.50 P5.
When on approach, transitioning from clean to dirty, the first "flap" increment is 'slats only'....that is to say, when you go from Flaps Zero to Flaps One, all you're putting out is slats (no flaps). The flap position, as depicted on the E/WD, shows "1" ..... not "1 + F".
Then, when selecting the next flap increment, i.e. "Flaps 2", you get trailing edge flaps going to the "2" position.
In terms of specific slat/flap movement, the following applies to the A-320: (The numbers are similar, but slightly different, for the A-321.)
POSITION SLATS FLAPS ECAM INDICATIONS
___________________________________________
0 0 0 (Slats/Flaps Up)
1 18 0 1
(This is during approach.)
1 18 10 1+F
(This is for takeoff.)
2 22 15 2
3 22 20 3
FULL 27 35 FULL
So, as we can see, there is a relatively large flap movement when working out flaps on approach, going from POSITION 1 to POSITION 2 (i.e. Zero to 15).
(Note: The 321 difference is with the flap...not the slat. This is due to the different flap design.)
I have no particular expertise in aeronautical engineering. I am just a 'driver', as most of us on this forum are. However, there are a few people on this forum who have extremely high levels of expertise and experience who can explain why you would get the pitch changes that you normally experience on the A-320 series Airbus when you move slats/flaps.
My personal opinion...and that's all it is...is that the pitch changes are normal and expected...as you'd get from any aircraft of this type of design...when moving slats/flaps.
PantLoad
Please reference Airbus FCOM 1.27.50 P5.
When on approach, transitioning from clean to dirty, the first "flap" increment is 'slats only'....that is to say, when you go from Flaps Zero to Flaps One, all you're putting out is slats (no flaps). The flap position, as depicted on the E/WD, shows "1" ..... not "1 + F".
Then, when selecting the next flap increment, i.e. "Flaps 2", you get trailing edge flaps going to the "2" position.
In terms of specific slat/flap movement, the following applies to the A-320: (The numbers are similar, but slightly different, for the A-321.)
POSITION SLATS FLAPS ECAM INDICATIONS
___________________________________________
0 0 0 (Slats/Flaps Up)
1 18 0 1
(This is during approach.)
1 18 10 1+F
(This is for takeoff.)
2 22 15 2
3 22 20 3
FULL 27 35 FULL
So, as we can see, there is a relatively large flap movement when working out flaps on approach, going from POSITION 1 to POSITION 2 (i.e. Zero to 15).
(Note: The 321 difference is with the flap...not the slat. This is due to the different flap design.)
I have no particular expertise in aeronautical engineering. I am just a 'driver', as most of us on this forum are. However, there are a few people on this forum who have extremely high levels of expertise and experience who can explain why you would get the pitch changes that you normally experience on the A-320 series Airbus when you move slats/flaps.
My personal opinion...and that's all it is...is that the pitch changes are normal and expected...as you'd get from any aircraft of this type of design...when moving slats/flaps.
PantLoad