Brake temps hot on downwind side.
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Brake temps hot on downwind side.
Why is it that on a manual landing with auto brake (A320), no input from the pilot to confuse things (assume letting the auto brake just about stop the aircraft on the runway) with a crosswind the downwind side tends to get hotter?
Because there's less cooling on that brake unit as it is in the lee of the aircraft. When it's stopped, the upwind side will be subject to greater airflow than the downwind side and either cool quicker, or not get as hot in the first place. Or am I missing something?
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Could it have anything to do with the weathercocking effect? Aeroplane tries to turn upwind so downwind brake has more work to do.
Of course this ignores the nose wheel steering keeping it straight but just a thought.
Of course this ignores the nose wheel steering keeping it straight but just a thought.
I don't know about the A320.
In the 1980's the runway at Nauru was 5600 feet long with no over-run areas. Depending very much on pilot technique (some were lead-footed) the brakes on the 737-200 could get quite hot after landing.
After parking on the small tarmac on Nauru and with parking brake released we would note the wind direction and with the APU running one aircon pack, we would turn off the pack that was downwind. The air exiting the two air conditioning packs was very hot and bathed the wheels.
The downwind pack, if left on, would have its efflux flowing around the nearest main wheel. This had the effect of bathing the brakes on that wheel with hot air.
So we figured we should turn that pack off and use the other pack which had its hot air outlet further away from a main wheel. Sounds complicated and I am not explaining it very well.
After 15 minutes or so, there was a distinct difference in brake temperature between the two sets of main wheels as they cooled down.
Later I read somewhere in a Boeing document that this procedure was recommended by Boeing as part of brake cooling on the ground.
In the 1980's the runway at Nauru was 5600 feet long with no over-run areas. Depending very much on pilot technique (some were lead-footed) the brakes on the 737-200 could get quite hot after landing.
After parking on the small tarmac on Nauru and with parking brake released we would note the wind direction and with the APU running one aircon pack, we would turn off the pack that was downwind. The air exiting the two air conditioning packs was very hot and bathed the wheels.
The downwind pack, if left on, would have its efflux flowing around the nearest main wheel. This had the effect of bathing the brakes on that wheel with hot air.
So we figured we should turn that pack off and use the other pack which had its hot air outlet further away from a main wheel. Sounds complicated and I am not explaining it very well.
After 15 minutes or so, there was a distinct difference in brake temperature between the two sets of main wheels as they cooled down.
Later I read somewhere in a Boeing document that this procedure was recommended by Boeing as part of brake cooling on the ground.
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I work on the theory that a hefty crosswind means more weight on downwind wheels, with more energy absorbed during moderate braking. Hadn't even thought about the weathercock effect and heavier braking on one side to keep it straight.
I think flapassym is right: Asymmetric braking against weathercocking is the major reason for hotter brakes on the downwind side.
Doesn't make sense, the autobrakes don't 'know' there's a crosswind, equal pressure will be applied on both sides.
Manual application on the other hand will certainly see hotter temps on the downwind side, even if only for the short amount of manual braking applied after AB disengagement.
I've seen that on many occasions.
Manual application on the other hand will certainly see hotter temps on the downwind side, even if only for the short amount of manual braking applied after AB disengagement.
I've seen that on many occasions.
No, but the aircraft does know if it is keeping straight and can 'tell' the autobrake? I wonder if autobrake uses differential braking to keep straight on the runway - otherwise it might veer off one way or the other. So if there was a strong crosswind, different brake temperatures would result.
I am just off to fly but will have a look for a reference later.
I am just off to fly but will have a look for a reference later.
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the autobrakes don't 'know' there's a crosswind, equal pressure will be applied on both sides.
In a crosswind, (with no aileron applied) the into wind wing generates a bit more lift than the downwind wing and more weight is transferred to the downwind wheels. The upwind wheels may have the brake pressure modulated to avoid tyre slip and the down wind wheels do most of the work.
If blogs unwittingly uses aileron to help "steer" the aircraft then the effect is even more pronounced.
See page 10 of http://www.airbus.com/fileadmin/medi...LAND-SEQ05.pdf
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Thanks to all. May I just pull these ideas together, without offending anyone...
Giggity giggity, Cenaurus – That’s a different question. I’m interested in what is happening during the landing roll only but thanks for the input.
Flapassym, Uplinker – I don’t think so but I’m no expert. My question is specifically about auto brake.
How would the autobrake sense the need for asymmetric braking? I’ve never heard of the auto brake doing this.
=================
Cough – Brake wear. I never thought of that. Can you explain further?
Stilton – thanks.
Fursty ferret, Goldenrivett – Asymmetric weight.
Yeah I think this may be a factor but I’d like to know for sure. I look forward to hearing more.
Just to be clear though, the auto brake is not trying to steer the aircraft as far as I know.
Giggity giggity, Cenaurus – That’s a different question. I’m interested in what is happening during the landing roll only but thanks for the input.
Flapassym, Uplinker – I don’t think so but I’m no expert. My question is specifically about auto brake.
How would the autobrake sense the need for asymmetric braking? I’ve never heard of the auto brake doing this.
=================
Cough – Brake wear. I never thought of that. Can you explain further?
Stilton – thanks.
Fursty ferret, Goldenrivett – Asymmetric weight.
Yeah I think this may be a factor but I’d like to know for sure. I look forward to hearing more.
Just to be clear though, the auto brake is not trying to steer the aircraft as far as I know.
the auto brake is not trying to steer the aircraft as far as I know.
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With absolutely no thought being given to this phenomenon before, nor having read any expert explanation, how about:
Given the auto brakes are trying to give you a fixed level of retardation/deceleration, they must surely add more braking effort to a faster wheel than a slower wheel and, therefore, get hotter. As the aircraft weather-cocks into wind the downwind wheels will be on the outside of the turn into wind and will accelerate, relative to the upwind wheels. Now those wheels are going faster, the auto brakes have to apply more braking; ergo......
Given the auto brakes are trying to give you a fixed level of retardation/deceleration, they must surely add more braking effort to a faster wheel than a slower wheel and, therefore, get hotter. As the aircraft weather-cocks into wind the downwind wheels will be on the outside of the turn into wind and will accelerate, relative to the upwind wheels. Now those wheels are going faster, the auto brakes have to apply more braking; ergo......
On the subject of brake use generally. It might be useful to be aware that some pilots in the simulator (and by association in the real aeroplane) have been known to inadvertently apply light braking during the take off roll, but without being conscious of it happening.
During the landing run, some simulators automatically display a page on the instructor panel that shows the brake pressure on each set of wheels being applied by the pilot at any instant. This same page automatically pops up if the pilot is (for example) unknowingly touches the brakes during the take off run.
During the simulator training of two cadets on a 737 simulator, the sequence included practice at rejected take off procedure at 100 knots. The simulated runway was reduced in length such that if the rejected procedure was conducted correctly the aircraft would come to a stop with 100 metres to spare.
While one cadet performed the rejected take off perfectly and stopping with 100 metres to spare , the other cadet would invariably overrun the end of the runway while still performing the actions swiftly and accurately. This had the instructor mystified until he by chance happened to be looking at the instructor screen while the cadet was in the middle of the take off run.
There was no specific reason for the instructor to look at his screen at that moment during the take off run - it just seemed a good idea at the time. What he saw surprised him. The brake pressure readings were popping up intermittently on the screen during the take off run. This could only mean the cadet was unknowingly touching the top of the brake pedals during the take off roll.
The extra drag caused by intermittent brake pressure had extended the take off roll. When at 100 knots IAS, the rejected take off procedure was started, the aircraft was already further down the runway that it should have been with a normal take off run. This explained the instances of the over-run.
The cadet was then reminded to keep his feet low on the pedals during the take off roll and it was explained to him he had his feet too high on the pedals thus causing inadvertent brake pressure. The cadet refused to believe this was happening and denied he had his feet too high up on the rudder pedals. This was a prime example of ethnic culture or loss of face at work.
In the end the instructor asked the PM to get out of his seat and observe what was happening on the brake pressure page during his colleagues next take off run. When it duly happened yet again, the instructor asked the PM to tell the offender in his own language what was happening re partial brake pressure on the take off roll. That satisfied `Face` and after that, the box was ticked off and there were no more problems.
In the simulator it is difficult for an instructor sitting at the back to see the exact position of a student's feet on the rudder pedals especially during a night take off scene. Hence it is useful for him to occasionally glance at his own screen to see if inadvertent brake pressure is being applied to the rudder pedals during take off. V1 could become invalid if the brakes are being dragged even slightly. And of course the brake temperatures could rise,
During the landing run, some simulators automatically display a page on the instructor panel that shows the brake pressure on each set of wheels being applied by the pilot at any instant. This same page automatically pops up if the pilot is (for example) unknowingly touches the brakes during the take off run.
During the simulator training of two cadets on a 737 simulator, the sequence included practice at rejected take off procedure at 100 knots. The simulated runway was reduced in length such that if the rejected procedure was conducted correctly the aircraft would come to a stop with 100 metres to spare.
While one cadet performed the rejected take off perfectly and stopping with 100 metres to spare , the other cadet would invariably overrun the end of the runway while still performing the actions swiftly and accurately. This had the instructor mystified until he by chance happened to be looking at the instructor screen while the cadet was in the middle of the take off run.
There was no specific reason for the instructor to look at his screen at that moment during the take off run - it just seemed a good idea at the time. What he saw surprised him. The brake pressure readings were popping up intermittently on the screen during the take off run. This could only mean the cadet was unknowingly touching the top of the brake pedals during the take off roll.
The extra drag caused by intermittent brake pressure had extended the take off roll. When at 100 knots IAS, the rejected take off procedure was started, the aircraft was already further down the runway that it should have been with a normal take off run. This explained the instances of the over-run.
The cadet was then reminded to keep his feet low on the pedals during the take off roll and it was explained to him he had his feet too high on the pedals thus causing inadvertent brake pressure. The cadet refused to believe this was happening and denied he had his feet too high up on the rudder pedals. This was a prime example of ethnic culture or loss of face at work.
In the end the instructor asked the PM to get out of his seat and observe what was happening on the brake pressure page during his colleagues next take off run. When it duly happened yet again, the instructor asked the PM to tell the offender in his own language what was happening re partial brake pressure on the take off roll. That satisfied `Face` and after that, the box was ticked off and there were no more problems.
In the simulator it is difficult for an instructor sitting at the back to see the exact position of a student's feet on the rudder pedals especially during a night take off scene. Hence it is useful for him to occasionally glance at his own screen to see if inadvertent brake pressure is being applied to the rudder pedals during take off. V1 could become invalid if the brakes are being dragged even slightly. And of course the brake temperatures could rise,
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9 Points - Just something I've observed. When you have a temperature mismatch between the brake units on the same wheel, its usually the case that the hotter one is an old unit with more wear than the newer one. Guessing it works something like (for the new brake unit) More mass = more material to absorb the temperature increase = lower peak temperature.
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the auto brake is not trying to steer the aircraft as far as I know
Autobrake simply applies equal pressure to both sides in order to achieve a set deceleration rate. A slipping wheel will be detected by the anti skid unit and its individual brake pressure will be reduced until the wheel spins up to speed again.
If the weight load of the aircraft is not evenly balanced due to the crosswind effect, then the upwind wheels will have less load on them, tend to start to skid earlier which will cause the antiskid units to reduce brake pressure on those wheels.
Thus the downwind brakes work harder and show it as an increase in temperature.
Last edited by Goldenrivett; 22nd Oct 2016 at 15:47. Reason: typo
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9 Points:
1. How do you use TR's?
2. On an AB do the auto brakes reduce as REV Thr is increased?
3. Is this phenomenon equal across the fleet?
4. Do you have brake temp gauges per wheel or per brake unit?
5. If per unit is there a difference, on the hotter side, between the front units and the rear units?
6. Do the brake units have depth pins on them? have you noticed a correlation between the depth reading and the difference in hotness of one side v the other?
Further; I'm dubious about the upwind wing creating more lift than the other. I understand the theory, especially on swept wing a/c, but...the spoilers come up PDQ to dump the lift and increase the brake effect. With in seconds both wings are well below stall speed.
1. How do you use TR's?
2. On an AB do the auto brakes reduce as REV Thr is increased?
3. Is this phenomenon equal across the fleet?
4. Do you have brake temp gauges per wheel or per brake unit?
5. If per unit is there a difference, on the hotter side, between the front units and the rear units?
6. Do the brake units have depth pins on them? have you noticed a correlation between the depth reading and the difference in hotness of one side v the other?
Further; I'm dubious about the upwind wing creating more lift than the other. I understand the theory, especially on swept wing a/c, but...the spoilers come up PDQ to dump the lift and increase the brake effect. With in seconds both wings are well below stall speed.
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Having flown an Airbus 310 before, this phenomenon of downwind brake temp going up was observed quite significantly.
The answer in my opinion is simply the control wheel or aileron deflection inputted by the pilot in landing roll. Assume a left cross wind, manual landing with automatic braking, the usual pilot tendency is to apply aileron into the wind (mostly overdo it) thereby inducing more a/c weight on the left set of wheels. Obviously this is an aerodynamic increase of weight on left set of wheels with same Hyd pressure on both sides. How much the airplane decelerates and how drifting is controlled by brake modulation is beyond the scope of this discussion. The left set of wheels have higher resistance to ground and hence temp rises faster.
Assume the same landing with an autopilot and from what I have observed the autopilot might use side slip/crab etc method but the input on landing roll really never showed a difference in brake temp on any side later on as much as in a manual landing.
To sum it up - more aileron on landing roll more difference on BRK temp.
The answer in my opinion is simply the control wheel or aileron deflection inputted by the pilot in landing roll. Assume a left cross wind, manual landing with automatic braking, the usual pilot tendency is to apply aileron into the wind (mostly overdo it) thereby inducing more a/c weight on the left set of wheels. Obviously this is an aerodynamic increase of weight on left set of wheels with same Hyd pressure on both sides. How much the airplane decelerates and how drifting is controlled by brake modulation is beyond the scope of this discussion. The left set of wheels have higher resistance to ground and hence temp rises faster.
Assume the same landing with an autopilot and from what I have observed the autopilot might use side slip/crab etc method but the input on landing roll really never showed a difference in brake temp on any side later on as much as in a manual landing.
To sum it up - more aileron on landing roll more difference on BRK temp.
Interesting account Centaurus.
There's still a few Pilots around that believe you should always have your feet 'up' on the rudder pedals at all times, even during the take off roll, steering with their heels in effect and of course easily / inadvertently applying the brakes.
There's still a few Pilots around that believe you should always have your feet 'up' on the rudder pedals at all times, even during the take off roll, steering with their heels in effect and of course easily / inadvertently applying the brakes.
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Pontius – the aircraft is prevented from weathercocking by the pilot.
Centaurus – my question specifically refers to auto brake only.
Cough – yeah could be. Would love to get this confirmed.
Goldenrivett – I’d say this would probably be the main reason, in my opinion, but Cough’s idea could also be it. Would love to get an experts opinion.
Rat 5 –
1. How do you use TR's?
As per SOP, usually fully on touchdown until 70kts then to idle until taxiing off the runway.
2. On an AB do the auto brakes reduce as REV Thr is increased?
The auto brakes on the airbus work to maintain a selected rate of deceleration based on the IRU groundspeed I believe, so the brake pressure would normally vary as needed to achieve the selected rate.
3. Is this phenomenon equal across the fleet?
I have not got enough data, this is not a scientific analysis it’s just an informal query.
4. Do you have brake temp gauges per wheel or per brake unit?
Per wheel.
5. If per unit is there a difference, on the hotter side, between the front units and the rear units?
See 4.
6. Do the brake units have depth pins on them? have you noticed a correlation between the depth reading and the difference in hotness of one side v the other?
Yes and I have not looked for this but will do in future.
*You’re dubious….
So can you propose an alternative theory?
Agg karan – on the fly by wire airbus we release the stick on touch down so there is no aileron input.
Stilton – not relevant to this discussion but if you have a low speed high thrust engine failure on a 45 meter runway and don’t start with your feet up you will not keep the airbus on the runway. This was demonstrated to me by 2 check Captains in 2 different airlines, one was an ex Airbus employed instructor. I flew A320/330/340 foot down for 18 years but am now a passionate foot up man. Just saying.
TngoAlphad _ mate you must be good when you’re rested if you are spotting the obvious like this when you are fatigued. Thanks.
So we have two theories:
1. More weight on the downwind side.
2. Brake wear issues.
As I think about it I think the brake wear issue might not hold up because it would be fairly evenly distributed between upwind and downwind but what I have observed is a downwind hotter trend so I'm tending towards theory 1.
Centaurus – my question specifically refers to auto brake only.
Cough – yeah could be. Would love to get this confirmed.
Goldenrivett – I’d say this would probably be the main reason, in my opinion, but Cough’s idea could also be it. Would love to get an experts opinion.
Rat 5 –
1. How do you use TR's?
As per SOP, usually fully on touchdown until 70kts then to idle until taxiing off the runway.
2. On an AB do the auto brakes reduce as REV Thr is increased?
The auto brakes on the airbus work to maintain a selected rate of deceleration based on the IRU groundspeed I believe, so the brake pressure would normally vary as needed to achieve the selected rate.
3. Is this phenomenon equal across the fleet?
I have not got enough data, this is not a scientific analysis it’s just an informal query.
4. Do you have brake temp gauges per wheel or per brake unit?
Per wheel.
5. If per unit is there a difference, on the hotter side, between the front units and the rear units?
See 4.
6. Do the brake units have depth pins on them? have you noticed a correlation between the depth reading and the difference in hotness of one side v the other?
Yes and I have not looked for this but will do in future.
*You’re dubious….
So can you propose an alternative theory?
Agg karan – on the fly by wire airbus we release the stick on touch down so there is no aileron input.
Stilton – not relevant to this discussion but if you have a low speed high thrust engine failure on a 45 meter runway and don’t start with your feet up you will not keep the airbus on the runway. This was demonstrated to me by 2 check Captains in 2 different airlines, one was an ex Airbus employed instructor. I flew A320/330/340 foot down for 18 years but am now a passionate foot up man. Just saying.
TngoAlphad _ mate you must be good when you’re rested if you are spotting the obvious like this when you are fatigued. Thanks.
So we have two theories:
1. More weight on the downwind side.
2. Brake wear issues.
As I think about it I think the brake wear issue might not hold up because it would be fairly evenly distributed between upwind and downwind but what I have observed is a downwind hotter trend so I'm tending towards theory 1.