Brake Temperature
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Brake Temperature
Upon arrival at the gate and after coming to a complete stop if you see the brake temperature rising would this indicate that the airplane has been chocked incorrectly?
What would a rise in brake temperature and pressure indicate in such a scenario?
What would a rise in brake temperature and pressure indicate in such a scenario?
Gender Faculty Specialist
I wouldn't have thought so. The chocks, whether positioned correctly or not shouldn't affect the brake temps at all.
The brake temps will generally rise a bit after you arrive on stand, due to the lack of airflow over the brake unit. If you have brake fans a la BAe146, then you will see the temps decreasing, hopefully!
Hope that helps.
The brake temps will generally rise a bit after you arrive on stand, due to the lack of airflow over the brake unit. If you have brake fans a la BAe146, then you will see the temps decreasing, hopefully!
Hope that helps.
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Brake Temps...
Brakes are devices that convert kinetic energy to heat energy. I don't have the reference with me (I'm in Asia, and my manuals are back in the U.S.), but, generally, the complete transfer of heat energy throughout the brake and wheel assemblies occurs approximately (on average) 30 minutes after landing.
Thus, if you have an aircraft equipped with brake temp indicators, you'll see the temp peak out about 30 minutes after landing. Brake fans, stiff winds, etc. all contribute to the reduction of that actual peak temperature, but the peak still occurs about this point in time...whatever that specific temperature may be.
Chocks in place, correctly or incorrectly placed, is an irrelevent issue.
Further, if you have brake fans, and you're using them, take note not to switch off the fans too soon. A common mistake is to (say 20 minutes after landing and maybe 15 minutes after brake fan activation) turn off the fans, thinking the temps have decreased to an acceptable value...only to see the temps rise, again, and peak at that 30 minute point.
Thus, it is perfectly normal to see the temps rise...chocked or not, fans or not...after gate arrival.
Regards,
Tom
Thus, if you have an aircraft equipped with brake temp indicators, you'll see the temp peak out about 30 minutes after landing. Brake fans, stiff winds, etc. all contribute to the reduction of that actual peak temperature, but the peak still occurs about this point in time...whatever that specific temperature may be.
Chocks in place, correctly or incorrectly placed, is an irrelevent issue.
Further, if you have brake fans, and you're using them, take note not to switch off the fans too soon. A common mistake is to (say 20 minutes after landing and maybe 15 minutes after brake fan activation) turn off the fans, thinking the temps have decreased to an acceptable value...only to see the temps rise, again, and peak at that 30 minute point.
Thus, it is perfectly normal to see the temps rise...chocked or not, fans or not...after gate arrival.
Regards,
Tom
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airplane chocked incorectly: release brakes and it will start moving,especially if not on a perfect horizontal apron.
Chockes have nothing to do with brake temperature...you have to use them to be able ro release brakes,so cooling them faster.
Chockes have nothing to do with brake temperature...you have to use them to be able ro release brakes,so cooling them faster.
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alexban
Who says that parked hot brake units cool faster if the brake pressure is released?
What do you expect to happen when you release the park brakes to chocked wheels? How about - nothing, except for brake pressure going to zero and perhaps a miniscule realignment of the brake discs.
Who says that parked hot brake units cool faster if the brake pressure is released?
What do you expect to happen when you release the park brakes to chocked wheels? How about - nothing, except for brake pressure going to zero and perhaps a miniscule realignment of the brake discs.
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Wouldn't released brakes expose the brake surface to air, allowing for slightly more heat dispersion than with applied brakes. It's probably a minor effect, but would theoretically let the brakes cool a little faster.
Adding to TomConard's post, the additional factor unspoken in his post is that there is the position of the thermal sensor to consider. Obviously it can't be on the business side of the brakes, and therefore it is not directly exposed to the heating. So the sensor takes time (due to the lag he describes) to actually see the brake temperature. Which means that the sensed peak may be lower than the real peak AND occur after it.
Adding to TomConard's post, the additional factor unspoken in his post is that there is the position of the thermal sensor to consider. Obviously it can't be on the business side of the brakes, and therefore it is not directly exposed to the heating. So the sensor takes time (due to the lag he describes) to actually see the brake temperature. Which means that the sensed peak may be lower than the real peak AND occur after it.
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Originally Posted by Mad (Flt) Scientist
Wouldn't released brakes expose the brake surface to air, allowing for slightly more heat dispersion than with applied brakes. It's probably a minor effect, but would theoretically let the brakes cool a little faster.
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By definition an Aircraft is incorrectly chocked when upon release of the parking brake the view out the window begins to move longitudinally about the axis of the eye, with or without engines running but usually in an uncommanded fashion. 
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Brake Cooling..
It's a well known fact that brakes cool better when they are released. If the brakes are set, the disks are squeezed together as a single unit. If the brakes are released, air is allowed to circulate between the disks and will allow for a quicker dissipation of heat.
As for properly putting chocks in place....there is no way of seeing it from the cockpit. If the airplane begins to roll...common sense says they werent put in correctly.
As for properly putting chocks in place....there is no way of seeing it from the cockpit. If the airplane begins to roll...common sense says they werent put in correctly.
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How can brake release assist hot disk brake unit cooling?
Without return springs or wheel movement how do the brake disks magically move apart when you release the park brake?
Same on your car having disk brakes. It is disk rotation which creates the microscopic gap between the disks or the pads.
Methinks we have a phurphy here which may be a carry over from drum braking systems.
Without return springs or wheel movement how do the brake disks magically move apart when you release the park brake?
Same on your car having disk brakes. It is disk rotation which creates the microscopic gap between the disks or the pads.
Methinks we have a phurphy here which may be a carry over from drum braking systems.
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Not [U]necessarily[U] true in fact.
If there is little or no airflow over the brakes then releasing the park brake can, in fact, reduce the rate of cooling, as the gap between the discs is tiny and heat is simply radiated across the gap from disc to pad (and v.v)
By leaving the park brake set the heat can be transfered and radiated (away) through the whole assembly.
BUT......
If you have a suitable breeze and especially if you are using brake fans then the better option is to have the park brake off. The airflow being sufficient to pass between the pads/disc and draw heat away (and cooler air in).
The actually difference in cooling times (no fans) with the park brake on or off is actually quite minimal anyway.
Having said that it may still be a significant factor for LCCs with their rapid turnarounds...I dont know?
Chocks? Complete red-herring.
The brakes will continue to heat up for several minutes after landing...its normal as TC notes above.
If there is little or no airflow over the brakes then releasing the park brake can, in fact, reduce the rate of cooling, as the gap between the discs is tiny and heat is simply radiated across the gap from disc to pad (and v.v)
By leaving the park brake set the heat can be transfered and radiated (away) through the whole assembly.
BUT......
If you have a suitable breeze and especially if you are using brake fans then the better option is to have the park brake off. The airflow being sufficient to pass between the pads/disc and draw heat away (and cooler air in).
The actually difference in cooling times (no fans) with the park brake on or off is actually quite minimal anyway.
Having said that it may still be a significant factor for LCCs with their rapid turnarounds...I dont know?
Chocks? Complete red-herring.
The brakes will continue to heat up for several minutes after landing...its normal as TC notes above.
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Mad Scientist of Flying
It's going back a while now but as far as I can remember the reason for leaving the parking brake off was solely for cooling. There was never a mention of the brakes seizing on.
It's going back a while now but as far as I can remember the reason for leaving the parking brake off was solely for cooling. There was never a mention of the brakes seizing on.
Organic brakes (Heat packs) in the days prior to carbon heat packs and temp sensors, were certainly prone to seizing if the brakes were left applied. This usually occurred after hard use or after numerous short hops. Changed a few for that very reason.
There used to be a great training video called 'Time to stop again' about a 737 (If I recall correctly), doing 20-30 min multi-sectors, showing the cumulative temp rise at each point. I remember showing it to some drivers who had absolutely no idea and were quite shocked!
There used to be a great training video called 'Time to stop again' about a 737 (If I recall correctly), doing 20-30 min multi-sectors, showing the cumulative temp rise at each point. I remember showing it to some drivers who had absolutely no idea and were quite shocked!
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If there is little or no airflow over the brakes then releasing the park brake can, in fact, reduce the rate of cooling, as the gap between the discs is tiny and heat is simply radiated across the gap from disc to pad (and v.v)
By leaving the park brake set the heat can be transfered and radiated (away) through the whole assembly.
By leaving the park brake set the heat can be transfered and radiated (away) through the whole assembly.
I would advise as seldomfixit suggests, one never measures the amount of brake wear with brakes off, unless you are minutes from finishing your shift and feel the next shift should change the worn brake unit
I would suggest that the issue of releasing the parking brake from a hot disc assembly is to aid even cooling - thus avoiding the possibility of distorting the discs. The pads & associated equipment would probably provide a greater heat path than say still air, for the section of disc that is clamped.