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Brakes and brake fans
Why is it Airbus are typically equipped with integral brake fans for cooling AND heavily utilized, and Boeing- to the best of my knowledge never been equipped with them and never has issues with hot brakes?
Re: Brakes and brake fans
Thrusty69 wrote:Why is it Airbus are typically equipped with integral brake fans for cooling AND heavily utilized, and Boeing- to the best of my knowledge never been equipped with them and never has issues with hot brakes?
Neither Boeing or Airbus make brakes, they are bought from the same suppliers.
Brake fans are optional equipment on Airbus, and as far as I know on Boeing’s as well. Seen them installed on 747s before.
None of the Airbus aircraft I currently fly have brake fans installed, I have no issue with getting external brake fans when required.
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- Francoflier
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Re: Brakes and brake fans
Brake fans are an option on Airbuses.
Brakes are heavy. If you fly mostly long sectors with plenty of cooling time during and between flight, you're better off with smaller, lighter brakes which are just dead weight most of the time anyway.
If you fly mostly short sectors with quick turnarounds, you'd opt for the brake fans as the extra weight doesn't change your burn much on short flights.
Boeing just goes for more simplicity at the expense of a bit more weight.
Brakes are heavy. If you fly mostly long sectors with plenty of cooling time during and between flight, you're better off with smaller, lighter brakes which are just dead weight most of the time anyway.
If you fly mostly short sectors with quick turnarounds, you'd opt for the brake fans as the extra weight doesn't change your burn much on short flights.
Boeing just goes for more simplicity at the expense of a bit more weight.
Re: Brakes and brake fans
Generally speaking, Boeing airplanes land at faster speeds than their Airbus competitors. This means brakes on Boeing aircraft handle more energy than the Bus’s do.
All designs have compromises and Boeing tends to compromise on higher landing speed to pick up efficiency elsewhere.
In the case of the 737 vs A320, the short landing gear, a carry forward of the original, necessitates a shallow AoA in order to prevent tail strike. Shallow AoA requires higher speeds, meaning the brakes have more energy to stop.
For the same gear height reason, the NG/MAX use double slotted flaps, which are heavier, whereas the Bus gets away with single slots on A319/A320 (which still keep slower speeds).
Yet, despite these small details, the 737 still weighs less than it’s competitor. The longer landing gears are quite heavy, and they also require heavier slides that are taller/longer, etc. (to be fair, some of 737 weight advantages come from the fact certain pieces are grandfathered to standards of the 60’s which are generally lighter).
Regardless, one way is not better than the other, it’s always a complex set of design compromises. At end of the day, both are essentially tied for fuel burn and total operating costs.
Boeing tends to have bigger brakes (and fans standard in some cases) because they land faster and dissipate more energy through the brakes.
All designs have compromises and Boeing tends to compromise on higher landing speed to pick up efficiency elsewhere.
In the case of the 737 vs A320, the short landing gear, a carry forward of the original, necessitates a shallow AoA in order to prevent tail strike. Shallow AoA requires higher speeds, meaning the brakes have more energy to stop.
For the same gear height reason, the NG/MAX use double slotted flaps, which are heavier, whereas the Bus gets away with single slots on A319/A320 (which still keep slower speeds).
Yet, despite these small details, the 737 still weighs less than it’s competitor. The longer landing gears are quite heavy, and they also require heavier slides that are taller/longer, etc. (to be fair, some of 737 weight advantages come from the fact certain pieces are grandfathered to standards of the 60’s which are generally lighter).
Regardless, one way is not better than the other, it’s always a complex set of design compromises. At end of the day, both are essentially tied for fuel burn and total operating costs.
Boeing tends to have bigger brakes (and fans standard in some cases) because they land faster and dissipate more energy through the brakes.
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- thepinkmachine
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Re: Brakes and brake fans
One difference is that Airbii don’t have wheel well fire detection systems and have a 300 deg C brake temperature limit for takeoff, in order to prevent fire in case of Hyd fluid leak. This 300 degrees limit is quite easy to exceed on landing and the brake fans are there to dissipate the heat on short turnarounds.
Boeings do have a wheel well fire detection, so the brake temp is less critical. They also have “quick turnaround weight” performance limits, limiting the landing weight on short turnarounds to keep the brake temps in check.
Boeings do have a wheel well fire detection, so the brake temp is less critical. They also have “quick turnaround weight” performance limits, limiting the landing weight on short turnarounds to keep the brake temps in check.
Re: Brakes and brake fans
Indeed Airbus gives the option. When we were in the configuration phase for A330's (for a Dutch Airline) we decided not to equipe the aircraft with brake fans. A matter of evaluating the route pattern and ground times versus extra weight and option cost.
Of course we experienced hot brakes and short turn arounds, It never really hampered the operation, although it may have meant waiting a bit longer.
One consideration was Brake Fan Reliablity: if one fan fails, you have one hot brake, and that is just as bad as 8 hot brakes.
Of course we experienced hot brakes and short turn arounds, It never really hampered the operation, although it may have meant waiting a bit longer.
One consideration was Brake Fan Reliablity: if one fan fails, you have one hot brake, and that is just as bad as 8 hot brakes.
Re: Brakes and brake fans
Does anyone know if a brake fan ops check is required after a tire change? I would think that an extra maintenance step would add up during the thousands of tire changes during the life of an aircraft.
Re: Brakes and brake fans
Most people test them anyway. Once you re-instate the circuit breakers, all you do is press the button.
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- shamrock137
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Re: Brakes and brake fans
DL_Mech wrote:Does anyone know if a brake fan ops check is required after a tire change? I would think that an extra maintenance step would add up during the thousands of tire changes during the life of an aircraft.
Yep, and they are deactivated before a tire change. That's on the 320 anyway. The ops check takes about 5 seconds if you have 2 people and a radio.
Re: Brakes and brake fans
Deactivating the brake fans for a wheel change is a step you don’t skip.......
Re: Brakes and brake fans
Lpbri wrote:Deactivating the brake fans for a wheel change is a step you don’t skip.......
I had heard that removing the electrical connector from an Airbus equipment cooling fan (running) can be quite a shocking experience. I assume this is similar (or digit removing).
Re: Brakes and brake fans
Francoflier wrote:Brakes are heavy.
Old wives tale, about 22 kg in total for 4 wheels like an A320 (5.16 kg each) https://www.safran-ventilation-systems. ... g/bcf-1802
thepinkmachine wrote:One difference is that Airbii don’t have wheel well fire detection systems.
Depends on the bus some have wheel fire detection, eg A340NG, A350
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- Francoflier
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Re: Brakes and brake fans
zeke wrote:Francoflier wrote:Brakes are heavy.
Old wives tale, about 22 kg in total for 4 wheels like an A320 (5.16 kg each) https://www.safran-ventilation-systems. ... g/bcf-1802
I was talking about the brakes themselves, not the brake fan units.
On a widebody, a set of discs can easily weight up to 100kgs per wheel.
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- acecrackshot
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Re: Brakes and brake fans
Bus brakes seem oddly susceptible to high brake temps at relatively low pressure altitudes. You can heat them up at 3000' pressure altitude fairly easily at a relatively low ambient temp while 20F higher ambient temp at 1000' they'll stay cool on a "harder" brake cycle.
That said, ground brake fans at the gate are probably the best bet unless you're operating in some pretty austere conditions.
That said, ground brake fans at the gate are probably the best bet unless you're operating in some pretty austere conditions.
Re: Brakes and brake fans
acecrackshot wrote:Bus brakes seem oddly susceptible to high brake temps at relatively low pressure altitudes. You can heat them up at 3000' pressure altitude fairly easily at a relatively low ambient temp while 20F higher ambient temp at 1000' they'll stay cool on a "harder" brake cycle.
That said, ground brake fans at the gate are probably the best bet unless you're operating in some pretty austere conditions.
There is absolutely nothing wrong with higher temps when carbon brakes are being used, they are most effect around the 250-300 deg C mark, I have no problem pulling into the gate with temps at 400-450 deg knowing they will have cooled down enough in 40 minutes to takeoff without brake cooling.
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- acecrackshot
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Re: Brakes and brake fans
The 320 has a 300c Limitation for takeoff, at least at the operator with whom I’m familiar. A solid braking on landing, quick turn, two mile taxi and 3000’ field elevation can routinely result in 300+C temps even at 20-25C field temp during the taxi back for takeoff. Put the same scenario at 1000’ FE and you’ll never see it.
Re: Brakes and brake fans
The 300 degree Celsius temperature limitation is not only due to a risk of a wheel well fire but it is also there to ensure that the brakes are cool enough to be efficient in a high speed rejected take off.
Airbus performs their brake energy tests with an initial brake temperature at about 150 degrees Celsius. To raise the temperature to this level, a 3 statute mile taxi run with three stops is performed. The test is also performed with 90% worn out brakes, aircraft at maximum take off weight and no reverse is accounted for during the stop.
So, that is what the aircraft is tested for. The 300 degrees Celsius is a compromise. It is assumed that the probability of an operator performing a take off at maximum take off weight with brakes at 300 degrees Celsius is remote. It is also assumed that the use of reverse (which is not used during testing) could help if the brake temperature is above the test temperature of 150 degrees Celsius.
Airbus performs their brake energy tests with an initial brake temperature at about 150 degrees Celsius. To raise the temperature to this level, a 3 statute mile taxi run with three stops is performed. The test is also performed with 90% worn out brakes, aircraft at maximum take off weight and no reverse is accounted for during the stop.
So, that is what the aircraft is tested for. The 300 degrees Celsius is a compromise. It is assumed that the probability of an operator performing a take off at maximum take off weight with brakes at 300 degrees Celsius is remote. It is also assumed that the use of reverse (which is not used during testing) could help if the brake temperature is above the test temperature of 150 degrees Celsius.
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