aerlingus330
Posts: 812
Joined: Tue Nov 30, 2004 2:21 am

Braking Cooling Times?

Sun May 08, 2005 2:54 am

Hi,
How long would Brakes on an A330/A340/747/777/767 take to cool in these situations-

-A normal Landing?
-An aborted takeoff?
-A fast Landing?

Edit: Also, what temperatures would the brakes be in these situations?

Thank-You,
AerLingus330

[Edited 2005-05-07 19:57:27]
Aer Lingus Airbus A330-300
 
air2gxs
Posts: 1443
Joined: Mon Jun 18, 2001 1:29 pm

RE: Braking Cooling Times?

Sun May 08, 2005 3:15 am

On the B767, you basically look at the temperature indication on the flight deck. If the EICAS says 5, you are looking at 60 minutes on the ground. Anything above that and you are probably going to change tires due to the fuse plugs melting.

The actually energy expended (absorbed?) by the brakes is dependant on quite a few factors: gross weight, speed, altitude at application, and temperature. One thing the AMM doesn't mention (suprisingly) is current brake wear. A worn brake can't absorb as much energy as newer brake. Though the charts are probably built around a worn brake.

The AMM uses this example:
-290,000lbs gross weight
-Brakes on speed of 100 knots
-Normal stop
-4000' pressure altitude
-OAT 86F
-1 mile taxi
-No revereser
That comes to a resultant brake energy of 18.5 million foot pounds and a recommended cooling period of 20 minutes.
 
B747FE
Posts: 217
Joined: Mon Jun 21, 2004 11:09 pm

RE: Braking Cooling Times?

Sun May 08, 2005 7:11 am

The temperature reached by the brakes would depend on several factors, posted above.
The indication in the 747 Classic is a vertical scale temperature, one for each gear, and one amber brake overheat light, mounted on the F/E panel. Should the overheat light illuminate, operation of the LF (left front), RF (right front), LR (left rear), and RR (right rear) selector switches will show heat condition of each brake. The meters are color coded to designated temperature range. Green is safe, for temperature between 0 to 300°F; amber is marginal, for temperature between 300 and 700°F; and red is unsafe, for temperature over 700 to 1000°F.
In general, after a normal landing brake indication is at the end of the green range. When temperature is at the beginning of the amber range (10 million foot pounds) would need 25 to 30 minutes ground cooling time or 5 minutes in-flight gear down cooling time.

Regards,
B747FE.
"Flying is more than a sport and more than a job; flying is pure passion and desire, which fill a lifetime"
 
amtrosie
Posts: 273
Joined: Thu Jan 06, 2005 6:44 am

RE: Braking Cooling Times?

Sun May 08, 2005 12:07 pm

A trick used down in the south (USA) is to place a ground air conditioning hose from the gate area close to the heated brakes. Always be careful not to get too close. You are trying to generate airflow over the brakes, more than directly "cooling" the brakes. It works well, especially on a quick turn.
 
Lemurs
Posts: 1320
Joined: Sat Mar 12, 2005 5:13 am

RE: Braking Cooling Times?

Sun May 08, 2005 2:46 pm

Quoting Amtrosie (Reply 3):
A trick used down in the south (USA) is to place a ground air conditioning hose from the gate area close to the heated brakes. Always be careful not to get too close. You are trying to generate airflow over the brakes, more than directly "cooling" the brakes. It works well, especially on a quick turn.

I was going to ask about exactly that. It seems to me that having some equip around "just in case" for brake overheat situations would be better than having the fuse plugs go and having to replace the tire set. Just enough to bring things down safely. Of course in that situation, I wouldn't want to be anywhere near those brakes...

[Edited for my "broken" spelling. Oy.]

[Edited 2005-05-08 07:47:09]
There are 10 kinds of people in the world; those who understand binary, and those that don't.
 
air2gxs
Posts: 1443
Joined: Mon Jun 18, 2001 1:29 pm

RE: Braking Cooling Times?

Sun May 08, 2005 7:40 pm

Quoting Lemurs (Reply 4):
Of course in that situation, I wouldn't want to be anywhere near those brakes

I've been around plenty of tires where the fuse plugs have melted. No danger, just a real loud hissing noise. Remember, the fuse plugs exist in order to prevent a tire from exploding due to an overheat condition.
 
aerlingus330
Posts: 812
Joined: Tue Nov 30, 2004 2:21 am

RE: Braking Cooling Times?

Sun May 08, 2005 11:17 pm

Don't they also use these fans for brake overheats-

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AerLingus330
Aer Lingus Airbus A330-300
 
air2gxs
Posts: 1443
Joined: Mon Jun 18, 2001 1:29 pm

RE: Braking Cooling Times?

Mon May 09, 2005 9:36 am

Yes, external brake fans can be used to shorten the cooling time. But they take time to set-up and are not at every location an air carrier flies. There is also speculation that forced air cooling may cause more damage to carbon brakes than just letting the tires go. The rapid cooling may cause cracking, spalling and glazing.

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