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Driver170

Brake cooling gear extended

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Here comes a stupid question but i can't get my head around this -

 

Lets take the 737 NG for an example: you takeoff with gear extended to cool down the brakes if terrain isn't an issue or performance permits. But how is that allowed? What if you have an RTO it will cause severge damage ie fuse plug melted as your wheels are already hot?

 

Also what is Category C/N

 

Is this steel and carbon brakes?

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But how is that allowed?

 

Not sure why it wouldn't be.

 

 

 


What if you have an RTO it will cause severge damage ie fuse plug melted as your wheels are already hot?

 

The fuse plus is specifically built to blow out to avoid severe damage.

 

What are you having trouble with?

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On short sectors pilots may delay retracting the gear to cool down the brakes, but if your brakes area already hot (hence leaving the gear down) why is it even allowed to takeoff if its still hot and in the caution zone incase of an RTO??

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Well, you're not taking off if the brakes are too hot. But they might be cool enough to takeoff but might benefit from cooling time in the slipstream for the next takeoff.

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Thought brakes  get  hot  after  landing  when applying brakes  too hard,  so  cant  see  how  the  brakes get  hot  when  taking  off

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My point is if the pilots are leaving the gear down after takeoff doesn't that mean the wheel brakes are too hot and what if you have a RTO, because mind your wheel brakes are hot thats why you are leaving the gear extended

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For the most part, brake temperature and energy absorption is checked prior to takeoff. In the jets I currently fly, the FMS also accounts for brake temperature in the data calculation page. After a rejected takeoff(or recent landing), you have to ensure you won't exceed the absorption capability of the brakes in case of another rejected takeoff. You would normally run a brake cooling chart using current brake temperature and reject speed(V1) to see the amount of cooling required. A big note to remember is that it can take 15 to 30 minutes for brake temperature to peak. Carbon brakes work very well with reduced heat build up and lower cooling times. When tankering gas through a quick turn to avoid fueling, I run the charts backwards to come up with a brake application speed that gives a cooling time equal to my turn time. I also check my reverser only landing distance to ensure i'm not going to depart the runway with my delayed braking. I can't really see a reason for me to delay gear retraction for cooling. When I flew DC10s, a long taxi (ie PHNL) could lead to some warm brakes by the time i reached the runway, but I always let them cool prior to departing. In that case, I wouldn't risk an abort leading to hot brakes and evacuation. I've heard of guys having a dragging brake during takeoff and elected to extend the gear after getting a brake temp warning during initial climb out.

 

The only time I have ever seen a need to let the gear hang was during my military days. We would fly into hot spots, drop cargo and immediately depart afterwards. In this case, you choose hot brakes over bullets to the fuselage. As soon as cargo was off, you departed and let the gear hang to lower the risk of a fuse plug melt or blown tire in the wheel well. Those were some crazy days.

 

In flightsim, you can do what you want. Would be nice if every developer modeled brake issues and forced you to consider brake temps.

Thought brakes get hot after landing when applying brakes too hard, so cant see how the brakes get hot when taking off

This is more aligned with quick turns. In the DC10, after normal braking, the brakes would still be warm to touch 8 hours after landing. When I flew heavies, the turn times were always cut for 4 hours. This was enough time to ensure brakes would not reach the caution or danger zone in the event of a rejected takeoff. Smaller jets can accept shorter turns. Airbuses always amazed me with their built in brake cooling fans. I wonder how well they worked.
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