747-400 Brake cooling

[jon b 2,047]

since it basically means you could take of with>your brakes at level 4, and land with them pre-heated at level>2 on a shorter flight - if there is one where the 747 would be>used. And IMHO that's not an ideal state.To right! don`t do that.In summer I quite often park next to an A330 at KLAS Las Vegas(2200ft asl and 40c+,I only mention temp because of the density altitude issue)They are always out with fans trying to cool his brakes.I`ve heard them have to come back to stand before because he can`t take off because his brakes are still too warm(taxi time also warms them)Jon

[Guest visualchaosfx]

I just use the reset brake temp thingie in the PMDG menu. I know thats not the answer your lookin for but hey, it works lol.

[fozzy 1]

Jumping in on this one.... it has been said the boing manuals say "don't use parking brake, don't taxi, don't get near the wheels for an hour". Wouldn't a taxi around (without using brakes) actually help the cooling process if the brakes are too hot? or do the brake pads always "work" a little bit anyway? Thanks, Luca

[mburkhard 23]

Luca,you are thinking about the brakes being cooled by the wind when moving around right? Like if you are on a bicycle and it's colder when moving than being at a stop.Unfortunately... You'd have to taxi VERY fast to have enough wind that would make an impact on cooling time. However, there's no airport in the world where you can taxi fast without using the brakes. If you'd want to taxi without brakes as you suggest, you'd have to maintain a speed of less than 10kts to avoid using the brakes. Not much airflow at those speeds...And that's why there are portable fans you can use to cool brakes, as mentioned in a posting further up.Regards,Markus

[Brian Doney 127]

Come now Markus,Surely you want to take this opportunity to beat Luca over the head with your knowledge, instead of sharing it with him in a respectful manner as you have, don't you ?Isn't that the status quo, anyway ? :-roll

[fozzy 1]

Not sure how it influences the cooling process (i'd need to take my physics book back out of the library of the forgotten books) i just thought that an even small air flux would be better than the convective effect of the brakes heating the air...I suppose they made their tests and have seen it doesn't do enough... :) Thanks, LucaPS: Please, can we stop trying to bash each other at every word which is spoken? doesn't make sense... if you all need to post as a reaction, write your post and save it in notepad, get a walk, and then read the post which enraged you again.. possibly you'll notice people don't always have something personal against YOU.

[Brian Doney 127]

Luca,I agree with you, and to be clear, my post was in no way intended as a flame towards Markus; he is indeed very gracious in sharing his knowledge, and I certainly appreciate that.Some others; however, need to drop the ego trip, IMHO. Ya know allot about airplanes/physics, etc., good for you; even better, you decide to share your knowledge with the rest of us, that's outstanding. Maybe, just maybe, we could do that with the understanding that not everyone is privy to the details some of us are, and drop the condescending tone towards those that don't quite match our perceived level of expertise.Guess I'm making a bigger deal out of it than I probably should, though, so I'll shut up.

[jon b 2,047]

Luca,taxying especialy at high weights will actualy add to the problem as it warms the wheels,not sure how or if it will in turn warm the brakes.I guess the heat is generated through friction with the ground and deformation of the tyre.Again refering to the boeing brake coling schedule, you have to make an addition for every mile you have taxied. cheersJon

[rgamurot 1]

So if I'm understanding the physics in this thread correctly, the brakes will cool pretty much at the same rate regardless of ambient air temperature. The only real difference is that the brakes will cool faster when they are at a higher temperatures and as it cools, the heat loss slows. This is because there is a greater difference between brake temperature and air temperature at first. As the brakes cool, the difference is reduced thus causing the cooling rate to drop. How am I doing so far?Now, given what Q said about taking the fans away cause the brakes to actually heat up again, could it be that there is little difference in cooling time because the core of the brake is still very hot? Also, could the outer portion of the carbon, for the most part, insulate the core keeping the temperature up? In this sense, although you cooled the outer sections of the brakes, the core reheats the cooled sections. Is this correct?Now the only thing I couldn't quite understand is that although the brakes will cool quickly initially, this cooling process according to others does not appear on the EICAS. I personally haven't dealt with hot brakes before. My brakes usually don't go over 2 and that's after landing. Anyway, is this because of the placing of the sensor (i.e. the sensors are in the brake core and doesn't detect the heat change as quickly) or is it because each number simply represents a different temperature range (0=0-500 / 1=501-1200 / 2=1201-2100 / etc.)? Or is it something else entirely?Ryan GamurotLucky to live Hawai'ihttp://www.precisionmanuals.com/images/forum/supporter.jpg

[fozzy 1]

Thanks Jon, so possibly they do heat up "normally" during taxi... I don't know how carbon behaves as far as the insulation of the inner part is concerned... but on racing bikes if you want to use carbon brakes you have to "keep them warm" as carbon brakes work better at higher temperatures than the usual alloy discs which need to be cooled. And on the manual of the PMDG it is recommended not to "pump" on the brakes but to use them steadily as this helps the cooling process.. I think there's something in how the brakes assemblies are built which we are missing... i'll try to ask a friend who works as a mechanic and see if he has an answer to this :) Not sure if this may help anybody to understand something more. :) Luca

[fozzy 1]

I checked with a friend who's aircraft mechanic... To make the story short the brake "discs" always work a little bit... at least they are in contact with the brake pads and so a litle friction always occurs. this is true for all bigger aircrafts. so it's not a boeing typical behaiour. Any mechanic wanting to jump in to correct or expand is welcome as i may very well have misunderstood the details :) Luca

[Qavion 19]

"Anyway, is this because of the placing of the sensor (i.e. the sensors are in the brake core and doesn't detect the heat change as quickly) or is it because each number simply represents a different temperature range (0=0-500 / 1=501-1200 / 2=1201-2100 / etc.)?"I don't have a lot of information on this kind of stuff, but I read that the numbers are proportional to brake temperature.My notes mention the following values for our 744's0 is a temperature of 176C or less5 is 482C9 is 788C or more Hope this helps.Cheers.Q>

[Tabs 2,790]

Remember too guys that the mere act of taxiing across the ground is heating up the gear via friction without even using the brakes. You have a ton of weight bearing down on a very small surface area that's in contact with the ground which creates a ton of friction. This is part of the logic behind why taking off or landing with a big tailwind is such a big no-no. You're increasing your groundspeed when you do that and thus the tires are rotating faster and getting hotter. They'll blow quite explosively if they get too hot.

[Guest stew286]

ok guys, Calm down dears it's only a simulator! In real life a brake overheat has to be called to atc ground after turnoff in severe case it could result in a fire or a burst tyre.Atc will normally send someone to inspect the gear.747 767 seem to be the main sufferers a320 also.On take off just leave the gear down a bit longer and reset the warning.I dont fly 747 or 767 but i have been behind a few with this problem but that is not very often and for action to be taken for brake overheat it would have to be abnormal. so lets all calm down i know it's our favourite sim and we all feel protective of our baby.At least it does show brake overheat what other sim does not MS.STU

[rgamurot 1]

Just as and interesting fact that I discovered, Concorde has (or had I guess) fans built right into each of the main wheels to help cool the brakes. I just thought that was neat when I found out.Ryan GamurotLucky to live Hawai'ihttp://www.virtualpilots.org/signatures/vpa296.png