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Chokdee
13th Aug 2002, 17:48
Any ideas on which assembly gets the hottest, fwd or aft. Thanks.:(

spannersatcx
13th Aug 2002, 20:32
Both the same.

john_tullamarine
14th Aug 2002, 01:48
... interesting .... unless the cooling or brake design is appropriately different, I would have expected the leading axle assembly to carry the higher load and experience the higher temperatures ..... ?

Kotare
14th Aug 2002, 01:56
Aft - shielded airflow

QAVION
14th Aug 2002, 04:04
"I would have expected the leading axle assembly to carry the higher load and experience the higher temperatures ..... ?"

If the temps are the same, as Spanners has no doubt observed, would antiskid/ torque-limiting systems play a part in this?

Rgds.
Q.

P.S. If AS and Torque-limiting have no effect, and they are still the same, perhaps the fronts do bear the higher load, but due to sheilded airflow at the rear, the front/rear temps work out at about the same value?

P.P.S. That's what I like about PPRuNe... You can get a number of different, sometimes opposing answers, but still feel more the wiser :)

Shore Guy
14th Aug 2002, 08:37
Perhaps a bit of thread creep here, but in the last couple of years have flown my first aircraft with brake temperature indicators (767-300 Ė understand itís an option, not standard equip.). I have noticed no difference between front and back axle temperatures. What I have noticed, and it came as a bit of a surprise, is the large difference in brake temperatures on upwind/downwind trucks landing in a crosswind. There are consistently higher temperatures on the downwind truck when landing in a crosswind. Seems myself and every other pilot I have flown with are using a bit more brake than we realized in conjunction with the rudder to keep the aircraft tracking straight after touchdown.

spannersatcx
14th Aug 2002, 14:54
Just done an 18 wheeler and all 16 brake temps read the same within 1 unit of each other.

sky9
15th Aug 2002, 16:56
Shoreguy
It might be that it is easier to apply brakes with your foot further away from you than nearest to you (the rudder pedal will be pointing towards the downwind side).

Another interesting point is that carbon brake temperatures stay lower with one hard application rather than after extended taxiing. I know that wear is less, however I was not expecting a brake temperature of 1 after a firm brake application to make the apron taxiway; and it didnít rise during the turnround either.
:)

BN2A
15th Aug 2002, 17:01
Higher temp on the downwind truck.....
Shielded Airflow again.
:D :D :D

Dan Winterland
16th Aug 2002, 23:10
This question appears in the 'How to pass your Cathay interview' book - perhaps why the Q was asked. I gather, the official answer is the front units - dunno why.

I've noticed the downwind brakes getting hotter on the EICAS page too. I suspect it's because the into wind wing generates lmore lift therefore applying more downward pressure on the downwind wheels making the braking action more effective. After all, the main reason for deploying spoilers on landing is to apply weight to the wheels earlier and make the brakes more effective.

1515Blue
19th Aug 2002, 21:51
I believe the wheels up front heat up more because it carries more weight since weight is shifted forward when braking. its the same reason why cars have drum brakes up front because they get more heat.

Dan Kelly
20th Aug 2002, 02:24
1515Blue,

Where do you live? I haven't seen a car with drum brakes on the front wheels for near on 15 or more years!

fruitloop
20th Aug 2002, 02:43
Dan
I think most realized the mistake in 1515blue's 'comment' :D

"Which gets hotter ?"Good question !!I'm sorry but not being a "pointy ender' I can't answer that but as to which has the shortest life,from experience on the 762/3 it is the 'front of the bogie and on the 742/3 generally the inboard bogie front !!

Cheers

Cough
20th Aug 2002, 11:02
Sure that I have posted this link before, but there was an article published in the Boeing Aero rag a little while ago on this subject.

Tis Here (http://www.boeing.com/commercial/aeromagazine/aero_17/brake_story.html)

1515Blue
20th Aug 2002, 16:03
sorry dan, i meant disc brakes. haha

2daddies
20th Aug 2002, 16:53
Folks,
Although it may vary on different types, the simple theoretical answer is that the REAR brakes on any given bogey get hotter for two related reasons;

1) The heat from the front brakes radiates to the rear, adding to the heat caused by the rear's normal braking action.

2) The front tyres and wheel assemblies block airflow from cooling the rear's brakes.

Actual relative brake temperature on any given aircraft type will vary depending on ambient conditions, length of taxi, brake usage, bogey design, brake wear and condition, tyre creep etc etc etc.