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Toasty Brakes! (QOTSII)

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To coincide with my post on uncomfortably warm hydraulics in the queen, I'd like to ask for some advice on managing brakes in hot conditions (and when they become very hot.)

I am currently doing a lot of cargo hops between Hong Kong and Nearby Asian Hubs in the 747 v3 (>2 hours.  Mostly to Taipei) as my virtual airline provides better earnings on flying heavies in Asia than at Home on many flights... (Very simplified explanation.). 

When on the ground in the queen taxiing around these hot airports (especially after landing and the airport temperature often in excess of 30 degrees Celsius), I often overheat the brakes even though I do not use the brakes much and only apply them sparingly (I don't slam the pedal down to the floor).  Does anyone have any advice for managing the temperature of brakes?  Any advice or information is appreciated. :)

(I don't know why but I am struggling to write this post in a clear and concise manner...)

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3 hours ago, VHOEI said:

Does anyone have any advice for managing the temperature of brakes?

Brakes get hot by absorbing energy. More energy is absorbed (exponentially) by increasing speed. Keep your speeds reasonable, and manage it with thrust to the best of your ability. Reduce your thrust well before getting to the point where you need to stop or slow down to turn. The plane will naturally slow, and at that point, all you need is a tap instead of a hearty application.

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The temps you are seeing are the gradual heat accumulation from the landing roll and not as much from taxi. After arrival once you get off the runway, keep you taxi speeds to nothing faster than you can already use to turn without brake application. The goal is to creep and that will help you avoid adding additional heat.

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IIRC topcat has a landing performance calculator which can be used to plan runway stopping distance

if you use the autobraking figures from the FCOM you can plan your landing using the minimum level of autobrake which will significantly reduce brake temperatures.

 

don't forget reverse thrust of course. i see many people completely disengage reverse thrust at 80 knots but you can keep it in idle reverse until lower speeds which aids in deceleration without needing to use stronger braking.

 

get into the habit of landing in the proper area of the runway too - if you try too hard to get -50fpm touchdowns you're going to have a lot of floaty landings which will necessitate strong braking especially if you are trying to make a specific turnoff at the request of ATC.

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To reduce the heat input into the wheels and tyres when taxying don't ride the brakes and never apply them with power applied.  At heavy weights you will need some power to break away and keep the aircraft moving, even on a level surface (use 1.08 EPR max with Qantas RR engines).  At light weights (e.g. after landing or taxying for takeoff on a short sector) the aircraft will want to accelerate, so keep your taxy speed below 20kts G/S in a straight line, brake to a slow speed then allow the speed to build up again and so on.  Don't stop the aircraft in a turn because this will center the steering, scrub the tyres which adds heat and it will need a lot of power to start moving again.  As a guide, use 10kts G/S max in a turn on a dry surface and 5 kts or less on a wet or slippery surface. The body gear steering will activate with a tiller input of 20 degs or more provided the G/S is below 15kts and this can aggravate any skid, especially if it happens on a wet surface. The BGS will be locked out if you allow the G/S to exceed 20kts.

On multiple short sectors the heat can build up in the wheels and tyres, so if they are still warm it is a good idea to drop the gear early on the approach to cool them down before landing. Cool the brakes in flight is a much quicker procedure than cooling them on the ground (allow 1 minute for each unit above normal).  For the landing always use autobrake and make the selection based on the stopping distance you want to achieve, which will be determined by the approach KIAS speed, autobrake selection and certain assumptions including airfield conditions up to 2,000ft amsl.  As a guide Autobrake 1 and 2 should be good enough for most routine landings.  Use Autobrakes 3 and 4 when the landing distance is limited in any way; including contaminmated runways.  Max autobrake is rarely used, because if you want to stop in the minimum distance then use full manual braking as it will actually stop the aircraft in a shorter distance - provided you don't float during the flare!  Reverse thrust should always be applied as soon as possible after touchdown because this allows the autobrake system to sense the deceleration and modulate the brake pressure to a minimum; thus reducing the amount of brake energy generated. Idle reverse will almost double the amount of energy the wheels and tyres have to absorb.  You should normally leave the autobrakes engaged until you are below 60 kts G/S and much slower if you are on a slippery runway.

Bertie Goddard 

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Incidentally, always consider shutting down No. 3 engine after landing - a normal procedure in some airlines.  This not only saves fuel it also helps to reduce the amount of brake energy necessary to overcome the forward thrust from the idling engines.

Bertie   

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