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Old 22nd Feb 2005, 11:49   #1 (permalink)
Hudson
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How hot are Hot brakes

It is good airmanship to check the temperature of the brakes during a walk-around inspection between landings. However, without a brake temperature gauge in the cockpit to read specific figures, it becomes a matter of subjective assessment based on experience.

One Boeing instructor told me that if you cannot hold your hand on the brake assemblies without burning yourself, then by definition the brakes are hot and appropriate time factors should be applied. I also read that in one of the early editions of the Boeing Airliner magazine.

With the trend for 30 minute turn-arounds, one man's hot brakes is another man's warm brakes. In one small airline I operated with, you could tell which pilots had flown the previous leg as some were heavy footed and you could invariably rely on a hot brake walk-around, while other pilots were better operators and used accurate threshold speeds coupled with proper reverse thrust and judicious use of manual brakes. Result was cool brakes and no risk of burning your hand. Autobrakes always heated up the brakes, which is why we did not use autobrakes unless absolutely necessary (slippery short runway, very strong crosswinds and short runway etc).

I would be most interested in other views on the subject of how hot is hot in terms of your own the walk-around check. More to the point what do you do about it - especially on quick turn-arounds.
 
Old 22nd Feb 2005, 12:13   #2 (permalink)
 
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Quote:
One Boeing instructor told me that if you cannot hold your hand on the brake assemblies without burning yourself, then by definition the brakes are hot
I would never touch a brake after a landing, you're likely to suffer extreme burns. Sorry but I've never heard anything so ridiculous in 20+ years.
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Old 22nd Feb 2005, 12:20   #3 (permalink)
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Not answering the question at all but...

I seem to remember reading somewhere that brake temperature must be below a certain temperature (obviously it varies by type) before departure, such that the brakes are sufficiently cold to deal with RTO. Does this figure change with runway length, take-off weight etc. or do manufacturers apply a blanket figure?

I wonder what impact brake cooling rates have on turnround time, and would LoCo's be more prone to using thrust reverse rather than brakes in order to keep temps down (I imagine it would also keep wear down if brakes are on-condition items, however I am completely ignorant of whether they are or not)
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Old 22nd Feb 2005, 17:11   #4 (permalink)
 
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Check temp gauge on lower ECAM!!!
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Old 22nd Feb 2005, 18:30   #5 (permalink)
 
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Hudson very interesting question!

C Prop, even if you have one im not sure completely addresses the problem. To the best of my knowledge Boeing test useing half worn cold brakes, Im not sure there is any data available, other than advisiory for any other config.

Quick turn and brake cooling schedule charts only, as im sure you are aware adress the fuse plug issue and not the ability of the brakes to absorb the energy during a high speed abort, I believe crews are misled in this area.

I personally agree with your Boeing instructor, and while i dont actually touch em I do get close!

What do I do about it, as you said try to plan a landing which will result in the coolest brake temp, and rarely flex after a short landing with a quick turn.

I am interested to hear views on releasing brakes after shutdown.

Rgds
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Old 22nd Feb 2005, 19:47   #6 (permalink)
LEM
 
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On the classic, there is no gauge, so after a crew change there's little you can do about assessment...

I personally approach my hand to the brake assembly, WITHOUT touching, just to have a vague idea... but actually, there is no way in which we can make a GO- NOGO decision.

If the previous crew landed below the max quick turnaround weight, then it's safe to takeoff. Period.

Personal assessments are b******* over these grounds, I think.

Re the need to release the brakes after parking: no doubt it's good airmanship to do that ASAP.
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Old 22nd Feb 2005, 23:45   #7 (permalink)
 
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On the B727 ,didn't have any Indication of 'how warm the brakes were'but if the station stop was less that 45mins-with high ambient temps one was advised to allow the gear to dangle in the slipstream for a period to avoid 'Hot Gear/fire 'indications...
Used to watch BA747 dangling the gear enroute to SEA from YVR,to have the gear 'cool' for the heavy Takeoff ex SEA-LHR.
On the 320 we had temp' indication-Auto brake LOW provided uniform temps which didn't seem to be a problem at Takeoff time,as opposed to heavy footed arrivals requiring some delays (or the gear fans if equiped)....
cheers..
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Old 23rd Feb 2005, 12:32   #8 (permalink)
 
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767

350C approx threshold from normal to hot
>410C is hot
will read up to >670C
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Old 23rd Feb 2005, 14:28   #9 (permalink)
 
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LEM, you could be one minute below quick turn time, a long taxi and subsequent high speed RTO near brake engery, and fuse plug melt temperatures could result in increased stopping distances and or tyre deflation. You are operating in an area that was not tested and is as far as I know not required by any agency, can you imagine the complexity of the charts, or the restrictive nature of those charts.

I appricate there is much fat built into the quick turn and brake cooling schedules which are regulatory requirements for (fuse plug) no melt requirements, however I do not believe the issue is quite (period) as you said, I am talking about a highly unlikely combination of events, however!

If you have access to a document which contridicts what I have said could you please direct me, the information I have is from a type specific perf engineers course at Boeing, could be that maybe I misunderstood, it was quite some time ago.

Many thanks
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Old 23rd Feb 2005, 15:21   #10 (permalink)

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I know that AP Racing use stick on thermometers to measure individual caliper temperatures when testing new brakes, and on race cars during events. They are the multi colour types and have a greater temp range than you would require (amazing how hot you can let stuff get if you don't care about durability)

Would that be the sort of thing that a Flight Safety/Engineering dept. would be interested in putting on to see what was happening in the real world? Cost is minimal, in the order of a couple of s each. Wouldn't have thought it would be a check every time thing, but would be usefull to get a "feel" for what did what to the temps. It could also act as a condition monitoring device, i.e. why is that one higher than that one? Could pick up a dragging brake that might not be felt.
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Old 23rd Feb 2005, 20:49   #11 (permalink)
 
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Crikey Hudson, are you sure that Boeing instructor was not pulling your leg?

!!! NEVER TOUCH THE BRAKES WITH YOUR HANDS !!!

I check my brake temps on a turnaround by touching the tyres with the back of my fingers. This will give an approximate indication of brake temp.

The back of the fingers trick I learnt from a fireman on one of my refresher courses, this is how they check the temp of a door or similar to judge how hot the fire is behind it. They use the back of the fingers because a) They are less sensitive so will be less painful if burnt and b) If an object is very hot the fingers will involentarily close around the hot object and you can't let go!

Back to your question. I cant quantify it but having touched my tyres on every turnaround I have ever done, I now know when they feel hot. If I find hot brakes (rare) I will get the F/O to touch the tyres as well to make the point about the relationship between braking techniques and brake temperatures.
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Old 23rd Feb 2005, 22:12   #12 (permalink)
 
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Hot Brakes

Simply put - your aircraft brake disks, apart from creating high friction on demand, are a repository for energy you want to throw away.

The design of the brake units must be capable of absorbing close to ALL of the energy you have built up on a take off when you abort and execute a desperate stop.

Nearly All of that energy is converted to heat.

If you start off with brake units already storing a lot of heat then your capability to subsequently complete an accelerate -stop is voided. You will end up in a heap !!

Nurse them guys and appreciate their limitations.
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Old 24th Feb 2005, 01:48   #13 (permalink)
 
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Lightbulb

If there are no gauges fitted there are some other accurate ways to tell brake temp visually:

Remeber the fish tank colour strips/stickers that changed to show the colour on the side? The were accurate to 1*c so something similar could be made or look at

Rally/Race car or high performance brake kits from Brembo or AP racing have 3 colours green, yellow, red paint that goes black when the max safe temp was exceeded and therefore the disks have to be changed.

This is especially true for carbon/ceramic applications as they have very high oxidation temps that when exceeded tend to burst into flames and braking effort fades gracefully away.

Look at the problems Porsche is having with its Ceramic Composite Braking system.
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Old 24th Feb 2005, 05:05   #14 (permalink)
 
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I do the similar way as CaptainSandL. Put the tip of my fingers onto the inner part of the tyres closest to the rim or wheel. After some practises,you could develope a scle yourself.
My company used to operate 737-400 (landing wt 54,884kg) into strip with 5600ft in lenght. The strip is so short that its markings are a set of Ls painted white known as Boeing markers.(boeing reckon if you don't land within the markers you won't makeit at the end!). Those landings heats up the brakes alot. you can see the white smoke comes out from the brakes everytime. 9 years on and not a single burst tyre or overrun! Nowadays the shortest we do is 5900ft. Smokes still but not as much. DON"T PUT YOUR HAND IN WHEN IT SMOKES, NOT EVEN THE TYRES!!
Cheers!
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Old 24th Feb 2005, 05:26   #15 (permalink)
 
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Blow Out Plugs

Anyone know the temperature at the blow out plugs when they are supposed to let go and any relationship between maximum design brake pack limit and the blow out plugs.?

Presumably the plugs will blow sometime after a brake pack reaches max temp. due time taken for the heat to reach the plugs.

The fire service guys should know and then give firm advice regarding liquids quelling brake fires. Have seen the result of that. Everthing comes apart with a huge bang which can be fatal to those too close.

Then there was that Caravelle which had been used to run to and fro along a Swiss runway to clear fog. Some time after the gear was put in the holes the resulting fire was terminal..
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Old 24th Feb 2005, 07:34   #16 (permalink)
 
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I seem to remember the 'plugs' let go about 500 degrees(had them up to 480 on a 'reject'320)...True some of the tires settle quit a time after the aircraft has stopped,after rejects,as you say the heat builds......
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Old 24th Feb 2005, 07:44   #17 (permalink)

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Quote:
Remeber the fish tank colour strips/stickers that changed to show the colour on the side? The were accurate to 1*c so something similar could be made or looked at
These exist and were what I was talking about above. the technology that AP Racing and the like use in raceing cars is incredible.

For 1 season they made Berylium calipers for F1 before they were banned, excellent properties from an engineering standpoint, but the dust/swarf was cancerous, machining could only be done in 1 factory in ex USSR and one in USA, and the billet of material for each caliper was something over 10,000.

If you were to give them a ring I'm sure they would send you a couple of temperature strips to play with.
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Old 24th Feb 2005, 09:10   #18 (permalink)
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Measuring hot surfaces

I would suggest an Infrared Thermometer.
Just point it at the brake disc, tyre or whatever surface you want to measure, (your colleageus forehead if fever is suspected being the reason for strange behaviour)
and you will get a reading with a few % accuracy.

The ones I know measure up to 500 C

It is a handheld thing sold at around 150 EUR.
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Old 24th Feb 2005, 22:37   #19 (permalink)
 
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oldebloke

How did you know the blow out plugs reached 480 degrees?

Has anyone been close to one when it let go?

And when one does lets go is the rim a throw-away or does maint just screw in a replacement?

And now you have me wondering what the metal composition is - must be some sort of alloy.
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Old 25th Feb 2005, 00:38   #20 (permalink)
 
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Milt,

I can't answer the first 2 questions, but..

Q 3. New plugs are "screwed" in, they are designed to protect the tyre and the rim

Q 4. They're made of a Stannic (Tin) alloy.

Regards,

Old Smokey
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