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OAT cold, brakes hot?


Stu Antonio

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Stu Antonio

Is it just me or does this issue still exist where in cold outside winter temperatures, the brakes get way hotter than on landings in summer?
I have 350+ pretty much at every landing these days, even though I'm landing not particularly heavy and with LOW brakes most of the time.
Can't recall this being the case a few weeks/months ago. Then again, it could be the good old Mandela effect :)

Anyone else got the feeling? 

 

 

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Darcy Coutts
2 hours ago, Stu Antonio said:

Is it just me or does this issue still exist where in cold outside winter temperatures, the brakes get way hotter on landings than in summer?
I have 350+ pretty much at every landing these days, even though I'm landing not particularly heavy and with LOW brakes most of the time.
Can't recall this being the case a few weeks/months ago. Then again, it could be the good old Mandela effect :)

Anyone else got the feeling? 

 

 

I agree, I get hot brakes almost every time now and I am very careful how I use them.  

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Peter Pukhnoy

I believe it's because the sim reports the aerodrome surface as being covered in ice during hard winter (or even just winter, I don't remember).

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Daniel Corbe

OAT affects the brakes far less than precipitation does.  If you use the brakes, they're going to get hot no matter what the temperature is.  

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Stu Antonio
4 minutes ago, Daniel Corbe said:

OAT affects the brakes far less than precipitation does.  If you use the brakes, they're going to get hot no matter what the temperature is.  

Well yeah, of course brakes are getting hot. What I‘m saying is that there once was a bug with the FSLabs that produced overly hot brakes specifically with cold outside temperatures and that I suspected (not implied) that this bug may have returned. I could be wrong. So I‘m asking for any similar observations by fellow users, that‘s all.

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Konstantin Lysenko

Same here. Even at the cruise where SAT is - 62 C brakes have +50-60 degrees. When using brakes in below zero temperature, they are getting hot much faster for some reason. 

Konstantin 

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Mark Adeane

Is it because - correctly or otherwise -  the brakes are working harder to achieve the specified decel rate on a low friction surface perhaps?

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ay.m3r1ck |3ern4rd
1 hour ago, Mark Adeane said:

Is it because - correctly or otherwise -  the brakes are working harder to achieve the specified decel rate on a low friction surface perhaps?

Shouldn't it be the opposite, lower grip / friction means you can't brake as hard? 

 

Also, it should take longer to reach hot brakes temp threshold when starting from - 20 than +30deg C! 

 

I am experiencing the same btw! In small Nordic airports I get 60-70deg brakes  when lining up, after 5 minutes of taxi only and with - 15 OAT. 

 

 

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António Abreu

Hey,

I'm also getting hot brakes (over 350 degrees Celcius) on almost every landing, even with OAT around 0 Celcius and very light aircraft (around 30 pax). There must be something wrong, I can't believe this is real but maybe a real world Airbus pilot could comment ...

Happy (and hot) landings

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Khoa Nguyen

I did some trips in and out of EDDF recently, OAT was in a range between -2° and 5°, LOW Brk, I havent got break hot yet

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Robin Locher

Hi, I also get hot brakes, with a 319 and AUTO BRK LOW. Arround 300 degrees.

It was in winter, and OAT around 0 degrees

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Tim Smith

Just landed in Munich 26L, 0c oat, no precip. Autobrake Medium and full reverse, only light manual braking from about 65kts down. Brakes were near 500c pulling onto the stand. Don’t think I’ve ever seen them so high in normal operations. 

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Stu Antonio

Okay, so I think have to take back my initial suspicion, it appears as if this may be a case of false perception :)

I created a test environment (no weather, same plane weights/settings etc.) and tested two OATs. I selected TOGA, accelerated to 120kt and did an RTO without revers thrust, brought it to a hold and waited. The outcome for both test-OATs was exactly the same each time (I did each one 5 times). There is no indication that a lower OAT creates hotter brakes. In fact, the way it's simulated looks pretty legit to me.

There might be other tests that could be done (taxi, landing), but in this environment, I have to say everything seems to be correct. :)

 

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Peter Pukhnoy
1 hour ago, Stu Antonio said:

it appears as if this may be a case of false perception

You were looking at the wrong thing. You have hot brakes because the surface is icy in winter at all times in the sim.

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Stu Antonio
17 minutes ago, Peter Pukhnoy said:

You were looking at the wrong thing. You have hot brakes because the surface is icy in winter at all times in the sim.

Oh damn, you are right! 
I did another test, this time not only -2 deg but I also set it to winter (which I didn't do before), and the temperatures went up fast... 
So that's the reason for the hotter brakes in winter.... Not the aircraft itself but the "always icy" runways... 

f16cmpU.jpg

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Bryan Richards

Kind of makes sense because the autobrake, even on LOW has to work harder on a slippery surface to achieve the programmed rate of deceleration. So it's not so much a bug of the fslabs, but rather a fault of the sim always having icy surfaces

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Holger Teutsch

Hhhm, when bringing an aircraft to a complete stop energy of motion is converted to thermal energy by aerodynamic drag (+ reversers)  + rolling drag + braking. The first one is only minimally affected by OAT.  The second one is very low even on a dry runway. So the remaining energy in converted to heat in the brakes. Why should that be higher on an icy runway?

See "Getting to grips with cold weather operations" chap. C. (figure C6)

Any real pilot here who can confirm that icy runways result in hot brakes?

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Mateusz Chalupniczak
22 hours ago, Bryan Richards said:

Kind of makes sense because the autobrake, even on LOW has to work harder on a slippery surface to achieve the programmed rate of deceleration. So it's not so much a bug of the fslabs, but rather a fault of the sim always having icy surfaces

I believe you are incorrect here, on slippery surfaces brakes have to work lighter in order for the wheels not to skid. Therefore landing distance is significantly extended.

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Stu Antonio
13 minutes ago, Mateusz Chalupniczak said:

I believe you are incorrect here, on slippery surfaces brakes have to work lighter in order for the wheels not to skid. Therefore landing distance is significantly extended.

But that would contradict the AutoBrake logic, that tries to archieve a certain amount of decelleration rather than applying an equal brake force each time. This whole thing is very very technical I guess. 

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Mateusz Chalupniczak
30 minutes ago, Stu Antonio said:

But that would contradict the AutoBrake logic, that tries to archieve a certain amount of decelleration rather than applying an equal brake force each time. This whole thing is very very technical I guess. 

You see logical error here :lol: key is that they are trying to achive certain decel rate, not achivieing. 

In normal dry conditions using reversers doesn't affect landing distance since the decel rate is the same for both reversers and autobreaks.
But in wet/slippery conditons autobreaks won't work as effective becuase of mentioned skid effect (and anti-skid system that releases brakes).

So in order to reduce landing distance you use reversers that a) takes away some "work" from brakes b) less brake "work" means less frequent anti skid so they are working steadier (better)

Hope it makes sense. :c

 

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Bryan Richards
56 minutes ago, Mateusz Chalupniczak said:

I believe you are incorrect here, on slippery surfaces brakes have to work lighter in order for the wheels not to skid. Therefore landing distance is significantly extended.

I see what you are saying. 

I always thought of it that if on a slippery surface if the deceleration rate for a given autobrake setting is such that it would cause the the wheels to skid, the anti-skid system would release the locked wheel and then the autobrake would then reapply braking, to try again and repeating the process. 

So in that case, just like how a single brake application is better for brake temperatures than multiple smaller or shorter braking applications when taxiing, I figured the same would apply here. Because of the anti-skid, the autobrake has to apply multiple brake applications to try and achieve the decel rate, and because the plane isn't slowing down because of the skid and anti skid system, the autobrake would use more brake pressure. 

 

Hope the way I typed it out makes sense, it's much clearer in my head lol. 

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Peter Pukhnoy

Does FSLabs actually model skidding on slippery surfaces? I don't think it would make much sense given the crude nature of the surface condition simulation in the sim.

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Stu Antonio

I haven‘t yet experienced difficulties maintaining the centerline.

I do however experienced a (heavy) A319 starting to roll from a full stand even with idle thrust in a CFM (just like the IAEs use to do). No idea if that also has to do with the winter-all-surfaces-are-icy-issue.  

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8 hours ago, Stu Antonio said:

I haven‘t yet experienced difficulties maintaining the centerline.

I do however experienced a (heavy) A319 starting to roll from a full stand even with idle thrust in a CFM (just like the IAEs use to do). No idea if that also has to do with the winter-all-surfaces-are-icy-issue.  

Did you have engine anti ice on?  Trying to taxi the A319 IAE with EAI on was a nightmare! Thing was just running away from me. Brake temps of 200c by the time I got to the runway. 

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Stu Antonio
54 minutes ago, Tim Smith said:

Did you have engine anti ice on?  Trying to taxi the A319 IAE with EAI on was a nightmare! Thing was just running away from me. Brake temps of 200c by the time I got to the runway. 

Anti Ice makes it worse, but there is definitely something strange here.

I just tested it on my current flight: Sitting in an fully loaded A321, OAT -2C, GW 81.3 tons, CFM engines, engine anti ice off, N1 idle 18.8% ..... and when I release the parking brakes, it starts moving! It's the same across all CFMs these days, I can't recall this ever happening before.... I suspect P3Ds "winter logic" messing something up. But IDK.

Here's a video:

 

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Andre Heilscher
22 hours ago, Stu Antonio said:

Anti Ice makes it worse, but there is definitely something strange here.

I just tested it on my current flight: Sitting in an fully loaded A321, OAT -2C, GW 81.3 tons, CFM engines, engine anti ice off, N1 idle 18.8% ..... and when I release the parking brakes, it starts moving! It's the same across all CFMs these days, I can't recall this ever happening before.... I suspect P3Ds "winter logic" messing something up. But IDK.

 

 

Hi Stu,

if you have low temperatures, you will get more oxygen in the air. So the turbines get better fuel burn and that gives you more power. This is like the real thing. The impact of the slippery surfaces can increase that feeling of course.

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Stu Antonio
Just now, Andre Heilscher said:

Hi Stu,

if you have low temperatures, you will get more oxygen in the air. So the turbines get better fuel burn and that gives you more power. This is like the real thing. The impact of the slippery surfaces can increase that feeling of course.

Very interesting. I had something like that in mind, but I thought that 15-20 degrees diffrence in temperature couldn’t possibly be enough to suddenly move 80t at idle thrust.
I imagine a half booked IAE A319 in cold weather with anti ice on must be a nightmare to taxi then :) 

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