Brake temperatures way too cold

[Olli Vainio 0]

I've been thinking there's a bug in brake temperatures for a while now but now I did test this out...I did 3 consecutive rejected takeoffs(at MTOW 285000kg) from about 170 knots using only wheel brakes. Result was that I got brakes only to about 440C and even getting temperature that high was really slow.I did some digging and there's a investigation report on Finnish Accident Investigation Board's website about a situation where there was a RTO situation with a MD11. In this situation the TOW was "only" 263385kg and after this one RTO the brake temps were recorded at over 700 degrees celcius.Surely, there a bug in modeling of the brake temperatures or something?//Olli

[Olli Vainio 0]

Any comments from the developers on this issue?//Olli

[FLEX1978 373]

Are you being serious? Do you really think you can compare 1 real world RTO to a flight simulator? Are you aware of how many factors affect brake temps in the real world? Fair enough there is quite a large difference between the accident investigation report and what your seeing but maybe you should go for a stroll spend some time with your friends, perhaps take your girlfriend out for a meal huh? Rob

[downscc 1,327]

We had a discussion or two during beta testing with MD11 pilots who thought the brake temperature simulations were realistic. A MGTOW RTO is a dangerous event usually resulting in the fuses inside the wheels melting and allowing the tires to deflate rather than explode due to the heat from the brakes and resulting tire fires. This event is not simulated, but I don't think MSFS is set up to accomodate that. Otherwise, the 400C range of temps you can obtain in the simulation are realistic, note how the temps will continue to rise long after coming to a complete stop. That is pretty real.

[Epikk 62]

Hello !Talking about temperatures behavior... there's a funny behavior with EGT after engines stop. In the PMDG MD11, EGT first quickly gets down to about 60-70

[michal 44]

I did some digging and there's a investigation report on Finnish Accident Investigation

I am inclining to believe you may be technically correct. Even "heavy" taxiing alone can raise brake temperatures to 400 C. and for example when Boeing was certifying 767 and performed the so called maximum energy RTO (with aircraft reaching around 170 kts) the brakes reached 1900 C during this test - this is when you get this famous red-orange "glow". But I would not blame PMDG for any shortcomings in this area. These are "extreme" hardware tests and really beyond the normal simulated environment.

[Olli Vainio 0]

Are you being serious? Do you really think you can compare 1 real world RTO to a flight simulator? Are you aware of how many factors affect brake temps in the real world? Fair enough there is quite a large difference between the accident investigation report and what your seeing but maybe you should go for a stroll spend some time with your friends, perhaps take your girlfriend out for a meal huh? Rob

I would compare more RTOs to if I'd have factual data on more than one.I still feel that the temperature behavior is not correct but since almost everyone seems to be ok with it I guess it won't matter...//Olli

[teropa 4]

Hi all,I am also inclined to agree with Olli. (I know him personally btw)It's next to impossible to cook the brakes in this MD-11, which isn't true to life. You can just forget about the brake temps altogether.Stay tuned...Terops> rjprest: you are out of line. It's because of findings such as these that make a great simulation even greater. If you don't have anything constructive to say, don't say anything.

[VHOJT 167]

Incidentally, if you were performing your RTOs at 285000kg, you are nowhere near MTOW. MTOW is approx. 396896kg. That could have some effect on your brake temp! You were performing your RTOs at maximum landing weight! One should hope maximum braking at MLW doesn't cause toooo much of an issue.Edit: That is if you speak of the 744

[Olli Vainio 0]

I've now replicated the EXACT same conditions in the simulator as described in the investigation report.Here is the investigation report(in Finnish): http://www.onnettomuustutkinta.fi/uploads/bl8h7kzdz83c5.pdfFacts as said in the report:TOW 263.3 metric tonnesRTO began at 115 knots using maximum braking and idle reverse.After about 30 minutes the fuse plugs melted on 2 wheels and recorded brake temperature were over 700 degrees celcius.Behavior in FSX with PMDG MD-11 and exact same conditions.I did two test runs and on the first run maximum recorded temperature on the hottest brake was 186 degrees celcius at 6min 40sec after RTO began. On the second run maximum temperature was 187 degrees and also around 6min 40sec after RTO.I understand that I've tested simulator behavior against only one factual report, but given that differences are so huge, I'm not willing to accept it as variance between simulator and real world.Some might argue also that this isn't important, but I disagree, you can't just slam on the brakes on the real aircraft without consequences and you shouldn't be able to in the simulator, either. There's the difference between good and excellent addon.And to VHOJT, if you would actually read my message you would find that I said MD11.//Olli

[mburkhard 23]

Talking about temperatures behavior... there's a funny behavior with EGT after engines stop. In the PMDG MD11, EGT first quickly gets down to about 60-70

[scandinavian13 5,192]

As long as N1/N2 is spinning there's still cool air going through the engine. Once that rotation stops the EGT will rise again before it will finally fall again to reach ambient temperature.Maybe other engines behave different but this is how the MD-11 engines behave...

That's what I was going to point out.This is also related to the reason for engine/APU cooldown periods. As long as air is moving through the engine, it keeps itself cool. Once that air stops, the heat sits in the engine. The engine keeps radiating heat, while the heat is held in by the engine casement, which causes the EGT increase.You're technically supposed to do the same with a car (especially if it is turbocharged), because once you stop the engine, the oil and coolant ceases to flow to cool the parts. Very few people do this, in either case. Some do, however: see "turbo timers".As for the original issue, I read the document and I find the same information in it (it's written in Finnish, just a warning), though I don't have the MD-11 to run in the sim. There is a discrepancy, to be sure, but perhaps it is not an issue with the programming of the MD-11, rather the FSX engine. I'm not sure, as I programmed neither.Before someone makes a weather comment, the weather is stated in the document to replicate the conditions, but an ambient difference in 10C when testing brake temperatures of 200C+ really doesn't make a different in friction temps.Cheers,Kyle

[downscc 1,327]

I stand corrected on the brake temp issue, it's being discussed by the PMDG gurus today, and there is a write-up on it.However, I want to a comment to: "You're technically supposed to do the same with a car (especially if it is turbocharged), because once you stop the engine, the oil and coolant ceases to flow to cool the parts. Very few people do this, in either case. Some do, however: see "turbo timers"." The turbo timeout is to allow the impelller to spin down before removing oil pressure, most cars now have a goose neck to keep oil on the bearing. The Teledyne TCM TSIO-520 in the C-414 I fly don't, so if we had a quick taxi to ramp we will sit on the ramp idling for a minute to let the turbos spool down and cool a little before pulling the mixture off.

[VHOJT 167]

A relative's Volvo had that strange feature! It was weird when I first drove it, I thought it had a mind of its own. Knowing what it does, it's interesting car manufacturers don't offer it much on turbo cars. Once I figured it out, the number of people who would tell you, 'you left your car on' was unbelievable!PS forgot this thread was so far down, sorry to bump it up with that!

[Epikk 62]

This is correct and these temperatures and timings are straight from the simulator (where you are allowed to move the fuel lever to ON to continue to read EGT after shutdown).As long as N1/N2 is spinning there's still cool air going through the engine. Once that rotation stops the EGT will rise again before it will finally fall again to reach ambient temperature.Maybe other engines behave different but this is how the MD-11 engines behave...Markus

Thank you very much Markus! Just learned something new... And yes, other engines behave different. Cheers.