XML Brake TEMP?

[mgh 89]

That's a clear and realistic explanation of what actually happens. The process, as you say, is dynamic and any temperature rise can only be calculated by integrating the heat flows in and out of the braking system with time. A consequence is that temperature can continue to rise even after the aircraft has stopped as heat continues to flow from the hottest parts. Before an aircraft can be released for takeoff it must be capable of braking safely if the takeoff has to be aborted. In the case of short turn round times it's possible that the brakes have not cooled suffieciently after the landing to permit this.On the B757"Wheel brake temperatures are displayed on the EICAS status page. Numerical values related to wheel brake temperature are displayed for each main gear brake.Brake temperature values range from 0 to 9. Temperature values are not instantaneous and tend to build for 10 to 15 minutes after brakes are applied.Initial range values of 0 to 2 are cyan numbers in a cyan box. For normal range values of 3 and 4, the number is cyan and the box is white for the first per truck that exceeds 2. Values in the high range of 5 to 9 have a white number and box.The BRAKE TEMP light illuminates for values of 5 and above."http://www.757.org.uk/systems/sys8.htmlModelling a realistic brake temperature system is not a trivial matter and needs more than simple equations.

[n4gix 4,947]

>>Converting joules to celsius, we get 4777

[Guest jahman]

>1 joule is equal to 0.000526565076466 celsius heat unit.So you're actually not converting "joules to celsius", you are converting "joules to celsius heat units".From http://www.sizes.com/units/celsius_heat_unit.htm we can see thata "celsius heat unit" is "the quantity of heat needed to raise the temperature of a one-pound mass of pure water at 1

[martinboehme 492]

> I only just got back to this thread. Anyway, I'm not sure the horse knows it's dead!Just to clarify what unfortunately seems to have been an ambiguous expression: By "dead horse" I was referring to the question of specific heat, and not to any poster on this forum. I thought that was clear, but maybe it wasn't...Cheers,Martin

[ozbeowulf 0]

Hi, Bill...I am happy to see your post and relieved to learn that I'm not the only one who is bemused by all the useless caterwauling.Cheers,Glenn

[mgh 89]

This thread has polarised between those who understand some of the basic physics involved and appreaciate that there is no simple realistic solution and those who don't and think that there is.For a simulation to be worth while it surely must have some relation to reality, ie to the physics involved. As I pointed out an a previous post measured brake temperature continues to rise even after the aircraft has stopped and it can take some time after that for it to fall to ambient levels. Surely any worthwhile simulation needs to reflect this basic behaviour?

[martinboehme 492]

OK, after getting that clarification out... just a few things I wanted to add. (Don't worry, there's a problem solution coming up in the second half of the post. ;) )First of all: People, can't we keep this factual, please? When someone makes a statement in a forum that seems to be wrong, that's not an invitation to start being unpleasant to them -- it's an opportunity to contribute by politely and factually putting right what looks wrong to you.That's the reason I jumped into this thread in the first place... I was hoping to get the thread back on track by injecting some facts. It's somewhat disappointing to see those posts getting largely ignored... Bill, I agree that what the original poster wanted was a solution, not a physics lecture. A workable solution will not be able to calculate all of the physical intracacies of what's going on, because they're much too complicated... but at the same time, it needs to be inspired by the underlying physics to obtain realistic-looking behaviour. Also, understanding the physics is useful because it tells you what you don't need to account for -- no need to find out what the brake pressure on your simulated aircraft is because, unless you get all of the other stuff accurate as well (which IMO is very, very hard to do), it's not going to do you much good.So in the spirit of discussing solutions, here's my suggestion for a simple approach that still shows fundamentally the right behaviour:A few times a second, do the following:Take the time difference between now and the last time you updated the brake temperature. Call it dt.Update the brake temperature according to the following formula:T_brake = T_brake + dt*(-c1*(T_brake - T_air)*v_air - c2*(T_brake - T_air) + c3*brake_strength*v_ground)T_brake is the brake temperature, T_air is the air temperature, v_air is airspeed, v_ground is ground speed, and brake_strength is the FS variable that tells you how hard you're applying the brakes.c1, c2 and c3 are constants that you'll have to adjust until the behaviour is realistic. It's probably easiest to do this outside of FS at first -- write a small program that sits in a loop evaluating the formula above, then plot the results. Adjust the constants until you're satisfied with the behaviour -- roughly, c1 controls how quickly you lose heat due to the air moving past the brakes, c2 controls how quickly you lose heat at rest, and c3 controls how quickly the brakes heat up from a certain amount of braking.Cheers,Martin

[n4gix 4,947]

>That of course is not a statement of fact but merely your>opinion. Actually, those of us delving into brake system>"physics trivia" are the ones giving the original poster the>solution! ;-)We are obviously speaking of entirely different paradigms. I maintain that what is required is merely to replicate the "expected behavior" of a system using a simplistic model that - truthfully - need not have anything to do with physics.If the end result is a numeric display that replicates the behavior described in - for example - the B757 'mgh' cited, the specific method by which that simple display is generated is frankly irrelevant!For sim purposes, I adhere strictly to the K.I.S.S paradigm... :)

[martinboehme 492]

>We are obviously speaking of entirely different paradigms. I>maintain that what is required is merely to replicate the>"expected behavior" of a system using a simplistic model that>- truthfully - need not have anything to do with physics.Full agreement!The problem I see with Ed's original suggestion is that it looks as if it is physically accurate, but isn't... if you use it, you'll waste time trying to find the values of constants (the coefficient of friction, the brake pressure) that won't end up giving a realistic result. Better to just throw in an arbitrary constant and tweak it until the result is right...Cheers,Martin

[WarpD 824]

And yet:c3*brake_strength*v_ground = fpVI didn't toss out all the other code to manipulate air cooling, etc... expecting the user would extrapolate further on their own.Unfortunately what ensued was patently absurd.So, by all means... tell me my formula is wrong... while you have the exact same equation buried in your response.Like I said... just don't need this kind of junk.

[martinboehme 492]

>c3*brake_strength*v_ground = fpV[...]>So, by all means... tell me my formula is wrong... while you>have the exact same equation buried in your response.No discussion about the structure of that formula -- in fact, I used it, albeit with different variable names, back in #36229, calling it "Ed's formula".My only point was: If we want to input real, physical values into the formula and get a result that makes sense, then p has to be not pressure but force, and we have to interpret the result not as heat but as power. Alternatively, we can just plug in an arbitrary "fudge factor" (call it c3) and tune that until we get the results we want to see.So I certainly didn't want to imply that your post was entirely wrong, or unhelpful, and I didn't mean to offend you; if I did so inadvertently, I apologize.Shake hands and make up?Martin

[Guest jahman]

Ed,>Unfortunately what ensued was patently absurd.I have re-read the posts are this thread has gone wrong because of *YOU*.In your post http://forums.avsim.net/dcboard.php?az=sho..._id=36096#36209You Say:QUOTEAssuming the following:f = friction coefficient of the brakes = 0.50p = pressure of the brakes = 3200 psiV = velocity = 250kts250kts = 128.6 meters per second0.50 * 3200 * 128.6 = 205760 joules205760 joules = 108 degrees C = 227 degrees FUNQUOTESo YOU are the one bringing physics to bear!Then when mgh points out, respectfully, factually and rightfully, that "205760 joules = 108 degrees C = 227 degrees F" is wrongwithout any provocation whatsoever you reply to mgh in a really RUDE and BOORISH manner:QUOTETo be blunt, you've just jumped into something as if you're the world's foremost expert on the subject. Well, you're not... and you're wrong. End discussion. Seriously.UNQUOTESo to recap, you are the one to bring the physiscs to bear, then you are rude and boorish when somebody points out that you have made a mistake in your equations and finally you pretend to end the discussion by weathervaning that the physiscs you brought to bear in the first place isn

[martinboehme 492]

>finally you>pretend to end the discussion by weathervaning that the>physiscs you brought to bear in the first place isn

[WarpD 824]

Like I said... Martin posts it... it's correct, I post it... it's incorrect.It's the same formula to calculate heat generated. Identical. Yet his is accurate and mine is not.By all means, explain.

[David Roch 1,982]

"When someone makes a statement in a forum that seems to be wrong, that's not an invitation to start being unpleasant to them -- it's an opportunity to contribute by politely and factually putting right what looks wrong to you."Nothing to add to Martin's wise words.Guys, this forum is one of the most interesting ones.Let's keep it also as pleasant as possible.Thanks