Brake pre-heating in F1?

[AshMcConnell]

Hi Folks,

Do they have any kind of brake heating system in F1, the equivalent of tyre blankets, to bring them up to the operating temperature?

I don't remember it ever being mentioned in the coverage, but I can see why it could be useful.

All the best,
Ash

[riff_raff]

AshMcConnell,

With the carbon-carbon brakes used in F1, temperature control is an important issue. Due to CRC's unique friction properties, the brakes do work best at somewhat elevated temperatures. But the brake cooling airflows must be designed to keep the brake rotors, calipers and hubs within acceptable limits under worst case braking conditions. So the brakes are naturally overcooled the rest of the time. Even if the brake rotors were preheated in the pits, by the time the car hit the end of the pit lane, the brake rotors would already have cooled down again.

Good question though.

[AshMcConnell]

Hi Riff Raff,

Thanks for the reply.

I didn't realise the cooling was quite so violent. So you think that ambient temperature is a sensible starting point for the brake temperature for our simulation?

We are currently simulating using Heat Capacity, Air Temp, Surface Area, Velocity and of course braking as factors. It seems to have reasonable behaviour at the moment, but we will have to tweak when we get some representative data. Would you have any specific data? (Assuming it doesn't break any NDAs).

Thanks for your help!
All the best,
Ash

[riff_raff]

Ash,

While CRC brake rotors can tolerate much higher temps than metal rotors, they still have limits. CRC can oxidize if the surface temperature gets too high.

Brakes create heating in the rotor mass through surface friction. The heat is dissipated through convection to the passing airflow. If you want to simulate brake temperatures, you have some of the basic information you'll need, such as rotor material specific heat, surface area, ambient air temp and velocity, and heat input rates.

You'll also need the thermal conductivity of the rotor material, which can be a bit tricky with CRC. The rotors are normally vented, so some of the convective heat transfer occurs within the vents, and some occurs at the rotor friction surface. But due to the lower thermal conductivity of CRC, the friction surface will be much hotter than the vents.

Keeping the friction surface of a CRC brake rotor within its oxidation limit (around 1800degF) is important. So a good starting point for your heat transfer analysis case would be to calculate the allowable heat input rate at the rotor friction surfaces such that these surfaces stabilize at 1800degF max, assuming steady state conditions for all other variables. This simplified case is not representative of what actually occurs during an entire braking event, but it's a good place to start.

I hope that helps, and good luck.
riff_raff

ps. I honestly apologize if I've given some bad technical guidance. I have no formal education in physics or heat transfer.

[AshMcConnell]

Hi Riff_raff,

Sorry, forgot to reply and thank you for your help. I got the message on my phone when I was out and forgot to follow it up .

Thanks again,
Ash

[Sayshina]

Just to elaborate on how Carbon/carbon works, when you hit the peddal you have no brakes, at least not enough to notice. They don't start to work until they hit their operating temp.

They take somewhere around 1/2 second to reach temp, and then suddenly they work. It's like a switch goes off.

As a driver you figure out your required stopping distance, add in that 1/2 second, grab as much brake as you possibly can when you reach that point, and then modulate as they come up to temp so you don't lock up. So in effect they're "preheating" the brakes at every corner.

Most drivers testing a car or bike with carbon brakes for the first time talk about nothing else, it's that impressive and that different from what they're used to.

None of that really helps you model the system though.

[Sean H]

Just to elaborate on how Carbon/carbon works, when you hit the peddal you have no brakes, at least not enough to notice. They don't start to work until they hit their operating temp.

They take somewhere around 1/2 second to reach temp, and then suddenly they work. It's like a switch goes off.

As a driver you figure out your required stopping distance, add in that 1/2 second, grab as much brake as you possibly can when you reach that point, and then modulate as they come up to temp so you don't lock up. So in effect they're "preheating" the brakes at every corner.

Most drivers testing a car or bike with carbon brakes for the first time talk about nothing else, it's that impressive and that different from what they're used to.

None of that really helps you model the system though.

That's really only true for the first lap perhaps. After that, the brakes retain the heat required. That is why they still run brake ducts, if they cooled off so much they didn't work every corner, they wouldn't run brake ducts.

I have had carbon/carbon on my bikes, cold they suck, warm they are good, hot they are great. I have had ceramics on my cars, they are very similiar. Iron rotors are good for door stops.

[Jersey Tom]

Iron rotors are good for door stops.

Door stops and probably a majority of racing in the world, sure.

[Sayshina]

That's really only true for the first lap perhaps. After that, the brakes retain the heat required. That is why they still run brake ducts, if they cooled off so much they didn't work every corner, they wouldn't run brake ducts.

I have had carbon/carbon on my bikes, cold they suck, warm they are good, hot they are great. I have had ceramics on my cars, they are very similiar. Iron rotors are good for door stops.[/quote]

Well, my personal experience involves a gp bike test around 15 years ago. It's entirely possible things have changed over time, although I'd expect the changes to take a lot more time than that.

At the time I believe the massive cooling requirements were more for bringing down max. temp in operation, which I was told can lead to massive wear and instantaneous failure. At any rate, you could put your hand on the rotors as soon as you came in to the pits, and now that I think about it I was warned to lean pretty hard on the rear when coming in.

I've never used ceramics, although I was under the impression they were an attempt to get some of the advantages of carbon without having to suffer the aforementioned drawback. It does seem that a lot of guys are pulling them in favor of iron, although I'm hearing that has more to do with cost than anything else. It seems they get banned a lot as well.

[olefud]

Brakes create heating in the rotor mass through surface friction. The heat is dissipated through convection to the passing airflow. If you want to simulate brake temperatures, you have some of the basic information you'll need, such as rotor material specific heat, surface area, ambient air temp and velocity, and heat input rates.

riff_raff

ps. I honestly apologize if I've given some bad technical guidance. I have no formal education in physics or heat transfer.

At the temps involved most of the heat is rejected by radiant cooling. Carbon would be more so with its higher emmisivity I expect.