F1 Braking at high speeds.

[xpensive]

You guys should perhaps be a tad more careful to stick to the original topic, mods are getting picky about this.

Anyway, conversion of energy, from kinetic such to very hot brakes and finally to hot air, by which the entropy in universe increases by the way, would quite obviously be the correct terminology for this phenomenon.

On the other hand, as power is energy per time-unit and the activity per se could indeed be scientifically described as a form of dissipation of energy, the xpression power-dissipation is still not incorrect to my mind.

What was the question here anyway?

[shamikaze]

At high speed, there is more aero-DF pushing the tyres down onto the tarmeac therefore increasing the grip/hold of the tyre onto the tarmac. So for the same retardation, you'll not have slip at high speeds whilst you will see slip at slower speeds.

Pretty sure the brakes are strong enough to make the tyres block at even those high speeds, but the risk comes with it that you'll destroy the tyre very quickly because of the high-friction coeficient of the tyre, heating the rubber to melting point and destroying/flat-spotting it very terribly with all negative consequences as a result. A slip at a lower speed has less such destructive force.

You can similate this with your hand. Rub it against an abrasive suface (ie sanding-paper), rub it slowly and then repeat rubbing it very fast ... Surely you'll feel the difference

GReetz,

S.

[The_Man]

The reason i feel that the braking is similar for the different drivers on the grid is because the the drivers are not actually putting all their efforts into braking. You always hear the pit to car radio taking about the management of the brake temperature. The carbon disks that are used in formula one are very temperature sensitive. If the drivers always apply maximum breaking then the brake temp will goto very high values and they will loose braking power there by easily locking the tyres and loosing not only grip but also on tyre life. So the amount of brakes applied is really a compromise. It helps with prevention driver fatigue too.

Another reason I think this is true is because the drivers can break late if they want to at times to attack or defend position. Here they are basically compromising once in a while the brake temp for late braking. That might also explain why we see more brakes locking only when the drivers break late.

[Giblet]

A lot of energy is lost in the braking, I want to know that how it can utilized in useful energy ?

I've read that an F1 car with carbon brakes generates 2500hp of braking force. That is a lot of unused hamsters. KERS (Kinetic Energy Recovery System) does generate under breaking, so there is part of it taken up in storage to be used later.

HERS (Heat Energy Recovery System) is the next step, but it's unclear if F1 will go in that direction in the near future.

Your link is well timed and somewhat well placed. I want to call it spam, but it seems rather legit and in the right place for all intents and purposes.

[Lurk]

F1 energy at 300km/h is 2.15MJ when tank is empty and it needs 2.5s to go from 300 to 0 km/h.
So it is more or less 1200 HP. Am I wrong ?

[xpensive]

True, but even 1200 Hp for 2.5 seconds is still no more than 2.2 MJ, which is the energy content of 65 cc of gasoline.

[Belatti]

To go back on topic, the answer to caitos question can lay in the fact that, if we consider pad/rotor as coulomb friction, "mu" has a variation that depends on the temperature (build up and dissipation), pad and rotor material and (at least in steel rotors) slots shapes.

Here you can see a compound comparison from Ferodos webpage:


So, if you set up a brake system to increase the initial bite (in order to have powerful enough brakes to lock wheels at 300kph) it will probably get a bit too sensitive at lower speeds, note the increase in "mu" when time (and temp) increases. Still it depends on the driver capability to modulate the pedal release.

[Belatti]

Note: I may be mistaken in the last post (regarding F1 brakes) because the compounds I ploted where designed for steel rotors. I ignore the peculiarities of carbon/carbon friction and "mu" variation and may be different.

[mep]

Somehow I like the blue graph. It has good initial bite and then drops like the grip drops with speed.
If the brakes needs more heat to build up friction the drivers can simply let the brakes grind little bit before braking.


Do F1 cars have any brake force booster?
How much braking power can a human body even produce?
Maybe the drivers just can't produce enough power/force to lock the tyres at highest speeds. The reason why they all brake more or less the same is that they have very similar weights. If one would be significant heavier he would suffer more during acceleration and corners.
Just a idea.

[747heavy]

as far as I know, F1 cars don´t have a brake force booster, so the driver
will need to press the pedal hard enough.
While not easy, it should be doable, and with different master cylinder sizes the teams can trade pedal force for pedal movement.
Most drivers probably prefer a stiffer/harder pedal.

But I think Timbo is spot on with his assessment in regards to the limiting factor.
As brake disc diameter is limited due to the wheel size (13"), the only way to generate more brake force is via more brake line pressure.
This assumes that all the teams have access to the same typ of brake disc/pad material and that the CoF of the C/C brakes is more or less the same for everyone, with slight variations.
Now brake system stiffness becomes the limiting factor, as to being able to transform a higher pedal force --> higher brake line pressure --> into a higher clamping force between pad and disc.

As the material stiffness is limited by the rules, this together with the flex in the brake lines poses one limiting factor.

As a illustration, see the following graphic.
While not of an F1 or car system (testing of Mountain bike brakes) it shows the system stiffness component, quite nicely (IMHO).
You see that for more and more hand/brake lever force you get less and less gain in
clamping force on the pad.
The rest of the force is used to "deform" components of the system.



some interesting data about braking force and energy for this F1 season, can be found here:

http://www.f1network.net/main/s107/st155787.htm

as an example braking into Turn 5 in Abu Dhabi, the cars will reach ~5g decceleration with an pedal force of ~149 kgf (1462N) needed.

[riff_raff]

Brakes are sized mostly by thermal capacity. The rotor and pads need to have sufficient thermal mass, high temperature structural strength, and heat rejection ability to dissipate the braking energies. The temperature rise in the brake pad/rotor must not exceed the safe limits for that material.

The braking torque is a function of the caliper piston forces applied to the pads, the moment radius that force is applied at, and the coefficient of friction at the pad/rotor interface. If the brake system is working properly, it is no problem for a driver to create enough braking force to lock the tires at any speed. The brake pedal/master cylinder/caliper piston is a very efficient mechanism for multiplying force.

The braking power, however, is the braking torque x rotor speed / HP constant. And the thermal energy that the brakes must reject is a function of braking power, not braking torque. So in terms of braking power, an F1 brake system will have to reject twice as much thermal energy (initially) when braking at 100mph as it would at 50mph, for the same applied brake pedal force. Obviously, things get more complex when one considers time in braking rates, since kinetic energy varies with the square of velocity.

As for stiffness in a braking system (pedals, calipers, etc.), that should not affect applied braking forces. It would only affect the perceived feedback sensitivity the driver feels. But of course this feedback sensitivity is super critical to keep drivers from locking the brakes.

Regards,
riff_raff

[timbo]

Brakes are sized mostly by thermal capacity. The rotor and pads need to have sufficient thermal mass, high temperature structural strength, and heat rejection ability to dissipate the braking energies. The temperature rise in the brake pad/rotor must not exceed the safe limits for that material.

First of all, brakes are sized by regulations. It was noted that one of the arguments against 18" tyres was that teams would use much bigger brakes.

If the brake system is working properly, it is no problem for a driver to create enough braking force to lock the tires at any speed. The brake pedal/master cylinder/caliper piston is a very efficient mechanism for multiplying force.

Don't you think this reasoning has its boundaries? E.g. aluminium is great material for building planes. You can build Concorde from it. But if you try to build Blackbird you're better look at titanium.
There's no comparable braking system that needs to produce same amount of braking power in general automotive applications without assistance.

The braking power, however, is the braking torque x rotor speed / HP constant. And the thermal energy that the brakes must reject is a function of braking power, not braking torque. So in terms of braking power, an F1 brake system will have to reject twice as much thermal energy (initially) when braking at 100mph as it would at 50mph, for the same applied brake pedal force. Obviously, things get more complex when one considers time in braking rates, since kinetic energy varies with the square of velocity.

Umm, don't you think it'd be quadruple anyway? And you say TE is not a function of torque, while braking power is, and TE is the function of BP.
Please clarify!

As for stiffness in a braking system (pedals, calipers, etc.), that should not affect applied braking forces. It would only affect the perceived feedback sensitivity the driver feels. But of course this feedback sensitivity is super critical to keep drivers from locking the brakes.

If your system is not thermally limited (at least for a single braking event that is) your limit would be in braking power available, no?
Also, why do you think there was a trend in regulations progressively banning stiff materials from brake calipers?

[riff_raff]

timbo,

First of all, brakes are sized by regulations.

Brakes are not sized by regulations, wheel dimensions are. Wheel diameter limits obviously limit the max diameter of the brake rotor, but it does not limit the thickness of the rotor. And as I noted, carbon brakes are mostly sized by thermal mass. So an increase in thickness is just as effective as an increase in diameter.

There's no comparable braking system that needs to produce same amount of braking power in general automotive applications without assistance.

If you look at an F1 braking system, you'll see that it is basically a lever and hydrostatic device that gives force multiplication. Consider, if you will, how a superbike can be brought to a halt from 150mph with just the squeeze of the fingers on your right hand.....

With regards to aluminum vs. titanium for brake calipers, you need to understand the principle of specific stiffness. While titanium has twice the modulus of aluminum, it also has twice the density. So their specific stiffness values are similar.

Umm, don't you think it'd be quadruple anyway? And you say TE is not a function of torque, while braking power is, and TE is the function of BP.
Please clarify!

Kinetic energy is 1/2MV^2, not 1/2MV^4. I did not imply that thermal energy is in no way related to torque. A measure of thermal energy, a Btu, is equal to .000393 hp/hr. And a hp is equal to 33,000 ft-lb/min. So obviously there is a relationship between torque and thermal energy.

If your system is not thermally limited (at least for a single braking event that is) your limit would be in braking power available, no?

With a carbon braking system, like in F1, the braking power limit is established by the ability of the brakes to transfer the heat energy built up in the rotor to the passing airflow without overheating the carbon rotor.

Also, why do you think there was a trend in regulations progressively banning stiff materials from brake calipers?

The banned material used for brake calipers was Al-Be alloy. This raw material costs over $300/lb.

Regards,
riff_raff

[xpensive]

The braking power, however, is the braking torque x rotor speed / HP constant. And the thermal energy that the brakes must reject is a function of braking power, not braking torque. So in terms of braking power, an F1 brake system will have to reject twice as much thermal energy (initially) when braking at 100mph as it would at 50mph, for the same applied brake pedal force. Obviously, things get more complex when one considers time in braking rates, since kinetic energy varies with the square of velocity.

Umm, don't you think it'd be quadruple anyway? And you say TE is not a function of torque, while braking power is, and TE is the function of BP.
Please clarify!

riff_raff is correct of course, Power is always Force time Speed, Force in this case is Braking torque over Tyre radius,
why Braking power is directly proportional to speed for the same Braking torque.

[timbo]

With a carbon braking system, like in F1, the braking power limit is established by the ability of the brakes to transfer the heat energy built up in the rotor to the passing airflow without overheating the carbon rotor.

I have a problem with this statement.
This problem mostly manifests itself over a race distance. It is not a limit for a single braking event IMO. If it was so, you'd see brake ducts as big as used in Canada on any track with a single hard braking point. In previous years (without Parc Ferme rules) cars were sometimes run without brake ducts during qualifying.
So, if driver had the ability to overstress brakes on a single lap we'd see drivers showing some extremely hard braking during qualifying.
As far as I can see, we see pretty narrow distribution of max g's during braking.

why Braking power is directly proportional to speed for the same Braking torque.

And here's what we are talking about. I stand that max braking is limited by max torque. riff_raff obviously stands that braking is limited by max power.