Acceleration of F1 car

[Jersey Tom]

NASCAR is better.

[xpensive]

Clearly that approach didn't work in this instance, for sure it could work.

Care to xplain why you seem to change your mind as you go?

[ringo]

"The braking capacity would be reduced non linearly as the speed drops too."

I'm not sure what you mean by this? Plus I don't see how simply making a statement like this on its own has any bearing on the topic?

Xpensive, I was referring to the tyres in relation to decceleration. Thank you for the lesson in units, clears everything up for me now. There is simply no need to consider energy and power. It can be done much more straight-forward using torque, speed, rolling radius and tractive effort.

No matter anyway, people can do it their own way, but it would be nice for them to find a way that works for them, which didn't happen in this case.

Well you were considering aerodynamics. Downforce is a squared speed relationship, so it is not linear. Tyre grip is related to the reaction force, most of it coming from the aerodynamic load. This has bearing on braking and deceleration of the car.

[Ciro Pabón]

The deceleration of a dragster is also larger than the one of an F1 car: once you deploy the parachutes and brakes, you have to resist 4 Gs (39 m/s2), more than a space shuttle astronaut during reentry. No Brembo carbon fiber brakes can provide you with the same decceleration, no matter what the forum says.

Brembo itself says otherwise
http://www.brembo.com/ENG/Formula1/2009 ... _eng13.pdf
Here's Monza data - 5g deceleration routinely, lap after lap. Try to do the same with chute

Oops. My mistake: the figures I had (also taken from Brembo site) peaked around 3.5 Gs, if I remember well, timbo, but that was only for Catalunya and Albert Park (around 2006), the only tracks I analyzed in deep. Thanks.

Which leads me to the following question: have the brakes improved during the last years?

If they haven't, why Brembo posted smaller deceleration values for those two particular tracks some years ago?

Is it because at Monza the speed is higher, thus the downforce is also larger, so you can get larger deceleration values? If that's so, then the braking force is dependent on downforce (something I hadn't thought about before, but, of course, very logical).

If I'm right, that degrading of braking force with smaller speeds or with less downforce wouldn't happen in the same degree with a parachute... because drag force is proportional to the square of the speed, while downforce is proportional to the cube of the speed: if your car is at low speed or if your car provides you little downforce, a parachute is better.

So, perhaps, maybe, possibly, that's the reason why parachutes are used in cars that are built for straight acceleration and, thus, minimum downforce and/or drag associated with it, while brakes should be used in cars that are built for lateral acceleration and maximum downforce (yeah, I know: pure speculation on my part until we get some figures, but I have always wondered why drag cars have to use parachutes instead of regular brakes: it seemed like overkill to me, until I read your post). So, I could say (if I'm right and I'm not sure about being right): try to brake a drag car at 500+ kph with a Brembo brake race after race.

That would explain (a mistery to me, until now) why the figures for maximum decceleration varied from curve to curve at those two tracks I mentioned. Double thanks, dear timbo.

Finally, my conclusion: the faster you go, the harder you can stomp on brakes. Am I right, forum?

[xpensive]

This would depend on the boundary conditions of the braking system as a whole I think? Xamples:

- If the limitation is tyre-to-road grip and the speed of your vehicle helps downforce, then yes.
- If heat dissipation from the brakes is the limit, hell no, as power is force times speed.

[WhiteBlue]

This would depend on the boundary conditions of the braking system as a whole I think? Xamples:

- If the limitation is tyre-to-road grip and the speed of your vehicle helps downforce, then yes.
- If heat dissipation from the brakes is the limit, hell no, as power is force times speed.

Heat dissipation is combatted by air scoops on the brakes. They increase the size when a limit is anticipated. So in real world terms only the tyre to road grip limits the deceleration and that is influenced by downforce.

[F1_eng]

Clearly that approach didn't work in this instance, for sure it could work.

Care to xplain why you seem to change your mind as you go?

How is that changing my mind? It's simply stating that the approach didn't work in this instance because it wasn't implemented correctly but it could work. Do you understand?

Clearly that approach didn't work in this instance, for sure it could work.

Well you were considering aerodynamics. Downforce is a squared speed relationship, so it is not linear. Tyre grip is related to the reaction force, most of it coming from the aerodynamic load. This has bearing on braking and deceleration of the car.

Certainly true, there is also another non-linearity to consider.

Ciro, you can say that the higher the speed, the more braking effort you can apply before locking the wheels, in a simplistic way. Remember also that downforce does not increase at the square of the speed in the real world because the ride height changes and infact at low rides, the downforce will decrease.

[xpensive]

Do you understand?

In all honesty, no.
Your statements are so scattered and the focus so all over the place it reminds me of some of my Ansys-engineers.

[DaveKillens]

A car devoid of any aero downforce pushes down with one G, regardless of velocity. But a car that generates downforce, as speed increases, downforce increases, and thus pushes the tires firmer against the road. More grip. That's exactly why Formula One cars have downforce-generating devices, to get more grip between the tires and road.

So when a Formula One car starts, it is going too slow to generate any downforce. As speed increases, so does downforce, and the grip. That's why many have heard the story about KERS not being used below 100 kph. The reason is that at low speeds, there is minimal grip, and the combination of engine torque and KERS would be strong enough to spin the tires. Once above 100 kph, there is enough downforce to push the tires hard into the road, and give enough grip to withstand the combination of engine torque and KERS.

The torque delivered to the driveshafts is determined by the engine torque, and the gearing. Thus, first gear delivers more torque to the driveshaft than top gear. Anyone driving a high-powered car learns the hard way that stomping on the gas in first gear will produce nothing but wheelspin, while it is perfectly OK to stomp the gas pedal in top gear.

And there's also weight transfer to consider. That too has an influence in tire grip.

[riff_raff]

Ciro,

Regarding your question, "have the brakes improved during the last years?", the answer for F1 cars is qualitatively yes, quantitatively no. The "feel" of CRC brakes and the system balance has gotten better, due to things like more optimized caliper structures and improved integration of brake and suspension functions. But the braking capacity of CRC brake systems is roughly the same for the past few years.

The limiting factor for a device like a friction brake, is how effective it is at absorbing the kinetic energy of the car and then dissipating that energy as heat. CRC brakes are very effective because they can sustain a huge temperature rise (ie. absorb a large amount of energy) within a low structural mass. But the ability of a CRC brake system to absorb energy is usually much greater than the traction capability of the tire it's attached to. As the old joke goes, "the brakes only stop the wheel; it's the tire that stops the car".

Another thing to consider is the difference between the static and sliding frictions of a tire contact. A tire that is not sliding has much greater traction capability than one that is sliding. In order to maximize braking (or traction) you want to load the tire right up to the point where it begins to slip, but no more. Once it begins to slip, its traction capability is instantly reduced.

Finally, from what I understand, F1 drivers usually apply the brakes and the throttle at the same time while cornering. The reason being so that the engine is already revved up and making power at the corner exit. And the brakes don't mind, since they have the thermal mass to easily absorb the extra engine power in addition to the braking power.

Best regards,
riff_raff

[ringo]

I have 2 unique cases concerning 2 unique F1 cars.

In terms of acceleration, the Williams FW CVT car should have been fastest if it raced. A continuous "gear ratio" should mean it's acceleration would have been seamless.

[youtube]http://www.youtube.com/watch?v=x3UpBKXMRto[/youtube]

And then in terms of deceleration, the Tyrell 6 wheel car. Just imagine the braking power coming from 4 disk rotors and 4 tyres up front; even though the wheels and rotors may have been smaller than average.

[youtube]http://www.youtube.com/watch?v=dchPW55k6pk[/youtube]

Very interesting machines.

[alelanza]

but I have always wondered why drag cars have to use parachutes instead of regular brakes

I know very little about dragsters, but here’s what came to mind. I would say they use parachutes,

Because they can:

- They only need to brake once,
- they don't need their braking to be very precise/controllable to setup the car for corner entry

Because they have to:

- Those tiny front wheels probably won't accomplish much in terms of braking, and despite the long wheelbase there's still weight shift.
- It seems to me that the structure of a dragster chassis is completely rear biased, ie the car is meant to accelerate or brake from the back. I think exerting a large braking effort from the front tyres at the end of that long nose would result in a very unstable condition, and that’s assuming the chassis can withstand massive force coming from the front.
- And finally the obvious one, they go reeeeaaaallly fast, so short of making the longest straights it’s better to reduce braking distance as much as possible

I also wonder if it allows them to get away with smaller brake discs, thus less mass to spin. Which I guess might not even be a consideration being their main issue is how to control and put all that power to the asphalt.

[xpensive]

but I have always wondered why drag cars have to use parachutes instead of regular brakes

I know very little about dragsters, but here’s what came to mind. I would say they use parachutes,

Because they can:....

Valid arguments, but I think our esteemed moderator is also wrestling with the concept of Power being Force times Speed.

- This concept applies to deccelleration as well, why the braking power at that speed would probably cook the hydraulics.
- Also, aerodynamic resistance goes with the square of the speed, why a parachute is four times as efficient at 500 km/h as at 250, while the breaking power disappears into thin air so to speak.

[autogyro]

The Van Doorne CVT fitted to the Williams F1 car used far to much energy to apply and move the cones to ever have a superior performance.
This is why Williams will never use the Toroidal system even if KERS returnes, drags out to much torque. They have dropped it and it will only be seen in lower powered vehicles and industry. CVTs and TVTs are a dead end for F1.
The fuel dragsters I have driven use expanding tyre diameter to effect a ratio change.
Derek Gardener had some interesting trandmission ideas for Tyrell that were prevented from use by regulations. I talked to him about them when he was running Borg Warner at Letchworth UK.

[riff_raff]

alelanza,

I know very little about dragsters, but here’s what came to mind. I would say they use parachutes....

The NHRA requires parachutes over a certain speed. The most important reason they are used is because they provide directional stability while slowing the car. With the lack of suspension, very long wheelbase, narrow track, and extreme rearward weight bias there's no way a top fuel dragster or funny car could safely stop from over 300mph by only braking the wheels, they would lose control. Some fighter jets and the space shuttle use drag chutes for the same reason.

But I do agree that they look totally cool. Plus they provide plenty of square footage for sponsorship advertisement.

Regards,
riff raff