16 replies to this topic

[confucius]

Just wondering - if anyone remembers the third pedal the McLaren ran in 98 for a while. Apparently the photographer Darren Heath noticed the Macs' front brakes (or was it rear brakes?) were glowing under accelaration and thought this to be weird.

I guess brakes arent supposed to glow under accelaration but how did he know that there would be a third pedal?

Also, what makes ppl suspect teams are running TC because their brakes glow?

[Wolf]

Confucius, the only reason I know of for glowing of the brakes is braking itself- heat created by friction cannot be given away so fast as it creates, so things during actual braking get quite hot down there. The third pedal is, AFAIK, also engaged during braking (yet on entry int the curve), distributing different braking forces to inner and outer wheels. The glowing, if seen on exit from curve, might mean heat transfer problems or that the brakes simply hadn't time enough to cool down.
The third issue not mentioned here is that red button on McMerc steering wheels that MH and DC pressed during exit from the curve (I remember german TV making quite a big fuss about it, wanting to get to bottom of it- and, needless to say, came out empty handed- apart from fistful of stupid answers from drivers and the team). I think that, on that occassion, Lauda and Jordan suggested that it might be a sort of differential locking (don't know if it was deemed to be legal). Any comments?

[PDA]

The third pedal allowed the driver to apply braking to one side, at the rear, only. Braking into the corner would be the normal, equal braking on each side. When starting to exit the corner, the driver applied brake to one side, which would limit the torque applied to that wheel, the excess torque would be transferred to the opposite wheel, applying turning moment to the car, allowing it to turn more tightly than would be the case without the "fiddle" brake. (The natural tendency when accelerating with a locked diff is to understeer, the additional turning moment helps overcome this tendency.). The system was banned, not becasue it was a form of traction control, but becasue it was deemed to be rear wheel steering, which is not allowed.

[Wolf]

PDA, sorry but I don't get it. How could braking on the exit from the curve enhance performance? The driver should be hard on the accelerator by then.

[desmo]

Here is an illustration of the third pedal, on the left, for the "fiddle brake."

PDA has it exactly right, F1 cars tend to understeer esp. under acceleration. This design allowed the Salisbury diff to achieve a greater torque-split ratio between the drive wheels than is possible using the clutch pack alone and thus imparting a turning moment at the back to aid turning while accelerating out of a corner. This could allow a better line through the corner as well as the early turn-in and apex demanded by a car that understeers under power needn't be neccessarily used.

[moog101]

Wolf, imagine slowing the inside wheel fractionally as you exit a corner, it would have the effect of twisting the whole car around that wheel (the 'moment' referred to elsewhere) Full throttle exiting a corner is not possible, so the power would be fed in (and HARDER than before because the car would not be understeering as much, if at all) and the corner/exit speeds would be significantly higher.

[PDA]

The way I thought about when I first heard about was as follows: When exiting a corner, the inside wheel is "light" and more subject to wheelspin, apply a brake on that side, and it will not spin, therefore better traction out of the corner. That applies with an open diff., such as we normally have on a road car. Race cars (and the better road cars) have limited slip diffs. which only allow a certain, predetermined slip of the iside rear wheel before locking the diff, allowing some drive out of the corner (even with some wheeelspin. Power is applied from a point just before the apex of the corner (exactly where depends on a combination of driver style and car capabilities) while the car is still turning. When the diff locks, it tends to drive the car straight, i.e. understeer. applying brake to the inside wheel slows it relative to the outside wheel. The amount of torque to be split between the wheels is the same, but as less is transmitted to the inside wheel, more is transferred to the outside wheel. this imparts a turning moment to the car (a bit like steering a tank or tracked bulldozer). Yaw control systems on quality sporting road cars do th same typoe of thing, except they are done automatically when electronic sensors detect wheelspin and excessive yaw. Mac thought their system was legal, becasue the driver controlled it (i.e. manual, not automatic). It was banned becasue the FIA stewards said it was not a manual traction control system, but a rear wheel steering system.

Is that any clearer?

[DangerMouse]

I’ve never seen any proof that it only applied one brake - if so I cannot see how the FIA cleared it (which they did) as applying one brake only clearly contravenes the regs, The system was completely mechanical and controlled by the driver so in my opinion it's no more a driving aid than a steering wheel or brake pedal.
All it did (according to McLaren) is independently apply the rear brakes at the drivers direct request which does not contravene any rule except Ferraris one of “we must be allowed to have an unfair advantage.”

The Ferrari “Automatic brake balance system” which was introduced the same time (98) was purely electronic and took brake balance away from the front wheels under heavy acceleration which meant left foot braking out of turns could be used as TC – the FIA allowed this despite it not being driver controlled and the fact it clearly contravened the rules!

One rule for one etc…..

[Wolf]

Now I get it. What could be read out of first PDA's post (obviously, I did not do it until later) is that pedal is used simultaneously with accelerator pedal. And that braking could actually improve 'mechanical grip' of the unloaded wheel (apart from preventing wheelspin) by adding vertical load to that wheel.
BTW, from you not referring to that 'corner exit' button on their (McMerc) wheels, am I to assume that it wasn't as big deal as Jerries tried to make it look?

[PDA]

DM - Mac stated that it applied one rear brake. A switch on the dash (or wheel) allowed the driver to choose which brake would be applied. Assymetric braking was not mentioned in the regs at that time. The regs were changed for the following year to make symmetrical braking compulsory.

Moving to 2001, if that rule persists, the new TC systems will not be able to use wheel brakes to achieve their purpose. More likely is power modulation via engine mapping.

[goGoGene]

The reason it was outlawed wasn't because it broke any rules, it was outlawed because if th eMcL kept winning races by more than a lap viewership would drop. The FIA did it to level the playing field, which to be honest I agree with....to an extent.

That being said, McL were smart and inovative within the rule, good for them.

ggg

[moog101]

Originally posted by DangerMouse

All it did (according to McLaren) is independently apply the rear brakes at the drivers direct request which does not contravene any rule except Ferraris one of “we must be allowed to have an unfair advantage.”

No, because then they'd be doing handbrake turns all the time. Remember, they are chasing the WDC, not the WRC.

If it were both rear brakes they could just use the handrake.

[DEVO]

Wolf,

The button on the steering wheel was used in conjunction with the fiddle brake (third brake pedal). I don't know if there were 2 buttons but by pushing the button you applied the brake pressure to one of the rear wheels. With just the third pedal you couldn't achieve selecting the rear wheel to brake with.

[Wolf]

One would think they'd make it automatized- with switch of a kind on steering wheel. If it's not deemed illegal, of course.

[MrAerodynamicist]

Originally posted by goGoGene
The reason it was outlawed wasn't because it broke any rules, it was outlawed because if th eMcL kept winning races by more than a lap viewership would drop. The FIA did it to level the playing field, which to be honest I agree with....to an extent.

That being said, McL were smart and inovative within the rule, good for them.

ggg

IMO, stuff is banned to quickly these days. McLaren should have been allowed to keep it until the end of the season at least. Why should teams try to be inventive if all that happens if they succed is that is gets banned straight away. Oh, and wasn't it the Brazilian stewards rather than the FIA who decided to ban it?

[Wolf]

BTW, how did it get in the car if it was illegal? Or did FIA change their minds (perchance under Ferrarri protest)?

[PDA]

Wolf - the point of the driver manually selecting which brake was used made it legal, or so MacLaren thought. It was cleared as legal by Charlie Whiting, the technical expert at the FIA, as a manual system. ferrari engineered the protest at Interlagos (although the protests were made by Minardi and Sauber, using briefs prepared by Ferrari) was that it was primarily a rear wheel steering system, and as such was outside the regulations. The stewards agreed, so Mac removed the system. It had been used for a number of races before Brazil with no questions being raised by the scrutineers or the stewards. I suspect (pure speculation) and this is also the view of Peter Wright, the engineer, that Mac did not argue all that strongly for teh sytem (they could have appealed) becasue they also had another system of a electronic differential which achieved a similar result automatically (and legally). Diffs are now severely restricted in what they are allowed to do. They could do much, much more in improving turn exit control and speed if allowed. Road cars are already doing this (Honda for one, in the Prelude and "R" types).