From: tvp53202@uxa.cso.uiuc.edu (Toby Vaughn Padfield)
Subject: Re: carbon brakes [was: something about the Honda RA168E engine]
Organization: University of Illinois at Urbana
Date: Wed, 7 Oct 1992 23:16:14 GMT

b102smi@utarlg.uta.edu (George M. Smiley) writes:

>(Mark Jackson) writes...
>(Richard Banks) forwards comments by A.H.Henry@gdr.bath.ac.uk (Andrew
>>Henry), buried in the middle of which we find:
>> 
>>>     The main advantage
>>>     with the carbon brakes is that they are about a half of the weight of
>>>     the iron ones.
>> 
>>Then how is it that they dramatically reduce stopping distance?  Or was
>>all of that "banning carbon fiber brakes is a Good Thing because it
>>will promote overtaking under braking" stuff posted a while back in
>>error?
>> 
>First off, it is Carbon-carbon brakes, not carbon-fiber. They do not 
>dramatically stop braking distances as has been suggested. It is possible
>to get the same performance from iron rotors if one is willing to use
>a thick, large diameter rotor. But, as Andrew pointed out, iron weighs
>a good deal more than carbon brakes and that weight is in fairly important
>place on the race car as it is affects suspension reaction.

>Another point to consider is the way the brake material reacts to heat.
>As tire adhesion went up, braking pressure increased and along with it 
>heat increased. Small iron rotors are unable to shed this increased heat
>and they will enventually shatter. (I've witnessed this on a motorcyle -
>not a fun thing at all.) Carbon-carbon brakes react in the opposite manner.
>Early designs had poor coefficients of friction and tended to react slowly
>until enough heat was built up to allow the carbon brakes to grab. So, in
>fact, iron brakes reacted in a linear fashion (the harder you braked the
>faster you slowed) whilst carbon brakes offered nonlinear response (one
>would brake poorly until enough heat built up and the fun began).

>However, this has become achient history. People much smarter than myself 
>have found ways (varying the weave pattern, varying the resins, even 
>modifying the carbon strands themselves) to create carbon brake systems
>with high coefficients and quick reaction times. However, they are in 
>no way superior to iron brakes eccept for weight and they cost an ever
>increasing amount of money as the resin materials grow ever more exotic
>and the processes more complex.

>I, for one, look for the day that engine builders begin to exploit
>carbon-carbon technology to make such stuff as pistons and connecting
>rods. Such designs would make for some very high-revving motors which
>in turn would lead to more power. There exist motorcycle race engines
>using both, but, they are few and far between. Why none in the self
>proclaimed leader of motorsport engineering, F1 ? 
	
	In the latest issue of Popular mechanics, it shows a picture of
an all-Carbon-composite? piston. I read it briefly on my way to a National
Guard drill on a military bus, with about 768 other guys, so I don't
remember all of the details, but they said they got something like 4%
better fuel economy, and a boost in power, while NOx and hydrocarbon
emissions were drastically reduced. The price was something like 40x more
than an aluminum piston. If someone wants to look it up, I'd like to see
the official results.
	Anyway, I guess that would be just too great an expense, even for
F1. Although, now that I think about it, I remember seeing something about
not being able to use composites in stuff like connecting rods, because
you can't really put a wrist pin in it, as well as the resin couldn't with-
stand that much heat. But, if a piston could, I don't see why a rod couldn't.
Kap Parfrey is the resident expert on composites here. Would you be so kind
as to help here, Kap?????????

TOBY...

>Against the rules ? Infeasible for larger motors ?

>Andrew ?

>George.
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