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*To*: rsco@lubrizol.com, quattro@coimbra.ans.net*Subject*: Re: A6 styling re A4/A8*From*: STEADIRIC@aol.com*Date*: Mon, 12 Feb 1996 15:12:08 -0500*Sender*: quattro-owner@coimbra.ans.net

>AHEM, Eric, the rest of us don't _ know_ it! > >It is not manifestly obvious to me how this can be the case. Perhaps you >could share the math with the rest of us....? > >Before you accuse me of being lazy, I've briefly discussed the problem with >a physicist here. the upshot of our admittedly naive investigation was that >aluminum rotors would probably make for somewhat diminished stopping due to >the specific heat of the (light) aluminum rotor vs the (heavy) iron rotor. >Decelerating at the same rate, the aluminum rotor will get 40% hotter. > > Al Fe >Density g/cm^3 2.7 7.86 >Sp. Heat J/(g*degK) .9 .44 > >with these numbers, I calculate that for equal volumes (we simply swap >aluminum for iron) the iron rotor will be 2.9 times more massive. for equal >masses, the iron rotor will heat 1 degK for each .48 degK the aluminum >rotor heats. 2.9*.48= 1.392. So, a rotor of Al equal in volume to the >original Fe rotor will be increase in temperature 40% more than the iron >rotor for a given deceleration (energy input). There. I did the math. > >regarding the kinetic energy of the rotors themselves, which I think is the >factor Eric is alluding to, it is (m w^2 r^2) I think, where m is the mass >of the ring, w is the angular velocity, and r is the radius of the >idealized ring. Frankly, I (waving my hands) think this will pale in >comparison the energy of a 3000 lb car travelling at 100 kmph or so. Yes but for the same heat rejection as an Iron rotor an aluminum rotor weighs 31.5% less.... A metal matrix rotor 40% lighter and a carbon rotor 70% lighter..... There are books on the subject....... Later! Eric Fletcher '87 5KCSTQIA2RSR2B STEADIRIC@aol.com

**Follow-Ups**:**Re: A6 styling re A4/A8***From:*dan_masi@MENTORG.COM (Dan Masi)

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