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From: tron@fluke.UUCP (Peter Barbee)
Newsgroups: net.auto
Subject: Re: Miscellaneous Ramblings
Message-ID: <915@vax1.fluke.UUCP>
Date: Wed, 27-Feb-85 19:02:06 EST
Article-I.D.: vax1.915
Posted: Wed Feb 27 19:02:06 1985
Date-Received: Fri, 1-Mar-85 20:09:51 EST
References: <330004@acf4.UUCP>
Reply-To: tron@fluke.UUCP (Peter Barbee)
Organization: John Fluke Mfg. Co., Inc., Everett, WA
Lines: 70

>they put in Car&Driver or R&T, that they mention that the 944 has a "high
>polar moment, making it resistant to crosswinds".  My physics isn't what it
>used to be, but doesn't a high polar moment imply the car will not be suited
>to lane changing and slaloms, all the things a sportscar is supposed to do?
>The car will be very stable, like a Caddy, but will slalom about as well as
>one too.
>
>R&T mentioned that the Porsche 944 engine was set forward to gain legroom for
>the driver and front seat passenger.  If i am not mistaken, it also has a
>transaxle.  This means that most of the mess of the car is over both axles.
>By contradiction, the 1963-1982 Corvette has its engine set back behind
>the front axle, the transmission between the driver and passenger.  
>The admittedly greater mass of the Vette is nevertheless better distributed.
>Why the
>Vette is low technology and the Porsche is high is beyond me.

Greater mass ? Better Distributed ?

1) high polar moment of inerita = high resistance to spinning (when compared
   to a lower polar moment of inertia), actually the polar moment of inertia
   is an area property, the second polar moment is a volume property but I 
   digress.

   What this means is that the car will require more force (friction force
   exerted at the tire/road interface) to change the relationship between
   the direction the car is pointed and the direction its momentum is
   traveling.  This is often known as the slip angle.   A fast driver (ok,
   a good fast driver) minimizes the slip angle by rarely turning the steering
   wheel faster than his momentum will change, this is because all energy
   that creates the slip angle is lost.

   So what does this all mean?  A 944 should resist spinning more than the
   average car at a small sacrifice in ease of turning. (yes this sacrifice
   *might* be measurable on a skidpad if you could figure out how to).
   To get an idea what the opposite effect is (low polar moment of inertia)
   have you ever driven a 914 (or maybe even an X1/9) ?  These cars can be
   driven very fast around corners but once they spin they really spin, like
   a top.  They don't have the weight out at the ends to slow them down.
   I'll admit I'm a bit prejudiced because my Alfetta uses a transaxle.

   Also, it might be of interest that it is much easier to attain a 50/50
   weight distribution with the use of a transaxle, an analogy is a high
   wire act - notice they use long poles for easy balance.

2) Better Distributed?
   Why is clumping the mass up in the middle better distribution than hanging
   it out on the ends?   Not enough data here to make any claims about 
   distribution.

3) I have always thought that 'Vettes in general were low tech mostly in terms
   outdated construction methods.  True racing cars have long ago proven the
   wisdom of uni-body construction but the 'Vette didn't go to it.  I realize
   that J. Buchanon's '66 rat motored missile has got more horsepower than I
   would be comfortable with but I'm not sure you could call it high tech.  
   Rather that motor represents doing what has long been known to improve 
   performance but because of sheer volume being able to do more of it.  
   I guess I'm argueing the meaning of high tech.  To me high tech is turbos
   and anti-skid brakes, not 427 cu. in. and power assisted drums.

   Do not think that I can't appreciate 'Vettes, I'm not selling US auto
   engineers short, I just like to be objective.

Abolish 55,
Peter Barbee

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