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From: an@hou2h.UUCP (A.NGUYEN)
Newsgroups: net.auto
Subject: Drag coefficient
Message-ID: <325@hou2h.UUCP>
Date: Fri, 2-Mar-84 13:02:54 EST
Article-I.D.: hou2h.325
Posted: Fri Mar  2 13:02:54 1984
Date-Received: Sat, 3-Mar-84 23:23:03 EST
Organization: AT&T Bell Labs, Holmdel NJ
Lines: 25

.

A Cd of say .35 means the vehicle has 35% of the aerodynamic
resistance of a barndoor of the same frontal area.  Notice that
low Cd alone does not mean less drag.  A Mercedes with a .35 Cd
would still have more drag than a Civic CRX of the same Cd, because
of the former's larger frontal area.

Streamlining isn't just making a swoopy shape (see Porsche 928.)
The object is to smooth the airflow around the vehicle.  Details
are important (see Mercedes Benz.)  Competitive swimmers shave
their body.  Aircrafts use paints that present a smoother surface
to the air rushing by.

Aerodynamic effects increase with velocity squared.  Double the
speed and air resistance is quadrupled.  Aerodynamic resistance
is the major power consumer above 30-40 mph approx.  Because of
this, streamlining is the most sensible way to improve performance
(gas mileage, acceleration from higher speeds, top speed, etc, see
Honda Civic CRX.)  Less power used to punch a hole in the air means
more power left to accelerate you from 50 to 70 mph for that quick
pass (left lane hogs take notice!)

	Au Nguyen