Monday, April 7, 2008

What's the most effective aerodynamic shape for a car?

As a result of the buzz surrounding the wind tunnel testing of the Chevy Volt, I've done a bit of research into what vehicle shapes provide the lowest wind resistance (cd, or coefficient of drag in techie talk). Since lower wind resistance equates to greater fuel efficiency, this is a point of considerable attention to the manufacturers of next generation vehicles.

More on the tech of aerodynamic design after the jump, but I thought it would be interesting to start the conversation with some of the most aerodynamic vehicles that have ever been created. Here we go....



The instant takeway here is that the symmetrical shape of the EV1 is no doubt the best design (of the bunch) from a purely aerodynamic perspective. The Honda Insight and CRX models represent a slight departure with the raised rear deck lid that provided obvious influence on cars to follow such as the 2004 Prius and others.

The overiding concern for vehicle manufacturers is to balance design asthetic with aerodynamic performance. This can get very complicated, especially given that even small changes in the shape of side mirrors can effect as much as a 10 point sway in CD.

In the next installment of this series we will take a look at the state of the art computer modeling software which designers use to see real time effects to CD as design changes are implemented.

The most suprising thing that jumps out in the comparison is the Lexus LS 430's suprisingly low CD number, despite it's comparitively blocky shape. One has to believe that the folks at Toyota have a trick or two up their sleeve in the area of aero design.

4 comments:

VoltJunkie said...

Interesting about the Lexus matching the Prius on aero. That car looks like a box, where did you get the number's from?

PetroZero said...

http://en.wikipedia.org/wiki/Automobile_drag_coefficients

tonami said...

The lexus' shape goes to show that there are more than one way to achieve outstanding Cdx numbers.

Most of the gains in the lexus comes from a fully covered underbody, gently flowing slab sides although not easily visible because of the lenght of the car. notice there are muscular hunches. Thats why the volt would have to get rid of most of those pronounced hunches that made it look so sporty.

And with a good aerodynamic eye one can see that the exit angle of airflow at the back window maintains laminar flow and helps reduce the negative pressure directly above the trunklid.

I don't know why carmakers have been toiling with cameras for side mirrors since the 80's and nothing has meterialized when there is a much simpler and cheaper alternative like the aerocivic
http://images.google.com/imgres?imgurl=http://www.sae.org/automag/globalview_10-99/images/03a.jpg&imgrefurl=http://forum.ecomodder.com/showthread.php%3Ft%3D95&h=160&w=250&sz=9&hl=en&start=11&um=1&tbnid=4j0--Zed9Qe_XM:&tbnh=71&tbnw=111&prev=/images%3Fq%3Daero%2Bcivic%2Becomodder%26um%3D1%26hl%3Den%26safe%3Dactive

tonami said...

sorry the link I wanted to post was http://forum.ecomodder.com/showthread.php?t=290