Low drag Aerodnynamics

[sasquatch]

I know It is not Formula one, but there are a lot of aerodynamics experts.

DaimlerChrysler have released a car that is based on the shape of a boxfish. They quote the Cd=0.19 whereas a normal car has a cd=0.3.

http://www.auto123.com/en/info/news/new ... 42136&pg=1

I want to know why is the drag reduced so much compared to a normal car. It doesn't look that different! I would be interested to hear your ideas because drag is becoming more important with decreased downforce levels

[Steven]

well I guess it's down to several things really

- There are no mirrors but a camera to look backward
- The back is rather small which reduces drag.
- I know from about a year ago that Renault one optimised a Clio to see how low they could get the Cv without making the car useless for all day traffic. I think I recall they got off 0.1 just by modifying the floor of the car. Therefore my guess is that they have made some kind of a smooth floor, somehow resembling the smoothness of the visible car parts.

[riff_raff]

sasquatch,

I'm sure if you look at the Cd for an open wheel race car, you'll find that it's probably around 0.8 to 1.0. Higher for a road race car, and a little lower for an oval track car.

Production cars don't need to make downforce. Also, aerodynamic drag losses increase exponentially with speed. Thus, the most effective way to reduce fuel consumption (or horsepower requirements) in any vehicle, is to reduce aerodynamic drag. Making a vehicle more aerodynamic also doesn't cost much more, as opposed to making it lighter.

Unfortunately however, most aerodynamicists have absolutely no concept of aesthitics. They can design a car body with low drag, but it'll be ugly as hell!

[RH1300S]

The basic shape is probably fairly good for low drag; I believe they call that cut off rear a Kamm Tail. Some time ago a certain Mr Kamm discovered that a long tapering tail was not as efficient as was once thought, partly due to the fact that it's required length increased surface area and friction drag.

Other comments already made re: lack of mirrors and it also seems almost anything else sticking out. You can bet the plan form is slightly tapered and underside is smooth (already suggested). Also, careful optimising of air flow through the car and cooling.

Many years ago when the Ford Sierra and Audi (was it the 80?) were being marketed as low drag cars; I read an interesting article about optimising the design. Ford looked at a fairly unusual shape to get low drag, Audi stayed much closer to the conventional 3 box design, but spent much time optimising details (like glass, rain gullies, joins between edges etc.) and achieved impressive numbers for the time.

Of course the CdA of this car would still be pretty high due to it's size.

I can't agree that low drag is the fuel economy holy grail; it's part of the picture ( a big part) for steady state highish speed cruising. Low weight is still necessary for good fuel economy while the car has to accelerate.

[Guest]

MAte )) Low Cx is good ) but you see that the face area is not little for this car))