Square shapes for aerodynamics ?

[Who]

I've long had an idea for front suspension that would work ideal with highly streamlined cars.

[Cd]

I found some more images of the G90 :[IMG]


I superimposed an image of the Audi A2 over the G90.
The roof angle is identical :


I'm completely baffled by the .25 .Cd that the A2 has, since it not only lacks wheel covers, but it also has wheel flares and a huge wake.

I would love to see an image of the underside of an A2. It must be totally smooth.

[Cd]

Just to the right of the tire in this image is a good view of the flat underside on the G90 :

[Cd]

A few more :

[LostCause]

Originally Posted by trebuchet03

All of these are wheeled land based and close enough to experience the ground effect (at least, they are designed to work with that - except for the Diablo which was just sculpted - tested later). I'm only showing human powered ones because a great deal of effort has been put into achieving ridiculously low cDA values

Generally, it's not a good idea to place limits on "best" 400 years from now, when the star trekian force field is perfected - we'll have the ability to have cD values of .0001 and under etc.

Very, very true. I suppose I shouldn't have claimed 0.15 to be the lowest possible value ever, but I still stand by that it is a realistic (not unbreakable) lower limit for conventional automobiles.

I intended the number to be used more as a guideline, to have people who are at 0.25 realize that the curve is shallowing out as you get closer to practical limits. 0.35 to 0.25 is relatively easy. 0.25 to 0.15 will be much, much harder for any conventional car to acheive. 0.15 and less will either require one-off innovation or the loss of conventional characteristics (i.e. tandem seating, severely reduced occupant space).

My eyes are opened a little wider, though. Thank you. In 400 years, I'll be hoping Scotty will be around to beam me places. cD 0.0001 will be horribly high...

Just wondering, how do you guys calculate cD for your HPV? Scale model, moving road surface windtunnels? CFD? Road tests? I know at our school we have a supersonic wind tunnel with a subsonic in the works...definately nothing full scale, though. Do you guys have time at nearby windtunnels?

- LostCause

[Cd]

I guess I'm 'beating a dead horse'by asking this once more, but I keep reading differing information.
One of the aerodynamicists that worked on the EV1 claims that there is nothing to be gained by having the windshield on a car lay back any more than 45 degrees. Also, pointed noses on cars have no real aero effect. As long as the flow transitions smoothly to the sides and top of the vehicle, you can have a bus with excellent aerodynamics.

So why then do I sometimes see comments about laying back a winshield for better aerodynamics ? And why are you guys putting pointed noses on your cars if it doesn't do anything but add weight and get stares ? The cars are not going Mach 1 !

( But then I see comments about a low front end being better for aero than a high front end .......... I'm really confused . )

[aerohead]

When you consider that Cd 0.11 has been achieved in an actual road-going vehicle,then Cd0.22 doesn't look so good.If GM will get rid of the square front,then they can cut drag by half again,and boost fuel economy by another 25%.

[Cd]

Originally Posted by aerohead

When you consider that Cd 0.11 has been achieved in an actual road-going vehicle,.

The Aptera ?

What I mean is something with four wheels that looks like a normal car .

The best figure that I have seen for an semi-normal looking car was .16 for the Precept.

( Which to me looks a lot like a Nissan Maxima with wheel covers )
Hmmmm.


So Phil, it sure would be interesting to see some results on a top speed test run at the Texas Mile. ( Down near Houston ) It's expensive though - around $ 250 but it sure beats driving to Utah and getting salt on your chassis .
Can you imagine though if you could see what difference your current aero mods make on a top speed run ?

[fabrio.]

about G90: from ople source

G90 — Opel’s Three-Liter Car
Concept vehicles such as the G90,
first presented at the Frankfurt IAA
auto show in 1999, play an important
role in the effort to further reduce
fleet fuel consumption. They represent
the state of technology at a
given moment in time and constitute
an important experimental platform
from which new solutions are developed
for large-scale production.
The vehicle’s name reflects its purpose:
“90” refers to the emission
value of 90 g CO2/km. This corresponds
to a gasoline consumption of
exactly 3.88 l/100 km for the fourseater
of the Astra-class.
ITDC engineers were thorough in
taking account of every parameter
which impacts significantly fuel consumption:
air and rolling resistance,
vehicle mass, and efficiency of the
drivetrain. With a drag coefficient of
cD = 0.22, the G90 sets a new
benchmark. Its body is similar to a
teardrop shape with a distinctly sloping
roof and sharply cropped rear.
The smooth, rear-rising underbody,
with its completely integrated
exhaust system, has proved particularly
efficient, allowing the air to pass
the body and merge behind the vehicle
more quickly.
Comprehensive lightweight construction
and the targeted use of aluminum and
magnesium result in an exemplary curb
weight of 750 kg. For the powertrain,
Opel chose a three-cylinder ECOTEC
gasoline engine with inlet port deactivation
and a manual transmission auto
shift (MTA). It is clear that the power
plant specialists in Rüsselsheim consider
the potential of the conventional gasoline
engine to be far from exhausted.
Weighing just over 80 kg, the G90’s
engine puts out 44 kW/60 hp and can
take the full-scale four-seater (with a
further 350 l of space for luggage) to a
top speed of 180 km/h.

[Cd]

Thanks Fabrio.
What frustrates me is that they ( GM /Opel ) could easily make ( and sell ) this car, yet choose not to.