Square shapes for aerodynamics ?

[MetroMPG]

I think that's because the car has quite a bit of "cab forward" design to it - ie. the mirrors are probably the same position relative to the driver as they are in most cars. Just a guess.

[Who]

I would have guessed the mirrors are back farther for aero reasons - seems to my very non-professional eye like they'd cause far less drag there...

[H4MM3R]

1985 Ford concept with a Cd of .137

[LostCause]

Originally Posted by basjoos

I thought the lowest Cd for a ground vehicle was 0.11, which is what they claim is the Cd for the Aptera.

All the texts I've read (Hoerner, Hucho, an SAE symposium, and another) claim that 0.15 appears to be the lowest cD for a blunt body, w/ wheels, in ground effect. In the symposium, one professor argued that cD could be lowered further by removing vehicle lift, but the issue was contentious. This was all before CFD, though (1970's).

The lowest theoretical drag shape near ground effect (w/ out wheels) was a shape very similar to the Aptera (~0.09-0.11 mark). The Aptera's wheels are far from aerodynamically clean (two control arms in the breeze). Solar cars supposedly have a cD of 0.09, but they don't seem like blunt bodies to me.

I should add that these might have been 2d shapes (i.e. infinite span). 3d shapes can have lower drag. If that is the case, sorry for being misleading.

I believe a slippery slope some might be falling into is claiming cD*A as cD, which is often done and easily confused.

- LostCause

[LostCause]

Originally Posted by H4MM3R

1985 Ford concept with a Cd of .137

That car looks more similar to the ideal 0.15 shape than a real car. Either the art has progressed (likely), cD*A is being claimed (possible), or we are getting into an issue of semantics (likely). I assume a body is defined as being blunt @ a certain fineness ratio. Also, I don't believe 0.15 was ever believed to be an impenetrable barrier, just a likely limit.

From memory, the ideal 0.15 car and ideal 0.09 GE shape:


Good contributions.

- LostCause

[trebuchet03]

Originally Posted by LostCause

Food for thought: the lowest cD of a wheeled vehicle in ground effect - ~0.15

- LostCause

Vector-One
cD = .1 even
Frontal Area = .42 m^2


Varna Diablo
cD = .11
Frontal Area = .183 m^2


Virtual Edge
cDA = .011m^2 (don't have the actual cD value)

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.

[elhigh]

Originally Posted by trebuchet03

[ 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.

Larry Niven's "sonic fold" from Ringworld.

[diesel_john]

notice the angled view, the photos never show an x,y,& z view. and you all know why, cause we would have it on our cars faster than you can say, (alt. print screen, paste).

[trebuchet03]

Originally Posted by diesel_john

... all cars would look the same ...

They don't now?













Sure, they have their subtle differences... Just like the streamliners I posted above... But, they look very much the same (other than the Mazda perhaps - it has a smile sort of look from it's grille)

I see no reason why we can't have variation and low drag - for instance


and




-Images ripped for all over the internets

[H4MM3R]

That VW is Sweet!