Interesting Aerodynamic Cars (Mike Vetter's ETV, also Avion)

[JulianEdgar]

Originally Posted by kach22i

Article using Ecomodder template, picture below is of another project.

https://www.google.com/amp/s/occamsr...-template/amp/

It's just vapourware - he hasn't done anything (yet, at least). And his final version uses the template in a very creative way - note the wheels way off the ground. Not that matters, of course - garbage in, garbage out.



However, much more interesting is his racetrack testing of drag and downforce/lift - methodology here and results here.

Testing methodology looks fine - coast downs only at high speed (90 - 70 mph) - and ride height and spring forces measured for lift/downforce.

[kach22i]

Originally Posted by JulianEdgar

.....- note the wheels way off the ground. Not that matters......

I think what the author of that article intended with that rescaled and elevated off the ground template overlay is the Miata is already set to go as far as angle under the car at the rear.

Therefore a future rear underbelly diffuser is deemed unnecessary at this time as there is lower fruit on the tree to harvest.

The image I posted of an aero-top is an example of a top that DOES NOT conform to the aero-template and is from the same article. I think the author posted it to illustrate not everyone follows the template yet that top is an improvement over stock nonetheless.

What perhaps the author should be congratulated on is pointing out this is a 3D template and one should not neglect the top view.

In fact, the top he is scheming to build may be covering up the gas cap in plan view following the template.

In short for the template to work on this car it will look more like a shooting brake station wagon. I get the feeling he cannot come to grips with this and is stalled.

[NeilBlanchard]

There is more information about the aerodynamic design of the Lucid Air, which will be one of, or possibly the lowest drag car, when it is produced:

https://www.youtube.com/watch?v=vdwNtswXvzA

They are going for all the efficiency they can get, out of all the parts of the car, so that longer range can be achieved from a smaller battery pack.

[kach22i]

Ford: EXP II
1981 Ford EXP-II (Ghia) - Concepts

[aerohead]

Originally Posted by JulianEdgar

It's just vapourware - he hasn't done anything (yet, at least). And his final version uses the template in a very creative way - note the wheels way off the ground. Not that matters, of course - garbage in, garbage out.



However, much more interesting is his racetrack testing of drag and downforce/lift - methodology here and results here.

Testing methodology looks fine - coast downs only at high speed (90 - 70 mph) - and ride height and spring forces measured for lift/downforce.

That use of the template would violate the ground reflection, mirror image, and fineness ratio, blowing the Cd all to hell.
There's only one way to use the template.

[freebeard]

Is that a fault of the user, or of the template? How would a template independent of ride height differ?

[aerohead]

Originally Posted by freebeard

Is that a fault of the user, or of the template? How would a template independent of ride height differ?

It's a misapplication of the tool. Like using a 1/4-inch ratchet to torque lug nuts.
The air 'sees' all vehicles in mirror reflection, with an imaginary, upside-down twin below the road surface.
The template contour is based upon this 1:1- scale. Shrinking the scale introduces a contour which no longer satisfies 'streamlined.'
The positive pressure gradient generated will overwhelm the turbulent boundary layer and trigger flow separation, the whole thing we're trying to avoid like the COVID.
As to ride height drag variability, we'd have to test it. Research on the Audi A2 proved that there is no universal absolute relationship between ground clearance and Cd. It remains an unknown quantity.
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Hucho does imply that by lowering a vehicle, one is 'integrating' the wheels further into the body, which he said would be part of a strategy for achieving Cd 0.09
I believe McLAREN, with respect to the SPEEDTAIL, noticed this part of his book.

[NeilBlanchard]

Another way to look at it, is the template has to be for the whole vehicle, or at least for the whole vehicle height.

A vehicle shaped like a cube - would not be lower drag by slapping a perfectly shaped roof on it.

Think of the early streamliners that had sleek bullet-shaped bodies - and then had large open spoked wheels and axles and leaf springs hanging out in the air flow. Sure, a piece of them were shaped well ...

[freebeard]

The air 'sees' all vehicles in mirror reflection, with an imaginary, upside-down twin below the road surface.

This seems weak. What is the mechanism by which the imaginary shape acts [through an impenetrable surface]/[in meat space]?

[aerohead]

Originally Posted by freebeard

This seems weak. What is the mechanism by which the imaginary shape acts [through an impenetrable surface]/[in meat space]?

'[T]he optimum shape in terms of drag is a half-body, which forms a complete body of revolution together with its mirror image- produced through reflection from the roadway.' Wolf Heinrich Hucho, page 15, Aerodynamics of Road Vehicles, 2nd-Edition,Butterworths, 1986.
This has to do with 'effective fineness ratio', a phenomena of aerodynamics, in which a vehicle is twice as 'thick' as what you observe.
In order to achieve the drag minimum of a Length / Diameter of 2.5: 1 streamline body, the car must be 5:1. The template.
A look at early wind tunnel testing reveals models humping, wheels -to-wheels in the air stream to accommodate this phenomena.
I don't have the book with me so I can't go any deeper.