Ultimate Aero Shape?

[RWebb]

What would be the ultimate aerodynamic shape for a car? i.e. a ground vehicle which uses wheels for propulsion

Assume a BEV so no need for air management for an internal combustion engine (only for passengers & brakes); no need for exhaust pipes

this post by kachi on the Transportation thread got me thinking about this

Originally Posted by kach22i

Artega GT preview
Artega GT preview - Car Body Design



Pictures: Testing electric hybrid car at Glenn L. Martin Wind Tunnel - baltimoresun.com

[jyl]

A big a length to width ratio, like 5:1 or more

Degree of pointy-ness at front and rear depends on speed design to operate at

[genrex]

If it's a vehicle for the general population, then it might be like the old Beetle with large doors, for easy access for grandma and grandpa. And not too low, so they can just pivot and stand up. So probably not very aerodynamic.

What is a BEV? B_____ Electric Vehicle?

__

[RWebb]

yes, Battery EV, so no IC engine with intake & exhaust & cooling penetrations in the body

also means no mechanical items on the bottom - so you can have a smooth undertray with diffusers or whatever

you would have axle shafts in the air flow, unless you used wheel hub motors, then you'd only have an electrical cable

[vash]

Water droplet shaped? trunk space is gonna suck.


Sent via Jedi mind trick.

[RWebb]

no - that is surrounded by air on all sides, and does not need to stick to the road

a car needs to optimize several things:

1. drag
2. downforce
3. side winds (baaaad in a rear engined 911)
4. airflow management - air for driver, passengers; air for engine intake; exhaust; for cooling brakes and engine


with an animal, you can often close off openings for various things and use slits (a favorite example, is that male dolphins can retract the penis and enclose it in a flesh covered slit when not deployed for operations); blowhole is similar

[onewhippedpuppy]

Symmetrical airfoil. Lift neutral so no induced drag (drag due to lift), laminar flaw over the entire surface (in theory).

[M.D. Holloway]

Teardrop with the fat end pointing in the direction of the air current...there is a reason nature does stuff...its lazy and wants to produce using the least amount of energy...

[URY914]

[URY914]

[RWebb]

Originally Posted by onewhippedpuppy

Symmetrical airfoil. Lift neutral so no induced drag (drag due to lift), laminar flaw over the entire surface (in theory).

ground vehicles are not so "easy" - still have to deal with the highly vorticed flow aft of the wheels

would we want some downforce at speed?

and what about the undertray?

[MDH]

Originally Posted by M.D. Holloway

Teardrop with the fat end pointing in the direction of the air current...there is a reason nature does stuff...its lazy and wants to produce using the least amount of energy...

I was thinking falling raindrop.....
at least until it splats on my head........
But I agree...fat end first.

[porwolf]

This is the shape of a 2002 VW study for the 1-Litre-Wagen, the WV-L1: This model is supposed to get 100 Km on 1.2 Liter of gas. That translates to a 200 MPG car. It is a Diesel- electric hybrid. The drag coefficient (Cd) is 0.159,[1] compared to 0.30 - 0.40 for typical cars.







Volkswagen 1-litre car - Wikipedia, the free encyclopedia

[onewhippedpuppy]

Originally Posted by RWebb

ground vehicles are not so "easy" - still have to deal with the highly vorticed flow aft of the wheels

would we want some downforce at speed?

and what about the undertray?

All true, I was just answering the "ultimate aero shape" portion. All of the theoretical stuff breaks down when you have to provide practical considerations. Maintaining the shape would be ideal, and the challenge. Fender skirts vs open arches, symmetrical body top and bottom, flush mounted and gasketed seams, narrow and low rolling resistance tires, all would help. You could use an aero device to create downforce at speed, basically a spoiler that slowly deploys to give the airflow shape some camber. It would be a challenge to keep the airfoil shape and still make a usable interior as well.

[kach22i]

Originally Posted by jyl

A big a length to width ratio, like 5:1 or more

Degree of pointy-ness at front and rear depends on speed design to operate at

Teardrop (blimp shape)

1:3 free air

1:5 in ground proximity

1:10 in proximity to another body plane surface (wheel blister or canopy)

More discussion here:
Aerodynamics - Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com

The neutral foil idea is nice, but you will want down-force at speed, and having a flat bottom curved top (Jaray - 1930's) does just the opposite.

I'm a big fan of what Luigi Colani did with the 300 mpg Vette, and inverted wing for the salt flats.

Quite a few of the solar cars and design student's cars are going this inverted wing route now.

My own automobile sketches have taken this direction as well, I'll post my sketches when I have the time.

[Don Ro]

I guess that my notion of the optimal aero design being already present in the cars that we can buy now is wrong (?). So many of the common high-end cars all look similar that I was under the impression that they found the optimal design.
MB, VW C1200, Hyundia, Kia, etc.
.
FYI...

My '83 Ford T-Bird Turbo Coupe's 145 horsepower 2.3 L 4-cylinder engine had a 143 mph top speed.
The 2,998 lb. car had a drag coefficient of .35 and would use 15 hp to maintain 60 mph...according to Ford engineers.

[cockerpunk]

"teardrop" is always the best shape for moving though fluids

[RWebb]

Originally Posted by Don Ro

I guess that my notion of the optimal aero design being already present in the cars that we can buy now is wrong (?). So many of the common high-end cars all look similar that I was under the impression that they found the optimal design.
...

maybe they did - but things change when you don't need to run an IC motor inside the car


and all you pro teardrop people... please read thru the thread first

[dlockhart]

Update this 1930s concept with modern material sciences

[kach22i]

Originally Posted by RWebb

maybe they did - but things change when you don't need to run an IC motor inside the car

True that, take for instance the Bugatti Veyron, if it were not for the dozen or so air inlets to feed and cool it's massive internal combustion engine the body shape would actually have a pretty low Cd.