Quote:
Originally Posted by 3-Wheeler
Hi Aerohead,
OK, I am going to ask a nit-picky question here.... 
So a car with wide spaced wheels and thus covered with an appropriately wide body will, for it's resultant frontal area, have a lower Cd.
So far so good.
However, the counter response to this is....
Make an appropriately sized 1) "cigar-shaped-fuselage" and cover the vehicle occupant, and 2) make proper sized airfoils for the appendages hanging outside the main fuselage, such as wishbone suspension members and wheels/tires.
I would think that this second vehicle, while having a higher Cd overall, would also possess a lower frontal area, and thus come away with an overall lower aero drag component than the "one-piece-body" shape.
Now my "discussion" above makes the assumption that this "body shape" is optimized for a single occupant, who is also the driver of the vehicle. I am not talking about the "new" VW 1L that has side-by-side seating and thus forces a wider body shape to the wind.
The width of the cigar body is, let's see, about 27 inches wide.... I had to measure the one that's in the basement right now....
I simply can not imagine how a car with a track width of let's say 60 inches, and a body that also is wide enough to cover this same width, and has a Cd of let's say 0.10 is going to ultimately have a lower overall drag component than a cigar shaped body with width of 27 inches and all external appendages covered with airfoils, with a Cd of let's say 0.15??
It may be that our responses to the main question above need to be qualified a little better to avoid over-simplifying the answer.
Just my opinion.
Jim. |
Jim,it's a good question.And I don't have a vast library to draw upon.
Mercedes did publish in the 1950s that when they enclosed their Gran Prix racer,even though the frontal area jumped,the overall drag factor (CdA) went down.
When So Cal Speed Shop wanted top performance,they enclosed their So Cal belly tank lakester inside a fully-enclosed streamliner body of greater frontal area.The car wrecked at Daytona Beach and was never raced again so we don't have a lot of numbers there.
GM's Firebird-1 scored a very mediocre Cd with it's rocket-ship,open-wheeled styling.Typical SUVs today have lower drag.
The 1987 OLDS AEROTECH started life as a March INDYCAR of approx.Cd 1.20.When they lost the wings the drag dropped to around Cd 0.57.Without wheels these bodies are Cd 0.25.By enclosing the car inside the long-tail AEROTECH body,the drag drops to Cd 0.19.
Matt Llewelyns(sp?) Sylph,which registered Cd 0.11( I think Michael Hackleman reported it even lower) in the Guggenheim tunnel at Cal Tech in model form would be an example of a 'lakester'-type form of low drag and frontal area.So your logic is dead on!
The thing for me is to look beyond the MPG euphoria Hucho warns about and consider safety,
Virtually every fatal auto accident I've ever witnessed involved side impact.
Without an enclosing side body,there is virtually zero crumple-zone to absorb kinetic energy of an impact and even with side-curtain airbags you can still sever the brain stem.
I thought about this with my mini-hypercar and elected to go with a fully-enclosed body with ample side pod protection.
I really like open wheel design,it's just that I can't trust Barbie and Ken to drive defensively.
So it's a safety prejudice I get trapped in.
The 'pumpkin seed' body might deliver only Cd 0.11,maybe better.That seems like a decent compromise for safety sake.
