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Old 01-05-2012, 01:32 PM   #22 (permalink)
3-Wheeler
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Quote:
Originally Posted by TEiN View Post
....It may be because of the necessarily wide tires hanging out there in the breeze (which may be mitigated somewhat on a low-drag eco-modder design with skinny wheels and tires), but open-wheeled raced cars have MUCH higher drag than their (all-other-things-being-equal) closed-wheel counterparts.....
TEiN,

Did you miss the spot in the middle of post #15 where I mentioned using airfoils to cover the skinny tires/wheels?

I still think the CdA of a cigar shaped body with properly done "exposed and airfoiled" wheels is lower than widening the entire bodywork to match.

I guess my mistake was mentioning the word "Indy" car in my statement above. We jump to the conclusion of downforce and so on. Not my intent here. Remember, we are looking for maximal aero efficiency.

No, the only point in referencing an Indy car is that the fuselage is "cigar shaped", but obviously we are more concerned with a "round at the front" and a "tapered tail" in the design of our fuselage shape.

Let me point out some quick math: Let's calculate the CdA of two prototypes.

Fenders covering wheels, and at 60" width
Assuming the height of our vehicle is 36 inches, then the frontal area is 15 sqft
Optimum body shape Cd = 0.10
CdA = 1.5

Cigar Shaped Body with Airfoiled Wheels
Assuming cigar body width of 27" and height of 36 inches, then frontal area of body is 6.75 sqft
Airfoils over wheels are 12" wide by 24" high; frontal area is 2 sqft x 2 wheels = 4 sqft
Optimum body shape Cd = 0.10
CdA of body .675
CdA of wheels 0.4

So far the exposed wheel vehicle has a lower CdA... However, this only applies to a cigar body width of 27". You're mileage may vary.

There will be an interaction between the cigar body and faired wheels, so let's subtract something for this... make the CdA 10% bigger to accomodate CdA = 1.18

Also, air compression under the wider vehicle will also take it's toll, so can it be fair to add %5 to it's CdA, due to this effect?

The overall length of the 60" body shape will need to be longer to still reach a Cd of 0.10, so this vehicle design will need to consider this....

To me the cigar shape with faired wheels comes out ahead of the enclosed wheeled vehicle, just based on the math above..... Less frontal area, and shorter overall length for same Cd.

Jim.

Last edited by 3-Wheeler; 01-05-2012 at 02:00 PM..
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