Quote:
Originally Posted by yugomodder
Ok, so I know the idea of an aerodynamic top for a car has been discussed but largely dismissed, but just hear me out. The template tapers slowly at first, but then later speeds up. If it's just a few degrees for the first part I could build an aerodynamic top that is just slightly taller than the existing roof, but then taper it down, and the accelerating taper coming of the back end would leave a smaller wake than the current Kammback design. I'm not sure how this could affect CdA and I guess I could test it eventually, but for now it's just a though experiment and I'd like to hear some theories as to what the effect would be.
This is a picture of the current Kammback with the template overlayed. I think it matches fairly well.
This is a picture of the current Kammback with the template overlayed as if the windshield were slightly higher and the taper started closer to the front of the car. As you can see, the template in this case would go below my current Kammback.
This last image is what the car would look like with a streamlined top according to the template.
Now to me this seems like it would at least reduce Cd, but I'm not sure about CdA. Also I'm not sure how I would get the hatch to work properly in this configuration if there even is any aerodynamic benefit. I just thought it was an interesting thought experiment, and I would like to share it with everybody.
Note: The aerodynamic top adds 1.75-2inches to the height of the car, but the tail comes down to 3.75-4 inches below it's position at the other Kammback. This means the top would add about 2% to the frontal area which means if drag is the only concern it would have to have a Cd that is an additional 2% less than that of the original Kammback. You could possibly get some more headroom if you re-did the interior a bit but you would also have slightly less glass out the back to see through, so there are trade offs either way.
Now that 2% less isn't just two percent, if the normal Kammback nets a 6% gain, then 2% is 1/3, meaning the new Kammback must be at least 1/3 more effective. The original Kammback cuts about 2in off the height of the wake area, where as the new one cuts 6inches off the height of the wake area. If it's all about the amount of wake area then the new Kammback should give three times the Cd reduction of the original one. Now there are other factors, but that's promising. If the frontal area actually increases by about 2% and the Cd is reduced by about 18% (6%*3) that would give a total new CdA which is 84% of no Kammback (1.02*0.82=0.8364) and about 89-90% of the other Kammback.
The front part coming off the windshield may help alleviate any small separation that occurs at the top of the roof, along with providing smoother airflow from which to streamline which could possibly net a small drag reduction.
*warning all of this information is deduced through logic based off of numbers which may or may not apply to this or your situation. Your mileage may vary*
Please let me know what you think! |
*if the windshield header has that sharp of a corner,then the roof addition would help maintain attached flow back to your new zero-point.
*the flow from there on back would have the benefit of the camber which Kamm would give the thumbs up to.
*my thought about the front is to leave the hood alone,but go after the actual nose of the car.
*from the hood top leading edge,you could project forward and down as you see with contemporary cars,with maybe at least(I want to say) 80mm radius.
* the nose should enclose the bumper,and the outer edges should wrap around with at least the 80mm radius as well.
*you could project the bottom of the nose down to the elevation where it intersects an imaginary line projecting from where your tire tread leading face hits the ground,up and forward at a 16-degree angle,as measured from the horizon.This will prevent a ground-strike with curbs and driveway ramps.
*rear wheel skirts aren't mandatory,but they'd help your Kamm boat tail work better.
*your roof/boat tail extension is dead on,so you're good there.
I don't see any reason why you couldn't match ,or come in lower than current production car Cds.
