Quote:
Originally Posted by AeroModder
Actually, kammbacks do create lift from the low-pressure zone above them created by the downward angle. The air fills up the gap generated as it moves through the air, causing the molecules to spread out more. If you take a look at the Honda Insight's wind-tunnel smoke testing, you'll see the gap widen between the surface and the smoke trail as you come to the rear edge, indacative of lowering pressure. Though if you added a kammback to, say, a 3 box sedan (fastback), you'd most likely see a reduction of rear lift, but it won't be eliminated.
The rear on that race car pictured would be more of a fastback, and I'm sure that ducktail spoiler adds quite a bit of drag with it's downforce.
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AeroModder,I'm going to have to respectfully disagree with respect to your assessment of the Kamm-back.
It's true that the eruption of the roof and accelerated flow over the windshield causes lift,although that's something we've got to live with if we're going to have a greenhouse on vehicles.
With respect to the roofline,the smoke trails spreading apart is indicative of the streamline flow deformation caused by the passage of the car,rebounding to it's undisturbed orientation,with a deceleration in the flow and consequent pressure rise.
With the Insight,the curvature of the roofline,in my opinion,is too aggressive,and what you are witnessing is flow separation,as the streamline is unable to follow that contour.
I agree that there will be lift over the hatch on the Insight,as the pressure above the hatch is that of at the point of separation.With a 'proper' Kammback,separation is impossible( that's it's premise) over the hatch,and is moved to the 'back' of the car where vertical lift cannot occur.
If your 3-box car has good flow up to the attachment point of the Kamm-back,aside from the lift ocurring at the windshield,it is not possible for the Kamm-back to add lift,only reduce it or eliminate it,as the pressure is acting on a vertical wall.
The Ford Mk IV has fully attached flow all the way to the 'end' of the car,and since the rear is cantilevered,the base pressure will actually produce downforce due to the torque acting between top and bottom of car.
Please GOOGLE an image of the 1994 Bugatti EB 110.This is a $350,000,207-mph supercar with perfect Kamm-back.And feel free to compare it to the Aerodynamic Streamlining Template.