Quote:
Originally Posted by drmiller100
length of the tail would then be 3.5 times the half a body width (two sides).
the arctan(3.5) is about 74, leaving the angle 16 degrees to the direction of travel.
My theory is there is theory, and what works in the real world. I think for the sides you have to run a shallower angle because direction of wind in relation to the car is a big deal, where when looking at the top of the car, you can run a steeper angle as teh top of the car doesn't care what angle the wind is.
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For Johansen's boat-tailed tail car he appears to have just factored the width of the car as it is more narrow than tall,and to economize on material,utilized this parameter for the contour.Rumpler did this with his cars as well as Jaray with his small cars.The fastest Bonneville streamliners,be they 4-wheel or 2-wheel,all use plan view boat-tailing as the dominant criteria.
The surface friction drag coefficient for the tail car is Cd 0.05,so when you subtract this out,it leaves Cd 0.05 for the tail itself.It would be Cd 0.045 if 'ideal',according to theory.
So to achieve Cd 0.045 it looks like the contour is plenty good with a max tangent angle of 22-23 degrees,which falls very close to Mair's 1969 research,and Emmelmann's from the 1970s.NASA's boat tail for the Ford Econoline of 1980 isn't remarkably different.
With respect to angles,or contour for top and sides,ideally,they would be verified in a wind tunnel to guarantee that no vorticity was being introduced.
If we limit tangent angles to respect the 22-23 degree 'rule' we ought to be safe.
Kenny Lion's BMW motorcycle streamliner which I crewed on in 1990 was measured at Texas Tech's wind tunnel at Cd 0.11.
Walter Korff's design of the Summer's Brothers Goldenrod is rated at around Cd 0.115.This car was designed for a top speed of 555 mph.It ran a 1-way pass at 425 mph in 3rd gear on 'slush,' on the low power HEMI engines.
So the plan-view streamlining is known to perform just fine
The non-ideal streamlined train gets over 50% better mpg at 100 mph than the 'standard' railroad train.