[timer]

Find a picture of a commercial jet that has blunt rear surfaces like a semitruck, instead of tapered tails. The kamm effect and toyota engineers...those japanese engineers will believe anything. There’s the story of how we let them steal a certain ship design from US in WWII, knowing they would copy it. Of course in the plan the center of gravity was above the center of buoyancy, what happened then when it slid out of dry dock? They’ll believe anything....

As to extensive wind tunnel testing, fish, birds, even airplanes flying in the real world have VAST experience in tapered vs blunt tails, you’re just trying to be cute or the devil’s advocate. Maybe you can hire on at airbus(airbust)and introduce them to the kamm effect and blunt tails.....

Sadly though, here the public whines about “freedom from foreign oil”. It should be “freedom from stupidity” as semitrucks roll on, pulled back into the suction zone of the hole they blow thru the air. A TAPERED TAIL would eliminate most of that rear aerodrag(fish tail)just as the aeroshell does over the cab(fish head).

Again, a box has 14 times the aerodynamic drag of an equal cross section torpedo, that’s right there in every physics book. In the movie : Flight of the Phoenix, the tail of the box is a tapered clam shell. Now if it works in a 300 mph aircraft, why not a 70 mph semitruck?

No, I’m not suggesting a solid shell tapered tail, it would either be a curved pyramid form made by an inflated balloon or open weave parachute, on a hinging frame, that deploys at high speed(above 35 mph), then retracts back onto the rear doors as the truck slows to a stop(below 15 mph). You could also have two (on each back door)that joined via magnetic zippers(top and bottom furrows to the rear point).

If this tapered tail boosts energy efficiency of the truck by 3 mpg, then on a 7 mpg rig : 7+3=10 mpg. With an annual fuel bill of $50,000, that’s about $15,000/year that stays in the trucker’s wallet instead of becoming the gov’t/big oil’s cash cow. So maybe you’re a front man for them with your kamm effect, or just intellectually lazy...

[Andy from Chapel Hill]

When the air (or any fluid) is parted by an object moving at speed, the time it takes for the air to “come back together” is finite. What Kamm said was that at about 60 mph, a car would have to be approximately 35-40 feet long in order for the parted air to rejoin without turbulence. Objects that are tapered with a reasonable cross-sectional area relative to their length would have a lower Cd (coefficient of drag). Thus, the “streamlining” only works when the ratios are correct. He further stated that it is a waste of time to try and streamline a car unless you are willing to design one 35-40 feet long. Trucks would have to be much longer. The Kamm Effect is simply cutting off the tail of the streamline and trading cargo space for an unworkably long vehicle.

Today, truck length is specified by law. Truckers know that economically the increased amount of cargo space with a Kamm-back far outweighs the fuel efficiency gains of making a streamlined tail within the legally permissible length.

There are designs that try to pressurize the area behind the chopped-off tail and many of them use NACA ducts to achieve this effect. See http://en.wikipedia.org/wiki/NACA_Duct

But, these designs do not lower drag much at automotive speeds, so they are usually left for race cars and aircraft.

Seriously, before you accuse the engineering world of plotting against your inflatable cones, please check out a book on aerodynamics from the library and learn the physics involved.

I do not think it is appropriate to use FreeRepublic’s bandwidth to educate you further.