[aerohead]

Back in the 90s I did a inflatable boattail for the T-100 ,when it was John Gilkison's.We took it on a camping trip near the Very Large Array,in New Mexico,and did a roundabout long way home,just to get more miles.For about 600 miles of driving,the inflated tail gave over 30-mpg.We were quite pleased with the performance.It was constructed of sewn naughahyde,tailored over patterns drawn for a 12-degree convergence angle (top and sides),stapled to an airtight box constructed to fit the tailgate region of the truck.A 12-VDC heater fan out of a Volkswagen Westfalia camper van provided the inflation pressure,which was powered through a simple electrical umbilical cord, alligator-clamped onto the truck's battery,and strung underneath the truck to the rear.A larger unit would no doubt help a 18-wheeler,although thats outside the scope of what I can take on.A fellow in Lubbock,Texas has a U.S.Patent on such a device for 18-wheelers.I've seen photographs of it.He has a lot to learn about aerodynamics,and could look to the German designs of the 1920s,where the concept originated.Hucho's book,"Aerodynamics of Road Vehicles",published by Butterworth's has a beautiful image of an ideal design.