Aerodynamics of a car and trailer?

Question

Hi, im building a work trailer, builder type, and i want to set it up as aerodynamic as possible, i have a station wagon to help but would i string line straight across the car from the front bumper to the trailer for stream? im working on speed of about 110-120 klph, the shell will be sheet aluminium and fully enclosed.

I know that due to variables there may be no exact formula but any advice would be greatly appreciated.

PS the venturi of truck tailgating although is not wise practice can actually create suction and pull u a long,I have done it and actually started to overheat the motor through no airflow, the suction is what i want to create with my trailer.

Thanks heaps

Answer 1

The only way you can minimize the drag on the truck/trailer combination is to build your truck/trailer like a semi + double trailer. What I'm saying is to have only a small gap between them. A good example would be if you took a train car out of a mile long train, the drag would not change very much, because one car is in the wake of another. You need to keep the front of the truck as streamlined as possible and the back of the truck must have the same profile area as the front of the trailer. In other words no wake from the truck. To minimize the drag on the trailer, the back end should be tapered to minimize the back pressure. (like an airstream trailer)but you'll lose space in the trailer).

Another thing you can do is minimize the protuberances (antennas and such hanging out on the sides and roof).

The only equation I can give you is the one for dynamic pressure;

q = 1/2* Rho*v^2 where Rho = .002387slugs/cu ft

v = speed (ft/sec)

You then get your drag by multiplying q times the frontal area (this is the area the wind sees).

Hope this helps!

Good Luck!