The back end of a Semi Trailer, in motion, creates a low pressure condition increasing the drag of the complete unit resulting in a fuel economy reduction. The length of the overall vehicle prohibits the addition of air deflectors to partially reduce this condition. While several attempts have been made to reduce this condition, none have proven effective and economical. As a result, the following concept is submitted as a possible solution.
Consider the real lower portion of the trailer as a space to install an air deflector that would force the air into the low pressure area of the trailer. The device would merely be a sheet metal deflector mounted on an angled track with casters. The air, moving under the trailer, would force the deflector out and direct the air into the low pressure area. As the vehicle slows down, the deflector would roll back to it position under the trailer. As the vehicle picked up speed, the air would force the deflector out to direct the air into the low pressure area.
Drawing BMIC 200, shows the location of the deflector in a retracted and extended position. The force of the air, under the trailer, would move the deflector out and direct the air into the low pressure area. As the vehicle slows down, the deflector would retract to its original position. Small deflectors, functioning in the same manner, can be added to the area at the rear of the tires.
The angled track can be replaced with a spring to retract the deflector. Other methods can also be used if the angled track created problems.
This is a very simple devise to reduce the drag at the rear of the trailer resulting in an improvement in vehicle fuel economy.