Fuel Savings by Means of Flaps Attached to the Base of a Trailer: Field Test Results

This paper presents field test results for fuel savings by means of flat flaps attached to the base of a standard semi trailer. The flaps are constructed from a fiberglass-epoxy-resin material and have a length equal to one-quarter of the trailer-base width (about 61 cm or 2 feet). They are attached along the rear door hinge lines on either side of the trailer and along the trailer roof-line so that no gap appears at the joint between the flap and the trailer base. The flap angle is variable and can be set to 10, 13, 16, 19 or 22 degrees.

Tests were conducted in May 2004 at the NASA Crows Landing Flight Facility in the northern San Joaquin Valley, California.

Analysis of the data show fuel consumption savings at all flap angle settings tested, when compared to the “no flaps” condition. The most beneficial flap angle appears to be 13 degrees, for which the fuel consumption is 0.3778 ±0.0025 liters/km compared to the “no flaps” control of 0.3941 ± 0.0034 liters/km. The error bounds expressed above mark the 99% confidence interval in the mean values given. That is, additional estimates of the mean fuel consumption would be expected to lie within the bounds given, approximately 99% of the time. The fuel consumption saving is-to reasonable accuracy-about 1.63 liters/100 kilometers. These savings represent the increment associated only with the change in drag due to the presence or absence of flaps. The result will hold for any truck of similar size and shape and engine performance regardless of the loading of the truck or the rolling resistance.