This section describes a methodology for determining aerodynamic drag area, CdA for use in determining input values for box vans as described in §§1037.515 and 1037.520.

(a) A trailer's aerodynamic performance for demonstrating compliance with standards is based on a ΔCdA value relative to a baseline trailer. Determine these ΔCdA values by performing A to B testing, as follows:

(1) Determine a baseline CdA value for a standard tractor pulling a test trailer representing a production configuration; use a 53-foot test trailer to represent long trailers and a 28-foot test trailer to represent short trailers. Repeat this testing with the same tractor and the applicable baseline trailer. For testing long trailers, the baseline trailer is a trailer meeting the specifications for a Phase 1 standard trailer in §1037.501(g)(1); for testing refrigerated box vans, use a baseline trailer with an installed HVAC unit that properly represents a baseline configuration correlated with the production configuration. For testing short trailers, use a 28-foot baseline trailer with a single axle that meets the same specifications as the Phase 1 standard trailer, except as needed to accommodate the reduced trailer length.

(2) Use good engineering judgment to perform paired tests that accurately demonstrate the reduction in aerodynamic drag associated with the improved design. For example, the gap dimension should be the same for all paired tests, and effective yaw angle between paired tests should differ by no more than 1.0°.

(3) Measure CdA in m2 to two decimal places. Calculate ΔCdA by subtracting the drag area for the test trailer from the drag area for the baseline trailer.

(b) The default method for measuring is the wind-tunnel procedure as specified in §1037.530. You may test using alternate methods as follows:

(1) If we approve it in advance, you may instead use one of the alternate methods specified in §§1037.528 through 1037.532, consistent with good engineering judgment, which may require that you adjust your test results from the alternate test method to correlate with the primary method. If you request our approval to determine ΔCdA using an alternate method, you must submit additional information as described in paragraph (d) of this section.

(2) The principles of 40 CFR 1065.10(c)(1) apply for aerodynamic test methods. Specifically, we may require that you use coastdown measurements if we determine that certain technologies are not suited to evaluation with wind-tunnel testing or CFD, such as nonrigid materials whose physical characteristics change in scaled-model testing. You may similarly reference 40 CFR 1065.10(c)(1) in your request to use coastdown testing as an alternate method.

(c) The following provisions apply for combining multiple devices under this section for the purpose of certifying trailers:

(1) If the device manufacturer establishes a ΔCdA value in a single test with multiple aerodynamic devices installed, trailer manufacturers may use that ΔCdA value directly for the same combination of aerodynamic devices installed on production trailers.

(2) Trailer manufacturers may combine ΔCdA values for aerodynamic devices that are not tested together, as long as each device does not significantly impair the effectiveness of another, consistent with good engineering judgment. To approximate the overall benefit of multiple devices, calculate a composite ΔCdA value for multiple aerodynamic devices by applying the full ΔCdA value for the device with the greatest aerodynamic improvement, adding the second-highest ΔCdA value multiplied by 0.9, and adding any other ΔCdA values multiplied by 0.8.

(d) You must send us a description of your plan to perform testing under this section before you start testing. We will evaluate whether plans for wind-tunnel testing meet the specifications of §1037.530, and will tell you if you may or must use any other method to determine drag coefficients. We will approve your request to use an alternate method if you show that your procedures produce data that are the same as or better than wind-tunnel testing with respect to repeatability and unbiased correlation. Note that the correlation is not considered to be biased if there is a bias before correction, but you apply a correction to remove the bias. Send your testing plan to the Designated Compliance Officer. Keep records of the information specified in this paragraph (d). Unless we specify otherwise, include this information with your request. You must provide any information we require to evaluate whether you may apply the provisions of this section. Include additional information related to your alternate method as described in §§1037.528 through 1037.534.