Document ID: chunk:federal_register_of_legislation:F2024L00446:reg:16:p5
Version: federal_register_of_legislation:F2024L00446
Segment Type: reg
Provision Reference: reg 16 (pt 5/108)
Character Range: 897184–900316

4.3.2.5.3. Aerodynamic drag modelling
              The aerodynamic drag coefficient CD(Y) shall be modelled as a five-term polynomial as a function of yaw angle Y as in the equation below:
              a0 to a4 are constant coefficients whose values are determined in the data analysis.
              The aerodynamic drag shall be determined by combining the drag coefficient with the vehicle's frontal area Af and the relative wind velocity vr:.
4.3.2.5.4. Final equation of motion
             Through substitution, the final form of the equation of motion becomes:
              4.3.2.6. Data reduction
              A three-term equation shall be generated to describe the road load force as a function of velocity,  , corrected to standard ambient temperature and pressure conditions, and in still air. The method for this analysis process is described in paragraphs 4.3.2.6.1. to 4.3.2.6.10. inclusive of this annex.
              4.3.2.6.1. Determining calibration coefficients
              If not previously determined, calibration factors to correct for vehicle blockage shall be determined for relative wind speed and yaw angle. Vehicle speed , relative wind velocityand yaw measurements during the warm-up phase of the test procedure shall be recorded. Paired runs in alternate directions on the test track at a constant velocity of 80 km/h shall be performed, and the arithmetic average values of ,  and  for each run shall be determined. Calibration factors that minimize the total errors in head and cross winds over all the run pairs, i.e. the sum of , etc., shall be selected where  and  refer to wind speed and wind direction from the paired test runs in opposing directions during the vehicle warm-up/stabilization prior to testing.
              4.3.2.6.2. Deriving second by second observations
              From the data collected during the coastdown runs, values for v, , , and Y shall be determined by applying calibration factors obtained in paragraphs 4.3.2.1.3. and 4.3.2.1.4. of this annex. Data filtering shall be used to adjust samples to a frequency of 1 Hz.
              4.3.2.6.3. Preliminary analysis
           Using a linear least squares regression technique, all data points shall be analysed at once to determine  given .
              4.3.2.6.4. Data outliers
              A predicted force  shall be calculated and compared to the observed data points. Data points with excessive deviations, e.g., over three standard deviations, shall be flagged.
              4.3.2.6.5. Data filtering (optional)
              Appropriate data filtering techniques may be applied and the remaining data points shall be smoothed out.
              4.3.2.6.6. Data elimination
              Data points gathered where yaw angles are greater than ±20 degrees from the direction of vehicle travel shall be flagged. Data points gathered where relative wind is less than + 5 km/h (to avoid conditions where tailwind speed is higher than vehicle speed) shall also be flagged. Data analysis shall be restricted to vehicle speeds within the speed range selected according to paragraph 4.3.2.2. of this annex.