Document ID: chunk:federal_register_of_legislation:F2024L00446:reg:6600:p21
Version: federal_register_of_legislation:F2024L00446
Segment Type: reg
Provision Reference: reg 6600 (pt 21/28)
Character Range: 850503–853709

dynamic pressure, N/ m².
              The absolute difference of the pressure coefficient  over a distance 3 metres ahead and 3 metres behind the centre of the balance in the empty test section and at a height of the centre of the nozzle outlet shall not deviate more than ±0.02.
              where:
            is the pressure coefficient.
              3.2.9. Boundary layer thickness
              At  (balance center point), the wind velocity shall have at least 99 per cent of the inflow velocity 30 mm above the wind tunnel floor.
              where:
                   is the distance perpendicular to the road where 99 per cent of free stream velocity is reached (boundary layer thickness).
              3.2.10. Restraint blockage ratio
              The restraint system mounting shall not be in front of the vehicle. The relative blockage ratio of the vehicle frontal area due to the restraint system, , shall not exceed 0.10.
           where:
            is the relative blockage ratio of the restraint system;
                  Arestr is the frontal area of the restraint system projected on the nozzle face, m²;
                  Af is the frontal area of the vehicle, m².
              3.2.11. Measurement accuracy of the balance in the x-direction
              The inaccuracy of the resulting force in the x-direction shall not exceed ±5 N. The resolution of the measured force shall be within ±3 N.
              3.2.12. Measurement precision
           The precision of the measured force shall be within ±3 N.
              4. Road load measurement on road
              4.1. Requirements for road test
              4.1.1. Atmospheric conditions for road test
              Atmospheric conditions (wind conditions, atmospheric temperature and atmospheric pressure) shall be measured according to paragraph 3.1. of this annex. Only those atmospheric conditions measured during coastdown time measurements and/or torque measurement shall be used for checking data validity and corrections.
              4.1.1.1. Permissible wind conditions when using stationary anemometry and on-board anemometry
              4.1.1.1.1. Permissible wind conditions when using stationary anemometry
              The wind speed shall be measured at a location and height above the road level alongside the test road where the most representative wind conditions will be experienced. In cases where tests in opposite directions cannot be performed at the same part of the test track (e.g. on an oval test track with an obligatory driving direction), the wind speed and direction shall be measured at the opposite parts of the test track.
              The wind conditions during run pairs shall meet all of the following criteria:
                  (a)  Wind speed shall be less than 5 m/s over a 5 second moving average period;
                  (b)  Peak wind speeds shall not exceed 8 m/s for more than 2 consecutive seconds;
                  (c)  The arithmetic average of the vector component of the wind speed across the test road shall be less than 2 m/s.
              The wind correction shall be calculated according to paragraph 4.5.3. of this annex.
              4.1.1.1.2. Permissible