This section describes an alternate method for calculating drag area, CdA, for tractors using constant-speed aerodynamic drag testing.
Where:
[PHI]veh = the vehicle direction, as described in § 1037.528(f)(2) .
Example:
w = 7.1 mi/hr
v = 69.9 mi/hr
[PHI]w = 47.0°
[PHI]veh = 0°
[PSI]air,th = 3.97°
Where:
Ttotal = mean of all corrected torques at a point in time.
v = mean vehicle speed.
fnwheel = mean wheel speed.
M = the measured vehicle mass.
ag = acceleration of Earth's gravity, as described in 40 CFR 1065.630 .
hinc = elevation at the start or end of each 10 second increment expressed to at least two decimal places.
Dinc = distance traveled on the road surface from a fixed reference location along the road to the start or end of each 10 second increment, expressed to at least one decimal place.
Example:
Ttotal = 2264.9 N·m
v = 31.6 m/s
fnwheel =598.0 r/min
M = 16508 kg
ag = 9.8061 m/s2
hinc,start = 0.044 m
hinc,end = 0.574 m
Dinc,start = 215.4 m
Dinc,end = 697.8 m
FRL70 = 4310.6 N
Where:
CdAi[speed] = the mean drag area for each 10 second increment, i.
Faero[speed] = mean aerodynamic force over a given 10 second increment =
FRL[speed] -
FRL10,test.
Vair[speed] = mean aerodynamic force over a given 10 second increment.
R = specific gas constant = 287.058 J/(kg·K).
T = mean air temperature.
pact = mean absolute air pressure.
Example:
FRL70 = 4310.6 N
FRL10,test = 900.1 N
Faero70 = 4310.6-900.1 = 3410.5 N
V2air70 = 1089.5 m2/s2
R = 287.058 J/(kg·K)
T = 293.68 K
pact = 101300 Pa
CdAi70 = 5.210 m2
40 C.F.R. §1037.534