Environmental Engineering Reference
In-Depth Information
over the trailer. In the previous section the inclusion of a covered trailer in tow on the
vehicle resulted in a very substantial increase in drag coefficient, due in large part
to the separation distance between towing vehicle and towed trailer. Semi-tractor-
trailers are designed to minimize the tractor-to-trailer spacing to reduce air drag.
Figure 11.6 is the semi-tractor used in the coast down testing to be described.
Figure 11.6 Class-8 semi-tractor used in coast down test (from Reference 4)
Dimensions and relevant data on the class-8 tractor are listed in Table 11.5,
where (11.3) has been used to estimate the frontal area. Ambient conditions at the
test site were a temperature of
5
C and barometric pressure of 30.37 in-Hg,
resulting in an air density of
r ΒΌ
1.331 kg/m
3
.
Table 11.5 Class-8 tractor specifications
Vehicle system
Unit
Value
Body: cab-over
Height
m
3.200
Track
m
2.146
Length
m
5.385
m
2
Area-frontal
6.182
GVWR
kg
9,020
Engine
L
V8, CIDI 400 Hp
Transmission
18 speed, MT
Tyres: (10)
P285/80-R24.5
mm
285
Section width:
w
s
mm
228
Section height:
h
s
in. (mm)
24.5 (622.3)
Rim diameter:
d
rim
Tyre dynamics
Rolling radius
mm
531
Revolutions/mile
#
480
