Page 10 - Combined_22_OCR

DISCUSSION

The data presented herein are preliminary and therefore are subject to change.
However, it can be readily used for determining a configuration suitable for competi­
tive racing. The aerodynamic forces which were acting on the 1368 NASCAR race
vehicle have been shown in Figure 6 compared to a recommended race configuration
for 1970. Horsepower required (strictly from an aerodynamic viewpoint) has been
reduced by approximately 118 HP (Figure 6(a)); front end lift has been reduced approx­
imately 550 pounds (Figure 6(b)) to the point that now past a body rake angle of -1.0°
a down force is actually applied to the front wheels; at the same time however, approx­
imately 285 pounds of lift force has been added to the rear wheels. Aerodynamically,
this wheel loading change indicates a rearward shift in the center of pressure which
will result in a more stable vehicle in the pitch plane. The yaw plane however exer-
sizes the predominate control on car handling characteristics. In Figure 6(e) it is
seen that a slight change occurs in the side force characteristics of the two cars as
they are allowed to yaw (dashed lines indicate extrapolated data from previous tests,
Reference 2). In this case the center of pressure on the proposed 1970 race car has
moved forward causing the car to be aerodynamically less stable in the yaw plane.
What effects in handling these changes in C.P. location actually cause are not
immediately apparent from these data since a baseline has not been established for a
good or bad handling car. References 3 through 5 state the importance of car center
of pressure location and static margin and show the effects of various side force C.P.
locations on a particular car!s handling.characteristics. However, other factors such
as tires, suspension and C.G. location also play important roles in the car stability
and handling performance. It is, therefore, recommended that track tests be con­
ducted specifically to collect data on the race car which can be used to form a basis
for vehicle handling performance.

The recommended 1970 configuration does not include any rear deck spoilers
or high flying wings which have been proposed for some Chrysler line cars. Previous
tests have shown, however, that rear deck spoilers act independently, aerodynamically,
of any changes made to the front end and that approximately 150 pounds down force can
be added to the rear wheels by a 45° - 1 inch spoiler with approximately a 3.5% drag
penalty (Reference 6). Use of a rear deck spoiler then should result in essentially a
zero lift car. No comment can be made at this time on car handling performance with
high flying wings.

In arriving at the recommended 1970 race configurations, three basic changes
were made to the standard car. First, the rather blunt front end shape of the standard
car creates unfavorable pressure distributions and air flow patterns that cause ex­
cessive drag and front end lift. Taking advantage of previous tests on a Dodge Charger
an 18" extension (aerodynamic fairing) was designed to fit onto the FW-23 bumper

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