Page 24 - Combined_73_OCR

In an earlier test conducted at Wichita State University on 3/8
scale clay models of several advanced Styling concepts, P I limited back-

light study was performed. Because of the three dimensional effects on
ttached flow, all backlight configurations tested had the sideglass to
0

backlight juncture rounded as much as possible in an attempt to hold
that variable constant. If the test results, presented in Figure 12, are

viewed in terms of the objective trends indicated, of particular interest

is the "bucket” in the axial force curve. This indicates that something

less than a full fastback is preferred from a performanc ft tandpoint;
thi effect has al c o o been observed by Mitamura (8). The cause of the

"bucket” effect is not known but it is postulated that the total axial

force component resulting from the pressure distribution over the fast-

back is greater than for the semi-fastback and/or that the base pressure
of the vehicle is slightly affected. A more complete study including

pressure surveys of the backlight region would be required to fully ex­
plain this phenomenon. Also of interest is the ’’bucket” hape of the

rear axle lift curve. If minimum lift is a desirable cirteria, and we

have stated this is the case for the Daytona, designing the backlight

to minimize axial force will tend to minimize rear lift.

The backlight of the standard Charger has a slope of 45° and the

inset nature of the backlight, when viewed from above, precludes flow

onto the backlight from the sides of the car. As we would expect, the

flow is separated over the entire backlight region. The Daytona back­

light has a slope of 22° and the side to backlight juncture has been

rounded. Flow attachment is now achieved with a resulting decrease in

axial force coefficient of .021 and a decrease in rear lift coefficient

of .065 at a zero yaw condition. The basic backlight shape is a close

-23-