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the road. Although, ideally, a moving representation of the road in the

tunnel is the only way to correctly simulate flow conditions, tests by

Beauvais, Tignor and Turner (2) indicate that with proper positioning

of the model, fixed ground planes can yield very acceptable results.

two dimensional, full span ground plane was used for the current tests.

At Wichita State University, the ground plane was mounted six inches

above the tunnel floor and extended the full length of the test section

(12 feet). To facilitate yaw studies, a center disk of the ground plane

was made moveable.

The model support system extends through the ground plane and con­

sists of four struts mounted directly to the balance and shielded from

the air stream between the tunnel floor and ground plane. The four

model wheels are attached to the struts thus giving model aerodynamic

forces and moments independent of ground plane forces and moments.

Approximately a 0.200 inch gap was maintained between the model wheels

and the ground plane; this amounts to raising the model by the average

displacement thickness of the ground plane boundary layer in the vicinity

of the model. This location is intended to minimize the effects of the

incorrect boundary layer at the ground plane and bring the lift data

into better agreement with actual car data.

A similar ground plane and model mounting set-up was used at the

Lockheed-Georgia tunnel. One important difference was that the ground

plane was larger (24' x 23” with model mounted at center), thus P

c n i—1 ightly larger ground plane boundary layer was present. Data differ-

ences attributed to the larger boundary layer will be discussed in the
corrections and correlation section.

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