Stingray SS

[Walter F.]

The stingray SS XP87 concept car , was probably the only concept car to ever be raced. I understand it was sucessful on the track. Since the design of the SS is almost identical to what would become the C2, why was there no mention of lift problems at speeds over 100 MPH as is the case with the C2. Wouldn't this issue have been addressed in the C2 production if it was an issue on the SS ?

[Duke W.]

Re: Stingray SS

It was simply called "Stingray" and was built on the "mule" (development) chassis for the 1957 Corvette Super Sport (SS) program that was raced at Sebring in 1957, but retired after only an hour or two with a disintegrated rear suspension bushing.

The mule chassis was purchased from GM by Bill Mitchell, supposedly for one dollar, with a provision that it would not be identified with General Motors. Then Mitchell and Shinoda designed and built a body on the principle of an "inverted airplane wing", but neither had any theoretical or practical ground vehicle aerodynamic experience. Their intuition was flawed.

In fact, no automotive manufacturers had a decent understanding of ground vehicle aerodynamics in that era. The design emphasis was on low drag, but such designs usually produced a lot of lift. Any pilot understands the "ground effect" - an increase in lift as the airplane approaches the ground on landing, and it's most noticeable on light aircraft, but the dots never got connected.

Various articles I read over the years reported that Dick Thompson said the Stingray was a handful at high speed, and he knew it had a lot of lift, but still won the 1960 SCCA C-modified national championship. Mitchell was financing the team out of his own pocket and didn't have the funds to do extensive testing and development.

The 1963 SWC design was tested at the Cal Tech wind tunnel, but it was a crude solid model that did not take into account the air flowing through the car. The Cd of the production car is about 0.5, and it has a lot of lift compared to about 0.3 for a modern Corvette, which has very little lift at high speed.

By the mid sixties manufacturers and high end race teams (like Jim Hall working with Chevrolet R & D under Frank Winchell) began serious study of aero using disciplined engineering approaches with a special emphasis on understanding and mitigating the causes of lift. Ford conducted wind tunnel testing on the GT-40 program, but the design was still flawed. At high speed the rear developed a rotary motion - like an arrow without feathers that caused a crash at LeMans in 1964 and a generally poor showing. Ferrari had a similar problem with the original GTO in 1962, and one story is that Richie Ginther suggested the addition of the "duck tail". For 1965 Ford redesigned the front and rear GT-40 bodywork including the addition of a rear spoiler and eliminated the sophisticated driver ventilation system that produced much more drag than expected. With those changes the 1965 GT-40 had both lower drag and less lift.

That's when we began seeing front air dams and rear spoilers, even on production cars like the original Z-28, and by the late sixties purpose built race cars like F1 and Group 7 (Can-Am) were sprouting huge wings. The ultimate product of that decade of aero development was the Chaparral 2J - the infamous "vacuum cleaner car" that was so much faster than any competitor it was outlawed after a few races.

Understanding of ground vehicle aerodynamics had come a long way in a decade.

Duke

[Walter F.]

Re: Stingray SS

Thats amazing that men like Zora and other Ford and GM engineers were so in the dark about air flow. I wonder if the people at Mercedes who seemed to master fuel injection early understood it better.

[Duke W.]

Re: Stingray SS

No, the European manufacturers were as clueless and everyone else. Mercedes did have an interesting air brake on the mid-fifties 300 SLR. A panel like the one that covers the convertible top on a Corvette popped up when braking, which helped save the brakes at the end of the Mulsanne Straight.

If you look at sports and sports racing cars from the fifties and early sixties, they have beautiful, swoopy bodies, which had low drag in free air, but then on the ground, drag increased significantly due to a phenomena called induced drag due to lift. Attaching air dams and spoilers would have increased free air drag, but actually reduced drag (and lift) on the ground due to decreasing induced drag due to lift.

I've asked the same questions as you. The auto industry, particularly those involved with racing, knew the cars were aerodynamically flawed, but didn't know how to solve the problems. So why didn't they hire a few experienced aero engineers from the aerospace industry? Maybe it was the NIH syndrome. There was very little cross-fertilization between aerospace and automotive back then.

Another issue was how the automotive industry was organized. The "designers" who had complete control over the physical design of the car were primarily artists, and engineers had virtually no input. Duntov, who was a brilliant intuitive engineer, certainly knew the designs were aerodynamically flawed and may have had some solutions, but had no control. "Design" was Mitchell's turf and he guarded it like a junkyard dog.

Nowadays, engineering and manufacturing are involved in the exterior design process from the get-go and full sized prototypes are tested in large wind tunnels.

Duke