Design flaw C2

[Walter F.]

I have read and have heard discussions about the C2 design being flawed . That at high speed the C2 is dangerous as the front end tends to lift. The same sources claim Duntov knew this to be true but since Mitchel was the designer and in charge the design of the Stingray nose was left alone. Any truth to this?
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[Tyler T.]

Re: Design flaw C2

I will attest to the lift at speeds over ~70mph. Solved by a 3 in lip/spoiler on front (bumper on), it also solved a tendacy to run hot at the higher speeds.

Tyler

[Wayne W.]

Re: Design flaw C2

I don't know about 70, but at 140 its light. What did Zora say? Its a pretty good car up to 140 then becomes a bad airplane.

But, Aren't you glad they didn't change it?

[Russ S.]

Re: Design flaw C2

I have heard, whether it's true or not I don't know that the C1s actual have better aerodynamics that do the C2s.

[Stuart F.]

Re: Design flaw C2

I also learned this quite by accident (almost) in 1963. My buddy and I were on our way to Las Vegas over the speed limit free roads of Nevada trying to run between 100 to 130 mph to get there in a hurry and see what my new Vette would do. Well, what with the great 6.70x15 U. S. Royal bias ply tires under us, who is afraid to run wide open - well I was. That thing was all over the road. Fortunately, it began to get dark and I went for the headlight open switch and immediately noticed a great improvement in stability once they were open. Apparently the headlights acted as an air dam to pull the front end down. Later we read where the body design was such that it acted like a wing creating lift.

To this day, day or night, when I'm out on the highway I open the headlights. Wide open it would probably slow the car down, but then I don't care so much to do high speed runs anymore.

Stu Fox

[Dick W.]

Re: Design flaw C2

Zora put Jr. Johnson in a Grand Sport at Daytona to test. He ran two-three laps, came in and told Zora "you *** **** SOB's are crazy if you expect me to drive that bastard" He had gone down the back straight somewhere over 170, turned the steering lock to lock with no steering response.

[Terry M.]

Re: Design flaw C2

Nothing new here. I can't speak for the C1s, but at speeds over 140 the C2s and C3s want to lift the nose. The C4s are a little better, they don't get light in the nose until about 175. I am told the C5s are better, but I can tell you the C6s were designed for top end and are rock steady as fast as they will run. At the risk of getting in trouble with Roy, we had both the NASCAR car and the 2013 427 Convertible brought by the Hendricks team on the lifts at San Diego as an adjunct to the Advanced Judging Seminar. I spoke to some of the chassis of the 427 Convertible and pointing out the aerodynamics of the bottom of that car was most of what I talked about. The C6 is as beautiful on the bottom as it is on top. I expect the C7 will exceed the C6 in aerodynamics. Improving the aero is free (well almost) speed and more importantly fuel mileage. In today's automobiles aero is almost as important as light weight.

[Douglas C.]

Re: Design flaw C2

The aerodyamic lift on the front of the C2 has as much do to with the air flow underneath the car as it does with the flow over the hood and fenders. Relatively high velocity air over the hood, leads to low air pressures, whereas slow moving, separated, or stagnant air under the front end - captured by the engine compartment for example, leads to high air pressure and the differential produces "lift".

Nowdays, most aerodynamic designs are done with computational models run on high-speed computers, where engine compartment and geometrical details under the car can be captured.

Everyone has seen photos of the '63 Vette showing upper surface streaklines in the Caltech Wind Tunnel. They probably weren't concerned with the flow UNDER the car and in the engine bay - so the whole aerodynamic effect was likely just "missed" in the tests.


--Doug (B.S.,M.S.,Ph.D., Aeronautical Engineering)

[Dave B.]

Re: Design flaw C2

Doug can correct me on this, but I suspect that when Stu opened his headlights, they acted as "spoilers" which separated the some of the air flow and killed some of the low pressure lift.

The headlights sound like a good idea...even with radials.

Dave

[Douglas C.]

Re: Design flaw C2

Actually, in looking at the Caltech tunnel pics, it appears that what they were really looking for was separated flow off the fastback of the Split Window. Any streaklines going backwards (against the primary tunnel flow direction) would indicate flow separation on the vehicle and therefore increased drag - generally not a good thing.

Seems much of the focus in automobile aerodynamics back in the old days was on drag, but not necessarily lift.

Both Lift and Drag vary as velocity squared - which is why you don't expereince the adverse Lift effect until you're going over 120+ MPH.

There's an old paradigm that's used in evaluating fighter jets - if it looks fast, it will proabably go fast! Maybe the same could be said for automobiles.


Caltech Tunnel.jpg

--Doug

[William C.]

Re: Design flaw C2

Just 'Zactly how fast are you follows driving these cars?

[Jim L.]

Re: Design flaw C2

I've tickled a buck forty in one of mine.

[Duke W.]

Re: Design flaw C2

Ground vehicle aerodynamic behavior in that era was not understood, which seems odd because aero engineers were very familiar with the "ground effect" when airplanes are close to the ground.

Designers of race cars tended to design curvy, swoopy bodies that appeared to have low drag, but lift was not well understood. Eventually as race cars got faster, stability problems arose. One story has it that Richie Ginther invented the rear spoiler, and it improved the handling and speed of the '62 Ferrari 250 GTO.

I don't think the Cal Tech tests on the Sting Ray Coupe were instrumented to record lift - just drag. Also, I believe the model was "solid", so it did not include air flowing through the car, which causes a big increase in drag and can have a significant effect on lift.

When Ford tested the first version of the GT40 with the elaborate driver ventilation system, the drag calculations were way low, and the car would not reach 200 MPH, which was the objective. They eliminated all the ducting and the car exceeded 200 MPH, however, it still had a stability problem that killed Walt Hansgen at Le Mans practice in 1964.

Further investigation indicated that the rear was developing a rotary motion at high speed similar to an arrow without a tail. The rear tires lost traction and the car went out of control. The cure was the rear spoiler and a redesign of the front end to keep air from getting under the car.

From the mid-sixties-on the learning curve was steep. A key to both low lift and drag is to keep air from getting under the car and minimize the amount of air that flows through the car to the absolute minimum for cooling. You can see all this in today's Sprint Cup cars.

Even if Cal Tech had realized that the Sting Ray was an aero disaster, I doubt if Mitchell would have changed the design. Fortunately, today, the designers work hand in hand with the engineers, which is why modern Corvettes have low drag and low lift with excellent aero-stability even when approaching 200 MPH.

Fortunately, for those of us who explored significant triple-digit speeds in the String Ray, it did not have a stability problem. The problem was front lift, which reduced steering response at high speed. At 150 MPH it did not want to change directions, and as long as there was no significant cross wind component, it was stable. Also it has very high drag by today's standards. The Cd is about 0.5. If the problem had been in the rear, like the GT40, some of us might not be around, today.

Duke

[George J.]

Re: Design flaw C2

Duke,
I think Hansgen died in '66 or '67. According to Dave Friedman's account, he was told repeatedly to slow down in practice, to the point of being called in to the pits, at least once, to be told so. He ignored the warnings and the worst happened. A shame.

George