I have read that the C2 's front end lifted at speeds approching over 90MPH. Was that problem corrected in the C3 and did the C1 suffer from the same issues?
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Re: C1vs C2 vs C3 Aerodynamics
I can say for certain the C1, 1957 in my case, lifted. As for the C3 my '77 and '78 get a bit "light". Steve -
Re: C1vs C2 vs C3 Aerodynamics
Lift and drag forces increase with the square of speed, so there is lift at all speeds, but it becomes noticeable as you approach triple digits.
Most cars generate lift, particularly at the front, but the C2 is probably one of the worst among high powered cars. C1s, were not as bad, and C3s were better because of the front air dam designs that prevented air from getting under the car.
A C2 is much better behaved with a front air dam, and the aftermarket has offered them over the years.
I can tell you from personal experience of getting my SWC up to a little over 150 MPH a couple of times that the front end gets noticeably high, but the car is stable as long as there is no significant cross wind. Steering response becomes increasingly numb because there is less weight on the front end. It basically wants to go straight. According to GM test data a production C2 coupe will have zero weight on the front wheels at about 200 MPH, but it would take well over 500 HP to achieve such speed.
Rear lift is also generated, but it is mild compared to front lift. Rear lift greater than front lift is unstable, which can lead to loss of rear adhesion and the car going out of control.
That's was killed Walt Hansgen at LeMans back in '64 with the original design GT-40. The rear developed a rotary motion as it approached 200 MPH - like an arrow without tail feathers - which broke the rear end loose causing the car to go out of control and crash.
The fix was the rear spoiler, which Ferrari had already installed on the GTO, and from what I've read the idea came from Richie Ginther who had no training in aerodynamics, but he certainly had great intuition!
Ground vehicle aerodynamics were not well understood at the time. The general philosophy was to apply aircraft shapes (something close to a teardrop) to achieve low drag, but all pilots understand the "ground effect". Airplanes can "float" when they get close to the runway, particularly, light airplanes, because the wings begin to generate more lift at the same angle of attack as they get closer to the ground.
I guess there were no automotive designers who were pilots back then, but they finally realized that controlling lift was more important than achieving the lowest overall drag coefficient, and trial and error began producing the front air dams and rear spoilers on race cars and the designs eventually spilled over to road cars. There is something called "induced drag due top lift" - lift creates more drag, so if you put airdams and spoilers on the wheeled teardrop it actually generates both less lift and less drag even though it may look like a kluge.
Bill Mitchell clearly had no understanding of automotive aerodynamics when he supervised the design of the C2, and further, I don't think he cared. It was all about style.
Then there was Dr. Kamm's discovery that if you chopped the tail off a teardrop, overall drag and lift aren't that greatly effected, particularly with a rear spoiler, and the C3 was the first road car with a "Kamm tail". I think it was Duntov who pushed for Mitchell to incorporate newly discovered air flow management techniques in the C3 design, but the coke bottle flanks were just style. They actually increased drag compared to a more slab-sided design.
DukeLast edited by Duke W.; August 1, 2014, 09:28 AM.Comment
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Re: C1vs C2 vs C3 Aerodynamics
September 1963; my buddy and I in Navada on our way to Las Vegas in my new Vette Convertable L-76 w/U.S.Royal bias ply 670x15's, on a long straight stretch of road at 120 mph pushing for 130 mph (all guts, no brains). My hands were full trying to hang on and keep it straight. With dark clouds brewing for an afternoon shower, I opened the headlights (wanting to be seen more than concern for my vision) and I discovered a significant improvement in front end stability. We knew little about aero then, but we were young and fearless enlisted men (boys) in Uncle Sam's Army stationed at White Sands, NM.
Yes folks, contrary to what you see and may believe by reading the latest 40th Anniversary edition of the Corvette Restorer, there were a few enlisted men who could afford new Corvettes (not just officers). Most of my peers were colledge grads drafted into the army to do the high tech work and teach the officers, 4F's, women an old men so they could get the credit to enhance their resumes.
I will admit that, perhaps with a few more peanuts in my monthly check, I may have ordered a split window coupe with the L-84 Fuel Injected Engine - not really. We had test driven a few coupes already and found the desert heat in them unbearable. Also, my previous experience with my 58 Fuelie taught me to keep it simple. The base hobby shop was not a place to tune an Injector.
In October I came down on levie to go to SEA, and I knew the country roads in Thailand and Laos were not going to be the best places to enjoy my new Vette at speed.
Stu FoxComment
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Re: C1vs C2 vs C3 Aerodynamics
Didn't I read somewhere that Zora said the C1 had less drag than at least the C2's. Not talking about lift.Comment
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Re: C1vs C2 vs C3 Aerodynamics
i've had my c-1, a 57 fi that appears bone stock, at 113 mph on drag strips with no noticeable lift on the front. i took our 67 400 hp coupe to the lancaster nationals/maple grove strip in 88 or 89 and that c-2 lifted at about 100 mph. mikeComment
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Re: C1vs C2 vs C3 Aerodynamics
Mike,
Do you remember the discussion we had with Zora and Elfie at the Joplin Regional several years ago. We were talking (shootin the Bull) and I related a story about lifting my 63 Coupe's front end. Zora took a break from his martini and said "You were going 140MPH" and then resumed slurping down the martini! I says, how did you know that? Zora said that they took the 63 to Boeing because that was the only wind tunnel in the world and it became a wing at 140MPH!
I said thanks for telling the world as that explains why a 64 FI Coupe killed two of my friends.
JRComment
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Re: C1vs C2 vs C3 Aerodynamics
I am finalizing the draft of an article for the Corvette Restorer on the topic of the 1978-79 Pace Car spoiler and included a reference from McLellan's book. Here's what I wrote:
Wind tunnels were used in the late 1970s to improve both high-speed stability and fuel efficiency. It also reduced front and rear lift. These factors resonate today with the C7 Corvette generation. Coefficient of drag (Cd) rated a particular vehicles ability to cut through the wind. Wind tunnel tests of the Pace Car, revealed that the drag coefficient could be reduced by use of the front and rear air deflectors. As a result, drag coefficient was reduced from 0.50 to 0.42 and the 1978 Pace Car was the final result. Those C3 Corvettes from 1979-82 with air deflectors benefited from these aerodynamic improvements. And those improvements continued through each Corvette generation as today’s Cd for the C7 is 0.27.Tom Russo
78 SA NCRS 5 Star Bowtie78 Pace Car L82 M2100 MY/TR/ConvComment
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Re: C1vs C2 vs C3 Aerodynamics
Probably 30yrs(?) ago I was eastbound on I-40, east of Okla City in the 56. Along came an 80-81(?) Vette and we were off and running (and ya, I stayed ahead of him). The last time I looked at the speedometer was at 135mph and the car was floating noticeably, but I just stayed with it. Finally, he gave it up (MAN WAS I GLAD). So for sure a 56-7 is not very stable beyond 120+.Comment
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Re: C1vs C2 vs C3 Aerodynamics
I've never heard that story, but a model of the '63 Coupe was tested in the Cal Tech wind tunnel. It was a solid model, so all the air flowed around the car, which is not very realistic. Wind tunnel testing was pretty crude back then - small solid models, no pressure taps - just ink dots that flowed in the direction of the localized boundary layer. The story was written up in Corvette News, and it may well have been the first time any scale model production car was tested in a wind tunnel.
Nowadays the major manufacturers all have wind tunnels that will test a real car plus sophisticated computational fluid dynamics programs that allow them to get most of the details pretty close before actually testing of the real car to do some final tweaks.
DukeComment
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Re: C1vs C2 vs C3 Aerodynamics
I've wandered if the function side vent on a 1965-67 C2 did anything to reduce the lift?
EDIT: HA! Duke answered the question in the 1965 side louver thread. It did not make a significant difference.
MikeLast edited by Mike E.; August 1, 2014, 06:44 PM.Comment
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Re: C1vs C2 vs C3 Aerodynamics
Here are all the pertinent aero numbers for C1 through C6 - Cd, CdA, Drag, Front Lift, Rear Lift, etc.
AeroCd.jpgAeroLift.jpgComment
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Re: C1vs C2 vs C3 Aerodynamics
John - those data I assume are at the same road speed, which is probably about 70 MPH. Can you confirm?
I just found this photo in Wally Wyss' review of Karl Ludvisgen's newly revised, "Corvette..."
This photo and three others are also in Corvette News Vol. 5 No. 6.
The model is 3/8s scale and they actually did record some static pressure data. That's Dr. Peter Kyropoulis of Cal Tech on the right inspecting the airflow pattern revealed by the dye drops. This and other photos from the test are also in Ludvisgen's seventies editions along with a pressure distribution graph of the upper body surfaces... I guess they didn't check the bottom side of the car, which probably tells quite a story.
Ludvisgen's original editions from the seventies were certainly a "must have" for anyone seriously interested in Corvette history, and I expect I will purchase the new one.
Duke
SWC Cal Tech test.jpgComment
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