The Can-Am era was a transitional point in race car design. The term “aerodynamics” as applied to racing car design can be divided into two periods: 1) low drag and 2) downforce. Prior to the adoption of big American V8s for racing in the early Can-Am era, increases in speed were accomplished by the reduction of aerodynamic drag. The Daytona Cobra Coupe was a perfect example as the increase in top speed of a Cobra roadster from 165 mph to 200 mph was accomplished by the simple adaption of changing the body to a slippery form.
However, higher speeds began creating unwanted lift so the designer’s next goal was to counteract lift by creating “downforce” with simple aerodynamic devices like spoilers and front air dams to reduce attached airflow that contributed to lift. The only detriment to such devices was they caused an increase in aerodynamic drag! So… the only way to solve that problem was to increase horsepower to overcome the drag. The Can-Am era essentially ended when horsepower became so expensive (e.g. turbo-charged Porsche 917s) that the privateer racers couldn’t compete. With no field to effectively compete with the “big money” required to win, the series died. It sure was fun while it lasted though! Probably the most exciting motor racing ever devised.
- Peter Brock
9 thoughts on “Back in the day of Can-Am, the McLarens ran full length aerodynamic fences nose to tail. After that time, it didn’t seem that designers used full length fences. I have always wondered why. It seems like a good way to keep the airflow on the top of the car and not spilling off. Was it a rules thing why designers stopped using them or was there an aerodynamic or stability issue?”
Hey Peter, It’s great to experience the revival of questions and considerations regarding the various designs and the effects thereof.
Ok, but if the fences worked so well. How come they were not continued. Even in the Can-Am series you didn’t see the them except on the McLarens. Porches didn’t have them, neither did the L&M Lola. And you don’t see them on any other Sports Prototype cars. Today you see all kinds of “flow control” devices on cars. But you don’t see nose to tail fences. That’s why I was wondering if there was some issue with them. The “tunnel” F1 cars were stopped because there was stability issues and they to “flat bottom” cars that made the issues go away and worked better as well.
If you want to have some fun, head down to Hillbank motors with a bunch of Chaparral photos in your hands. Then look at the Cobra 289 roadster, the Daytona coupe, the coupe and roadster version of the Corvette Grand Sport and then your photos and ask yourself, what is going on here?
Why was the Daytona top speed faster than the Cobra roadster and the Grand Sport roadster top speed faster than the Grand Sport coupe?
That’s just for openers. Look at the photo of the Chaparral “sucker” car and ask how come the LAP TIME of this car was so fast that McLaren got it banned from competition?
Fun and games
I have always looked to Jim Hall and Colin Chapman as the masters. The rest have just used that groundwork to improve their designs.
Would the exaggerated dorsal fin on LMP cars be a modern equivalent?BRE
The dorsal fins might add some directional stability but it does not focus the air flowing over the body to create downforce…PB
Any thoughts specific to the longitudinal fences the original post asks about?
It was a very successful design (still valid today) that only went out of favor when McLaren quit because Porsche’s 917Ks had a power advantage that put the McLarens on the trailer. The 917s didn’t use the design because with their power advantage they didn’t have to. No one else used the design because, as with the McLarens, it wouldn’t have been enough to overcome the 917K’s power. PB
Along with the TransAm it was a great era and we probably will never see such good racing again. This was not the last time Porsche screwed up a good series. Thanks for the info.