Scott Lear
Scott Lear
12/7/17 11:16 a.m.

It’s easy to take modern automotive aerodynamics for granted, as most cars built in the past couple of decades have been shaped either in a wind tunnel or via computer simulation. Either way, the goal is the same: to cut through the air without too much fuss.

The benefits are many. Fuel economy goes up. The ride is quieter at speed. And in the case of anything even vaguely performance-oriented, carefully shaped undertrays, factory wings and other aero tricks work to negate or even overcome the unnerving sensation of lift that used to appear as a car approached triple-digit speeds.

It was not always thus. In the 1950s, the archetypical sports car–from the Porsche 550 and AC Ace to the Ferrari 250 TR and Jaguar D-Type–was an open-cockpit affair. No matter how low-slung or swoopy the bodywork of these beauties appeared to the human eye, however, parasitic turbulence was sapping horsepower at speed. By the early 1960s, with maximum velocities climbing and aero becoming more of a factor on the long straights of Le Mans and elsewhere, competitive evolution had begun shaping the future.

Although they stuck up higher than the open-top racers, aero-sculpted coupe designs were showing their legs on the flat-out bits, and everyone scrambled to come up with their own slippery hardtop. Carroll Shelby’s once-potent Cobra was in need of a new profile to keep pace in international racing, and Peter Brock noodled up a solution. The team couldn’t have been more fortunate: Brock’s resulting Daytona Coupe design was capable of nearly 200 mph given enough road, and the Shelby went on to beat the Ferrari 250 GT for a World Sportscar GT class championship in 1965.

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Mr. Lee
Mr. Lee UberDork
12/7/17 11:36 a.m.

Love this car. The shape is just... Right IMO.

nderwater
nderwater UltimaDork
12/7/17 12:06 p.m.

Ditto that. I really enjoyed this article, too. Great job Scott!

NickD
NickD UltraDork
12/7/17 12:41 p.m.

The interesting thing about these is that the back was not Brock's original design. He said in an interview that he had the rear designed more like a 911, and it was better aerodynamically but Carroll Shelby hated how it looked, so then he changed the design to what we now know. Aerodynamically though, it was a huge step backwards and they fought and fought trying to get it to work, simply because Shelby liked how it looked better.

mfennell
mfennell Reader
12/7/17 1:30 p.m.

Do you have a link to that?  The Kamm tail, based on the work of German Reinhard von Koenig-Fachsenfeld, was revolutionary.  All accounts I ever read say it was Brock's idea to use it and everyone told him it wouldn't work.    http://www.roadandtrack.com/motorsports/a26376/coupe-de-grace-shelby-daytona-coupe-story/

 

BROCK: I sketched up a few ideas— ballpoint pen on legal pads. Nothing fancy. I'd been sketching the lines in my mind and on paper for some time. While at GM, I'd found some translations of studies on automotive aerodynamics done by Dr. Wunibald Kamm in Germany in the late 1930s. The data seemed perfectly logical—why try to dispute the laws of physics? The shapes, however, looked so strange that no manufacturer was willing to risk trying them in production.

BROCK: Shelby seemed immune. Either he didn't understand what I had cre- ated, or he didn't care what anyone else thought. All he asked was, "Do you think it'll work?" Yeah, I replied. "Okay, let's build it." That was it—pure Shelby.

¯\_(ツ)_/¯
¯\_(ツ)_/¯ UltraDork
12/7/17 1:31 p.m.

Shelby is now suing you for using the name Shelby on your website.

NickD
NickD UltraDork
12/7/17 1:56 p.m.
mfennell said:

Do you have a link to that?  The Kamm tail, based on the work of German Reinhard von Koenig-Fachsenfeld, was revolutionary.  All accounts I ever read say it was Brock's idea to use it and everyone told him it wouldn't work.    http://www.roadandtrack.com/motorsports/a26376/coupe-de-grace-shelby-daytona-coupe-story/

 

BROCK: I sketched up a few ideas— ballpoint pen on legal pads. Nothing fancy. I'd been sketching the lines in my mind and on paper for some time. While at GM, I'd found some translations of studies on automotive aerodynamics done by Dr. Wunibald Kamm in Germany in the late 1930s. The data seemed perfectly logical—why try to dispute the laws of physics? The shapes, however, looked so strange that no manufacturer was willing to risk trying them in production.

BROCK: Shelby seemed immune. Either he didn't understand what I had cre- ated, or he didn't care what anyone else thought. All he asked was, "Do you think it'll work?" Yeah, I replied. "Okay, let's build it." That was it—pure Shelby.

Boy, I really wish I could remember. I almost want to say it was in an interview with Hot Rod Magazine.

Driven5
Driven5 SuperDork
12/9/17 1:49 p.m.
NickD said:

The interesting thing about these is that the back was not Brock's original design. He said in an interview that he had the rear designed more like a 911, and it was better aerodynamically but Carroll Shelby hated how it looked, so then he changed the design to what we now know. Aerodynamically though, it was a huge step backwards and they fought and fought trying to get it to work, simply because Shelby liked how it looked better.

I think you may be misremembering.  There are numerous references to Brock discussing the Kamm papers as being his inspiration, not it just being some styling whim of Shelby.  The initial opposition he faced was because the rear was so unconventional looking, unlike the much more conventional steeply tapering 911 rear.  And ultimately the 911 rear is significantly worse aerodynamically than the Daytona Coupe.

The inefficient rear shape of the 911 is why not only did the tall 'ducktail' spoiler on the original Carrera RS kill the rear lift that made it so challenging to race at high speeds, but also managed to actually reduce the drag coefficient at the same time.  It was actually the rear spoilers on other race cars, like the Daytona Coupe, that caused one of the Porsche engineers (Tilman Brodbeck) to investigate and develop it for their own use.  The same 'ducktail' spoiler effect was also leveraged for the aerodynamic improvements on the 964 and later cars, with the automatically raising rear spoilers.

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