A BOND/MACMINN LE MANS COUPE IS HONORED AT AMELIA CONCOURS PART 2

YESTERDAY IN PART 1, R&T’S JOHN R. BOND PROPOSED “An American Car for Le Mans” in his “Sports Car Design” series. Today in Part 2, a challenge is addressed of optimizing aerodynamics, circa 1958, with styling. Then, pencil in hand, John estimates performance of the design.

The Bond/MacMinn Le Mans car. This and the following images by Strother MacMinn from R&T, February 1958.

Aero Versus Styling. John certainly had appropriate colleagues for this complex tradeoff of design: “In this project,” he wrote, “we were extremely fortunate in having Strother MacMinn of Los Angeles’ Art Center  School as an ally. As for the aerodynamic background, one of the local aircraft companies unknowingly made a considerable contribution. Twelve aircraft technologists, all with strong automotive enthusiast tendencies, spent several evening-long conferences on this proposal.” 

Tradeoffs. “The aerodynamics committee,” John said, “immediately asked for more overhang at both ends, which pleased MacMinn the stylist, but not J.B. the weight trimmer. The overall length was increased from 158 to 189 inches. [Today’s Corvette is 182.3 in. long.] A Kamm-type chopped tail was considered, but the aero men felt the extra length was worthwhile. Again, MacMinn was pleased….”

“At the front,” John recounted, “great care was exercised to insure neither positive nor negative lift. The windshield lies back at 66º from vertical.” 

A Rear “Blac.” “As shown,” John said, “what appears to be a sort of external roll bar is actually a boundary layer air control. The ‘Blac’ is slightly V shaped in plan view, and a true jet-type air-foil in cross-section; it has an angle of attack of 3º.”

“What the Blac does,” John explained, “is best explained by saying that it greatly reduces air turbulence over and behind the long, sweeping ‘fast back.’ It also tends to reduce the rear-end lift effect inherent with a fast back. The lift itself, however, is not considered as serious as the induced drag, which is a by-product of the lift forces. Our experts felt that this device would make an otherwise 180-mph machine able to reach possibly 190 mph.”

A Multi-purpose Air Scoop. “About 80% of the entering air passes through the radiator core and is, as gently as possible, split and deflected out to the side outlets, just above the full-length sponson-type fuel tanks.” 

The remaining intake air is split between cooling the front inboard brakes and, on the driver side, supplying air to the cockpit. Cockpit air outlets were considered but “discarded as a threat to air flow. Instead, all cockpit air is exhausted at the extreme rear end of the body.” 

Rear Brake Cooling. On its way exiting the bodywork, cockpit air cools the inboard rear brakes as well.

The Stylist’s Viewpoint. Mac got a dense half-page for erudite comments. For example, he observed, “The V shape of the Blac device, arrived at by following the points farthest away from the body centerline, resulted in a not unpleasant parallelism with the forward cab form.”

“Ahead of the front wheels,” he noted, “the nose (in top view) was also tapered to deflect some air around the sides and create a high-velocity, low-pressure point just behind the front wheels, where the air exit from the engine compartment is located.”

“Ovoid character in the side window outline, tying in with the base of the windshield,” Mac said, “tends to harmonize with the general sweep character of the body, and provides side-rear vision aft of the driver’s head at eye level.”

Mac’s Theories. “All of this is theoretical,” Mac admitted, “but as sound as preliminary consideration can make it. Complete wind tunnel tests would, of course, be the only way to a satisfactory solution, contingent on the necessary modifications and adjustments.”

John’s Penciling. In “Sports Car Design 43,” R&T April 1958, John started with an estimated 7.24 lbs per horsepower (290 bhp; a starting-line test weight of 2100 pounds): “In addition to a power to weight ratio at least equal to the record lap-holder (3.8 Ferrrari, 125.6 mph) we have a well designed coupe body which greatly reduces the power required to attain competitive speeds on the Mulsanne straight. As mentioned previously, our aerodynamic consultants estimate a Cw factor of .25 or less, which would give us a theoretical top speed of 200 mph with only 242 bhp available at the rear wheels.”

Furthermore, John estimated acceleration by comparing the R&T special with that 3.8 Ferrari. “Using every known method of calculating and comparing, it seems quite possible that an American car for Le Mans could be built which could break the Le Mans lap record and would be capable of averaging 115 mph for 24 hours.

John’s Conclusion. “Our only purpose in describing this machine at some length was to show how the problem should be approached and analyzed. Also, as Dr. Naillinger of Mercedes-Benz once admitted, it was good for our own morale.” 

Ha. I knew this was going to turn into a three-parter. ds 

© Dennis Simanaitis, SimanaitisSays.com, 2024