When Jaguar won Le Mans the second time in 1953, it had become a pretty competitive scene, with serious contenders from Ferrari, Lancia, Maserati, Gordini and Aston Martin. Mercedes had won the previous year with their 300SL in its debut at the 24 Hours. During that same year, the Coventry engineers came up with a prototype that explored some new frontiers in structure and aerodynamics, but held to a tradition which was key to Jaguar's success: doing a lot with a little. While the Italians explored new engine architecture including V6, V8 and V12 configurations along with the usual inline fours and sixes, the Coventry crew settled on refining their existing engine design while saving weight, and cheating the wind, with an aircraft-inspired integration of body and chassis. After all, they already had a reliable power unit, and felt there were bigger and easier gains to be made in structure and aerodynamics. Also, winning with the proven twin-cam six would enhance the sales appeal of road-going Jags, all of which used the same basic engine design...
Innovation showed up in the design of the stressed-skin central chassis tub, comprising the cockpit, front and rear bulkheads in elliptical section, and side bulkheads, largely formed in sheet aluminum. To the front bulkhead a tubular aluminum subframe attached, and this carried the engine and front suspension, along with rack and pinion steering. Front and rear suspension were adapted from the C-Type, so they employed torsion bars. The live rear axle was suspended by trailing links connected to a single transverse torsion bar. Based upon experience with the C-Type, engineers had decided a live rear axle would suffice at Le Mans, and winning there was their main objective. Four-wheel disc brakes carried over from the C-Type, but these were still a novelty in endurance racing. The new car would be about ten percent lighter than the C...
Along with the simplified structure came a new aesthetic reduced, as in a piece of modern jazz, to a series of repetitive, almost-hypnotic essentials. The car would be oval in plan and section, and the shape would be repeated in elliptical elements like the fender profiles, wheel arches, tapered tail section, and most memorably, in the air intake which replaced the traditional grille. It replicated the elliptical section through the stressed-skin cowl and side bulkheads, and added another refinement: the edges of this opening were in themselves curved in section, so the air intake more resembled something from a jet aircraft than just a hole punched or cut into sheet metal. As Robert Cumberford pointed out, it was a civilized way to make an opening. The body design was created in-house by Malcolm Sayer, an aerodynamicist who had worked in the aircraft industry and who drew his plans and sections at full scale with ship's curves on the wall. Along with the aircraft-inspired structure, the D-Type adopted a deformable fuel bladder mounted in the tail, and a vertical stabilizing fin merged with the driver's headrest on many examples.
Sayer insisted on keeping frontal area to a minimum, so the engineers adapted a dry-sump lubrication system to the 3.4 liter XK engine to reduce height, and canted it 8.5 degrees from vertical. The engine retained the iron block and aluminum head configuration from the C, but larger valves were added to the wide-angle head in 1955, and engine displacement was increased to 3.8 liters in 1957, the third year in a row, and final one, that the D-Type won Le Mans. D-Types also won at Reims and Montlhery, and closer to home at Silverstone and Goodwood. The D-Type was rare viewed against the background of production cars, but it was a very popular racing car. In addition to the 18 cars built for Team Jaguar from 1954-57, 53 customer cars were built. These figures include both the original "short-nose" type and that "long-nose" variation which appeared in 1955. When the 16 road-going XK-SS versions of the D-Type are added (these had weather protection and bumpers, sort of), the tally is 87. Maserati and Aston Martin built far fewer of their comparable road racers. Back during the car's schematic phase, test driver Norman Dewis would sometimes walk into Jaguar's design studio and puzzle over the big drawings covered with formulas, section markings and Malcolm Sayer's scribbles, and he'd say he wasn't sure he could see a car in there. Now, with the 20-20 vision that hindsight brings, we can all see that car pretty clearly...
Footnote + Thanks:
I want to thank Dennis Varni of Los Gatos, CA and the Revs Institute in Naples, FL for allowing access to their cars. The dark green Varni D-Type is a 1955 example that raced at Sebring. The Revs Institue car is also from 1955, and is one of the five "long-nose" examples on the starting line at Le Mans that year. The low-penetration nose is 7.5 inches longer, and incorporates additional intakes flanking the central air intake.
I also want to thank Ian Avery-DeWitt for sorting through about 700 photos taken at the Revs Institute this past winter.
Photo credits:
Top: Jaguar Cars, as featured in primotipo.com
2nd: George Havelka
3rd: the author
4th: D-Type Plan & Elevation Drawings: Christian Tavaré for Model Maker Plans Service
5th: the author
6th & 7th: Ian Avery-DeWitt
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