Aerodynamic design

Aerodynamic design / Air-oh-dy-nam-ik dee-zyne/ noun (uncountable)

Aerodynamic design is the practice of shaping a vehicle to minimise its resistance to movement through the air, a force known as drag. For decades, British manufacturers treated this principle with the sort of suspicion usually reserved for foreign food or enthusiastic dancing. An upright, commanding radiator grille was a sign of quality, and if it had the aerodynamic properties of a shoebox, that was the air's problem. The gradual acceptance that a car which slipped through the atmosphere with less effort might go faster and use less petrol was a slow, painful dawn. It transformed vehicle design from drawing handsome boxes to a complex science, creating icons of efficiency and, occasionally, cars that looked like they had been left too close to the fire.

The Full Story of Aerodynamic Design

The concept of cheating the wind is as old as the automobile itself, yet in Britain, mainstream industry treated it with suspicion. While German engineers in the 1920s and 30s were creating bizarre, teardrop-shaped vehicles like the Rumpler Tropfenwagen, most British manufacturers preferred tradition. There were exceptions. Sir Dennistoun Burney, the airship designer, built his rear-engined Burney Streamline between 1929 and 1931, complete with independent suspension and genuinely aerodynamic bodywork. The Prince of Wales bought one, and Crossley Motors even licensed the design. In 1934, Belgian coachbuilder Jonckheere rebodied a Rolls-Royce Phantom I with flowing Art Deco curves and a sloped radiator grille, one of the few classic Rolls-Royces whose grille was not vertical. Yet these were curiosities rather than trends. The Burney was unstable in crosswinds with its rear-mounted engine, and most British buyers wanted their Bentley or Rolls-Royce to present itself to the air with the unapologetic frontage of a stately home. Aerodynamics remained largely the preserve of continental eccentrics and wealthy experimentalists.

The Second World War and the dawn of the jet age changed perceptions. Speed and efficiency were suddenly connected to national pride and technological prowess. Engineers who had spent years shaping aircraft to fly faster and farther began to look at the motorcar with fresh eyes. One of the key figures was Frank Costin, an aerodynamicist from the de Havilland aircraft company. His work for Lotus and Vanwall in the 1950s brought genuine scientific principles to racing cars for the first time. The beautiful, low-drag bodywork of the Lotus Elite proved what could be achieved when you stopped fighting the air, extracting giant-killing performance from a small engine simply by being efficient enough.

While Costin was applying science, the mainstream industry was still largely in the hands of stylists. The transition was often one of imitation. The sweeping lines of Italian coachbuilders became fashionable, and by rounding off a few corners and raking a windscreen, a manufacturer could claim a "streamlined" design without actually visiting a wind tunnel. It was more about visual flair than measurable results, but it looked good on the showroom floor.

The great leap forward in British aerodynamics came from one man: Malcolm Sayer. A mathematician and artist who had worked in the aircraft industry, Sayer was hired by Jaguar. He was not a stylist in the traditional sense. He shaped the C-Type, D-Type, and the legendary E-Type using mathematical formulae and calculations to define their curves. The breathtaking beauty of these cars was not decoration but consequence. The E-Type's form followed its function with a purity that few other road cars have ever matched. Sayer gave Britain a genuine, world-leading claim to aerodynamic mastery, and he did it with mathematics rather than guesswork.

By the 1970s, the "wedge" became the dominant styling trend, seen on the Triumph TR7 and Lotus Esprit. These cars looked fast standing still, though their sharp edges were not always as efficient as they appeared. The real democratisation of aerodynamics arrived with the 1982 Ford Sierra. Developed extensively in a wind tunnel, its "jelly mould" shape was a radical departure from the beloved, boxy Cortina it replaced. Traditional buyers were aghast. Motoring journalists printed cartoons of it melting. Yet, its drag coefficient of Cd=0.34 was exceptional for a mass-produced family car. The Sierra weathered the storm of criticism and, in doing so, made aerodynamics a core engineering principle for every car that followed. It proved that efficiency could sell, even if it meant looking a bit odd for a while.

For The Record

Is a teardrop the perfect aerodynamic shape?

For an object moving at subsonic speeds, yes, a three-dimensional teardrop is close to ideal. A car, however, needs to accommodate wheels, an engine, and people, and must function in the presence of the ground. These compromises mean a pure teardrop is impractical, though its principles guide the overall shape.

Does a lower drag coefficient always mean a better car?

A low drag coefficient (Cd) is only part of the story. The total drag force also depends on the car's frontal area and speed. A huge lorry might have a good Cd value but still require enormous power to push its massive frontal area through the air. Stability and lift are also critical; a perfectly slippery shape that generates lift at speed is a deathtrap.

Were early 'streamlined' cars actually effective?

Some were, particularly those that followed the teardrop principle like the Tatra T77. Many others were simply styling exercises. They adopted the look of streamlining with swooping fenders and fastback shapes without any scientific basis, sometimes making the cars less stable than the boxy designs they replaced.

What is the difference between drag and downforce?

Drag is the resistance to forward motion. Downforce is a perpendicular force that pushes the car onto the road, increasing grip. Generating downforce with wings and spoilers almost always increases drag. The art of race car design is achieving the required downforce for the smallest possible drag penalty.

Why was the Ford Sierra so important?

It brought wind tunnel-driven design to the masses. Before the Sierra, advanced aerodynamics was largely the preserve of sports cars and exotic machinery. Ford invested heavily in making a mainstream family car exceptionally efficient, and its commercial success forced every other manufacturer to follow suit. It normalised the modern car's shape.

Is adding a big spoiler to a road car a good idea?

On a typical family saloon at legal road speeds, a large rear spoiler does very little besides add weight and drag. It is largely a cosmetic accessory. On a high-performance vehicle at track speeds, a properly designed wing is essential for generating the downforce needed for stability and cornering grip.