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4 classic cars that set the standard for aerodynamics

In the current age of stringent emissions standards and scarce resources, aerodynamics are very firmly on the agenda for carmakers. What might surprise you is that long before computer modeling and wind-tunnels, as early as the 1920s in fact, some trailblazing innovators produced vehicles which were as slippery as many of the cars of today. Here are four classic cars that set the standard for aerodynamics in the auto industry.

The Rumpler Tropfenwagen. Image: German Museum of Technology [GFDL or CC BY 3.0]

RUMPLER TROPFENWAGEN

Designed by Austrian aircraft designer Edmund Rumpler in 1921, the Rumpler Tropfenwagen is widely regarded as the first production car to employ streamlined design. During this era of aerodynamic design, engineers looked to nature for inspiration and observed the shape of a water droplet as it fell through air. They assumed that the air would reshape the droplet into its most aerodynamic form. Thus, the name “Tropfenwagen” literally translates as “drop-car”. Much later, scientists discovered that a water drop is not actually the most aerodynamic shape, but it was a good start nevertheless.

Launched at the 1921 Berlin car show, the Tropfenwagen was able to seat five adults and could reach a top speed of 110 kmh, despite the fact that the engine only produced 36hp. The driver sat on his own in order to accommodate the single pane curved window at the front of the vehicle. Astonishingly, the car had a drag coefficient of just .28, a value that would still be competitive with today’s vehicles: For example, a modern Audi A3 has a drag coefficient of .31 (and lower figures denote more streamlined vehicles).

Despite all of its impressive technical innovations, however, the Tropfenwagen was a commercial failure and only approximately 100 vehicles were manufactured. This has been ascribed to the vehicle’s unusual appearance and its lack of storage space. Only two remaining examples exist, which are exhibited at the Munich Transport Museum and the German Museum of Technology in Berlin.

THE AUREL PERSU AUTOMOBILE

Aurel Persu Automobile, Image: Bundesarchiv, Bild 102-09892 / Georg Pahl / CC-BY-SA 3.0 [CC BY-SA 3.0 de]

When you think of bleeding-edge automotive technology today, you probably do not think of Romania. However, it was a Romanian aircraft specialist who conceived and engineered one of the most important innovations in vehicle aerodynamics in history.

In 1922, Aurel Persu had the idea to place all four wheels within the aerodynamic line of the vehicle rather than outside its body. Although we take this for granted on modern cars, this played a major role in reducing wind resistance and had never been tried before, even on highly innovative cars like the Tropfenwagen. This meant that despite the vehicle’s somewhat more conventional shape, it had a drag coefficient of just .28. At a speed of 100kmph, the vehicle would have required merely a fifth of the fuel of the average contemporary vehicle. Although only one vehicle was ever built, it travelled 120,000 km in its lifetime and is now on display at the Dimitrie Leonida Technical Museum in Bucharest.

THE CHRYSLER AIRFLOW

The 1936 Chrysler Airflow. Image: Greg Gjerdingen [CC BY 2.0], via Wikimedia Commons

Unveiled in 1934, the Chrysler Airflow was one of the first US production road cars to use wind tunnel tests and streamlining to optimize the aerodynamics of the vehicle. These tests revealed that typical vehicles of the day featuring a “two-box” design, such as the Ford Model B, were so aerodynamically unrefined that it would be more efficient to drive them in reverse.

Chrysler’s engineers decided to employ a unibody construction to achieve good rigidity with less weight and a more aerodynamic shape. The front hood and grill were rounded and the the windscreen was recessed at an angle. Rather than using curved glass to improve the airflow around the windscreen, two flat panes of glass were placed in a v-shape. Although the wheels were not placed within the aerodynamic line of the vehicle, they were shielded with large wheel arches.

In terms of consumer tastes, the Airflow was too far ahead of its time, and sales were disappointing as a result. Including updated models released in 1935, 1936 and 1937, a total of 11,292 Airflows were produced. However, the design went on to influence countless models by other manufacturers in the decades which followed.

An honorable mention here goes to Paul Jaray, an Austrian aerodynamic engineer who developed the Czechoslovakian Tatra 77 vehicle. Jarray patented the idea of a streamlined car and Chrysler ultimately settled with him out of court to obtain the right to use his patent.

A 1969 Dodge Charger Daytona. Image: PSParrot [CC BY 2.0], via Wikimedia Commons

DODGE CHARGER DAYTONA

So far, we have been mostly talking about drag coefficient, but when it comes to race cars, there are many other factors to consider. As the previous examples show, many of the early pioneers in the design of aerodynamic vehicles came from a background in the aviation industry. However, there are some key differences when designing a car rather than an aircraft.

Most importantly, while drag coefficient measures how efficiently an object can glide through air, a car does not glide through the air, it travels on a road. Needless to say, if a car begins to leave the road and take-off at speed, this makes the vehicle very difficult to keep under control.

For this reason, engineers in the 1960s began to pay more attention to reducing front-end lift and increasing downforce. This was exactly the challenge presented by the Dodge Charger when competing in Nascar races in the United States. Although the Charger had ample power and could theoretically reach speeds of up to 320 kmh, drivers reported that steering became noticeably volatile at high speed.

After extensive research and wind-tunnel testing, the engineers opted to add a large nose cone to replace the previously upright front grill and an enormous 584mm rear wing, which gave the Daytona an audacious look. The purpose of the wing was to prevent what aerodynamic experts call “flow separation”, whereby an air flow leaves the body of the vehicle behind the rear window causing additional drag. The facelift resulted in significantly less front-end lift, more downforce and less flow separation.

The car broke the Nascar top-speed record when it reached 322 kmh on March 24, 1970 and it went on to win a total of six races over the 1969 and 1970 seasons.