A car design of 1922 has still proven today that the airfoil is the most efficient aerodynamic form or shape for an object which travels through air and inevitably encounters air resistance, be it an aircraft or in this case, an automobile.
The car called a Persu, was designed by a Romanian engineer Aurel Persu. Its profile has a tell tale resemblance to a bird airfoil, as can be seen in pics and videos below. His patented design achieved a drag coefficient of 0.2 which is the lowest even by today’s standards of aerodynamics for automobiles. It won’t be farfetched to assume that the inspiration came from the bird wing, and rightly so, succeeded in realizing a winner 100 years back. This design beats the Teslas of modern day.
Figure below shows a typical bird airfoil with linear approximations of the deflector and inductor surfaces, as analyzed in the Zone-Theory of Aerodynamic Lift. Not only does the deflector smoothly displace the oncoming air, in directions up and away from the rest of the car body, the inductor further ensures smooth exit of air over the body, leaving behind little low pressure which can produce a suction drag on the car. This beautifully synchronized pneumatic action of displacement and exit realizes the lowest drag of 0.2. The flat back road vehicles have to go a long way towards realizing this inherent flaw in their aerodynamic shape, which restricts their energy efficiency. Interestingly, you can clearly see the Salman Effect in action in this design, as the bird airfoil creates minimal suction pressure at the rear end of the car.
The design and performance of the Persu was so outstanding that the government issued a commemorative postage stamp to celebrate this engineering achievement of last century.
The car is another testimony to the correctness of the Zone-Theory of Lift, which breaks down the airfoil into the characteristic Deflector and Inductor surfaces. The Inductor however is not so active in producing Lift force in this case, as flying rear axle is not desirable for automobiles. Its aerodynamic action is more of releasing the rearward low pressure to mainly avoid vacuum buildup behind the car thus further reducing the drag.
All of the foregoing discussion once again proves that airfoil is the most efficient aerodynamic form, gifted to mankind by nature. We see it at work in bird, fish, aircraft, and now even in the design of the forgotten Persu car of more then 100 years old. Its definitely no coincidence that Aurel Persu must have seen it in birds, and proceeded to manufacture an outstanding car shape, of all times. For more info see youtube videos at links below.