are one of the most important aspects of a vehicles exterior
design. Aerodynamics and their importance in the hierarchy
of a vehicles overall design changes depending on the type
of vehicle. For example in the case of a pickup truck the
utilitarian use means aerodynamic efficiency is not of great
importance. But for racing and sports cars aerodynamics play
a very important role in determining the vehicles overall
Aerodynamics have been studied for over a century. Edmund
Rumpler, a German engineer, was one of the pioneers of aerodynamic
design. The shape of his 1921 Tropfenwagon prototype was modeled
on the shape of a water droplet. Unfortunately for Rumpler
the shape meant that the Tropfenwagon was quite ugly and the
vehicle was a sales flop.
A vehicles aerodynamic drag is expressed
as a drag coefficient
(Cd). Most production cars have a Cd of between 0.30 and 0.35.
Streamlined cars which have been optimized for aerodynamic
efficiency like the Toyota Prius and Honda Insight have lower
Cd values of around 0.26.
Some unorthodox vehicles which have been designed to offer
the most streamlined shape
as possible, like the Aptera,
have a drag coefficient of just 0.06. This is due to its extremely
smooth shape and enclosed wheels.
The Aerodynamic design of a vehicle does not just revolve
around reducing drag. For high performance vehicles downforce
is an important consideration. Some modern sports
cars have adjustable spoilers which can alter the downforce
acting on the car depending on speed. This has the effect
of giving the best of both worlds. At low to middling speeds
the downforce is low to reduce drag. At higher speeds, to
improve the vehicles stability, the downforce can be increased
- at the expense of increased drag.
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