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Fluids
Human
powered vehicles operate in a fluid environment. The bicycle and
rider interact with the air through which the system is moving and experience
aerodynamic forces that increase quadratically with the air-speed.
A
boat operates at the interface between two fluids, the water that provides
the "lift" and some drag, and air. These fluids have different properties
(density, viscosity, etc.,) and these must be understood in order to
design an efficient boat. Options such as replacing the displacement hull
with hydrofoils need tod be considered if high speed boats are to be designed.
Airplanes
rely on the air to provide the lift required to keep them
in flight. This fluid also contributes a drag force on the aircraft and as with
the bicycle this increases as the square of the airspeed. The power required
to maintain flight is close to the limit of human capability and the aircraft
system requires a careful balance of lift and drag forces and perhaps flight
close to the ground to take advantage of the "ground effect"
if long distance flights are to be achieved.
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