Aerodynamics is defined as the study of the flow of air around specified shapes. For craft that
must interact with the air around them, the study of aerodynamics affects many aspects of the
art design. Through aerodynamic refinements, airplanes can fly higher, faster, further and
more efficiently; automobiles can be made more stable, more quiet, more efficient, and faster.
In our case, we're looking for a: fast (the world speed record), stable
(the boat must be stable enough to become pilotable) and efficently
(the power is limited) boat (and don't forget the
hydrodynamics part).
In the following, you'll see a short introduction to aerodynamics:
Lift :
Lisf is the force that allows aircraft to stay in the air. When air moves over a wing,
the air speed above the upper arched surface of the wing is higher than under the
more flat lower surface of the wing. This is because the air above the wing has to travel
faster to meet the air flow under the wing at the trailing edge of the wing. In accordance to
aerodynamics laws, the faster the air speed, the lower the pressure. This means that the air
pressure above the wing drops while the pressure under the wing remains normal.
This difference in air pressure produces a force called lift acting in the
direction of the low pressure area, that is, towards the upper surface of the wing.
Therefore, the faster air moves over the wing the greater the lift.
If you integrate the pressure profile around the wing, you obtain the lift
of the wing. This value is proportionnal to the square speed.
In the analytical expression of the Lift, there is a non dimensional
coefficient (Cz) wich represents the Lift "potential" of the profile.
Also, the Cz
depends upon the angle of attack (Which is the angle at which the wing moves
through the air).
Drag:
Drag is the resistance to the forward movement of an aircraft.
The amount of drag depends on many factors: a difference between pressures
on the leading and trailing edges of the wing, air viscosity and aircraft's shapes
- boat's shapes as well (friction drag or parasitic drag) - as on the lift and Angle of Attack
(induced drag). Of course, is is necessary that drag should be balanced by thrust. Drag is
proportional th the square of the airspeed and, hence, drag increases geometrically with increase
in airspeed requiring ever greater thrust levels.
Parasitic drag is a function of a particular vehicle's size and shape and is a major
concern of designers. Normally, the greater the frontal area if the vehicle, the higher
the drag.
Induced drag is produced by lift and is bound up with the forming of vorticies on the wingtips
(turbulence), which produce extra drag. The generation if vorticies is caused by the air flow
from the lower surface of the wing to the upper one over the wingtip. The higher the Angle of Attack
, the greater intensity of turbulence, i.e. an amount of induced drag.
