Aerodynamics is the study of forces and motion of
objects through the air.
Basic knowledge of the
is highly recommended
before getting involved
building and/or flying
A model aircraft that is hanging still in
air during strong winds may be subjected to the same aerodynamic forces as a model aircraft that is flying fast during calm weather.
The aerodynamic forces depend much on the air density.
For example, if a
Glider gliding at 25 meters
a given altitude during low atmospheric
pressure, it may glide
to 40 meters during high
The air density depends on
atmospheric pressure and
The air density
increasing of the air temperature and/or with decreasing of the
The air density increases with
decreasing of the air temperature and/or with increasing of the
A flying aircraft is subjected to pressure depending on the airspeed
and the air density. This pressure increases exponentially with
increasing of the airspeed. The aircraft's resistance to the airflow
(drag) depends on the shape of the fuselage and flying
An aircraft that is intended to fly fast has a thinner and
different wing profile than one that is intended to fly
That's why many aircraft change their wing profile on
landing approach by lowering the flaps located at the wings trailing edge and the slats at the leading edge in order to keep
enough lifting force during the much lower landing speed.
The wing profile of a slower aircraft is usually
this causes the air on the wing upper side to accelerate downwards,
making the pressure on the upper side lower than the underside,
thereby a lift force is created.
The lift force of a
symmetric profile, is based on the airspeed and on a
positive geometric angle of attack to the on-coming flow.
always flows toward areas of lower pressure and away from areas of
higher pressure, thus the air over the wing top accelerates as it
enters the lower pressure region (where the air curves toward the
wing), whereas the air under the wing slows down as it enters the
higher pressure region (where the air curves away from the
So, one may also say that the wings create lift by reacting
against the air flow, driving it downwards, producing downwash.
The top of the wing is often the major lift
contributor, usually producing twice as much lift as the bottom of
The following picture shows the airflow through two wing profiles.
The uppermost profile has a lower angle of attack than the lowest
one. When the air flows evenly through the surface is called a
laminar flow. A too high angle of attack causes turbulence on the
upper surface and dramatically increases the air resistance (drag)
this may result in an abrupt loss of lift, which is known as stall.
The aircraft generates lift by moving through
the air. The wings have airfoil shaped profiles that create a
pressure difference between upper and lower wing surfaces, with a
high pressure region underneath and a low pressure region on top. The lift produced will be proportional to the size of the wings, the
square of airspeed, the density of the surrounding air and the
wing angle of attack to on-coming flow before reaching the stall
How does a glider generate the velocity needed for flight?
simple answer is that a glider trades altitude for velocity. It
trades the potential energy difference from a higher altitude to a lower altitude to produce kinetic energy, which means velocity. Gliders are always descending relative
to the air in which they are
How do gliders stay aloft for hours if they constantly
The gliders are designed to descend very slowly. If the
pilot can locate a pocket of air that is rising faster than the glider is descending, the glider can actually gain altitude,
increasing its potential energy.
Pockets of rising air are
called updrafts. Updrafts are found when the wind blowing at
a hill or mountain rises to climb over it. (However, there may also be a
downdraft on the other side!) Updrafts can also be found over
dark land masses that absorb more heat from the sun than light land
masses. The heat from the ground heats the surrounding air, which
causes the air to rise. The rising pockets of hot air are called
Large gliding birds, such as owls and hawks,
are often seen circling inside a thermal to gain altitude without flapping their wings. Gliders can do exactly the same thing.