The Principles of
Flight
Fig 1
Have you ever found yourself wondering how
planes fly? Or the difference between a glider
and a plane? How aeroplanes, despite being
far heavier than air remain suspended mid-air?
Well, here is the answer to those questions; the
ultimate paper aeroplane cheat book.
Firstly, the main difference between a glider and
a plane, is that gliders have three forces acting
upon them and planes have 4. The force that
gliders don’t have is thrust. Thrust is the force
creating by a plane’s engines and propels the
plane forward. This means that gliders, that have
no engines, can never achieve sustained
horizontal flight on a windless day. (Fig 1).
The other three fundamental forces of flight that
the glider and the powered plane share are lift,
weight and drag. Lift is the force that pushes the
plane above the ground. It is created by a
plane or gliders wings. Weight is the force that
brings the plane back to ground and drag is the
force that slows the plane. (Fig 1).
Air pressure is key to sustained flight. A high
quality plane design will create areas of high air
pressure under the wings. In a model plane or a
powered plane, this is achieved using Bernoulli’s
Principle. (Fig 2). Bernoulli’s Principle states that
an increase in air velocity results in a drop of air
pressure. This can be tested by holding a piece
of paper length ways in front of your face. If you
blow air onto the top side of the paper, the
paper will almost achieve a horizontal state. In a
regular plane (not made out of paper), the wing
cross section will show that the bottom side is
Fig 2
straight and the bottom side is curved. This
means that the air is travelling faster over the
top of the wing than the bottom of the wing.
Going back to Bernoulli’s principle stating that
higher velocity results in lower pressure, the
wings rise because there is less air pressure
above the plane then below it. This is also
applicable to propellers.
Fig 3
But while this information is key to achieving a
working real plane design, its quiet useless in
designing a paper plane. Keeping in mind
that you can’t change the thickness of a
paper plane wing, there is a different way to
create sustained flight.
To achieve a gliding paper plane, there has
to be an equilibrium between the planes
centre of gravity and its ‘centre of lift’. The
best planes will have the ratio embedded in
the design, but by folding the paper at the
back or sides of the plane to create flaps, the
centre of lift can be moved.
Attached is a plane design. The Harrier (Fig 3),
is an excellent design that employs these
principles and adding flaps to it will only cause
it to stall. The second, the Bulldog Dart (Fig 4,
no instructions provided), can achieve an
excellent glide by folding the outer side part
of the wings inwards, increasing the amount
of air pressure below the wings.
Patrick Litchfield
Fig 4
Harrier
References
Isaacs, Alan. A dictionary of physics.
Oxford [England: Oxford University
Press, 2000. Print.
Macaulay, David. The way things work.
Boston: Houghton Mifflin, 1988. Print.