Why do airplanes fly? by Lukasz Szymura #scichallenge2017
Author: Łukasz Szymura
Have you ever
wondered what keeps
them up there?
How do they do it?
Here's how it's done:
An aircraft in flight is
acted upon by four
forces: lift, gravity,
thrust and drag.
Each of these opposes
each other, and
balances each other out
Lift = Gravity
Thrust = Drag
What about this flying?
What are they and
what do they do?
Thrust: It's the force that moves an airplane forward
through the air. It's made by a propeller or a jet engine.
Drag: This is the air resistance that tends to slow
the forward movement of the airplane.
Gravity: It's the force that pulls all objects towards
Lift: This is the upward force that is created by
the movement of air above and below a wing.
When a motor-driven aircraft is moving at high speed,
the air moves in the opposite direction according to
the principle of relative motion.
The aerodynamic lift
is generated by the
air movement with
respect to the
The wing is inclined
with respect to
the direction of flight
at an angle known as
the attack angle.
Slope of the wings relative to the flowing air
Air flow from both sides of the wings
(differential pressure) - Bernoulli's Law
Pumping large amounts of air down through
the wings - Coanda effect
How to understand that?
Dynamic pressure depends on fluid velocity.
The air that has a higher velocity, that is,
at the top of the wing, will therefore have
a lower static pressure than the air at the
The sum of the static pressure (normal
pressure) and the dynamic pressure in
a given fluid stream (liquid or gas) is constant.
How does it work?
Let's see examples …
Slightly bent A4 paper so that it hangs freely down.
We strongly blow in the horizontal direction and the sheet floats upward.
Two lightly bent sheets of A4 paper are held side by side so that they hang vertically
We blow heavily between the sheets and the sheets are getting closer to each other.
Put a sheet of A4 paper on two piles of books.
If we blow strongly under a sheet of paper, the paper bends down.
This is a physical
a stream of fluid (gas or
liquid) tends to adhere
to the nearest surface.
Let's see how it looks in practice …
Coanda effect - example
We hang a ping pong ball on the string. We run a tap.
When the ball gets into a stream of water flowing from
the tap, it will be drawn into the stream.
How do you explain this experiment?
The behavior of the ball can be also
explained by Bernoulli's law
Clarification with Bernoulli’s Law
The ping-pong ball stays within
the column of air coming from
the hair dryer because of air
The air coming from the hair dryer
is moving faster than the air
around it, and this means that
it also has a lower air pressure than
the air around it.
So the ball is kept within the
column of lower air pressure
because of the higher-pressure air
Airplanes fly because they are able to generate a force called Lift which
normally moves the airplane upward.
Lift is generated by the forward motion of the airplane through the air.
This motion is produced by the Thrust of the engine(s).
Enjoy your flight !