Why do paper airplanes fly?

The four main factors which affect the aerodynamics of an airplane are:-

1/ Thrust - the forward motion or speed of the aircraft.

For paper airplanes this is provided by your throwing the plane forward. Also if you throw your airplane with differing strength this will also change the airflow as the wings move through the air.

2/ Drag - the resistance of the aircraft against the wind.

As paper airplanes do not have any form of continuous motion ie an engine and a propeller; your airplane needs to be built sleek. This will keep the drag to a minimum.

3/ Gravity - the force that keeps all things on the earth. To alleviate this force an object needs to become light in weight;

4/ Lift- where the push of the wind under the wing is greater than the push on the top of the wing. This upward pushing makes the aircraft lighter.

This is where we have a lot to thank Lawrence Hargraves for as this was his discovery which by the way the Wright brothers used to further their passion for powered flight.

source: http://www.airplane-and-aircraft.com/aerodynamics-of-paper-airplanes.html

So out of the four factors that influence the flight of a airplane. And out of the four, the only one that I will be changing is the 'thrust', which is measured in newtons (N), and not just in any random fashion. I will need to build some sort of plane launcher, so that my experiment will be a fair test.
The 'drag' will be controlled as the experiment will be conducted at home.