Paper Flight
Epic Long Distance Flyers
Like all other aircraft, paper model aircraft fly thanks to the force of lift, which is generated by their wing airfoil shape as it passes through the air.
The general theory of lift for thin airfoil shapes, such as the ones of the Paper Flight gliders, has this lift generated by the difference in air pressure between top and bottom of the airfoil, generated by the relative difference in airflow speed between the upper and lower airfoil surface.
Aerodynamics
As the model flies through the air, it is acted on by physical forces.
Airspeed is initially imparted by the hand of the person throwing the model, or else from the energy release of a catapult elastic. Thereafter, it is maintained by the force of gravity, which imparts acceleration on the models mass, which is expressed as weight.
The model does not immediately fall to earth thanks to the aerodynamic force of lift, which keeps the model airborne for a longer period of time.
The model's airspeed is balanced by the aerodynamic force of drag, which reduces the airspeed of the model in proportion to the cross-sectional area of the model, and the disturbed airflow caused by the model's skin surface roughness.
The model does not pitch over (or dive), thanks to the balancing aerodynamic force of tail lift.
The model's performance all comes together in the form of the following force diagram, which, for a gliding model is known as either the glide slope, or the lift-to-drag ratio.
Here, the model is able to travel a distance d for a loss of height h. Dividing d/h gives the glide ratio, which for Paper Flight gliders falls between 12:1 and 15:1 depending on design, in ideal conditions and trim.
This means that for every meter of altitude lost, the glider is able to travel between 12 and 15 meters forward.
This is done by minimising the glide angle, Theta.