# Paper plane physics question

## Main Question or Discussion Point

Hello Guys.

Maybe you got in the past some similiar questions :)

I'm a game developer and I'm programming a game with a paper plane and I want to achieve a nearly real physic.

What I got so far:

trust = the speed when I throw the paper plane.
drag = dragcoefficient * airdensity * trust² * surface / 2
lift = 0.5 * airdensity * velocity² * wingarea * lift coefficient
gravity = weight * 9.822 / (24 frames per seconds)
velocity = trust - drag - lift + gravity

So, my problem now is this:

• the correct lift coefficient:
How can I calculate the lift coefficient with aoa? Here on this forum I found the following formula:
Cl = Cl(2d slope) * (AR/AR+2)*aoa

But what is 2d slope, and how can I calculate the Cl when I don't have the Cl? And what is AR?
• When I throw the paper plane, and it's moving upwards, the speed is increasing. But it must be decreasing:
I know, that I calculate the lift into velocity. So it must be increasing. But how is it in reality?

Greetings and thanks

Wolv3r

Related Classical Physics News on Phys.org
Paper airplanes (at least the ones I use) have no internal thrust; no motors, engines, or propellers. They are therefore more like gliders and less like true powered airplanes. This means that unless they hit an up-drafting air current which externally provides lift, the paper airplane can only fall over the long-term. It can momentarily ascend as part of its overall downward path, but only at the expense of its forward momentum. It momentarily exchanges kinetic energy for gravitational potential energy (like a pendulum).

rcgldr
Homework Helper
The 2d slope is the CL versus AOA curve for a 2d (idealized) wing, which would be similar to a wing with infinite span. AR is aspect ratio, the (wing span) / (wing chord). Link to a web page about paper airplanes:

http://paperplane.org/Aerodynamics/paero.htm