# Paper plane physics question

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

## Answers and Replies

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