Flight modes, stability and modeling of gliders*

A plain piece of paper flutters and tumbles through air, whereas a paper airplane glides smoothly if its leading edge is appropriately weighted. We reproduce this transfomration in flight experiments involving simple plates with different center of mass (CoM). Periodic modes such as fluttering, tumbling and bounding give way to steady gliding and then downward diving as the CoM is shifted towards the front edge. To explain these observations, we formulate a quasi-steady model which successfully accounts for the observed modes. Our results seem to explain what makes a paper plane stable, and our model will be useful for many other problems.