Some students learn best when they can see aerodynamic principles in action. I'd really like to be able to show a student how a spin occurs.
Is there a way to make a paper airplane that will enter a developed spin?
Besides the location of the center of gravity, two things determine how an aircraft spins, and both are not well shaped for spinning in paper airplanes:
Also, for spinning it needs a stalled wing, some asymmetry and some time until the spin fully develops. To create a strong pitch-up moment, masses at the tip and the end of the fuselage are also needed. A pure paper airplane will have too much yaw damping and too little inertial pitch up to spin.
Size should be less of an issue because separated flow changes less with Reynolds Number, and spin tunnels regularly use scales of 1:20 or 1:30 with good results. But I wonder whether the low wing loading of a paper airplane will prevent spins - the models used in spin tunnels are carefully sized not only for geometric agreement, but also for their masses and mass distribution.
Maybe it will be better to show your students videos from spin tunnel tests.
I don't know if this will work for you, but I used to put little tears towards the body on the leading edge of the paper airplanes I made. Then I'd bend the leading edge of the wing down a bit to create a stronger airfoil. I'd do this simply to increase lift at low speed, kind of like slats. But I wonder, if you put a tear on only one side and adjusted it properly, perhaps you could make it so that one wing stalls out before the other?
Or, perhaps to be a bit more accurate, you could just go with tears on both sides but adjust one down further than the other. That way it's pretty apparent that on wing is developing more lift at low speed.