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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?

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Awesome question. I'd guess it should be possible, but perhaps not easy. It needs to have just the right amount of pitch authority to keep the wing "stalled" without pulling it into tight loops. It also needs a center of mass slightly forward of the center of lift so that it pitches down in a stall. Then theoretically all you need is a little roll/yaw input (make a flap on the vertical fin). Are you good with paper airplanes? I'm not :) Looking forward to some real answers! – dvnrrs May 7 '14 at 19:55
(That said, I am such a student... but I think it would be just fine for an instructor to show me by holding the paper (or model) airplane and talking through the steps slowly, moving the airplane through the motions. This would be really cool for its own sake, but maybe not strictly necessary for educational illustration. The paper airplane is going to move pretty fast, and it will be hard to "see" the crucial concept that the wing(s) are stalled due to high AoA and one wing is stalled "more" than the other.) – dvnrrs May 7 '14 at 20:01
Balsa wood is probably better than paper. – DJClayworth May 7 '14 at 21:23
Possibly irrelevant but Towards Disposable Low-Cost Folded Cellulose-Substrate UAVs has some discussion of flight modes in section 3.3. – RedGrittyBrick May 8 '14 at 13:26
@DJClayworth RC aircraft would be even better to show such thing, but paper is cheaper and easier to carry inside a teacher's bag (e.g. inside a book) – Manu H Jul 10 at 14:33

2 Answers 2

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:

  • The wings (obviously): They should ideally be straight with an aspect ratio between 5 and 10. Swept wings will also spin, but straight wings make spinning and recovery easier.
  • The forward fuselage. Here a rounded shape which is higher than wide is ideal and will promote flat spins. The two-dimensional shape of paper airplanes will not produce the vortices which drive the yaw rate in spins.

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.

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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.

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