Summer Camp and Hang Gliding

by Brian Vant-Hull

I have the privilege of spending a couple weeks each summer teaching physics to teenagers at a math and science camp for gifted kids. It's an incredible atmosphere, with so much going on behind the scenes that my first attempt to describe it ended up rambling into 10 pages or so, and those were just the parts I thought would be funniest. So now I'll try to focus on the hang gliding aspects, with the whole rest of the experience encapsulated in a single paragraph.

The camp is located about 45 minutes from Ocean City on the campus of the University of Maryland Eastern Shore, one of the most beautiful campuses in America (they've got a sign out front to prove it, and a $25 fine for walking on their prize winning grass). The camp is sponsored in large part by the largest employer of mathematicians in the country: the National Security Agency. I'm talking code crackers here. About half the teaching staff are volunteers from the NSA, teaching courses like cryptanalysis and advanced problem solving: a fun bunch of people actually. We aren't allowed to publish any pictures of them, but we are allowed to take them out and get them drunk all night. Which we did. Frequently. One night at Ocean City we even went skinny dipping off the boardwalk. I'm proud to say I led the charge, and once they saw I wasn't getting arrested, they all came in. If this doesn't demolish the stereotype of the NSA, let me just mention that they are nearly all rabid fans of Buffy the Vampire Slayer. We watched part of the first two seasons nearly every night. Spooks from the NSA. Go figure.

Back to the Hang Gliding. I was part of the two-member team teaching "All the World's a Physics Toy". Originally they spent the first week talking about rockets and then built and fired model rockets; the second week they talked about roller coasters and other carnival rides before going down to Ocean City to ride and take measurements to compare against calculations. I thought the first week was kinda lame compared to hang gliding, so I completely redid the curriculum with the new focus, culminating with a trip to Ridgely. (Good timing, you guys!)

We started by talking about the definitions of velocity and acceleration, then programmed our calculators with a simple numerical analysis routine which would calculate position at any time given the initial conditions and accelerations (which we could tie into the forces later). We used this to calculate the path of a projectile, with results so accurate that they could shoot a stuffed animal off my head from the other side of the room. One of the kids decided we were practicing cruelty to class mascots, so swiped the stuffed frog and presented it to the head of the cryptanalysis team, who was known for having a soft spot for stuffed frogs. Last year when a similar thing happened it resulted in all sorts of coded messages flying back and forth; most being cracked within 20 minutes by the professionals from the NSA.

From there we proceeded to vectors, with treasure map directions and a twist: they had to locate the treasure without crossing the grass, and the directions would lead them across forbidden territory. Can anyone say "vector components?". Then Newton's laws for forces let us combined motion with vectors and the real world. Hang gliding involves balance, so we talked about torque and designed mobiles from plans the kids designed based on calculations.

Finally we could talk about fluid flow. By making fairly simple assumptions about the way air flowed around a wing, we could use vector principles to calculate both the size and direction of the forces. Note that there was no need to even mention pressure at this point. In this view the shape of the wing is seen mainly as a method to reduce drag-inducing turbulence while efficiently deflecting air downwards. Stability factors such as sweepback and dihedral ended the discussion with demonstrations involving toy gliders. All this was done in a single morning, with the kids designing and building airfoils out of balsa and paper in the afternoon. Hopefully next year we can do some wind tunnel work.

The next morning we brought in the pressure concept, and showed how the only way the air could flow the way it did was if the pressure patterns took on a particular arrangement. The speed was related to pressure via Bernoulli's equation, but, contrary to popular belief, it's not easy to apply Bernoulli's equation in this particular case without some very advanced math: unlike fluid flow in a pipe the airfoil problem has no defined boundaries. Something called conformal mapping is required, with a gratuitous fluid circulation thrown in to make the flow lines look right. The whole approach is so deeply buried in mathematical theorems it's useless for anyone to even think about applying the Bernoulli principle to the wing without rigorous training. Pilots, by the way, almost never get enough training to apply the theory correctly. So half the morning was spent helping the kids disentangle reality from mythology.

The other half of the morning was spent talking about glider control via weight shift, followed by stability and tails. In the afternoon they attached the wings to the body, using a tail for stability since designing a single wing for stability like our hang gliders is pushing handicraft far beyond normal limits. Then we test flew them. "Flew" should perhaps go in quotes; I had required that they be able to adjust the angle of attack of both the wing and tail, which makes for rather flimsy construction. The video we have of the test launches makes for some pretty hilarious viewing. But no matter, at least they learned the principles of flight, even if they didn't have enough time to tweak them into actual flight.

So after watching the gliders they designed crash and burn, they got to go out to Ridgely and fly for real in a glider designed by someone they had never met. Fortunately, it was never put to them in this way until after the flights were over. But Sunny's ground session would have inspired confidence in any case. I think most of us have never witnessed in full the way they broach the topic of hang glider safety to the uninitiated, but with their combination of measured presentation style and key facts they could win over any mom in the world.

I wish I'd had Sunny or Chad along on the morning of registration. As I've mentioned before I was able to talk to most parents before they read the waiver, and they all signed. But I missed a couple. After registration we had a big parents meeting where we all described the classes. My partner stood up and said something like "we'll take your kids and spin them around in loops, and drop then down long inclines, and take them up half a mile in the air and let them go, and they'll still be around to calculate what happened to them". Then I stood up and said "if any of you missed me this morning, make sure you catch me right after this meeting...I have some waivers for you to sign." They all laughed. "No, really, I mean it" I said with a hurt quaver in my voice. They giggled, and even when the camp director re-iterated that I was serious there was still some snickering. No one came up to me after the meeting. The ten out of twelve who did fly had a great time, though they never could find the words to describe it. Sunny pointed out that the girls were relaxed and into it, while the guys were all rather tense. Remember this is a geek camp. The four adults were more articulate, weighing the benefits of the thrill of a wingover versus the altitude it burned off. Even the two kids who couldn't fly had a good time: for one thing, time in camp is so structured they never really get free time, and here they had 5 hours of it. They got to meet the world record holder for loops in a hang glider, when Chad walked up to the group all tanned in tank top and sunglasses, coolness incarnate. And they could play pi chess (don't even get me started) and laze in the sun, and we all went out for pizza at Sam's afterwards.

So if you have kids of the teenage persuasion who don't cringe at the thought of algebra, send 'em along. They'll be safe enough with us: it is the National SECURITY Agency after all.