| Cost: | Difficulty:
|
Danger 1: (No Hazards) | Utility:
|
------------------------
|
Using a Kite as an Experimental Platform
|
|||
|
--------------------- |
|||
|
by Shawn Carlson |
|||
|
--------------------- |
|||
|
I thus concocted a plan. As soon as we escaped our wedding reception, I drove my new bride to the beach and unfurled my best kite, a large triangular beauty with a thousand feet of string. I picked a favorite local spot for flying kites, just in front of the cliffs at Torrey Pines State Reserve, near La Jolla, Calif., where I knew I could count on the steady onshore breeze to form an updraft. It all worked. Still in her wedding gown, Michelle stood ankle-deep in wet sand, acting giddy as a schoolgirl as she let the wind carry the kite skyward. Six years later we still talk about the magic of that moment. And so began a family tradition. Just last month we took our two-year-old daughter to that same beach for her first taste of handheld aeronautics. When she begged me to send her teddy bear aloft, she reminded me of how kites have for centuries provided amateur scientists with inexpensive access to high altitudesÑrecall Ben Franklin's famous investigation of lightning. That experiment has come to symbolize an ordinary person's ability to carry out scientific research. Indeed, this column sported a logo featuring Franklin's kite for many years. So it's embarrassing to admit just how little about kites has been published here, a deficiency that this month's offering should help to rectify.
Kites are wonderfully inexpensive platforms for aerial photography, something countless scientists, from archaeologists to geologists, use in their research. The view obtained from easy kite heightÑsay, 1,000 feet (300 meters) upÑis perfect for monitoring all kinds of environmental changes. But picture taking is not all that's possible: new lightweight data loggers and sensors of all kinds should make for an explosion of kite-based research of other types. Aspiring meteorologists could, for example, determine temperature as a function of altitude using a thermocouple and a simple pressure sensor. And lifting a hot-ball anemometer (see the November 1995 column) would reveal the speed of the wind aloft. Although I describe here only kite-borne aerial photographyÑa technique called KAP by its practitionersÑI'm certainly looking for clever research projects of other kinds using kites. If you've done such work, please let me know so that I can share your inventiveness with this column's many interested readers.
What's the best kind of kite for carrying scientific equipment? That's a hard one to answer. Franklin was limited to the basic diamond-shaped flyer, but kites are now available in a wide variety of designs. For gentle zephyrs not exceeding about 10 miles (16 kilometers) per hour, the "Rokkaku" type is a good lifter. A large one covering 30 square feet sells for around $130 at your local kite store, or you can contact Into the Wind (800-541-0314). For moderate to stiff breezes (about 10 to 20 miles per hour) KAPers often prefer the "flow-form" or "parafoil" designs. There are no rigid supports in these lightweight wind catchers, which resemble puffy parachutes and fold up for easy transport. Such kites will fly well in a moderate autumn breeze and will pull like tractors in strong wind. A flow-form kite with an area of roughly 30 square feet sells for about $120. My favorite variety is the delta wing. This kite also proves stable in moderate winds, and one measuring a dozen feet across (about $160) can deliver approximately 130 pounds (579 newtons) of pull in a stiff blow. That's enough to loft some 30 pounds. To lift heavier loads, KAPers sometimes connect two kites in tandem, spaced roughly 100 feet apart. But be prepared. Even a single large kite in a strong wind exerts enough force to pull an adult over. So don't wrestle with a monster kite unless you have the right equipment to control it. Leather gloves are a must. And your line should be rated at least two and a half times the largest tug your kite is likely to deliver. Experienced flyers often wear leather tool belts to which they attach carabiners and other types of rock-climbing equipment to control the line. Another tip: I cut a notch to weaken the crossbar on each of my deltas to ensure that the kite will fail before my string does. Getting a suitable kite up in the air should be straightforward, but doing photography with it is a bit tricky. Fortunately, one can learn from the experience of others: amateur scientists have been hoisting cameras with kites since the beginning of the 20th century. The earliest pioneers had only limited success because they lacked a platform that would remain level and stable no matter what. An ingenious Frenchman named Pierre Picavet solved that problem in 1912. His suspension system, which now bears his name, is shown above. The instrument package hangs below two perpendicular rods, which are each about one foot long. This large cross is attached to the kite string by threading approximately 50 feet of cord through eight small pulleys. The tiny pulleys sold at hobby stores for radio-controlled model sailboats are ideal (lacking a local source, you can try Proctor Enterprises; 503-678-1300). The Picavet assembly is free to slide about as the kite changes altitude, which keeps the instrument platform level. To isolate the Picavet from the large side-to-side swaying that kites often execute in high winds, attach the assembly about 100 feet below the kite. Use a metal ring, such as a large key ring, and a lark's head knot [see inset at left] to attach the Picavet at two points on the kite string about six feet apart. With the wind rushing over it, any taut kite string will develop high-frequency vibrations, which can propagate through the Picavet and blur your images. Large rubber O-rings attached to the kite line help reduce this annoyance [see illustration at left]. The rubber rings used to hang mufflers, available from your local auto supply store, are inexpensive and quite effective at damping vibration.
Other point-and-shoot cameras would work, too. But the more limited self-timers on most other models require you to reset them after each photo. Although it is tedious to have to reel in your kite that often, thousands of breathtaking aerial photos have been taken in this way. With any camera, use a film speed of at least ASA 400 and set the shutter to the shortest possible exposure for the light conditions to avoid motion blur. Advanced practitioners adapt equipment intended for radio-controlled model airplanes. These "servos" can both rotate and tilt the camera, and also trigger the shutter on command. Consult the Web site of the Society for Amateur Scientists to learn more about such options. Whatever strategy you adopt, it's a good idea to affix "landing gear" made of practice golf balls to the camera housing as shown. They make for a softer touchdown should the wind die off suddenly, delivering the instrument gondola all too quickly back to terra firma.
The Society for Amateur Scientists (SAS) is a nonprofit research and educational organization dedicated to helping people enrich their lives by following their passion to take part in scientific adventures of all kinds. The Society for
Amateur Scientists
American Science & Surplus offers a unique mix of industrial, military and educational items, with an emphasis on science and education. We supply a wide range of unusual and hard to find items (some say bizarre stuff) to the hobbyist, tinkerer, artist, experimenter, home educator, do-it-yourselfer, and bargain hunter. American Science
& Surplus |
Just weeks before we were married, my wife, Michelle, confessed that she
had never flown a kite. I was stunned. Flying kites was such a wonderful
part of my own childhood that I couldn't imagine growing up without it.
So I figured it was my responsibility to show her how. And this seemed
an opportune time, because I wanted to demonstrate that getting married
didn't mean we had to settle down into a stodgy adulthood; instead we
could play together for the rest of our lives.
