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These projects are a lot of fun for a bunch of creative kids to do on a nice breezy day. The initial goal is to see who can make the smallest kite that flies with stability. Once that is accomplished, the groups may wish to proceed on to "morphing" their kite eventually into a very, VERY small hand-thrown glider. (Somewhere in the military community is a rather nice monetary prize for the person who can create a very small airplane - about the size of a tennis ball, which can be used for reconnaissance.)
How often have you gone to the beach and seen people flying kites - really big, impressive ones? Imagine your joining them. You have a big smile on your face, a little tiny kite at the end of a spool of thread. Up and up goes your mini-kite. It appears to be soaring high above the others because yours looks so small up there. See what fun you can have! What is especially nice is that when yours crashes, it is so small that it doesn't break.
Of course, you need to know a little about kite-making. Here are a few things about one type of kite - the simplest form of all - the diamond shaped kite, . Once you get one of these to work, then you can experiment and try other shapes and sizes, such as the "tombstone," .
Diamond shaped kite necessities:
THE SIMPLE DIAMOND-SHAPED KITE
FIG 1: Select two struts such that one is at least 50% longer than the other. The longer one we'll call the keel, and the shorter one the rib. Put notches in the ends as shown. Place them at right angles, and tie them together. (Hint: if you are making a very small kite, you might find that the rigidity of your paper is enough and struts aren't needed, and then you can skip many of the following steps! BUT, read them anyway so that you will learn some of the principles.)
FIG 2: Probably the best way to apply the paper surface to your kite is right at the beginning when you lay out the struts. Cut out the paper so that it is about 1 inch larger than the struts indicate. The excess will eventually be folded over the periferal string, which you will make in the next figure. Clip all the corners off so that when the paper is eventually folded over the periferal string, the string will be exposed at the corners so that it can be slipped into the slots at the ends of the struts.
FIG 3: Pull the opposite ends of the struts together so that they curve upwards, and tie them in place by running strings (shown in red) across from end to end. The amount of bowing should lift the ends of the sticks off the table about 1/10 the distance as the kite is wide. Next, run a string (blue) all the way around connecting all the strut-ends. Besides holding the struts at right angles to each other, this string will become the edge over which you will fold the kite's surface paper.
KEEPING ONE SIDE FACING THE WIND. Three-dimensionally, these won't lie flat on a table. They are bowed: the ends of both the long keel and cross-piece are pulled together just a little so that the staves are slightly bent. This pulling together of the stave-ends can be by either cross-strings or by a "circular" string that goes all the way around the edges of the kite). Doing this will make the belly of the kite face into the wind and stay that way due to the streamlining effect of the curvature of the kite's surface.
KEEPING THE TOP OF THE KITE "UP." It's all a matter of balance, and balance can be helped along with either some added weight or some pure drag (drag without lift). Some people wrap some heavy wire around the bottom of keel to add weight to the bottom of the kite. However, it should be pointed out that "weight" becomes a sledgehammer at the moment of a nose-dive crash. Frequently you have seen kites with long tails of knotted cloth. That's both weight and drag that gives no lift at all. Thus the bottom of the kite is held down. Another solution - that moves in the direction of airplanes is the use of a real tail - one with horizontal and vertical stabilizers (the main part of the kite would be like the wings where most of the lift happens).
ANGLE OF ATTACK. You just don't tie your string to the middle of the kite and expect it to climb in the wind. If you do that, it will just flutter at the end of horizontal string. Instead to points on the keel that halfway between the ends and where the rib cross, you must attach a bridle string across the belly of the kite. Then attach your tow line to this bridle at a point that is a bit above the string's center. Thus if you dangle the kite from the tow-line, the top of the kite will be further off the floor than the bottom. Thus when your friend acts as "holder" upon take-off and holds the kite top up, not only will the belly of the kite be facing the wind, but also the kite will be tilted into the wind. Thus when the wind hits the kite, it will want to "slide" UPwards on the wind. Make sure that the connection between the tow-line and the "angle of attack" bridle string won't slip. But it would be good if you made the connection adjustable - by YOU and not the wind. Perhaps you could have some evenly spaced knots in the bridle. The knot from your tow-line then couldn't slide over those knots during the stresses of flight.
FLIGHT! By trial and error you will now make adjustments to the tail and attack angle, and soon your SIMPLE kite will be flying.
HOW HIGH? In any given wind speed, your kite can only fly as high as its weight AND angle of attack will allow it to go. Perhaps in the past, you have not noticed that both these factors are variable. The weight of your kite increases as you let out string - that added string adds more and more weight.
Then the angle of attack diminishes as the kite climbs. Let's start out by assuming that the string always forms a straight line between you and the kite. As the kite climbs, it is riding on the edge of a circle and the string is the radius. It finally comes to a height where the angle of attack allows the kite to have just enough lift to carry all the weight but no more. However, that was assuming that the string formed a straight-line radius. But in reality it is not straight. The string is drooped due to the pull of gravity all along its length (officially, that shape of curve is called a catenary). But what counts is the angle that the string makes right at the connection with the "attack" string.
When you momentarily give the string a tug, the line will straighten out ever so little, but enough to change the attack angle ever so slightly - but enough to make the kite suddenly climb a few feet, before settling back to where it was.
Turning a Glider into a Kite
Buy an inexpensive small bulsa glider from a toy store and apply what you have learned above to convert this from being a glider into a kite.
What can you do to your kite or glider so that you can adjust the angle of attack while it is up in the wind? (Hint: two tow-lines. But how does that work?!)
What can you do to your kite or glider so that you can make it move sideways while it is up in the wind?
Making a Mini-Kite
At first you will probably think that all you have to do is scale everything down from full-size to mini-size. But it is not that hard! Indeed, it is much easier. You see, paper has its own inherent rigidity and very small bits of paper won't need any miniature wooden struts. The curve of the mini-kite can easily be made with folds in the paper. See how easy it can be!
Oh, there is one thing though that you must be mindful of: use very thin paper - you must avoid too much weight. All other principles of large kites should apply. Thus you will need thread for the bridle and towline, maybe some string for a tail, and a kite made of thin paper.
By the way, the smallest stable kite made so far was 4mm x 3mm.
Making a Towed Glider
Perhaps the first thing you should do is purchase a small bulsa glider at a toy store. After you have it assembled, you will note when looking at the glider from the front that the wings are straight as shown to the right.
For greatest stability, you want the wings to slope slightly upwards from the fuselage to their tips as shown to the right. This works because when the plane banks off to one side, the wing on that side has much more lift than that on the other side where it is sloping up even more steeply.
Bending the wing requires that you know an old woodworker's trick: mark the fuselage line on the wing with pencil (not with ink). Thoroughly steam both sides of the fuselage line over the spout of a boiling teakettle. Immediately place the wing on a dinner plate so that it spans the plate. Next you want to place a weight on the fuselage line so that the center of the wing is bent all the way down so that it rests on the bottom of the plate. Perhaps you have a large diameter pencil or other cylindrical object that you can lay atop the fuselage line, and then weigh it down by placing a heavy bowl on the pencil.
Allow the wing to cool AND dry. It should retain its slightly V-shape once the weight is removed.
Insertion of the wing in the slot in the fuselage might now be a problem because when you first bought the wing it was flexible enough to bend into an airfoil () as it was pushed through the slot. But now with the V-bend, it cannot flex into the airfoil. So you must do a little corrective surgery on the slot and make it straight. Test the wing for a fit, but do NOT glue it in place.
Steam both outer 2/3 of each end of the wing, and help them to hold the airfoil shape by themselves. Once you are satisfied that the shapes are good AND identical, then insert the wing and glue it in place.
Making a Mini-Glider
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