I found an old retro slingshot glider plan in a DIY-magazine from the last years of 80'-s. Before the world of plastic components like (pvc-foam or depron) we modellers used cardboard, silk paper, sometimes pinewood and perhaps the most important material: balsa wood.
This small glider originally requires simple cardboard (as for example a pizza box). I have already made some model airplanes of this material, and I may claim, the cardboard pizza box-material is very useful to make models, but now I wanted to do some innovations with modern materials, and that's why I built it from pvc-foam instead of cardboard, to build a very light indoor plane for beginners.
The pvc-foam is available as packing element, you can find it as containers of cake, pizza, and other foods. I was lucky for I've managed to get some larger sheets of it from a packing set which was to cover the surfaces of big picture frames. But in my country the creative shops sell this sheet, too. You will need the 2-3 mm flat, micro-bubble size foam. If there is not any chance to get foam, you may build this project with also cardboard (original version), full balsa or depron.
In this ible I'll show the foam-version, because using a 2-3 mm pvc foam the weight of the full model will be cca. 3 gramms. Just to compare: this is the weight of one smaller screw that you'd balance the original cardboard model in the nose! To reach this incredible weight, we need balsa for fuselage: go to the creative shop near your home, and buy a 3x3 mms stick; these are normally 1 meter long, and I bought mine for cca. 30 cents, (or 0,3 euros). Be careful, this material is very light, and fragile at that lenght, but this is we need to build an almost weightless model. My "ultra light" glider can fly 20-30 meters indoor (gymnasium or a large hall, aula, atryum, etc.), and even more outdoor, if you start it against the wind. But be careful: even a smaller wind may be dangerous when gliding - never forget its 3 gramms weight! Better to use it indoor only, or in almost total calm weather. However, in a big outdoor field or meadow when summer, the lifting thermic streams may jolt this little model very rough.
Step 1: Begin the Building
The plans can be printed from here, originally the intension of the (unnamed) designer was to create a slingshot plane, but in my opinion this small model can fly nicely as a free gliding one, too. Using this ible you can build both of them, if you want. (The slingshot model is made of cardboard and pinewood, and cut the original groove on the bottom of the cockpit to attach a strong rubber band.)
For the "ultra light" follow these instructions:
balsa stick for the fuselage (3x3 mms, ~30 cms)
pvc-foam for wings and cockpit (max. A4-size, 2-3 mm thickness)
some anti-slip rubber foam pads (or any other similar material) to set the weight balance
rubber band for wing support
a small double sided adhesive tape to assemble the foam and balsa
Step 2: Printing, Copying and Cuttig
First print the plans on an A4 sheet, and cut out the wings and cockpit.
Don't mind the fuselage stick, that is not important now, you don't need to do anything with it at this moment. Place the cut templates on the pvc-foam, and draw exactly outlines.
Cockpit: Here I made a small change: while I didn't want to shoot the plane with a rubber band, I left over the groove from the cockpit, to make the whole fuselage stronger; you can see the strenghtened arch of it on my pics. Of course, you can copy and cut it unchanged, so then wou will be able to sling it, but in this case you must build the model from cardboard. The foam cockpit variant is for only a ligthweight glider version.
Wings: After the copying, cut the elements with a sharp cutter. Don't use scissors, it causes deformed edges on the wings.
After you cut the main wing piece (including both of the wings), find its geometrical center, and, as seen on my picture, press a ruler on that line, exactly. Now you halved the wings into a right and a left wing piece, and now you can fold them a bit. DON'T fold it more than some degrees; when you will assemble this part to the fuselage, that's enough to bend them a little.
Fuselage and wing support: And now see again the plans, and find the fuselage stick; this is a simple 3x3 mm balsa stick with 18 cms lenght. Cut it from the whole stick, and cut one 2,5 cm long piece, and two 5-5 cm long pieces for the wing support, too. And finally cut a 2,5x5 cm rectangle from the foam sheet - these are the parts of the wing support.
This part isn't drawn on the original plans, just I designed it to build this small modell more portable - at the original plans required the wings to glue onto the fuselage, but this method, to make wings removeable, is a well working way to build small models more portable, and, when it crashes on the ground, the wing can perhaps release itself, without damage; which is the main purpose of this design. For this reason you will need a very weak rubber band, too. Stronger rubber band may damage the foam made fuselage.
Step 3: Assembling and Gluing
When ready, take the balsa stick (18 cms), and glue it firmly to the "BODA" cockpit part. Line the parts well, and do it exactly. Then glue the vertical tail piece onto the other side of the fuselage stick, (see on the plans, where) and place the model on a flat surface, while the glue dries. The cockpit and the vertical tail piece must be in the same level.
Now build the wing support together: you've cut a 2,5x5 rectangle before, and the three short balsa pieces. Using the double sided adhesive tape, assemble them exactly as seen on the pics: the 2 long pieces go onto the 5 cm edges on the upper side, the short piece goes onto the one of the 2,5 cm edge from the OTHER side. (See this on the auxiliary plans I made.) When ready, glue this support on the cockpit, exactly the given place, at the head of the balsa stick. Everything must be symmetric, and the 2,5 cms stick under the support must be glued toward the nose of the model, as seen on the photos! Other words: that small stick must lift the leading edge (the edge to forward) of the wing!
Some explanations on the wing support:
(For those theoretical guys, who are interested in the "why"-s and "how"-s. Not so deadly required to build this small model, jump over, if find it boring...)
Why need that short stick under the support? Because the angle of the wing and the horizontal tail piece causes the climbing ability of an airplane; not so easy to determine the optimal value, but usually we can get a good result with these proportions I use. On the original plans this angle isn't important, because the original model was a slingshot started plane, started with huge speed, and so the lifting force on its wings became serious even without this angle.
The force, which can lift the airplanes higher, depends on the mentioned angle (between the horizontal tail piece and the wings), the speed, and the airfoil (the shape) of the wing. The bigger the speed, the higher the airplane can climb. But, while this light weight model hasn't big speed when gliding, we need this other way to gain some lifting. And this is the angular way, but it's a nonlinear and difficult rate; if we would increase it more, the wing couldn't work as a lifting instrument, the plane would stall, and fall like a dead butterfly. Well, this was the theory. And, since I've tried this small plane, I may claim, the theory works:-)
And why the other two, upper edges on the support? You can see the pics, the rubber band stresses the middle of the wings at the bended line to the cockpit, while the edge sticks on the support form a flattened "V" shape from the wing pair. This "V" helps to keep the horizontal balance of the airplane. When the model tilts, this shape of the wings sets the balance automatically.
Going on the assembling
O.K. Almost ready. Now take the horizontal tail, and insert a double
sided adhesive tape at its centre line, and attach it to the very end of the fuselage, after the vertical tail piece. Look at the plans, if not clear, where. Be exact everywhere, because the gliding ability depends on the symmetry and the accuracy.
To attach the wings pull the rubber band on the fuselage, press the wings on the support piece, and pulling the rubber band carefully toward the nose, moving under it, and release. This procedure will fix the wings, gives a small pressure as necessary on the middle line of the bent halfwings to keep them is "V"-shape, but lets some room for the motion of the wings at an unwanted impact.
Step 4: Balancing and Trying
Well, now you can admire on your work, but it can't fly yet, because it isn't balanced. To do this, get some adhesive foam spots (people use them to stop the slipping of their chairs on the floor), or anything else, that you can cut, and glue, and light enough for this procedure. I like this anti-slippers, these are well useable and well cuttable.
Now take your model, and place the root of its wings onto your fingers at the point I marked with a red spot on the plans. Now try to glue small foam spots symmetrically on the two sides of the nose, to reach that stable state, when the model is balanced on your fingers. I had to use 6 pieces, you will more or lesser - must be tried. Do it exactly and symmetrically as I have mentioned before. To see the proper angles and positions, refer the explanation drawing here.
And now you are ready to try the model: find a good place indoor (at least first!), and push the model on the air, not upwards, but a bit downwards, almost horizontally, slowly and carefully.
- If it is glidingsmoothly, with a small sinking, you are ready. It must fly even 20-30 meters, if the circumstances are lucky and optimal.
- If it is sinkingrapidly, decrease the nose weights, if it is nodding, climbing and sinking periodically, increase the weights.
- If the model is falling in a "corkscrew", or turning around more than some degrees, you have built it non-symmetric, the wings and tail pieces are in bad position or are inclined, perhaps crooked. You must refer the view to the pic.
During the gliding the model must find the horizontal balance, when something tilts it, and it's a good result, if advances along a line, doesn't turn to right or left.
We are ready! Go and fly!