Building a great performing glider doesn’t have to involve high tech materials. The Birdycan be built with one of four different tail configurations (at left). What makes the Birdy so easy to construct is the fact that it is completely made from Wausau cardstock (above center). No wood or composite items are used, making it the perfect model project for young modelers and supplies are as close as your local retail store. Jose found after a few tests, that the colored Wausau paper (above right) was stronger than the previously used white. The colors also help in the end decoration of the model and the high visibility colors certainly lend well to the model’s name.
The bet was to enlarge the wing to the di- agonal length of the sheet (I used the diago- nal to the right) and the rest of the pieces at the same rate. I was building plane after plane and the results in flight were disap- pointing. I could hardly get one to fly straight, and I had to resort to the chronic use of ailerons and rudder to counter the cork screwing tendency. When looking in anger at my best and worst gliders face to face, and eventually looking at all of them, I realized that the wing was viciously warp- ing down in the left wing and up in the right wing. That meant something.
There I go, downsizing the plane to fit in different orientations on the paper and printing the wing in the three remaining di- rections: across the page, along the page and diagonal to the left. And there I go, building two of each and flying all of them the next Saturday morning. The warping continued, in one or the other direction, including not only the wing, but also the stabilizer and the rudder, which had been positioned just where there was more room. I realized that in order to solve the prob- lem, I had to find the direction and angle at which the paper fiber was aligned. The solu- tion was to moisten one piece of my card- stock and seeing it curl, concave with re- spect to the front of the sheet and at an angle of 5 degrees to the right with respect to the longitudinal axis. I laid the wing (and its reinforcement) along this orientation. The alignment determined the maximum wingspan to fit on the sheet. With the wing done, it was then time to re-size and re-de-
sign the fuselage, the stabilizer and rudder for the classic tail.
For the sake of simplicity and time, I used the symmetry axis fold-and-cut technique for the fuselage and nose pieces. I call it the “butterfly fold and cut” trick.
The fuselage was made of four layers of cardstock, making it as slim and light as possible, yet strong enough in order to pre- vent “bananaing” (for it not to bend) at the waist when holding it for catapulting. The fuselage also comprised the tabs where the wing and the tail will sit on.
The rudder and stabilizer were made as small as possible for the sake of lightness, yet still effective in flight. They were also laid at a 5 degree angle and tab reinforced in the leading edge.
The nose was prolonged forward as to bal- ance the tail weight without the help of pa- perclips, coins or other extraneous ballast, but by gluing just two double nose pieces on each side (however, some minute amount of sticky tack ballast could be handy). In order to prevent bending the fuselage when the glider hits hard head on, these nose pieces run one centimeter under the wing. The catapult hook is not in the fuselage halves (which would impede a folding mid- dle line), but in the nose pieces. Finally, after many trials and errors, a multicolored Classic Tail Birdy emerged from the cardstock.
U, V, and T Birdies With the Classic Tail Birdy ready, the least of the problems was to make the other
tail variants. The only thing to bear in mind was not to make the other tails heavier or lighter than the Classic one, to avoid moving the c.g. and falling into the problem of bal- ancing the plane differently for each ver- sion. Therefore, the dimensions of the other three tails are in function of the constant tail weight, and voilà!
The “T” tail was the only one that required a little trick in order to minimize oscillation during launch and flight: “Z” folding the rudder in the middle as to create a column that holds and better supports the stabilizer on top.
Wing area and wing load ratio In order to calculate the wing load ratio, it is a must to know the wing area. When the wing is round in shape… how to obtain the area? As Shakespeare said, “That’s the question.”
The trick is simple. Trace the wing con- tour on a piece of thick cardboard of known area, let’s say 100 cm2, and known weight (in reality, I should say the mass), let’s say, 20 grams. Cut out the wing shape and weigh it; let’s say it is 12 grams. By applying the rule of three… Abracadabra! you know the area of the wing depending on its weight. Which in our example would be 60 cm2. I used a variant of this trick for working
out the T, U and V tail pieces, using a specif- ic weight in order to figure out the area.
And the rubber band?
Of course you can hand throw your glider, but (as I read once) “if you don’t want to
The Birdyfeatures a one-piece wing with a reinforcement built into the leading edge. Simply cut the wing as shown on the plans (at left) then fold over and glue. Inducing a bit of a wing warp or camber (above) is easily achieved.
FLYING MODELS 33
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