The Double Dangerous Book for Boys. Conn Iggulden
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Название: The Double Dangerous Book for Boys
Автор: Conn Iggulden
Издательство: HarperCollins
Жанр: Сделай Сам
isbn: 9780008299682
isbn:
On to the wings. You’ll need two narrow 8in (200mm) balsa spars for this. We’ve heard of one built entirely of wooden coffee stirrers, which isn’t a bad idea, though balsa is perfect. Lightness is crucial – the less weight the better.
The two wing wires are bent twice at 90 degrees. One end will go into the twin tubes from before, as shown below. More thread and glue will keep the wires stable. We cut the wires so that a little bit poked out at the back of the tubes. With the pliers, you can twist those ends up a fraction. It stops the wings falling out all the time.
That is the hardest part over with, believe it or not. There might be some fiddly bits to finish, but the main job is done.
JOINING THE CRANK AND THE WING SPARS
This is where the wooden coffee stirrers or ice-lolly sticks cut lengthways come in. You’ll need to drill a tiny hole at each end. Remember to use scrap wood underneath. Our first stick had holes 2¾in (70mm) apart for the inner batten, with a fraction more – 72mm – for the outer one. The plastic stoppers are vital to stop it all falling apart. Cut a piece of electrical wire and use pliers to tug out the copper core, leaving only the plastic sheath. You can then cut that into small pieces and wiggle them on.
The inner batten sits at the bottom of the ‘U’ on the crank – the first position. Line up the highest position of the crank with a wing position of no higher than 40 degrees up from horizontal. Any higher and it can be unstable. Mark your holes and drill. Once attached, you should be able to turn the crank and watch one wing rise and fall through its entire motion. If for some reason it doesn’t work – which happened to us on the second run-through – the problem will lie with the length between the holes or the angle of the wire crank. Adjust – half of making something is fiddling around when the thing just refuses to work and you can’t see why.
Once you have one wing rising and falling on the crank’s turn, you can attach the second. This outer batten sits on the part of the crank furthest from the main body – the second position. You’ll need more bits of electrical plastic sheath to hold it in place. Line up both wings so that they’re symmetrical at the midpoint of the sequence, mark your holes and drill. Be prepared to drill a line of holes and try each one if it doesn’t quite work. Keep your temper. You will be proud you did – and ashamed if you didn’t.
Once you have the wings moving smoothly, you’ll need to attach a hook at the back to hold the elastic band. The crank will wind it, so this is just a piece of wire, held with thread and glue. Something like this:
For the tail, we first tried a short wide one, which was completely useless. This bird is front-heavy, so it needs a long tail to give it a chance of stability in the air. With a main body 7in long, our best tail was 8in (20cm). We bent a narrow wire into a shape of an isosceles triangle with an apex of 45 degrees, and fixed coffee stirrers to it with glue and a few turns of thread. The top wire was then fixed with glue and thread to the main body. It’s trickier to wind the thread with the wings attached, so the tail should go on first.
To cut out the tail, just put the plane on a flat surface upside down, use sticky tape to hold the plastic in place, mark it with a felt-tip pen and cut it. Superglue will hold the tail to the wooden struts.
Our first wings were made from white paper, which looked fantastic, like something Leonardo da Vinci might have dangled from his workshop ceiling on a thread. If you’re after a model, that will look great. The trouble is that the paper tore really easily – and even though they were easy to fix, with strips of more paper and a dab of glue, we ended up cutting up a supermarket plastic bag and making a new tail and wings out of that instead. Fiddling and improving is the key here.
THE WINGS
We tried two wing shapes – curved and later a triangle. Both seemed to work. They should be taut, however. Leaving them to flop about just leads to rips.
The first wings were formed as a big semicircle of 16in radius (40cm). We used a circular tray to trace it on tissue paper. We then cut out a smaller semicircle at the centre point, to keep the mechanism clear. When you are finished, it is a thing of beauty and enormously satisfying to use. Photograph it immediately, before you snap it in two.
When you wind the elastic for the first time, it’s quite possible it will jam. The band pulls tight on the front assembly and friction is the enemy. The plastic bead on the outer side of the crank will help, but a drop of oil on every moving part is vital.
The elastic is two bands doubled and doubled again. We tried various kinds, but thin ones seemed to provide better power than thick ones. Buy a box of them and put oil on the bands to ease friction.
That’s it. Wind it up forty or fifty turns, find a high place and let it fly. Fetch it back, raise the tail a little and let it fly again. If there is a bad landing, be prepared to fix it on the spot with superglue and thread. The mechanism is a wonder to behold – it moves a little bit like the mandibles of an insect. Making a rear winder is easy enough, with a cork to help turn the wire and a groove to lock it, ready for take-off.
FINAL THOUGHTS
After half a dozen flights, our first ornithopter snapped almost entirely in half while we were wrestling with the crank. One of the wing spars broke at the same time. The amazing glue-and-thread combination restored it all well enough to flap again! No damage is so great that it means the end – though it will get heavier.
One bead works better than two. Flapping speed is vital, so you might consider purchasing a range of rubber bands.
Remember, the purpose of this is to build a flying machine, yes, but also to introduce you to the combination of balsa, thread and glue. Using the same set-up, you could get a small plastic propeller from a model shop and glue it to a hook instead of a crank. An epoxy glue would be more suited to holding the propeller in place. If you add a fixed wing made from either balsa sheeting or paper, it shouldn’t be too hard to make a small prop plane. Pictures of planes you have made can be sent to the authors care of the publishers – and are very welcome. Good luck.
QUESTIONS ABOUT THE WORLD – PART ONE
The first Dangerous Book asked and answered a number of questions: Why is a summer day longer than a winter day? Why is it hotter at the Equator? What is a vacuum? What is latitude and longitude? How do you tell the age of a tree? How do we measure the earth’s circumference? СКАЧАТЬ