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MODELING
We build models of rockets. Tips for a modeller
Directory / Radio control equipment I built my first model of a rocket in October 1961, a student of the first seminar for leaders of aviation clubs in the Moscow region. Its organizer was Nikolai Nikolaevich Ukolov, the then head of the Moscow Regional Station for Young Technicians. And the classes were conducted by Viktor Fedorovich Eskov - head of the laboratory of the Central SYUT of Russia. We, a group of about 30 people, made a rocket based on a flying model in 3-4 hours. We immediately received good methodological material both on models and on engines. At that time, model rocket engines (MRDs) were made by ourselves: ordinary cardboard hunting cartridges of 12 and 16 calibers were stuffed with a powder mixture with coal, sulfur and nitrate in a special device.
Briefly about those first models. On a mandrel with a diameter of 21 mm, a body of drawing paper was glued in two layers. Its length is about 400 mm. Stabilizers were cut out of tin and soldered to two belts (hoops) fixed in the lower part of the case. The head fairing was turned on a lathe from wood. That first seminar was a good starting point for the development of rocket and space modeling. Appropriate literature began to be published, and not only in the capital. In April 1962, large regional competitions in rocket models were held near Moscow, in which about 180 people took part. In subsequent years, the geography of missile centers expanded. They were joined by Krasnodar, Perm, Kharkov, Simferopol, Ivanovo, Yaroslavl and other cities. Unfortunately, in the late 1990s, interest in rocket modeling fell noticeably in the country. This is due to the fact that a large number of institutions of additional education were closed - clubs and stations for young technicians. But they were mainly engaged in rocket modeling. Over the past seven or eight years, the situation has gradually improved, because children require attention and care. This article opens a kind of rocket modeling school on the pages of our magazine. We hope that publications on this subject will help to promote knowledge of rocket and space technology among young people, schoolchildren, and will allow them to manufacture and launch their first rocket. The word "rocket" entered our lexicon about fifty years ago, and today any boy of three or four years old knows it. And not only knows, but imagines what it means. Before we talk about miniature rockets, let's clarify what a rocket model is, consider the basic requirements for building and launching rocket models. The flying rocket model is driven by a rocket engine and rises into the air without using the aerodynamic lifting force of the bearing surfaces (like an airplane), it has a device for safe return to the ground. The model is made mainly of paper, wood, destructible plastic and other non-metallic materials. A variety of rocket models are models of rocket planes, which ensure the return to the ground of their glider part by sustainable planning using aerodynamic forces that slow down the fall.
There are 12 categories of rocket models - for flight altitude and duration, copy models, etc. Of these, eight championship (for official competitions). For sports models of rockets, the starting weight is limited - it should be no more than 500 g, for a copy - 1000 g, the mass of fuel in the engines - no more than 125 g and the number of stages - no more than three. Launch weight is the weight of the model with engines, rescue system and payload. A model rocket stage is a part of the hull containing one or more rocket motors, designed to separate in flight. The part of the model without an engine is not a stage. The stepping of the structure is determined at the moment of the first movement from the starting engine. To launch a rocket model, only industrial model solid fuel engines (MREs) should be used. The structure must have surfaces or devices that hold the model aircraft on a predetermined take-off path. It is impossible for a rocket model to be freed from the engine if it is not enclosed in a stage. It is allowed to drop the engine casing of model rocket planes that are lowered by parachute (with a dome with an area of at least 0,04 sq. m) or on a belt with dimensions of at least 25x300 mm. At all stages of the model and separating parts, a device is needed that slows down the descent and ensures the safety of landing: parachute, rotor, wing, etc. The parachute can be made of any materials, and for the convenience of observation, have a bright color. The rocket model submitted to the competition must have identification marks consisting of the initials of the designer and two digits with a height of at least 10 mm. The exceptions are copy models, the identification marks of which correspond to the marks of the copied prototype. Any flying rocket model (Fig. 1) has the following main parts: body, stabilizers, parachute, guide rings, nose fairing and engine. Let's explain their purpose. The body serves to accommodate the parachute and the engine. Stabilizers and guide rings are attached to it. Stabilizers are needed to stabilize the model in flight, and a parachute or any other rescue system is needed to slow down free fall. With the help of guide rings, the model is installed on the bar before the start. To give the model a good aerodynamic shape, the upper part of the hull begins with a head fairing (Fig. 2). The engine is the "heart" of the rocket model, it creates the necessary thrust for flight. For those who wish to join rocket modeling, to make a working model of an aircraft called a rocket with their own hands, we offer several samples of such products. I must say that for this work you will need available material and a minimum of tools. And, of course, it will be the simplest, single-stage model for an engine with an impulse of 2,5 - 5 n.s. Based on the fact that according to the FAI Sporting Code and our "Rules of Competition" the minimum diameter of the case is 40 mm, we select the appropriate mandrel for the case. An ordinary round rod or tube 400 - 450 mm long is suitable for it. These can be components (tubes) of a hose from a vacuum cleaner or fluorescent lamps that have served their time. But in the latter case, special precautions are needed - after all, the lamps are made of thin glass. Consider the technology of building the simplest models of rockets. The main material for the manufacture of simple models recommended for beginner designers is paper and foam. Hulls and guide rings are glued from drawing paper, a parachute or a brake band is cut out from long-staple or colored (crepe) paper. Stabilizers, head fairing, clip under the MRD are made of foam. For gluing, it is desirable to use PVA glue. Model making should start from the body. For the first models, it is better to make it cylindrical. Let us agree to build a model for the MRD 5-3-3 engine with an outer diameter of 13 mm (Fig. 3). In this case, for its fastening in the aft part, it will be necessary to grind a clip 10 - 20 mm long. Important geometrical parameters of the body of the model are the diameter (d) and elongation (X), which is the ratio of the length of the body (I) to its diameter (d): X = l/d. The elongation of most models for stable flight with tail should be about 9 - 10 units. Based on this, we determine the size of the paper blank for the case.
If we take a mandrel with a diameter of 40 mm, then we calculate the width of the workpiece using the formula for the circumference: B \u8d? The width of the workpiece turned out to be about 10 mm. For those who are not yet familiar with geometry, children in the second or third grades, we can recommend another simple way. Take a mandrel, wrap it twice with a thread or a strip of paper, add 8 - 10 mm and find out what the width of the blank for the case will be. It should be borne in mind that the paper must be arranged with fibers along the mandrel. In this case, it twists well, without kinks. We calculate the length of the workpiece by the formula: L = ?d or stop at the size of 380 -400 mm. Now about gluing. After wrapping the blank paper around the mandrel once, we coat the rest of the paper with glue, let it dry a little and wrap it a second time. Having smoothed the seam, we place the mandrel with the body at the heat source, for example, at the radiator, after drying, we clean the seam with fine sandpaper. We make guide rings in a similar way. We take an ordinary round pencil and wrap a strip of paper 30 - 40 mm wide on it in four layers. We get a tube, which, after drying, is cut into rings 10 - 12 mm wide. Subsequently, we glue them to the body. They are guide rings for starting the model. The shape of the stabilizers can be different (Fig. 4). Their main purpose is to ensure the stability of the model in flight. Preference can be given to the one in which part of the area is located behind the cut of the aft (lower) part of the hull. Having chosen the desired shape of the stabilizers, we make its template from thick paper. According to the template, we cut out stabilizers from a foam plastic plate 4–5 mm thick (ceiling foam plastic can be successfully used). The smallest number of stabilizers is 3. Having stacked them on top of each other in a bag, we cut them off with two pins and, holding them with the fingers of one hand, we process along the edges with a file or a bar with glued sandpaper. Then we round or sharpen all sides of the stabilizers (having previously disassembled the package), except for the one with which they will be attached to the body. Next - we glue the stabilizers on the PVA in the bottom of the case and cover the sides with PVA glue - it smoothes the pores of the foam. We turn the head fairing from foam plastic (preferably PS-4-40 grade) on a lathe. If this is not possible, it can also be cut out of a piece of foam and processed with a file or sandpaper. Similarly, we make a clip under the MRD and paste it into the bottom of the body. As a rescue system for the model, which ensures its safe landing, we use a parachute or a brake band. The dome is cut out of paper or thin silk. For the first starts, the diameter of the dome should be chosen in the order of 350 - 400 mm - this will limit the flight time - because you want to keep your first model as a keepsake. After attaching the lines to the canopy, we stow the parachute (Fig. 6). After manufacturing all the details of the model, we assemble it. We connect the head fairing with a rubber thread (shock absorber) to the upper part of the body of the rocket model. We tie the ends of the parachute dome lines into one bundle and fasten it to the middle of the shock absorber. Next, paint the models in bright contrasting colors. The starting weight of the finished model with the MRD 5-3-3 engine is about 45 - 50 g. The first flight duration competitions can be held with such models. If space for launches is limited, we recommend choosing a 100x10 mm brake band as a rescue system. Starts are spectacular and dynamic. After all, the flight time will be about 30 s, and the delivery of models is guaranteed, which is very important for the "rocketmen" themselves. The rocket model for demonstration flights (Fig. 7) is designed to be launched with a more powerful engine with a total impulse of 20 n.s. She can also carry a payload on her board - leaflets, pennants. The flight of such a model is spectacular in itself: the launch resembles the launch of a real rocket, and the release of leaflets or multi-colored pennants adds to the spectacle.
We glue the case from thick drawing paper in two layers on a mandrel with a diameter of 50-55 mm, its length is 740 mm. We cut out the stabilizers (there are four of them) from a foam plastic plate 6 mm thick. After rounding the three sides (except for the longest - 110 mm), we cover their side surfaces with two layers of PVA glue. Then, on their long side, which we then attach to the body, we make a groove with a round file - for a snug fit of the stabilizers to the round surface. We glue the guide tube in a known way on a round mandrel (pencil), cut it into rings 8-10 mm wide and attach it to the PVA to the body. We turn the head fairing on a foam lathe. From it we also make a clip under the MRD with a width of 20 mm and glue it into the bottom of the case. We coat the outer surface of the head fairing two or three times with PVA glue to remove roughness. We connect it with the upper part of the body with an elastic band, for which an ordinary linen elastic band 4 - 6 mm wide is suitable. The parachute dome with a diameter of 600 - 800 mm is cut out of thin silk, the number of lines is 12-16. We connect the free ends of these threads with a knot into one bundle and fasten to the middle of the shock absorber. Inside the case, at a distance of 250 - 300 mm from the bottom cut of the paper, we glue a lattice of thick paper or rails, which does not allow the parachute and payload to fall to the bottom of the model at the time of take-off, thereby violating its centering. Filling the payload entirely depends on the imagination of the model designer. The starting weight of the model is about 250 - 280 g. Starting device Reliable launch equipment is essential for the safe launch and flight of the model. It consists of a starting device, a remote start control, conductors for power supply and an igniter. The launching device must ensure the movement of the model up until the speed necessary for safe flight along the intended trajectory is reached. Mechanical devices built into the launcher and assisting in the launch are prohibited by the Competition Rules for model rockets of the Sporting Code. The simplest starting device is a guide rod (pin) with a diameter of 5 - 7 mm, which is fixed in the starting plate. The angle of inclination of the boom to the horizon should not be less than 60 degrees. The launcher sets the rocket model in a certain direction of flight and provides it with sufficient stability at the moment of leaving the guide pin. It should be noted that the greater the length of the model, the greater should be its length. The rules provide for a minimum distance of one meter from the top of the model to the end of the bar. The launch control panel is an ordinary box with dimensions of 80x90x180 mm, you can make it yourself from plywood 2,5 - 3 mm thick. On the top panel (it is better to make it removable), a signal light, a lock key and a start button are installed. You can mount a voltmeter or ammeter on it. The electrical circuit of the launch control panel is shown in Figure 7. Batteries or other batteries are used as a current source in the control panel. For many years in our circle, four dry cells of the KBS type with a voltage of 4,5 V have been used for this purpose, connecting them in parallel into two batteries, which, in turn, are connected to each other in series. This supply is enough to launch a rocket model during the entire sports season. This is about 250 - 300 launches. To supply power from the control panel to the igniter, it is desirable to use stranded copper wires with a diameter of at least 0,5 mm with moisture-resistant insulation. For reliable and quick connection, plug connectors are installed at the ends of the wires. Crocodiles are attached at the connection points of the igniter. The length of the current-carrying wires must be over 5 m. The igniter (electric igniter) of engines of rocket models is a spiral of 1-2 turns or a piece of wire with a diameter of 0,2-0,3 mm and a length of 20-25 mm. The material for the igniter is nichrome wire, which has high resistance. The electric igniter is inserted directly into the MRD nozzle. When current is applied to the coil (electric igniter), a large amount of heat is released, which is so necessary to ignite the engine fuel. Sometimes, to enhance the initial thermal impulse, the spiral is covered with powder pulp, having previously been dipped in nitrolac. When launching model rockets, safety precautions must be strictly observed. Here are some of them. Models are launched only remotely, the launch control panel is located at a distance of at least 5 m from the model. To prevent inadvertent ignition of the MRD, the blocking key of the control panel must be kept by the person responsible for the start. Only with his permission at the command "Key to start!" a three-second pre-start countdown is made in reverse order, ending with the command "Start!". Author: V.Rozhkov
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Comments on the article: Nicholas My granddaughter asked me to make a rocket, but I have not done this for 20 years and have forgotten a lot. When I looked at your information, I remembered everything and had already made 90% of it. Thank you. a guest Very interesting! Camron Thank you for the article! I am currently engaged in aircraft and rocket modeling at DOSAAF ![[lol]](https://diagram.com.ua/comments/smilies/lol.gif){kind=small}
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