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MODELING
S1B missile models. Tips for a modeler
Directory / Radio control equipment The category of high-altitude models (S1) is one of the "oldest" in rocket modeling. Since 1985, from the sixth world championship, she has firmly “registered” in all world and European championships. It should be noted that our athletes immediately became leaders in it and out of eleven world championships of the last twenty years they became champions seven times. A convincing victory at the 16th World Championship at Baikonur in the class of models for flight altitude was won by V.A. Menshikov, a repeated champion of Russia, prize-winner and winner of the European and world championships. His model - "high-rise" class S1B rose to 612 m. Depending on the specific impulse of the engines, the diameter and length of the hull, category S1 is divided into five classes. For many years, the championship classes have been S1B - for young men and S1C - for adults. After recent changes in the FAI code, the technical requirements for models have become the same: a minimum diameter of 40 mm at the middle of the length of the rocket (not less than 500 mm). And yet - in category S1, the minimum diameter of the body (rear section of any stage) should not exceed 18 mm. Classes S1B and S1C are distinguished by the maximum total impulse of the engines and the starting weight of the model. In youthful ones, the impulse is not more than 5 n. s., weight - no more than 60 g, in adults, respectively - no more than 10 n. With. and 120 g. Another general requirement for models in this category. When using two "working" stages, the impulse of the model rocket engine (MRE) must be the same at both stages - 2,5 n each. With. (in class S1B) and 5 n. With. (for class S1C). It is allowed to use any number of engines, in any combination of them, provided that their total momentum does not exceed the allowable value for this class. The aim of the competition in the high-altitude model category (S1) is to achieve the highest altitude determined by appropriate measurements. Each participant can make three flights - according to the best result, the winner is determined. In case of equality of results, the sum of two flights is taken to identify the best one. And if it is the same, then the sum of all three determines the champion. To determine the altitude result, all models of this category are tracked in flight from at least two calibrated measuring instruments (theodolite, TZK) located at the ends of the base line with a length of at least 300 m in direct line of sight from the launch site. Operators working with measuring devices fix angles both relative to the vertical axis (azimuth) and relative to the horizontal (elevation) with an accuracy of 0,5 degrees. The angle data obtained from the observation of the model is converted into height data by triangulation.
For those who want to make their first high-altitude model, we offer a drawing and description of a simple single-stage model of class S1B for an engine with a total impulse of 5 N. With. (Fig. 1). The material for its construction is available - paper, polystyrene. The body is glued from two layers of writing paper (0,1 mm thick) on a mandrel with a diameter of 40 mm. The dimensions of the workpiece in this case are 300x270 mm. When choosing a blank, the paper fibers must be placed along the mandrel - there will be no folds and kinks. For work, you can use PVA glue, slightly diluting it with water. After the knurled tube has dried, the seam should be treated with sandpaper and coated twice with nitro-lacquer. The tail element is also made using the same technology, using a conical mandrel. After drying and appropriate processing, it is clamped into the chuck of a lathe and faceted to a size along the length of 102 mm. Then glued out of paper and a 107 mm long engine clip using a mandrel with a diameter of 13,2 mm. Two frames made of polystyrene are fixed on the clip at both ends. One (lower) - power, the other (upper) - docking. With the help of it, the connection of the tail element and the body is carried out. Before this, the clip is glued into the tail element. A small piece of thread (halyard) is fixed to the upper part of the body from the inside to connect it with other parts of the model. The head fairing is an ogival shape, machined from dense foam on a lathe. The length of the landing skirt is 25 mm. After processing, it is reinforced from the outside - covered with a layer of PVA glue and sanded, getting a smooth surface. A loop of thread is glued into the end of the skirt, to which a parachute and a suspension thread are subsequently attached. Stabilizers (there are four of them) are cut according to a template from 4 mm thick ceiling foam. The blanks are folded into a bag and processed along the contour. Each is then profiled both in top view - reducing the thickness to 2 mm, and in front view - giving a streamlined symmetrical profile. To increase rigidity, the side surfaces of the stabilizers are pasted over with writing paper and treated with fine-grained sandpaper, achieving a good, even surface. Stabilizers are attached to the tail cone with the help of water-dispersed glue-express "Joiner". The assembled model (with engine) must be weighed and balanced - after all, stable flight is the key to successful performance in competitions. One of the tasks in the design of sports models of rockets is to ensure their stabilization, that is, stable flight on a given (vertical) trajectory. It should be noted that one of the ways to ensure the stability of rocket models - aerodynamic - is already incorporated in their designs - by installing stabilizers. But for the category of "high-rises" it would be useful to check whether the given aircraft is stable or not under the influence of external forces. A necessary condition for aerodynamic stability is the relative position of the center of gravity (c. t.) and the center of pressure (c. d') of the model. If c. t. is located in front of c. then the model will be stable. If c. t. models behind c. D., then no. The ratio of the distance from c. t. to c. e. to the length of the rocket model determines the "margin of stability". For models with stabilizers, it should be about 5 - 10%. The center of gravity of the model (in the starting readiness) is determined by balancing it on the edge of the school ruler. To find the center of pressure, you can use two methods: practical and calculated. For the first of any sheet material - plywood, cardboard, plastic - a figure is cut out along the contour of the rocket model and c. that is, the same flat figure. This will be c. d. models. But it must be admitted that errors are inevitable. Practical conclusions can be confirmed by the second - by calculation. For it, a side view of the model is drawn and the area of each of its elements (fairing, body, stabilizers, etc.) is determined. Mark in the figure c. t. each element. The area of each of the geometric figures, which is determined by known geometric formulas, is multiplied by the distance from the top of the model to q. m. of this element and get the moment of resistance of a flat figure. The sum of the moments divided by the total area will give the location of the geometric center of gravity of the contour or the center of pressure of the model. For this model of the E1V class rocket, it will be equal to 215 mm. For changes in the position of c. so it is possible to load the head fairing. The originality of the two-stage model of the S1B class rocket is the connection of the stages through the MRD body of the second stage and the sub-caliber form of the upper stage body. The proposed method of connecting the steps is almost a jeweler's work, it requires certain skills and abilities. The shape of the hull of the second stage is sub-caliber (with a variable section), and from the point of view of aerodynamics, the solution is absolutely correct and competent. After all, the flight of the model to a height occurs mainly on the second stage (on the first - up to a height of 10 - 15 m). So the choice of the author in terms of the shape of the corpus is completely justified. And now specifically about the model. The body of the first stage is molded from two layers of fiberglass with a density of 20 g/m2 on a figured mandrel with the largest diameter of 40 mm and the smallest diameter of 18,7 mm. After the resin hardens, the workpiece (together with the mandrel) is clamped into the lathe chuck and processed from the outside with sandpaper of different grain sizes. Then they are covered with two layers of yacht varnish "Parade L20" and cut to the lower length - 344 mm. The following is glued inside the case: from above, a mounting sleeve with an inner diameter of 10,2 mm and a width of 10 mm; below - five frames: four - with an inner diameter of 4 mm and one - bottom, its diameter is 10,2 mm. Inside the frames, a fire guide is fixed - a fiberglass tube 329 mm long and 4 mm in diameter. To its lower cut for a length of 9 mm, the bushing of the "landing" of the MRD of the first stage is glued. It is put on it by the inner surface of the upper part of the engine housing. At a distance of 50 mm from the lower cut of the first stage housing, a through (diametrical) hole with a diameter of 1 mm is made in it, which also passes through the fire guide. A thread is threaded into this hole before the start for attaching the brake band (rescue system) of the first stage. The stabilizers (there are three of them) of the first stage are made of a 3 mm balsa plate, profiled, reduced to a free edge to a thickness of 0,5 mm and butt-mounted to the hull with epoxy resin. Then they are covered with two layers of varnish. The body of the second stage, as mentioned above, is sub-caliber, made in the same way as the body of the lower stage - molded on a mandrel of variable diameter: the largest is 18,9 mm and the smallest is 10,1 mm. After the resin hardens, the resulting workpiece is clamped into a lathe and, at 270–300 rpm, is processed with sandpaper and varnished. After letting it dry, they are trimmed in size (length - 134 mm without head fairing).
Inside the hull, in the lower (stern) part, the thrust and centering bushings and the frame are glued, having previously made a hole in them with a diameter of 10,2 mm according to the MRD. In the upper part of the body, a halyard (a thread about 800 mm long) is fixed from the inside to connect with the head fairing and fasten the brake band. Its length is at least 3 m, width - 25 - 30 mm. The stabilizers of the second stage (there are four of them) are cut out of a balsa plate 1 mm thick, the sides are reinforced with fiberglass, butt-attached to the tail section of the hull. The head fairing is an ogival shape, carved from linden, well processed and varnished. A loop for attaching a halyard is glued into the lower end (skirt). The flight weight of the model without MRD and rescue system is about 20 grams. The "high-rise" starts on two "Delta" engines with an impulse of 2,5 n. With. The MRD of the first stage of the moderator does not have. Its task is to give the model a starting "push", to accelerate it to a certain speed. Its operation time is no more than 1 - 1,2 s. The operating time of the MRD second stage moderator is selected practically and is about 6 - 6,5 s. Preparing the model for the launch is a responsible matter, it requires skills and a certain sequence. Let's talk about this in detail. In this design (according to the method of connecting the steps), the order in which they are prepared does not matter. For example, let's start with the first (lower) step. On the outer side of the case, in the place of the diametrical hole, we will fix the brake tape-strip made of foil polyethylene with dimensions of 25x300 mm, previously folded into an "accordion". With a cotton thread threaded through the hole, we press and tie the brake band to the body. After that, we insert the MRD into this frame and "put" it on the sleeve (the connection must be tight, without backlash). Then, from above, we pour a little gunpowder into the fire guide - one measure (a piece of a sleeve from a small-caliber rifle 4 mm long). Next, we lay the brake band in the body of the second stage, after filling it with talcum powder, cotton wool and paint (to create a colored cloud for better observation of the height of the rescue system opening). Then, with a tight fit, we “put” the MRD of the second stage, leaving its 18 mm long skirt free. On it with a little effort we put on the bushing of the first stage body. The end of the engine rests against the upper cut of the fire guide. The distance between the steps at the place of their connection should not be more than 1,5 - 2 mm. For a guarantee, 5 - 6 powders can be poured into the nozzle of the engine of the second stage. The model takes off from a gas-dynamic installation of the "piston" type, while the MRD skirt of the first stage enters the holder of this installation. After the launch, at a height of 10 - 15 m, the expelling charge of the first stage engine is activated. The fire impulse is transmitted through the fire tube to the engine of the second stage, and it "goes" up. And at the same time, the fixing thread of the first stage rescue system burns out, the brake band opens - and it lands. Author: V.Rozhkov
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