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PERSONAL TRANSPORT: GROUND, WATER, AIR
Aerosleigh theory. Personal transport
Directory / Personal transport: land, water, air Many years of experience in designing a wide variety of machines shows that in order to successfully complete the work, it is necessary to adhere to a strict sequence at all its stages - from the birth of an idea to its embodiment in metal. Fans who build their own snowmobiles, as a rule, make a serious Mistake, ignoring one of the first obligatory moments in the design process - the development of technical specifications for the structure they create. The terms of reference (or technical requirements) are the starting document for all further work: calculations, detailed design development, and its subsequent manufacture. It records what the designer would like to receive from the machine, unit, part. That is, a specific design goal is set, which must be achieved in the process of work. It should be emphasized that it is very difficult to set the task correctly, taking into account the real possibilities of its subsequent solution, but without the necessary initial data. However, this can be done if you first study the experience accumulated by others, familiarize yourself in detail with previously built, tested and shown good results designs. A certain baggage of theoretical knowledge will also be required, especially in the operation of the machine and its individual units - and without this it is impossible to outline an exact program of action. Properly drawn up technical requirements largely determine not only the scheme of the future machine, but also its most important elements. The shape and dimensions have not yet been developed, the design of individual units has not been indicated, and the task already allows you to have all the basic data that will be required in calculations and design. Each designer is individual in his creative solutions. Therefore, snowmobiles created by amateurs - even of the same type, similar in purpose, the power of the installed engine - can be different both in terms of technical characteristics and in terms of the solution of the general scheme and individual components. This largely depends on a number of private reasons, which are determined by the availability of materials and finished components, production capabilities, the availability of a workshop, machine tools, the necessary tools, and even local operating conditions. In the technical requirements for amateur-built snowmobiles, the following issues must be recorded and preliminarily resolved. Operational and technical characteristics A set of requirements for it depends on a clear definition of what a car is created for: for example, the snowmobile's cross-country ability on winter impassable roads, the general layout and many other characteristics. If, for example, the sled will be used for hunting, the vehicle must have a high degree of maneuverability. The degree of passability of snowmobiles, their running characteristics are determined by the dynamic coefficient of "quality", which is found by the formula: K \uXNUMXd T / Gx, where K is the dynamic coefficient, T is the traction force of the propeller in kgf, developed by it when working on the spot, that is, without the progressive movement of the snowmobile, Gx is the running weight of the snowmobile in kgf. The value of the coefficient K for amateur-built snowmobiles ranges from 0,2-0,3. But it should be remembered that the larger this value, the more passable the car will be in winter off-road conditions. The constructor chooses the value of the dynamic coefficient, but should strive to be at least 0,2. The above formula K can also be used to determine T and Gx. T \uXNUMXd Gx K; and Gx = T/K, These quantities for preliminary calculation can also be determined as follows: T=0,8N Tu, where N is the engine power in l. s., 0,8 - coefficient that ensures the reliability and service life of the engine; Tu is the specific thrust of the propeller in kgf, that is, the force it develops in kgf per liter. With. engine power. The specific thrust Tu depends on the diameter of the air coil and the engine power. It is determined by the load on the area swept by the propeller, decreasing with an increase in this load. With engine power up to 12 liters. With. - 4,5 kg/l. s., 20 l. With. - 4,0 kg/l. s., 50 l. With. - 3,5 kg/l. s., 100 l. With. - 3,0 kg/l. s., 260 l. With. - 2,6 kg/l. With. More precisely, the traction force is determined by the formula: T = (33,25 h D N)2/3 where 33,25 is the coefficient; h - the efficiency of the propeller (for self-made ones it varies depending on the correctness of the calculation and the quality of manufacture from 0,65 to 0,82, or from 65 to 82%); D is the propeller diameter in meters, and N is the engine power. The value of Gx can be determined based on the fact that the running weight should not exceed 12 - 15 kgf per one horsepower of engine power. Carrying capacity of the snowmobile It includes the weight of the crew, passengers, cargo and fuel. This load is given for snowmobiles with skis on soles made of ordinary carbon steel, the coefficient of trembling on snow is taken as 100%. When using materials with a lower coefficient of friction instead of steel - brass, low-pressure polyethylene, fluoroplast-4 - this value can be increased. In this case, G1x is determined from the expression G1x = Gx 100/f, where f is the ratio of the coefficient of friction of the starting material to the coefficient of friction of carbon steel. For materials used on ski soles, the coefficients of friction will be as follows: carbon steel 1,0, or 100%, wood (ash) 0,97, arctilite 0,935, stainless steel 0,810, duralumin 0,790, polyethylene 0,735, fluoroplast 0,730, brass 0,710. Stroke range The distance that the snowmobile must cover on the available fuel and oil in the tanks, without refueling en route. Fuel supply The fuel reserve mentioned above, in turn, determines the required capacity of the fuel tanks (plus 5% of the emergency reserve). Speed In the technical requirements, two values of the speed of the snowmobile are usually recorded: Vt - technical, that is, the speed of the actual movement along the route, without taking into account the time spent on parking along the way. Vmax - the maximum possible, that is, the speed that the snowmobile can develop when the engine is running at maximum power and at full (calculated) load. The maximum speed is determined at a measured distance when driving on virgin snow at an outside temperature of -5 to -20 °, in other words, with good skiing on the snow. The measured distance should be straight, without obstacles from snow sastrugi, hummocks; its length is not less than 0,5 km. Turning radius It is measured on the inside track of the snowmobile skis at a speed that ensures the safety of its implementation, usually 5 km / h. Gradeability Specifies the angle of incline available for a machine with a normal weight load. Additional requirements In this section of the terms of reference, the snowmobile builder writes down what, in his opinion or on the basis of studying previous experience, should be reflected in the design of the future machine. This includes limiting the size of the car or, conversely, increasing the length of the body for the transportation of some oversized cargo. Some requirements may also reflect the designer's view of the desired scheme of the machine or its individual elements - based on the study of existing experience. For example, "aerosleighs should be made according to a four-ski pattern - as more stable and having less resistance to movement compared to a three-ski", etc. Safe Operation The propeller is one of the most dangerous (to others) structural elements. High speeds make the circle described by it transparent, the human eye does not perceive its "plane". Therefore, it is essential: Screw guard To warn people of danger, it is usually painted with bright red paint. Braking system It is most often provided by lever-pin or scraper devices. System starts the engine The most commonly used by most amateurs, starting the engine by turning it by the propeller by hand (with the ignition on) is strictly prohibited. Need a starter. Outdoor lighting In winter, daylight hours are very short, and polar night sets in in the northern latitudes, so headlights must be installed on the snowmobile to allow the driver to see the road clearly. Layout drawing of the snowmobile After drawing up the technical requirements, you can proceed to the next stage of work - the preliminary calculation and execution of the layout drawing of the snowmobile. These works are carried out in parallel. In this case, the terms of reference will be a guide: it will be specified in the process of calculations. Such a drawing is the basis for designing a future machine. It determines the placement of all structural elements, the driver's and passengers' seats, outlines the general contours of the hull, the location of doors, windows, hatches, and links all the main dimensions. Many lovers of technical creativity, in an effort to speed up the work, omit such an important step as making machine drawings. This is an erroneous practice. Experience shows that the time spent on the implementation of the drawings, the development of details and dimensions on them, pays off a hundredfold due to the reduction in the cost of linking and fitting parts during construction, not to mention the fact that negligent designers lose more due to the forced alteration of individual parts . The layout drawing is made in three projections on a scale of at least 1:5, if necessary, with additional sections, cuts and callouts of individual nodes. During the layout process, you should also pay attention to safety requirements. The main ones are as follows. On open-type snowmobiles, the distance from the driver's back to the plane of rotation of the propeller must be at least 0,8 m. Rotating drives located behind the driver's back - pulleys, chains, belts - must be covered with protective shields. In a closed case, it is important to ensure reliable fastening and ease of use of doors and hatches. Not the last place in these requirements is the need for a good view of the road from the driver's seat: the angle of view through the windshield should provide visibility already from 5 m from the toes of the front skis. It is useful to protect the windshield from freezing - for example, by installing double windows, and also to provide windshield wipers. Fuel tanks and batteries must be separated from the cab by a sealed partition. The cabin should be heated by autonomous heaters: it is impossible to lay exhaust pipes along the body for this purpose. The propeller across the width of the machine should not protrude beyond the outer edges of the skis; the distance from the end of the blade to the bottom of the body is at least 50 mm, and to the soles of the skis - at least 250 mm. The ends of the rear skis should not fall into the plane of rotation of the propeller. And what is the preferred exterior color of the aerosleigh? Any, but always bright, well distinguishable in the snow from a great distance. An important requirement for the design is a margin of safety: it must be calculated based on overloads of at least 5 Gx. If operation is expected on frozen rivers and reservoirs, it is desirable to provide the machine with buoyancy - in case of an ice break. When driving in the evening and at night, marker lights are required on the propeller guard: green on the right, red on the left. For the construction of snowmobiles, materials should be used that meet the requirements of GOST, taking into account their performance at low temperatures up to -50 °. Author: I. Yuvenaliev
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