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MODELING
Universal free-flying model. Tips for a modeler
Directory / Radio control equipment Schematic models of airframes and aircraft, as you know, began to fly much earlier than their full-size prototypes. Having paved the way for real aircraft into the sky, they still help novice aircraft modellers to take their first steps in small aviation today. The only pity is that modern "schematics" practically do not differ from those that our grandfathers did: all the same pine slats, aluminum wire, aircraft model rubber, a little tissue paper, thread and glue. No new materials, no advanced design and technological techniques. We offer novice aircraft modellers a simple universal model, which is not much more complicated than a schematic one in manufacturing, but its aerodynamics and, accordingly, flight data are at a completely modern level.
The aircraft model can be made both in the variant of a glider and rubber-engine aircraft, however, it makes sense to first assemble it in the first variant, and then, after the modeler has mastered the skills to launch and adjust this aircraft, equip it with a propeller and a rubber motor. The aerodynamic scheme of the model is a high-wing aircraft with a high aspect ratio wing. The design is mixed, with the use of packaging foam, plywood and all the same lime and pine slats. The fuselage of the model consists of an H-beam, glued from 1 mm plywood, and foam filling. The fuselage is assembled with epoxy glue. In its rear part, bosses are installed that fix the keel and tail hook of the rubber motor, in the front - a lime boss with a propeller hub. The latter is made from a piece of a rod from a ballpoint pen or, better, a gel pen, you only need to expand the plastic tube on one side with a heated cone-shaped rod.
In the middle part of the fuselage, a lodgement under the wing is formed, for which a recess is cut out and sewn up with 1,5 mm lime veneer. To fasten the wing to the fuselage with the help of rubber rings, beech pins with a diameter of 6 mm are used, glued into the fuselage at the leading and trailing edges of the wing. The wing is fixed with a pair of beech pins 4 mm in diameter embedded in the wing along its symmetry axis; corresponding holes are drilled in the cradle for these pins. The keel is a foam-filled frame, the leading edge and root rib of which are cut from pine slats, and the trailing edge from 2mm plywood. The horizontal tail is a stabilizer consisting of a pine frame and foam filling, and elevators hung on it. The latter are made of linden and connected to the stabilizer with the help of peculiar loops - pieces of soft steel wire (for example, from a paper clip), which allows you to select the optimal angle of the rudders when debugging the model. The wing is also of mixed design, consists of two consoles. The basis of each is a foam core, reinforced with a pair of pine spars and a pine trailing edge. The core is cut out of a foam bar with a thermal cutter made from a bow saw, you only need to replace the toothed hacksaw tape with a nichrome wire heated by an electric current. Cutting also requires a pair of templates cut out of duralumin in accordance with the table of control sections - they are guides when cutting foam. The degree of heating of the nichrome wire is selected empirically using LATR: it should be such that after the wire passes through the foam, a smooth vitreous crust remains on it. At the finished foam core, the trailing edge is cut off and a pine lath is glued with epoxy resin instead. Further, on the upper and lower surfaces of the wing at a distance of 50 mm from the leading edge (30 percent of the chord), triangular grooves are cut under the spar flanges. To do this, you can use a sharpened joint knife or, much better, a special tool, the device of which is shown in the figure. The spar shelves are triangular pine slats, they can be made by cutting square slats diagonally on a mini-"circular" or by cutting off part of the slat with a miniature planer. The shelves are glued with the same "epoxy". From the consoles prepared in this way, a single wing is assembled, for which a jumper installed between the spar shelves is used. The latter is made of two chamfered plywood plates, glued together in such a way that it has two dovetail grooves that provide a rigid docking of the consoles. The rear edges of the consoles are glued "on the mustache". Lastly, two hollow lime endings are glued to the wing.
Finishing foam surfaces, in principle, can only consist in their sequential grinding with skins of decreasing grain size, however, it is still better after this operation to prime the foam with epoxy glue, after it has cured, sand the surfaces again and paint them with car enamel of a suitable color. Before launching the model in the airframe version, it is necessary to choose the alignment by placing a suitable load in the channel under the rubber motor. Centering in this case should be located at 25 - 30 percent of the length of the MAR of the wing. If at launch the model will dive steeply, then the elevators should be bent a little up, while climbing (climbing with loss of speed) - down. The flight path of a correctly adjusted model aircraft should be a straight downward line. To launch the glider from the rail, it is necessary to attach a wire hook to the bottom of the fuselage. To convert a glider into an airplane, you will need a propeller. It can be made from a suitable lime bar in strict accordance with the theoretical drawing. The concave parts of the screw are trimmed with a miniature cycle or glass fragments of suitable curvature. After the final finishing, the screw is balanced, for which it is put on a knitting needle placed on two horizontal steel rulers. At the same time, a heavier blade will pull down, it needs to be sanded off with a sandpaper. A properly balanced screw, when swung, should stop on the knitting needle in any position. The finished screw is covered with several layers of parquet varnish. The screw shaft is bent from steel wire with a diameter of 1,5 - 2 mm. A smooth brass washer is installed between the sleeve of the front fuselage boss and the propeller. Table of control sections of the aircraft model wing (values X, Yv and Yn - in mm) It is also necessary to prepare a rubber motor. To make it, between two nails hammered into a suitable board at a distance of 650 mm from each other, wind round aircraft model rubber (its weight should be in the range of 35 - 40 g). At the front and rear ends of the rubber band, with the help of strong sewing threads, loops are formed under the hook of the screw shaft and under the rear hook. After manufacturing, the rubber motor should be washed with soap and water, dried and lightly lubricated with castor oil. And between flights, store in a hermetically sealed plastic bag. The first adjustment flights are made when the rubber motor is twisted by 100-150 revolutions. If the flight of the model is stable, then the twist of the rubber motor should be gradually brought to full - to the second "wings" along the entire length of the rubber motor. Author: I.Sorokin
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