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MODELING
Cord aerobatic training model aircraft. Tips for a modeler
Directory / Radio control equipment In our time, line aircraft modeling differs significantly from traditional, sports. Now, the creation of models is most often taken not by those who are going to participate in sports competitions, but by those who just want to feel the magical feeling of power over an obedient cord aerobatics. At the same time, model shops provide considerable assistance to novice aircraft modellers, where you can purchase both complete sets of elements for assembling cord models, as well as individual parts and blanks for their manufacture. There are also trading companies that distribute their goods by mail. However, enthusiasts have not yet died out, for whom the true pleasure is not only piloting the model, but also the process of its independent design and manufacture. We bring to the attention of just such enthusiasts a simple and very volatile training pilotage for a compression engine with a displacement of 2,5 to 3,5 cm3. The model is designed according to the low-wing scheme with a symmetrical profile wing. When creating the model, quite accessible materials were widely used, in particular, various wooden school rulers were used in the manufacture of many parts. In addition, balsa and lime blanks, as well as pine slats, were used in small quantities. The fuselage of the model is assembled from wooden plates (school rulers 2 mm thick), pine slats with a section of 3x3 mm and plywood 3 mm thick. It should be noted that the width of the rulers is, as a rule, insufficient for the blanks of the fuselage walls, so they will have to be glued in pairs using epoxy glue. In addition, it is desirable to bring their thickness to 1,5 mm using the simplest device from an electric drill and a grinding disc. Frames are also cut from rulers 2,5 - 3 mm thick. The assembly of the fuselage is carried out on the simplest slipway - a flat board. First, the top panel of the fuselage is assembled - for this, the wall, cut from the ruler, is contoured with pine slats with a section of 4x4 mm; docking is carried out using epoxy glue. After polymerization of the glue, the top panel is fixed on the slipway board, and the frames and tail boss made of linden are fixed on the panel. Further, the lower spars are docked to the frames (at this stage of assembly they must be solid, from the engine compartment to the tail boss) and beech bars of the motor mount with a section of 6x10 mm. All these elements of the fuselage are connected at the joints with epoxy glue.
Before starting to sew up the fuselage, a fuel tank soldered from 0,3 mm thick tinplate is glued into the latter. The tank is a rectangular parallelepiped with a capacity of about 50 ml, in which copper tubes are soldered - filling, draining and power tube. A flexible silicone tube with a weight at the end is pulled onto the latter from the inside of the tank, which ensures fuel intake for any evolution of the model. After installing the tank, the side and bottom walls of the fuselage are adjusted and glued together. Further, a cutout for the wing is made in the lower and side walls of the fuselage, and a lime boss is fixed on frame No. 4 with an M4 threaded nut glued into it for attaching the wing. After that, the lodgement under the wing is sealed with linden veneer 1 mm thick. The horizontal plumage is type-setting, its frame is glued together from lime rails. After assembly, the front edge of the stabilizer is rounded, its frame is sanded and covered with a metallized lavsan film. The elevator is carved from balsa plate. After priming and painting, it is pivotally connected to the stabilizer by three "figure eight" loops made of nylon threads. The finished stabilizer is fixed with epoxy glue in the slot of the tail boss of the fuselage. The keel is all-balsa, after grinding, priming and painting, it is also attached to the cut of the fuselage tail boss. The assembled fuselage is primed and painted with "sadolin" type auto enamel - it is a opaque and fuel-resistant paint with good gloss, it is best to paint with a spray gun, but a good result is obtained when coating with a foam sponge (you must first swirl it, it does not dissolve whether the sponge used enamel). It is advisable to start the manufacture of the wing with the preparation of ribs from school rulers 2 mm thick, the leading and trailing edges and the shelves of the spar from pine laths. The ribs are sawn with a jigsaw with a slight allowance for finishing, which is best done with a simple fixture. The latter consists of two duralumin templates, made in accordance with the wing profile, and two threaded studs with nuts. The blanks of the ribs are located between the templates and are pulled together with studs and nuts; the resulting package of ribs is processed together, so that they are exactly the same. The wing is also assembled using a slipway made of a flat board with a plaza fixed on it - a sheet of paper with a full-size wing frame depicted on it. Initially, the frame parts are fixed on the slipway with the help of stationery clothespins and sewing pins, and after checking for assembly accuracy and the absence of distortions, the seams are filled with epoxy glue. In the middle part of the wing, three lime bosses are glued - near the trailing edge for fixing the wing on the fuselage, in the spar area - for attaching the landing gear, and at the leading edge, for a docking beech pin with a diameter of 6 mm. The surface of the wing between the two central ribs is sewn up with lime veneer about 1 mm thick. At the end rib of the right semi-wing, between the spar flanges, a lead weight of 20 g is fixed with threads and glue. The control rocker is sawn out of duralumin sheet 3 mm thick; to install it in the wing, a box of lime rails is used, glued between the spar shelves. The leashes of the control cord (they are located inside the wing, between the rocking chair and the cords) are made of a steel cord folded in half. At the exit point of the leashes, two springs are installed into the holes in the wingtip, wound coil to coil of wire with a diameter of 0,3 mm. In the control system of the model, flaps are used, which, when the elevator moves up (the handle - towards itself), deviate down by an angle of about 10 degrees, which somewhat improves the flight characteristics of the model and facilitates its landing. The flaps are all-balsa, each of them, after grinding and painting, is hinged on the wing with “eight” loops made of nylon threads. Between themselves, the flaps are connected by a torsion bar made of steel wire with a diameter of 1,5 mm. The chassis of the model is bent from OBC wire with a diameter of 3 mm. The wheels are plastic, rubberized, with a diameter of about 40 mm and a thickness of about 10 mm - from a child's toy. Fixing the wheels on the chassis - from the inside with steel washers soldered to the axle shafts and from the outside - with nuts and lock nuts with M3 thread. The landing gear is attached to the central part of the wing with a duralumin bracket using self-tapping screws.
The engine hood is glued from two layers of fiberglass and epoxy resin on a plasticine blank. After polymerization of the binder, the workpiece is sanded and coated with car enamel. The hood is attached to the fuselage with miniature self-tapping screws. The flight qualities of the model in general and the controllability in particular largely depend on the correct centering - it must coincide with the point corresponding to 20-25 percent of the wing chord, counting from the leading edge. To fine-tune the centering to the optimum, you can use a weight, installing it in the front or rear of the fuselage. To start the aerobatics, steel cords with a diameter of 0,25-0,3 mm and a length of at least 15 meters should be used. It makes sense to test the new model in calm weather. You need to launch the model together - the pilot holds the control stick, and the mechanic starts and regulates the engine, and also holds the model until the start, which is performed at the pilot's command. The model takes off, as a rule, after a run of 2-3 meters. Next, the pilot should, with a slight movement of the control stick "towards himself" (this is done by moving the whole arm, not the hand), raise the pilotage to a height of about 2 meters and master the control of the model in level flight. And only after that you can move on to the simplest aerobatic maneuvers - slides, turns and peaks, and then to more complicated figures - classic and square loops and eights. Author: I.Sorokin
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Comments on the article: a guest Well done! Attract young people to aircraft modeling.
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