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PERSONAL TRANSPORT: GROUND, WATER, AIR
Helicopter AV-1. Personal transport
Directory / Personal transport: land, water, air Dear aviation enthusiast! This article may be useful to you in the development and construction of a light helicopter. The proposed rotorcraft (AV-1) is the fruit of a long passion for aviation, the result of persistent and painstaking work over five years, of which two years were spent on construction, and the rest on testing, fine-tuning, mastering piloting, repair, modernization. The design meets several important requirements for an aircraft in the use of an amateur: the ability to store in a small room; transportation to the place of flights - by car, motorcycle and even manually; assembly within 18-20 minutes by one person (using only two wrenches). The problem of safety in the event of an engine and transmission failure in flight has been solved quite reliably. The design of the main rotor (HB) and the control system has features that "forgive" such piloting errors as overweight of the main rotor and overloads. Of course, the design of the helicopter was significantly affected by the cramped conditions in which it was manufactured, as well as difficulties with materials and equipment, so it is clear that the machine is far from ideal. But I'm happy with it. To begin with, I will give examples of calculations of the main structural elements. So, the diameter of the main rotor AB-1 is chosen from the condition of the load per unit area of the swept disk (Ps) within 6-7 kg/m2. This value was taken based on the results of processing statistical data of flying light gyroplanes, helicopters with a specific load (p) in the range of 6-8 kg/hp. In my case, based on the estimated flight weight (t) of the device 180-200 kg (empty weight 100-120 kg) and having an engine with a power (N) of 34 hp, of which two should have been spent on the tail rotor drive, we obtain the following values of the load per unit of power, the area of the swept HB disk (Som) and the diameter of the HB (D):
The HB diameter of 6,04 m is very close to the HB size of a Bensen gyroplane with a 40 hp engine. and weighing 190 kg. With such initial data, there was hope that the helicopter would fly. But in order for it to fly as a vehicle, it is necessary that the HB (T) thrust be significantly greater than the mass of the apparatus (at least 1,4 times). This provides sufficient vertical rate of climb and flight altitude. Now let's calculate the maximum T in the hovering mode in a normal atmosphere (760 mm Hg, 18°C). In this case, the empirical formula was used: T \u33,25d (2N Dn) 3/XNUMX, where: n=0,6...0,7 - coefficient. As a result, the thrust turned out to be 244,8 kg, which is very close to that actually obtained during the tests of the AB-1. (Based on the named ratio 1,4, the flight weight of the apparatus must not exceed 175 kg.) Description of the design of the helicopter will begin with the so-called fuselage. The cabin compartment has a truss structure in the form of a tetrahedral pyramid, the vertical edge of which (the main frame) sort of separates the cabin compartment from the engine. It is made of duralumin (D16T) pipes: vertical and lower - 40x1,5 mm, and front - 30x1,5 mm. Above the cab there is a power connecting element - a frame for the main gearbox, at the bottom - a horizontal cross member of the engine mount. The second power cross member (at the level of the seat back) is made of a dural tube of rectangular section 30x25x1,5 mm; it serves to fasten the intermediate gearbox, seat back and main landing gear assemblies.
The "compartment" of the engine in the form of a trihedral pyramid is made of steel pipes (steel 20) with a section of 30x30x1,2 mm. The lower edge has attachment points for the engine, landing gear braces and tail boom. The tail boom is riveted from a duralumin sheet 1 mm thick. It consists of three parts: two cones (diameter at the top 57 mm) and a cylinder between them (diameter 130 mm) with external ribs, which serve as a reinforcing stringer and a zone for riveting the skin elements. Reinforcing frames are riveted in the places where the braces are attached. ny engine with a working volume of 750 cm3. The crankcase and crankshaft are taken from the K-750 motorcycle; pistons, cylinders and heads - from MT-10. The crankcase is lightened and adapted to work with a vertical shaft arrangement (the oil system has been changed). It is possible to use other engines, the gross weight of which is not more than 40 kg and the power is not less than 35 hp. Of particular note is the stabilization system of the apparatus. The AB-1 uses a BELL-type system, but with a higher stabilization coefficient (0,85), which almost completely removes the pilot's concern for balancing the helicopter in the hover mode. In addition, it limits the angular velocity on turns, protecting the helicopter from overloads. At the same time, controllability is ensured due to the shape of the loads in the form of flat disks (selected experimentally). The length of the rods is chosen from the condition that the loads in the form of flat discs should "sit" well in the flow. Therefore, the circumferential speed of the loads was chosen to be 70 m/s, and at 600 rpm this corresponds to the length (radius) of the rod close to 1 m. -1,5° there should be a moment that, when transmitted through the lever mechanism to the axial hinge of the HB blade, will be equal (or greater) to the friction moment in the bearings of the axial hinge under the working axial load. The main gearbox is designed to transmit torque to the main rotor shaft. Inside it passes the rod of the HB common pitch control mechanism. It ends with a fork, which, with its side protrusions, engages with the forks of the blade bushings, rotating the mechanism of the stabilization system. When the rod is moved vertically (from the handle) using the levers of the collective pitch mechanism, the angle of installation of the propeller blade (and, accordingly, its pitch) changes. A swashplate (SW) is installed on the upper cover of the gearbox housing, which serves to change the position of the plane (actually a cone) of rotation of the HB relative to the vertical axis of the apparatus (the axis of the main shaft of the gearbox) due to the change in the angle of attack of the blades opposite in sign: the angle of attack of the blade going down, decreases, going up - increases. In this case, there is a change in the magnitude and direction of the horizontal component of the HB thrust vector. The gearbox housing is split along a plane perpendicular to the shaft axis, welded from 30KhGSA sheet steel 1,3 mm thick. The bearing seats are also machined from 30KhGSA steel, welded into the covers, after which heat treatment ("hardening", high tempering) is carried out to relieve stress and increase strength. Then the flanges were milled, the covers were assembled and the seats of the bearings and holes were bored out on a coordinate machine. The bottom cover is made of D16T alloy. The main shaft is made of steel 40HNMA, heat treated to Gvr -110 kg/mm2. The shaft diameter is -45 mm, the diameter of the inner hole is 39 mm, the wall thickness in the area of the splines of the HB sleeve is 5 mm. Shaft surfaces are polished, splines and bearing seats are copper-plated. The driven gear and the drive shaft-gear are made of steel 14KhGSN2MA-Sh and have 47 and 12 teeth, respectively, with a module of 3 and an engagement angle of 28°. The teeth are cemented to a depth of 0,8-1,2 mm and heat-treated to a hardness of HRC = 59-61. The outer ring of the swashplate is detachable (like a collar), made of D16T alloy (milled from a sheet 35 mm thick), and the inner ring and cardan are made of steel 30KhGSA. Cardan ring bearings - 8001 8Yu. Swashplate bearing - 76-112820B. The tail rotor module (PB) is assembled on a glass, telescopically connected to the tip of the tail boom. He can move for The front landing gear is freely oriented, without shock absorption, it has a wheel 250x50 mm (from roller skis). The main landing gear is made of steel pipes and equipped with pneumatic shock absorbers. Wheels of the main supports - 300x100 mm with a cut tread (from the map). This "haircut" is carried out to reduce weight, improve streamlining and facilitate movement "skid" on the grass during training or during unsuccessful landings. The lower braces of the chassis are made of steel pipes 20x1 mm. The helicopter is equipped with a four-stroke two-cylinder boxer engine with a working volume of 750 cm3. The crankcase and crankshaft are taken from the K-750 motorcycle; pistons, cylinders and heads - from MT-10. The crankcase is lightened and adapted to work with a vertical shaft arrangement (the oil system has been changed). It is possible to use other engines, the gross weight of which is not more than 40 kg and the power is not less than 35 hp. Of particular note is the stabilization system of the apparatus. The AB-1 uses a BELL-type system, but with a higher stabilization coefficient (0,85), which almost completely removes the pilot's concern for balancing the helicopter in the hover mode. In addition, it limits the angular velocity on turns, protecting the helicopter from overloads. At the same time, controllability is ensured due to the shape of the loads in the form of flat disks (selected experimentally). The length of the rods is chosen from the condition that the loads in the form of flat discs should "sit" well in the flow. Therefore, the circumferential speed of the loads was chosen to be 70 m/s, and at 600 rpm this corresponds to the length (radius) of the rod close to 1 m. -1,5° there should be a moment that, when transmitted through the lever mechanism to the axial hinge of the HB blade, will be equal (or greater) to the friction moment in the bearings of the axial hinge under the working axial load. The main gearbox is designed to transmit torque to the main rotor shaft. Inside it passes the rod of the HB common pitch control mechanism. It ends with a fork, which, with its side protrusions, engages with the forks of the blade bushings, rotating the mechanism of the stabilization system. When the rod is moved vertically (from the handle) using the levers of the collective pitch mechanism, the angle of installation of the propeller blade (and, accordingly, its pitch) changes. A swashplate (SW) is installed on the upper cover of the gearbox housing, which serves to change the position of the plane (actually a cone) of rotation of the HB relative to the vertical axis of the apparatus (the axis of the main shaft of the gearbox) due to the change in the angle of attack of the blades opposite in sign: the angle of attack of the blade going down, decreases, going up - increases. In this case, there is a change in the magnitude and direction of the horizontal component of the HB thrust vector. The gearbox housing is split along a plane perpendicular to the shaft axis, welded from 30KhGSA sheet steel 1,3 mm thick. The bearing seats are also machined from 30KhGSA steel, welded into the covers, after which heat treatment ("hardening", high tempering) is carried out to relieve stress and increase strength. Then the flanges were milled, the covers were assembled and the seats of the bearings and holes were bored out on a coordinate machine. The bottom cover is made of D16T alloy. The main shaft is made of steel 40HNMA, heat treated to Gvr -110 kg/mm2. The shaft diameter is -45 mm, the diameter of the inner hole is 39 mm, the wall thickness in the area of the splines of the HB sleeve is 5 mm. Shaft surfaces are polished, splines and bearing seats are copper-plated. The driven gear and the drive shaft-gear are made of steel 14KhGSN2MA-Sh and have 47 and 12 teeth, respectively, with a module of 3 and an engagement angle of 28°. The teeth are cemented to a depth of 0,8-1,2 mm and heat-treated to a hardness of HRC = 59-61. The outer ring of the swashplate is detachable (like a collar), made of D16T alloy (milled from a sheet 35 mm thick), and the inner ring and cardan are made of steel 30KhGSA. Cardan ring bearings - 8001 8Yu. Swashplate bearing - 76-112820B. The tail rotor module (PB) is assembled on a glass, telescopically connected to the tip of the tail boom. It can be pulled out to tension the drive belt. In this case, however, it is necessary to rebuild the length of the tail rotor control cables. It is driven from an intermediate gearbox using a chain and two belt drives. The tail screw is articulated (has a horizontal combined and axial hinges), rotates from front to back. Its diameter is 1,2 m, the number of revolutions per minute is 2500. The RV bushing consists of a crosspiece and two cups riveted with blades. Two bronze bushings serve as axial bearings, and the M24x1,5 thread perceives the centrifugal force. Sealing is carried out by a rubber ring, which is fixed with a washer and a spring ring. The leashes of the axial hinges are offset from the axis of the horizontal hinge (HH) by 30°. Lubrication - MS-20 oil, poured into a glass before assembly. The horizontal hinge is assembled on bronze bushings and a cemented pin, which is fixed on the GSh fork from rotation. When assembling the blades with a glass, special attention was paid to the alignment of their axes. Now a little about the choice of the main parameters of the propeller blades. The average aerodynamic chord (MAC) of the blade is calculated from the condition that the filling factor of the swept disk (K) will be in the range of 0,025-0,035 (the smaller value is for high circumferential speeds, 200-220 m/s; and the larger one is for smaller ones, 170-190 m/s), according to the formula: bmin = (SHB K)/DHB ; where bmin is the minimum MAR. Main technical characteristics:
On the AV-1 helicopter for the main rotor, the value of the coefficient K = 0,028, since the circumferential speeds are selected within the range of 190-210 m/s. In this case, the SAR is taken equal to 140 mm. On an aircraft, it is desirable to have everything very light. But in relation to HB, we can talk about the minimum allowable mass, since the mass of the blade depends on the centrifugal force necessary to create a cone of rotation of the main rotor. It is desirable that this cone be within 1°-3°. It is hardly possible and even undesirable to manufacture blades with a mass of 2-3 kg, since the reserve of kinetic energy will be small during an emergency landing on autorotation with detonation, as well as when switching to autorotation mode from a motor flight. A mass of 7-8 kg is good for an emergency, but at maximum speeds, the HB will give significant centrifugal force. On AV-1, a blade weighing in the range of 4,6-5,2 kg is used, which provides a maximum load from centrifugal forces up to 3600 kgf. The strength of the HB sleeve is designed for this load (with a 7-fold margin of safety); its mass is 4,5 kg. The proposed blade shape and twist are the result of experiments with blades of various shapes, twists and profiles. HB blades must satisfy two conflicting requirements: good autorotation (that is, to provide a low rate of descent in autorotation in the event of an engine failure) and use engine power with maximum efficiency in a motor flight (for rate of climb, maximum speed and economy). Consider options for blades for a helicopter and for a gyroplane. A good gyroplane has a twist. fixed, that is, the angle of installation of the blade at the butt is negative (-5°...-8°), and the end section is positive (+2°). The profile is plano-convex or S-shaped. Currently, the NACA 8-H-12 profile (S-shaped, 12 percent) is widely used. The shape of the blade in plan is rectangular. A good helicopter has a straight twist, that is, the butt has a positive installation angle (+8°...+12°) in relation to the end section. Profile NACA 23012, the relative thickness of which at the end is 12%, and at the butt - 15%. The shape of the blade in plan is trapezoidal, with a narrowing of 2,4-2,7. The shape of the blade in plan was calculated by the finite element method for the case of flight at a speed of 110 km/h and an overload margin for the blade "going backwards" - 1,4. At a speed of HB 580 rpm, a diameter of HB of 6 m and a flight weight of 200 kg, the blade was 80 mm wide at the end, and 270 mm at the butt (narrowing 3,4). The extra width of the blade at the end leads to an extra consumption of engine power to overcome the turbulent resistance of the profile, so it is beneficial to minimize the wetted surface of the sections operating at high speeds. On the other hand, in order to have a reserve of lift at the end sections of the blade when the NV is loaded or when switching to autorotation (the most probable piloting errors by an amateur pilot), it is necessary to have blades somewhat wider than the calculated ones. I adopted the narrowing of the blade 2, the root chord is 220 mm, and the end chord is 110 mm. In order to reconcile a helicopter with a gyroplane in one apparatus, it was necessary to use blades without twist. More difficult with profiles. The end part of the blade (Rrel = 1 - 0,73) has a NACA 23012 profile with a relative thickness of 12%. In the section Rrel = 0,73-0,5 - a transitional profile from NACA 23012 to NACA 8-H-12, ' only without an S-shaped tail. In the section Rrel = 0,5-0,1, the K|ACA 8-N-12 profile of variable relative thickness: 12% for Rrel = 0,5 and 15% for Rrel = 0,3-0,1. Such a blade pulls well in all flight modes. On autorotation, the speed of descent of the helicopter was 2,5 m/s. During the test, an autorotation landing was made without undermining, braking was carried out by pitch and the vertical speed was extinguished to zero, and the run was only about 3 m. On an ultralight helicopter, in the event of an engine failure, the RV transmission is disconnected, since its drive requires energy generated by the autorotating HC, which would worsen the autorotation and increase the rate of descent. Therefore, for RV there is no need for a symmetrical blade profile. It is best to choose a plano-convex type R3. To increase the efficiency, it is desirable to use a twist (8 °). In addition, to increase the efficiency of the propeller, it is desirable to have a trapezoidal blade shape in plan with a narrowing equal to 2 and a filling factor of the swept disk in the range of 0,08-0,06. Good results are also given by the NACA 64A610-a-0,4 profile with a relative thickness of 12%. Blades can be made using various technologies. For example, from a solid pine board. As blanks, two boards of straight-grained, knotless, medium-density pine are selected, cut so that the dense layers face the future leading edge and go at an angle of 45 °. The board is profiled according to a template reduced by the thickness of fiberglass gluing and painting (0,8-1,0 mm). After finishing, the tail part of the part is lightened. For this, the spar part and the trailing edge are marked out. The spar part at the butt is 45% of the chord, and at the end - 20%. Next, holes are drilled with a diameter equal to the distance from the trailing edge to the spar in increments of 40-50 mm. After that, the holes are filled with rigid PS or PVC foam, ground flush and glued with fiberglass. The butt part is usually pasted over in several layers, with a smooth transition to the main canvas. Another way to make blades is from several gorse. The workpiece is glued out of three or four gorse, which can be solid ribbons or glued from two strips of different density. It is desirable to make the spar part of the gorse from birch or larch. First, a blank of gorse with a thickness three times greater than the finishing one is glued from two laths. After that, it is cut into two and processed to the desired thickness. At the same time, the spar part of different gorse blades is made of different widths (by 10-15 mm) for binding. You can separately glue the spar from 3-4 gorse, and the tail section - from one or two. After profiling, an anti-flutter weight must be glued into the leading edge at a length of 0,35 R from the end of the blade, since the end sections of the blades are mainly subject to flutter. The weight is made of lead or mild steel. After gluing, it is processed according to the profile and is additionally attached to the spars of the spar with a strip of fiberglass on epoxy resin. After that, you can paste over the entire blade with fiberglass. During the manufacture of the blade, it is necessary to constantly control the weight of the parts, so that after assembly and processing, the mass of the blade differs as little as possible from the calculated one. Author: V.Artemchuk
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Comments on the article: a guest I also finish the plane with landing on the water.
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