The construction of a vehicle that would allow moving both on land and on water was preceded by an acquaintance with the history of the discovery and creation of original amphibious vehicles on air cushion (WUA), study of their fundamental structure, comparison various designs and schemes.
For this purpose, I visited many Internet sites of WUA enthusiasts and creators (including foreign ones), got acquainted with some of them in person. In the end, for the prototype of what was conceived boats() took the English "Hovercraft" ("hovering ship" - as the WUA is called in the UK), built and tested by local enthusiasts.
Our most interesting domestic machines of this type were mostly created for law enforcement agencies, and in recent years for commercial purposes, they had large dimensions, and therefore were not very suitable for amateur production.
My device is air cushion(I call it "Aerojeep") - three-seater: the pilot and passengers are arranged in a T-shaped pattern, like on a tricycle: the pilot is in front in the middle, and the passengers behind are side by side, one next to the other.
The machine is single-engine, with a split air flow, for which a special panel is installed in its annular channel a little below its center. The boat-AVP consists of three main parts: a propeller unit with a transmission, a fiberglass hull and a "skirt" - a flexible fencing of the lower part of the hull - so to speak, a "pillowcase" of an air cushion. Corps "Airjeep".
It is double: fiberglass, consists of inner and outer shells. The outer shell has a rather simple configuration - these are just inclined (about 50 ° to the horizontal) sides without a bottom - flat almost across the entire width and slightly curved in its upper part. The bow is rounded, and the back has the form of an inclined transom.
In the upper part, along the perimeter of the outer shell, elongated holes-grooves are cut, and at the bottom, a cable enclosing the shell is fixed in eyebolts from the outside for attaching the lower parts of the segments to it.
The inner shell is more complicated in configuration than the outer one, since it has almost all the elements of a small vessel (say, boats or boats): sides, bottom, curved gunwales, a small deck in the bow (there is no only the upper part of the transom in the stern), while as one piece.
In addition, in the middle of the cockpit along it, a separately molded tunnel with a can under the driver's seat is glued to the bottom. It houses the fuel tank and battery, as well as the gas cable and the rudder control cable. In the aft part of the inner shell, a kind of poop is arranged, raised and open in front.
It serves as the base of the annular channel for the propeller, and its deck-bridge-separator of the air flow, part of which (supporting flow) is sent to the shaft opening, and the other part to create propulsive thrust.
All elements of the hull: the inner and outer shells, the tunnel and the annular channel, were glued on matrices of glass mat with a thickness of about 2 mm on polyester resin. Of course, these resins are inferior to vinylester and epoxy resins in terms of adhesion, filtration rate, shrinkage, as well as release. harmful substances when dried, but have an undeniable advantage in price - they are much cheaper, which is important.
For those who intend to use such resins, let me remind you that the room where the work is carried out must have good ventilation and a temperature of at least 22°C. The matrices were made in advance according to the master model from the same glass mats on the same polyester resin, only the thickness of their walls was larger and amounted to 7-8 mm (for the casing shells, about 4 mm).
Before pasting the elements with working surface the matrix was carefully removed all the roughness and scuffs, and it was covered three times with wax diluted in turpentine and polished. After that, a thin layer (up to 0.5 mm) of gelcoat (colored varnish) of the selected yellow color was applied to the surface with a sprayer (or roller).
After it dried, the process of gluing the shell began using the following technology. First, using a roller, the wax surface of the matrix and the side of the glass mat with smaller pores are smeared with resin, and then the mat is placed on the matrix and rolled until the air is completely removed from under the layer (if necessary, a small slot can be made in the mat).
The subsequent layers of glass mats are laid in the same way to the required thickness (4-5 mm), with the installation, where necessary, of embedded parts (metal and wood). Excess flaps along the edges are cut off when gluing "wet". It is recommended to use 2-3 layers of glass mat for the manufacture of the sides of the hull, and up to 4 layers for the bottom.
In this case, all corners should be additionally glued, as well as the places where fasteners are screwed in. After the resin has hardened, the shell is easily removed from the matrix and processed: edges are turned, grooves are cut, holes are drilled. To ensure the unsinkability of the Aerojeep, pieces of foam (for example, furniture) are glued to the inner shell, leaving only channels for air passage around the entire perimeter free.
Pieces of foam plastic are glued together with resin, and strips of glass mat, also lubricated with resin, are attached to the inner shell. After separately manufacturing the outer and inner shells, they are joined, fastened with clamps and self-tapping screws, and then connected (glued) along the perimeter with strips of smeared polyester resin the same glass mat 40-50 mm wide, from which the shells themselves were made.
After that, the body is left until the resin is completely polymerized. A day later, a duralumin strip with a section of 30x2 mm is attached to the upper joint of the shells around the perimeter with rivets, setting it vertically (the tongues of the segments are fixed on it). Wooden skids measuring 1500x90x20 mm (length x width x height) are glued to the bottom of the bottom at a distance of 160 mm from the edge.
One layer of glass mat is glued on top of the runners. In the same way, only from the inside of the shell, in the aft part of the cockpit, a base is made of wood slab under the engine. It is worth noting that the same technology used to make the outer and inner shells also glued smaller elements: the inner and outer shells of the diffuser, rudders, gas tank, engine cover, wind deflector, tunnel and driver's seat.
For those who are just starting to work with fiberglass, I recommend preparing the manufacture boats from these small elements. The total mass of the fiberglass body, together with the diffuser and rudders, is about 80 kg.
Of course, the manufacture of such a hull can also be entrusted to specialist firms producing fiberglass boats and boats. Fortunately, there are many of them in Russia, and the costs will be commensurate. However, in the process self-manufacturing will be able to gain the necessary experience and the opportunity to further model and create various elements and structures made of fiberglass. Propeller installation.
It includes an engine, a propeller and a transmission that transmits torque from the first to the second. The engine used is BRIGGS & STATTION, produced in Japan under an American license: 2-cylinder, V-shaped, four-stroke, 31 hp. at 3600 rpm. Its guaranteed motor resource is 600 thousand hours.
The start is carried out by an electric starter, from the battery, and the operation of the spark plugs is from a magneto. The engine is mounted on the bottom of the Aerojeep hull, and the propeller hub axle is fixed at both ends on brackets in the center of the diffuser raised above the hull. The transmission of torque from the output shaft of the engine to the hub is carried out by a toothed belt. The driven and driving pulleys, like the belt, are toothed.
Although the mass of the engine is not so great (about 56 kg), but its location on the bottom significantly lowers the center of gravity of the boat, which has a positive effect on the stability and maneuverability of the machine, especially such an “aerofloating” one.
Exhaust gases are led into the lower air stream. Instead of the installed Japanese one, you can also use suitable domestic engines, for example, from snowmobiles "Buran", "Lynx" and others. By the way, for a single or double WUA, smaller engines with a capacity of about 22 hp are quite suitable. With.
The propeller is six-blade, with a fixed pitch (angle of attack set on land) of the blades. An integral part of the propeller installation should also include the annular channel of the propeller, although its base (lower sector) is made integral with the inner shell of the housing.
The annular channel, like the body, is also composite, glued from the outer and inner shells. Just in the place where its lower sector joins the upper one, a fiberglass dividing panel is arranged: it separates the air flow created by the propeller (and, on the contrary, connects the walls of the lower sector along the chord).
The engine, located at the transom in the cockpit (behind the passenger seat), is closed on top with a fiberglass hood, and the propeller, in addition to the diffuser, is also a wire grill in front. Soft elastic fencing "Aerojeep" (skirt) consists of separate, but identical segments, cut and sewn from a dense lightweight fabric.
It is desirable that the fabric is water-repellent, does not harden in the cold and does not let air through. I used a Finnish-made Vinyplan material, but a domestic percale-type fabric is fine. The segment pattern is simple, and you can even sew it by hand. Each segment is attached to the body as follows.
The tongue is thrown over the side vertical bar, with an overlap of 1.5 cm; on it is the tongue of the adjacent segment, and both of them, in the place of overlap, are fixed on the bar with a special clip of the “crocodile” type, only without teeth. And so on the entire perimeter of the "Aerojeep". For reliability, you can also put a clip in the middle of the tongue.
The two lower corners of the segment with the help of nylon clamps are suspended freely on a cable wrapping around the lower part of the outer shell of the housing. Such a composite design of the skirt allows you to easily replace a failed segment, which will take 5-10 minutes. It would be appropriate to say that the design turns out to be efficient if up to 7% of the segments fail. In total, they are placed on a skirt up to 60 pieces.
The principle of movement of the "Aerojeep" is as follows. After starting the engine and running it for Idling the device remains in place. With an increase in the number of revolutions, the propeller begins to drive a more powerful air flow. Part of it (large) creates propulsion and provides the boat with movement forward.
The other part of the flow goes under the dividing panel into the side air ducts of the hull (the free space between the shells up to the very bow), and then through the slots in the outer shell it evenly enters the segments.
Simultaneously with the start of movement, this flow creates an air cushion under the bottom, lifting the apparatus above the underlying surface (be it soil, snow or water) by several centimeters. The rotation of the "Aerojeep" is carried out by two rudders, deflecting the "forward" air flow to the side.
The rudders are controlled from a two-arm motorcycle-type steering column lever, through a Bowden cable running along the starboard side between the shells to one of the rudders. The other steering wheel is connected to the first rigid rod. On the left handle of the two-arm lever, the carburetor throttle control lever (analogue of the throttle grip) is also fixed.
For operation hovercraft it must be registered with the local state inspection for small boats(GIMS) and get a ship's ticket. To obtain a certificate for the right to drive a boat, you also need to take a course in managing a small boat. However, even these courses are still far from having instructors for piloting hovercraft.
Therefore, each pilot has to master the management of the WUA on their own, literally bit by bit gaining relevant experience.
Hovercraft "Aerojeep": 1-segment ( dense fabric); 2-mooring duck (3 pcs.); 3-wind visor; 4-side strap fastening segments; 5-handle (2 pcs.); 6-protection of the propeller; 7-ring channel; 8-rudder (2 pcs.); 9-rudder control lever; 10-access hatch to the gas tank and battery; 11-pilot's seat; 12-passenger sofa; 13-engine casing; 14-engine; 15-outer shell; 16-filler (polystyrene); 17-inner shell; 18-dividing panel; 19-air screw; 20 - propeller bushing; 21-drive toothed belt; 22-knot for fastening the bottom of the segment
Theoretical drawing of the hull: 1 - inner shell; 2-outer shell
Scheme of transmission of a propeller installation: 1 - output shaft of the engine; 2-leading toothed pulley; 3 - toothed belt; 4-driven toothed pulley; 5 - nut; 6-distance bushings; 7-bearing; 8-axis; 9-hub; 10-bearing; 11-distance sleeve; 12-support; 13 propeller
Steering column: 1-handle; 2-arm lever; 3-rack; 4-bipod (see photo)
Steering scheme: 1-steering column; 2-Bowden cable, 3-braid attachment to the body (2 pcs.); 4-bearing (5 pcs.); 5-steering panel (2 pcs.); 6-double-arm lever-bracket (2 pcs.); 7-connecting rod steering panels (see photo)
Flexible fencing segment: 1 - walls; 2-lid with tongue
The high speed characteristics and amphibious capabilities of hovercraft (AHVs), as well as the relative simplicity of their designs, attract the attention of amateur designers. In recent years, many small WUAs have appeared, built independently and used for sports, tourism or business trips.
In some countries, such as the UK, USA and Canada, serial industrial production small WUAs; ready-made devices or sets of parts for self-assembly are offered.
A typical sports WUA is compact, simple in design, has independent lifting and propulsion systems, and easily moves both above ground and above water. These are predominantly single-seat vehicles with carburetor motorcycle or light air-cooled automobile engines.
Tourist WUAs are more complex in design. Usually they are two- or four-seater, designed for relatively long journeys and, accordingly, have trunks, large-capacity fuel tanks, and devices to protect passengers from bad weather.
For economic purposes, small platforms are used, adapted to transport mainly agricultural goods over rough and swampy terrain.
Main characteristics
Amateur WUAs are characterized by the main dimensions, weight, diameter of the supercharger and propeller, distance from the center of mass of the WUA to the center of its aerodynamic drag.In table. 1 compares the most important technical data of the most popular English amateur WUAs. The table allows you to navigate in a wide range of values of individual parameters and use them to comparative analysis with your own projects.
The lightest WUAs have a mass of about 100 kg, the heaviest - more than 1000 kg. Naturally, the smaller the mass of the apparatus, the less engine power is required for its movement, or the higher performance can be achieved with the same power consumption.
Below are the most characteristic data on the mass of individual components that make up the total mass of an amateur WUA: an air-cooled carburetor engine - 20-70 kg; axial blower. (pump) - 15 kg, centrifugal pump - 20 kg; propeller - 6-8 kg; motor frame - 5-8 kg; transmission - 5-8 kg; propeller nozzle ring - 3-5 kg; controls - 5-7 kg; body - 50-80 kg; fuel tanks and gas lines - 5-8 kg; seat - 5 kg.
The total carrying capacity is determined by calculation depending on the number of passengers, the given amount of cargo carried, the fuel and oil reserves necessary to ensure the required cruising range.
In parallel with the calculation of the mass of the AWP, an accurate calculation of the position of the center of gravity is required, since the driving performance, stability and controllability of the vehicle depend on this. The main condition is that the resultant of the air cushion support forces pass through the common center of gravity (CG) of the apparatus. At the same time, it should be taken into account that all masses that change their value during operation (such as, for example, fuel, passengers, cargo) must be placed close to the CG of the device so as not to cause it to move.
The center of gravity of the apparatus is determined by calculation according to the drawing of the lateral projection of the apparatus, where the centers of gravity of individual units, structural units of passengers and cargo are applied (Fig. 1). Knowing the masses G i and the coordinates (relative to the coordinate axes) x i and y i of their centers of gravity, it is possible to determine the position of the CG of the entire apparatus by the formulas:
The designed amateur WUA must meet certain operational, design and technological requirements. The basis for creating a project and design of a new type of WUA are, first of all, the initial data and technical conditions that determine the type of device, its purpose, gross weight, load capacity, dimensions, type of main power plant, running characteristics and specific features.
From tourist and sports WUAs, as, indeed, from other types of amateur WUAs, ease of manufacture, the use of easily accessible materials and assemblies in the design, as well as complete safety of operation are required.
Speaking about driving characteristics, they mean the height of the hovering of the AWP and the ability to overcome obstacles associated with this quality, maximum speed and throttle response, as well as the length of the braking distance, stability, controllability, and cruising range.
In the WUA design, the hull shape plays a fundamental role (Fig. 2), which is a compromise between:
- a) contours that are round in plan, which are characterized by the best parameters of the air cushion at the time of hovering in place;
- b) drop-shaped contours, which is preferable from the point of view of reducing aerodynamic drag during movement;
- c) a pointed nose ("beak-shaped") hull shape, optimal from a hydrodynamic point of view during movement on a rough water surface;
- d) the form that is optimal for operational purposes.
Using statistics on existing structures, which correspond to the newly created WUA type, the constructor must set:
- weight of apparatus G, kg;
- air cushion area S, m 2 ;
- length, width and outline of the hull in plan;
- lifting system engine power N v.p. , kW;
- traction motor power N dv, KW.
- pressure in the air cushion P v.p. =G:S;
- specific power of the lifting system q v.p. = G:N c.p. .
- specific power of the traction motor q dv = G:N dv, and also start developing the configuration of the AWP.
The principle of creating an air cushion, superchargers
Most often, in the construction of amateur WUAs, two schemes for the formation of an air cushion are used: chamber and nozzle.In the chamber scheme, which is most often used in simple designs, the volume flow of air passing through the air path of the apparatus is equal to the volume flow of air of the blower
Where:
F is the area of the perimeter of the gap between the support surface and the lower edge of the apparatus body, through which air exits from under the apparatus, m 2 ; it can be defined as the product of the perimeter of the air cushion fence P and the gap h e between the fence and the supporting surface; usually h 2 = 0.7÷0.8h, where h is the hovering height of the apparatus, m;
υ - speed of air outflow from under the device; with sufficient accuracy, it can be calculated by the formula:
where P c.p. - air cushion pressure, Pa; g - free fall acceleration, m/s 2 ; y - air density, kg / m 3.
The power required to create an air cushion in a chamber circuit is determined by the approximate formula:
where P c.p. - pressure after the supercharger (in the receiver), Pa; η n - coefficient useful action supercharger.
Air cushion pressure and air flow are the main parameters of an air cushion. Their values depend primarily on the dimensions of the apparatus, i.e., on the mass and bearing surface, on the hovering height, speed of movement, the method of creating an air cushion and resistance in the air path.
The most economical hovercraft are the AUAs large sizes or large load-bearing surfaces where the minimum pressure in the cushion allows a sufficiently large load capacity to be obtained. However, independent construction of a large-sized apparatus is associated with difficulties in transportation and storage, and is also limited by the financial capabilities of an amateur designer. With a decrease in the size of the WUA, a significant increase in air cushion pressure is required and, accordingly, an increase in power consumption.
In turn, negative phenomena depend on the pressure in the air cushion and the rate of air flow from under the apparatus: splashing while moving over water and dusting when moving over a sandy surface or loose snow.
Apparently, the successful design of the WUA is, in a certain sense, a compromise between the contradictory dependencies described above.
To reduce the power consumption for the passage of air through the air channel from the supercharger into the cavity of the pillow, it must have a minimum aerodynamic resistance (Fig. 3). The power losses that are inevitable during the passage of air through the channels of the air path are of two kinds: the loss due to the movement of air in straight channels of constant cross section and local losses due to expansion and bending of the channels.
In the air path of small amateur WUAs, losses due to the movement of air flows along straight channels of constant cross section are relatively small due to the insignificant length of these channels, as well as the thoroughness of their surface treatment. These losses can be estimated using the formula:
where: λ is the coefficient of pressure loss per channel length, calculated according to the graph shown in fig. 4, depending on the Reynolds number Re=(υ d): v, υ - air velocity in the channel, m/s; l - channel length, m; d is the diameter of the channel, m (if the channel has a non-circular cross section, then d is the diameter of a cylindrical channel equivalent in cross-sectional area); v - coefficient of kinematic viscosity of air, m 2 / s.
Local power losses associated with a strong increase or decrease in the cross section of the channels and significant changes in the direction of the air flow, as well as losses for air intake into the supercharger, nozzles and rudders, are the main costs of the supercharger power.
Here ζ m is the coefficient of local losses, depending on the Reynolds number, which is determined by the geometric parameters of the source of losses and the speed of air passage (Fig. 5-8).
The supercharger in the AUA must create a certain air pressure in the air cushion, taking into account the power consumption to overcome the resistance of the channels to the air flow. In some cases, part of the air flow is also used to form a horizontal thrust of the apparatus in order to ensure movement.
The total pressure generated by the supercharger is the sum of the static and dynamic pressures:
Depending on the type of WUA, the area of the air cushion, the height of the apparatus and the magnitude of the losses, the constituent components p sυ and p dυ vary. This determines the choice of type and performance of superchargers.
In a chamber air cushion scheme, the static pressure p sυ required to create lift can be equated to the static pressure behind the supercharger, the power of which is determined by the formula above.
When calculating the required power of an AVP blower with a flexible air cushion guard (nozzle circuit), the static pressure downstream of the blower can be calculated using the approximate formula:
where: R v.p. - pressure in the air cushion under the bottom of the apparatus, kg/m 2 ; kp - pressure drop coefficient between the air cushion and the channels (receiver), equal to k p = P p: P v.p. (P p - pressure in the air channels behind the supercharger). The value of k p ranges from 1.25÷1.5.
The blower air volume flow can be calculated using the formula:
The regulation of the performance (flow rate) of the AVP blowers is carried out most often - by changing the rotational speed or (less often) by throttling the air flow in the channels with the help of rotary dampers located in them.
After the required power of the supercharger is calculated, it is necessary to find an engine for it; most often, hobbyists use motorcycle engines if power up to 22 kW is required. In this case, 0.7-0.8 of the maximum engine power indicated in the motorcycle passport is taken as the calculated power. It is necessary to provide for intensive cooling of the engine and thorough cleaning of the air entering through the carburetor. It is also important to obtain a unit with a minimum mass, which is the sum of the mass of the engine, the transmission between the supercharger and the engine, as well as the mass of the supercharger itself.
Depending on the type of WUA, engines with a displacement of 50 to 750 cm 3 are used.
In amateur WUAs, both axial superchargers and centrifugal superchargers are used equally. Axial superchargers are intended for small and simple structures, centrifugal - for AVP with significant pressure in the air cushion.
Axial superchargers typically have four or more vanes (Figure 9). They are usually made of wood (four-blade) or metal (superchargers with a large number of blades). If they are from aluminum alloys, then the rotors can be cast, and welding can also be applied; it is possible to make them of welded structure from steel sheet. The pressure range generated by axial four-blade superchargers is 600-800 Pa (about 1000 Pa with a large number blades); The efficiency of these superchargers reaches 90%.
Centrifugal blowers are made of a welded metal structure or molded from fiberglass. The blades are made from bent thin sheet or with a profiled cross section. Centrifugal superchargers create pressure up to 3000 Pa, and their efficiency reaches 83%.
Choice of traction complex
Propulsors that create horizontal thrust can be divided mainly into three types: air, water and wheeled (Fig. 10).Air propulsion means an aircraft-type propeller with or without a nozzle ring, an axial or centrifugal supercharger, as well as an air-jet propulsion. In the simplest designs, horizontal thrust can sometimes be created by tilting the AWP and using the resulting horizontal component of the force of the air flow flowing from the air cushion. The air mover is convenient for amphibious vehicles that do not have contact with the supporting surface.
If we are talking about WUAs that move only above the surface of the water, then you can use a propeller or a water jet propulsion. Compared to air propulsion, these propulsion units allow you to get much more thrust per kilowatt of power expended.
The approximate value of the thrust developed by various propellers can be estimated from the data shown in Fig. eleven.
When choosing elements of a propeller, one should take into account all types of resistance that occur during the movement of the WUA. Aerodynamic drag is calculated by the formula
The water resistance due to the formation of waves when the WUA moves through the water can be calculated by the formula
Where:
V - WUA movement speed, m/s; G - WUA mass, kg; L is the length of the air cushion, m; ρ is the density of water, kg s 2 /m 4 (at a sea water temperature of +4 ° C it is 104, river water - 102);
C x - coefficient of aerodynamic resistance, depending on the shape of the device; is determined by blowing WUA models in wind tunnels. Approximately, you can take C x =0.3÷0.5;
S - cross-sectional area of the WUA - its projection on a plane perpendicular to the direction of movement, m 2 ;
E - wave resistance coefficient, depending on the AWP speed (Froude number Fr=V:√g·L) and the ratio of air cushion dimensions L:B (Fig. 12).
As an example, in Table. 2 shows the calculation of resistance depending on the speed of movement for a device with a length of L = 2.83 m and B = 1.41 m.
Knowing the resistance to movement of the apparatus, it is possible to calculate the engine power required to ensure its movement at a given speed (in this example, 120 km / h), assuming the efficiency of the propeller η p equal to 0.6, and the efficiency of transmission from the engine to the propeller η p \u003d 0 ,9:
As an air propulsor for amateur WUAs, a two-blade propeller is most often used (Fig. 13).
The blank for such a screw can be glued from plywood, ash or pine plates. The edge as well as the ends of the blades, which are mechanically affected by solid particles or sand sucked in together with the air flow, are protected by brass sheet fittings.
Four-bladed propellers are also used. The number of blades depends on the operating conditions and the purpose of the propeller - for the development of high speed or the creation of significant thrust at the time of launch. A two-blade propeller with wide blades can also provide sufficient thrust. Thrust is generally increased if the propeller runs in a profiled nozzle ring.
The finished screw must be balanced, mainly statically, before being mounted on the motor shaft. Otherwise, it will vibrate when it rotates, which may cause damage to the entire machine. Balancing with an accuracy of 1 g is quite sufficient for amateurs. In addition to balancing the screw, its runout relative to the axis of rotation is checked.
General layout
One of the main tasks of the designer is to connect all the aggregates into one functional whole. When designing the apparatus, the designer is obliged to provide a place for the crew, placement of units of the lifting and propulsion systems within the hull. At the same time, it is important to use the designs of already known WUAs as a prototype. On fig. Figures 14 and 15 show structural diagrams of two typical amateur-built WUAs.In most WUAs, the body is a load-bearing element, a single structure. It contains the units of the main power plant, air channels, control devices and the driver's cab. The driver's cabs are located in the bow or central part of the apparatus, depending on where the supercharger is located - behind the cab or in front of it. If the WUA is multi-seat, the cabin is usually located in the middle part of the vehicle, which makes it possible to operate it with a different number of people on board without changing the alignment.
In small amateur WUAs, the driver's seat is most often open, protected in front by a windshield. In devices of a more complex design (tourist type), the cabins are covered with a transparent plastic dome. To accommodate the necessary equipment and supplies, the volumes available on the sides of the cabin and under the seats are used.
At air engines AVP control is carried out using either rudders placed in the air flow behind the propeller, or guide devices fixed in the air flow flowing from the air-jet propulsion unit. The control of the device from the driver's seat can be of an aviation type - using the handles or levers of the steering wheel, or, as in a car, the steering wheel and pedals.
In amateur WUAs, two main types of fuel systems are used; with gravity fuel supply and with an automotive or aircraft-type gasoline pump. Fuel system components such as valves, filters, oil system together with tanks (if a four-stroke engine is used), oil coolers, filters, water cooling system (if it is a water-cooled engine) - they are usually selected from existing aviation or automotive parts.
Exhaust gases from the engine are always discharged to the rear of the vehicle and never to the pillow. To reduce the noise generated during the operation of WUAs, especially near settlements, automobile-type silencers are used.
In the simplest designs, the lower part of the body serves as a chassis. The role of the chassis can be performed by wooden skids (or skids), which take on the load when in contact with the surface. In tourist WUAs, which are heavier than sports WUAs, wheeled chassis are mounted, which facilitate the movement of WUAs during stops. Usually two wheels are used, mounted on the sides or along the longitudinal axis of the WUA. The wheels have contact with the surface only after the cessation of the lifting system, when the AUA touches the surface.
Materials and manufacturing technology
For the manufacture of WUA wooden structure They use high-quality pine lumber, similar to those used in the aircraft industry, as well as birch plywood, ash, beech and linden wood. For gluing wood, a waterproof glue with high physical and mechanical properties is used.For flexible fences, technical fabrics are mainly used; they must be exceptionally durable, resistant to atmospheric influences and humidity, as well as to friction. In Poland, fire-resistant fabric covered with plastic-like PVC is most often used.
It is important to perform the correct cutting and ensure that the panels are carefully connected to each other, as well as fastening them to the device. To fasten the shell of the flexible fence to the body, metal strips are used, which, by means of bolts, evenly press the fabric against the body of the apparatus.
When designing the form of a flexible air cushion fence, one should not forget about Pascal's law, which states that air pressure is distributed in all directions with the same force. Therefore, the shell of the flexible barrier in the inflated state must be in the form of a cylinder or a sphere, or a combination thereof.
Housing design and strength
Forces are transferred to the WUA hull from the load carried by the vehicle, the weight of the mechanisms of the power plant, etc., as well as loads from external forces, impacts of the bottom against the wave and pressure in the air cushion. The supporting structure of the hull of an amateur WUA is most often a flat pontoon, which is supported by pressure in an air cushion, and in the floating mode ensures the buoyancy of the hull. The hull is affected by concentrated forces, bending and torsional moments from the engines (Fig. 16), as well as gyroscopic moments from the rotating parts of the mechanisms that occur during the AWP maneuvering.The most widely used are two constructive types of buildings for amateur WUAs (or their combinations):
- truss construction, when the overall strength of the hull is ensured by flat or spatial trusses, and the skin is intended only to hold air in the air path and create buoyancy volumes;
- with load-bearing skin, when the overall strength of the hull is provided outer skin, working together with the longitudinal and transverse set.
The design of the cab and its glazing should ensure the possibility of a quick exit of the driver and passengers from the cab, especially in the event of an accident or fire. The location of the windows should provide the driver good review: line of sight must be between 15° down and 45° up from the horizontal line; side view must be at least 90 ° on each side.
Power transmission to propeller and supercharger
The simplest for amateur manufacturing are V-belt and chain drives. However, a chain drive is used only to drive propellers or superchargers whose rotation axes are located horizontally, and even then only if it is possible to select the appropriate motorcycle sprockets, since their manufacture is quite difficult.In the case of V-belt transmission, to ensure the durability of the belts, the diameters of the pulleys should be chosen as maximum, however, the circumferential speed of the belts should not exceed 25 m/s.
The design of the lifting complex and flexible fencing
The lifting complex consists of an injection unit, air channels, a receiver and a flexible air cushion guard (in nozzle schemes). The channels through which air is supplied from the blower to the flexible enclosure must be designed taking into account the requirements of aerodynamics and ensure minimal pressure loss.Flexible fences of amateur WUAs usually have a simplified form and design. On fig. 18 shows examples of design schemes of flexible barriers and a method for checking the shape of a flexible barrier after it has been mounted on the body of the apparatus. Fences of this type have good elasticity, and due to the rounded shape they do not cling to the unevenness of the supporting surface.
The calculation of superchargers, both axial and centrifugal, is rather complicated and can only be performed using special literature.
The steering device, as a rule, consists of a steering wheel or pedals, a system of levers (or cable wiring) connected to a vertical rudder, and sometimes to a horizontal rudder - an elevator.
The control can be made in the form of an automobile or motorcycle steering wheel. Considering, however, the specifics of the design and operation of the WUA as an aircraft, the aviation design of the controls in the form of a lever or pedals is more often used. In its simplest form (Fig. 19), when the handle is tilted sideways, the movement is transmitted by means of a lever fixed on the pipe to the elements of the steering cable wiring and then to the rudder. The movements of the handle back and forth, possible due to its hinged fastening, are transmitted through the pusher, passing inside the tube, to the wiring of the elevator.
With pedal control, regardless of its scheme, it is necessary to provide for the possibility of moving either the seat or the pedals for adjustment in accordance with individual features driver. Levers are most often made of duralumin, transmission pipes are attached to the body with brackets. The movement of the levers is limited by openings in the cutouts in the guides mounted on the sides of the apparatus.
An example of the design of the rudder in the case of its placement in the air flow thrown by the propeller is shown in Fig. 20.
The rudders can either be fully rotatable or consist of two parts - fixed (stabilizer) and rotatable (rudder blade) with different percentages of the chords of these parts. Rudder profiles of any type must be symmetrical. The rudder stabilizer is usually fixed to the body; main bearing element The stabilizer is a spar to which the rudder blade is hinged. Elevators, very rare in amateur WUAs, are constructed on the same principles and sometimes even exactly the same as the rudders.
Structural elements that transmit movement from controls to steering wheels and engine throttles usually consist of levers, rods, cables, etc. With the help of rods, as a rule, forces are transmitted in both directions, while cables work only for traction. Most often, amateur WUAs use combined systems - with cables and pushers.
Editorial
Increasingly, fans of water-motor sports and tourism are paying more and more attention to hovercraft. With a relatively low power consumption, they allow you to achieve high speeds; shallow and impassable rivers are accessible to them; hovercraft can hover above the ground and above the ice.For the first time, we introduced readers to the issues of designing small SVPs back in the 4th issue (1965), placing an article by Yu. A. Budnitsky “Soaring Ships”. In was published short essay development of foreign SVPs, including a description of a number of sports and pleasure modern 1- and 2-seater SVPs. The editors introduced the experience of independent construction of such an apparatus by Riga resident O. O. Petersons in. The publication of this amateur design aroused especially great interest among our readers. Many of them wanted to build the same amphibian and asked for the necessary literature.
This year the publishing house "Sudostroenie" publishes a book by the Polish engineer Jerzy Ben "Models and amateur hovercraft". In it you will find a presentation of the fundamentals of the theory of the formation of an air cushion and the mechanics of movement on it. The author gives the calculation ratios that are necessary for the independent design of the simplest hovercraft, introduces the trends and prospects for the development of this type of ships. The book contains many examples of designs of amateur hovercraft (AHVs) built in the UK, Canada, USA, France, Poland. The book is addressed to a wide range of fans of self-construction of ships, ship modellers, water motorists. Its text is richly illustrated with drawings, drawings and photographs.
The journal publishes an abridged translation of a chapter from this book.
The four most popular foreign SVPs
American hovercraft Airskat-240
Double sports SVP with a transverse symmetrical arrangement of seats. Mechanical installation - automob. dv. "Volkswagen" with a power of 38 kW, driving an axial four-bladed supercharger and a two-bladed propeller in the ring. The control of the SVP along the course is carried out using a lever connected to a system of rudders placed in the stream behind the propeller. Electrical equipment 12 V. Engine start - electric starter. The dimensions of the device are 4.4x1.98x1.42 m. The air cushion area is 7.8 m 2; propeller diameter 1.16 m, gross weight - 463 kg, maximum speed on water 64 km / h.American SVP firm "Skimmers Incorporated"
A kind of single SVP scooter. The body design is based on the idea of using a car camera. Two-cylinder motorcycle motor with a power of 4.4 kW. The dimensions of the device are 2.9x1.8x0.9 m. The air cushion area is 4.0 m 2; gross weight - 181 kg. The maximum speed is 29 km/h.English hovercraft "Air Ryder"
This two-seat sports apparatus is one of the most popular among amateur shipbuilders. The axial supercharger is driven by a motorcycle, dv. working volume 250 cm 3 . Propeller - two-blade, wooden; powered by a separate 24 kW motor. Electrical equipment with a voltage of 12 V with an aircraft battery. Engine start - electric starter. The apparatus has dimensions of 3.81x1.98x2.23 m; ground clearance 0.03 m; rise 0.077 m; pillow area 6.5 m 2; empty weight 181 kg. Develops a speed of 57 km / h on water, 80 km / h on land; overcomes slopes up to 15 °.Table 1. shows the data of a single modification of the device.
English SVP "Hovercat"
Light tourist boat for five or six people. There are two modifications: "MK-1" and "MK-2". The centrifugal supercharger with a diameter of 1.1 m is driven by a car. dv. "Volkswagen" with a working volume of 1584 cm 3 and consumes power of 34 kW at 3600 rpm.In the MK-1 modification, movement is carried out using a propeller with a diameter of 1.98 m, driven by a second engine of the same type.
In the MK-2 modification, a car was used for horizontal thrust. dv. "Porsche 912" with a volume of 1582 cm 3 and a power of 67 kW. The apparatus is controlled by means of aerodynamic rudders placed in the stream behind the propeller. Electrical equipment with a voltage of 12 V. The dimensions of the apparatus are 8.28x3.93x2.23 m. The air cushion area is 32 m 2, the gross weight of the apparatus is 2040 kg, the speed of movement of the modification "MK-1" is 47 km / h, "MK-2" - 55 km/h
Notes
1. A simplified method for selecting a propeller according to a known resistance value, rotational speed and translational speed is given in.2. V-belt calculations and chain drives can be performed using the standards generally accepted in domestic engineering.
Hovercraft is a vehicle capable of moving both on water and on land. Such a vehicle is not at all difficult to do with your own hands.
This is a device where the functions of a car and a boat are combined. As a result, we got a hovercraft (HV), which has unique off-road characteristics, without loss of speed when moving through water due to the fact that the hull of the vessel does not move through the water, but above its surface. This made it possible to move through the water much faster, due to the fact that the friction force of the water masses does not provide any resistance.
Although the hovercraft has a number of advantages, its scope is not so widespread. The fact is that not on any surface this device can move without any problems. It needs soft sandy or soil soil, without the presence of stones and other obstacles. The presence of asphalt and other solid bases can cause damage to the bottom of the vessel, which creates an air cushion when moving. In this regard, "hovercraft" are used where you need to swim more and drive less. On the contrary, it is better to use the services of an amphibious vehicle with wheels. The ideal conditions for their use are impassable swampy places where, apart from a hovercraft (Hovercraft), no other vehicle can pass. Therefore, SVPs have not become so widespread, although rescuers of some countries, such as Canada, for example, use such transport. According to some reports, SVPs are in service with NATO countries.
How to purchase such a transport or how to make it yourself?
Hovercraft is an expensive type of transport, the average price of which reaches 700 thousand rubles. Transport type "scooter" is 10 times cheaper. But at the same time, one should take into account the fact that factory-made transport is always different best quality compared to do-it-yourselfers. And the reliability of the vehicle is higher. In addition, factory models are accompanied by factory warranties, which cannot be said about designs assembled in garages.
Factory models have always been focused on a highly professional direction, connected either with fishing, or with hunting, or with special services. As for homemade SVPs, they are extremely rare and there are reasons for this.
These reasons include:
- Pretty high cost, as well as expensive maintenance. The main elements of the apparatus wear out quickly, which requires their replacement. And each such repair will result in a pretty penny. Only a rich person can afford to buy such an apparatus, and even then he will think once again whether it is worth contacting him. The fact is that such workshops are as rare as the vehicle itself. Therefore, it is more profitable to purchase a jet ski or ATV to move on water.
- The working product creates a lot of noise, so you can only move around with headphones.
- When driving against the wind, the speed drops significantly and fuel consumption increases significantly. Therefore, homemade SVPs are more of a demonstration of their professional abilities. The vessel not only needs to be able to manage, but also be able to repair it, without significant costs.
Do-it-yourself SVP manufacturing process
Firstly, it is not so easy to assemble a good SVP at home. To do this, you need to have the ability, desire and professional skills. Technical education will not hurt either. If the latter condition is absent, then it is better to abandon the construction of the apparatus, otherwise you can crash on it at the first test.
All work begins with sketches, which are then transformed into working drawings. When creating sketches, it should be remembered that this apparatus should be as streamlined as possible so as not to create unnecessary resistance when moving. At this stage, one should take into account the factor that this is, in fact, an air vehicle, although it is very low to the surface of the earth. If all conditions are taken into account, then you can begin to develop drawings.
The figure shows a sketch of the SVP of the Canadian Rescue Service.
Technical data of the machine
As a rule, all hovercraft are capable of a decent speed that no boat can reach. This is if we take into account that the boat and the SVP have the same mass and engine power.
At the same time, the proposed model of a single-seat hovercraft is designed for a pilot weighing from 100 to 120 kilograms.
As for driving a vehicle, it is quite specific and, in comparison with driving a conventional motor boat doesn't fit in at all. The specificity is associated not only with the presence of high speed, but also with the method of movement.
The main nuance is related to the fact that when cornering, especially on high speeds, the ship skids heavily. To minimize this factor, it is necessary to lean to the side when cornering. But these are short-term difficulties. Over time, the control technique is mastered and miracles of maneuverability can be shown on the SVP.
What materials are needed?
Basically, you will need plywood, foam plastic and a special design kit from Universal Hovercraft, which includes everything you need to assemble the vehicle yourself. The kit includes insulation, screws, air cushion fabric, special adhesive and more. This set can be ordered on the official website by paying 500 bucks for it. The kit also includes several options for drawings for assembling the SVP apparatus.
Since the drawings are already available, the shape of the vessel should be tied to the finished drawing. But if there is a technical education, then, most likely, a ship will be built that does not look like any of the options.
The bottom of the ship is made of foam plastic, 5-7 cm thick. If you need an apparatus for transporting more than one passenger, then another such foam sheet is attached from below. After that, two holes are made in the bottom: one is for air flow, and the second is for providing air to the pillow. Holes are cut with an electric jigsaw.
At the next stage, the lower part of the vehicle is sealed from moisture. To do this, fiberglass is taken and glued to the foam using epoxy glue. In this case, irregularities and air bubbles may form on the surface. To get rid of them, the surface is covered with polyethylene, and on top also with a blanket. Then, another layer of film is placed on the blanket, after which it is fixed to the base with adhesive tape. It is better to blow air out of this “sandwich” using a vacuum cleaner. After 2 or 3 hours, the epoxy will harden and the bottom will be ready for further work.
The top of the hull can have an arbitrary shape, but take into account the laws of aerodynamics. After that, proceed to attach the pillow. The most important thing is that air enters it without loss.
The pipe for the motor should be used from styrofoam. The main thing here is to guess with the dimensions: if the pipe is too large, then you will not get the thrust that is necessary to lift the SVP. Then you should pay attention to mounting the motor. The holder for the motor is a kind of stool, consisting of 3 legs attached to the bottom. On top of this “stool” the engine is installed.
What engine is needed?
There are two options: the first option is to use the engine from the company "Universal Hovercraft" or use any suitable engine. It can be a chainsaw engine, the power of which is quite enough for a home-made device. If you want to get a more powerful device, then you should take more powerful engine.
It is advisable to use factory-made blades (those in the kit), as they require careful balancing and it is quite difficult to do this at home. If this is not done, then the unbalanced blades will break the entire engine.
How reliable can an SVP be?
As practice shows, factory hovercraft (SVP) have to be repaired about once every six months. But these problems are minor and do not require serious costs. Basically, the pillow and the air supply system fail. In fact, the likelihood that homemade device will fall apart during operation, it is very small if the “hovercraft” is assembled correctly and correctly. For this to happen, you need to run into some obstacle at high speed. Despite this, the air cushion is still able to protect the device from serious damage.
Rescuers working on similar devices in Canada repair them quickly and competently. As for the pillow, it can really be repaired in an ordinary garage.
Such a model will be reliable if:
- The materials and parts used were of good quality.
- The machine has a new engine.
- All connections and fastenings are made reliably.
- The manufacturer has all the necessary skills.
If the SVP is made as a toy for a child, then in this case it is desirable that the data of a good designer be present. Although this is not an indicator for putting children behind the wheel of this vehicle. It's not a car or a boat. Managing SVP is not as easy as it seems.
Given this factor, you need to immediately begin to manufacture a two-seater version in order to control the actions of the one who will drive.
Roads are one of the most serious and intractable problems for rural residents, especially during the spring flood. An ideal alternative to any vehicles in such conditions are all-terrain vehicles on an air cushion.
What is such a transport?
The vessel is a special vehicle, the dynamics of which is based on the air flow injected under the bottom, which allows it to move on any surface, both liquid and solid.
The main advantage of such transport is its high speed. In addition, its navigational period is not limited by the conditions environment- You can move on such all-terrain vehicles both in winter and in summer. Another plus is the ability to overcome obstacles no more than a meter in height.
The disadvantages include a small number of passengers who are able to carry all-terrain vehicles on an air cushion, and a fairly high fuel consumption. This is explained by the increased power of the engine, aimed at creating an air flow under the bottom. Small particles in the pillow can cause static electricity.
Advantages and disadvantages of all-terrain vehicles
It is quite difficult to say exactly where to start choosing such a model of a vessel, since it all depends on the personal preferences of the future owner and his plans for the purchased transport. Among the huge number of characteristics and parameters, all-terrain vehicles on an air cushion have their own advantages and disadvantages, many of which are known to either professionals or manufacturers, but not ordinary users.
One of the disadvantages of such vessels is their frequent stubbornness: at a temperature of -18 degrees, they may refuse to start. The reason for this is condensation in the power plant. In order to increase wear resistance and strength, economy-class all-terrain hovercraft have steel inserts in the bottom, which their expensive counterparts do not have. A sufficiently powerful engine may not pull the rise of transport to a fairly small coast with a slope of a couple of degrees.
Such nuances are found only during the operation of the all-terrain vehicle. To avoid disappointment in transport, before buying it, it is advisable to consult with experts and view all available information.
Varieties of all-terrain vehicles on an air cushion
- Junior courts. Perfect option for outdoor activities or fishing in small ponds. In most cases, such all-terrain vehicles are purchased by those who live far enough from civilization and can only be reached by helicopter to their place of residence. The movement of small vessels is in many ways similar to, but the latter are not capable of side sliding at speeds of the order of 40-50 km / h.
- Large ships. Such transport can be taken already for serious hunting or fishing. The carrying capacity of the all-terrain vehicle is from 500 to 2000 kilograms, the capacity is 6-12 passenger seats. Large vessels almost completely ignore the onboard wave, which allows them to be used even at sea. You can buy such all-terrain vehicles on an air cushion in our country - vehicles of both domestic and foreign production are sold on the markets.
Principle of operation
The functioning of an air cushion is quite simple and is largely based on a physics course familiar from school days. The principle of operation is to raise the boat above the ground and level the friction force. This process is called "exit to the pillow" and is a time characteristic. For small vessels, it takes about 10-20 seconds, for large ones it takes about half a minute. Industrial all-terrain vehicles pump air for several minutes in order to increase the pressure to the desired level. After reaching the required mark, you can start moving.
On small ships capable of carrying from 2 to 4 passengers, air is forced into the pillow using banal air intakes from the traction engine. The ride starts almost immediately after the pressure is set, which is not always convenient, since there is no reverse gear for all-terrain vehicles of the junior and middle class. On larger all-terrain vehicles for 6-12 people, this disadvantage is compensated by a second engine that controls only the air pressure in the pillow.
hovercraft
Today you can meet many craftsmen who independently create such equipment. The all-terrain vehicle on an air cushion is assembled on the basis of another transport - for example, the Dnepr motorcycle. A screw is installed on the engine, which in the operating mode pumps air under the bottom, covered with a cuff made of leatherette, resistant to impact. negative temperatures. The same motor carries out the movement of the vessel forward.
A similar do-it-yourself hovercraft is created with good technical specifications- for example, the speed of its movement is about 70 km / h. In fact, such transport is the most profitable for self-manufacturing, since it does not require the creation complex drawings and chassis, while differing in the maximum level of patency.
All-terrain vehicles on an air cushion "Arktika"
One of the developments of Russian scientists from Omsk is an amphibious cargo platform called "Arktika", which was put into service with the Russian army.
Amphibious domestic vessel has the following advantages:
- Full cross-country ability - transport passes on the surface of any terrain.
- It can be used in any weather and any time of the year.
- Large load capacity and impressive power reserve.
- Safety and reliability provided by design features.
- Compared to other modes of transport, it is economical.
- Ecologically safe for the environment, which is confirmed by the relevant certificates.
"Arktika" is a hovercraft capable of moving on the surface of both water and land. Its main difference from similar transport, which can only temporarily stay on the ground, is the possibility of operation both in swampy, snowy and icy areas, and in various water bodies.
Unsatisfactory network condition highways and the almost complete absence of road infrastructure on most regional routes makes it necessary to look for vehicles that operate on other physical principles. One such means is a hovercraft capable of moving people and goods in off-road conditions.
Hovercraft, bearing the sonorous technical term "hovercraft", differs from traditional models of boats and cars not only in the ability to move on any surface (pond, field, swamp, etc.), but also in the ability to develop a decent speed. The only requirement for such a "road" is that it should be more or less even and relatively soft.
However, the use of an air cushion by an all-terrain vehicle requires quite serious energy costs, which in turn entails a significant increase in fuel consumption. The functioning of hovercraft (HVAC) is based on a combination of the following physical principles:
- Low specific pressure of SVP on the surface of soil or water.
- High movement speed.
This factor has a fairly simple and logical explanation. The area of contact surfaces (bottom of the apparatus and, for example, soil) corresponds to or exceeds the area of the SVP. Technically speaking, the vehicle dynamically generates the necessary amount of support rod.
The overpressure generated in special device, tears off the machine from the support to a height of 100-150 mm. It is this cushion of air that interrupts the mechanical contact of the surfaces and minimizes the resistance to the translational movement of the hovercraft in the horizontal plane.
Despite the ability to move quickly and, most importantly, economically, the scope of the hovercraft on the surface of the earth is significantly limited. Asphalt areas, hard rocks with the presence of industrial debris or hard stones are absolutely not suitable for it, since the risk of damage to the main element of the SVP - the bottom of the pillow, increases significantly.
Thus, the optimal hovercraft route can be considered one where you need to swim a lot and in some places drive a little. In some countries, such as Canada, hovercraft are used by rescuers. According to some reports, devices of this design are in service with the armies of some NATO member countries.
Why is there a desire to make a hovercraft with your own hands? There are several reasons:
That is why SVPs have not received wide distribution. Indeed, as an expensive toy, you can buy an ATV or snowmobile. Another option is to make a boat-car yourself.
When choosing a working scheme, it is necessary to determine the hull design that optimally matches the given specifications. Note, do-it-yourself SVP with assembly drawings homemade items create is realistic.
Ready-made drawings of homemade hovercraft abound in specialized resources. The analysis of practical tests shows that the most successful option that satisfies the conditions that arise when moving through water and soil are cushions formed by a chamber method.
Choosing material for the main structural element hovercraft - hulls, consider several important criteria. First, it is simplicity and ease of processing. Secondly, small specific gravity material. It is this parameter that ensures that the SVP belongs to the “amphibian” category, that is, there is no risk of flooding in the event of an emergency stop of the vessel.
As a rule, 4 mm plywood is used to make the hull, and superstructures are made of foam. This significantly reduces the own weight of the structure. After pasting the outer surfaces with foam and subsequent painting, the model acquires its original features appearance original. Polymeric materials are used for cabin glazing, and the remaining elements are bent from wire.
The manufacture of the so-called skirt will require a dense waterproof fabric made of polymer fiber. After cutting, the parts are sewn together with a double tight seam, and gluing is done using waterproof glue. This provides not only a high degree of structural reliability, but also allows you to hide mounting joints from prying eyes.
The design of the power plant involves the presence of two engines: marching and forcing. They are equipped with brushless electric motors and two-bladed propellers. A special regulator carries out the process of managing them.
The supply voltage is supplied from two batteries, the total capacity of which is 3,000 milliamps per hour. At the maximum charge level, the SVP can be operated for 25–30 minutes.
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