Hovercraft. Hovercraft - working principle - hovercraft transport hovercraft principle

At the end of the 19th century, many engineers and inventors began implementing new ship designs. It soon became clear that the best way to overcome the natural resistance of water and, therefore, increase the speed of a ship’s movement was to eliminate the friction of the ship’s hull on the water, raising it entirely above its surface while moving. In addition, for the convenience of passengers, it was necessary to develop vehicles that would eliminate the possibility of constant exposure to waves on the ship's hull.

The first experiments carried out by such inventors as Porter, Hans, Deneson, Tomamhul, Forlanini, Crocco and others marked the birth of two completely new types of vessels - hovercraft and hydrofoils. The hovercraft rises entirely above the surface of the water through the action of either a static or dynamic air cushion. The SPK moves due to the difference in hydrodynamic pressure that occurs on the upper and lower planes of the hydrofoil during its movement through the water environment. Both types can have a technical implementation on different vessels, so it is not surprising that disagreements often arise when assigning hovercraft and spp to a certain class. However, each project has its own distinctive features.

Hovercraft

There are two main types of devices that use the proximity of a supporting surface. Some of them move above the surface, with the help of a static air cushion they create, while others, when moving, receive aerodynamic lift like an airplane, but under their body a dynamic air cushion is formed.

There are two schemes for the formation of a static air cushion:

Chamber, when air is supplied directly to the dome space;
Nozzle, when it is fed through nozzles located around the perimeter.

The simplest one is reflected in the chamber diagram from the concepts of the proximity effect of the supporting surface. The air, via the lift system's supercharger, is fed directly into the bell-shaped or inverted pudding bowl-shaped space under the canopy, where it creates a cushion of compressed air that lifts the craft above the surface to a predetermined hovering height. Air is supplied to the under-dome space in a volume sufficient to replenish its losses as a result of leakage from under the bottom of the vessel. Modern vessels with a chamber air cushion formation system are equipped with a flexible canopy made of elastic material that sags between the hull and the surface, providing greater ground clearance over obstacles or waves.

Modern hovercraft

Among the vessels created according to this scheme, it is worth noting the hovercraft with skegs, in which the air cushion is held by rigid side walls or keels and transverse flexible fences in the bow and stern, and the hovercraft of the “Neviplane” type designed by Bertin and the “Terraplane” platforms, which have a multi-chamber formation scheme air cushion, consisting of many domes-chambers, each of which is equipped with a light flexible fence. Due to the relative simplicity of the design, vessels with a chamber air cushion formation system, equipped with a flexible fence, have gained preference among light hovercraft enthusiasts, especially among those who design and build such devices at home.

There is a type of hovercraft in which the air cushion is formed according to a nozzle design developed on the basis of the original principle put forward by Christopher Cockerell. In this case, the air cushion is created and maintained with the help of constantly supplied jets of air, which escape through nozzles located along the outer perimeter of the base of the ship's hull. The flexible barriers with which this type of vessel is equipped can be in the form of a continuation, either only of the external walls of the air channels, or of both internal and external ones.

Depending on the principles of the aerohydrodynamic configuration, ekranoplans are made according to the “flying wing” and aircraft designs. In the first case, the body of the ekranoplan usually consists of a low aspect ratio wing, on the sides of which end float washers are installed. When moving, as a result of high-speed air pressure, an aerodynamic lift force is generated on the wing. The hull and the entire airframe, including the tail empennage of an ekranoplan, made according to an airplane design, as a rule, resembles an ordinary one or two-hull seaplane (flying boat). The main feature of an ekranoplan, which distinguishes it from an airplane, is that its aerodynamic and structural layout allows the device to fly at a low altitude from the screen (water or ground surface).

At the same time, the aerodynamic quality increases significantly, which in turn leads to a decrease in fuel consumption and thereby almost doubles the flight range and payload of the ekranoplan. The advantages of flight using the proximity effect of the supporting surface were proven 50 years ago. Then this effect helped the pilots of the first civil aircraft to increase their flight range when crossing areas of the South Atlantic. Pilots of the Royal Air Force and British transport aviation during the Second World War often resorted to his “services” when returning to their native shores, especially if fuel was running low or the plane was damaged.

One of the leading designers of devices of this class is Dr. Alexander Lippisch, the “father” of the delta wing and the creator of the fastest fighter of the Second World War - the Me-163. A characteristic feature of the design of the Aerofoilboat X-112A ekranoplane, made according to an aircraft design, is that by using an inverted V-shaped wing, it was possible to eliminate keel instability - one of the main problems for everyone who flew close to the surface, especially on airplanes with conventional wings, at the moment of approaching the surface. A normal phenomenon in aviation is a shift in the center of pressure towards the tail of the aircraft, which leads to a tilt of the nose when moving. Dr. Lippisch's design is made differently.

Ekranoplan hovercraft

Thanks to the well-chosen tail design and wing shape, its ekranoplan demonstrates reliable flight stability. Its stability is such that it can, if necessary, fly above the screen or free fly at almost any altitude, and then return to flight above the screen again. This allows it to overcome high banks, coastal or port structures, river meanders, bridges, etc. However, when leaving the screen coverage area, the economic advantages of the ekranoplan are lost, since in order to fly freely and maintain altitude, it is necessary to increase engine power, and thereby fuel consumption.

Flexible fencing

If flexible fencing had not been invented, the idea of creating a hovercraft would hardly have advanced far from the stage at which it was treated as simply an interesting technical novelty. Thanks to the use of flexible barriers, the height of the air cushion at a given lifting force increased tenfold and the size of vessels intended for operation in rough sea conditions decreased by 75%. The resulting economic benefits are perhaps best illustrated by comparing the size of vessels equipped with flexible barriers with those without, which would be required to service the English Channel line, where wave heights often exceed 2 m. ground clearance of 2.2-2.4 m, the required dimensions and engine power would be approximately 700-800 tons.

The use of fencing on a modern hovercraft SR.N4 makes it possible to reduce its weight to 200 tons. In addition, for a larger vessel without flexible fencing, the engine power would be 54.4 thousand hp. s., i.e. four times more than provided by four Marine Proteus gas turbines on the SR.N4 hovercraft. The leading companies in the design and manufacture of flexible fencing for hovercraft are: FPT Products Limited, part of the British Hovercraft Corporation, Hovercraft Development Limited, Avon Rubber Company. After the first tests of the simplest types of flexible fencing in the form of a rubber cavity, the British Hovercraft Corporation decided in 1965 to switch all research activities to the development of a type of fencing based on the so-called two-tier flexible fencing with segmented elements.

In such a system, compressed air from the lifting system's superchargers first enters a flexible receiver, and then through nozzles into the area under the bottom of the vessel, which leads to the formation of an air cushion. At the base of the flexible receiver below each nozzle, there is a segment element open at the end through which air is directed inward to the center of the air cushion zone. Initially, segmented elements were used to eliminate splashing and reduce drag when moving on the open sea. But they significantly prevent wear and aging of the entire flexible fence, and since they can be easily replaced, they help reduce operating costs.

Drawing of flexible fencing on hovercraft

At first, the height of the segmental elements in relation to the height of the entire flexible fence was approximately 30%, over time this ratio increased to 50%. In accordance with the original designs, vessels such as the SR.N4 and SR.N6 were operated with a stern trim of 1.5°, with the bow slightly raised, which reduced the possibility of a sharp decrease in speed in the event that the bow of the flexible fence "raked" water. As a result of this operating mode, the aft segmental elements had significantly more wear than the bow ones. They withstood operation for 100 hours, while the bow ones lasted about 500 hours.

Largely as a result of research undertaken by the British Hovercraft Corporation and British Rail on the SR.N4 and SR.N6 ships, a new cone-shaped flexible guard, lowering towards the stern, appeared in 1972. Its height at the bow was increased by approximately 75 cm, which made it possible to maintain the required trim of the vessel, and then it decreased to normal at the stern. This meant that the ship was now, as it were, “landed” on a fence designed with a stern trim of 1.5°C. As a result of this improvement, both vessels experienced a significant reduction in wear on the stern end flexible rail segments. A noteworthy feature of the flexible guards designed by the British Hovercraft Corporation is the presence of stability nozzles in them, which improve the stability of the vessel.

The SR.N6 has two stability nozzles installed in the form of a flexible container:

Longitudinal keel;
Divided in half transversely.

On the much larger SR.N4, the air cushion is divided into three compartments as the longitudinal stability nozzle is mounted from the stern only to the transverse nozzle. Thanks to the division of the air cushion into compartments, relatively high stability is achieved against pitching and rolling, which in turn prevents excessively long contact of the fence with the surface of the water. Under certain unfavorable conditions, the bow of the flexible fence may come into contact with the surface of the water, due to which the braking gradually increases, and then “burrowing” of the bow may occur. If this phenomenon is not foreseen, a sudden reduction in the ship's speed, known as "plowing", will follow, and this can lead to a serious loss of stability and possibly a capsizing moment.

As the outer edge of the bow of the flexible fence stretches towards the center of the vessel (indicated in terminology as “buckling”), there is a sharp decrease in the stabilizing moment of pressure in the air cushion. As the bow trim angle increases, the stern tends to rise above the surface, creating too much clearance. An abrupt, significant drop in speed occurs, and in small vessels, in addition, the danger of capsizing increases under the influence of passing waves, increasing the pitch angle.

In order to facilitate the solution to the problem of “buckling” and “plowing”, the British Hovercraft Corporation company proposed to raise the line of attachment of the flexible fence on the vessel SR.N4MK.2 and the boat VN.7. In the first of them, the anti-buckling system is attached to the bow of the flexible fence. This system provides the necessary resistance to the influence of the water surface and prevents “buckling” and “plowing”. The bow flexible fence on the VN.7 boat is deformed upon contact with water, thereby delaying the occurrence of “buckling” and providing a righting moment. Vessels of type SR.N4 operate at wave heights of more than 1 m and speeds of 50 knots or more.

Hovercraft - "SVP"

The contact of a flexible fence with the surface of the water, under such operating conditions, causes increased loads similar to those experienced, for example, by car tires during an off-road race. The degree of wear of segmental elements of flexible fencing can be illustrated by the experience of Hoverlloyd Limited, which uses three SR.N4 vessels for transport between Ramsgate and Calais. Every year, each hovercraft of this company is in operation for 4000 hours and during this time wears out 1500 segment elements. Their cost is the main expense item when operating a hovercraft, to which, of course, one should add the labor costs of specialists for repairing and replacing segment elements.

Currently, research is underway into the properties of various materials and their processing technologies, which would improve the wear resistance characteristics of segmental elements. Wear occurs mainly at high speeds. It reaches its highest level with average sea waves and a hovercraft speed of 50 knots. With a calmer sea surface, the impact of water on the segmental elements is less significant, so the degree of wear is reduced. The same thing happens in stronger waves, when the speed of the hovercraft decreases to 30-40 knots. One method to solve the problem of developing better flexible fencing materials is to use lighter, more flexible fabrics. There is evidence in favor of the theory that, due to their flexibility, such materials have less braking effect when in contact with water.

One of the leading projects based on this theory is the tilting sectioned flexible fencing developed by Hovercraft Development Limited. Such hovercraft as HD.2, VT1 and VT2 from Vosper Thornycroft, EM.2 and many other new vessels that are being built or are already in operation are equipped with flexible fencing of this type. This guard is also used in industrial applications, including heavy lifting platforms weighing up to 750 tonnes, vehicles and hovercraft trailers. Such a flexible fence consists of large transversely divided elements of an open type - segmental elements connected to the body using an open loop. The cushion is not divided into separate compartments and since the air flow has no obstacles, when moving between the flexible fence loop and the air cushion, the ratio of pressure levels in them is almost the same and therefore the loss of internal energy is negligible.

For the manufacture of flexible fencing, thin fabric is used and, as a result of its low level of inertia, the smooth movement of the vessel is ensured. Due to the fact that the segmental elements of a flexible fence occupy a significant portion of its entire height, this system allows the vessel to overcome high waves and obstacles. Another advantage that the use of this system gives is that the bottom body on which it is used has a surface beveled from the bottom to the sides. Thus, when the vessel is deprived of an air cushion, the internal connection points of the segmental elements can be reached without resorting to jacks, which greatly simplifies the care and maintenance of the flexible fence.The British Hovercraft Corporation came to the conclusion that the most suitable materials for the manufacture flexible fencing are those whose fabric base is nylon or terylene, coated on top with natural rubber or neoprene rubber.

Fabrics made from various materials, including glass, cotton, synthetic fibers and even steel, were tested, but the results were unsatisfactory. It turned out that steel and glass are unable to withstand the constant impacts of waves, and cotton fabrics and fabrics made of artificial fiber do not have sufficient abrasion resistance and cannot withstand long-term use. At the initial stage of development of the flexible fencing system, substances such as RVC nitrile and polyurethane were also used for the flexible receiver. Flexible barriers make up about 15% of the total mass of the 10-ton SVG1 SR.Nh and 10% of the 200-ton SR.N4.

Military hovercraft

Also, to improve operational and mass indicators, flexible fencing sizes are usually chosen that meet the necessary requirements for the operation of the vessel. The width of the flexible fence, as a rule, corresponds to the highest wave height in the area of the sea where the vessel will operate. Tests have shown that to ensure vessel stability, the width of the flexible fence should not exceed 15-20% of the width of the air cushion.

The vast majority of hovercraft are capable of operating in conditions in which the wave height is at least twice the height of the flexible fence, especially if the waves are long and can be overcome without the base of the bow of the hovercraft coming into contact with them. The largest company producing hovercraft in France is SEDAM, which owns the license to produce devices of the Naviplan and Terraplan series under Bertin's patents. A special feature of these projects is the use in them of a system of multiple discharge chambers proposed by Bertin, the air for which comes from the supercharger of the lifting system, either separately for each or for entire groups of chambers.

The chamber has a separate flexible enclosure into which air is supplied through a nozzle. In turn, they are all surrounded by a single peripheral flexible fence along the perimeter of the hovercraft body. The Perisell model, one of the latest developments in this area, combines the features of a flexible fencing system with segmental elements and a Bertin chamber system. Instead of fringe or segmental elements at the base of the flexible container, it contains separate large chambers. This design has advantages over a flexible fencing system with segmented elements in terms of stability when stopped on an air cushion. The SES-100A was one of the first hovercraft to use this new type of flexible fencing.

Energy installations

The power supply of the hovercraft lifting and propulsion systems depends on the composition of the equipment adopted in each specific hovercraft size project, the environment in which the vessel will be operated and on the required tactical and technical indicators. In addition, there are other factors that should be taken into account both by those who build the hovercraft and by those who exploits them.

Among them:

Engine power;
Vessel weight;
Fuel consumption;
Service life before major overhaul;
Approximate cost of operation;
Possibility of provision spare parts;
The scale of support resources available to the manufacturer of hovercraft engines.

The power plants of modern hovercraft can include various types of engines - from converted radio-controlled, outboard, motorcycle gasoline engines, to the four Rolls-Royce Marine Proteus gas turbines used on the SR.N4 with a capacity of 3600 hp. With. (2600 kW) each. Between these extreme examples we can note the Chrysler V8 car engine with a power of 200 hp. With. (147 kW) on a six-seater hovercraft SH-2 from Sealand, three water-cooled diesel engines of the Cummins system on HM-2 ships from Hovermarine and a gas turbine with a capacity of 900 hp. With. (660 kW) "Marine Gnome" on 58-seater sea passenger ferries of the SR.N6 Mk.1 series.

To date, not a single manufacturer has secured orders for engines for hovercraft to such an extent that it would be possible to justify the design of special systems for this purpose. Therefore, conventional standard designs are currently used as hovercraft propulsion systems, in which, to the extent possible, improvements necessary for operation in marine conditions have been applied. In such engines, most parts and assemblies must be tested for resistance to corrosion, which is an inevitable consequence of exposure to sea air saturated with salt.

Gas turbine vessels designed for offshore use are equipped with thick filters made of loosely woven metal or plastic fibers that are placed in the engine air intakes to remove water and particulates from the air. As an additional measure to prevent salt and sand particles from entering the engine, engine air intake is commonly used directly from the lift system supercharger chamber.

Soviet passenger hovercraft

On most ships weighing 8-10 tons or more, manufacturers prefer to install a gas turbine engine that has the best ratio of power to speed and weight per unit of power (kg/hp). However, many transport workers in developing countries would choose a conventional diesel engine instead of a gas turbine engine, since its operation, fuel supply and maintenance of components are cheaper. In addition, it is much easier to find a qualified engineer for diesel engines than for gas turbine engines.

Although some of the modern high-speed light diesel engines are quite acceptable for small passenger and combat STOLs weighing up to 25 tons, the main engines for larger vessels remain various models of gas turbines developed on the basis of aviation ones. The 2,000-ton SES class apparatus, designed for the needs of the US Navy, will be equipped with six General Electric LM-2500 gas turbines with a capacity of 20 thousand liters each. With. (18.4 MW) each. Two of them transmit power to the lift system superchargers, and four - to the water jet propulsors. These turbines are among the most powerful gas turbines in the world, however, to power the propulsors alone on the next generation SES class ships, the total mass of which will be about 12.5 thousand tons, four times more power will be required. It is calculated that these ships, while overcoming the hump of resistance to movement at a speed of 42 knots, will require a power of about 515 thousand hp. With. (290 MW).

High speed and long range can be achieved using a significant amount of energy. Factors such as increased requirements for fuel quality and its high cost forced the United States government to begin studying the possibility of using nuclear power plants on large skeg-type stabilization stations. Much of the research to date has been conducted in Cleveland, Ohio, at the National Aeronautics and Space Administration's (NASA) Lewis Research Center, led by Frank I. Rohm.

Nuclear power plants being developed by NASA for use on SES-class ships must be identical to systems designed for aircraft. The reactor, surrounded by a vessel and a protective baffle system, heats a liquid (such as helium) under high pressure, which is piped to a heat exchanger located between the ramjet engines and the compressor of a typical turbofan engine. In this case, the engine can operate on thermal energy supplied through a heat exchanger or as a result of combustion of fuel in conventional chambers.

To ensure absolutely safe operation of the reactor, various protective measures were considered in detail. The shell surrounding the reactor is designed to completely prevent the release of nuclear fission products that could occur in the event of a serious accident or destruction of the reactor. And the materials chosen for the manufacture of the protective screen must, according to the design, not only withstand impact from contact, but also evenly distribute the heat accumulated during melting. Since the cost of nuclear fuel is only about one-third to one-sixth that of chemical fuel, significant savings result. It has now become possible to build reliable reactors designed to operate without loading for 10 thousand hours.

Military small hovercraft

Another attractive feature is that for large ships of the SES class, the mass of the nuclear power plant will be less than 10% of the mass of the entire ship, equal to 5-10 thousand tons. NASA experts believe that over time it will be possible to achieve a reduction through the use of nuclear energy operating costs, up to two cents per ton-mile. They argue that it would theoretically require the construction of an entire fleet of 1,500 to 10,000 ton SES class vessels that would be used to transport 10% of the world's cargo turnover. Moreover, this 10%, according to theorists’ calculations, should be “appropriated” by the hovercraft precisely because it will be possible to reduce the cost of their freight to two cents per ton-mile. The prospect of operating such vessels looks even more attractive than these figures indicate, given the possibility of new trade routes, which will undoubtedly arise due to the low cost, plus the much higher speed of transportation.

Lifting systems

The superchargers of the lifting system are entrusted with the task of providing the hovercraft with air for its air cushion. Blowers are often considered the heart and lungs of these vessels, as the hovercraft is essentially a blower system designed to lift above the surface and move certain loads. The blower continuously delivers a significant volume of compressed air to the bottom of the boat, where it disperses and forms a cushion of air, which then lifts the boat above the surface and holds it in a stable position. The amount of air entering the cushion must be sufficient to replenish the air that flows out along the perimeter of the hovercraft. Currently, there are mainly two types of superchargers used. As a rule, the larger the vessel, the greater the air flow into the cushion and the higher the pressure in it, although much depends on the design, weight and purpose of each individual device.

The smallest modern amphibious passenger hovercraft requires a cushion pressure of about 10-15 lb/ft 2 (44-66 kg/m 2) and an air flow of 100-200 ft 3 /s (2.8-5.6 m 3 /s), and the largest hovercraft - 60-70 lb/ft 2 (260-310 kg/m 2) and air flow up to 27,000 ft 3 /s (760 m 3 /s).

Lifting systems:

Axial;
Centrifugal.

Although the use of a mixed system, combining features of both types, was also successful in some cases. An axial blower, like a conventional aircraft propeller, drives air in a direction parallel to the axis of rotation, while a centrifugal blower captures air between the blades and then expels it through centrifugal acceleration outward in a radial direction. Axial blowers are mainly used in vertical duct systems. They direct the air flow downwards, directly into the air cushion.

The relative simplicity of their design and the ease of construction are the reason that they are readily used by manufacturers of small hovercraft with a chamber cushion formation system, especially by amateurs who build vessels outside of factory conditions. But due to the relatively low air flow rates, these blowers have to be operated at high speed, which leads to an increase in noise levels. Since on large ships the air must be distributed over the entire length and width of a fairly long receiver before entering the cushion, in this case there are significant advantages of a centrifugal blower. It provides a higher level of static pressure, at a lower rotation speed, and also allows for higher air flow in the cushion. The centrifugal blower has a simple design, its installation is simple, and it is durable and reliable in operation.

Hovercraft diagram

However, in their indefatigable desire to provide greater comfort and efficiency, the designers did not lose sight of the possibility of using several axial superchargers with variable pitch impeller blades on ocean-going hovercrafts, not only to provide control of the air flow of the lift system, but also as means for controlling the horizontal movements of the vessel. An analysis of the entire spectrum of wave forces was carried out, after which it became obvious that theoretically in the low frequency zone, where most of the wave energy is found, it is quite possible to neutralize horizontal movements by changing the pitch of the impeller, similar to how changing the pitch of a propeller in aviation . The research results give reason to hope that horizontal accelerations can be reduced by more than four times, and the ship's movement will meet comfort standards.

Propulsors

There are very few types of propulsion that have not been tested on a hovercraft, from sails to propellers and from propellers to water jet propulsion. The propulsion unit is selected taking into account the purpose of the vessel and the technical and operational indicators that it must have. Air propulsion of one type or another is usually installed on amphibious hovercraft, while water-jet propulsion or propellers are more suitable for ships designed to travel exclusively above the water surface. We list the types of propulsion systems currently used or proposed for use in the future.

Air propulsion

Propellers;
Air propellers in the nozzle;
Air-jet turbofans;
Gas turbine jet sails.

Water propulsion

Propeller screw;
Water cannon;
Paddle wheel.

Movement in contact with the ground

Wheels;
Crawler;
Pushing with hands;
Towing with a tractor;
Horse towing;
Towing by helicopter.

Hovering over the rails

Air propeller;
Gas turbine jet turbofan;
Linear induction motor.

Despite the abundance of proposed alternatives, more than 90% of modern hovercraft are propelled by propellers, and most other devices use propellers or water-jet propulsion. However, it seems that there is an increasing trend towards the use of hydrodynamic propulsion or hybrid systems, since if you calculate the propulsion system for a 10,000-ton skeg hovercraft, which must have a speed of 100 knots, it turns out that it will need to be installed on it, either 10 propellers with a diameter 18.3 m each, or 10 direct-flow turbofan propulsors with a diameter of 10.5 m. In order to achieve the appropriate level of thrust using only hydrodynamic means, only two supercavitating propellers with a diameter of about 9 m would be required, or 4 water-jet propulsors with a diameter of 3.7 m each.

In other words, as the size of ships increases, the use of propellers in many cases is impractical due to the size of the propellers themselves and their foundations, while the use of hydrodynamic systems, with equal engine power, provides the specified characteristics, with very realistic dimensions. Reducing the diameter of propellers leads to a drop in their efficiency due to a reduction in the mass of the air stream, which causes an increase in the required engine power.

Despite the fact that propellers are unacceptable as propulsion for large hovercraft due to their size and quantity, they remain the most effective type of propulsion for hovercraft at speeds of 150 kts and above. However, with regard to technical and operational characteristics, propellers are inferior to water-jet propulsion and propellers when operating at low speeds.

Skeg hovercraft

Tests of another type of air propulsion for hovercraft - a propeller in a nozzle - have shown that such a propulsion device provides better technical performance at low speeds, but the nozzles themselves significantly increase the total weight of the vessel, and at speeds of more than 100 knots they increase drag, which significantly reduces the efficiency of the propulsion device. For a large high-speed vessel, perhaps the most promising is a system that uses direct-flow turbofan propulsors at high speeds, in combination with semi-submerged supercavitating propellers, providing speed up to 70-80 knots and overcoming the drag hump.

The most important advantage of a direct-flow turbofan propulsion system is that, while technical and operational characteristics are relatively identical to those of a propeller, the diameter of the fan impeller is half as large. In addition, it is significantly lighter, has lower noise levels and can be configured with a number of different installations. As the concept of wide-body aircraft-airbuses develops in the aircraft industry in the coming years, it will become possible to produce various direct-flow turbofan engines with a power of up to 40 thousand hp. (30 MW). SES-class hovercraft have rigid side keels, which are ideal structures for housing water-jet propulsors, or propellers and their drives.

Since the lower parts of the skegs are submerged in water, providing stability and promoting stable movement on the course, the propulsors are usually installed at the rear of the skegs. The design speed of the 100-ton US Navy skeg vessels SES-100A and SES-100B was 70-80 knots. The SES-100A is the first water-jet-powered hovercraft to achieve such high technical and operational performance, and the SES-100B is the first ship with semi-submersible supercavitating propellers to reach a speed of 80 knots.

There is certainly significant potential for further development in both systems, but it is unlikely that the speed records they set can be surpassed in the near future, thanks to the use of more resistant types of metals and improved design. Nevertheless, losses in their efficiency are almost inevitable. The use on the SES-100B of a partially submerged supercavitating propeller with a drive in the skeg transom was a new approach to solving the problem, since there was no need to install a propeller shaft, support struts and bearings, which created additional resistance during movement. The efficiency of this type of propeller turned out to be the same as the efficiency of a fully submerged propeller, and the thrust and torque generated on it were proportional to the area of the disc of the submerged propeller.

Propeller installation on hovercraft

Among specialists in marine propulsion, there is an opinion that the creation of such supercavitating propellers, with the help of which it is possible to achieve a speed of 100 knots or even more, is a very real task. There are designs of wedge-shaped propellers, the blade profile of which has a sharp leading edge and a square trailing edge, which leads to cavitation on the upper surface and its disappearance far below, under the rotation zone of the blades.

Another idea is a supercavitating marine propeller with variable blade curvature. If it is implemented, the same effect is expected that was achieved by the use of variable-pitch propellers on aircraft. By setting a certain curvature of the propeller blades, the helmsman could provide the optimal amount of thrust for the initial stage of reaching the air cushion, for movement at medium or highest speeds. The Hamilton Standard variable-curvature propeller has blades divided into segments in the central part in such a way that it allows individual adjustment of both parts of the blade.

When the ship's speed exceeds 45 knots, the use of supercavitating propellers becomes simply necessary. Even during the first tests of hydrofoil boats of the US Navy, it was discovered that at a speed of 45-50 knots, the bronze stern propellers of the RSN-1 vessel were subject to erosion on both sides and needed to be repaired or completely replaced after 40 hours of operation. Since then, alloys that use more resistant metals have begun to be used. There is a particularly high demand for titanium and its alloys, as they have great strength, high levels of cavitation and corrosion resistance. The first ships to install the improved propellers were the HS Denison and the 320-tonne AGEH-1 Plainview, which has two four-bladed titanium propellers each 1.5 m in diameter.

Water jet propulsors

The use of a water jet as ship propulsion is one of the oldest technical concepts. The first patent for such a propulsion was received by the Englishmen Toogood and Hayes in 1661. In 1775, this propulsion was tested by Benjamin Franklin, and in 1782, James Ramsey first used it on a passenger ferry on the Potomac River, between Washington and Alexandria. The efficiency of a water-jet propulsion system is lower than that of a propeller, so work on its creation was not carried out intensively enough. For many years, the scope of application of water-jet propulsion was limited to relatively inexpensive pleasure craft and amphibious combat boats, until in 1963 Boeing announced the creation of a gas turbine experimental vessel, the Little Squirt.

The interest shown by Boeing in this type of propulsion is mainly explained by the desire to create additional opportunities for the design of new ship propulsors as opposed to the supercavitating propeller and the extremely expensive Z-shaped transmission system, the use of which on the ship when operating at high waves was previously considered the only acceptable one. The Little Squirt, equipped with a double suction centrifugal pump, achieved a high propulsion system efficiency of 0.48 at a speed of 50 knots.

Hovercraft - "KVP"

Largely due to the interest shown by Boeing in water-jet propulsion, the US Navy came to the decision to consider such a propulsion as an alternative option, using it on the SES-100A type hovercraft for comparison with a supercavitating propeller. Although the research and testing program for water-jet propulsors resulted in the creation of easy-to-use and reliable installations, difficulties arose due to cavitation in tubular connections and pumps, as well as the need to create water intakes with a variable area. Twisting of water intakes, roll and pitch, as well as mechanical alignment of water intakes to avoid cavitation, at speeds up to 80 knots - these are the problems that are constantly being studied in order to create a project for a skeg hovercraft with a speed of more than 100 knots.

Recently, significant efforts have been aimed at studying another, long-known type of marine propulsion for hovercraft - the paddle wheel. Its main promoter is Christopher Cockerell. He is currently working on creating a water-rowing propulsion system that follows the contour of waves, with a large surface area. It is designed specifically for hovercraft. Thanks to the use of a comb design, the 20-foot paddle wheel that was once installed on ships that sailed the Mississippi is reduced to a modern model with a diameter of only 5 feet (about 1.5 m).

To propel a 2000 ton vessel, the total area of the immersed blades must be at least 150 square feet (14 m2). Christopher claims that his wheel can provide this area with a blade depth of just 2 feet (60 cm), with a total width of about 75 feet (about 23 m) across all components. The wheels will be placed behind the ship on special arms, which will allow them to follow the contour of the waves. Height sensors located in front of the wheels will generate impulses for the control system. Of course, this is a very ingenious development that provides unique advantages. Among its attractive properties, it should be noted the low noise level, shallow draft, and the possibility of easy access to all components during maintenance.

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A brief history of creation and basic principles of operation of a hovercraft

Hovercraft- ships, boats that support themselves above the supporting (land or water) surface with the help of an air cushion created by ship fans. Unlike conventional ships and wheeled vehicles, hovercraft (hovercraft) do not have physical contact with the surface over which they move. And unlike aircraft (airplanes, ekranoplanes, ekranoplanes), they cannot rise above this surface to a height exceeding a certain part of their horizontal size.

For a given mass and speed, a hovercraft requires 3–4 times more power than a car; they lose the same amount to ordinary courts. However, the movement of a hovercraft requires 2–4 times less power than the flight of airplanes or helicopters.

Effective use of SVP

Hovercraft are used in cases where road, rail and conventional water transport cannot be used effectively. The Hovercraft can transport landing groups from a large landing ship to the shore at speeds reaching 60 knots (100 km/h).

Unlike conventional means of crossing, hovercraft can not stop near the shore, but can go further and even overcome a 5% rise or an obstacle up to a third of the height of the skirt. These vehicles can be used in shallow, clogged and arctic waters, and in open areas.

The idea of hovercraft

The idea of hovercraft propulsion was first formulated by the Swedish scientist E. Swedenborg (1716). Earlier than in other countries, SVP technology was taken up in Austria and Russia.

Main types of hovercraft

There are three types of SVP:

chamber;
nozzle;
and multi-row nozzle.

In all schemes, an air cushion is created between the apparatus and the supporting surface using powerful turbojet engines and high-pressure fans.

Chamber type

In the simplest of schemes - chamber- under the dome-shaped bottom (into the stilling chamber), a centrally installed fan supplies air.

Nozzle type

In a nozzle-slot design the cushion is created by a flow of air from an annular nozzle formed by a skirt and a central part with a flat bottom. An air curtain around the perimeter of the vessel prevents air from escaping from the cushion. One of the variants of the nozzle slot scheme is a scheme with a perimetric water curtain, suitable for movement over the water surface.

Multi-row nozzle

In a multi-row nozzle design, the cushion is formed by rows of annular recirculation nozzles with different levels of generated pressure. In the last two cases, less powerful fans are required to create the cushion.

Selected developments

The Ford Motor Company proposed creating the Levaped hovercraft, which has a very thin air cushion, like a kind of gas bearing, and it can only move over a special smooth surface such as a rail track.

The Canadian branch of the Avro company is developing a nozzle-type hovercraft with such powerful fans that it can rise and fly like a jet plane.

Thrust generation and control

The forward motion of a hovercraft (hovercraft) can be provided by:

horizontal nozzles into which air flows from lifting fans;
by tilting (trimming) the vessel in the direction of travel so that a horizontal component of the thrust force arises;
by installing the air intakes of lifting fans in the direction of movement so that when air is sucked in, the required thrust force is also generated;
conventional propellers. Sometimes the driving force is created by a combination of these methods. The most effective way to create thrust is with propellers, but rotating propellers on a hovercraft pose a danger to both passengers and crew.

SVP braking principle

The braking mode of the hovercraft, as well as turning without lateral skidding, is ensured by turning the flow of traction devices. To improve directional stability, vertical stabilizers are installed, like on airplanes. The lift height is controlled by the main fans of the hovercraft.

From the point of view of science, a hovercraft is not a ship at all, but an air cushion that can also move. At rest she floats on water, but at work she moves through the air on a layer 5 feet thick.

And only the flexible rubber curtain of the cushion touches the surface of the water. And inside the curtain, a powerful air-injection device blows onto the surface of the water, forming a cushion. At the same time, propellers installed on the deck push the ship forward. Gas turbine engines power both the blowing device and the propellers.

Hovercraft can also travel on land, but most often they are used as ferries. And they reach speeds of about 75 miles per hour, which is twice the speed of the fastest ships. However, such hovercraft are not stable enough to navigate rough seas or winds.

Crossing waters by air

The drawn-in air, using a blowing device, presses on the water once it gets inside the flexible curtain.

A cushion of compressed air lifts the vessel above the water. Only the edge of the flexible curtain touches the water.

The reverse thrust created by the stern propellers turns (based on the principle of jet propulsion) into the forward movement of the ship itself.

This type of hovercraft carries passengers. Larger models are used as ferries for vehicles and heavy cargo.

Stopping and turning a hovercraft

To perform quick or difficult maneuvers, a pair of extensions called hydraulic rods are extended down from the ship's hull.

How a hovercraft turns

While moving, the ship turns around using rudders. Having turned them to the left, the ship turns to the port side, that is, turns to the left.

If you need to give the right steering wheel, then this is done by turning the steering wheel to the right.

Lateral propulsors are needed in order to stop the lateral drift of the vessel. In addition, if the propulsion is on the starboard side, the ship turns its bow to the port side.

The Hovercraft company handed over to the customer a cargo-passenger hovercraft, built under the supervision of the River Register in the small size class *3.

Purpose. The cargo-passenger amphibious hovercraft type "Neptune 23GrPasMl" is designed to transport cargo in an amount of no more than 1700 kg or passengers in the amount of 6 people and cargo not more than 1250 kg.

Acceptable areas of operation. The vessel can be operated in coastal sea areas and inland water basins. Restrictions during operation - wave height of 1% probability up to 1.2 m, distance from the shelter site no more than 11 km (6 miles). A place of refuge is any piece of land, a bay, a ship in a roadstead, where a ship can hide from bad weather.

Operating period. The vessel can be operated all year round. Type of surface: - on the water surface without depth limitation; - in shallow water, including zero depth and shallows; - on the frozen and snow-covered surface of reservoirs, in the absence of hummocks along the route that are higher than the height of the air cushion; - on ice slush and floating ice; - on a waterlogged swampy surface and in rare thickets of reeds with a height that does not impede visibility for driving. The vessel is allowed to exit and move on unobstructed areas of the flat shore. When driving on ice or snow-covered surfaces of water bodies, there is no restriction from the place of refuge.

Temperature conditions. Operation is permitted at outdoor temperatures from minus 40ºС to plus 40ºС.

Wind restrictions. Wind speed is limited to 12 m/s.

Time of day restrictions. The vessel can be operated both in daylight and in the dark. When operating at night, additional lighting is installed (high beam spotlights).

Architectural and structural type. An amphibious-type hovercraft with a two-tier flexible fence around the entire perimeter, a separate lifting and propulsion complex with two twin centrifugal superchargers and two variable-pitch propellers in aerodynamic nozzles, with an aft location of the engine compartment, with simplified hull shapes, and five watertight bulkheads.

Norms and Rules. Hovercraft was developed to comply with the requirements of the “Guide to the classification and inspection of small vessels” R.044-2016 of the Russian River Register and the “Technical Regulations on the Safety of Inland Water Transport Facilities” Decree of the Government of the Russian Federation dated 08/12/2010 N 623 (as amended on 04/30/2015) .

Main dimensions:

Composition of the payload when transporting cargo and passengers:

Fuel consumption. Fuel consumption when driving through calm water with an operating load at a speed of 40-45 km/h is about 30 l/h. Specific consumption under these conditions is 0.6-0.8 l/km.

Load location. The cargo is placed on the deck. The deck is located between the salon and the fuel tank compartment. The deck has dimensions; length 4.0m, width 2.0m. It is possible to cover the deck with an awning. The deck has brackets for securing cargo. The deck has an anti-slip surface. It is possible to increase the width of the cargo area into hinged sections. The total deck area will be 4x4sq.m. In the area of the deck, a removable railing is installed on the hinged sections.

Travel speed. A Hovercraft with an average operational load has in windless, calm weather: maximum speed on water - 65 km/h maximum speed on an ice surface 75 km/h Operating speed. The operating speed on water is 40-45 km/h, on dense snow-covered surfaces 50-60 km/h.

Amphibious qualities. The amphibious qualities of the hovercraft are ensured by the separation of the body from the screen due to the holding of an air cushion under the body by a flexible enclosure. The lifting height depends on the speed of the superchargers (engines), the load and the running trim angle. The maximum achievable height of the air cushion is about 0.75 m. The height of the air cushion is measured from the supporting hard surface to the bottom of the housing.

Flexible fencing. To form an air cushion on the vessel, a flexible fence is provided around the entire perimeter. The flexible two-tier fencing consists of an upper tier - a receiver and a lower tier - removable elements. The flexible fencing has an internal contour consisting of longitudinal and transverse inflatable keels. The flexible fencing material is rubberized fabric based on nylon textiles.

Frame. General information. Sheets and profiles made of aluminum alloys are used as the material for the main body, set, and foundations. Rolled sheets are used grade Amg5M, GOST 21631-76. Profile steel grade Amg6M or D16T according to GOST 8617-75.

Chopping. General information. The cabin is made of fiberglass and has an aerodynamically streamlined shape. The cabin is made of a three-layer structure, the middle layer of which is insulation. The outer layer is made of fiberglass based on polyester resin with fiberglass reinforcing material. The middle layer is made of tile foam. The inner layer is made of fiberglass, covered with lining - pile fabric.

Main engines. It is planned to install two automobile diesel engines produced by Cummins, brand ISF2.8, as the main engines - four-cylinder with in-line vertical arrangement of cylinders, turbocharged, with intermediate cooling of charge air, with distributed fuel injection "Common Rail". The maximum permissible speed is 3200 rpm. The main characteristics of each engine: maximum power, kW (hp) - 110 (149.6); number of cylinders, pcs. - 4; cylinder volume, l - 2.8.

Fuel system. The fuel system consists of two fuel tanks, each with a capacity of 200 liters.

Transmission. The hovercraft is equipped with two power units that distribute engine power to the supercharger and the propeller. The power unit includes flat-toothed drive belts, pulleys with shafts mounted in bearings. The hovercraft is equipped with two independent transmissions on the left and right sides, each of which transmits torque on its side from the power unit to the propeller and supercharger. The transmissions include cardan drives.

Propulsors. The hovercraft uses two variable-pitch propellers in aerodynamic fixed nozzles as propellers. The variable pitch propeller support unit and the reverse mechanism are located in the pylons of each nozzle. The material of the propeller blades is fiberglass coated with aramid fabric (Kevlar). The angle of rotation of the propeller blades is changed by electric pedals and controlled by direction indicators installed in the control panel.

Airbag blowers. Two twin centrifugal superchargers are provided as air cushion superchargers. Air cushion blowers operate separately, each on its own side. The superchargers are mounted on shafts supported on both sides by self-aligning bearings. The material of the superchargers is fiberglass with the addition of carbon and aramid fabrics (carbon and Kevlar).

Transportation. Transportation by road is provided without restrictions within a size of 2.5 m. The vessel will be shipped in a 40HC container. This involves dismantling the side mounted sections, attachments with rudders hung on them, and propeller pylons. Dismantled products are sent separately in a 40-foot container or by road.