Ekranoplan (WIG craft)
Ekranoplans ("surface plane") and seaplanes are waterborne platforms that take advantage ofthe broad water surface for takeoff and landing. This gives the platform the advantage over land-based aircraft of not being limited by landing field location and dimensions for operation. Militarily, they can operate in areas with non-prepared landing surfaces as long as the payload can be unloaded. They may be commercially viable since many of the commercially important cities worldwide are located at a shoreline.
According to its capabilities, a ground-drive vehicle is located between ships and airplanes, combining their best qualities. The “screen effect” is to create an “air cushion” between the body / wings of the machine and the surface of the water by means of the incoming flow. Rising above the sea, the device acquires stability and the ability to "slide" with minimal fuel consumption. At the same time, instead of the sea, there can be any other flat surface - an ice field, snow or a steppe. In terms of economy and payload, WIGs outperform aircraft and helicopters, and in speed - on hydrofoil vessels. From a military point of view, these machines are good for their stealth for radar. A device flying at low altitude is invisible to enemy radars, while the lack of contact with water precludes the detection of sonars and the likelihood of running into a mine.
The expanse of the water lets the wing span of the platform be larger than limits placed by standard runway widths, allowing spans of greater than 200 feet. It also allows longer takeoff distances if needed. The largest wingship built to date uses captured air pressure under the wings provided by a separate power system to augment the dynamic lift provided by the fuselage in contact with the water and aerodynamic lift on the wings to achieve lift-off. The seaplane gets its takeoff lift from water dynamic lift on the fuselage and aerodynamics. The choice between which platform is selected for the mission is based on aerodynamic performance, power required for takeoff and cruise, fuel usage rate, and payload fraction.
In 1929, the Dornier DO-X seaplane was constructed. In 1930-31, this 56-ton seaplane used the ground effect to increase its range and payload during transatlantic flights. In 1935, Toivo Kaario of Finland built an experimental wing-in-ground effect vehicle. It was powered by a 16 hp engine and carried a man over the snow at speeds up to 12 knots. He obtained the first patent for a surface effect craft.
In 1958, Rostislav Alekseyev, an engineer based in Nizhny Novgorod, began a project to create bis first wingship model for the Russian Navy. This work led to the construction of the SM-series ekranoplan test vehicles, most of which were built/tested in the early- to mid-1960's. In 1961, the SM-1 achieved a speed of 200 km/hr and demonstrated wingship stability and dynamic parameters near the surface. Major disadvantages proved to be high takeoff and landing speeds, and over-sensitivity to surface roughness. In 1962, Alexeyev was the first to incorporate under-wing blowing to improve the takeoff and landing aerodynamics of the SM-2 model. The blowing system, however, aggravated the pitch stability problem in a tandem wing configuration.
In 1963 Alexeyev devised a pitch stability solution by taking the aft wing away from the influence zone of'the forward wing, and out of the blowing zone. This led to the airplane-type configuration used in most of the subsequent Russian designs, characterized by forward wing-in-ground-effect employing underwing blowing and an aft wing out of ground effect. During this same year, the SM-2P, which used this configuration, was built and tested. R.Ye.Alexeyev developed the first prototype of a combat ground effect vehicle. The prototype ship with a wingspan of 38 meters and a length of 92 meters was dubbed the "Caspian Sea Monster" in the West. The leviathan was lifted into the air by a dozen engines that were designed for strategic bomber aircraft.
Traditional names associated with this general technology area are: ram wing; wing-in-ground effect (WIG); and ekranoplan (Russian). The specific technique of aiding takeoff and, perhaps, landing by directing the efflux offorward mounted propulsion units under the wing is called air injection in Russia and power augmentation or power augmented ram (PAR) in the US.
The advantages of the ground effect vehicles over other types of military transport were their cost, cargo capacity and speed. The leadership of the USSR and the Ministry of Defense valued them. One of the main features of the amphibious vehicle is its invisibility to enemy radar. The prototype flew at an altitude of 4 to 14 meters (too low for radars) above the sea surface and did not touch the water during flight (and thus not detectable by sonar either). The prototype was able to carry a cargo equal to its own weight (240 tons) while expending five times less fuel than transport aircraft with similar cargo capacities.
Wing-In-Ground (WIG) effect craft take advantage the fact that the aerodynamic efficiency of a wing, and particularly its lifting capacity, improves dramatically when is operated within approximately one-half of its span above ground or water, in what is termed ground effect. If the wing's natural accelerated flow passing over it is further accelerated by the high-velocity exhaust of a turbojet engine, the lifting capacity of the wing is even more greatly enhanced. An ekranoplan is able to move near the surface of water or land due to the so-called ground effect. The oncoming airflow under the wing creates extra lift, an air cushion. It can reach speeds of up to 500 km/h and has some obvious advantages. Moreover, there are various types of ground effect vehicles that are able to ascend above ground level for extended periods of time and function as airplanes. These are ground-effect aircraft.
While conventional WIG watercrafts have found use as military and transport vehicles, they are not optimally suited for use in a variety of circumstances, and require specially trained personnel to operate them. For example, such craft are limited to areas where speed restrictions are above about 50 mph and where they have sufficient space to reach 10-30 feet above the water's surface while travelling at such high speeds. They do not effectively travel at lower speeds of below about 50 mph because the lift and drag components necessary to maintain ground effect in conventional WIG craft require thrust/lift ratios that translate into high speed operation. Additionally, because conventional WIG craft turn by banking, i.e. tipping their wings like an aircraft as they travel approximately 10-30 feet above the water, tight, emergency or avoidance turns are generally precluded.
Because of the length of the wing and the low altitude at which they travel above the water, if emergency turns are attempted they often result in the wing of the craft contacting the water. As will be appreciated, if the wing of a craft traveling at between 50-100 mph is tipped and strikes the water, the result is an almost certain crash, as the craft will likely cartwheel out of control upon impact of the wing with the water. Due to both the high speed of travel and the inability of conventional WIG craft to execute tight, emergency turns, traveling across a crowed harbor, bay or river is not feasible with such craft as they pose a safety risk to the occupants and other watercraft. With conventional WIG craft it is important that they do not exceed maximum ground effect altitude due to the design and shape of the wing, which does not provide safe lift above ground effect vertical limitations.
In addition to the foregoing, when they are not flying a ground effect WIG craft become poor boats, as they are typically only capable of travel at approximately 5 to 10 mph. The missing speed "gap" between 10 mph (the upper limit for a WIG craft as a boat) and 50 mph (the lower limit of a WIG craft in ground effect) severely inhibits WIG crafts' utility. The majority of conventional WIG crafts are still using outdated and inefficient amphibious airplane fuselages with large wing designs attached that have not evolved appreciably since World War II, in order to fly in ground effect. In order to breach the water's surface, these craft need approximately 4.times.-5.times. thrust in calm waters to break free of the surface. WIG crafts are also forced to take off into the wind, like a conventional amphibious airplane, which affects ability in limited waterway space and rough sea state conditions.
The ekranoplan is a high-speed transporter, a combination of a heavy-lift plane and a light motorboat. Designed by Rostislav Alexeyev and used by the Soviet and Russian navies from 1987 until the late 1990s, the ekranoplan flies using the lift generated by the ground effect of its large wings when moving less than four meters above the surface of the water. This type of vehicle uses the so-called ground effect – the extra lift of large wings when they’re used in proximity to the water’s surface.
During the 1960s, numerous WIG vehicle technologists focused on the apparent "hole" between ships and aircraft as an opportunity for new types of craft. If vehicles could be designed to fill this hole, they would have better range and payload performance than aircraft, and speeds much faster than ships. WIG craft can arguably fill this void by flying very close to the surface (less than one-tenth of the span). Cruising at this altitude reduces drag by about 25% and reduces speed by about 20%. Therefore, for the open ocean application with given wave heights, bigger is better.
For this reason, these vehicles were designed to travel at a maximum of three meters above the sea, but at the same time may take off, fly briefly and land safely if faced with waves up to five meters in height. Thanks to their ability to fly at a low altitude, ekranoplans could spend less fuel, fly under the radar and avoid anti-aircraft systems. These craft were originally developed by the Soviet Union in the 1960s as high-speed military transports, and were used mostly on the shores of the Caspian Sea and Black Sea.
Ekranoplans do glide just a few meters over the water surface, but they can also leave the ground effect zone and gain an altitude of up to 300 meters – enough to clear any obstacles. Leaving the ground effect flight means higher fuel consumption, but it allows an ekranoplan a certain degree of flexibility – not as much as a plane but considerably more than a ship or a hovercraft.
The apparent success of these machines hid some very real problems, not least of which were serious stability and control deficiencies. In the opinion of several highly experienced NASA test pilots manual control of a wingship over extended periods of time would be a very demanding task even in benign weather and day-time conditions. Verbal contacts with the Russian wingship technical community confirmed the opinion of the American pilots.
For the technology area of providing artificial dynamic stability for wingships, the Russians experimented with what they term as "automatic motion control system" or AMCS. It is clear that the requirement for artificial stabilization was realized and established by the Russian wingship designers as early as 1964. Both the ORLYONOK and the LUN are equipped by AMCS which developed by te Central Research and Development Institute "Electropribor."
In sharp contrast with the design of the Lippisch reverse delta wing planform, the Ekranoplan type ground effect vessels are all square planform vessels. Changes to the fore and aft pitch of this type of ground effect crafts is damped at the trailing edge, through the air under the wing's resistance to further compression between the craft and the water surface. In the case of the Ekranoplan square planform design, this line of "compressive stability" runs across the craft in a straight line, and puts a critical stability control point into the fore and aft moment. This must be carefully controlled by the trail plane and elevator, much like flying balanced on a see-saw.
The situation in a Lippisch's reverse delta wing planform was quite different. The trailing edges of both wings extend from the rear of the craft and pass the craft's center of gravity to the front. The critical stability line is not across the craft but at a tangent to it. This makes the fore and aft pitch stability much more forgiving. This in turn reduces the pilot skill demands, and also allows stretching the overall performance envelope to include kinetic jumps. Not so with the Ekranoplan square planform.
Under low flying conditions radar sensors measuring altitude, tilt and velocity of craft trace the variable profile of wave disturbance practically without averaging, thus making it difficult to gauge the motion parameters in relation to the undisturbed level of the sea surface. It is necessary to combine radar with other sensors in order to provide high accuracy. A "near perfect" landing is one in which, after flare-out, the resultant velocity ofthe vehicle is nearly tangent to the free water surface. In this instance, the craft settles into the water with minimal impact loads. Unfortunately. realistic flight path angles at water conact are not zero and the vehicle is at some positive trim angle relative to free water surface.
At speeds below takeoff, the hull continuously strikes the oncoming wave train. It develops impact loads which may be significant since hydroskis or other landing load alleviating devices may not he used during takeoff. The wing end plates are constantly penetrating the oncoming waves and must be designed to withstand large side forces if the vehicle is yawed. Large spray sheets are developed as the hull slams into oncoming waves. The large kinetic energy of the spray can damage wing flaps if they are extended and not designed with load alleviating device.
These machines had tremendous power requirements to get off the water. It has a massive turning circle, and is fairly slow to accelerate. Its poor maneuverability means it cannot turn and run from a fight, and so is a fairly easy target if caught in a confined space, or if surrounded and pushed against the shoreline.
Substantial amounts of sea water can enter the engines at takeoff and landing as "green water" plus small liquid particles of water are ingested with the air. Both are undesirable, but the small particles are likely the worst since this causes salt deposits in both compressors and turbines which rob needed operational margins in core EGT and stability. The Russians initially used very complex doors and Venetian blind type inlet systems, despite the large inlet pressure losses one might anticipate from such devices. Their LUN under construction was to use a much simpler system. The hardware seen used an inlet bullet nose shaped like an onion or Greek Orthodox church spire, point end into the wind, to deflect large drops and spray larger than 3-5 microns in diameter. Separation occurs when the high inertia drops cannot follow streamlines.
The design of a wingship structure requires the merger oftwo technologies: aircraft design and high-speed-ship design. The design of structures for large wingships is very complex because the vehicles have to operate in the boundary conditions of air and the ocean's surface. This environment is further complicated by the ocean's wave action. In addition, the overall structural configuraüon of a wingship is influenced by the type of payload it carries, by the mission requirements such as speed, range, flight altitudes, and by the takeoff and landing sea conditions and the takeoff and landing speeds.
In 1998, all the flights of the ekranoplans were suspended, in what could indicate the end of the era of these vehicles. A project to manufacture ekranoplans in Russia was suspended indefinitely in the 1990s due to a lack of financing and economic chaos.
Currently more and more people are recalling the development of the construction of ground effect vehicles. In March 2014 scientists at the Far Eastern Federal University announced the beginning of the development of the first experimental model of a passenger ground effect vehicle. Previously, the Border Service of the FSB of Russia had announced its intention to resume the development of this type of ship riding on a dynamic air cushion. The Russian Ministry of Defense has also expressed its interest. However, funding for its development has not yet been included in the government armaments program lasting until 2020.
KB Alekseeva presented at the forum "Army 2015" WIG projects that can be used in various, including military purposes. As the correspondent Voennoe.RF enterprise booth presented WIG - a platform that saturation will occur in accordance with the requirements of the customer. In particular, they will be able to carry a gun. One of the promising directions of use of WIG - work in the Arctic. These machines are able to from the ice and snow off and landing.
Where to build the advanced airfoil, it had not been decided. Perhaps KB Alekseeva will implement the project on its own, it has a production site may give production counterparts. Winged is a high-speed vehicle, flying within the aerodynamic action of the screen, that is a relatively small (a few meters) height from surface of the water, land, snow or ice. With equal weight and speed WIG wing area is much smaller than that of the aircraft. According to the International Classification, WIG are sea-going vessels.
In 1992 the US Congress directed the Advanced Research Projects Agency (ARPA) to investigate the wingship vehicle concept and directed the Department ofDefense (DoD) to report back on whether it had a validated military requirement for such a vehicle. The investigation found in 1994 that: (1) By far, the largest wingship programs have been Russian; (2) There have been no operational deployments; (3) A Russian wingship lifted the greatest weight ever from the water; (4) Russian programs focused on tactical military missions ~ not the strategic supply mission, which was the initial US emphasis; and (5) Several efficiency-reducing wingship features detract substantially from the efficiency gains resulting from flight very near the sea.
The investigation concluded that: (1) several military missions which emphasize the speed and persistence of a wingshipare promising; (2) wingships approaching the efficiency and capacity required for strategic mobility are ten times the gross weight of the largest wingship to date and five times the gross weight that any experienced US or Russian design team would suggest; (3) based on their evolution to date, and within the bounds of current andforseeable projected technology and projected life cycle cost, wingships do not appear promising for the long range strategic lift mission in the forseeable future; and (4) western technology and modern Russian technology could improve the performance of Russian-style wingships.
Since the collapse of the USSR and the closure of the Lun and Orlyonok-type military ekranoplane construction programs in the interests of the Ministry of Defense, there are regular reports in the media about the development of ekranoplanes in the interests of both the military and the civilian sector.
By 2017 the production of multi-purpose ekranoplanes was reviving in Russia. Sector-specific design bureaus were working on projects, and both light and heavy multipurpose machines are being created. High payload, cost effectiveness and the ability to cover huge distances in a matter of hours make WIG indispensable for solving a wide range of tasks, including combat.
The main developer of such technology in Russia is traditionally the Nizhny Novgorod Central Design Bureau named after Alekseev - the leading Soviet and Russian enterprise for the design of ekranoplans, hydrofoil vessels, air-cavern ships, air-cushion ships, boats. The bureau is engaged in a whole line of "cruise ships".
Everyone is afraid of the new. The new always has more enemies than the old.
|Total Thrust (MT)||110||37||104||104|
|Join the GlobalSecurity.org mailing list|