Ground effect vehicle

Aquaglide 2 from the Russian manufacturer ALSIN at the ILA in Berlin 2006

A ground-effect vehicle ( Russian экраноплан ekranoplan - «umbrella glider» , English ground-effect vehicle (GEV) or wing-in-ground (WIG) effect craft ) is an aircraft that flies at a very low altitude over flat surfaces, mostly water, and thereby the Exploits ground effect . The Russian name Ekranoplan is not only a synonym for ground-effect vehicles in Russian, but also describes a special Russian development among the previously known ground-effect vehicles. It is necessary to differentiate between ground effect vehicles, which are free-flight aircraft, and ground effect vehicles that are actually bound to the area close to the ground. This distinction can be explained by the precise description of the ground effect.

Basically, the ground effect is understood to mean the special flow conditions of a wing close to the ground. There the lift force is greater than with free flow around wings. With increasing height, the ground effect decreases and is usually no longer present from half the span.

Ground effect vehicles are designed for economy, long range or increased payload and can close the gap between fast air vehicles and powerful water vehicles in their possible applications. Depending on the design, they are classified under special watercraft or actual aircraft. Ground-effect aircraft, however, are more restricted than aircraft and less effective than ships .

Basics

The ground effect is based on the one hand on the fact that an air roll ("roller") forms under the wings and fuselage of every aircraft near the ground during flight, which moves with the aircraft and on which it can glide. The efficiency of the wing is thus improved and the fuselage of many ground-effect vehicles is given an aerodynamic efficiency in the first place. The significantly increased dynamic lift due to the ground effect with the same air resistance makes ground effect flight more economical than flight at higher altitudes.

A second effect, which has the greater part in increasing the efficiency of a ground-effect vehicle, is the elimination of the lower part of the wake vortex . This forms at the end of the wing of every aircraft and is responsible for a large part of the air resistance. In normal aircraft, attempts are sometimes made to improve the drag coefficient by adding winglets to the wing tips. However, since the wake vortex can only propagate in the air, the lower part of the wake vortex is cut off from the ground or the sea when flying low. The improved efficiency results in an increased range or significantly increased payload.

Designs

There are basically two types of ground-effect vehicles: the free-flight single-wing aircraft based on the principle of Alexander Lippisch , Hanno Fischer and Rostislaw Alexejew (Ekranoplan) and the tandem airfoil flair boats by Günther W. Jörg, which work exclusively with ground effect . In the case of single-wing ground effect vehicles, which can also leave the ground effect as aircraft, additional constructive measures must be taken to regulate the flight altitude in the area close to the ground, usually of an electronic type (stabilizers). The Tandem-Airfoil-Flairboate work on the principle of a damming vehicle with tandem wings, completely self-stable without additional aids and cannot leave the ground effect. The problem of the single-wing ground effect vehicles suddenly shooting up does not arise here due to the design.

In terms of the ground effect, single-wing ground effect vehicles, apart from the problem of sudden shooting up, keep their flight altitude inherently stable. In the "Caspian Sea Monster" of the Soviet Union (see below) the impact of the ground effect is so great that once the ground effect has been achieved, only two of the ten engines have to work to keep the aircraft fully loaded and at a stable altitude at cruising speed. The other engines are switched off after reaching the ground effect and cruising speed. Only long-haul flights without a stopover are more efficient.

With increased drive power, most single-wing ground-effect vehicles can also switch to free flight for a short time, for example to overcome obstacles. The possible time of the free flight and thus also the distance that can be bridged between two ground-effect surfaces is limited by the fuel reserves carried along , which run out much faster without a ground effect than with real aircraft of comparable mass. Economic savings therefore depend above all on route planning and intended use.

With large single-wing ground-effect vehicles such as the Russian Ekranoplanen, landing and take-off on land is not possible due to the huge take-off and landing stretches without significantly expanding the runways of the land airfields currently in existence. The problem of the expensive, space and mass consuming chassis was not solved with these machines. They are designed exclusively for splashing. Smaller hybrid machines can often land.

Stall

All ground-effect vehicles, the delta-winged and the tandem-winged wing, have a shorter wing in relation to the length of the fuselage than that of aircraft designed for greater altitudes. Since the wake vortex spreads conically from the wing tips towards the rear, in a ground effect vehicle with only one wing, such as Ekranoplan, Lippisch X-113 and Successor, the wake cones of the two wing ends can meet before the end of the fuselage. When this happens, the tail drops suddenly, the vehicle first climbs steeply, then, leaving the ground-effect flight , falls below its minimum flight speed and crashes due to a stall on the wings.

The arrangement of tandem wings based on the principle of the engineer Günther W. Jörg, on the other hand, brings about a targeted use of the flow of the front wing with a constructive introduction to an additional lift of the rear wing. The dreaded pressure point migration of the single-winged / delta-winged "ground-effect aircraft" listed above, which leads to uncontrolled behavior of the vehicle, is avoided with this design. The interaction of both tandem wing configurations results in a smooth, stable movement over the water surface at a defined height.

There are a number of measures to counteract the dreaded effect of pressure point migration in ground-effect aircraft with only one pair of wings:

The empennage build so high that the meeting of the wake turbulence does not reach the elevator and rudder.
Increase the wingspan so that the wake vortices only meet behind the ground effect vehicle. However, this would have a negative effect on maneuverability and the curb weight would increase significantly.
Move the controls with so-called " duck wings " from the stern to the bow.
Move the center of gravity forward.
Shape the wings in such a way that the wake turbulence is not conical, but rather twirled towards the rear and this twirl does not touch the rear of the ground-effect vehicle.
After all, you can let the electronics fly the aircraft in order to be able to counter the sudden rise in time.

In the west it was customary to find purely aerodynamic paths. In the east, all engines were brought forward, so the weight was shifted, the tail fin was built as high as possible and the electronics (analog computers, still with electron tubes ) were used to assist the pilot in the flight.

Another problematic effect is caused by the air roll, which generates a strong wind against the direction of flight and can damage structures and vegetation when flying over solid ground . Aerodynamic disturbances can lead to turbulence , especially when changing the soil type (water, steppe, scrubland) , which can lead to stalling or destabilization of the flight. Theoretically, this is taken into account in ground-effect aircraft that are used inland and, for example, have to fly over land stretches between two lakes. The use of additional engines increases fuel consumption because the ground-effect aircraft is used like a normal aircraft. To increase flight safety, flight lanes can be used with ground types familiar to the pilot. If technically possible, these vehicles can briefly go into free flight in wooded or mountainous terrain and leave the air roll.

Altitudes

The air roll (cylinder) is generated by the aircraft itself and adapts to the new flight data within a few seconds if the flight behavior changes. For single-wing ground-effect vehicles, which are basically also free-flight, this is not clearly delineated, but a horizontal whirlwind in which there are optimal positions for the position of the machine for certain purposes. As the flight altitude drops, the vehicle does not get into the eye of the whirlwind, but instead compresses the roller to a smaller diameter, making it more load-bearing. With increasing flight altitude, the role also becomes larger, less stable and increasingly unstable. At altitudes above about eight meters, most ground effect vehicles, including all smaller types, lose their role. It should be able to be aerodynamically extended, for example by enlarged wings, up to twelve or more meters, whereby free-flight properties come to the fore. Many types can then continue to fly, but use a lot of fuel. However, some heavy construction types cannot leave their role at all and rise only slightly higher even with extreme drive power. The size of the roll, speed and possible flight altitudes depend on the technical data of the types and the behavior of the pilot. For each type and purpose, there are different specifications that the pilot must learn. As everywhere in aviation, greater heights also offer more safety for single-wing ground-effect vehicles.

Smaller machines are often designed in such a way that the optimum heights for efficiency or economy are between two and three meters. The machines are flown in such a way that they drop to their optimal altitude as often as possible. Larger machines are often designed in such a way that the optimal heights above water for economy or with high payloads are between 5 and 8 meters. However, there is no aerodynamically defined minimum flight altitude over smooth, unobstructed ground. Technically, optimal heights of well under one meter up to a hull just above the ground would also be possible, but this makes conflicts with waves, sea marks or people more frequent. When in the water, the air roll is retained even when the hull is already gliding in the water and only collapses when the speed drops. Even very large machines from 75 to over 100 meters in length, which are incorrectly referred to as "flying ships" despite their free-flight properties, could in principle be designed so that the optimal flight heights are less than one meter flight height (fuselage), but this is due to the difficult maneuverability these machines are at high risk. In addition, with this optimization the long-term flight over the open sea becomes inefficient because the cruising altitude in waves is above the economic optimum.

For ground-effect vehicles based on the tandem wing principle, the design results in an altitude close to the surface, which is also dependent on the size of the boat, but does not go beyond an imaginary "axle height" of the vehicle. The special construction basically means that the function depends on the presence of a water surface and therefore has an optimum and a maximum, which, however, cannot be exceeded. Self-regulating and stabilizing properties ensure that this type of ground-effect vehicle remains safely and automatically in ground-effect flight.

In general, the following applies to free-flight ground effect vehicles:

The deeper the machine flies

the more stable the role and the flight,
the cheaper the operation,
the more frequent approaches to unforeseen bumps in the ground or watercraft,
the more the "stripping" of the roll affects the flight height of the machine after the obstacle,
the stronger the storm damage to objects flown over,
the more limited the application possibilities over solid ground.

The higher the machine flies

the more free-flight properties are used,
the more fuel is consumed
the greater the application possibilities (flight over solid ground).

Flying over watercraft, pack ice , dunes , but also bathers or water sports enthusiasts is associated with dangers . At higher speeds, the air cylinder acts like a fast-moving solid and hits the obstacle. It can also be "stripped" off buildings or table icebergs , whereby the machine can sink or tip over after the obstacle. Today, this can be compensated for by quickly reacting electronic safety mechanisms, which increase the engine output for a short time and allow the vehicle to fly freely immediately after the obstacle until the role is rebuilt. Small vehicles, however, are much easier to steer. When changing the type of soil, especially on rising terrain, the flight altitude is increased slightly beforehand. The role is not stripped off by overgrown soil, but slowed down and swirled and loses a percentage of its load-bearing capacity . However, flying over other aircraft at any altitude inevitably leads to an accident with the vehicle being flown over, because the forces acting in the role exceed the tolerance limits of any type of construction currently in use. ^[Receipt?]

The idea of using low altitudes to devastate enemy airports, helipads, troop gatherings, etc. by surprising overflights with large ekranoplans is considered to be militarily out of date. The machines are considered easy targets and can be fought well with missiles.

German development

Test series X-113 / X-114

In the West, the first successful tests of aircraft designed purely as ground-effect vehicles were carried out in 1971 with the X-113 developed by Professor Alexander Lippisch . A series of test flights over Lake Constance confirmed the functional principle, but showed that the stable flight condition, which is important for practical operation, was achieved with the prototype with a wingspan of only 5.89 m so close above the surface that the slightest swell made a flight in the ground effect impossible . Building on the X-113, the Rhein-Flugzeugbau company built the six-seat, amphibious model RFB X-114 as a test vehicle on behalf of the Federal Ministry of Defense , before further development was abandoned. In 2004 the company Wigetworks Private Limited, Singapore acquired a license for the technology. The prototype airfish 8 was also acquired.

Tandem airfoil flair boats

Tandem Airfoil Flairboat Jörg III in the Bodden .

Based on the findings of the X-113 test series by Professor Lippisch, the engineer Günther W. Jörg recognized the system's susceptibility to failure in practical use. For a pilot, it was only possible for a short time and with maximum concentration to control the behavior of the X-113 in a stable manner in ground effect flight. As a result of a systematic series of models away from the single-wing ground-effect vehicle via various wing shapes, the design principle of the tandem wing emerges. With the two-winged Tandem Airfoil Flairboat , excellent flight behavior is achieved with simultaneous inherent stability of the system in the ground effect. Due to the self-regulating flight characteristics, it is not possible for the vehicle to leave the ground effect; a tandem airfoil flair boat is therefore also classified as a type A ground effect vehicle.

The first manned tandem Airfoil Flair boats of the TAF series were built in 1973/1974 and approved as ships in 1974 by the then Federal Ministry of Transport. A series of 16 manned vehicles in different sizes and material combinations followed in the years up to 2004. In 1984 Günther Jörg was awarded the Phillip Morris Research Prize for the transport and traffic sector for his research results.

The research results of the series are currently being implemented in Germany at Tandem WIG Consulting and transferred to the latest technologies.

A product range of type A ground effect vehicles is ready for economic implementation. In particular, the sizes 2.4, 8, 12 seater or also

in the cargo version (cargo) are available as tried and tested tandem airfoil flair boats. The tandem wing system opens up new markets for commercial traffic including people

Large flying boat.

Seafalcon

Seafalcon in 2007 on the Warnow in Rostock .

The Rostock company Meerestechnik Engineering GmbH (MTE) has developed an eight-seater ground effect vehicle called the " Seafalcon ". Since the end of 2006 it has been tested on the Warnow in Rostock and on the Baltic Sea off Warnemünde. According to its classification, the vehicle corresponds to a water vehicle (boat) and, like many similar constructions, is not designed for land-based operation. Two slightly modified diesel engines, each with 100 kW of the A-Class from Mercedes-Benz, are used as drive . The hull of the vehicle has been completely made of fiber reinforced plastics. Therefore, the vehicle has an extremely small mass. Seafalcon GmbH has held all rights to the vehicle since 2014.

Soviet and Russian ekranoplane

The Soviet Navy built a number of very large ground-effect vehicles under the name Ekranoplan , of which the " Caspian Sea Monster " became known for the first time in the west through satellite images .

The official name of the ship was KM , the abbreviation for корабль-макет (Russian for ship demonstration model ). It was built in 1964 and had a wingspan of about 40 meters, a length of over 100 meters and a weight of up to 544 tons - twice the heaviest aircraft at the time. Driven by ten jet engines , the machine reached up to 500 kilometers per hour with a payload of 280 tons. Eight of the ten engines were needed just to lift off the water surface.

The machines were extremely sluggish in flight, difficult to steer and had an extremely large turning circle. When changing the flight direction by 180 degrees, watering, turning in the water and then restarting could be tactically more favorable. However, the high payload made it possible to transport large quantities of material to the target area. The purely military advantage of these machines over ships and submarines was, in addition to their high speed, that they had no draft during the flight and were therefore not detected by the active sonar of enemy boats. Compared to aircraft, the advantage, in addition to the large payload, was the low flight altitude, which makes radar detection difficult. This advantage of difficult localization was partially negated by technical progress; Since the mid-1980s, modern aircraft, especially early warning aircraft, have been able to detect low-level aircraft, helicopters and ground-effect vehicles over the sea.

Civil protection options are seen today in disaster control and rapid aid in the event of accidents on the high seas. However, there is no internationally available application of the technology.

According to ministers, Russia intended to build a new military model with missile armament in 2018. In 2015, the Russian fleet had expected such a system with a payload of up to 300 tons by 2020.

Spasatel model

In an old industrial complex in Nizhny Novgorod , there is still a giant among ground-effect vehicles: the 73.8 meter long and 19.2 meter high Spasatel was intended to carry up to 500 passengers as an ambulance. Although the funds for the project have been canceled, the employees are still working on the completion of the vehicle.

A copy of the Lun class was stored in the port of Kaspijsk on the Caspian Sea and stood there on a floating platform (coordinate 42 ° 52 '54.9 " N , 47 ° 39" 24.3 " E ). 700 meters to the east there is an Ekranoplan of the Orljonok class (A-90) as well as the remains of a dismantled specimen on the bank ( satellite image from October 16, 2005). In 2020 it was towed to Derbent , where it will be an exhibit in Patriot Park . 42.881925 47.656746

Overview of variants

In addition to the well-known KM model, there were a number of various predecessors and successors of the KM:

SM-1 : Three-seat test machine with a single-jet engine mounted above the aircraft fuselage.
SM-2 : Three-seat test machine with a ship-like hull and internal thruster.
SM-2P7: This version was intended for research into beam diversion to improve the load capacity. The SM-2P7 was a single-seat machine with an air inlet in the nose for the engine.
SM-3 : The specialty of the SM-3 was the large wing depth and a sled-like nose.
SM-4 : Two-seat Ekranoplan with several air inlets and a small oar in the nose.
SM-5 : Further developed Ekranoplan, in which the load capacity has been improved through the use of jet engines and directional nozzles to divert the air flow under the wings. It was equipped with additional protection from spray above the main air inlets.
SM-8 : Large Ekranoplan with 4 jet engines attached to each side of the cockpit.
KM : Like the SM-8 , the KM had eight jet engines mounted above the cockpit. In addition, it had two travel engines at the stern.
Lun : The Ekranoplane of the Lun class were developed with a view to a mobile rocket platform (variant Lun), later with regard to a rescue platform (variant Spasatel ). The drive concept of the Lun largely corresponded to that of the KM. Only the two rear engines of the KM are not found in the Lun.
A-90 : The A-90 Orljonok was developed from the beginning for military and civil purposes. The A-90 used two jet engines for take-off, while a rear-mounted turboprop was used for locomotion . The Russian Navy received at least five such copies.

Ekranoplan "Tungus"

The shipbuilding company “Aerohod” (Nizhny Novgorod, Russia) has been testing a ground-effect vehicle model called “Tungus” since 2014. After evaluating the tests, the development and construction of vehicles with a seating capacity of 4 to 70 passengers is planned.

Ground effect on other vehicles

The hybrids of ship and hovercraft known as surface effect ships are, like pure hovercraft, not ground effect vehicles in the actual sense, because they do not achieve their "hovering effect" aerodynamically through propulsion, but are generated by one or more air currents directed downwards between Side pockets are “caught” and “taken along” during the advance. The eponymous term surface effect ( surface effect ) is (Engl. At this point from the ground-effect ground effect ) to distinguish.

The helicopters hovering in one place are at the moment of hovering flight ( hover ) not in the ground effect even at low altitudes, since at this moment, strictly aerodynamically, they are more like overpowered hovercraft without side pockets and not the ground effect vehicles "riding" on "air rolls". The resulting effect is also referred to as the floor effect .

In supersonic flight aircraft located may also be in the lowest conceivable altitude not use the ground effect, since the "air role" "outdated" at supersonic speed and is "suspended".

In the case of zeppelins , blimps and other (semi) airships , the ground effect is undesirable because it endangers the structure, which is why these aircraft are often operated at altitudes of one and a half times the fuselage length. This example also documents that the ground effect does not depend solely on the existence of wings, but that an arbitrarily shaped fuselage of an aircraft contributes to the ground effect.

Ground effect hovercraft

Vehicles combined with air cushion and ground effect vehicles are referred to as ground effect air cushion vehicles . Such a floor-effect hovercraft initially generates an air cushion by pumping air under the fuselage, which lifts the vehicle off the ground, with an apron around the fuselage restricting the escape of air under the fuselage (principle of the hovercraft ). When the vehicle then glides close to the ground above the surface of the earth, the compressed air under the wings then creates an additional air cushion, which allows the vehicle to glide above the ground (principle of the ground effect vehicle). Ground-effect hovercraft have the advantage over pure hovercraft that they consume significantly less fuel, since the energy-consuming lifting of the vehicle by air pumps under the fuselage is limited to the lifting and landing phase. Compared to pure ground effect vehicles, they have the advantage that they can take off and touch down on land, which makes it easier for passengers to get on.

Ground-effect hovercraft with a fairly simple design are manufactured by the US company Universal Hovercraft under the Unregistered Trade Mark name Hoverwing ™. This Hoverwing is not with the developed in Germany in 1997 Hoverwing confuse who was a pure ground effect vehicle and had no Hovereigenschaften.

In Korea, Wing Ship Technology has developed a ground-effect hovercraft called the WSH-500, intended for passenger transport . The WSH-500 is 29.1 m long, 27.2 m wide and 7.5 m high. It can carry 50 passengers and has a cruising speed of 180 km / h with a range of around 1000 km. A larger ground-effect hovercraft for 150 passengers is being planned.

literature

Michael Halloran, Sean O'Meara: Wing in Ground Effect Craft Review . Commonwealth of Australia , February 1999 ( seaphantom.com [PDF; 9.1 MB ] Study on History and Perspectives from the Royal Melbourne Institute of Technology ).

Web links

Commons : Ground Effect Vehicle - Collection of Images

French site about Ekranoplane

Russian Aviation Page: Ekranoplans ( Memento from August 22, 2010 in the Internet Archive )

Julian Edgar: Between Wind and Waves: Ekranoplans. (English)

Photos of the Lun at englishrussia.com: outside view , inside view

Photos of the Beriev WWA-14 , a Soviet experimental aircraft with ground effect properties, at englishrussia.com: exterior view , interior view

Caspian Sea Monster - The Caspian Sea Monster , Part 1/3 , Part 2/3 , Part 3/3 - Documentation about the probably largest Ekranoplan KM , video, 24:57 min. (English)