Wing In Ground Effect

Dehradun Institute OF TechnologyWing In Ground EffectPME-657

NameAmit kumar singhBranch Mechanical EngineeringYearFinal year

Table of ContentsIntroduction3History4Theory5Lift and Drag6Geometry7Ground Effect8Chord Dominated Ground Effect (CDGE)9Span Dominated Ground Effect (SDGE)10Pitching Moment11Effect of Height above the Ground12Effect of Different Wing Sections12Efficiency Benefits Compared to Aircraft13Comparison to Water Borne Craft13Design14Wing Planform and Cross-section15Wing Dimensions15Tail Plane16Take off and Landing17Engine18Fuselage18Benefits of WIG Effect19Disadvantages of WIG Effect19Applications of WIG Craft20Recent developments20Conclusion23References24

Introduction The wing in ground effect is a phenomenon that creates an increase in lift experienced by an aircraft as it approaches the ground for landing, when vortices of air become trapped between the wings of the aircraft and the ground creating a cushion effect. The wing in ground (WIG) effect is a phenomenon that affects all aircraft in some way. Ground may refer to not only land, but also water, ice, snow and sand. The effects of the wing in ground effect can be beneficial or detrimental to the aircraft. Wing in ground effect craft is more efficient than regular aircrafts.

History Aerosledge No. 8 First functional ground effect craft developed during in 1935 by a Finnish engineer , Toivo J Kaario. In 1960s USA, USSR and Germany started experimenting with WIG crafts. Ekranoplan Russian built WIG crafts Among the largest WIG crafts ever built Utilized PAR-WIG (Power augmented ram wing in ground effect) Lippisch series of WIG crafts Designed be a German scientist Alexander Lippisch, initially built in America, later sold to a German company. 1963 X-112 Aerofoil boat , Single seat. 1970 X-113 Single seat with out of ground effect capability. 1977 X-114 Six seat. 1979, the Soviet built A-90 Orlyonok became one of the first WIG craft to be used for operational service for the Soviet Navy. In 1987, the Lun-class Ekranoplan was introduced by the USSR. This craft was equipped with missile launchers, designed for anti submarine warfare.

Theory Wing The most efficient design to produce lift. Wings generate lift because the movement of the wing through air results in a higher static pressure on the lower surface than on the upper surface. This difference in pressure results in an upwards force known as lift which allows the aircraft to overcome its weight force acting downwards. WIG aircraft however make use of the ground effect, which is the name given when a boundary occurs below and close to the wings lower surface. In practice, this boundary is the Earths surface either water or land. The presence of a boundary close to a wing results in Increased static pressure on the lower surface hence increasing the lift generated. As the efficiency of a wing is determined by the lift to drag ratio, the efficiency of a wing increases due to the ground effect.

Lift and Drag As a wing moves through air a resultant force in generated. This resultant force can be decomposed into lift (perpendicular to the free stream velocity) and induced drag (parallel to the free stream velocity). Other forms of drag are also present which are the result of friction as the aircraft moves through the air and are referred to collectively as parasitic drag. The total drag is the combination of both parasitic drag and the induced drag. Lift and drag can also be discussed in terms of geometry alone.

Geometry The geometry of the aerofoil being used can significantly alter the aerodynamic characteristics with a variation in angle of incidence. Thickness At slow speeds thick aerofoils will be used and at fast speeds relatively thin cross sections. Aspect ratio The ratio of the wing span divided by the chord length. Gives a measure of how much lift is generated at the wing tips. Higher the aspect ratio the more efficient the wing.

Aspect Ratios

Ground Effect Ground effect is caused by the presence of a boundary at small distances below a wing and its effect increases as the distance between the boundary and wing decreases. The boundary results in the flow around the wing being altered which causes an increase of lift and decrease of drag. This alteration can be considered to be the superposition of two separate effects Chord dominated ground effect (CDGE) Span dominated ground effect (SDGE) CDGE increases lift, and SDGE which is responsible for a reduction in drag.

Chord Dominated Ground Effect (CDGE) In CDGE the mechanism behind the change in the aerodynamic characteristics of the wing is the change in static pressure on the underside of the wing. This occurs because the total pressure in the flow field around the wing must remain constant. The total pressure is comprised of both dynamic pressure and static pressure and hence the sum of these two components must also remain constant. In the region between the wing and the boundary, the velocity of the air is decreased resulting in a reduction of the dynamic pressure in this region. Hence the decrease in dynamic pressure must result in an equal increase in the static pressure. The increase in static pressure is known as ram pressure and is what gives rise to the increase in lift generated by the wing.

Span Dominated Ground Effect (SDGE) In SDGE, the vortices are bounded by the ground and hence their strength is limited by the distance of the wings above the ground. Because of this reduction in strength of the vortex, the wing appears to have a higher effective aspect ratio than its geometric aspect ratio. The induced drag is inversely proportional to the aspect ratio, hence the ground effect results in decreased induced drag.

Pitching Moment As a wing moves through the air, the pressure distributions on both the upper and lower surfaces create a moment about the aerodynamic centre of the wing. This moment will cause the plane to pitch and hence is called the pitching moment. In order to keep the aircraft stable it is necessary to balance this moment which is generally achieved using additional lifting surfaces such as a canard or tailplane. In ground effect, the pressure distribution on the lower surface of the wing is altered which results in the aerodynamic centre of the wing changing position. This change of position changes the pitching moment produced by the wing and hence alters the moment which must be balanced in order to keep the WIG craft stable.

Effect of Height above the Ground The effects on an aircraft experiencing ground effect are generally height dependent. In order to predict the behaviour of WIG craft, three separate models are used, each within specified heights of the boundary. Zone 1 is up to a height of 20% the chord length and has a high level of constriction in the vertical direction. In zone 1 it is CDGE which dominates. Zone 3 is between a height of 1 chord length and 10 wing spans and is dominated by SDGE resulting in a marginal increase in efficiency compared to OGE flight. Zone 2 Between these two regions is zone 2 in which a combination of the two ground effects exists. During cruise, it is important to maximize the ground effect while maintaining a safe operation altitude above the boundary.

Effect of Different Wing Sections Wing section is the cross-sectional profile of a wing, the airfoil. There are a few aerofoils which have been designed to specifically exploit the ground effect. In order to do this the wings must possess the following characteristics Achieve high lift to drag ratios (high efficiency) over a range of altitudes, Have good stall characteristics in and out of ground effect The centre of pressure should not change significantly with height.

Efficiency Benefits Compared to Aircraft In theory it is possible to create WIG craft which have a higher efficiency to aircraft because of the increased lift to drag ratio. They also generally have the benefit of no take off or landing length restrictions which are imposed on aircraft. In theory WIG craft are capable of carrying larger payloads, having a increased range. However, before the theoretical benefits can be fully achieved it is necessary to address three key obstacles preventing WIG craft from doing so. Currently turbo prop and jet engines operate more efficiently at lower air temperatures which are located at higher altitudes. As Wig craft fly in close proximity with the Earths surface it is required that the hull be reinforced considerably more than conventional aircraft as collisions with waves or other obstacles will be more likely. In order to do this Increased structural weight will mean less payload can be carried The hull might not be as aerodynamic, increasing drag. In order to balance the pitching moment, more balancing surfaces such as tail planes or canards must be added. These surfaces also increase the structural weight and drag of the craft.

Comparison to Water Borne Craft The major advantage which WIG craft have over conventional waterborne craft is the potential for significantly increased travelling speeds. WIG craft are capable of carrying high payloads while travelling at high speeds and are also not very affected by high sea states. In fact high while high sea states may restrict the payload or range capabilities, there is no significant reduction in cruise speed. WIG craft are however limited from taking off or landing depending on the sea conditions which does restrict their operation.

Design A number of compromises are required in achieving an efficient design solution for WIG craft. The best solution will depend on the specifications required for the crafts operation. WIG aircraft have been categorized into three divisions according to their operational purpose. The divisions are: Type A: A craft which is certified for operation in ground effect. Type B: A craft which is certified to temporarily increase is altitude to a limited height outside the influence of the ground effect but not exceeding 150m above the surface. Type C: A craft which is certified for operation outside of the ground effect and exceeding 150m above the surface. Type A are incapable of flying out of the ground effect, they require a simpler design solution as they as they do not need to deal with the problem of variable stability. Type B is limited as it can only perform leaps to altitude compared to type C which can remain out of the ground effect. Type C operates in free air when out of the ground effect when in this mode the control and aerodynamics are the same as an aircraft.

Wing Planform and Cross-section The most common planform shape configurations are delta, rectangular, tandem and ram wing. The delta wing allows stable flight in ground effect. The advantage of the delta wing is it is self stabilising and is the main form of type B ground effect craft. There are two types of tandem wings a bi plane style and a canard style. The canard style design improves the take off efficiency as it creates an air cushion to lift the craft above the water at lower speed, thereby reducing water drag, which is the crafts biggest problem. The planform shape depends on the desired maneuverability and speed of the craft. There has been little research into the optimisation of cross sectional shapes specifically for ground effect flight, however one wing shape that has been designed for ground effect operation is the S section. Its name describes the shape of the camber line of the wing section and intends on reducing the large pitching moment generated. However such optimised sections have a detrimental effect during out of ground effect flight.

Wing Dimensions Span- Flight maneuverability is governed by the span length. A large span requires the aircraft to attain a higher altitude before making a turn to avoid contact with the water. Chord - The efficient height range for ground effect flight is largely dependent on the chord of the wing. A WIG craft design should have a relatively long chord length Aspect ratio In order to maintain the surface area they require a low aspect ratio. A better height range is achieved with a higher aspect ratio this however is a trade off for maneuverability.

Tail Plane A large tail plane is typically used to overcome the large pitching moment generated by the wing when flying in ground effect. The addition of a tailplane to maintain stability and control adds further drag and structural weight to the craft which decreases the overall efficiency. The larger the tailplane and further from the main body of the craft the greater the inefficiency. Ekranoplan The designers of the Ekranoplan decided to make the tailplane 50% of the area of the wing and position it outside of the ground effects. The advantage of this was that the aerodynamic characteristics did not alter with the height of the aircraft. However this design was extremely inefficient.

Take off and Landing Aircraft operating from water require much more thrust than those operating from land. WIG Aircraft must overcome the drag of the water during take off, which requires a considerable amount of thrust which can not be utilised in cruise. To reduce the amount of thrust required during take off and improve the overall take off performance, WIG craft could utilize Hydrofoils Partial hovercraft technology. Power augmentation ram effect or PAR. Using flaps or other aerodynamic devices The structural loads experienced during landing are not as critical as those during take off. However the impact loads experienced by the hull can be reduced by the development of hydrofoils.

Engine The operational performance is the major factor to be considered in the selection and placement of the engine. The takeoff phase requires the most thrust than any other phase of WIG craft. Hence this governs the placement, size and quantity of the engines. The type of engine used is determined by the amount of thrust required for take off and the desired operational speed. The most common engines that have been utilised in WIG craft are The Piston engine is used for low speed, low power and low altitude The turbo prop engine is used for higher power requirements at moderate speeds If high speeds are required for operation the jet engine is most efficient as they have a high thrust to weight ratio. For all engines it is necessary to have resistance to corrosion from the salt water environment, which can cause a compressor stall. The excess power required for take-off that cannot be used in cruise has two effects on the performance of the craft during cruise. The engines are forced to operate at an inefficient thrust level in cruise The engines may even be shut down which causes increased drag due to their windmilling.

Fuselage Since the craft flies at low altitude the fuselage is not required to be pressurised so designers are not restricted to a circular cross section shaped fuselage. The aircraft can be designed to hold large cargo which would dictate the shape of the fuselage which would not normally fit into a pressurised transport aircraft. The hull shape should be designed to minimise the drag through the water and hence the time taken to reach take off is reduced and increases the low speed performance of the aircraft.

Benefits of WIG Effect The primary benefits of the wing in ground effect come from the additional lift provided by this phenomenon. This lift allows the craft to remain airborne with less power required from the engine. This improves craft fuel efficiency and allows it to fly further and with a greater payload. This increased fuel and energy efficiency also makes a craft more environmentally friendly and less noisy. The close proximity of the craft with the ground also reduces lift induced drag. These benefits provide enormous potential for WIG craft to be used for high speed cargo transport. WIG craft could potentially do the job of a ship, only much faster since they dont experience water drag to the extent that ships do. Disadvantages of WIG Effect While the wing in ground effect is, for the most part, beneficial to aircraft, it does pose some dangers to regular aircraft and provides limitations to the design of WIG craft. Corrosion The craft will suffer extensive corrosive damage, particularly on load bearing structures, when flying close to sea level if its material is not sufficiently corrosion resistant. Require extensive maintenance Having exposed mechanical components of an aircraft, such as propellers. These components can be relatively fragile and vulnerable to water spray from the sea. This can lead to further aircraft damage. These factors result in the craft having a reduced reliability and greater perceived risk. Increased cost and structural weight due to Large engines to overcome water drag. Strengthened hull structure Large tail plane Pitch Instability Applications of WIG Craft There are many possible applications for WIG aircraft in both a civil and military sense. Large transport aircraft. Sea and rescue craft. Coastal guard operations. Small crafts can be used for commuters and light transport. Naval operations

Recent developments Research and development of WIG effect technology and vehicles is currently very active. Russia, China, Germany, and the USA are currently leading these developments. WIG effect vehicles are being developed for a variety of functions including passenger transportation, cargo ships, and for use as sports craft as well as for military applications. The recent projects in WIG crafts are Boeing Pelican - Designed primarily for long-range, transoceanic transport, the Pelican would fly as low as 20 feet above the sea and carry 1,400 tons of cargo. Airfish Commercial WIG craft based on Lippischs inverted delta wing design. WIG Train Developed in Japan. Train based on the WIG effect.

Boeing - Pelican

Intended as a large-capacity transport craft for military or civilian use, it would have a wingspan of 500 feet (150 m), a cargo capacity of 1,400 tons (1,300 metric tonnes), and a range of about 10,000 nautical miles (18,000 km). Powered by four turboprop engines, its main mode would be to fly 2050 ft (615 m) over water, though it would also be capable of overland flight at an altitude as high as 20,000 ft (6,100 m) albeit with a decreased range of about 6,500 nautical miles (12,000 km). It would operate from conventional runways, with its weight distributed over 38 fuselage-mounted landing gears with 76 wheels.

Airfish

WIG Train

Conclusion The benefits of the wing in ground effect have been known and exploited for many years. Yet the dangers and perceived risks of wing in ground flight have held back the design and evolution of WIG craft over many decades. To this day there is relatively little government funding into research and development of WIG craft. Previous developments in WIG craft design have largely problematic and plagued with accidents, yet the accomplishments that have been made have shown that the WIG effect has great potential and that WIG craft can be designed for practical applications. The ability to have the speed of a plane with the payload of a boat has the potential to revolutionize societys means of cargo transport, while the recreational potential of WIG craft remains appealing to many. Despite the troublesome development history of WIG craft and consequent withdrawal of large scale funding, great interest still exists in many aeronautical enthusiasts and academics, who continue to work in order make WIG craft performance acceptable so that they may one day become commercially feasible and successful.

References http://www.aerospaceweb.org/question/aerodynamics/q0130.shtml http://f1-dictionary.110mb.com/ground_effect_wing.html http://www.se-technology.com/wig/index.php http://en.wikipedia.org/wiki/Ground_effect_vehicle http://en.wikipedia.org/wiki/Ground_effect_(aircraft) Wing in Ground Effect Craft Review by Michael Halloran and Sean O'Meara Wing in Ground Effect (WIG) aircraft The University of Adelaide, Australia http://www.addington-barker.info/wing_in_ground_effects.php Between Wind and Waves: Ekranoplans , Skimming the sea at 400 km/h! , By Julian Edgar http://autospeed.com.au/A_111531/cms/article.html

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