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Australian Hovercraft. Hoverflight 30 Composite. 1992
Australian Hovercraft. Hoverflight 25 Trail able Aluminium. 1992
Worlds First Wing in Ground Effect Marine Craft fully surveyed to IMO Rules. Manufactured in Australia. Picture provided by new owners in Singapore.
The FS8 should already be appointed a thrifty, environmentally friendly successor of the seaplanes in the Maldives Islands since 2003. Why the machines then weren't acquired despite a great announcement in the Maldivian media anyway is unknown. Probable isn't the FS8 sufficiently fit to fly at only 2m of altitude over the high swell between the atolls anyway.
The Dragon Commuter is an extremely high speed, highly efficient marine vessel. Registered, operated and maintained at typically low marine craft overheads. The FS8 lifts totally clear of the water surface to ride a self-generated airwave at speeds above 55 knots. The primary function of the FS8 is for economical, over water transportation in tropical regions of the world of either 2 crew plus 8 passengers or 2 crew plus 840 kgs payload. The Dragon Commuter is only available to commercial operators with certified crews trained at the Flightship Training School (FTS).
By virtue of a Flightship's aerodynamic design, sustainable free flight is not possible above ground effect. Under United Nations International Maritime Organisation (IMO) legislation, ground effect craft are recognised universally as marine vessels for construction, insurance, operator licensing and registration requirements. The purchase and operating costs are therefore considerably less than traditional aircraft, while still being able to travel at a speed comparable to a light aircraft.
The Dragon Commuter has a maximum water surface clearance capability of up to 2 metres over the crests of 2 metre waves. A range of up to 300 nm, a cruising speed of 170 km/h (86 knots) is achievable and the range reserves are over 4 hours of operation. The FS8 is moulded and fabricated from low maintenance FRP composites. Waterborne propulsion is provided by silent, retractable electric thrusters in the wing tip floats. Maximum external noise emission in the cruise mode is 75 dBA at 100 metres. This is far less than a heavy diesel truck @ 90 dBA on the highway or a jet aircraft taking off at 125 dBA.
All design and construction details for every craft built are under International Shipping Registry Classification with Germanischer Lloyd. Crew training and operating safety standards for the FS8 are based on IMO HSC high speed code operational standards. This ensures the highest levels of quality are rigidly maintained in every phase of production. Standard equipment provided with the FS8 includes SOLAS life jackets, life rafts, flares, VHF radio, depth sounder, ECDIS and computer navigation system, GPS, radar transponder, 15nm MARPA forward looking radar, pitch and roll alarm presets, altimeter, air speed indicator and full cabin air conditioning to tropical capabilities.
Ground effect is still the most efficient form of powered flight known to man. The Wright brothers used ground effect when they flew their first aircraft the 'Flyer' in 1903. It took a further six years for the brothers to find an engine big enough and light enough to lift the same aircraft out of ground effect into free flight. When an aerodynamic wing is close to a ground plane, such as water, lift is increased by as much as 45% and induced drag decreased by up to 70%. This is vastly different to normal operation of an aircraft wing in free flight away from the ground. The main benefits when a craft is operating within ground effect are that speed, payload and fuel economies are considerably more efficient than with traditional boat, plane and helicopter transport. Span dominated ground effect results in a reduction of induced drag (D). Chord dominated ground effect results in increased lift (L). The overall effect of both span and chord dominated effects is an increase of the L/D ratio.
Technical data, stand May 2004
Movies of this craft can be e-mailed to interested people.
typical cruising speed of the PBY was 100 to 120 miles per hour or 90 knots.
cruise at 50 to 70 knots. The
aircraft had an enormous range and loitering capability with an over all range
from 2,500 to 2,900 miles and a service ceiling of 15,000 to 22,400 feet. The
PBY is a large high wing monoplane with a total wingspan of 104 ft. and a total
wing area of 1,400 square feet. The aircraft measures in at 63 feet 10 inches
and has a gross weight of 31,800 pounds to 36,000 pounds.
Wing in Ground Effect Aircraft. Built and proven for military.
Phanto m Works
concept for a colossal cargo aircraft designed to skim a few metres above the
surface of the ocean has been revealed by researchers at the aerospace company
concept aeroplane, called the Pelican Ultra Large Transport Aircraft (ULTRA),
would exploit an aerodynamic phenomenon known as the "wing-in-ground
effect" to glide just six metres above the waves.
on top of a cushion of air, the airplane would experience 70 per cent less drag
than a normal plane and could therefore travel further using the same amount of
152 metres from nose to tail and with a wingspan of 109 metres, the Pelican
ULTRA would be the largest plane to ever fly - if it is built. The world's
largest existing plane, the Russian Antonov 225, is 84 metres long. The Pelican
ULTRA is designed to carry 1400 tonnes of cargo over a distance of 16,000
kilometres in one journey.
wing-in-ground effect occurs at an altitude equivalent to 10 to 25 per cent of
the wing's width at the point where it joins the fuselage. The effect increases
the ratio of lift to drag for a wing. The phenomenon has been investigated for a
wide variety of aeroplanes in the past because it offers potentially large cost
land, the Pelican UTLRA would travel at a more conventional altitude of 6000
metres or more.
of strategic development for Boeing Advanced Airlift and Tankers, adds:
"Cruise altitude will be adjusted according to sea state, and if the seas
get too rough, the Pelican can easily climb to high altitude to continue the
at Phantom Works, the Boeing research department responsible for Pelican ULTRA,
say the airplane could have numerous military and commercial users. It could
carry 17 tanks at ten times the speed of any container ship.
Pelican ULTRA has been proposed as part of a military transport project and
positive conclusions from the US Army's Advanced Mobility Concepts Study, due in
2003, could set the stage for development.
All pictures below are kits from Universal Hovercraft. Go to www.hovercraft.com
These are Wing in Ground Effect Hovercraft. (WIG)
Buy Plans and components from www.hovercraft.com
Follow this link to the wig page
Wing In Ground effect aerodynamics
Ever since the beginning of manned flight pilots have experienced something strange when landing an aircraft. Just before touchdown it suddenly feels like the aircraft just does not want to go lower. It just wants to go on and on due to the air that is trapped between the wing and the runway, forming an air cushion. The air cushion is best felt in low wing aircraft with large wing areas. This phenomenon is called (aerodynamic) ground effect. The Wright brothers probably have not even flown out of ground effect in their early flights, they benefited from ground effect without even knowing it existed.
Around 1920 this effect was first described and some (theoretic) research was carried out in this field (e.g. ref.840). From that time on pilots knew ground effect and sometimes even used it on purpose. The seaplane Dornier DO-X could only cross the Atlantic when it was flying with its hull just above the wave crests. In the second World War pilots knew that when they lost an engine or fuel on the way back from the enemy that they could reach home by flying just a few metres above the sea, thus needing less power and saving fuel.
Dornier Do X
From Wikipedia, the free encyclopedia
The Dornier Do X was a German flying boat that was the largest aircraft in the world when it was produced. Only three were made—two served with Italy (the X2 and X3) until 1934 and the other was destroyed during World War II while on display at a Berlin museum. While not a commercial success, the Dornier Do X was one of the most impressive aircraft of all time.
Two phenomena are involved when a wing approaches the ground. Ground effect is one name for both effects which is sometimes confusing. These two phenomena are sometimes referred to as span dominated and chord dominated ground effect. The former results in a reduction of induced drag (D) and the latter in an increase of lift (L). The designations span dominated and chord dominated are related to the the fact that the main parameter in span dominated ground effect is h/b (height/span), whereas in chord dominated ground effect it is h/c (height/chord).
Span dominated ground effect
When aeronautical engineers mention ground effect they usually mean span dominated ground effect. The drag of an aircraft can be split up into different contributions. The two main sources of drag are called friction drag and induced drag. As the name suggests the friction drag is caused by friction between the air and the skin of the craft and is therefore dependent on its wetted area. Induced drag is sometimes also called lift induced drag because it is the drag due to the generation of lift. When a wing generates positive lift the static pressure on the lower side of the wing is higher than on the upper side. The average pressure difference times the surface area of the wing is equal to the lift force. At the wingtip there is a complication: the high pressure area on the lower side meets the low pressure area on the upper side therefore the air will flow from the lower side to the upper side, around the wingtip. This is called the wingtip vortex. These vortices are found with all aircraft in flight, sometimes they are visible at an air show: when an fighter flies at a high angle of attack, the water in the air condenses in the low pressure vortex and you see two curled lines extending backwards from the wingtips. The energy that is stored in those vortices is lost and is experienced by the aircraft as drag.
The amount of induced drag is dependent on the span wise lift distribution and the aspect ratio of the wing. A high aspect ratio wing has lower induced drag than a low aspect ratio wing since its wingtip vortices are weaker. That is because the rest of the wing is "further away" from the tip so that the high and low pressure areas at the tip are smaller.
There is not enough space for the vortices to fully develop when a wing is approaching the ground. Therefore the amount of "leakage" of pressure from the lower side is less and the vortices become weaker. The vortices are also pushed outward by the ground, apparently the effective aspect ratio of the wing becomes higher than the geometric aspect ratio. This is a common way to account for span wise ground effect. Wieselsberger has (theoretically) found this in the 1920's by applying Prandtls lifting line theory (ref.201). From this theory it follows that induced drag reduces to approximately 50% at a ground clearance of 10% of the wingspan.
Chord dominated ground effect
As described above, ground effect increases lift. The air cushion is created by high pressure that builds up under the wing when the ground is approached. This is sometimes reffered to as ram effect or ram pressure. When the ground distance becomes very small the air can even stagnate under the wing, giving the highest possible pressure, pressure coefficient unity.
The high pressure air cushion can clearly be seen in the illustrations. The pressure around an airfoil has been calculated with and without ground effect, both at a five degree angle of attack. In free air the (2D) lift coefficient was 0.8 and at a ground clearance of 0.05 times the chord it was 1.1. The high pressure at the bottom of the airfoil in ground effect is caused by the ram effect. The nose suction peek is also somewhat more pronounced in ground effect, which indicates that separation is likely to occur at the nose. This has been confirmed by wind tunnel tests.
Ground effect not always increases lift. It is possible under certain conditions that lift reduces when an airfoil approaches the ground. This is the case when the bottom of the foil is convex and the angle of incidence is low, in that case a venturi is created between the foil and the ground where high-speed low-pressure air sucks the airfoil down. This is illustrated with 2D calculation results below. This venturi-type ground effect, albeit more extreme, is used by race car designers to make it "stick" to the road at high speeds.
The combined result of the two phenomena described above is an overall increase of the ratio between the lift and the drag (L/D). The lift increases when the ground is approached and because of the increasing lift the induced drag may not even decrease in absolute numbers, but even a slight increase still leads to an increased L/D ratio.
The L/D ration is commonly used to express the efficiency of a vehicle. When a vehicle is in stationary motion its weight is equal to its lift and its propulsive thrust is equal to its drag, therefore the L/D ratio is an expression for the amount of weight that can be carried with a certain amount of thrust. The higher this ratio, the higher its efficiency and the lower its fuel consumption (for a given weight). As the L/D of a wing increases with decreasing ground clearance the craft becomes more efficient in ground effect.
The maximum L/D of a transonic airliner in high-altitude cruise flight approaches 20 and small subsonic turboprop commuter aircraft may be around 15. Already in the early sixties Lippisch showed that in ground effect higher values could be reached, hisX-112 achieved an L/D value as high as 23 in ground effect flight.
Ever since the very first experimental WIG boats have been built in the nineteen-thirties, longitudinal stability has been recognised as a very critical design factor. When not designed properly WIG boats show a potentially dangerous pitch up tendency when leaving (strong) ground effect. Powerboats sometimes show the same tendency, when they meet a wave or a wind gust they may suddenly flip backwards.
The reason for this behaviour is the fact that the working line of the lift vector of a wing is located relatively far aft at very small ground clearances and moves forward when climbing out of ground effect. The stability problem can be overcome by installing a relatively large horizontal tail and although a WIG boat cannot be stabilised by c.g. movement alone, the location of the c.g. is very important for achieving acceptable longitudinal stability. A more in depth explanation is found in thetheory section.
Some wing plan forms are more stable than others, the reversed delta from Lippisch proved to be very good, therefore it has been very popular lately (e.g. in the Airfisch series craft). Not only the plan form, but also the wing section is important for stability. Recent research showed that wing sections with an S-shaped camber line are more stable than conventional wing sections. Many new designs have such an S-foil.
Ground effect wing sections
So far not many wing section families have been designed especially for operation in ground effect. The designers of WIG boats sometimes just utilised one of the commonly known wing sections for aircraft for their WIG designs, such as the NACA sections. A very popular wing section used to be the Clark Y section, because of its flat bottom, which was assumed to be good in ground effect. More recent and advanced WIG designs always have wing sections that have been optimised for that specific craft.
Aerodynamicists tend to think of wing sections in terms of a camber line and a thickness distribution. For aircraft that operate in free air this makes sense, but in ground effect the shape of the lower side of the wing is very important. In many cases designers opt for a flat lower side because a convex lower side may in certain situations lead to suction at the lower side, either hydrodynamic or aerodynamic. A concave bottomed wing section leads to very poor longitudinal stability: it further exaggerates the abovementioned pitch up tendency.
An example of a recent airfoil that was developed specifically for use in ground effect is the DHMTU family of airfoil sections. These allow tuning of upper and lower side separately. Both the DHMTU and NACA 4 digit sections can be studied with theAirfoil Calculator of this site.
Although the design of the upper side is less important than the lower side, here also some general rules apply. The nose radius of the profile must not be too small because that may lead to very early separation in strong ground effect. Furthermore an S-shaped camber line is favourable for stability, so with a given (non S-shaped) bottom this leads to a very pronounced S-shaped upper side.
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