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ЭКРАНОПЛАН: ДОВОДЫ «ЗА» И «ПРОТИВ»
Д. В. Телегин, Л. В. Фомин Научный руководитель - П. Р. Чирков Руководитель по иностранному языку - А. Н. Ефимова
Сибирский государственный аэрокосмический университет имени академика М. Ф. Решетнева
Российская Федерация, 660037, г. Красноярск, просп. им. газ. «Красноярский рабочий», 31
Е-mail: efimova.antonina2012@yandex.ru
Экранопланы имеют в основе технологию, использующую особый физический эффект, который позволяет двигаться над ровной поверхностью с очень небольшим расходом топлива при выходе на крейсерскую скорость. Экранопланы не стали надёжным транспортным средством, и не достигли коммерческого успеха из-за множества недостатков. Но они представляют оригинальное техническое решение, по-прежнему используются для местных пассажирских перевозок на прибрежных транспортных линиях, и возможно, у них есть будущее.
Ключевые слова: технология, воздушное судно, эффект экрана, функционирование, подъёмная сила, лобовое сопротивление, взлёт, расход топлива.
GROUND EFFECT AIRCRAFT: PROS AND CONS
D. V. Telegin, L. V. Fomin Scientific Supervisor - P. R. Chirkov Foreign Language Supervisor - A. N. Efimova
Reshetnev Siberian State Aerospace University 31, Krasnoyarsky Rabochy Av., Krasnoyarsk, 660037, Russian Federation Е-mail: efimova.antonina2012@yandex.ru
Ground effect vehicles use a technology based on a special physical effect allowing them to move above plain surfaces with low fuel consumption at cruising speed. Ground effect vehicles have not become a reliable means of transportation and have not achieved commercial success because of many drawbacks. But they present a specific technological solution, are still used locally by some coastal transportation lines, and may have a future.
Keywords: technology, aircraft, ground effect, operation, lift, drag, fuel consumption.
Ground effect vehicles are sometimes called a means of transportation, which is partially a plane and partially a boat. That is not true, as this type of craft by all its parameters belongs to the flying vehicle category. The idea of a boat persists due to the most common application of such vehicles - the operating variants are usually not large, and are based on (and take off) vast water surfaces. But actually, they can fly just as efficiently as a modern jet does in thin air at a height of 30,000 feet (9,144 meters), not necessarily above water. These craft have the potential to be faster than hydrofoil ships and trains, more efficient at lower speeds than commercial aircraft, and as amphibious as hovercraft. These features leave them seemingly well-positioned to fill in a substantial gap at the transportation market. Also, a vehicle that flies so low officially operates outside the bounds of airspace and the stringent regulations that govern it. Instead, it remains classified as a ship and is subject to maritime law, making it much cheaper to certify, craft and pilot.
Ground effect was originally observed in maritime birds flying close to the sea surface to travel longer distances with less effort. In World War II, German flight crews flew close to the sea surface to extend the range of their bombers, as well as presumably trying to avoid radar detection. RAF flight crews found empty Lancaster bombers difficult to land on short runways because of ground effect. The effect is caused by ground interference with airflow patterns around an aircraft when the aircraft is within one
Секция «Актуальные на учные проблемы в мире (глазами молодьш исследователей)»
wingspan of the surface. If the approach airspeed is too fast, the aircraft will tend to float down the runway, delaying touchdown. This applies to all fixed-wing aircraft, including sailplanes and superlight planes.
A wing generates lift, in part, due to the difference in air pressure gradients between the upper and lower wing surfaces. During normal flight, the upper wing surface experiences reduced static air pressure and the lower surface comparatively higher static air pressure. The air pressure pattern about an aircraft flying outside ground effect becomes almost cylindrical, with positive pressure below the wings and negative pressure above the wings. These pressure differentials are felt quite a distance from the airframe, and the cylinder of affected air has a diameter close to the wingspan of the aircraft. When the aircraft is close to the surface, the almost cylindrical vortex-induced circulation around the wing outside ground effect is modified by coming into contact with the surface. Flying close to a surface increases air pressure on the lower wing surface, nicknamed the "ram" or "cushion" effect, caused primarily by the ground interrupting the wingtip vortices and downwash behind the wing. This flattens the cylindrical circulation pattern and reduces the down-flow angle of the airflow behind the wing. The flattening on the circulation pattern spreads the pattern outwards below the wing, thus increasing both the effective span of the wing and its aerodynamic aspect ratio. The result is lower induced drag, which increases the speed and lift of the aircraft. While in the ground effect, the wing requires a lower angle of attack to produce the same amount of lift. The reduced induced drag requires less thrust in order to maintain the same velocity. Another important issue regarding ground effect is that the makeup of the surface directly affects the intensity; this is to say that a concrete or other smooth hard surface will produce more effect than water or broken ground.
The Soviet Central Hydrofoil Design Bureau was the first to design a balanced operating model of ground effect craft. The vehicle came to be known as an ekranoplan. Some manned and unmanned prototypes were built, ranging up to eight tons in displacement. This led to the development of a 550-ton military ekranoplan of 92 m (301 feet) length. "Caspian Sea Monster" was designed to travel a maximum of 3 m above the sea, but it was found to be most efficient at 20 m, reaching a top speed of 560 km/h; to 740 km/h in research flights. It had rectangular wings in combination with a large T-tail. The drawback with the rectangular lift wings is that the lift is concentrated to a line running across the vehicle, meaning it is a bit like flying a see-saw. This lack of longitudinal stability has occasionally caused incidents, such as the CM nose-diving into the water and an Orlyonok (a smaller craft) breaking into two. The lift to drag ratio also tended to be no better than a commercial aircraft, so this format has not found favour elsewhere.
Unfortunately, the obstacles standing in the way of success for ground effect vehicles are rather obvious. The reliance on ground effect for lift requires vast, unobstructed routes, whether over land or water. Over land, only sparsely inhabited and relatively flat regions in the Eurasian Steppe have been seriously considered as potential paths; routes over seas, lakes and wide rivers prove far more suitable. Take-off from water is a notoriously difficult maneuver. A wall of water forms in front of the vehicle's bow during the takeoff and has a tendency to stick to the hull's surfaces, adding unwanted dead weight during lift-off. Once the vehicle is on the move over water, waves continuously disrupt the craft's ability to maintain an altitude ideal for achieving maximal lift. Because of these challenges, a ground effect vehicle needs about two to three times more power for takeoff than it does for cruising. The additional weight of stronger engines and higher fuel consumption cuts deep into the craft's utility - and profitability - as a way of transporting cargo and passengers.
Existing vehicles, worked out mostly as a side-line products of different aircraft- and ship-building enterprises travel over medium distances of 300-800 kilometers (186-311 miles), both long enough to offset the effort of takeoff and short enough to reduce the utility of climbing to high cruising altitudes. Most of these routes exist over the world's river deltas, archipelagos and seas in Indonesia, Australia, Greece, the U.S. state of Alaska, the Persian Gulf, coastal mainland Southeast Asia and the Baltic states. But even there these vehicles are quickly outpaced by other, more successful transportation means - ferryboats, general aviation short-range planes, high-speed trains travelling through tunnels. Traveling over waves at high speeds also requires sturdy structural framing resistant to salt sprays, harbors for take-off and landing, and always favorable weather conditions. That is why the commercial usage of ground-effect craft, along with seaplanes and hovercraft, has never lead to profits and good income for the services. They still occupy very small niches at larger transportation markets, and their future usage seems to be limited to merely technical and special applications.
References
1. Scott J. (2003) Ground Effect and WIG Vehicles. Available at: http://www.aerospaceweb.org/ question/aerodynamics/q0130.shtml [29.02.2016].
2. Ekranoplan. Available at: http://www.moscowtopnews.com/?area=postView&id=886 [29.02.2016].
3. Ground effect vehicle history. Available at: http://www.rylandresearch.co.uk/ground-effect-vehicles/ground-effect-vehicle-history [18.02.2016].
4. WIG craft, a new word in aviation (2006). Available at: http://sputniknews.com/analysis/ 20060929/54377090.html [29.02.2016].
5. Ground Effect Vehicles: Adopting an Orphaned Technology (2015). Available at: https://www.stratfor.com/weekly/ground-effect-vehicles-adopting-orphaned-technology [18.02.2016].
© Телегин Д. В., Фомин Л. В., 2016
