КУРСОВАЯ РАБОТА
на тему
Milestones of flight In the 14th century Leonardo da Vinci foresaw the possibility of the man-made airplane and man-made helicopter. Man started with the non-power driven machines. A hot air balloon was the first vehicle to lift man from the surface of the Earth. The there appeared winged heavier-then-air craft. Yet, the achievement of man-directed flight came with the engine. The aerostatics of lighter-then-air activity has given way almost completely to the airplane. A first powered flight in a man-carrying airplane has been made by A. F. Mjaisky in 1884. It was 19 years before the Wright’s brothers flight. The Mojaisy and Wright airplanes led the way into the air age. These airplanes had all essential features of the modern airplane. However, it was to take many years* before the airplane developed into a successful, stable, controllable, highly maneuverable and reliable machine. The airplane has a long and varied history. The First World War stimulated the development of aviation and shoved the potential of the airplane. It was proved that the airplane could cover distances in shorter time than other methods of transportation could. Progress in aircraft design has been directed primarily at speed, and yet more speed. Speed and more speed in plane travel became the order of the day**. Aircraft speeds had made rapid advances. The maximum level of flight speed of a piston-propeller aircraft was 490 m. p. h. (M=0.64). Modern planes, however, travel at supersonic speeds: supersonic means any speed grated than that of sound, but hypersonic begins at M-5. (The Mach number (M) refers to the speed at which an aircraft is traveling in relation to the speed of sound.) So speed has become a main characteristic of aeronautical development. The demand for increased speed was met by many widely different developments. Research began to follow two lines: one which dealt with aerodynamics and the other with the power plant. Airplane designers were experimenting with new types of internal and external constructions: wing areas and front areas was reduced; streamlining was improved; external bracing was eliminated; undercarriages became retractable. The biplane using two horizontal systems connected by a series of struts and wires gave way to the high-wing monoplane and later to the low-wing monoplane. However air speed increases stem chiefly from engine research and development. Airplane speed has received great impetus with the advantage of the jet age. Jet propulsion had broken down most of the barriers*** to further advanced in the speed of the man-carrying vehicles. The advent of the jet had brought a new level of speed. This newest mode of transport comes almost to doubling the speed of earlier conventional aircraft. In the early 950s it was clear that the days of the piston-engined aircraft were numbered. It is easily understandable that any technological advance is accompanied by some difficulties. The new era of fast, high-flying jets brought with it great benefits, opportunities and challengers. Along the path of progress, the technical effort required has multiplied many times. This has resulted in the evolution of several airplane and engine designs to achieve the flight efficiency. Near the speed of sound the density of air is no longer**** constant of the compression of the air takes place in front of the airplane. The compressed air comes up against the airplane with shock. This result in a shock wave, representing a sharp ____ * it was to take many years – потребовалось много лет ** the order of the day – насущная задача *** barrier – препятствие **** no longer – больше не dividing line causing a sudden drop in the speed of airflow, and an increase in the ___ pressure and density of air. The airflow behind the shock wave becomes turbulent, as a result there is a lost of lift, increase of drag, change of trim, violent buffering and sometimes considerable pressure on the control surfaces. This has brought into being a new wing from, that of the jet’s sweptback wings. However, the sweptback wing is desirable under certain flight conditions but undesirable under others. At present there appeared delta-wing airplanes. With such wings the planes can fly several times faster then the speed of the sound. However, the delta-wing configuration gives rise to a number of aerodynamic complications at low speeds. Aircraft designers are seeking ways of changing the sweptback angle during the flight. At present the ever-increasing efforts in the development of variable-swept wings are strongly apparent. A plane with a variable-geometry wing combines contradictory qualities of planes with straight and swept wings. It has better flying characteristics in varying flying conditions: variable-swept wings provide high lift-to-drag ratios at both subsonic and supersonic speeds. The jet engine which brought the aircraft with the highest top speeds at the same time caused the most acute landing and approach problems. Takeoff was as much a difficulty. Designers found themselves facing the age old problem of giving higher top speeds without impossible landing characteristics. The problem was that of length of runways and landing strips. The runways were extended to lengths of three kilometers and more. Besides the high-speed aircraft requires a long, specially prepared runway. Much effort is being devoted by scientists, engineers and designers to the means whereby* they can somehow obtain the shortest takeoff and landing. All palliatives** had been tried. The tricycle undercarriage with its means of splitting the air from the main wings after touchdown, the wheel brakes, the airbrakes and the wing slots. These things were bringing with them new problems to be solved. Some advances thoughts were expressed about the possibility of aircraft commonly called VTOL***, that is, an aircraft which will land and take off without forward run. The idea was that of using thrust to obtain direct lift for a man-carrying vehicle. An associated plan was the use of vectored thrust. Vectored thrust means thrust that can be controlled and have its direction changed. It seems to offer a means of using the same engine both for the vertical takeoff and the vertical descent and for hovering and for forward propulsion. Thus the two vertical takeoff types will have either vectored thrust or direct jet lift. Recently there came into existence an aircraft with a short run. A short run type has a wing system which can be deployed in one certain manner for takeoff and for landing and in another different manner for high speed cruise. The new jet propulsion system gave rise to its own engine system problems, for ____ ____ * whereby – тем самым ** palliatives – средства, методы *** VTOL (Vertical Takeoff and Landing) – самолет с вертикальным взлетом и посадкой instance, the fuel consumption problem. Jet engines are good appetizers*. Fuel makes up a big part of modern jet airplane’s total gross weight. The largest jets have fuel tanks in the wings storing in excess of 21,000 gallons of fuel. The fuel required for takeoff, climb and acceleration represents an important 26% of the total fuel load. Thus nowadays the reduction of fuel consumption is problem number one because power-to-weight ratio of specific weight has always been and remains the critical factor in prime movers for aircraft. The scientist all over the world are trying to find an economic fuel. Some scientists speak of atomic planes that will circle the Earth eighty times on one pound of fuel. Nuclear energy for propulsion will go away** with a large bulk of fuel. Besides nuclear aircraft has three- or four-fold improvement in performance over the present day chemical aircraft. The first tests of nuclear-powered aircraft are no longer in the realm of the impossible though the practical difficulties of handing such a device are obvious. Increases in speed have offered many associated advantages, among them the possibility of escaping from the gravity of the Earth being the most important. However, no ordinary flying machines are of the use for space travel. Aircraft, of either old or new design, cannot operate except when they have air around them. Gas turbine engines cannot run outside the atmosphere. With the advent of the rocket engine it became possible. It was the rocket that broke the gravitational bonds which had held man to the Earth. The step into space from the airplane was a very large one indeed. Yet, it was aviation that gave the propulsion rocket its opportunities for full development. The first manned space flight was made on the 12th April 1961. It was Vostok 1 carrying Yuri Gagarin that introduced the era of manned space flight. That was a milestone of great and lasting significance. Nowadays different plans for a system of manned orbital bases, nuclear rocket for translunar and interplanetary journeys, and orbit-to-orbit propulsion system for shunting heavy payloads to different orbits are worked at. Recently the Space Shuttle has been called the keystone to the practical age of space travel. There is no doubt*** that its development represent the next great opportunity and challenge for mankind in the field of flight. * are good appetizers – потребляют много топлива ** will go away – избавит *** there is no doubt – нет сомнения
