Principle of flight
Ordinary fixed-wing aircraft flight buoyancy originates from the wings fixed on the fuselage. When a fixed-wing airplane flies forward, the relative motion of the wings and the air generates buoyancy toward the upside. The buoyancy of a helicopter comes from the same principle; however, the wings on a helicopter are not fixed to the airplane and move forward with it; instead, they rotate on top of the airplane. So the "propeller" on a helicopter is actually a rotating wing, properly called a "rotor". While the rotor provides buoyancy, it also causes the airplane and the rotor to rotate in opposite directions and must be balanced by opposite forces. Most helicopters use a small propeller or fan at the tail to push in the opposite direction, while some newer helicopters rely on air blowing out of the tail to counterbalance the thrust generated by the wall effect, which has the advantage of significantly reducing noise and avoiding the possibility of damage to the tail rotor, thus improving the safety of the aircraft. Some of the larger helicopters use rotor blades that rotate in different directions to counteract each other's rotational forces on the fuselage.
History
Mankind has longed for the freedom to fly since the dawn of time. Ancient myths tell the story of man's early dreams of flight, which were all about rising up in the air, free-flying like a modern helicopter, hovering in the air, and landing on a spot at will. For example, the flying carpets of the Arabs and the chariots of the Greek gods were vertical take-off and landing vehicles. However, they only existed in myths and stories, and the scientific and technological level of that era was too low to create a manned flying machine, so it can be said that it was a period of human flight fantasy. Even in this period of fantasy, the basic idea of the helicopter was created, and the principles of the modern helicopter were demonstrated. The most valuable and representative ones are the ancient Chinese toy "bamboo dragon" and the painting of the Italian Leonardo da Vinci. The most valuable and representative are the ancient Chinese toy "Bamboo Dragon" and the paintings of the Italian Leonardo da Vinci.
The history of the bamboo dragonfly is well documented in the Jin Dynasty (265-420' AD). It was written by Ge Hong in the book "Hug Park Zi". It utilizes the aerodynamic force of a propeller to achieve vertical lift, demonstrating the basic working principle of a modern helicopter rotor. Volume 9 of the Concise Encyclopedia Britannica writes: "The helicopter was one of the earliest human visions of flight, and for many years it was believed that the first person to come up with the idea was Leonardo da? Vinci, but it is now known that the Chinese made helicopter toys before medieval Europeans." The toy traveled to Europe in the 14th century, bringing with it the Chinese creation. The Europeans studied and developed it as an aerial vehicle. "
The father of British aviation, "George? Kelly (1773-1857) had made several bamboo dragonflies, using clockwork clockwork as the power to drive the rotation, the flight altitude had reached 27m. With the development of productive forces and the progress of human civilization, the history of the development of helicopters from the period of fantasy into the period of exploration. After the industrial revolution in Europe, the mechanical industry rapidly emerged, especially the development of automobiles and ships at the beginning of this century, which prepared engines and propellers for flying machines. After the aviation pioneers brave and hard creation and testing, in 1903 the Wright (Wright) brothers created a fixed-wing aircraft skidding takeoff success. During this period, although he put a lot of hard work and effort in the development of helicopters, but due to the complexity of helicopter technology and poor engine performance, its successful flight more than 30 years later than the airplane.
The early 20th century was a period of exploration in the development of the helicopter, with a variety of experimental models being introduced. The diversity of experimental aircraft programs demonstrated the technical immaturity of the exploratory phase. After years of practice, only the longitudinal and ****-axis bi-rotor types of these programs were retained and are still in use today. The twin-rotor transverse scheme was not continued in the family of helicopters, but was inherited and developed in the tilt-rotor/wing-type vertical take-off and landing vehicle.
The Russian Yuliev took a shortcut by proposing a design that used the tail rotor to equalize rotor counter torque and built a test machine in 1912. The single-rotor helicopter with tail rotor became the most popular form to date, accounting for more than 95 percent of the world's helicopters.
After the early 20th century efforts to explore for the development of helicopters has accumulated valuable experience and made significant progress, a number of test aircraft to achieve a short vertical lift and short flight, but from the practical is still a long way to go.
The development of the aircraft industry has led to a rapid improvement in the performance of aero-engines, providing important conditions for the success of the helicopter. The first breakthrough in rotor technology, thanks to the Spaniard Ciervao he in order to create "no stall" aircraft to solve the safety problems of fixed-wing aircraft, the use of self-rotating rotor instead of the wing, the invention of rotorcraft. The successful application and development of rotor technology on rotorcraft provided another important condition for the birth of the helicopter.
August 1907, the Frenchman Paul? Kearney developed a full-size manned helicopter, and on November 13 of the same year, a successful test flight. This helicopter was called "the first human helicopter". In 1938, a young German, Hannah Reich, flew a twin-rotor helicopter in a perfect air show at the Berlin Stadium. This helicopter is considered by the helicopter industry to be the world's first helicopter to be successfully flown. In 1936, the German company Fokker, after making many improvements to the earlier helicopter, publicly demonstrated the FW-61 helicopter of its own making, which set a number of world records a year later.
In the spring of 1939, Igor Sikorsky of the United States? Sikorsky completed all the design work for the VS-300 helicopter and built a prototype in the summer of the same year. This single-rotor helicopter configuration with tail rotor became the most common helicopter configuration today.
In the 1940s, the U.S. Walter Sikorsky Company developed a 2-seat light helicopter, the R-4, which was the world's first helicopter to go into mass production, and the first military helicopter used by the U.S. Army Air Corps, the Navy, the Coast Guard, and the U.K. Air Force and Navy. The helicopter's company number was VS-316, VS-316A, the U.S. Army Air Corps' number was R-4, the U.S. Navy's and Coast Guard's number was HNS-1, the British Air Force named it the Gophers Gadfly 1 (Hoverfly1), and the British Navy named it the Gadfly. "Gadfly" (牛虻).
By the late 1930s, helicopters had been successfully flown in France, Germany, the United States and the Soviet Union, and were rapidly improved to the point where they were practical. The military needs of World War II accelerated this process, pushing helicopter development from the exploratory phase into the practical phase, and helicopters began to be put into production lines. By the end of World War II, German factories had produced more than 30 helicopters, and the United States delivered more than 400 R5 and R6 helicopters.
The second half of the 20th century helicopters into the aviation utility period, the helicopter's field of application continues to expand, the number of rapidly increasing. So far there have been tens of thousands of helicopters ten served in various sectors of the national economy and military field. Until today, after more than 100 years of unremitting efforts of mankind, helicopter technology technology breakthroughs, so that its application effectiveness and flight performance continue to improve, so as to be more suitable for the expansion of the use of the technology is also gradually tending to mature.
In the 1990s, helicopter development entered a completely new stage, the emergence of visual, acoustic, infrared and radar integrated stealth design of armed reconnaissance helicopters. Typical models are: the U.S. RAH-66 and S-92, international cooperation "Tiger", NH90 and EH101, etc., these new helicopters are also known as the fourth generation of helicopters. The helicopters of this period adopt advanced engine full digital control system and automatic monitoring system, and are integrated with on-board computer management system. Its important characteristics are the use of advanced stabilization and control devices, the use of electric and optical transmission manipulation instead of conventional manipulation systems, and the use of highly integrated electronic equipment. Computer technology, information technology and intelligent technology. At the same time, the helicopter electronic equipment toward highly integrated direction. Advanced Jetlink inertial guidance, satellite navigation equipment and combined navigation technology, advanced communication, identification and information transmission equipment, advanced target identification, targeting, weapons launch and other fire control equipment and advanced electronic countermeasures equipment, the use of bus information transmission and data fusion technology, and is developing in the direction of sensor fusion. On-board electronics, fire control and flight control systems are interconnected through redundant digital data buses, realizing information **** enjoyment. Multi-functional integrated display technology is used, with a small number of multi-functional displays instead of a large number of individual instruments, through the keyboard control display helicopter flight information, the use of central computers for communication, navigation, flight control, enemy identification, electronic countermeasures, system monitoring, weapons fire control information for integrated processing and thus integrated control. The use of such advanced integrated electronic equipment greatly simplifies the helicopter cockpit layout and instrument panel layout, system components have been simplified, the weight is greatly reduced. More importantly, it greatly reduces the pilot's workload and improves the helicopter's aircraft quality and performance.
Classification
Single-rotor tail rotor helicopter
The most common type of helicopter, a horizontal rotor is responsible for providing the lift of the aircraft, and a small vertical propeller is responsible for counteracting the rotor's reaction force. Representative models: the Mi-26 transport helicopter developed by the Soviet Union's Miri Design Bureau and the AH-64 helicopter gunship developed by McDonnell Douglas of the United States.
Single Rotor Tail Rotorless Helicopter
One horizontal rotor is responsible for providing lift and blowing air out of the tail to counteract the rotor's reaction force with thrust generated by the wall effect. Representative model: MH-6 helicopter produced by McDonnell Douglas in the United States.
Twin-rotor helicopter
Longitudinal
The two rotors are arranged longitudinally in the front and rear, rotating in the opposite direction, mostly seen in large transport helicopters. Representative model: CH-47 "Chinook" transport helicopter made by Boeing.
*** Shaft type
Two rotors are arranged on the same shaft, and there is no tail rotor, the advantage is good stability, but the technology is complex, so it is less common. Representative model: Kamov Design Bureau of the Soviet Union developed the card-50 helicopter gunship.
Side-rotor helicopter
Also known as the tilt-rotor helicopter, a mixed-technology helicopter that combines the characteristics of both fixed-wing aircraft and helicopters. The helicopter takes off with horizontally juxtaposed twin rotors, and in flight rotates the rotors 90 degrees forward into two true propellers, following the pattern of a normal fixed-wing aircraft. The advantage of doing so is that it can reduce flight resistance and increase flight speed, the highest can be more than 600 kilometers per hour, while saving fuel and improving range, the disadvantage is that the structure is complex, high failure rate, and thus extremely rare. Representative model: the United States Bell and Boeing jointly manufactured V-22 transport helicopter.
--------- -wmj007 finishing --------
< p>(a) A brief history of the development of helicoptersChina's Bamboo Dragonfly
China's Bamboo Dragonfly and the Italian Da? Finch's sketches of helicopters provided inspiration for the invention of the modern helicopter and pointed out the right direction of thinking, and they are recognized as the starting point of the history of the development of helicopters.
The bamboo dragonfly, also known as the flying spiral and the "Chinese gyro", is a strange invention of our ancestors. Some people believe that bamboo dragonflies existed in China in 400 B.C. Another, more conservative estimate is that it was during the Ming Dynasty (around 1400 A.D.). These folk toys called bamboo dragonflies have been passed down to the present day.
Modern helicopters, though millions of times more complex than bamboo dragonflies, have similar principles of flight. The rotor of modern helicopter is just like the blade of bamboo dragonfly, the rotor shaft is just like the thin bamboo stick of bamboo dragonfly, and the engine that drives the rotor is just like our hands rubbing the bamboo stick. The blade of a bamboo dragonfly is rounded at the front and sharp at the back, the upper surface is rounded and arched, and the lower surface is flat and straight. When the airflow passes through the upper surface of the arch, the flow rate is fast and the pressure is small; when the airflow passes through the lower surface of the straight, the flow rate is slow and the pressure is large. So the upper and lower surfaces of the formation of a pressure difference between the upper and lower surfaces, will produce an upward lift. When the lifting force is greater than its own weight, the dragonfly will rise up into the air. The helicopter rotor generates lift for the same reason as the bamboo dragonfly.
The Encyclopedia Britannica states that this "helicopter toy," known as the "Chinese gyroscope," was invented in the mid-15th century when Leonardo da Vinci was drawing the screw rotor. The Encyclopedia Britannica states that this "helicopter toy," known as the "Chinese gyro," arrived in Europe in the mid-1500s, before Leonardo da Vinci drew up his design for a helicopter with a screw-on rotor.
Volume 9 of the Concise Encyclopedia Britannica states, "The helicopter was one of the earliest of man's visions of flight, and for many years it was believed that Da Vinci was the first to conceive of the idea, but it is now known that Da Vinci was the first to develop the idea. Vinci, but it is now known that the Chinese made helicopter toys before medieval Europeans."
Drawing by Leonardo da Vinci, Italy
Italian Leonardo da Vinci came up with the idea of a helicopter and sketched it in 1483.
An imaginary drawing of a helicopter drawn by Leonardo da Vinci in 1475 was found in the Milan library in Italy in the late 19th century. It was a huge spiral made of sized linen that looked like a giant screw. It spins on spring power and when it reaches a certain speed, it takes the body into the air. The pilot stood on the undercarriage and pulled on a wire rope to change the direction of flight. Westerners say this was the earliest blueprint for helicopter design.
Humanity's first helicopter
In August 1907, Frenchman Paul? Kearney developed a full-size manned helicopter and successfully flew it on November 13th of the same year. This helicopter is known as the "first human helicopter". The helicopter, called the "Flying Bicycle," not only left the ground 0.3 meters under its own power and completed vertical liftoff, but also flew continuously for 20 seconds, realizing free flight.
Paul Kearney's helicopter is equipped with two helicopters. Kearney developed a helicopter with two rotor blades, the main structure of a V-shaped steel tube, the fuselage consists of a V-shaped steel tube and six steel tubes composed of star-shaped parts, and the use of steel cables to strengthen to increase the rigidity of the frame structure.V-shaped frame in the middle of the installation of a 24-horsepower Antainette engine and the operator's seat. The fuselage was 6.20 meters long and weighed 260 kilograms, with a pair of 6-meter diameter rotor blades at each end of the V-frame, each with two blades.
The world's first successful helicopter test flight
In 1938, a young German girl, Hannah Reich, piloted a twin-rotor helicopter in a perfect flight performance at the Berlin Stadium. The helicopter is considered by the helicopter community to be the world's first successful test flight.
In 1936, the German company Fokker, after making many improvements to earlier helicopters, publicly demonstrated its FW-61 helicopter, which set several world records a year later. This is a fuselage similar to fixed-wing aircraft, but no fixed wing of the large twin-rotor transverse helicopter, its two rotor with two sets of thick metal frame to the upper right and upper left respectively, the two rotor rotors are mounted horizontally on the top of the bracket. The rotor blades are pointed in planform and are attached to the hub with waving and oscillating hinges. Longitudinal maneuvering is performed by tilting the rotor rotating plane with an automatic tilt, and yaw maneuvering is achieved by tilting the two pairs of rotors in different directions. The total pitch of the rotor blades is fixed and the rotor pull is varied by changing the rotor speed. The rudder and horizontal tail are utilized to increase stability, and the FW61 rotor hub is equipped with a cyclic pitch device to change the pitch of the rotor blades during rotor rotation. There is also a joystick to change the pitch of the blade to change the tilt of the rotor surface to realize the flight direction control.The FW61 relies on this set of cycle pitch device and joystick to ensure its maneuvering flight. The rotor diameter is 7 meters. The power plant was a 140 hp piston engine. This is the world's first helicopter with normal maneuverability. It has a speed of 100 to 120 kilometers per hour, a range of 200 kilometers and a take-off weight of 953 kilograms.
The first practical helicopter
In the spring of 1939, Igor K. Sikorsky of the United States completed the construction of the VS-VS-1 helicopter. Sikorsky completed all the design work for the VS-300 helicopter, and a prototype was built in the summer of the same year. This is a single-rotor helicopter with a tail rotor, equipped with a three-bladed rotor, rotor diameter of 8.5 meters, the tail is equipped with a two-bladed tail rotor. The fuselage is a welded steel tube structure with a V-belt and gears for the transmission. The landing gear is of the rear three-point type, and the pilot's cockpit is fully open. The power plant is a four-cylinder, 75-horsepower, air-cooled engine. This single rotor with tail rotor helicopter configuration has become the most common helicopter configuration today.
Since the first tethered flight, Sikorsky has continued to improve the VS-300, gradually increasing the power of the engine. the VS-300 made its first free flight on May 13, 1940, with a 90-hp Franklin engine.
The world's first helicopter to enter mass production
The R-4 was a 2-seat light helicopter developed by the U.S. Walter Sikorsky Company in the 1940s, and was the world's first helicopter to enter mass production, as well as the first military helicopter used by the U.S. Army Air Corps, the Navy, the Coast Guard, and the British Air Force and Navy.
The aircraft's company number is VS-316, VS-316A. The U.S. Army Air Corps number is R-4, the U.S. Navy and Coast Guard number is HNS-1, the British Air Force will be named "Gophers Gadfly" 1 (Hoverfly1), the British Navy named it as the "Gadfly". "Gadfly" (Gadfly).
Early piston-engined and wooden-blade helicopters
In the 1940s to the mid-1950s was the first stage of the development of practical helicopters, the typical types of aircraft in this period are: the United States of America's S-51, S-55/H-19, Bell 47; the Soviet Union's Mi-4, Ka-18; the United Kingdom's Bristol-171; the Czech Republic's HC-2 and so on. The helicopters of this period can be called the first generation helicopters.
The Bell 47 is a single-engine light helicopter developed by Bell Helicopter, the development began in 1941, the test aircraft Bell 30 began flying in 1943, and was renamed Bell 47 in 1945, and was awarded the Certificate of Airworthiness by the U.S. Civil Aeronautics Administration (CAA) on March 8, 1946, which was the world's first civil helicopter to obtain an airworthiness certificate. The aircraft was a single rotor with a tail rotor layout and a two-bladed blade seesaw rotor. There are stabilizer bars under the rotor at right angles to the blades. A common auto-tilt allows total and cyclic pitch maneuvering. An all-metal tail rotor with two paddles is located behind the tail beam.
The Ka-18 is a single-engine, twin-rotor***axial light utility helicopter designed by the Kamov Design Bureau of the USSR, which flew for the first time in mid-1957, and went into batch production shortly thereafter. It has two sets of 3-bladed ****shaft rotor blades rotating in opposite directions, and the blades are of wooden construction. It is equipped with a 275-hp nine-cylinder star-piston engine. The fuselage is a welded steel tube structure with a light metal skin and a hard-shell tail beam. The cockpit can accommodate one pilot and three passengers. Four-wheeled landing gear is used, and the front landing gear wheels can be freely steered.
The helicopters at this stage were characterized by the following features: the power source was a piston engine, which had low power, low specific power (about 1.3 kilowatts per kilogram) and low specific volume (about 247.5 kilograms per meter3). Rotor blades of wood or mixed steel and wood construction were used, with a short life span of about 600 flight hours. The rotor blade wing type is symmetrical wing type, the tip is rectangular, the aerodynamic efficiency is low, the rotor lift-to-drag ratio is about 6.8, the rotor efficiency is usually 0.6. The body structure adopts the all-metal frame type, the empty weight and the total weight ratio is large, about 0.65. There is no necessary navigation equipment, only a single function of the visual flight instrumentation, the communication equipment is the electronic tube equipment. Dynamic performance is poor, the maximum flight speed is low (about 200 km/h), the vibration level is about 0.25g, the noise level is about 110 dB, and the ride comfort is poor.
Turboshaft-engined and metal-blade helicopters
The mid-1950s to the late 1960s was the second phase of practical helicopter development. Typical models in this phase are: the U.S. S-61, Bell 209/AH-1, Bell 204/UH-1, the Soviet Union's Mi-6, Mi-8, Mi-24, the French SA321 "Super Wasp" and so on. Specialized helicopter gunships, such as the AH-1 and Mi-24, began to appear during this period, and these helicopters became known as second-generation helicopters.
The helicopters of this stage were characterized by the following features: the power source began to use the first generation of turboshaft engines. The turboshaft engine produced much more power than the piston engine, which greatly improved the helicopter's performance. The specific power of the first-generation turboshaft engine is about 3.62 kW/kg, and the specific volume is about 294.9 kW/m3. Helicopter rotor blades were developed from wood and steel-wood hybrid structures to all-metal blades with a life span of 1,200 flight hours. The rotor blade airfoil is asymmetric, the blade tip is simply pointed and swept back, the aerodynamic efficiency is improved, the rotor lift-to-drag ratio reaches 7.3, the rotor efficiency is increased to 0.6. The fuselage structure is an all-metal, thin-walled structure, the ratio of the empty weight to the total weight is reduced to around 0.5. Vibration-damping energy-absorbing landing gear and seats have been adopted. The fuselage shape began to consider streamlining to reduce aerodynamic drag. The helicopter cockpit began to be arranged in longitudinal rows, resulting in a narrower fuselage. Performance improved significantly, with maximum flight speeds reaching 200~250 km/h, vibration levels reduced to about 0.15g, noise levels at 100 dB, and ride comfort improved.
Third-generation helicopters
The 1970s to 1980s is the third stage of helicopter development, the typical models are: the U.S. S-70/UH-60 "Black Hawk", S-76, AH-64 "Apache
The third phase of the aircraft is characterized by the US S-70/UH-60 "Black Hawk", S-76, AH-64 "Apache", the USSR's KA-50, Mi-28, the French SA365 "Dolphin", and Italy's A129 "Mongoose".
At this stage, specialized civil helicopters appeared. In order to study the aerodynamics of helicopters and other issues, this time also designed and manufactured specialized helicopter research aircraft (such as the S-72 and Bell 533). Countries competing to develop specialized armed helicopters, promoting the development of helicopter technology.
This stage of the helicopter has the following characteristics: turboshaft engine development to the second generation, changed to a free turboshaft structure, so it has better speed control characteristics, improved starting performance, but acceleration performance is not as good as the fixed-shaft structure. The weight and size of the engine was reduced, and both life and reliability were improved. Typical engine fuel consumption is 0.36 kg/kWh, about the same as a piston engine. The rotor blades are made of composite materials, and their life is substantially improved over metal blades, to about 3,600 hours. The airfoils are no longer borrowed from fixed-wing aircraft, but are specially developed for helicopters, i.e., the two-dimensional curve change airfoils. The paddle tips are parabolically swept back. The hub of the paddle widely uses elastic bearings, and some of them are hingeless. The tail rotor has begun to use the culvert tail rotor with high efficiency and safety. The rotor lift-to-drag ratio reaches about 8.5, and the rotor efficiency is improved to about 0.7. The sub-structure of the fuselage is also made of composite materials, and the proportion of composite materials in the total weight of the fuselage is usually about 10%, and the ratio of empty weight/gross weight of the helicopter is usually 0.5. For the military helicopters, especially the helicopter gunships, the anti-bombing and crash-resistant requirements have been put forward. The U.S. military has proposed the military helicopter crashworthiness standard MIL-STD-1290, which has become the design standard for military helicopters. To meet these standards, military helicopters have adopted crew armor protection and specially designed crash-resistant landing gear, seats and fuel systems. Electronic systems have evolved to a semi-integrated type. Helicopters use large-scale integrated circuit communications equipment, integrated autonomous navigation equipment, integrated instrumentation, and hybrid electronic and mechanical maneuvering mechanisms. The electronic equipment on board rely on a two-way digital data bus interconnection, through which information can be transmitted and received. The helicopter has a partially integrated cockpit in a hybrid arrangement. The use of a first generation night vision system gives the helicopter night flight capability. This more advanced semi-integrated electronic equipment allows the helicopter to significantly increase the communication range, navigation distance and accuracy, reduce the number of instruments, reduce the pilot's workload, and provide the helicopter with the ability to maneuver/stick-to-the-ground flight as well as flight in unfavorable meteorological/nighttime conditions, which improves the overall performance of the helicopter. Dynamic performance has been significantly improved. The helicopter has a lift-to-drag ratio of 5.4, an all-aircraft vibration level of about 0.1 g, a noise level of less than 95 dB, and a maximum flight speed of 300 km/hr.
Modern helicopters
The 1990s is the fourth stage of helicopter development, the emergence of visual, acoustic, infrared and radar integrated stealth design armed reconnaissance helicopters. Typical models include the U.S. RAH-66 and S-92, international cooperation "Tiger", NH90 and EH101, etc., known as the fourth generation of helicopters.
This stage of the helicopter has the following characteristics: the use of the 3rd generation of turboshaft engines, this engine is still using the free turboshaft structure, but the use of advanced engine all-digital control system and automatic monitoring system, and with the on-board computer management system integrated together with a significant technological advances and comprehensive characteristics. The fuel consumption rate of the 3rd generation turboshaft engine is only 0.28 kg/kWh, which is lower than that of the piston engine. Its representative engines are T800, RTM322 and RTM390. the paddles are made of carbon fiber, Kevlar and other advanced composite materials, and the life of the paddles reaches infinite. The new propeller tips come in a wide variety of shapes, the more prominent ones being parabolic swept-back and swept-forward and swept-back again BERP tips. These new tips have the *** same characteristics that can weaken the compressive effect of the tip, improve the aerodynamic load distribution of the blade, reduce the vibration and noise of the rotor, and improve the aerodynamic efficiency of the rotor. Ball flexible and bearingless paddle hubs are widely used, and the connecting parts of the paddle hub shell and the paddle blades are made of composite materials, which makes the structure more compact, the weight greatly reduced, and the drag greatly reduced. The rotor lift-to-drag ratio reaches 10.5, and the rotor efficiency is 0.8. At this stage, a tail rotorless counter-torque system is applied, which has the advantages of good maneuvering response characteristics, low vibration, low noise, and does not need a tail drive shaft and tail reduction, so that the number of parts is greatly reduced, thus improving maintainability. Composite materials are being used in helicopters on an unprecedented scale. Helicopters began to use composite main structures, and the proportion of composite material applications rose dramatically, usually accounting for 30 to 50% of the weight of the airframe structure. Civilian helicopters of this period had an empty weight/gross weight ratio of about 0.37. Highly integrated electronic equipment. Computer technology, information technology and intelligent technology have been applied to helicopters, and helicopter electronic equipment has developed in the direction of high integration. The helicopters in this period adopt advanced stabilizing and increasing control devices, replace the conventional manipulation system with electric and optical manipulation, adopt advanced Jetlink inertial guidance, satellite navigation equipment and combined navigation technology, advanced communication, identification and information transmission equipment, advanced target identification, aiming, weapon launching and other fire control equipment and advanced electronic countermeasure equipment, adopt bus information transmission and data fusion technology, and are developing in the direction of sensor fusion. On-board electronics, fire control and flight control systems are interconnected through redundant digital data buses, realizing information **** enjoyment. Multi-functional integrated display technology is adopted, with a small number of multi-functional displays instead of a large number of individual instruments, displaying helicopter flight information through keyboard control, and utilizing the central computer for integrated processing of information on communication, navigation, flight control, enemy identification, electronic countermeasures, system surveillance, weapon fire control, and thus for integrated control. The use of such advanced integrated electronic equipment greatly simplifies the helicopter cockpit layout and instrument panel layout, system components have been simplified, the weight is greatly reduced. More importantly, it greatly reduces the pilot's workload and improves the helicopter's aircraft quality and performance. The helicopter's overall lift-to-drag ratio reaches 6.6, the vibration level is reduced to 0.05g, the noise level is less than 90 decibels, and the maximum speed can reach 350 kilometers per hour.
(ii)
Principle of Flight of Helicopter
The helicopter has a large propeller on the head and a small propeller on the tail, which is designed to counteract the reaction force generated by the large propeller. The helicopter's engine drives the rotor blades to provide lift and hold the helicopter in the air, and the rotor blades also drive the helicopter to tilt to change direction. The rotational speed of the propeller affects the lift of the helicopter, which enables it to take off and land vertically.
The Invention of the Helicopter
In 1939, the first helicopter was invented by an American named Seacors. The shape of the fuselage was not much different from that of the current one, and it is still being used by designers.
Use of helicopters
Helicopters are widely used because they have many advantages that are difficult or impossible to do with other vehicles. Helicopters are mainly used for sightseeing and tourism, fire rescue, maritime emergency, anti-smuggling and anti-narcotics, firefighting, business transportation, medical assistance, communications, and spraying pesticides and insecticides to eliminate pests, detecting resources, and other sectors of the national economy. resources, and other sectors of the national economy. The world's helicopter team is gradually growing.