Helicopter flight principle

Helicopter is mainly composed of airframe, lift (including rotor and tail rotor), power and transmission system and airborne flight equipment. The rotor is generally driven by a turboshaft engine or a piston engine through a mechanical transmission system consisting of a transmission shaft and a reducer, and can also be driven by the reaction force generated by the jet from the tip of the blade. At present, there are mechanically driven single-rotor helicopters and double-rotor helicopters in actual use, of which single-rotor helicopters have the largest number.

The maximum speed of a helicopter can reach more than 300km/h, the dive limit speed is nearly 400km/h, the use ceiling can reach 6000m (the world record is 12450m), and the general range can reach about 600 ~ 800 km. The range of internal and external auxiliary fuel tanks can reach more than 2000 kilometers. Helicopters have different takeoff weights according to different needs. At present, the largest heavy helicopter put into use in the world is the Russian Mi -26 (with a maximum takeoff weight of 56t and a payload of 20t).

The outstanding feature of helicopter is that it can do low altitude (a few meters above the ground), low speed (starting from hovering) and the nose direction remains unchanged, especially suitable for small-area vertical take-off and landing. Because of these characteristics, it has broad uses and development prospects. In the military field, it has been widely used in ground attack, aircraft take-off and landing, weapons delivery, logistics support, battlefield rescue, reconnaissance patrol, command and control, communication, anti-submarine mine clearance, electronic countermeasures and so on. Used for short-distance transportation, medical rescue, disaster relief and lifesaving, emergency rescue, lifting equipment, geological exploration, forest protection and fire fighting, aerial photography, etc. The transportation of people and materials between offshore oil wells and bases is an important aspect of civil use.

At present, compared with airplanes, helicopters have higher vibration and noise levels, greater maintenance workload, higher use cost, lower speed and shorter flight range. The future development direction of helicopters is to improve these aspects.

Brief history of helicopter development

Bamboo Dragonflies in China

China's bamboo dragonfly and Italian Leonardo da Vinci's helicopter sketches provided inspiration for the invention of modern helicopters and pointed out the correct thinking direction. They are recognized as the starting point of the history of helicopter development.

Bamboo dragonfly, also known as flying snail and "China gyro", is a strange invention of our ancestors. Some people think that there were bamboo dragonflies in China in 400 BC, and another conservative estimate is that it was in the Ming Dynasty (AD 1400). This kind of folk toy called bamboo dragonfly has been passed down to this day.

Although modern helicopters are thousands of times more complicated than bamboo dragonflies, their flight principles are similar to those of bamboo dragonflies. The rotor of modern helicopter is like the blade of bamboo dragonfly, the rotor shaft is like the thin bamboo pole of bamboo dragonfly, and the engine that drives the rotor is like the hand that rubs the bamboo pole hard. The leaves of bamboo dragonfly are blunt at the front and sharp at the back, and the upper surface is relatively round and the lower surface is relatively straight. When the airflow passes through the upper surface of the circular arch, the speed is fast and the pressure is small; When the airflow passes through the flat lower surface, its velocity is slow and its pressure is high. Therefore, a pressure difference is formed between the upper surface and the lower surface, and an upward lift force is generated. When the lift is greater than its own weight, the bamboo dragonfly will fly. Helicopter rotors generate lift for the same reason as bamboo dragonflies.

The Encyclopedia Britannica records that this kind of "helicopter toy" named "China Gyro" was introduced to Europe in the middle of15th century, that is, before Leonardo da Vinci drew the helicopter design with propeller and rotor.

The ninth volume of The Concise Encyclopedia of Britain wrote: "Helicopter is one of the earliest flying ideas of human beings. For many years, people have always thought that Dada first put forward this idea. Finch, but now we all know that China made helicopter toys earlier than medieval Europeans. "

A painting by Leonardo da Vinci in Italy

Italian Leonardo da Vinci put forward the idea of helicopter in 1483 and drew a sketch.

At the end of 19, an imaginary picture of a helicopter drawn by Leonardo da Vinci in 1475 was found in Milan Library, Italy. This is a huge spiral body, made of pulped linen, which looks like a huge screw. It is powered by a spring, and when it reaches a certain speed, it will take the body into the air. The driver stands on the chassis and pulls the wire rope to change the flight direction. Westerners say this is the earliest blueprint for helicopter design.

Man's first helicopter

1August 907, Frenchman Paul? Kearney developed a full-scale manned helicopter, which was successfully tested in June of the same year 165438+ 10/3. This helicopter is called "the first human helicopter". The helicopter named "Flying Bicycle" not only left the ground 0.3 meters by its own power, but also flew vertically for 20 seconds, realizing free flight.

The helicopter developed by paul cornu has two rotors, the main structure is a V-shaped steel pipe, and the fuselage is composed of a V-shaped steel pipe and six star-shaped blades, which are reinforced with steel cables to increase the rigidity of the frame structure. The 24 horsepower Antainette engine and the operator seat are installed in the middle of the V-shaped frame. The fuselage is 6.20 meters long and weighs 260 kilograms. A pair of rotors with a diameter of 6 meters are installed at both ends of the V-shaped frame, and each rotor has two blades.

The world's first helicopter with a successful test flight.

1938, Hannah Reich, a German girl, performed a perfect flight show in Berlin Stadium with a twin-rotor helicopter. This helicopter is considered by the helicopter industry to be the first successful helicopter in the world.

1936, after improving the early helicopters in many ways, Fokker Company of Germany publicly demonstrated its own FW-6 1 helicopter. 1 year later, this helicopter created many world records. This is a large twin-rotor tandem helicopter with a fuselage similar to that of a fixed-wing aircraft, but without a fixed wing. Its two rotors are supported on the upper right and left by two groups of thick metal frames respectively, and the two rotors are horizontally installed on the top of the bracket. The plane shape of the blade is sharp, and it is connected with the hub through flapping hinge and dragging hinge. The automatic tilter is used to tilt the rotor rotation plane for longitudinal control, and the yaw control is realized by tilting the two rotors in different directions. The total pitch of rotor blades is fixed, and the rotor tension is changed by changing the rotor speed. Use rudder and horizontal tail to increase stability. FW6 1 Rotor hub is equipped with a periodic pitch changing device, which can change the blade pitch during the rotor rotation. There is also a pitch control lever, which can change the inclination of the rotor surface and realize the flight direction control. FW6 1 ensures its maneuvering flight through this set of periodic range-changing devices and joysticks. The diameter of the rotor of the plane is 7 meters. The power unit is a piston engine with power 140 horsepower. This is the first helicopter with normal maneuverability in the world. The speed of the aircraft is 100 ~ 120km, the range is 200km, and the takeoff weight is 953kg.

The first practical helicopter

1939 Spring, Igor, USA? Sikorsky completed all the design work of VS-300 helicopter and built a prototype in the summer of the same year. This is a single-rotor helicopter with a tail rotor. Equipped with a three-blade rotor with a diameter of 8.5m and a Shuang Ye tail rotor. Its fuselage is welded steel pipe structure, and the transmission device consists of V belt and gear. The landing gear is rear three-point, and the cockpit is fully open. The power plant is an air-cooled engine with four cylinders and 75 horsepower. This single-rotor helicopter configuration with tail rotor has become the most common helicopter configuration at present.

Since the first tethered flight, Sikorsky has continuously improved the VS-300 and gradually increased the engine power. 1940 On May 13, VS-300 made its first free flight, when a 90-horsepower Franklin engine was installed.

The world's first helicopter put into mass production.

R-4 is a two-seat light helicopter developed by Walter Sikorsky Company in the 1940s. It is a 1 helicopter put into mass production in the world, and it is also the first military helicopter used by the US Army Air Force, Navy, Coast Guard, British Air Force and Navy. The company numbers of this machine are VS-3 16 and VS-3 16A. The number of the US Army Air Force is R-4, and the number of the US Navy and Coast Guard is HNS- 1. The British Air Force named it "syrphid fly" 1(Hoverfly 1), and the British Navy named it "gadfly". Early piston engines and wooden paddle helicopters

From the 1940s to the mid-1950s, it was the first stage of the development of practical helicopters. Typical aircraft types in this period are: S-5 1, S-55/H- 19, Bell 47; Soviet Mi -4 and Ka-18; Bristol, England-171; Czech HC-2 and so on. Helicopters in this period can be called the first generation helicopters.

Bell 47 is a single-engine light helicopter developed by American Bell Helicopter Company. The development work started at 194 1, and the testing machine bell 30 started at 1943. It was renamed as Bell 47, 1945, and obtained the airworthiness certificate of CAA on March 8, 2006. The machine is a seesaw rotor, single rotor and tail rotor layout, with two blades. There is a stabilizer bar under the rotor, which is at right angles to the blades. Ordinary automatic turning machine can operate the change of total pitch and periodic pitch. All-metal tail rotor with two blades at the back of the tail beam.

Ka-18 is a single-engine dual-rotor light multi-purpose helicopter designed by Kamov Design Bureau of the Soviet Union. /kloc-0 made its first flight in mid-1957, and put it into mass production shortly thereafter. Two pairs of three-blade axial flow rotors with opposite rotating directions are adopted, and the blades are made of wood. Install 1 9-cylinder star piston engine with 275 horsepower. The fuselage is welded steel pipe structure, light metal skin and hard shell tail beam. The cockpit can accommodate 1 pilot and 3 passengers. With four-wheel landing gear, the front landing gear wheel can rotate freely.

The helicopter at this stage has the following characteristics: the power source is a piston engine, with low power, low specific power (about 1.3 kW/kg) and low specific capacity (about 247.5 kg/m3). The life of rotor blades with wood or steel-wood mixed structure is short, about 600 flight hours. The airfoil of the blade is symmetrical, the tip is rectangular, and the aerodynamic efficiency is low. The rotor lift-drag ratio is about 6.8, and the rotor efficiency is usually 0.6. The machine body structure adopts all-metal frame type, and the empty weight accounts for a large proportion of the total weight, about 0.65. There is no necessary navigation equipment, only a single-function visual flight instrument, and the communication equipment is electronic tube equipment. Poor dynamic performance, low maximum flight speed (about 200 km/h), vibration level of about 0.25g, noise level of about 1 10 dB, and poor ride comfort. Turbine shaft engine and metal blade helicopter

The mid-1950s to the late 1960s was the second stage of the development of practical helicopters. Typical aircraft types at this stage are: S-6 1 from the United States, Bell 209/AH- 1, Bell 204/UH- 1, Mi -6, Mi -8, Mi -24 from the Soviet Union, and SA32 1 "Super. During this period, special armed helicopters began to appear, such as AH- 1, Mi -24 and so on. These helicopters are called the second generation helicopters.

The helicopter at this stage has the following characteristics: the first generation turboshaft engine is used as the power source. The power generated by turboshaft engine is much higher than that of piston engine, which greatly improves the performance of helicopter. The specific power of the first generation turboshaft engine is about 3.62 kW/kg, and the specific capacity is about 294.9 kW/m3. Helicopter rotor blades have developed from wood and steel-wood mixed structure to all-metal blades, and their service life has reached 1200 flight hours. The blade profile is asymmetric, the blade tip is simply sharpened and swept back, and the aerodynamic efficiency is improved. The lift-drag ratio of the rotor reaches 7.3, and the rotor efficiency is improved to 0.6. The machine body structure is all-metal thin-walled structure, and the ratio of empty weight to total weight is reduced to about 0.5. Energy-absorbing landing gear and damping seat are adopted. The fuselage shape began to streamline to reduce aerodynamic drag. The helicopter cockpit began to be arranged in series, which made the fuselage narrow. The performance is obviously improved, the maximum flight speed reaches 200 ~ 250km/h, the vibration level is reduced to about 0. 15g, and the noise level is 100 dB, which improves the ride comfort.

Third generation helicopter

The 1970s and 1980s were the third stage of helicopter development, with typical models as follows: American S-70/UH-60 Black Hawk, S-76, AH-64 Apache, Soviet Ka -50 and Mi -28, French SA365 Dolphin and Italian A65438+.

At this stage, specialized civil helicopters appeared. In order to deeply study the aerodynamics of helicopters, special helicopter research machines (such as S-72 and Bell 533) were designed and manufactured. Countries compete to develop special armed helicopters, which promotes the development of helicopter technology.

At this stage, the helicopter has the following characteristics: the turboshaft engine developed to the second generation and changed to the free turboshaft structure, so it has better speed control characteristics and improved starting performance, but its acceleration performance is not as good as that of the fixed-axis structure. The weight and volume of the engine are reduced, and the life and reliability are improved. The fuel consumption of a general engine is 0.36kg/kWh, which is similar to that of a piston engine. Rotor blades are made of composite materials, and their service life is much longer than that of metal blades, reaching about 3600 hours. The airfoil is no longer used for reference from fixed-wing aircraft, but is specially developed for helicopters, that is, the airfoil with two-dimensional curve change. The tip of the blade is parabolic and swept back. Elastic bearings are widely used in wheel hubs, some of which are hinged. Efficient and safe ducted tail rotor has been applied to tail rotor. The rotor lift-drag ratio is about 8.5, and the rotor efficiency is improved to about 0.7. The substructure of the airframe is also made of composite materials, and the ratio of composite materials to the total weight of the airframe is usually about 10%, and the ratio of empty weight to the total weight of the helicopter is generally 0.5. For military helicopters, especially armed helicopters, the requirements of bullet resistance and crash resistance are put forward. The US military put forward MIL-STD- 1290, which has become the design standard of military helicopters. In order to meet these standards, military helicopters adopt crew armor protection, and specially design crash-resistant landing gear, seat and fuel system. The electronic system has developed to a semi-integrated type. Helicopters use large-scale integrated circuit communication equipment, integrated autonomous navigation equipment, integrated instruments, electronic and mechanical hybrid control mechanisms, etc. The electronic equipment on the ship is connected through a bidirectional digital data bus, through which information can be sent and received. The helicopter adopts the mixed layout of local integrated cockpit. The use of the first generation night vision system enables helicopters to fly at night. This advanced semi-integrated electronic equipment significantly increases the communication distance, navigation distance and accuracy of the helicopter, reduces the number of instruments, reduces the workload of pilots, and enables the helicopter to fly on the ground and under bad weather/night conditions, thus improving the overall performance of the helicopter. The dynamic performance is obviously improved. The lift-to-drag ratio of the helicopter reaches 5.4, the vibration level of the whole helicopter is about 0. 1g, the noise level is lower than 95dB, and the maximum flight speed reaches 300 km/h. ..

Modern helicopter

The 1990s is the fourth stage of helicopter development, and an armed reconnaissance helicopter with stealth design, which integrates vision, acoustics, infrared and radar, appeared. Typical models are: American RAH-66 and S-92, international cooperation Tiger, NH90 and EH 10 1 etc. , known as the fourth generation helicopter.

The helicopter at this stage has the following characteristics: it adopts the third generation turboshaft engine. Although this engine still adopts the free vortex shaft structure, it adopts the advanced digital control system and automatic monitoring system of the engine, and is integrated with the airborne computer management system, which has remarkable technical progress and comprehensive characteristics. The fuel consumption of the third generation turboshaft engine is only 0.28kg/kWh, which is lower than that of the piston engine. Its representative engines are T800, RTM322 and RTM390. The blade is made of advanced composite materials such as carbon fiber and Kevlar, and its life is infinite. There are many new blade tip shapes, among which BERP blade tips with parabolic swept back and forward swept back are more prominent. The common characteristics of these new blades are that they can weaken the compressibility effect of the blades, improve the aerodynamic load distribution of the blades, reduce the vibration and noise of the rotor and improve the aerodynamic efficiency of the rotor. Spherical flexible bearingless hub has been widely used. The hub shell and the blade connection part are made of composite materials, which makes the structure more compact and greatly reduces the weight and resistance. The lift-drag ratio of the rotor reaches 10.5, and the rotor efficiency is 0.8. At this stage, the tailless reaction torque system has the advantages of good control response characteristics, small vibration and low noise, and there is no need for tail transmission shaft and tail deceleration, which greatly reduces the number of parts, thus improving maintainability. Composite materials are widely used in helicopters as never before. Helicopters began to use composite main structures, and the application proportion of composite materials increased greatly, usually accounting for 30~50% of the weight of fuselage structure. During this period, the empty/total weight ratio of civil helicopters was about 0.37. Highly integrated electronic equipment. Computer technology, information technology and intelligent technology have been applied in helicopters, and helicopter electronic equipment is developing in a highly integrated direction. During this period, the helicopter has adopted advanced stabilization and control devices, replaced the conventional control system with telex and optical transmission control, adopted advanced strapdown inertial navigation, satellite navigation equipment and integrated navigation technology, advanced communication, identification and information transmission equipment, advanced fire control equipment such as target identification, aiming and weapon launch, advanced electronic countermeasures equipment, and adopted bus information transmission and data fusion technology, which are developing towards sensor fusion. The onboard electronics, fire control and flight control systems are connected through redundant digital data buses to realize information sharing. Adopt multifunctional integrated display technology. A small number of multifunctional displays are used to replace a large number of single instruments, and the flight information of helicopters is displayed through keyboard control. Information such as communication, navigation, flight control, friend-or-foe identification, electronic countermeasures, system monitoring and weapon fire control is integrated by the central computer. The use of this advanced integrated electronic equipment greatly simplifies the layout of the helicopter cockpit and instrument panel, simplifies the system components and greatly reduces the weight. More importantly, it greatly reduces the workload of pilots and improves the quality and performance of helicopters. The lift-to-drag ratio of the whole machine reaches 6.6, the vibration level is reduced to 0.05g, the noise level is less than 90 dB, and the maximum speed can reach 350 km/h. ..

The flight principle of helicopter

There is a big propeller on the helicopter head and a small propeller at the tail. The small propeller is used to counteract the reaction force generated by the large propeller. The helicopter engine drives the rotor to provide lift and lift the helicopter into the air. The rotor can also drive the helicopter to tilt and change direction. The propeller speed affects the lift of the helicopter, so the helicopter can take off and land vertically.

/Li jianjiang 123/blog/item/54d 7a 2 db 07 179665d 1 164e 6 f . html

Maneuvers in the horizontal plane, such as acceleration and deceleration, hovering, turning, horizontal "8" maneuver, snake maneuver, etc. ;

Maneuvers in the vertical plane, such as jumps and dives;

Space three-dimensional maneuvers, such as hovering descent, combat turning, turning and turning in jumping.

These actions are simple stunts. Among the complex stunts, there are somersaults, tumbling, Lan Wieseman stunts and some other stunts, such as flying backwards. Under certain conditions, these stunts can be done on some types of helicopters. In addition, according to the characteristics of helicopter movement, maneuvering flight can be divided into two types: stable and unstable, and the acceleration remains constant, which is called stable maneuvering, such as stable hovering; Variable acceleration maneuver is called unstable maneuver. The following analysis of several typical maneuvers. The following analysis of several typical maneuvers.

Horizontal linear acceleration maneuver

When the speed increases, the fuselage resistance also increases. In order to keep the same acceleration, it is necessary to increase the blade inclination angle and rotor tension. If not, the helicopter's level flight acceleration will be reduced to zero, and the helicopter will level flight at a higher flight speed.

Horizontal turn

Suppose the helicopter turns to the right at a certain speed and height, that is, the so-called horizontal turn with equal height and constant speed. In this case, the lateral inclination of the paddle is 17.3 degrees, and the rotational tension is increased by 5%. At this time, the vertical component of the rotor tension balances the gravity of the helicopter, and the normal overload is equal to L keeping the altitude unchanged. The horizontal component of the rotor tension points to the right, and a lateral overload of 0.3 1 1g is obtained, which is the lateral force required for the helicopter to turn horizontally.

Vertical maneuvering flight

Vertical maneuvering flight usually needs to change altitude, speed, total distance, flight attitude and radius of curvature. Assuming that the helicopter flies in a circle in the vertical plane, it is called vertical somersault; See the figure below. In order to simplify the analysis, it is assumed that the helicopter speed remains constant during the somersault, and the helicopter is only affected by gravity (this assumption is actually impossible because there are other forces). When the radius and speed remain unchanged (see the left figure below), it shows that the centripetal force of the helicopter remains unchanged. At the bottom of the somersault, gravity and rotor tension are in opposite directions; When going up and down vertically, gravity is perpendicular to the pulling force; At the top of the somersault, gravity and tension are in the same direction. This clearly shows that the pulling force generated by the rotor needs to be constantly changed in order to keep the centripetal force unchanged and point to the center of the circle. When the helicopter is at the bottom of the somersault, the rotor must produce three times the weight of the helicopter, and the blades should be tilted forward 28.5 degrees or backward 24.5 degrees. Such a requirement is difficult for most helicopters.