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 Leonardo da Vinci was the first person to put forward this idea, but now it is known that China made helicopter toys earlier than Europeans in the Middle Ages. " 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. This aircraft is operated by four people. The spinning toys popular in Leonardo da Vinci's time may have inspired the great inventor's design. He proposed that vertical flight can be achieved by rotating the helicoid around the vertical axis. 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. In fact, Leonardo da Vinci said that his invention only provided a helicopter power, not a real working plane. Westerners say this is the earliest blueprint for helicopter design. Although modern scientists think that the "helicopter" designed by Leonardo da Vinci may never take off, this design is still one of his most famous inventions. Today, Leonardo da Vinci is still regarded as the originator of the concept of twin-rotor helicopter.

early stage

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.