Working principle of helicopter propeller

The working principle of helicopter propeller is as follows:

(1) When the propeller rotates, the blades constantly push a large amount of air (propulsion medium) backwards, which produces a forward force on the blades, that is, propulsion. The aerodynamic component in the forward direction on the blade constitutes the pulling force. The components in the plane of rotation form a torque that prevents the propeller from rotating, and this torque is balanced by the torque of the engine. The angle between the chord of the blade section (equivalent to the chord of the wing) and the plane of rotation is called the blade installation angle.

(2) When the propeller rotates once, the forward distance guided by the blade installation angle is called the pitch. In order to keep the blade segments and the relative airflow in a favorable attack angle range, the installation angle of each segment also decreases with the increase of the distance from the rotating shaft. This is why each blade has a twist.

(3) The efficiency of propeller is expressed by the ratio of propeller output power to input power. With the increase of forward speed, the efficiency of propeller increases continuously, and the efficiency is higher in the range of 200 ~ 700 km/h, and the flight speed increases again. Due to the compression effect and wave resistance at the tip, the efficiency drops sharply.

The highest efficiency of propeller in flight can reach 85% ~ 90%. The diameter of propeller is much larger than that of jet engine, and the air flow rate as the propulsion medium is larger. Under the condition of the same engine power, the air speed behind the propeller is low and the thrust is greater, which is very beneficial to take off (requiring large thrust).

Helicopters can be divided into:

1, utility helicopter

The earliest helicopter developed and produced should be counted as a general-purpose helicopter-that is to say, it can do most of the work, but it is not very professional to do any work. It can transport, rescue, communicate, rescue and attack with weapons, but it is not very good at doing other work except transportation, so on the basis of general helicopters, special helicopters have been gradually developed.

2. Transport helicopters

Mainly by transportation, with large carrying capacity. Due to different modes of transportation, it can also be divided into lifting helicopters and storage helicopters.

3. Search and rescue helicopter

Helicopters developed with search and rescue as the main work direction usually carry search equipment, rescue slings and rescue facilities. , usually modified on the basis of medium-sized general-purpose helicopters.

4. Armed helicopter

Early helicopter gunships were refitted from general helicopters and equipped with weapons such as machine guns and rockets. With the development of technology and the improvement of requirements for armed helicopters, modern armed helicopters have been specially developed and designed.

Second, the advantages of helicopters

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.

Extended data:

1. The first helicopter in the world is the vs300 developed by Sikorsky Company, which really has the flight characteristics of modern helicopters. The structure of single rotor with tail rotor has laid the foundation for the most commonly used aerodynamic layout of modern helicopters.

2. The smallest helicopter in the world is a single-person subminiature helicopter developed in Japan. The helicopter is equipped with a 37 kW forced cooling engine. The main rotor is about 6 meters in diameter and its own weight is only 1 15 kg.

3. The biggest helicopter in the world is Mi-12 carrier pigeon heavy transport helicopter developed and produced by the Soviet Union in 1960s. The maximum takeoff weight of this aircraft is 105 ton, the diameter of main rotor is 35 meters, the fuselage is 37 meters long and the cargo hold is 28 meters long. Can transport medium-sized tanks and artillery, equipped with four 4.78 MW engines, with a load of 40 tons.

At present, X2 helicopter with the fastest cruising speed in the world has a top speed of 463 kilometers per hour. ..

5. The highest flying helicopter is the French model SA-3 158 "Rhea" helicopter. June 2 1972 On June 2 1, the pilot Jean paulette set a world record for flying at an altitude of 65,438+2,442 meters.

6. The helicopter that flies farthest is the American OH-6 helicopter. 1April 6-7, 966, the plane was piloted by a pilot ferry, setting a world record for a straight-line voyage of 356 1.55 km.

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