Propeller plane. The blades of the aircraft. Propeller.
Bladed propeller plane, also known as a propeller or blade of the machine, which is rotated by means of the engine. Using screws converts torque from the engine thrust.
Propeller propulsion acts in such aircraft as the aircraft tsiklozhiry, gyros, snowmobile, hovercraft, WIG and helicopters turboprop and piston engines. For each of these machines screw may perform different functions. The aircraft is used as a rotor, which generates thrust in the helicopter and provides a lift and taxiing.
All screws of aircraft are divided into two main types: the screws with a variable and fixed pitch rotation. Depending on the design of aircraft bolts can provide push or pull rod.
By rotating the rotor blades capture the air and make it swing in the opposite direction of flight. In front of the screw creates a low pressure, and behind - with the high pressure zone. The rejected air gets radial and circumferential direction, thereby lost some of the energy that is supplied to the screw. Sama twist airflow reduces the streamlined system. Agricultural aircraft conducting processing fields have poor uniformity of dispersion of chemicals from the flow from the propeller. This problem is solved in the apparatus, which have a coaxial arrangement of screws in this case is compensated for by operation of the rear propeller which rotates in the opposite direction. These screws are installed on aircraft such as the An-22, Tu-142 и Tu-95.
Technical parameters bladed propellers
The most significant characteristics of screws, on which the traction and the flight itself, of course, propeller pitch and diameter. Step - is the distance that can move the screw by screwing in the air for one complete revolution. Before 30-ies use screws with constant pitch rotation. Only at the end 1930-ies almost all aircraft equipped with propellers with replaceable step rotation
Circle diameter of the screw - a size which describe blade tip during rotation.
The pace of the screw - real distance, passing the screw in one turn. This characteristic depends on the speed and rpm.
Geometric pitch propeller - a distance that could pass the screw in the solid medium in one revolution. From tread propeller blades slidably different air in the air.
The angle of the propeller blades and install - slope of the blade section to the real plane of rotation. Due to the presence of blades twist angle of rotation is measured in the cross section, in most cases it 2 / 3 entire length of the blade.
The propeller blades are the front - cutting - edge and back. The cross section of the blade has a profile of the wing type. The profile has a chord of the blade, which has a specific curvature and thickness. To increase the strength of the propeller blades use a chord which is thickened to the root of the propeller. Chord section are in different planes, as the blade is made swirling.
Pitch is the main characteristic of the propeller, it is primarily dependent on the angle of the blades. Step measured in units of distance per revolution. The larger the step makes the screw in one turn, the greater the volume of discarded blade. In turn, the increase in pitch leads to additional load on the power unit, respectively, the number of revolutions is reduced. Modern aircraft have the opportunity to tilt the blades without stopping the engine.
Advantages and disadvantages of propellers
The efficiency of the screws on the modern aircraft reaches a target of 86%, which makes them popular aircraft industry. It should also be noted that the turboprop machines significantly efficient than jets. All the screws have some limitations both in operation and in a constructive manner.
One such restriction is the "blocking effect" that arises with increasing diameter of the screw, or by adding the number of revolutions and the thrust in turn stays on the same level. This is due to the fact that there are portions of the propeller blades with supersonic or transonic airflow. It is this effect does not allow the aircraft to develop a screw speed is higher than 700 km / h. Currently the fastest machine screws with a domestic model range bomber Tu-95Which can develop the speed to 920 km / h.
Another drawback of the screw serves high noise, which is regulated by international norms of ICAO. The noise from the propellers do not fit into the standards of noise.
Modern design and future aircraft propellers
Technology and experience allows designers to overcome some of the problems with noise and improve traction, past limitations.
Thus it was possible to bypass the effect of locking through the use of a powerful turboprop type NC-12, which transmits power to the two coaxial screw. They rotate in opposite directions to pass locking enabled and increase traction.
Also used on the screws thin saber blades that are able to prolong the crisis. This allows higher rates of speed. This type of screw is installed on the aircraft of type AN-70.
Currently being developed to create supersonic screws. Despite the fact that the design is a very long time when considerable cash injections, to achieve a positive result and failed. They have a very complicated and precise shape, which greatly complicates the calculations of designers. Some ready-made screws supersonic type shown that they are very noisy.
The conclusion of the screw in the ring - the impeller - is a promising direction of development, because it reduces the flow around the blade terminal and the noise level. It is also possible to increase security. There are several planes with fans that have the same structure as that of the impeller, but the apparatus is further equipped with the air flow direction. This greatly improves the efficiency of the propeller and motor.
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