Jet drive a helicopter rotor
The main difference between the jet engine of the piston is in a jet engine the energy of combustible fuel is used to create a traction force directly, by dropping back with high velocity air and combustion products, whereas in a piston engine energy combusted fuel is used to rotate the propeller, which creates with the necessary traction for movement.
From this, we can conclude that the easiest way of rotation of the main rotor of the helicopter by means of jet engines is the installation at the ends of the blades of the rotor.
Therefore, the thrust of each engine must be equal 38,2 kg. Jet engine with the thrust will weigh quite a bit about 10 kg. The weight of all three engines will be 30 kg.
In single-rotor helicopter with tail rotor weight 1500 kg weight of the engine will be about 300 kg, and the weight of the transmission - about 100 kg.
When compared with a helicopter jet engine helicopter, having a piston engine, the difference in weight of their composition for this example 370 kg. Due to this difference can be increased fuel capacity. As a result, the range of the jet engine, despite the high cost of fuel, can be the same as a helicopter with a piston engine. Using a helicopter jet at small distances by the incomplete filling of fuel can significantly increase its capacity.
Jet drive rotor has many advantages compared to piston-driven motor. When you install jet engines at the ends of the blades is not required transmission tons. e. gears, shafts l t. etc. For such a helicopter tail rotor needed only to provide directional control, as there is no reaction torque on the screw on the fuselage, because the drive screw is on the screw; in this case, the tail rotor will consume less power because its diameter is small. The weight of the helicopter as a whole will be significantly less. For example, in the case of a piston engine instead of a ramjet engine weight of the helicopter, which has the same carrying capacity will be approximately 30 ° / for less.
However, along with the jet drive is typical number of shortcomings. The main one is that the jet engines have low efficiency, leading to higher fuel consumption. Moreover, the jet drive is difficult to implement, since
it is necessary to simultaneously satisfy a number of conflicting requirements.
If at the end of the rotor blade mounted jet engine, the change of the blade setting angle results in a change in the direction of the engine thrust. For example, by increasing the setting angle a thrust no longer lies in the plane of rotation, and make it a certain angle a, so that the thrust will give two components: in-plane rotation that will generate torque, and the rotational axis of the screw, which go directly to increase the lift and increase the angle of the blade stroke.
The magnitude of these components traction during one revolution will change all the time, which will cause the appearance of a large vibration of the helicopter. To eliminate this drawback, it is necessary to mount the engine on a rod or tube around which the movable blade is positioned so as to change the angle of attack of the blade going around this rod or pipe without deviating the axis of the engine.
The pipe may serve as backbone for supplying fuel to jet engines.
The difficulty installing the motor at the ends of the rotor blades is also that the jet engine is operating with a high effect only at high peripheral speed of the blades, since in this case, a sufficient dynamic pressure at the inlet of the diffuser of the engine. On the other hand, the large circumferential speed leads to the fact that on the profile of the blades stall flow arises, which reduces the efficiency of the propeller.
But that's not all the difficulties. Whatever light was no jet engine, it is a concentrated load at the end of the blade and substantially increases the centrifugal force, the blade tends to break. Therefore, as compared with the rotor having a drive piston of the engine, the strength of the rotor blades from jet engines must be increased. In addition, the separation of the masses from the axis of rotation of the blades creates a high moment of inertia of the rotor and the resistance force of the engine, located at a great distance from the axis, it creates a large drag torque. All this, taken together, impairs the ability to self-rotation of the rotor during the transition to unpowered flight in the event of failure of jet engines.
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