Demonstrator of Sikorsky's X2 demonstrator. Lockheed Martin's technology is used in the X2 Photo: US Lockheed Martin
However, there was a difference in the form of the aircraft between "X2" and "X3". The "X2" uses a counter-rotating rotor as a countermeasure against torque, and the propeller for propulsion is provided in the tail. The X3, on the other hand, is a single-rotor aircraft with two propulsion propellers, one on each side of the main wing.
Composite helicopters perform like regular helicopters at low speeds. Therefore, it is necessary to have a mechanism to deal with the anti-torque of the rotor, but the "X2" dealt with it with a counter-rotating rotor. The X3, on the other hand, uses propellers for propulsion on the left and right. A regular fixed-wing aircraft cannot fly straight unless the left and right engines are synchronized. However, compound helicopters are different. In helicopter mode, if the propulsive force of the left and right propellers is intentionally different, the anti-torque can be canceled.
And Kawasaki's "K-RACER" has the same layout as the "X3". However, this is an unmanned aircraft, much smaller than the "X3", which is a repurposed manned aircraft. Since there are no people on board, the risk is low, and it can be done cheaply. It seems that the engine uses the supercharged engine of the company's motorcycle "Ninja H2R". This area makes good use of the available resources.
When I looked into it, it was a 4-stroke DOHC, 4-valve, 4-cylinder engine with a displacement of 998cc. Since the rpm is high, the rpm must be lowered all at once with the reduction gearbox, but the circumstances around that are very similar to the turboshaft engine.
So, I thought about which part of the compound helicopter would be the key.
First, it functions as a helicopter during takeoff, landing and low-speed flight. this is good I suspect the problem lies in the transition when the speed increases.
As the speed increases, the main wing ("K-RACER" or "X3") or counter-rotating rotor ("X2") begins to generate lift. However, at that time, it is necessary to reduce the rotation speed of the main rotor. This is a story about lift, and the challenge is to "make a smooth transition between two different lift sources."
For propulsion, the propulsion was generated by the main rotor, but when the speed increases, the propulsion propeller will generate the propulsion. Again, the challenge is to "smoothly transition between two different propulsion sources."
Furthermore, in the case of the "K-RACER" and "X3", at low speeds it is necessary to create a difference in the propulsive force generated by the left and right propellers to cancel out the counter torque caused by the main rotor. However, if the counter torque generated by the main rotor decreases when the speed increases, the difference must be reduced accordingly. If the anti-torque is no longer generated, it is necessary to synchronize the thrust generated by the left and right propellers.
In other words, it is necessary to realize the adjustment of the propulsive force generated by the main rotor and the propulsion propeller smoothly and without failure. Otherwise, it would be useless consultation.
In addition, neither the main rotor nor the propulsion propeller is simply controlled by increasing or decreasing the rotation speed. Since the number of rotations is controlled by pitch control while keeping it within a certain range, it must be done precisely. However, this is the same regardless of whether it is done manually or under computer control.
The difference between manual control and computer control will be the part of "whether the process of controlling while maintaining harmony can be performed without error". The story of "difficulty in control in transition flight" is especially common in VTOL (Vertical Take-Off and Landing) aircraft. It's not just about compound helicopters.
For example, Rolls-Royce's Pegasus engine (Harrier's engine), which combines a jet engine with a thrust vectoring device. Transitional flight becomes impossible if the operation of changing the direction of the thrust vectoring nozzle and the operation of adjusting the engine thrust are not in harmony. When the Harrier was developed, it had to be done manually, but now it can be computer-controlled like the F-35B, making it much easier to fly. Computers are various.
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