Helicopter control systems are quite diverse, but in our time we can highlight perhaps three of the most popular and used ones – this is the tail rotor, Fenestron and Notar. All of them are aimed at compensating the reactive moment from the helicopter’s main rotor, are designed to prevent the helicopter from spinning around its axis, and are the most important units in helicopter control. They have their own distinctive design features, pros and cons. Let’s consider each of them in more detail.
1. Helicopter tail rotor.
The tail rotor is designed to control the helicopter along the course, its purpose is to counteract the reactive torque from the main rotor and prevent the helicopter from spinning, the so-called yaw in aviation – the angular movement of the aircraft relative to the vertical axis.
The tail rotor is driven by the interaction of the cardan shafts through the main rotor gearbox, creating thrust perpendicular to the helicopter axis vertically. The pitch, that is, the angle of inclination of the rotor blades is carried out using the control pedals in the helicopter cockpit. In practice, two-blade propellers are most often used, such as those installed, for example, on the Robinson 44, but depending on the technical features, the weight of the helicopter, there are control propellers with three, four and five blades.
The tail rotor partially takes away engine power, on average up to 10 percent. The single-rotor helicopter control scheme is quite simple to operate, does not require significant costs in terms of maintenance and repair, in comparison with other schemes. But in turn, the control screw creates more noise compared to the Fenestron or Notar.
2. Fenestron
Fenestron is a closed type tail rotor, the meaning of the word, translated from Latin as “window” or “small window”. Fenestron is part of the helicopter keel, installed in the annular channel, as a rule, is part of the helicopter stabilizer.
In most cases, the diameter of Fenestron is two or more times smaller, compared to the diameter of the usual tail rotor. The number of blades can be in the range from 8 to 18. Visually, the tail assembly itself with the use of Fenestron looks much larger than with a conventional bladed tail rotor.
Fenestron has a positive effect on aerodynamic characteristics, reduces the resistance of the helicopter in the air, is safer for people servicing the helicopter, due to the closed type of the body. Another important quality of Fenestrons is minimal vibration due to the higher speed of rotation of the blades, thereby increasing the level of comfort when piloting a helicopter. The combination of Fenestron and a 4-5 blade rotor reduces helicopter vibrations to a minimum, making these types of aircraft more suitable for air ambulances.
In some cases, more power is required to hover a helicopter, compared to a conventional control rotor. But as a rule, machines with Fenestrons initially have a greater smell of engine power compared to lighter helicopters. Having a higher level of noise indicators at high frequencies, Fenestron still works quieter than a conventional tail rotor for our perception.
3. Notar
Notar — no tail rotor, translated from English means “without a tail rotor”. The system purpose is to counteract the reactive moment, as in the case of a tail rotor or Fenestron.
On a helicopter equipped with the Notar system, you will not find the usual propeller. The design feature is the rotating nozzles on the tail boom. A fan is installed inside the fuselage. The air flow, partly from the main propeller, enters through the air intakes with the help of a compressor, then the fan accelerates the air flow through the tail boom to the controlled nozzles. Thus, the pilot can control the helicopter, that is, maneuver left and right relative to the helicopter axis.
Helicopters with Notar are considered one of the safest, moreover, one of the “quietest” in the world. This installation is serially installed on helicopters of the American company MD Helicopters.
31 JANUARY 2021