The global helicopter industry utilizes two types of configurations: single- and coaxial rotor helicopters. Most of the choppers utilize the single rotor configuration. The groundbreakers of the chopper-building industry recognized the advantages of coaxial configuration. On multiple occasions, early scientists had attempted to incorporate the technology behind coaxial configuration. However, they only managed to come up with single-rotor helicopters whose stability was maintained by the presence of a tail rotor. The single-rotor choppers became widely used in the West as well as in the Soviet Union. Despite the employment of a considerable amount of effort and resources, improvements to the single-rotor configuration did not tackle the fundamental flaws that scientists had pinpointed (Syal, 2008).
In 1947, a Russian designer named N. Kamov began to research on the development of two sets of rotating blades. The sets were to facilitate the development of what came to be known as coaxial-rotor choppers. Over the next fifty years, the company that Kamov established managed to develop a series of coaxial choppers, an achievement that culminated to the production of the famous Ka-32 as well as the Ka-50 Black Shark.
Most of the choppers in the Ka-series had small dimensions, a fact that resulted in an increased thrust-to-weight ratio. The configuration improved aerodynamic symmetry and maneuverability. These choppers were, therefore, preferred for military transportation. Later, they became available for use in the civil aviation industry (Leishman, 2006).
The embodiment of the principle of reactive moment compensation has made the coaxial choppers special and essentially different from the helicopters with a single-rotor configuration. To provide for a reactive force in choppers with a single-rotor configuration, manufacturers fix a tail rotor to the helicopter’s airframe. On the contrary, choppers with coaxial-rotor configuration enables the reactive moments of its two rotors to directly compensate each other in their axis of rotation. This configuration, therefore, eliminates the need for additional forces. The reactive moments of the rotors are automatically compensated throughout the chopper’s flight, a situation which does not require the inference of the pilot. In order to result into a zero reactive moment, the operation of pedals needs to create a disparity between the chopper’s lower and upper engines (Lakshminarayan, 2009). This would facilitate a balanced flight as the reactive moments are utilized for the control of direction.
In order to achieve the reactive compensation for choppers with a single-rotor configuration, pilots need to remain attentive throughout the flight. They are required to keep adjusting the side force provided by the rear rotor in order to maintain the flight balance. With regard to power, coaxial choppers have been known for their efficiency. In these choppers, the entire power is utilized in the rotor drive where it is consumed in the lift development (Prouty, 1989). With single-rotor choppers, the tail rotor consumes between 10 and 12 percent of the available power (Lakshminarayan, 2009). This reduces the intensity of the lift. In the long run, power wastage in the single-rotor choppers can be tremendous.
The coaxial-rotor configuration improves the hovering ability. During hovering, the upper rotor narrows its racing to a considerable level, a situation that enables the rotor below to take in the additional air. This serves to increase the racing cross-section of the rotor thereby reducing the power utilized in the lift development. The coaxial rotors’ contra-rotation reduces power significantly.
Due to their power efficiency, choppers with coaxial-rotor configurations have been found to be 16 to 22 percent more superior to those with a single-rotor configuration. This is due to the elimination of the need to compensate the reactive moment as is the case with the single rotor choppers. A coaxial configuration presents a tactical advantage, especially during military exercises. Firstly, coaxial choppers are lighter and smaller than single-rotor ones. A coaxial configuration has managed to reduce the size of choppers by between 35 and 40 percent (Lakshminarayan, 2009). Their fine hovers and power efficiency facilitates the reduction of their rotor diameters. Additionally, a tail rotor increases the chopper dimension by over 20% as compared to the coaxial ones.
The weight distribution and size reduction minimizes the directional and longitudinal moments of inertia. This facilitates controllability, a situation which facilitates maneuvering in difficult environments. Stability and controllability are made possible through the provision of an aerodynamic symmetry. Technological advancement has facilitated progress in the manufacture of helicopters. Chopper designers are increasingly turning to symmetric aerodynamic conformation. Increased understanding of aerodynamic symmetry has helped achieve controllability of helicopters. Due to the lack of tail rotor, coaxial-rotor helicopters are not subjected to a constant effect challenge of an alternating side force (Prouty, 1989). Coaxial design provides for a smooth association between aerodynamic damping and control. Consequently, the two factors enhance the level of controllability.
Due to aerodynamic symmetry presented by the coaxial-rotor configuration, the relation between lateral and longitudinal movement is unnecessary. Nevertheless, there is the independence of control, a situation which makes mastery and flying easy to accomplish. The lack of side force, yaw moment, flight mode variables, as well as lateral and directional control facilitates the improvement of controllability and control. These factors enhance flight safety in extreme conditions. The choppers manage to maneuver in low altitude, broken terrain, landing pads, and high barometric altitude (Prouty, 1989). These choppers are easy to fly even when some of the components malfunction.
Unrestrained efficiency enables coaxial helicopters to perform flat maneuvers. The efficiency is rooted in their superior designs which concentrate much of the functionality in their coaxial rotor. This increases the lift development, directional and longitudinal control, collective pitch control, as well as the propulsive force. With the concentration of the entire control system as well as the accessibility of a directional control makes the chopper achieve independence in its angle of slide. These factors, together with the absence of a tail rotor provide a coaxial-rotor chopper with countless opportunities for undertaking flat maneuvers, even at a high angle of slide. The empennage in a coaxial-rotor chopper presents no limitations with regard to the angle of slide. In fact, it is designed to cater for changes in the angle of the slide as long as the changes are within 180° (Leishman, 2006).
Flight testing, experimental research and lab tests have proved that coaxial-rotor choppers are safe in all flight modes. The dimension of a helicopter is one of the factors that determine its safety during flights. Since coaxial-rotor helicopters are smaller in size, their flight safety is enhanced especially in low attitude and when obstructions are in the vicinity. This is very important for combat helicopters. Moreover, its empennage cannot be damaged by the obstacles during flight. These kinds of choppers have little restrictions on their deflecting pedals. As such, their pedals can be utilized to their full capacity, as opposed to the single-rotor choppers (Leishman, 2006). The use of pedals in a single-rotor configuration is limited by safety requirements necessary for the operation of the tail rotor.