Summary
This paper examines the Loss of Tail Rotor Effectiveness (LTE), which is a common problem associated with single engine helicopters that rely on tail rotors for control. The LTE problem is a common problem that leads to injuries deaths if the pilot fails to recover. Therefore, the coaxial rotor configuration is a possible alternative that can eliminate the problem. Although the coaxial rotor system is already in use in the military, introducing the system in civil aviation will assist in eliminating the LTE problem.
Problem
The loss of tail rotor effectiveness is a common problem associated with single engine helicopters fitted with tail rotors. In brief, the LTE is an unanticipated yaw that does not subside of its own accord. This problem usually occurs at airspeed lower than 30 knots leading to a possible loss of control (Coton, Marshall, Galbraith, & Green, 2004). As figures 1 and 2 show, varying airflow from the main rotor blades is a major cause of LTE depending on whether the main rotor blade is spinning clockwise or anticlockwise directions. In particular, the main rotor produces a torque that causes the fuselage to rotate in the opposite direction.
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Significance of the Problem
Studies show that LTE may lead to serious helicopter crushes if the pilot fails to regain the control of the aircraft (Cuzieux, Basset, & Desopper, 2012; Siliang, Zhengfei, Pei, & Mengjiang, 2016). According to a report by National Transportation Safety Board (2017), the LTE problem led to 55 accidents between 2004 and 2014. Unfortunately, the pilots in the 55 cases were unable to recover when their aircrafts encountered the unanticipated yaw. These statistics show the significance of the problem in the functioning of helicopters that rely on tail rotors. Therefore, researchers should consider fixing the problem as the produce the next-generation helicopters for the military and civilian use. The idea is to seek an alternative way of maintain the much-needed balance without using the tail rotor.
Development of Alternative Function
Understanding the basic principles of helicopter aerodynamics can help in addressing the loss of tail rotor effectiveness. The most promising solution to this problem is the use of coaxial main rotors. Under this rotor system, two main rotors are mounted on a single mast; therefore, they share the same axis of rotation but turn in opposite directions. This alternative allows the pilot to achieve the much-needed control since the rotors produce different lifts leading to differential torque. Although this configuration leads to low speeds due to the air drag caused by the movement of air in opposite direction, the problems associated with the tail rotor is fully eliminated. Also, mounting the rotors close together reduces the drag significantly.
A study by Prior (2010) revealed how coaxial rotor system saves 20% of power output by eliminating the tail rotor. This alternative has already been tested and used successfully in military helicopters. For example, the KAMOV Ka-50 is of the most effective attack helicopter in Russia’s arsenal that employs coaxial rotor system (Prior, 2010). The United States is also developing a second generation helicopters that rely on coaxial rotors under the Sikorsky Program (Prior, 2010). These examples show the future of the aviation industry where coaxial rotor systems can eliminate the problems associated with tail rotors such as the LTE.
Recommendations
In summary, coaxial rotor system offers an excellent alternative that can eliminate the loss of tail rotor effectiveness. Although the alternative is already in military helicopter, it is yet to be fully adopted in civilian helicopters. Therefore, the aviation industry should consider introducing coaxial rotor system for commercial purposes. This will assist in eliminating helicopter crushes caused by loss of tail rotor effectiveness.
References
Coton, F. N., Marshall, J. S., Galbraith, R. M., & Green, R. B. (2004). Helicopter tail rotor orthogonal blade vortex interaction. Progress in Aerospace Sciences , 40 (7), 453-486.
Cuzieux, F., Basset, P. M., & Desopper, A. (2012). Modeling of loss of tail rotor effectiveness conducting to unanticipated yaw. In 28th International Congress of the Aeronautical Sciences ICAS .\
National Transportation Safety Board (2017). Loss of Tail Rotor Effectiveness in Helicopters. Retrieved from: https://www.ntsb.gov/safety/safety-alerts/Documents/SA_062.pdf
Prior, S. D. (2010). Reviewing and investigating the use of Co-Axial rotor systems in small UAVs. International Journal of Micro Air Vehicles , 2 (1), 1-16.
Siliang, D., Zhengfei, T., Pei, X., & Mengjiang, J. (2016). Study on helicopter antitorque device based on cross-flow fan technology. International Journal of Aerospace Engineering , 2016 .
