Performance comparison between a conventional helicopter and compound helicopter configurations

Abstract

The compound helicopter is a high-speed design concept that is once again being explored due to emerging requirements for rotorcraft to obtain speeds that significantly surpass the conventional helicopter. This increase in speed, provided efficient hover capability is maintained, would make the compound helicopter suitable for various roles and missions in both military and civil markets. The aim of this paper is to investigate the compounding of the conventional helicopter and how the addition of thrust and wing compounding influences the performance of this aircraft class. The paper features two compound helicopters. The first configuration features a coaxial rotor with a pusher propeller providing additional axial thrust, and is referred to as the coaxial compound helicopter. The second configuration, known as the hybrid compound helicopter, features a wing and two propellers providing thrust compounding. In this study, the performance of these two compound helicopter configurations are assessed and compared with a conventional configuration. The paper presents the standard performance parameters of each configuration which include the power required in steady level flight, the maximum range, the maximum endurance and the hover ceiling of each of the aircraft configurations. Furthermore, a performance analysis of each configuration flying standard helicopter missions is conducted. The results of the hybrid configuration show that the addition of the wing to the design successfully offloads the main rotor at high speeds; however, significant propulsive power is required by the propellers to overcome the airframe drag. Concerning the coaxial configuration, the power required by the coaxial compound and baseline configurations are comparable at low speeds. However, in high-speed flight a significant amount of power is required by the propeller to divorce the coaxial rotor of its propulsive duties. The results also reinforce the importance of reducing airframe drag in a potential compound helicopter design.