A Rotorcraft with the Hybrid Propulsion System and Variable Electromechanical Transmission

Aeronautical and Space-Rocket Engineering


Аuthors

Palchenko N. V.*, Efremov A. A.**

National Helicopter Center Mil & Kamov, 26/1, Garshina str., Tomilino, Moscow region, 140070, Russia

*e-mail: n.palchenko@nhcmk.ru
**e-mail: aa.efremov@ nhcmk.ru

Abstract

Current trends in helicopter engineering indicate common requirements for the rotorcraft flight performance, regardless of the rotorcraft size category and within a defined range of missions. These characteristics exceed performance characteristics of the existing helicopter models by 1.5–2 times, including a flight range of at least 1,000 km and a cruising speed of at least 400–450 km/h, while maintaining the same specified payload weight and functionality.
The task of the energy efficiency enhancing of the propulsion system and the main rotor operation can be addressed through a set of technical, technological and software solutions for the development of an advanced propulsion system with so-called “electric propulsion” technologies.
A qualitative improvement in the flight performance of the advanced rotorcraft, while maintaining its basic functionality, can be achieved only through the application of innovative technical solutions. The most relevant trends include:
1.    Efficiency improving the of the propulsion system, which can be achieved through implementation of the following technologies:
    shutdown of one thermal engine in cruising flight for a twin-engine helicopter. The shut-down engine remains in a “standby” mode, referred to as the “start-stop” technology;
    ensuring operation of the thermal propulsion system in the most optimal mode through implementation of the electric energy recuperation technology.
2.    Technical solutions enabling high-speed flight, including drag reduction of the advanced rotorcraft, provided that the increase in propulsion system power remains rational.
International experience shows as well that the most effective approach consists in the main rotor unloading and the power redistribution between the main rotor and extra propulsive devices. Examples of demonstrators such as the Sikorsky Defiant-X, S-97 Raider, and Airbus Racer confirm the potential of this approach.
A fully electric propulsion system for rotorcraft is technically feasible; however, at present it is practically unreasonable due to the insufficient specific characteristics of electrical components. A more realistic trend is the application of hybrid systems, in which thermal engine is combined with both electrical and electromechanical components.
The authors proposed a technical solution formalized as an invention and registered with the Federal Institute of Industrial Property as Patent No. 2822499 dated July 8, 2024, entitled “Rotorcraft with an Electromechanical Continuously Variable Transmission and a Method for Balancing the Power of an Aircraft Electrical System” [1].
Based on the results of the research work performed by JSC “National Helicopter Center Mil&Kamov”, the key requirements for the electrical units characteristics were formulated, along with a set of technical solutions for the rotorcraft development by electric propulsion technologies. To substantiate clearly the electrical technologies applicatioin feasibility, a comparative numerical simulation was performed between a hypothetical advanced coaxial rotorcraft equipped with a hybrid propulsion system, variable electromechanical transmission, wing, and propulsive unit, and a coaxial helicopter with a conventional transmission and propulsion system, with identical maximum take-off weight and payload values.
The effect of the proposed set of technical solutions application was assessed according to the following parameters:
1.    Performance of a standard transport operation involving transportation of a total cargo weight of 20 tons over distances of 200 and 300 km;
2.    Effective work performed by the advanced rotorcraft when carrying out a transport operation at maximum range with a specified payload;
3.    Transport productivity.
The calculation results showed that the rotorcraft with a hybrid propulsion system and variable electromechanical transmission has advantages over a helicopter of conventional design in a number of parameters:
•    maximum flight speed – 1.6 times higher;
•    cruising speed – 1.6 times higher;
•    maximum flight range – 1.5 times higher;
•    time required to perform a transport operation involving the transportation of 20 tons of cargo over a distance of 200 km – 1.8 times shorter;
•    time required to perform a transport operation involving the transportation of 20 tons of cargo over a distance of 300 km – 2.1 times shorter;
•    useful work during cargo transportation at maximum range – 1.5 times higher;
•    transport productivity – 1.6 times higher.
The obtained results, even with account for the assumptions made, clearly demonstrate that the development of advanced rotorcraft within the concept of a “helicopter with a hybrid propulsion system and variable electromechanical transmission” is a promising and well-substantiated innovation for further development of the helicopter technology. This concept allows flexibly varying the main rotor rotational speed depending on the flight mode, reducing the main rotor drag, redistributing the power to generate thrust by the propulsive units, and safely shut down one engine during horizontal flight through with the “start-stop” system.

Keywords:

next-generation rotorcraft, electric power propulsion system of a rotorcraft, hybrid propulsion system of an advanced rotorcraft, variable electromechanical helicopter transmission, flight performance characteristics of an advanced rotorcraft, main rotor blade tip speed, rotorcraft electric propulsion technologies, helicopter with a hybrid propulsion system and variable transmission

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