The Advanced Propulsion Unit Computing for the Tiltrotor Air Taxi

Aeronautical and Space-Rocket Engineering


Аuthors

Vasilkov N. D.1*, Ivanov N. S.2**, Karpovich E. A.3***

1. Central Aerohydrodynamic Institute named after N.E. Zhukovsky (TsAGI), 1, Zhukovsky str., Zhukovsky, Moscow Region, 140180, Russia
2. National Research University “Moscow Power Engineering Institute”, 14, Krasnokazarmennaya str., Moscow, 111250 Russia
3. Moscow Aviation Institute (National Research University), 4, Volokolamskoe shosse, Moscow, А-80, GSP-3, 125993, Russia

*e-mail: vasilkovnd@nrczh.ru
**e-mail: ivanovniks@mpei.ru
***e-mail: karpovichea@mai.ru

Abstract

The article presents power and mass-and-size characteristics computations of propulsion systems of various types for the vertical takeoff and landing tiltrotor scheme air taxi of 2500 kg mass, ensuring flight range of 600 km with the speed of 500 km/hour. The study is based on the upper level engineering technique developed by the authors intended for technical layout forming of the innovative propulsion systems, including fully electrical and various hybrid architectures. The computational algorithm accounts for the aircraft aerodynamic characteristics and incorporates detailed models of propellers and electrical components. The work employs two empirical models of propellers, namely regression-based model for mass evaluation calibrated by the data of 114 propellers, and a model for the required power and diameter evaluation, derived from the classical Crouch and Gerr correlations refined by the authors by the database on 62 aircraft of various types. Five schemes of the propulsion systems, including electrical  with the hydrogen-based fuel cells generation system, as welll as parallel and series schemes of the hybrid propulsion system, based on one or two gas turbine engines, were considered according to the payload mass maximization criterion. The technique accounts for the efficiency and specific mass characteristics of all key components ‒ electric motors, electric generators, power electronic converters, gearboxes, and batteries ‒ assuming the current state of technology. The results of the mass and energy balance computations demonstrate that the highest theoretical payload mass of 725.2 kg is ensured by the configuration with an electric propulsion system utilizing hydrogen fuel cells. This is stipulated by the higher energy efficiency of hydrogen compared to aviation kerosene, despite the relatively greater mass of the tank and fuel cells. It is noted herewith that practical application of this scheme is restrained by the absence of the developed hydrogen infrastructure and current technological limitations. Among the hybrid configurations, the parallel hybrid propulsion system with a single Rolls-Royce M250 gas turbine engine is recognized as the most efficient, enabling a payload mass of 679.9 kg. The analysis reveals a consistent trend: for this class of aircraft with a takeoff mass of 2500 kg, configurations with a single gas turbine engine demonstrate, on average, higher payload values than the options with two gas turbine engines. Installation of the two gas turbine engines on such a compact aircraft leads to the excessive in propulsion system mass growth and can be justified only by the redundancy requirements for the emergency landing capability ensuring in the event of failure, rather than by the payload optimization. Computations confirm the fundamental feasibility of transporting between 570 and 725 kg of the payload over the specified range for all considered schemes. The obtained results substantiate the advisability of further in-depth design of the tiltrotor with the selected propulsion system configurations.

Keywords:

vertical take-off and landing aircraft, tiltrotor air taxi, hybrid propulsion system, hydrogen fuel cell, regression model for propeller performance evaluation

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