Article
A Virtual Test Bench of a Parallel Hybrid Propulsion
System for UAVs
Luca Boggero
†
, Sabrina Corpino
†
, Andrea De Martin *
,†
, Giuseppe Evangelista
†
,
Marco Fioriti
†
and Massimo Sorli
†
Department of Mechanical and Aerospace Engineering, Politecnico di Torino, 10129 Torino, Italy
* Correspondence: andrea.demartin@polito.it
† These authors contributed equally to this work.
Received: 4 June 2019; Accepted: 27 June 2019; Published: 2 July 2019
Abstract:
The article proposes the design of a test bench simulator to test a parallel hybrid propulsion
architecture for aeronautical applications. The virtual test bench simulates, in a scaled version, the
real test bench, designed for a power of about 0.4 MW. After presenting the architecture of the real
propulsion system, the virtual test bench is described. The real system is basically composed by a
paralleled electric motor and thermal engine which provide mechanical power to the propeller. Saving
cost and volume the test bench is composed by electric motors simulates the behaviors of the real
propulsion system despite their differences. The dynamic relationships expressing the transmission of
torque between the components, and the method of down-sizing the power delivered are highlighted.
Particular attention is given to the real inertia actions that must be simulated on the virtual test bench.
An application of the proposed methodology is then presented through the simulation of the take-off
phase, and the torque time histories, angular velocities and powers generated on the virtual test
bench are used to verify the corresponding time histories expected in the real system.
Keywords: virtual test bench; hybrid propulsion; UAV
1. Introduction
The hybrid-electric propulsion is rather innovative technology used to combine the mechanical
power generated by one (or more) electric drives with a thermal engine. It can be safely considered a
mature and widely used solution in the automotive field, where it is emerging due to environmental
concerns and he associated with the reduction of the operating costs due to the lower fuel
consumption [
1
]. Similar advantages are expected in the aeronautics field, where the application are
still few and mostly limited to UAVs. In recent years a number of studies on the subject have been
published, including several theoretical studies [
2
–
7
], definition of test benches [
8
–
10
] and aircraft
prototypes [
11
,
12
]. So far, the majority of the available literature is focused on the design and the
performance analysis of one of two alternative architectures: the serial hybrid configuration and the
parallel one. The serial hybrid solution is peculiar of the Diamond DA36 E-Star, the first aircraft
equipped with a hybrid-electric propulsion system. In this solution, the thermal engine provides
the mechanical power to an electrical generator, which hence supplies the electrical drive and its
batteries [
11
]. This architecture might be however not suitable for short haul airplanes, since it can
excessively increase the mass of the propulsion system due to the several power conversion steps [5].
The use of a parallel architecture, in which the two power sources are independently generated and
combined through a gearbox, is then particularly attractive as it might entail a lighter propulsion
system. Moreover it would allow to exploit different combinations of the two power sources to achieve
the most efficient solution as a function of the operating conditions. In example, it could be possible to
add the contribution of both the electric motor and the thermal engine during the maximum power
Aerospace 2019, 6, 77; doi:10.3390/aerospace6070077 www.mdpi.com/journal/aerospace
