Simulation and modelling of a hydrogen-electric aircraft

This project aims to develop a Simulink model of the Stralis A36-HE Bonanza aircraft and hydrogen electric propulsion system (HEPS). This model will be used to support the design process for the A36-HE Bonanza technology demonstrator project and as a basis for Stralis’s Hardware-in-the-Loop testing.

Participants

• Stralis Aero
• Queensland University of Technology

Project background

Australia’s path to net-zero emissions requires all parts of the transport sector to transition and adopt new technologies and renewable fuel solutions, including one of the hardest to abate sectors which is aviation.

Stralis is developing a hydrogen-electric propulsion system (HEPS) for aircraft and will install it into a Beechcraft Bonanza A36 aircraft. This is a key step in the longer term Stralis roadmap to retrofit a Beech 1900 aircraft (19 seats) and develop a larger, 50-seat, clean-sheet aircraft design. Stralis intends to manufacture and market these solutions, capitalising on the sustainable aviation transition to become a world class aircraft manufacturer.

In order to obtain best outcomes from the HEPS development process, it is beneficial to consider the propulsion system and aircraft performance holistically. This will allow optimisation of the requirements for each component in the system to get the lowest Cost per Available Seat Kilometre (CASK), the key aircraft operating cost metric that is beneficial to minimise.

Mathworks Simulink is a suitable tool for system modelling and is widely used in the aerospace and automotive industries, as well as education and academia. Stralis is already using this software tool, and additionally has a Speedgoat high performance computer (for real-time simulation, data acquisition and control) that allows the simulation to interact with the physical world in real time. The aim of this project is to develop a model of the entire HEPS and the aircraft in Simulink, to support the HEPS development, aircraft retrofit design and future aircraft design.

The Simulink model developed as an output of this project will inform Stralis’s next steps and decision making, in particular for investment and future designs, and has the potential to inform broader government policy, initiatives, and investment to help drive the development, production and future use of HEPS and similar technologies in aircraft.

Project objectives

The project objective is to develop a Simulink model for a hydrogen-electric propulsion system and aircraft that can be used to:

1. Validate design requirements at the system, sub-system, and item levels
2. Inform the design of the system and components (e.g. used for trade studies)
3. Develop, evaluate, and validate system control software
4. Provide a basis for Hardware-in-the-Loop (HIL) testing of system components

UPDATE: January 2025

In mid-December 2024 Stralis Aircraft successfully completed a hydrogen-electric powered propeller spin on a ground-demonstrator aircraft at Brisbane Airport. The test, shown in the video below, was using the aircraft known as “Clyde”, a sister ship to “Bonnie”, which is the experimental flight-demonstrator Bonanza A36 aircraft Stralis will fly later this year. This hydrogen-electric propeller trial is the first of its kind in the Southern Hemisphere.

“This is a huge win for Stralis. We have safely trialled the introduction of hydrogen in a controlled environment at Brisbane Airport for use in aircraft propulsion, which required strong collaboration and upskilling of everyone involved. This lays the foundation and builds momentum as we work towards Australia’s first hydrogen-electric flight next year, ”said Bob Criner, CEO and Co-founder of Stralis Aircraft.

For more on the trial, and the aircraft, see: Stralis Aircraft developing cleaner and cheaper hydrogen-electric plane

PROJECT WRAP-UP

iMOVE’s Simulation and modelling of a hydrogen-electric aircraft project, run with Stralis Aero and the Queensland University of Technology, has been completed, and we present here an overview of findings from the work.

Project objectives

The project objective was to develop a Simulink model for a hydrogen-electric propulsion system and aircraft that can be used to:

1. Validate design requirements at the system, sub-system, and item levels
2. Inform the design of the system and components (e.g. used for trade studies)
3. Develop, evaluate, and validate system control software
4. Provide a basis for Hardware-in-the-Loop (HIL) testing of system components

Following this simulation work Stralis would then look to install a hydrogen-electric propulsion system (HEPS) in a Beechcraft Bonanza A36 aircraft.

The end result of all of this is to then retrofit HEPS in a Beech 1900 aircraft (19 seats), and on the success of that develop and manufacture a larger, 50-seat, clean-sheet aircraft design.

Modelling an aircraft

The machine modelled in this project was s follows:

• Beechcraft Bonanza A36 retrofitted with Stralis HEPS
• 26kg LH₂ carried in wingtip tanks
• 180 kW electric motor with integrated drive
• 2 x 110 kW HT-PEM fuel cells
• 10,000 ft operating altitude
• 156 knot cruise speed
• 500-kilometre range

Insights

Propeller

• It was determined early in the project that a fixed pitch propeller would not be sufficient to meet the target performance of the aircraft.
• For the final model a constant speed propeller with electric actuator would need to be implemented.

Fuel cell voltage constraints

• Pressure / temperature sensitivity of fuel cell voltage highlighted voltage constraints.
• Fuel cell must be at temperature for take-off; may need engine run-up under brakes.

Fuel cell thermal management during idle/taxi

• Determined that under low-power conditions cathode air supply alone exceeded fuel cell cooling requirements.
• Required cathode air flow to be throttled for idle/taxi (via turbo).

Recommendations and future work

Partitioning the model

Currently the bulk of the model is implemented as a single Simcape physical network. This means that every part of the model is coupled by a single Simscape solver. This has a number of disadvantages including:

• Requiring the solver for all parts of the model to use the same timestep;
• Limiting the solver to use a single CPU core for simulation;
• Increasing the complexity of the solution of initial conditions of the model;
• Increasing the likelihood that small changes anywhere in the model could result in failure of the simulation;
• Reducing the ability to modularise the model, and
• Reducing simulation speed.

To address all of these issues, it would be of great benefit to partition the single large Simscape model into smaller modules, each with their own independent solver. This would drastically improve the performance of the model by allowing different subsystems to be simulated at different rates, and in parallel across multiple CPU cores. It is likely that this step would also be required if the model were to be used in any real-time simulation context.

Upgrade model to latest MATLAB/Simulink version

It is recommended that prior to any further development, the model be upgraded to the current version of MATLAB/Simulink, in order to be able to access additional modelling functionality and features available in the current version (e.g. use of local solvers for model partitioning).

Move to centralised scope management

Currently the visualisation block implements a large number of scopes for debugging and visualising model output. Simulink provides a centralised “Scope Viewer” function which can eliminate the need to place and route these individual scope block, which at the scale of this simulation model, could significantly improve maintenance and navigation tasks.

Extend model to simulate duplicated systems explicitly

Currently there are a number of duplicated systems in the aircraft model that are not explicitly simulated (loads that are mirrored, doubled etc). This means that certain behaviours cannot be modelled (partial system failures, serial warm-up of systems etc.).

For full fidelity it would be best to explicitly duplicate and simulate these systems in the model. It is recommended that this is not attempted until the model is appropriately partitioned, due to the additional complexity this would introduce to the model.

Final report

Final reports for the project have been produced, and are being used internally.

We can, however, make available a presentation document, Modelling and simulation of the Stralis Bonanza A36-HE hydrogen-electric aircraft.