Understanding the Challenges

Most, if not all, of these emerging design ideas in PAV/eVTOL aircraft face similar challenges when it comes to proving qualified flight and ensuring an understanding in fine detail of those issues which can mean the difference between success and failure.  This is very evident when attempting to scale up designs and evaluate core stability and control, flight control system design and evaluation, and the development of high fidelity simulation model standards for pilot training and certification.

PAV/eVTOL aircraft are generally unconventional in their design, operation and performance and these facts present specific challenges in their on going development and analysis. These challenges break down into a number of  areas:

• The distribution of mass and its impact on inertias throughout all phases of flight.
• The impact of multi rotor vortices and their interactions especially in downwash and upwash dynamics and downwash ingestion.
• The flight control system logic that is able to model pilot control inputs and the corresponding response of the motors, rotors, and aircraft.
• Changes in the torque required from electric motors and the resulting aircraft response to increases and decreases in power.
• Better understand the aircraft responses and rates of change and their impact on pilot initiated oscillations (PIO’s), resulting in a potential loss of control.
• Failure modes and outcomes
• Being able to demonstrate tangible and measurable progress and improvement to stake holders and investors.

High Fidelity Simulation

The j2 Universal Tool-Kit already has all the components necessary to develop a high fidelity digital twin. This built in capability comes from a background of aircraft and UAV design and engineering, working with many unconventional designs to ensure safe and stable flight.   This ensures that the engineers and designer have all the information necessary to maintain controlled stable responses over a range of conditions from hover to forward flight and back.  This information can then be used in scheduling to enable smooth transition. The pilot-in-the-loop simulation capabilities enables the design to be fully tested and evaluated against any

The engineering origins of the j2 Universal Tool-Kit ensures that the focus is on developing accurate results.  This experience is built into the software so there is no need to write code or develop block diagrams to build up the model.  j2 Builder provides a comprehensive hierarchical structure where detailed data tables can be created and located to provide the correct aerodynamic characteristics and motors positioned to give the appropriate moment arms.  With j2 Freedom, its possible to create manoeuvres that can be run over a range of known, fixed, initial conditions.  The manoeuvres can be repeated as the design evolves to provide a consistent testing and simulation environment.

As further information is developed so high fidelity simulations of subsystems such as electrical, hydraulic, flight control can be integrated with the model through the j2 Developer API to produce a complete Digital Twin of the whole aircraft.

Aircraft Certification

Understanding the challenges, experience in the area of Stability & Control and Aircraft Certification, and an existing High Fidelity Modelling and Simulation environment has put j2 Aircraft Dynamics in the ideal position to investigate the certification of PAV/eVTOL aircraft.  We are already working with organisations to support the development of standards for handling qualities and ultimately certification.  Whilst the optimum approach to piloting is still to be determined, what has become paramount is that the Certification will require more than some preliminary gaming simulation and a comment that “it flies great”.  The certification process requires detailed modelling and simulation of the aircraft across the complete flight regime.  This needs to be backed up  and cross referenced to flight test that can demonstrate the validity of the modelling environment. With j2 Flight, flight test data can be collated and compared to the model through Reprediction and the model can then be refined via the automatic Regression techniques.

Due to the complex nature of the systems and the almost total reliance on flight control laws, a lot of the failures and safety cases will need to be thoroughly tested in a simulation environment.  These tests need to be repeatable and need to have a full Digital Twin that covers all aspects of the system under test and not a generic gaming solution.