On our way to safe and autonomous operation

January 2019

To be able to market our technology, it is crucial that we comply with strict safety standards. Each of our tethered aircraft will see up to 6000 flight hours per year in sometimes extreme weather conditions.

That is why we embarked on a certification path with the European Aviation Safety Agency (EASA). Only commercial aviation has as yet demonstrated the quality and reliability levels needed for the financial viability of our innovative Airborne Wind Energy System (AWES). Therefore we adopted the lessons learned in aviation. We are convinced that process-based engineering and other safety requirements in the aviation industry, will lead to better quality and also allows for production in large numbers: all systems will be exact copies of each other.

One of the aviation industry safety requirements, is that any critical failure is mitigated by an independent solution. Whereas the main control code in the autopilot takes care of nominal behavior and deals with detection and recovery of any single system failure, an independently developed back-up landing algorithm runs continuously in parallel to take over should the main code for some reason falter. The impact of hardware failure is reduced significantly through redundancy. Our autopilot relies on a triple redundant aviation-grade on-board computer, and three complete sets of navigation sensors. The data of all sensors is accessible for each computer. With this architecture we can achieve safety and reliability levels approaching that of commercial aviation.

We’re currently building our third generation, pre-commercial prototype AWES “AP-3”. The AP-3 seeks to demonstrate predictable wind power generation at a level of safety, autonomy and availability not yet shown by any other AWES.

The main control code is the primary responsible for the AP3 performance: it controls the AWES systems in air and on-ground to generate power and safely respond to any weather condition or system failure.  On AP3’s first flights a human pilot will still be present to remotely fly the aircraft in case the main control code is for any reason unable to do so. As the AP-3’s aerodynamic behavior is very specific to energy generation and not to regular flight, it may proof difficult for a human pilot to remotely operate the aircraft. An augmentation system supporting manual control has therefore been developed. This system, called BOB, will aid the pilot to safely fly the aircraft back home. It has undergone rigorous requirement, functional and robustness based testing, processes used also in commercial aviation grade certification. The back-up landing algorithm will make use of and build upon BOB for its innermost control loops and will be developed with the same level of rigorous testing. It will make the human pilot obsolete.

We’re currently testing the algorithms and strategies of the autopilot. In the coming months we’ll also be working on ao. sensor integration and the connection with the actuators for the control surfaces. BOB has already been successfully tested. The autopilot will be installed into the AP3 aircraft after summer. We will then start with runway tests followed by aerodynamic characterization of the aircraft in low wind. The autopilot will be tuned in tranquil conditions for autonomous and safe operation, before we demonstrate a tethered flight, full cycle automation and power generation in increasingly challenging weather conditions in Ireland.