In this case study, Mejzlik explains how it developed a two-bladed 30 x 18.7 folding propeller prototype for XSun’s SolarXOne drone, optimized for maximum efficiency at target motor speed.
At the end of 2018, we were approached by Benjamin David, CEO/CTO, Founder of XSun. At that time, he needed to design a propeller for his new project. A drone weighing up to 25 kg with a wingspan of 4.6 m. Each wing with an area of 2.8 m2 is covered with solar panels, which have the task of keeping the drone in the air for as long as possible. Benjamin made no secret of his ambition to break the world record for the length of a non-stop flight.
Benefiting from years of experience in AirBus Defense & Space, XSun is pioneering the idea of using space technology for flights at lower altitudes. The result of this approach is an autonomous drone powered by solar electric propulsion. At first glance, it was clear that it would be an interesting challenge and, as is our good habit, we gladly accepted it.
Their SolarXOne drone is a double-support wing drone that has been designed optimizing aerodynamics and aircraft performance for long-range and high-altitude operations. The aerodynamic design together with the use of the latest manufacturing techniques for manufacturing leads to a highly optimized system in compliance with the most demanding requirements for solar drones.
The priorities of the project were clearly stated and from them flowed the main requirements for the design of the propeller for Mejzlik Propellers – “The No. 1 priority was the propeller efficiency for max range and max endurance at level flight.”
For belly landing a folding propeller was required likewise to minimize the propeller drag during the cruise phase of the flight. As a result of this project, Mejzlik Propellers will provide a fully customized propeller for this use case and plane shape. The propeller will be paired with the right motor to make sure to get the right efficiency point.
At the beginning of the project, it was not specified what motor would be used to drive the drone. This complicated the whole development as the propeller needed to be optimized for the best possible results in terms of whole propulsion system efficiency. During the course of the project, various motors were considered and continuous testing was carried out. In the end, to meet XSun’s requirements, Maxon adapted one of its brushless drone motors, the ECX 87 Flat. From an energy point of view, the aim was to keep power consumption as low as possible while optimizing the weight. In order for the design to meet the demanding efficiency requirements, Mejzlik worked intensively on the design with Maxon. The propeller was optimized for maximum efficiency at target motor speed. Finally, a two-bladed 30 x 18.7 folding propeller prototype was produced.
The first full test of the propeller and the entire drone was carried out in August 2019. This means that a newly designed, fully optimized propeller was delivered within 8 months of first contact with our company. Furthermore, the testing went well and the customer was satisfied:” We are super happy with the propeller. Climbing performance was great, no vibration, good folding, nice sound,” said Denis Pitance, the XSun test engineer.
In July 2020, for its first long-range solar flight, the SolarXOne succeeded in flying silently for 12 hours without any CO2 emissions, and completely independently.
The whole Mejzlik Propellers team warmly welcomed the success of the SolarXOne project, knowing that this is just a beginning. At the moment, XSun is running tests of one of our OTS propellers on its new SolarXOne.3 project. We are expecting another great challenge related to a custom propeller for this project and are really looking forward to it.
Lessons learned from the story
The highest thrust is not always a priority for the customer. Increasingly, we encounter requests to optimize the propeller from the point of view of propulsion system efficiency, specific form factor or acoustic performance. Due to the global trend towards renewable resources and the transition to emission-free propulsion systems, we are aware that these requirements will become increasingly important for customers. We are glad that on a project like the one for XSun and many others, we have shown that any optimization is not a problem for us and we can deliver a solution based on demanding requirements. An indisputable plus of the project for XSun was further development of cooperation with Maxon Group.