Although not the first to try and build a DIY solar-powered remote control airplane, [ProjectAir]’s recent attempt is the most significant one in recent memory. It follows [rctestflight]’s multi-year saga with its v4 revision in 2019, as well as 2022’s rather big one by [Bearospace]. With so many examples to look at, building a solar-powered RC airplane in 2024 should be a snap, surely?

The first handicap was that [ProjectAir] is based in the UK, which means dealing with the famously sunny weather in those regions. The next issue was that the expensive, 20% efficient solar panels are exceedingly fragile, so the hope was that hot-gluing them to the foam of the airplane would keep them safe, even in the case of a crash. During the first test flights they quickly found that although the airplane few fairly well, the moment the sun vanished behind another cloud, the airplane would quite literally fall out of the sky, damaging some cells in the process.

For the final revision, a storage battery was picked, which got charged with an MPPT charger. The airplane itself was changed to be as low-drag as possible, with 60 photovoltaic (PV) cells stuck to its wings. This resulted in the somewhat spindly, swept wing, tail-less pusher design. After debugging a fun issue with EMI from the motor and the navigation module a test flight could be performed, which had the airplane autonomously keep a fixed course. That’s when everything went horribly wrong.

During the subsequent crash investigation, it was found that a total power loss occurred, due to the MPPT charger overcharging the battery, possibly due to a shared ground with the PV cells. Simultaneously, likely due to rushing the testing as bad weather was incoming, the backup battery on the controller was not installed, resulting in the airplane plummeting once primary power ran out. Fortunately, all of these are fixable issues, while providing a learning experience at the cost of an RC airplane and the PV cells that got destroyed in the crash.

Perhaps most importantly, this shows that even if much of building one’s own PV RC airplane in 2024 is just sticking off-the-shelf modules together, there’s no substitute for good engineering, not to mention assembly & pre-flight checklists.