Back in 2007, I had the pleasure of working on a project to prototype an unmanned aerial system (UAS) that would fly for over six hours. My team’s design won. We were able to fly the system for six straight hours, and the UAS had only used under 50% of its fuel in those six hours–and we even fueled it at 50% in order to save weight. Our experiments projected right at 24 hours of flight on two gallons of two-stroke gasoline.
One alternative we looked at for that program was a sodium borohydride fuel cell that had extended the flight time of a Raven UAS from 90 minutes to five hours. I was fascinated by the fuel cell UAS, because of its simplicity. The governing formula was as follows: NaBH4 + 2H2O → NaBO2 + 4H2 + heat. What this formula shows is that rather than filling up an aircraft with explosive gasoline or heavy batteries, all one would need is water, borax salts, and heat. The only unneeded by-product would be anhydrous metaborate.
The ION Tiger UAS appears to have extended this concept to a 22-hour flight time. I am excited to see that something I worked on is being improved upon, yet sad to see that more research is not being done on such a thing.