Dave Cadogan, Director Innovation, Air Liquide

There are many excellent conventional Unmanned Aerial Vehicle (UAV or “drone”) technologies available today. Unfortunately, most of these technologies are difficult to transport in a compact state, are not rugged or damage tolerant, and therefore can have high lifecycle costs. One interesting alternative is inflatable structures. These structures can be engineered to be robust, reusable, and can pack into very small volumes for transport. By pressurizing them with a compressed gas, their outer hull becomes rigid so they can withstand aerodynamic and impact loads, just like a soccer ball or bicycle tire. Over the last 30 years, numerous inflatable UAVs have been successfully developed and flown under military and commercial contracts. The first inflatable planes were developed by Goodyear from 1955 to 1962. 

These full-size single occupant aircraft were envisioned to be air-dropped behind enemy lines to downed pilots for self-rescue. Inflatable UAVs ranging from a one foot wingspan, hand-launched drone to a vehicle near the size of a Cessna 150 have been built and flown. Inflatable aircraft can be carried in backpacks to remote locations, fired out of large guns or delivered by missile to then be deployed in flight, or simply flown conventionally. Any shape or size inflatable aerostructure can be made including wings, fuselages, or even landing skids/floats. Transportability is the key advantage for many applications of inflatable structures, but impact attenuation can also be an attractive attribute. In cases like commercial package delivery where the aircraft is flying over heavily populated areas, an inflatable aircraft (fixed wing or Vertical Take-Off and Landing) can provide impact safety if the vehicle malfunctions or is brought down by weather, etc. Numerous laboratory and flight tests have been performed on experimental aircraft to demonstrate the damage tolerance of inflatable wings.

Another novel technology that is finding application in UAVs is hydrogen-powered propulsion systems. Two technical paths are in development; hydrogen fuel cells, and liquid hydrogen-powered engines. UAVs powered by hydrogen fuel cells are commercially available today but have not yet seen broad use.  

However, a hydrogen fuel cell powered drone recently set the world record for uninterrupted flight for a drone, proving the benefits of hydrogen in various applications. Hydrogen power is beginning to see global adoption in cars and trucks because of its low environmental impact and high energy density compared to other fuels. Zero-carbon drones are a possibility for the future if hydrogen is sourced with renewable technologies. Hydrogen power makes especially good sense for applications where the fleet returns to a base of operations daily, such as with food or product delivery systems being envisioned. This is because the refueling infrastructure can be localized and strategically deployed to reduce system implementation costs. With a new fuel source like hydrogen, the fuel sources and distribution network are as important as the power plant technology itself.

Inflatable structures are not the solution for all drone applications, but can offer interesting and important technical and cost advantages over conventional aerostructures in some applications, and are worth consideration in aerial platform development. Hydrogen powered drones have demonstrated their utility and will gain broader acceptance as the Hydrogen Economy and its distribution systems grow. Therefore, it seems likely that the future of drone technology will involve compressed gasses one way or another.