When people suggest possible uses for electric multicopter drones, it frequently seems like they're forgetting something – presently, most such aircraft can only fly for a maximum of around 25 minutes per battery charge. Horizon Energy Systems, however, is developing a quadcopter that should do a lot better. Known as the Hycopter, the fuel cell-powered drone is hoped to be capable of 4-hour flight times once completed.

In a clever design feature, the Hycopter stores 120 g (4.2 oz) of hydrogen gas at 350 bar (5,076 psi) in its existing structural tubing – no separate canister is required.

Although those refillable tubes are made of clear acrylic in the pictured display model, they'll be constructed from polymer-lined 5 mm-thick carbon fiber tubing in the functional prototype. According to Horizon, that amount of hydrogen should provide the same amount of energy as 3 kg (6.6 lb) of lithium batteries.