Spanish company Quaternium has destroyed its own record for gasoline-electric drone endurance with a 10-hour, 14-minute flight. But how does that stack up against hydrogen and batteries, and what are the implications for the emerging eVTOL market?
Drone endurance records don't make for particularly riveting video watching, but they're an interesting way to keep track of the state-of-the-art in multirotor energy storage and powertrain efficiency. Flight endurance is the biggest technical problem that needs to be solved in order to get eVTOL air taxis airborne in a commercially viable way, and even if the biggest non-technical problem – getting these things certified by aviation bodies – is likely going to be bigger and more expensive to solve, it seems the money's there to make that happen.
So when we received news recently that Quaternium had broken the 10-hour mark with an electric quadcopter using a 2-stroke combustion engine and 16 liters (4.2 gal) of 95-octane gasoline as a range extender, we wondered how that setup compared to electric and hydrogen options. Check out the Quaternium video below.
We know batteries are terrible for endurance, so it comes as no surprise that the battery figure is much lower. The current Guinness World Record for battery-powered rotorcraft endurance is pretty long in the tooth, from back in 2015. Sait Oksuz from Istanbul squeezed 1 hour, 51 minutes, 51 seconds out of a rotorcraft weighing less than 5 kg (11 lb). And while this has likely been eclipsed since, it seems unreasonable to expect it got anywhere near 10 hours.
Hydrogen, on the other hand, is more fiddly to deal with, and less energy-efficient from an energy generation to power output perspective, but it offers significant energy density advantages when used in a fuel cell electric setup. And those energy density advantages are compounded when the hydrogen's stored cryogenically as a liquid.
Back in April 2019, South Korean company MetaVista mounted a 6-liter liquid hydrogen cylinder and an 800-W Intelligent Energy fuel cell power module to a drone and recorded what stands as the longest ever multirotor flight at an eyebrow-raising 12 hours, 7 minutes and 5 seconds. Masochists can undergo the brutal experience of watching that video here.
So a 6-liter tank of liquid hydrogen beats 16 liters of gasoline by nearly 20 percent. These are the kinds of figures that are driving the push to make hydrogen the clean aviation fuel of the future.
Many hurdles remain. Liquid hydrogen is just beginning to break out of space technology labs, where it's been used for decades as rocket fuel, combined with liquid oxygen. It needs to be kept very cold, because it boils at -252.9 °C (−423.2 °F), and thus requires special handling. Its energy density by mass is excellent, but by volume it's terrible, so the tanks need to be quite large, and hydrogen's tiny molecules tend to sneak out between the gaps in the molecular structure of whatever container you try to store it in, leaking out at a rate around 1 percent a day and making long-term storage untenable.
But it can be generated using green electricity, potentially on site at airports and vertiports where hydrogen aircraft can refuel much faster than they can charge a battery. With range and endurance boosts come significant bottom-line benefits for aircraft operators, and seeing these endurance boosts quantified in these world record multicopter flights gives even more credence to hydrogen's potential as an aviation game-changer.
Sources: Quaternium, Guinness book of World Records, Intelligent Energy
