With a clattering on the asphalt runway, the Navy’s Hybrid Tiger drone shortly hauled itself into the sky. It then remained airborne for at the least 24 hours, even because the temperatures dipped under freezing within the sky above the Aberdeen Proving Floor in Maryland.
Drone flights typically aren’t outstanding, however this one was for a easy motive—the complete time the Hybrid Tiger was within the sky, it drew energy from two distinct programs: photo voltaic panels within the wings, and a compact hydrogen gas cell within the physique.
The flight marked a serious milestone for this system from the Navy Analysis Laboratory, an indication that the drone is at the least half as succesful as supposed. Hybrid Tiger’s profitable day within the air began November 18, 2020, though the Navy introduced the success in mid-April.
“The flight was successfully a efficiency check in worst-case situations: temperatures falling under zero levels Celsius, winds gusting to 20 knots, and comparatively little photo voltaic vitality as we approached the photo voltaic solstice Dec. 21,” mentioned Richard Stroman, a mechanical engineer from the NRL Chemistry Division, in a launch. “Regardless of all of that, Hybrid Tiger carried out nicely.”
A typical long-endurance drone, akin to an MQ-9 Reaper, stays aloft for hours and hours by burning a whole bunch of gallons of jet gas to energy an engine, which in flip drives the Reaper’s pusher propeller. Noise from this engine provides the Reaper its distinctive loud buzz, a sound that’s conspicuously absent from the Hybrid Tiger.
Whereas flying, the Hybrid Tiger needed to make due with the daylight it may seize and the onboard hydrogen. “Comparatively little” photo voltaic vitality is just not none, and the Hybrid Tiger’s skinny however highly effective photovoltaics are constructed to maintain it even on minimal energy. A 2018 paper on the drone highlights the effectivity of the thin-film photo voltaic arrays on the drone’s wings. The arrays, two on every wing and one on the tail, weigh in at a complete of two.2 kilos, or about 5% of the drone’s complete weight.
It has a small airframe, with only a 24-foot-long wingspan and a most takeoff weight of solely 55 kilos. From that physique, the Naval Analysis lab hopes to finally coax flight instances of over 48 hours, reaching a distance of round 1,150 miles.
Different solar-powered drones explored by the Navy have flown at altitudes above 9,000 ft, the place clouds are not often dense sufficient to obscure incoming daylight and the winds are constant. The Hybrid Tiger, as an alternative, operates under that threshold, drawing energy partially from rising heat air in thermals, like vultures or condors do. Hovering algorithms, developed for simply this objective, will help hold the drone aloft whereas minimizing the vitality expenditure wanted to take action.
Additional powering the Hybrid Tiger is the hydrogen gas cell, massive sufficient for 14 gallons of hydrogen. The paper describes the watt-hour effectivity of the gas cell as 5 instances higher than that of lithium-ion batteries on the identical weight.
In distinction to pure solar-powered craft, the hydrogen gas cell works nicely at night time, supplementing the Hybrid Tiger’s energy and preserving it aloft till daylight can deliver the return of photo voltaic electrical energy. Just like the hovering algorithms, the promise is that good vitality administration—from temperature to altitude to route—will autonomously make sure the drone can keep airborne for at the least a day. Altogether, the bundle is designed for an plane that may stay within the sky whereas expending as little vitality as potential. A presentation from 2018 prompt this might yield stretches of flight 70 miles lengthy with out the drone needing to make use of its motor.
When Hybrid Tiger was first introduced in 2017, the purpose was for an formidable flight time of three.5 days, although that seems to have been scaled again since. Janes, a protection publication, additionally reported on the time that the eventual design of the drone was to incorporate “a small intelligence, surveillance, and reconnaissance payload.”
In actual fact, Hybrid Tiger was born as a scout and a spy. The 2021 launch mentions solely a payload, regardless of any sensors, however it’s straightforward to see the scouting mission within the drone’s physique, even when it’s not probably the most publicly marketed a part of the craft.
Hybrid Tiger borrowed its gas cell, airframe, and far of its inspiration from Ion Tiger, a hydrogen gas cell drone developed by the Navy from 2009 to 2013. Ion Tiger reportedly flew for about 48 hours in 2013. It was constructed to hold a digital camera, able to each daytime and infrared video seize, in addition to a communications relay. This design is, broadly, the usual sensor bundle on scouting drones of its period, and sure continues to the Hybrid Tiger kind.
Practically twenty years into improvement, the Hybrid Tiger seems to exhibit its basic promise: a protracted endurance drone with minimal gas wants, able to working in a variety of climate situations, silently observing the world under. If the testing continues to achieve success, and if the drone’s particular mixture of energy sources could be constructed affordably at scale, the way forward for scout drones is a quiet one, as flying cameras with silent engines sip energy from the solar and surveille the world for days at a time.