Source: cnBeta
If a multi-rotor drone can use a high-density power source like gasoline instead of a low-density lithium battery, then further increase the load load and air dwell time. But there are technical flaws in using gasoline engines, and due to the strange, peak torque curve, there is hardly enough response to keep the multicopter aircraft balanced in the rapidly changing wind.
In order to solve this problem, the industry has tried a variety of solutions. One of the most impressive schemes is to run the electric motor and the internal combustion engine simultaneously directly on each propeller shaft, with a gas engine providing constant torque, while the electric motor starts only when high-speed adjustments are required.
Flowcopter from Edinburgh offers a completely different solution. Its heavy-duty cargo drones use aviation-certified internal combustion engines that drive digital displacement pumps (mainly used on off-road vehicles and industrial vehicles) and then run hydraulic motors on propellers.
These pumps are capable of distributing and adjusting hydraulic flow between several different outputs under digital control and have the various near-instant response times required to balance the drones in flight. Each hydraulic motor will provide up to 96 kilowatts (129 hp) of power while weighing just 5.5 kg (12 lbs) and costing less than $1,000 each. Flowcopter says: "No electric product can compare to it."
Digital displacement pumps, internal combustion engines, and fuel systems can weigh a lot, but gasoline provides much more available energy per kilogram than lithium, so Flowcopter estimates that the benefits will outweigh its drawbacks. The company promises a tank of gasoline that lasts up to 6 hours and has a range of up to 900 kilometers (560 miles), a direct multicopter aircraft without an efficient flying wing flight mode. During those six hours, it will support itself solely with the power of the propeller. In shorter missions, the payload will reach 150 kg.
Flowcopter has built a prototype that looks rather primitive and has done some tethered flight tests. It's a little wobbly, but it does fly. As the world's first hydraulic hybrid multicopter aircraft, this is an impressive achievement.