Is the oil-activated direct-drive drone program viable? Is there any specific case?

Oil-driven UAVs can be divided into oil-driven variable pitch and oil-driven speed control according to the control mode, while the common oil-driven speed control is only oil-driven multi-engine direct-drive type, which is usually called oil-driven direct-drive multi-rotor, such as Shenzhen's Changfeng Tiangma plant protection UAV.

The oil-activated direct-drive multi-rotor uses multiple engines to provide power, each engine drives a rotor, the rotor pitch is fixed, the rotor speed is controlled by adjusting the engine throttle to change the lift, and the rotor is directly mounted on the engine's rotor shaft, without the need for a transmission structure. The advantages are no transmission structure, simple mechanical maintenance, fewer parts, low manufacturing cost, lower maintenance costs. However, its disadvantages are also more obvious, because the number of engines is large, and the engine maintenance workload is large. This involves a late maintenance problem.

Many things must have a reason since they exist. Obviously, the oil-activated direct-drive drone program is also feasible, or else people's companies can't build it, and it has been promoted for use in Xinjiang and other places.