With the development of the UAV market in recent years, multi-rotor UAVs have quickly attracted the attention of the majority of consumer groups due to their excellent control performance and the convenience of vertical take-off and landing, and have become the best-selling products to date. Compared with other UAVs, the multi-rotor UAV has unique advantages. Compared with fixed-wing aircraft, it has the advantages of vertical take-off and landing, and can hover at fixed points; compared with single-rotor helicopters, it does not have a tail rotor device, so It has the advantages of simple mechanical structure, high safety and low use cost. The many advantages of multi-rotor drones make them promising in the B-end market of drones, but they also face many problems, such as the load capacity and endurance time of electric drones in the fields of electric cruise, logistics and transportation, firefighting, and plant protection. become an important factor restricting its development. At this time, fuel-powered multi-rotor drones have brought hope to the B-end market with their advantages of large load capacity and long endurance.

Common classifications of oil-powered multi-rotor

Common oil-powered multi-rotor drones include four-rotor, six-rotor, and eight-rotor drones. The biggest feature of multi-rotor drones is that they have multiple pairs of rotors, and the steering of each pair of rotors is opposite to offset each other’s anti-torsion torque.

During flight, multi-rotor drones need to continuously adjust the lift generated by each rotor to maintain a stable flight attitude. There are two commonly used ways to change lift. One is that the engine speed is constant, and the lift is changed by adjusting the propeller pitch, which is called the variable pitch method; the other is that the propeller pitch is constant, and the lift is changed by adjusting the engine speed, which is called the speed control method. What are the characteristics of each of the two methods?

Variable pitch, also known as pitch change and pitch control: The advantage is fast response speed. The disadvantage is that it requires a complex mechanical structure to adjust the propeller pitch, which is costly and requires high maintenance costs.

Speed ​​regulation is also called variable speed and variable speed. The advantage is that the mechanical structure is simple, the speed-regulating multi-engine direct drive mode has no transmission structure, and the engine directly drives the propeller. The cost of construction is low and the maintenance cost is low. The disadvantage is slower response time.

Common fuel-powered multi-rotor energy supply methods include pure fuel-powered and hybrid fuel-electric. According to the control method, pure oil drive can be divided into oil drive pitch and oil drive speed regulation mentioned above; oil drive pitch can be subdivided into single engine transmission and multi-engine transmission; common oil drive speed control only has multi-engine transmission. Direct drive type. There is only one common speed control method for oil-electricity hybrids, which can be divided into two types: oil power generation and oil power addition.

Oil-powered single-engine transmission variable pitch multi-rotor

An engine is used to provide power, and the power is transmitted to each rotor through a complex transmission structure and changes the direction of rotation. Each rotor rotates at the same speed, and the lift is changed by adjusting the propeller pitch to maintain a stable attitude.

Advantages: The number of engines is small and the maintenance workload of the engines is small. quick response.

Disadvantages: The transmission mechanism for transmitting engine power to each rotor is complex, and each rotor requires an independent pitch-variable mechanical structure, resulting in a very complex mechanical structure. The overall fuselage is heavy, the manufacturing cost is high, the mechanical maintenance is difficult, and the overall maintenance cost is high. .

Oil-driven multi-engine transmission variable pitch multi-rotor

Multiple engines are used to provide power. Each engine drives a rotor. Each engine rotates at the same speed. The lift is changed by adjusting the propeller pitch to maintain a stable attitude. A transmission structure is required between the engine and the rotor. You can use a forward and reverse engine, or you can only use a forward engine and reverse direction through the transmission mechanism.

Advantages: simple transmission structure and fast response speed.

Disadvantages: There are many engines and the workload of engine maintenance is heavy. Each rotor requires an independent transmission structure and pitch mechanical structure. The mechanical structure is complex, the overall fuselage is heavy, the manufacturing cost is high, and the overall maintenance cost is high.

Oil-powered multi-engine direct-drive multi-rotor (fuel direct-drive multi-rotor)

Common oil-operated speed-regulated multi-rotors adopt a multi-engine speed-regulated direct drive method, which is usually called an oil-operated direct drive multi-rotor.

The oil-driven direct-drive multi-rotor uses multiple engines to provide power. Each engine drives a rotor. The pitch of the rotor is fixed. The lift is changed by adjusting the engine throttle to control the speed. The rotor is directly installed on the rotating shaft of the engine without the need for a transmission structure.

Advantages: No transmission structure is required, the mechanical structure is simple, the number of parts is small, the manufacturing cost is low, and the maintenance cost is low.

Disadvantages: There are many engines and the workload of engine maintenance is heavy. The overall body is heavier, and the efficiency and response speed are average.

Hybrid multi-rotor

Gas-electric hybrid multi-rotor, according to the power mode, can be divided into two types: oil power generation and oil and electricity combined power generation.

Oil-powered multi-rotor

The oil-powered multi-rotor uses a single engine to provide power to drive a generator to generate electricity, and then uses this electrical energy to drive the motors on each rotor to generate lift, without the need for a power battery. Each rotor is directly fixed on the motor shaft and there is no transmission structure.

Advantages: Only fuel is consumed, and energy replenishment is convenient. The motor responds quickly.

Disadvantages: It requires an engine and generator, the overall fuselage is heavier, and the load capacity is small.

Oil powered multi-rotor

Oil-powered multi-rotor generally uses a single engine to drive the main rotor to provide lift, and multiple electric rotors need to be equipped with power batteries to adjust their attitude. The rotor is directly fixed on the rotating shaft of the motor or engine, without a transmission structure.

Advantages: No generator required, no transmission structure, and the overall body is lighter. The motor responds quickly.

Disadvantages: Need to add fuel and carry power batteries, replenishing energy is inconvenient.

All of the above solutions basically have cases of successful first flights. Since the multi-engine direct drive solution has significant advantages such as simple mechanical structure, easy maintenance, and large load capacity, it has already been widely used in commercial applications.

Among them, the Tianma-1 plant protection drone, which is fully independently developed and produced by Shenzhen Changfeng Information Technology Co., Ltd., is equipped with an intelligent spraying system. It adopts RTK positioning technology, dual-antenna direction finding technology, and centimeter-level radar height measurement technology. It has a large payload and spraying capabilities. Features such as precision, high positioning accuracy, resistance to geomagnetic interference, terrain-imitating flight and fully autonomous operation can greatly improve operating efficiency and reduce operating costs. It has been promoted and used in Xinjiang and other places.

The future development trend of multi-rotor

The development trend of oil-driven multi-rotor mainly lies in two aspects, one is the engine and the other is the rotor.

Electronic injection : Electronic injection engines use electronic control devices to replace traditional mechanical systems (such as carburetors) to control the engine’s fuel supply process. The use of EFI engines has the advantages of fuel saving, improved reliability, improved response speed and environmental adaptability.

Inspiration integration : The motors currently used in engines on the market include DC motors and alternators with regulators, which belong to the starting system and the charging system respectively. They are fixed on the engine body respectively. The installation arrangement is inconvenient and requires a large installation space. , multiple parts have a high failure rate. Without an effective monitoring controller, the power generation efficiency is not high, and the speed and power cannot be quickly adjusted according to the mechanical needs. Integration of inspiration means the integration of starting system and charging system. The starting motor can be used as a generator and has the function of generating electricity. The integrated generator start can reduce costs, reduce the weight of the machine body, and improve the convenience of use.

Let’s talk about the development of rotorcraft. If multi-rotor drones want to make breakthroughs in efficiency, they have to consider combining the principles, advantages and disadvantages of fixed wings with multi-rotor drones to come up with better solutions.

Composite wing : It adopts a composite wing layout of fixed wing and multi-rotor. The multi-rotor can take off and land vertically without the need to take off by taxiing on the runway. It has the characteristics of long flight time, high speed and long distance of fixed-wing UAV. It is effective. Improve efficiency.

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