The power devices used by unmanned aerial vehicles mainly include reciprocating engine, turbojet engine, fanjet, turboprop engine, turboshaft engine, ramjet engine, rocket engine, electric engine, etc.
In terms of application, the turboprop engine is suitable for medium and high altitude long-range unmanned aerial vehicles.
At present, the power system used by mainstream civil unmanned aerial vehicles is usually reciprocating engine and motor.
Carburetor is essentially a pipe. There is a pipe that can be adjustable board, called rectifier plate, which controls the gas flow through the pipe. There is a narrow section in the pipe, called Venturi tube (Venturi). In this narrow channel, the gas flow rate becomes faster and the pressure becomes smaller. There is a small hole in the narrow channel, called nozzle, through which carburetor sucks fuel at low pressure.
The supercharger is used to increase the intake pressure of the engine and the oxygen content in the compressed air, which usually increases the output power of the engine with the same exhaust volume by 20% ~ 50% or even higher.
Igniter is used to ignite the mixed gas of fuel and air.
At present, more than reciprocating engine unmanned aerial vehicles use controlled silicon contactless capacitor discharge igniters. Capacitive discharge igniter consists of Hall effect sensor, ignition control box, ignition coil and spark plug.
The electric power system mainly consists of power supply, speed control system and power motor.
The power supply of electric unmanned aerial vehicles usually adopts chemical batteries, mainly including Ni-MH batteries, nickel-chromium battery, lithium polymer batteries and lithium ion batteries.
Voltage, capacity and discharge capacity are the main parameters of chemical batteries.
The unit of voltage is volt (V). According to the Ohm theorem, voltage equals current (A) multiplied by resistance (Ω). When using, the voltage of the battery is constantly changing, which will generate voltage drop. The larger the load, the larger the current, the smaller the voltage. After removing the load, the voltage of the battery can be restored to a certain value.
The nominal voltage of lithium polymer battery is 3.7V, the full voltage is 4.2V, the storage voltage is 3.8V, and the protection voltage is 3.6V. The total voltage after the battery is connected in series is equal to the sum of each monomer voltage; The total voltage after parallel connection is still equal to the monomer voltage.
Serial connection is represented by “S” and parallel connection is represented by “P. 6S2P means that six single batteries are connected in series first, and then two groups of 6s batteries are connected in parallel.
The unit of capacity is mAh. mA is the unit of current, 1000mA equals 1 amp (I .e. 1A = 1000mA). For example, a battery of 16000mAh indicates that it can discharge for one hour with a current of 16000Ma.
Capacity can also be expressed in watt-hour (Wh), Watt is the unit of power, 1W = 1VA. For example, a 6s 16000mAh battery has a fully charged watt-hour capacity =(6 × 4.2V)×(16Ah)= 403.2Wh.
Generally speaking, the larger the volume of the battery, the more power it can store, but the heavier the weight.
After the batteries are connected in parallel, the total current is equal to the sum of each monomer current, and the total capacity is equal to the sum of the capacity of each monomer battery.
Discharge rate (C)
The discharge capacity of the battery is expressed by the discharge rate (C), and the larger the C value, the stronger the discharge capacity of the battery. The product of C value and battery capacity represents the maximum discharge current of the battery. For example, for a 16000mAh 25C battery, its maximum discharge current = 16A × 25 = 400A.
Charging rate (C)
The charging process has a considerable impact on the battery life. High current charging will damage the performance of the battery. General manufacturers require charging with 0.1C current. However, because of its superior performance, lithium polymer battery can be charged with 1C current under the condition of ensuring cooling and ventilation.
electrical adjustment (ESC)
Electrical adjustment (Electronic Speed Controller,ESC), all called Electronic Speed Controller. It adjusts the rotating speed of the electric machine according to the control signal. Electrical adjustment is divided into brush electrical adjustment and brushless electric speed controller electrical adjustment, which are used for Brush Motor and brushless motor respectively.
Brushless electric speed controller generally has 7 or 8 lines. Electrical adjustment power cord (one red and one black, representing positive and negative poles) is used to connect batteries, output cable (3) is used to connect motors, signal lines (3 with BEC function and 2 without BEC function) used to connect to flight control or receiver.
The so-called BEC(Battery Elimination Circuit) function means that the signal line of electrical adjustment can output a voltage of about 5V, which can supply power to the receiver, and the receiver can supply power to steering gear; Or it can be used to connect the flight control to supply power to the flight control.
Motors are divided into brush motors and brushless motors. Brush Motor has low efficiency and is gradually no longer used in the field of unmanned aerial vehicles.
The parameters of the motor mainly include kV value and size. kV value refers to the rotation speed that the motor can reach per volt voltage.
The size is expressed in 4 digits, for example, 2212 and 2810. The first two bits indicate the diameter of the stator, and the second two bits indicate the height of the stator. Unit: mm.
Generally, high kV motor is equipped with small paddle, and low kV motor is equipped with large paddle.
Vortex jet, vortex axis, vortex propeller and vortex fan
Small turbojet engines have been applied in a few high-speed unmanned aerial vehicle targets and attack unmanned aerial vehicles.
Vortex shaft engine is suitable for medium and low altitude, low speed short distance/vertical takeoff and landing unmanned aerial vehicle and tilting rotor unmanned aerial vehicle. The aircraft takeoff quality can reach 1000kg.
The turboprop engine is suitable for medium and high altitude long-range unmanned aerial vehicles, and the takeoff quality can reach 3000kg.
Fanjet is suitable for unmanned aerial vehicles and unmanned fighter planes in high altitude and long voyage, and the takeoff quality can be very high.
Propeller is used to generate lift, pull or thrust.
Propeller paddle blade is twisted. Paddle blade from hub shaft to blade tip, its installation angle is from large to small, and the linear speed is from small to large, which ensures that the lift generated by paddle blade from hub shaft to blade tip is consistent.
The propeller has fixed pitch propeller and variable pitch propeller. Fixed pitch paddle can also be divided into climbing paddle and cruising paddle. Multi-rotor and fixed-wing UAV usually use fixed-pitch propellers, whose dimensions are expressed by diameter and pitch, in English (in), and 1 inch equals 2.54 centimeters.
Pitch refers to the distance through which the propeller rotates for one week. Unmanned aerial vehicles generally use 2-leaf paddles, while a few use 3-leaf paddles or 4-leaf paddles. Under other conditions with the same conditions, the efficiency of 2-leaf paddle is higher than that of multi-leaf paddle.
Counterclockwise rotating paddle is positive paddle (CCW,Counter ClockWise), ClockWise rotating paddle is reverse paddle (CW, ClockWise).