CN107368090B - Fixed-wing solar unmanned aerial vehicle time-of-flight estimation method - Google Patents

Abstract

The invention discloses a method for estimating the flight time of a fixed-wing solar-powered unmanned aerial vehicle. : Calculate the energy consumption status, that is, the energy consumption of the aircraft per flight day; Step 3: Based on the energy balance criterion, estimate the flight time window under ideal conditions; Step 4: Consider the actual battery capacity, accurately estimate the flight time window. The invention can easily estimate the flight time of the solar unmanned aerial vehicle, can be applied to almost all places on the earth, and has a wide range of adaptation. The method of the invention is simple and convenient, only needs several parameters, and is easy to be applied in engineering.

Description

A method for estimating flight time of a fixed-wing solar-powered UAV

technical field

The invention relates to the field of solar unmanned aerial vehicle design and mission planning, in particular to a method for estimating flight time of a fixed-wing solar unmanned aerial vehicle.

Background technique

Flight time estimation is of great value to the initial design evaluation of solar-powered UAVs and later mission planning and decision-making. Unlike traditional aircraft, solar-powered drones use solar radiation as the main energy, while traditional aircraft use fossil fuels as the main energy. The total amount of energy it carries can be known, and the energy usage is relatively easy to predict. The development of more than a century has been very mature. However, the total amount of energy carried by solar drones needs to collect solar radiation energy in real time and store it in energy storage batteries. Difficulties such as long-term weather forecasting is itself a very complex problem that has not been well resolved. At present, from the public information collected, there is very little research on the flight time estimation of solar-powered UAVs.

In the traditional aircraft performance estimation theory, the flight time estimation is attributed to the steady-state or quasi-steady-state performance index of the aircraft, which can be divided into analytical method and graphical method according to different calculation methods. The analytical method expresses the target variable as an analytical function according to the kinematic equation, dynamic equation and mechanical analysis of the aircraft. Its mathematical derivation is rigorous, the physical concept is clear, and it can directly and accurately solve the mathematical formula of the required performance parameters. Graphical method, by calculating a number sequence composed of several numerical values, and then finding a required value as the solution to the problem. This method is mainly based on the thrust method, the power method and the energy method. It is widely used in engineering applications by combining the calculation of original data and applying it to high-order equations that cannot or are difficult to be solved analytically.

When estimating the endurance of solar-powered UAVs, although its flight quality does not change, the total amount of energy has a very large uncertainty, which brings great challenges to the estimation of the endurance of solar-powered UAVs. However, the endurance performance is very important for reconnaissance. It is one of the most critical indicators for evaluating mission capabilities, and it is also one of the key assessment indicators for solar drone designers to evaluate the initial design of solar drones. , which is of great significance for its task decision-making and design evaluation. More importantly, for solar drones, how to determine this kind of special aircraft indicator system to promote the standardization of its design and application will also promote the maturity and progress of the solar drone industry chain. The first thing to solve is: how to define the performance indicators suitable for evaluating the battery life of solar drones, so as to better reflect the battery life characteristics of solar drones, the evaluation method is objective, and the indicators can be measured or counted.

SUMMARY OF THE INVENTION

The purpose of the present invention is to solve the above problems, and propose a method for estimating the flight time of a fixed-wing solar-powered UAV for a given model, flight location and flight time under clear weather conditions. This method uses the solar UAV energy production model to calculate the energy production power of the solar UAV at different locations and times. Combined with the energy consumption of the UAV mission profile and the energy reserve capacity limit of the UAV backup power supply, the solar UAV is based on the energy storage capacity limit. The day is the energy cycle, and the daily energy balance in 365 days of one year is counted to finally obtain the continuous flight performance of the solar-powered UAV. Finally, based on the sustainable flight performance characteristics of solar-powered UAVs, the concept of solar "flight time window" is proposed to describe the battery life of solar-powered UAVs more conveniently. The invention can be used for solar aircraft design, control and mission planning, especially in the fields of solar aircraft design and mission planning, and the method can be used to verify and analyze the feasibility and rationality of solar aircraft design scheme and mission planning.

A method for estimating flight time of a fixed-wing solar-powered UAV, comprising the following steps:

Step 1: Count the energy production status of solar drones, that is, the total energy production of solar drones per flight day;

Step 2: Calculate the energy consumption status, that is, the energy consumption of the aircraft per flight day;

Step 3: Based on the energy balance criterion, estimate the flight time window under ideal conditions;

Step 4: Accurately estimate the flight time window considering the actual battery capacity.

The advantages of the present invention are:

(1) It is relatively simple to estimate the flight time of solar-powered UAVs;

(2) The method has a very wide range of adaptability and can be applied to almost all places on the earth;

(3) The estimation method is simple and convenient, only needs a few parameters, and is easy to be applied in engineering.

Description of drawings

Fig. 1 is the schematic diagram of the energy balance relation of solar-powered unmanned aerial vehicle of the present invention;

2 is a schematic diagram of the flight time window of the present invention in conjunction with a certain type of unmanned aerial vehicle;

Figure 3 is a flow chart of the specific implementation of the present invention.

Detailed ways

The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments.

The present invention utilizes the principle of energy balance as shown in Figure 1. Based on the solar-powered UAV energy production model, the energy production status of a given UAV cruising target area is counted for 1 year and 365 days; secondly, the dynamic relationship when the UAV is cruising is given. , calculate the energy consumption for one flight day; finally, according to the continuous cruise relationship of the UAV, determine whether the UAV flight day is a sustainable flight time window, so as to determine the battery life of the solar UAV.

In view of the above concept, the described method for estimating flight time of a fixed-wing solar-powered UAV, as shown in Figure 3, includes the following steps:

Step 1: Statistics of energy production

Based on the solar drone energy production model, the target location is counted, and the solar drone energy production status at each moment is 365 days a year;

I _h =I _b sinα _e +I _d (2)

b=1.219-0.043τ _b -0.151τ _d -0.204τ _b τ _d (5)

d=0.202+0.852τ _b -0.007τ _d -0.357τ _b τ _d (6)

In the formula: I represents the solar radiation constant

I ₀ represents the solar constant, n _days of the sun (starting on January 1st, January 1st is 1).

I _h : the total solar radiation intensity received on a unit horizontal plane;

I _b : the direct solar radiation intensity received on a unit horizontal plane;

I _d : the direct solar scattering intensity received on a unit horizontal plane;

m _r : air mass ratio;

τ _b , τ _d : direct and scattered optical depths, which are obtained by look-up table and difference value;

b, d: direct and scattered air quality index;

α _e : The altitude angle of the sun, which is complementary to the zenith angle.

The current sun altitude and azimuth can refer to the following formulas (8) and (9):

sin(α _e )=sin(n _lat )sin(δ)+cos(n _lat )cos(δ)cosω(t) (8)

δ=0.4093sin(2π(284+n)/365) (10)

ω(t)=0.2618×(12-t _local ) (11)

Among them, α _s represents the solar azimuth angle; α _e represents the solar altitude angle; n _lat represents the latitude of the flight location; δ represents the solar declination angle; ω(t) represents the solar time; t _local represents the local current time.

The incident angle of sunlight entering the solar drone wing surface is calculated with reference to the following formula:

Among them, λ is the incident angle of sunlight entering the solar aircraft wing surface, θ is the pitch angle of the solar drone, ψ is the yaw angle of the solar drone, and φ is the roll angle of the solar drone.

The solar radiation intensity of the solar drone wing surface and the energy production power of the solar drone:

P _in = η _sol SP _s (λ) (14)

Among them, P _s (λ) represents the solar radiation intensity per unit area of the airfoil when the aircraft attitude is (ψ, θ, φ); ρ _r is the ground reflectivity, which can be obtained by looking up the table. S is the wing area; η _sol is the solar cell efficiency; P _in is the current solar UAV energy production power.

The total UAV energy production E _uav in one flight day can be obtained according to formula (14)

Among them, n _day is the specified solar day; t ₀ is equal to 0, which is equivalent to 0:00 on the flight day; t _f is 86400, which is equivalent to 24:00 on the flight day in seconds.

Step 2: Calculate energy consumption

The energy consumption of the UAV is mainly for the aircraft to overcome the aerodynamic resistance to do work, in addition to the energy consumption of avionics equipment and the energy consumption of the mission load, the total energy consumption P _out can be expressed as

P _out =P _propuls +P _av +P _pld (16)

Among them, P _propuls is the power required by the electric propulsion system, which is related to the flight state of the UAV; P _av is the power consumption of the UAV onboard electronic equipment (such as flight control computer, satellite navigation module, data link, etc.) Generally, there is little change in human-machine flight, and it is assumed to be a constant value in the present invention; the power consumption (such as cameras, infrared sensing equipment, etc.) required by the _Ppld mission load is related to the equipment carried on the mission, and in the present invention is also assumed to be a constant value.

For solar-powered UAVs, most of their flight states are based on constant-height and constant-speed cruise. When they are in constant-height and constant-speed stable and level flight, since the power consumption required by the electric propulsion system is used to overcome the resistance, the power of the propulsion system P _propuls can be written as

Among them, η _prop is the propeller efficiency, η _mot motor and gearbox power transmission efficiency, η _ctrl drive efficiency, V is the flight speed, D is the flight resistance, which can be calculated as follows:

α分别为空气密度、零升力系数、攻角引起的升力系数以及攻角。Among them: ρ,

α are air density, zero lift coefficient, lift coefficient due to angle of attack, and angle of attack, respectively.

When the drone is in level flight, its gravity and lift are equal:

L=mg (22)

L=ρV ² SC _L /2 (23)

Among them, L is the lift force, m is the mass of the aircraft, and g is the gravitational acceleration;

Combined formula (22) and formula (23), the _CL cruise speed is:

为零升阻力系数；K为空气动力系数；R_a为展弦比；ε为Oswald效率因子；L为无人机升力；C_L为升力系数。where C _D is the drag coefficient;

zero-lift drag coefficient; K is the aerodynamic coefficient; R _a is the aspect ratio; ε is the Oswald efficiency factor; L is the lift of the drone; C _L is the lift coefficient.

In the time period [t ₀ , t _f ], the total energy consumption of the UAV E _out (t ₀ , t _f ) can be calculated by formula (14):

Combining Equation (16) and Equation (25), E _out (t ₀ ,t _f ) can be expressed as

Step 3: Based on the energy balance criterion, estimate the flight time window under ideal conditions

Based on the principle of the energy method, when the battery capacity of the solar drone is not considered (that is, in an ideal state), to achieve day and night flight, the solar drone must satisfy the energy relationship in equation (27).

E _{uav ≥E propuls} +E _av +E _pld (27)

Among them, E _uav produces energy for the drone.

时(从1月1日开始，1月1日为1)，太阳能无人机可进行昼夜飞行(即满足式(27))，且

为连续飞行日。则

即为粗略估计的飞行时间窗(太阳能无人机航时)。当飞行地点选择在南半球时，其可进行昼夜飞行日取值一般形式为

和

本发明如不做特别说明，太阳能无人机飞行地点为北半球。

表示可进行昼夜飞行日，除与飞行任务、无人机自身属性相关外，飞行地点对其也影响较大，所以

是针对某一飞行地点而进行估算。In the present invention, the flight time of the solar drone can be defined as the set of flight days (in days) that can complete the day and night flight in one year, which is used to characterize the endurance of the solar drone when flying in clear sky. This indicator is the main indicator to measure the ultra-long endurance characteristics of solar-powered UAVs. The specific description is as follows. Assuming that the flight location is selected somewhere in the northern hemisphere, combined with the characteristics of solar radiation throughout the year in the northern hemisphere, the solar radiation is generally stronger in summer, and the n _day value of the flight day is

time (starting from January 1st, January 1st is 1), the solar drone can fly day and night (that is, satisfying equation (27)), and

For consecutive flight days. but

It is the roughly estimated flight time window (solar drone flight time). When the flight location is selected in the southern hemisphere, it can be used for day and night flight. The general form of the day is as follows:

and

Unless otherwise specified in the present invention, the flying location of the solar unmanned aerial vehicle is the northern hemisphere.

Indicates that day and night flight days can be carried out. In addition to the flight tasks and the attributes of the drone itself, the flight location also has a great influence on it, so

It is estimated for a certain flight location.

After clarifying the definition of the flight time window, it is necessary to obtain the boundary date of the flight time window based on the statistical law of solar radiation and solar radiation, so as to calculate the estimated flight time window of the solar UAV under ideal conditions, as shown in Figure 2 in April 3rd and September 7th. Assuming that the solar UAV performs steady-state flight (fixed altitude and speed) and the storage capacity of the UAV's backup power supply is large enough, it will be very difficult to solve the analytical solution of the flight time. Calculate the energy production of each flight day in 1 year separately, and draw the energy consumption of each flight day, and then calculate the energy consumption of each flight day in 1 year according to the energy consumption calculation method, and draw it in the same coordinate system. The intersection of the energy production curve and the energy consumption curve is the boundary value of the flight time window. That is, according to formulas (1)-(15), calculate the total energy production of solar drones on each flight day; then calculate the energy consumption per flight day of the aircraft according to formulas (16)-(26); finally, according to formula (27) Determine the time-of-flight window boundaries to determine the time.

Step 4: Accurately estimate the flight time window considering the actual battery capacity

In addition to satisfying the energy relation (27), the criterion for judging the energy storage capacity of the UAV is as follows:

为太阳能无人机上午生产功率与消耗功率平衡时刻，

为太阳能无人机下午生产功率与消耗功率平衡时刻，E_bat为电池所含能量总额，单位瓦时，可按式(29)计算：in,

To balance the power production and power consumption of solar drones in the morning,

is the balance time between the production power and the consumption power of the solar drone in the afternoon, E _bat is the total energy contained in the battery, in watt-hour, and can be calculated according to formula (29):

E _bat =C _bat U _bat (29)

Among them, C _bat is the capacity of the energy storage battery, in ampere hours, and U _bat is the nominal voltage of the energy storage battery. Substituting Equation (29) into Equation (28) can be organized as follows

中的所有日期

进行筛选，得到新的跨昼夜连续飞行日

组成的集合

即为实际可行的飞行时间窗。Then, using the formula (30), the time-of-flight window in the ideal state obtained in step 3

all dates in

Screening for new consecutive flight days across day and night

a collection of

That is the practical flight time window.

Example:

Assuming that the parameters of a solar drone are shown in Table 1, the cruising location is Beijing (39.93°N, 116.28°E, 55 meters above sea level), and the estimated parameters of solar drone energy production are shown in Table 2. First, the energy production status of solar UAVs per day in Beijing for 365 days a year is calculated by formula (1)-formula (15). Secondly, according to equations (16)-(26), the energy consumption of the UAV is calculated. Then, according to equation (27), the UAV energy production and consumption balance relationship is obtained to obtain the UAV flight time window under ideal conditions. Finally, according to the actual capacity of the battery from equations (28) to (30), screen the obtained flight time window in the ideal state, and obtain the flight time window that is practical and feasible, as shown in Figure 2.

Table 1 A UAV parameter table

Table 2 Estimated parameters of solar UAV energy production

Claims (1)

1. A method for estimating flight time of a fixed-wing solar-powered UAV, comprising the following steps: Step 1: Count the energy production status of solar drones, that is, the total energy production of solar drones per flight day; Specifically: Obtain the total energy production E _uav of the solar drone per flight day:

Among them, n _day is the specified sun day; t ₀ is 0, t _{f is} 86400, t represents time; P _in represents the current solar UAV energy production power, specifically: P _in = η _sol SP _s (λ) Among them, P _s (λ) represents the solar radiation intensity per unit area of the airfoil when the aircraft attitude angle is (ψ, θ, φ); η _sol is the solar cell efficiency; S is the wing area, and P _s (λ) is specifically:

Among them, I _b represents the direct solar radiation intensity received on the unit horizontal plane,

I is the solar radiation constant,

I ₀ is the solar constant; τ _b is the direct optical depth; m _r is the air mass ratio,

b represents the direct air quality index, b=1.219-0.043τ _b -0.151τ _d -0.204τ _b τ _d ; I _d represents the direct solar scattering intensity received on a unit horizontal plane,

τ _d represents the scattering optical depth; d represents the scattering air quality index, d=0.202+0.852τ _b -0.007τ _d -0.357τ _b τ _d ; I _h represents the total solar radiation intensity received on a unit horizontal plane, I _h =I _b sinα _e +I _d ; α _e represents the altitude angle of the sun; λ is the incident angle of sunlight entering the airfoil of the solar aircraft; φ is the roll angle of the solar drone; ρ _r represents the ground reflectivity; Step 2: Calculate the energy consumption status, that is, the energy consumption of the aircraft per flight day; Specifically: Obtain the total energy consumption E _out (t ₀ ,t _f ) of the UAV in the time period [t ₀ ,t _f ] of each flight day of the aircraft:

Among them, P _propuls is the power required by the electric propulsion system; P _av is the power consumption of the UAV airborne electronic equipment; P _pld is the power consumption required by the mission load;

Among them, η _prop is the propeller efficiency; η _mot motor and gearbox power transmission efficiency; η _ctrl drive efficiency; V is the flight speed; D is the flight resistance:

Among them, ρ,

α is the air density, the zero lift coefficient, the lift coefficient caused by the angle of attack, and the angle of attack; m is the mass of the aircraft; g is the acceleration of gravity; C _D is the drag coefficient;

Zero lift drag coefficient; K is aerodynamic coefficient; R _a is aspect ratio; ε is Oswald efficiency factor; C _L is lift coefficient; Step 3: Based on the energy balance criterion, estimate the flight time window under ideal conditions; Specifically: Ideally, the energy of solar drones satisfies: E _{uav ≥E propuls} +E _av +E _pld (27) Among them, E _uav produces energy for the UAV; The flight time of the solar drone is defined as the set of flight days that complete the day and night flight in one year. Assuming that the flight location is selected somewhere in the northern hemisphere, the value of the flight day n _day is

, starting from January 1st, and January 1st is 1, the solar drone will fly day and night, which satisfies Equation (27), and

is a continuous flight day, then

It is the roughly estimated flight time window, that is, the solar drone flight time. When the flight location is selected in the southern hemisphere, the value of the day and night flight is in the form of

and

Step 4: Accurately estimate the flight time window considering the actual battery capacity; Specifically: In addition to satisfying the energy relation (27), the criterion for judging the energy storage capacity of the UAV is as follows:

in,

To balance the power production and power consumption of solar drones in the morning,

is the balance time between the production power and the consumption power of the solar drone in the afternoon, E _bat is the total energy contained in the battery, in watt-hour, calculated according to formula (29): E _bat =C _bat U _bat (29) Among them, C _bat is the capacity of the energy storage battery, the unit is ampere hour, U _bat is the nominal voltage of the energy storage battery, and the formula (29) is substituted into the formula (28) as follows

Then, using the formula (30), the time-of-flight window in the ideal state obtained in step 3

all dates in

Screening for new consecutive flight days across day and night

a collection of

That is the practical flight time window.

Images