Today Unmanned Aerial Vehicles (UAV) are integrated into the diferent duties of human activity. Multiple advantages of UAV stimulate continuous growing number of practical applications in industry 4.0. Precision level of modern onboard positioning sensors supports accurate trajectory maintaining in a fully automatic mode for most short-length missions. Efective trajectory planning is a key element of mission success. In the paper, we study mission planning stage with a focus on UAV navigation. Flight phase classification is used for lateral UAV navigation and safe altitude is calculated based on a digital elevation model. Trajectory calculation for efective UAV missions includes estimation of true and magnetic heading angles; pitch angle; ground speed; time of flight and safe altitude. Forecasted weather data of wind speed and direction are used for ground speed estimation and efective mission planning. In numerical demonstration, we use specially developed software for efective mission planning of power lines exploration with UAV of airplane type.
Nowadays Unmanned Aerial Vehicles (UAV) play an important part in the global economy [
UAV could use copter structures with any number of engines. Copter structure provides the possibility of holding in a particular point of airspace, changing direction of flight in any side, vertical take-of, and landing. Most commercially available copter UAVs are electrical engine lift generation that significantly limits time and range of system use.
UAV of airplane type is a high speed and long range of operation. Commercially available small
and medium UAVs of this type provide about 50kg of payload for ranges in 300-500 km. Most airplane
types of UAVs require a runway or specially developed launch system. Also, it highly uses a parachute
recovery system for landing due to required runway and specific skills of flight technique to landing
successfully [
Any commercial UAV application requires maintaining a defined trajectory in the airspace [
UAV operates in the atmosphere, actually, most UAVs use a lower troposphere, where most weather
phenomena are concentrated. Unfortunately, commercially available autopilots deal with normal
weather conditions only. Excessive wind speed, precipitation, drizzling, rain, snow, fog, and other
weather phenomena degrade UAV performance and create a high risk of mission fault that may be
result of particular failures in UAV systems [
Many studies in aviation focus on trajectory correction due to avoidance of entering part of airspace
with dangerous weather phenomena action [
In the paper, we study a process of UAV trajectory calculation for upcoming flight that is a main part of mission planning. Also, we consider the positive impact of wind side and speed on UAV mission performance based on weather forecasts.
Mission planning is an important stage of UAV flight preparation which includes: trajectory planning of
upcoming flight, considering weather forecasts, planning settings of payload use, planning take-of and
landing, prepare UAV and payload for mission. Each of these tasks is critical for mission completion
success. For example well-planned trajectory and ideally tuned on-board systems of UAV don’t make
sense in case of payload fault. Accurately moved airframe is not efective due to fault in the main task
of the mission. UAV mission is successfully completed only in case the main goal of mission is reached.
Another important component is the technical state of each system component [
In this paper, we are mostly focused on trajectory planning and calculation in order to guarantee safe UAV operation. Trajectory planning for upcoming flight requires selection of waypoints passing UAV through which makes it possible to use payload to reach the main goal of mission (Figure 1). Trajectory is specified as a sequence of waypoints through which UAV should fly. Waypoints usually are specified in geodetic coordinates of latitude and longitude. Also, most applications require linear moved UAV between waypoints. For each waypoint, an altitude is specified. Based on flight mode altitude could be specified as a range from WGS-84 ellipsoidal model in case of using GNSS, or could be a pressure altitude calculated by a barometrical sensor and counted from isobaric line of constant pressure (760 mmHg).
Vertical plane planning for UAV mission should take into account relief altitude, natural and artificial constructions. Specified waypoints and altitude of its reaching form a flight plan for upcoming mission. Flightplan is coded by a particular data format and is loaded to autopilot module to launch a mission.
Commercially available UAVs usually include flight planning software in the general packet. Such software uses a graphical interface for interaction with a particular mapping tool for the selection of waypoints for planned trajectory. In most cases, waypoints are selected manually “on the map” by specifying coordinates based on required mission. Flight plan could be segregated into seven main phases, based on mission criteria (except transportation mission): • Take-of and climbing; • En-route (moving to point of payload use); • Maintaining to initial point of payload use;
During mission planning a point of take-of could be selected based on requirements of UAV [
Trajectory planning should be taken in accordance with rules of airspace use. Most countries limit
maximum altitude to use UAV by 500 m, however, in particular conditions altitude limit could be
extended up to 1000 m about ground level (AGL). Many commercially available UAVs have built-in
protection system to limit their use near airports and airplanes. Flight planning software avoids
trajectory creation through prohibited areas in which UAV could be dangerous. As an example, airports
are covered by prohibited areas which are approximately in a 5 km radius. Runways and areas of
airplanes moving at low altitudes are also specified as restricted. Using waypoints or trajectories
through these areas is prohibited. As an example, a configuration of prohibited areas of four airports
(UKBB, UKKK, UKMM, UKKT) in Kyiv’s vicinity is shown in Figure 2. Waypoints of flight plan are
selected taking into account uncertainty area of on-board positioning system. On-board positioning
system measures UAV coordinates with particular precision [
Many commercially available UAVs are equipped with ADS-B-in modules to receive digital data about location of closed airplanes. Autopilot has a simple algorithm to compare UAV coordinates and air trafic around. In case if UAV became close to the airplane, autopilot informs pilot about restricted zone around airplane and initiates engine stop mode. The common safety range is 60 meters of a direct range around airplane position.
Trajectory planning takes into account performance of UAV which is limited by the maximum range
of operation [
Calculation of total trajectory length (D) is mostly done by the assumption of a small operational range and linear legs that connect waypoints: = √︀(−1 − )2 + (−1 − )2 + (−1 − )2
= ∑︁ =1 (1) (2) where is the total trajectory length; is a leg length; , , are coordinates of i-th waypoint in ECEF; n is the number of legs.
Trajectory planning requires setting an altitude for each waypoint. An altitude could be specified as pressure altitude or WGS-84. The WGS-84 altitude provides a hard-fix UAV-to-Earth ellipsoidal model. Static pressure fluctuates based on weather action that makes pressure altitude in relation to the place and time. During vertical profile planning of upcoming flight it is important to use minimum descending altitude, which could be called safe altitude. Safe altitude marks an altitude range from the ground which is dangerous to operation due to the high risk of collision with nature or artificial constructions.
A digital elevation model could be used to specify terrain [
Artificial constructions and nature (stones, trees, bushes, etc.) could be taken into account by personal image study along the planning trajectory. Some UAVs may use LIDAR, imaginary, or ultrasonic sensors for virtual environment study in-flight to maintain a safe distance from dangerous elements of nature. In the case of manual control remote pilot could make a decision on a minimal descent point for each point of planned trajectory based on visual data from on-board cameras.
A sequence of waypoints for upcoming UAV mission has to be used for navigation data calculation. Navigation data is required for manual piloting mode as well as for autopilot initial data setting. These data include: • Length of each flight plan leg; • True and magnetic heading angles; • Pitch angle (important for airplane type of UAV); • Ground speed; • Time to fly between waypoints (ETE); • Estimated time of arrival at each waypoint (ETA); • Getting relief data.
Heading is an angle in a horizontal plane between the North direction and the direction of UAV movement along the flight plan leg counted clockwise in the point of UAV location. Heading could be True or Magnetic. True heading is based on using True poles of Earth in which rotation axis is passing through. Magnetic heading uses Earth’s magnetic field configuration. Magnetic heading helps to predict magnetic compass readings along a particular flight plan leg. Actually, the shortest line between two waypoints results in a constant heading angle. Therefore, each leg corresponds to a particular true heading angle and a small variation of magnetic heading.
True heading angle could be calculated based on leg orientation in the space of local cartesian frame with a reference point in waypoint coordinates. Local North-East-Up cartesian reference frame is useful for true heading angle (THA) calculation (Figure 3). True Heading Angle (THA) could be calculated as follows: ⎧ ⎪arctan ︁( )︁ , ⎪ ⎪ ⎪ ⎪⎪ + arctan (︁ )︁ , ⎪ ⎪ ⎨ ⎪⎪⎪⎪ 3 , ⎪⎪ 2 ⎪⎪⎩ 2 , if > 0 and ≥ 0 if < 0 if = 0 and < 0 if = 0 and > 0 THA = 2 + arctan (︁ )︁ , if > 0 and < 0 (3) where and are coordinates of i-th waypoint in the North-East-Up cartesian reference frame. where is a pitch angle of trajectory at i-th leg.
Time to flight between waypoints (ETE) is calculated based on initial settings of airspeed. In case wind data is available, airspeed could be recalculated to ground speed. Obtained values of ground speed are used for estimation of the time to flight at each leg of flight plan: where is the ground speed of UAV at i-th leg of a flight plan.
Estimated time of arrival at the waypoint (ETA) is calculated as a cumulative sum at each waypoint:
Magnetic heading angle (MHA) could be estimated based on the world magnetic model [
MHA = THA + where is a declination angle at i-th waypoint.
In case of fault in primary positioning with GNSS, a simple magnetic heading reading could be used to navigate UAV to the next waypoint, based on the dead reckoning method.
The pitch angle could be calculated based on geometry of a particular trajectory leg. Pitch angle indicates vertical UAV inclination during climbing or descending for airplane type of UAV: ⎛
= arctan ⎝ √︁2 + 2 ⎠
⎞ =
= ∑︁ =1 (4) (5) (6) (7) Flight profile calculation is another important element of mission planning. A digital relief elevation model (DEM) has to be used to get terrain distribution along the planed trajectory. Most DEMs use a grid of a particular cell size. Relief altitude is assumed equal along cell space. Getting relief distribution along planed trajectory means detection of grid cell numbers based on input geodetic coordinates of each point. Precision of SRTM data is specified as cell size. Since 2014 global DEM from SRTM has been available with one arcsecond which is 30 meters cell size.
A safe altitude is calculated as relief altitude plus safety bufer: = + ℎ (8) where is number of considered points of planned trajectory; is a relief altitude by SRTM; ℎ is a safety bufer for a particular environment.
In case of wind action along the flight path, ground speed (GS) could be calculated from forecasted wind direction (WA) and wind speed (W): = √︀ 2 + 2 − 2 ( + − ) (9) During trajectory selection, it should be noted that wind speed and wind direction should be taken into account. Actually, part of trajectory in which expect to use payload could not be changed. However, a side of payload use and approaching schemes should be selected based on positive input for tailwind.
Weather plays an important role in the operation of UAVs. Weather conditions afect many aspects of UAV operations and functionality. Poor visibility greatly complicates the operation of a UAV, as most UAVs use cameras to collect information about the environment, and fog or rain can interfere with their observation capabilities. One of the reasons for this may be air safety, as low visibility increases the risk of collision with other airspace users. Rain, snow, and fog can become intense and impair visibility. Due to precipitation, there may be high humidity, which has a negative impact on the operation of sensors and electronics in UAVs and can cause short circuits or malfunctions
Humidity is measured by a hygrometer or weather station. It has a great impact on radio signal propagation. The higher the humidity, the worse the quality of communication and thus the shorter the range of the total system.
Icing of UAV in the air leads to many problems in their operation. Icing occurs at temperatures between +1 C° and -50 C°. The main types of icing are ice, frost, and frost. Ice that accumulates on the surface of the vehicle increases its weight, which leads to changes in flight characteristics and recalculation of control parameters.
There may be changes in the aerodynamic characteristics of the UAV, increasing air resistance, which leads to a decrease in speed. Ice accumulated on sensors and cameras can damage their operation. In order to have a chance of successfully completing a UAV mission, you need to know the air temperature near the ground, the dew point temperature, the UAV altitude, and the air speed.
Icing occurs due to uneven distribution of atmospheric pressure and is directed from areas with high pressure to areas with low pressure. Due to constant changes in atmospheric pressure, wind direction, and speed are constantly changing. At high altitudes, the wind may increase due to reduced air friction on the ground.
The Earth’s surface has diferent terrain and humidity levels, which leads to uneven heating under the influence of sunlight. Darker and drier areas warm up faster than lighter and more humid areas, releasing more heat into the air. In addition, slopes and elevations also afect heating: southern slopes are warmer than northern ones, and eastern slopes warm-up earlier than western ones. These factors create conditions for the thermal activity of air. Warm, heated air rises upward, creating upward heat lfows or thermals, while cold air from colder areas replaces it, forming a local or thermal wind. This leads to an increase or decrease in the wind in the ground layer in the presence of a background wind. Without a background wind, the local wind blows in diferent directions and not periodically.
The efect of wind on UAVs is quite important to consider when flying. Strong winds afect flight stability. Under the influence of a strong side wind, the aircraft begins to roll unstably or change direction. Wind afects the speed of an unmanned aerial vehicle. When flying against the wind, the aircraft moves more slowly and this increases the flight time. When flying into the wind, the flight speed increases.
Flying against strong winds increases the energy consumption of the batteries, which reduces the lfight time and limits the range. Wind causes a loss of control over the aircraft. The stronger the wind blows, the stronger and larger the rotor behind the obstacle can be. It is important to understand that the length of the rotor behind an obstacle depends on the square of the height of the obstacle. When landing, it is advisable to land on the windward side in front of an obstacle, such as a forest belt, rather than behind it, given the wind direction.
Before flying, the crew needs to study the weather conditions. Pilot can obtain this information from National or regional weather services, aviation weather services, and they can also use various websites or mobile applications. In general, many factors can afect UAVs, but the most important ones that operators should consider when planning their route and making preliminary calculations have been highlighted. Also, when choosing a route, it is imperative to take into account the radius of application, maximum flight range, the most favorable flight duration speed, the most economical flight speed, and the speed per wind direction at altitudes.
In numerical demonstration, we consider as an example of flight trajectory planning for automatic power lines checking mission. We use UAV -10 for detailed power lines filming with post-flight picture analysis to identify deterioration of technical condition of mechanical constructions. UAV performance is following: • Propulsion: one electric engine; • Take-of mass 4.5 kg; • Max mission duration: 0.6 hours; • Cruise airspeed: 72 km/h; • Max barometrical altitude: 2000 m.
UAV requires a special runway or a launch pad. Landing is provided with a parachute system. Payload will be automatically pointed to power line construction. Exploared part of the power line is approximately 5 km placed in wild nature. Team members are going to launch UAV from a launch pad located in 3 km from the power lines location and expect UAV to land with a parachute in an area with no trees or brushes. An appropriate place for landing is approximately 11.6 km from the final point of payload use. The configuration of flight flight-planned trajectory of the upcoming flight is represented in Figure 4. It will include take-of, landing, and 9 waypoints of en-route (WP 1-WP 9). The main task is using a payload at legs WP3-WP4 and WP4-WP5 to explore derogative state of a power line construction. During the planning coordinates of WP3-WP5 a sun location was taken into account and harmful action of electromagnetic field closed to power lines. Landing area is selected based on smallest nature configuration. Therefore after finishing use payload UAV has to travel to landing area located far away from the active area. Mission start has been planned at 11:23:02 UTC. Results of planned trajectory calculation are presented in Table 1. For calculation GS we use actual weather data for each waypoint. Due to the low length of total trajectory, wind data could be constant for each waypoint. We use a wind speed is 1.3 m/s which is applied with wind direction at 270°. Also, we expect to use constant cruise speed along the whole trajectory. Total trajectory length is 27 km which takes more than 20 min to meet the main mission goal. The mission is planned to be in fully automatic mode. The team is used only for launch equipment deployment, then launch and UAV maintenance after parachute landing.
Terrain altitude calculated for each point of trajectory based on SRTM is shown in Figure 5. Also, we use a 30 m safe altitude above relief to avoid collision with nature. At the legs of payload use, we descend UAV to 16 m to move payload close to observed construction.
Trajectory planning of upcoming UAV mission should be based on lateral flight path selection and correct safe altitude. Trajectory should be set up with a sequence of waypoints and a specified altitude for each of them. Configuration of waypoints should be selected with criteria of meeting the main goal of the mission, which means moving a payload along a specified trajectory. Weather can significantly influence a mission, thus actual weather parameters should be compared with peril values to meet performance of UAV. Trajectory of up-coming mission should be selected considering wind direction. Approach to a leg of payload use should be wind-efective to make additional lift force input produced by a tailwind. Efectively selected trajectory could significantly improve performance of UAV used, mostly in total trajectory length and time of system use.
Efectively planned mission could be fully performed in automatic mode in rural areas in various applications. As an example exploitation of pipeline and power lines in rural areas. UAV could use high-resolution camera payloads for imaging (as well as other payload types) with geolocation and camera orientation logging. Collected during the mission data could be used for further data analysis.
The author(s) have not employed any Generative AI tools.