Flight Duration Research Articles

A numerical investigation of debris initialisation in tornado-like wind fields

The process of debris initialisation is examined for two tornado-like vortices with swirl ratios (S) of 0.3 and 0.7. The vortices were modelled using Large-eddy Simulation and the motion of spherical debris were calculated using Lagrangian-particle tracking. A total of 2700 individual debris particles, corresponding to three different groups (A, B and C) with different Tachikawa numbers (K=2.5, 1.2 and 0.6 respectively) were released. The vortex S=0.7 has greater magnitude of tangential velocity (∼12.7 m/s) compared to vortex S=0.3 (∼11.7 m/s). The corresponding maximum vertical velocities in the flow when S=0.3 were approximately twice those corresponding to S=0.7; this resulted in longer flight durations for debris group A, B and C, i.e., 65%, 73% and 58% longer respectively. An analysis of the spatial displacement of the vortex centre relative to the centre of the simulator shows that both vortices have a maximum displacement of less than 0.02 m. This suggests that the low wandering motions of the vortices have minimum effect on the debris initialisation. The vertical velocity component is shown to be key for the generation and sustaining of debris flight. For example, for S=0.3, approximately 22% (group A), 5% (group B) and 10% (group C) more particles were being initialised compared to S=0.7. The ensemble averaged flow fields associated with flight initiation show the greatest difference at low elevation (less than 0.11 m) compared to non-initialising conditions. It was also found that the tangential and radial velocity components have relatively little impact on flight initialisation. The findings presented in this research provide a fundamental insight into the physics which govern debris initialisation in tornado-like flow.

Changes in the Vickers hardness, wettability, structural and mechanical properties of the «shielding composite» under the exposure to cosmic radiation

The article presents the results of the study of the structure and surface of the «Shielding composite» (polymer composite for radiation shielding), which was in space on the Russian segment of the ISS for 225 days. The research was conducted as part of the space experiment “Shielding Composite” on the Russian segment of the ISS in 2022. The polymer composite was used to make the container that was installed in the cosmonauts’ cabin for the entire duration of the orbital flight. Being in space resulted in a slight decrease in the microhardness of the outer surface, but did not affect the deeper layers or the inner structure of the composite: microhardness of the outer surface decreased by 0.19 HV (4.5 %); microhardness of the inner surface increased by 0.79 HV (18.6 %); cross section remained unchanged. The results of ultrasound scanning of the upper cap of the container showed a slight decrease in the ultrasonic wave propagation velocity (by 4 %) and the modulus of elasticity of the composite (by 9 %) after space tests of the composite. There is an insignificant decrease (up to 5 %) in free surface energy of the composite after being in space for 225 days. Water wetting contact angle of the composite increased from 100.98 ± 2.60° to 106.85 ± 14.28° and diiodo-methane wetting contact angle increased from 57.50 ± 8.33° to 59.55 ± 7.22° after cosmic exposure.

Bioenergetic Analysis and Fatigue Assessment During the Fran Workout in Experienced Crossfitters.

To quantify the physiological demands and impact of muscle function t of the Fran workout, one of the most popular CrossFit benchmarks. Twentyexperienced CrossFitters-16 male: 29 (6)years old and 4 female: 26 (5)years old- performed 3 rounds (with 30-s rests in between) of 21-21, 15-15, and 9-9 front squats to overhead press plus pull-up repetitions. Oxygen uptake and heart rate were measured at baseline, during the workout, and in the recovery period. Rating of perceived exertion, blood lactate, and glucose concentrations were assessed at rest, during the intervals, and in the recovery period. Muscular fatigue was also monitored at rest and at 5 minutes, 30 minutes, and 24 hours postexercise. Repeated-measures analysis of variancewas performed to compare time points. Aerobic (52%-29%) and anaerobic alactic (30%-23%) energy contributions decreased and the anaerobic lactic contribution increased (18%-48%) across the 3 rounds of the Fran workout. Countermovement jump height decreased by 8% (-12 to -3) mean change (95% CI), flight duration by 14% (-19 to -7), maximum velocity by 3% (-5 to -0.1), peak force 4% (-7 to -0.1), and physical performance (plank prone 47% [-54 to -38]) were observed. It appears that the Fran workout is a physically demanding activity that recruits energy from both aerobic and anaerobic systems. This severe-intensity workout evokes substantial postexercise fatigue and corresponding reduction in muscle function.

Creation of new logistics for the export of arctic mineral resources as a condition for their sustainable development

An overview of possible transformations of logistic schemes for the export of mineral raw materials mined in the Arctic zone of the Russian Federation is presented. The existing system of transportation of mineral raw materials by sea, rail, inland water, road and air transport is considered. The description of mineral resource centers forming the cargo base of the Arctic transport system is given; their typification by types of transport for the export of products is given. A change in logistics schemes in connection with access to new markets in the changed geopolitical conditions was considered. The need for changes does not apply to rail, inland water, road and aviation transport, which provide mainly domestic transportation. Major changes affect pipeline and maritime transport. It was concluded that it is necessary to create liquefied natural gas production facilities at the exit points to the coast of the poorly devoured seas of main gas pipelines in order to monetize pipeline gas and expand the throughput capacity of main oil pipelines suitable for port oil loading terminals of the Baltic and Black Seas. The conditions for delivery to Asian oil export markets by sea have deteriorated due to the increase in the duration of circular flights and the cost of tanker freight. In addition, the possibility of an increase in the cargo traffic of the oil export to the Asian market in the Northern Sea Route was questioned due to the lack of a high deadweight cargo fleet and the required Arctic ice classes. The proposal on the need to revise strategic planning documents adopted in other political and economic conditions based on the current realities is justified.

Project Lyra: Another possible trajectory to 1I/’Oumuamua

The first interstellar object to be discovered, 1I/’Oumuamua, exhibited various unusual properties as it was tracked on its passage through the inner solar system in 2017/2018. In terms of the potential scientific return, a spacecraft mission to intercept and study it in situ would be invaluable. As an extension to previous Project Lyra studies, this paper elaborates an alternative mission to 1I/’Oumuamua, this time also requiring a Jupiter Oberth Manoeuvre (JOM) to accelerate the spacecraft towards its destination. The difference is in the combination of planetary flybys exploited to get to Jupiter, which includes a Mars encounter before proceeding to Jupiter. The trajectory identified is inferior to previous finds in terms of higher ΔV requirement (15.6 kms−1), longer flight duration (29 years) and less mission preparation time (launch 2026), however it benefits from a feature absent from previous JOM candidates, in that there is little or no ΔV en route to Jupiter (i.e. a free ride) which means the spacecraft need not carry a liquid propellant stage. This is marginally offset by the higher ΔV needed at Jupiter, requiring either 2 or 3 staged solid rocket motors. As an example, a Falcon Heavy Expendable with a CASTOR 30B booster followed by a STAR 48B can deliver 102kg to 1I/’Oumuamua by the year 2059. Other scenarios with shorter flight durations and higher payload masses are possible.

Aeroballistic optimization of long-range guided ammunition

PurposeThis paper aims to describe the use of optimization approaches to increase the range of near-future howitzer ammunition.Design/methodology/approachThe performance of a gliding projectile concept is assessed using an aeroballistic workflow, comprising aerodynamic characterization and flight trajectory computation. First, a single-objective optimization is run with genetic algorithms to find the maximal attainable range for this type of projectile. Then, a multi-objective formulation of the problem is proposed to consider the compromise between range and time of flight. Finally, the aerodynamic model used for the gliding ammunition is evaluated, in comparison with direct computational fluid dynamics (CFD) computations.FindingsApplying single-objective range maximization results in a great improvement of the reachable distance of the projectile, at the expense of the flight duration. Therefore, a multi-objective optimization is implemented in a second time, to search sets of parameters resulting in an optimal compromise between fire range and flight time. The resulting Pareto front can be directly interpreted and has the advantage of being useful for tactical decisions.Research limitations/implicationsThe main limitation of the work concerns the aerodynamic model of the gliding ammunition, which was initially proposed as an alternative to reduce significantly the computational cost of aerodynamic characterization and enable optimizations. When compared with direct CFD computations, this method appears to induce an overestimation of the range. This suggests future evolution to improve the accuracy of this approach.Originality/valueTo the best of the authors’ knowledge, this paper presents an original ammunition concept for howitzers, aiming at extending the range of fire by using lifting surfaces and guidance. In addition, optimization techniques are used to improve the range of such projectile configuration.

Clinical outcomes of traumatic pneumothoraces undergoing conservative management following detection by prehospital physicians

ObjectiveTo describe the clinical and transport characteristics of patients diagnosed with a suspected traumatic pneumothorax and managed conservatively by prehospital medical teams including secondary deterioration during transfer and the subsequent rate of in-hospital tube thoracostomy. MethodsRetrospective observational study of all adult trauma patients diagnosed with a suspected pneumothorax on ultrasound and managed conservatively by their treating prehospital medical team between 2018 and 2020. Descriptive analysis was performed comparing patients who did and did not receive in-hospital tube thoracostomy. ResultsIn total, 181 patients were diagnosed with suspected traumatic pneumothoraces on prehospital ultrasound of which 75 (41.4%) were managed conservatively by their treating medical team whilst 106 (58.6%) underwent pleural decompression. There were no recorded cases of emergent pleural decompression required in transit. Of the 75 conservatively managed patients, 42 (56%) had an intercostal catheter (ICC) placed within four hours of hospital arrival and another nine (17.6%) had an ICC placed between four- and 24-hours post-hospital arrival. There was no significant difference in prehospital clinical characteristics between patients who did and did not receive an in-hospital ICC. The detection of a pneumothorax on the initial chest x-ray and larger pneumothorax volume visualised on computed tomography imaging were significantly more common in patients receiving in-hospital ICCs. Aviation factors including flight altitude and duration of flight were not associated with subsequent in-hospital tube thoracostomy. ConclusionPrehospital medical teams can safely identify patients who have a traumatic pneumothorax and can be transported to hospital without pleural decompression. Patient characteristics at the time of hospital arrival combined with the size of pneumothorax identified on imaging appear most likely to influence subsequent urgent in-hospital tube thoracostomy placement.

Estimation and flight verification of fuel consumption rate of small fixed-wing UAV for a long flight duration

Estimation and flight verification of fuel consumption rate of small fixed-wing UAV for a long flight duration

Engineering and navigating calculation the flight of unmanned aircrafts of tactical class

The regulatory documents of the Ministry of Defense of Ukraine provide for navigational training of the crews of unmanned aircraft complexes and establish the necessity of having a navigational plan and an engineering-navigator flight calculation at the workplace of an external UAV pilot. The article notes that today there are no normative documents that would establish the content and scope of engineering and navigational calculations and methods of their implementation for unmanned aircraft complexes of tactical classes. The article as a whole is devoted to the consideration of issues of methodical support of navigator training of crews of unmanned aerial systems of the tactical class with an electric power plant. It is indicated that, based on the tactical and technical capabilities of UAVs of tactical classes, the nature of the tasks performed by them and the typical educational level of their external pilots, the creation of the most simplified methodology for performing basic engineering and navigational calculations of UAV flights is required. The mathematical complexity of such a method should not go beyond general secondary education. When performing navigational calculations of aircraft flights, the main difficulty is created by the problem of taking into account the influence of the wind. Simple algorithms for calculating the correction to the wind drift course, road speed and flight duration on straight sections of the route and sections of U-turns in the presence of wind are proposed. Algorithms for calculating the total need for energy resources for a flight along a given route and for separate sections of the route, including additional energy resource needs for sections of altitude gain, are proposed. Recommendations for evaluating the energy capacity of the battery available for flight performance are given. An algorithm for calculating the critical reserve of energy resources, which is necessary for the possibility of returning the UAV from the farthest point of the route under meteorological conditions for the scheduled flight time, is proposed. Options for full and abbreviated engineering and navigational calculations are offered.

VR-Supported Analysis of UAV—Magnetic Launcher’s Cart System

The subject of the research is a model of a magnetic launcher, which is an innovative alternative to commercially occurring unmanned aircraft launchers (UAV). As the take-off is an energy-demanding phase of the flight; therefore, abandoning the power supply of the UAV during this phase significantly affects increasing the potential range and duration of UAV flight. The magnetic launcher offers the significant advantage of minimizing friction between the starting cart and the launcher, resulting in the higher energy efficiency of the system. Research conducted so far has shown that the possibility of accelerating the aircraft on the longer runway offered by the launcher reduces aircraft overloads occurring during take-off. As a result, the launcher, aircraft, and onboard equipment are much safer. This paper presents the system’s mathematical modeling and numerical simulation results for micro-class UAV take-off and landing using the analyzed magnetic launcher. The computer program for analyzing system dynamics was implemented in the MATLAB environment. Simulation results were visualized graphically and as animations in Virtual Reality. The VR application was implemented in Unity and ran on VR goggles Oculus Quest2. The simulations carried out show that—in the absence of control—an important factor reducing the takeoff distance and affecting the aircraft load is the adoption of a non-zero takeoff thrust of the UAV. The initial pitch angle also has a significant impact on the takeoff process. With an increase in this parameter, the length of the takeoff distance decreases and the lift-off speed decreases, but too much pitch angle may result in the aircraft descending in the first moments of flight, which could lead to a collision with the launch rails.

Exposure to a 900 MHz electromagnetic field induces a response of the honey bee organism on the level of enzyme activity and the expression of stress-related genes.

There are many artificial sources of radiofrequency electromagnetic field (RF-EMF) in the environment, with a value between 100 MHz and 6 GHz. The most frequently used signal is with a frequency of around 900 MHz. The direction of these changes positively impacts the quality of life, enabling easy communication from almost anywhere in the world. All living organisms in the world feel the effects of the electromagnetic field on them. The observations regarding the influence of a RF-EMF on honey bees, describing the general impact of RF-EMF on the colony and/or behavior of individual bees, such as reduction in the number of individuals in colonies, extended homing flight duration, decrease in breeding efficiency, changes in flight direction (movement of bees toward the areas affected by RF-EMF), increase in the intensity and frequency of sounds characteristic for those announcing the impending danger. In this work, we describe the changes in the levels of some of the stress-related markers in honey bees exposed to varying intensities and duration of RF-EMF. One-day-old honeybee worker bees were used for the study. The bees were randomly assigned to 9 experimental groups which were exposed to the following 900 MHz EMF intensities: 12 V/m, 28 V/m, and 61 V/m for 15 min, 1 h and 3 h. The control group was not exposed to the RF-EMF. Each experimental group consisted of 10 cages in which were 100 bees. Then, hemolymph was collected from the bees, in which the activity was assessed AST, ALT, ALP, GGTP, and level of nonenzymatic antioxidants albumin, creatinine, uric acid, and urea. Bees were also collected for the analysis of rps5, ppo, hsp10, hsp70, hsp90, and vitellogenin gene expression. Our study shows that exposure to a 900 MHz electromagnetic field induces a response in the honey bees that can be detected in the level of enzyme activity and the expression of stress-related genes. The response is similar to the one previously described as a result of exposition to UVB irradiation and most likely cannot be attributed to increased temperature.

Comparison of logistic regression and artificial neural network model for apron allocation assignment

Management of the parking apron is one of the most essential airport ground service operations for flight operations to run smoothly. Effective airport ground service management will have a direct effect on the cost and duration of flights. Therefore, in this paper, we address the issue of using machine learning techniques, such as logistic regression analysis and artificial neural network (ANNs) models, for classified targets of stand locations assignment of an arriving flight. Also, this could assist ground controllers to assign apron allocation and improve the efficiency and predictability of airport operations which reduce the time required for airport ground processing to increase flight capacity. In order to evaluate the performance of the proposed method, simulation results reveal that ANN has the lowest error rate and the highest accuracy. Therefore, ANN is the effective classification technique for this data set.

Songbirds initiate migratory flights synchronously relative to civil dusk

BackgroundEach spring and fall billions of songbirds depart on nocturnal migrations across the globe. Theory suggests that songbirds should depart on migration shortly after sunset to maximize their potential for nightly flight duration or to time departure with the emergence of celestial cues needed for orientation and navigation. Although captive studies have found that songbirds depart during a narrow window of time after sunset, observational studies have found that wild birds depart later and more asynchronously relative to sunset than predicted.MethodsWe used coded radio tags and automated radio-telemetry to estimate the time that nearly 400 individuals from nine songbird species departed their breeding or wintering grounds across North America. We also assessed whether each species was most likely beginning long-distance migratory flights at departure or instead first making non-migratory regional flights. We then explored variation in nocturnal departure time by post-departure movement type, species, age, sex, and season.ResultsWe found that 90% of individuals from species that were likely initiating long-distance migratory flights departed within 69 min of civil dusk, regardless of species, season, age, or sex. By contrast, species that likely first made non-migratory regional movements away from the migratory destination departed later and more asynchronously throughout the night. Regardless of post-departure movement type, 98% of individuals departed after civil dusk but otherwise showed no preference in relation to twilight phase.ConclusionsAlthough the presence of celestial orientation cues at civil dusk may set a starting point for departure each night, the fact that species likely beginning long-distance migration departed earlier and more synchronously relative to civil dusk than those first making non-migratory regional movements is consistent with the hypothesis that departing promptly after civil dusk functions to maximize the potential for nightly flight duration and distance. By studying the onset of migration, our study provides baseline information about departure decisions that may enhance our understanding of departure timing throughout migration.

Dog barks influence the physiological stress and behavior of a wild primate

Non-lethal impacts of dogs on primates have seldom been assessed. We used an experimental approach to determine if mantled howler monkeys (Alouatta palliata) perceive dog barks as an aversive stimulus and thus display physiological and behavioral responses toward simulated barks. For one year (1754 h of observations) we studied 16 adult males belonging to five groups in Los Tuxtlas (Mexico), and recorded the occurrence of naturally occurring dog barks, their sound pressure level (SPL), and the behavioral responses of howler monkeys to barks. We then exposed males to bark playbacks at two SPL treatments, 40 and 80 dB in a total of 50 experiments. We assayed glucocorticoid metabolite concentrations in fecal samples (fGCM) as a marker of the physiological stress response of males. We also recorded the duration of vigilance, vocalizations, and flight in relation to playbacks. Naturally occurring barks were frequent and usually elicited behavioral responses by males. fGCM concentrations increased after bark playbacks and with stimuli intensity. Time spent vigilant increased following playbacks independently of stimuli intensity but both vocalizations and flight were linked to stimuli intensity: vocalizations were the longest after barks played-back at 80 dB, but males spent more time fleeing in response to 40 dB bark playbacks. These results provide evidence that dog barks are pervasive in the habitat of mantled howler monkeys living at Los Tuxtlas and disturb males, both physiologically and behaviorally. Although the potential costs of physiological and behavioral responses could not be determined, there is sufficient evidence to assume that they do have negative impacts on individuals. Therefore, our study provides avenues for future research on dog-wildlife interactions and valuable information for the design of conservation actions aimed at mitigating the impact of dogs on mantled howler monkeys.

Long-duration wind tunnel flights reveal exponential declines in protein catabolism over time in short- and long-distance migratory warblers

During migration, long-distance migratory songbirds may fly nonstop for days, whereas shorter-distance migrants complete flights of 6 to 10 h. Fat is the primary fuel source, but protein is also assumed to provide a low, consistent amount of energy for flight. However, little is known about how the use of these fuel sources differs among bird species and in response to flight duration. Current models predict that birds can fly until fat stores are exhausted, with little consideration of protein's limits on flight range or duration. We captured two related migratory species-ultra long-distance blackpoll warblers (Setophaga striata) and short-distance yellow-rumped warblers (Setophaga coronata)-during fall migration and flew them in a wind tunnel to examine differences in energy expenditure, overall fuel use, and fuel mixture. We measured fat and fat-free body mass before and after flight using quantitative magnetic resonance and calculated energy expenditure from body composition changes and doubly labeled water. Three blackpolls flew voluntarily for up to 28 h-the longest wind tunnel flight to date-and ended flights with substantial fat reserves but concave flight muscle, indicating that protein loss, rather than fat, may actually limit flight duration. Interestingly, while blackpolls had significantly lower mass-specific metabolic power in flight than that of yellow-rumped warblers and fuel use was remarkably similar in both species, with consistent fat use but exceptionally high rates of protein loss at the start of flight that declined exponentially over time. This suggests that protein may be a critical, dynamic, and often overlooked fuel for long-distance migratory birds.

Sensory organization of postural control after long term space flight.

Alterations in motor control systems is an inevitable consequence of space flights of any duration. After the flight, the crew-members have significant difficulties with maintaining upright balance and locomotion, which last several days following landing. At the same time, the specific mechanisms of these effects remain unclear. The aim of the study was to assess effects of long-term space flight on postural control and to define the changes of sensory organization caused by microgravity. 33 cosmonauts of Russian Space Agency, the members of International Space Station (ISS) flights of duration between 166 and 196 days took part in this study. Computerized Dynamic Posturography (CDP) tests, which include assessment of visual, proprioceptive and vestibular function in postural stability, was performed twice before the flight and on the 3rd, 7th, and 10th days after landing. The video analysis of ankle and hip joints fluctuations was performed to investigate the basis of postural changes. Exposure to long-term space flight was followed by considerable changes of postural stability (-27% of Equilibrium Score value in the most complicated test, SOT5m). Changes in postural strategies to maintain balance were observed in the tests which provide the challenge for vestibular system. In particular, increased hip joint involvement (+100% in median value and +135% in 3rd quartile of hip angle fluctuation RMS in SOT5m) into postural control process was revealed. Decrease of postural stability after long-term space flight was associated with alterations in vestibular system and biomechanically was revealed by increased hip strategy which is less accurate, but simpler in terms of the central control.

Unmanned Aerial Vehicle as Encryption Key Distributor for Secure Communications in Smart Grid

We use symmetric cryptography for secure communications with resource limited smart grid control devices. We propose the novel idea of using the unmanned aerial vehicle (UAV) as a physical courier to carry secret key bits generated at the control center to remote control devices. While distributing secret keys, the UAV may be attacked in an attempt to sabotage secure communications. The UAV may fly a longer route to avoid attackers but it has a limited on-board battery capacity and must visit each device within a time limit to prevent a secret key deficit. We formulate an optimization to find the lowest attack risk flight route for secret key distribution while taking into consideration key deficiency and battery capacity. Such optimization is NP-hard. We further propose an efficient algorithm to find a low-risk flight route in less than a second, even for a large power grid system with more than a hundred nodes. For large systems, we modify the proposed algorithm to find a low-risk flight route as well as to determine the required UAV flight duration and battery size. Extensive simulation results confirm the superiority of the proposed algorithm against a baseline scheme that is ignorant of attackers.

Forced Quadcopter Control

The problem of analytical synthesis of the control acceleration of an unmanned aerial vehicle (UAV) of a multirotor type is being solved in relation to a light quadrocopter with a high flight duration. The optimal control is analytically determined for a given minimized quality functional in the form of the minimum time required to transfer the UAV from a given initial to a given final position in space. A mathematical model of the movement of the UAV mass center in a given plane relative to the earth's surface is considered. A feature of the proposed technique is the solution of the problem of maximum speed (forced control) based on the consideration of the laws of kinematics of uniformly accelerated motion of a rigid body. For given characteristics of the maximum allowable speed and control acceleration of the UAV, the moments of switching of the control signal are analytically calculated, which can be implemented in the UAV autopilot. This allows, in contrast to classical methods for solving the problem of forced control, to get rid of the need to solve a two-point boundary value problem and consider additional transversality conditions. The computer simulation of the obtained analytical results in the form of processes of changing the control acceleration, as well as the UAV motion parameters, has shown the efficiency of the proposed technique and the prospects for its use at the initial stage of the synthesis of the UAV control system.

UAV-Aided Secure Short-Packet Data Collection and Transmission

Benefiting from the deployment flexibility and the line-of-sight (LoS) channel conditions, unmanned aerial vehicle (UAV) has gained tremendous attention in data collection for wireless sensor networks. However, the high-quality air-ground channels also pose significant threats to the security of UAV-aided wireless networks. In this paper, we propose a short-packet secure UAV-aided data collection and transmission scheme to guarantee the freshness and security of the transmission from the sensors to the remote ground base station (BS). First, during the data collection phase, the trajectory, the flight duration, and the user scheduling are jointly optimized with the objective of maximizing the energy efficiency (EE). To solve the non-convex EE maximization problem, we adopt the first-order Taylor expansion to convert it into two convex subproblems, which are then solved via successive convex approximation. Furthermore, we consider the maximum rate of transmission in the UAV data transmission phase to achieve a maximum secrecy rate. The transmit power and the blocklength of UAV-to-BS transmission are jointly optimized subject to the constraints of eavesdropping rate and outage probability. Simulation results are provided to validate the effectiveness of the proposed scheme.

Aerial Surveillance in Cities: When UAVs Take Public Transportation Vehicles

This paper considers using unmanned aerial vehicles (UAVs) to survey important sites across a city. When the sites are relatively far from the UAVs’ depot, the UAVs may not be able to reach many of the sites. Suppose that a UAV can take public transportation vehicles (PTVs) like a passenger. Then, it may reach a site that is unreachable by flying only. Based on this UAV-PTV scheme, we investigate a task-UAV assignment problem, which assigns a set of surveillance tasks to UAVs. We formulate a mixed-integer linear programming (MILP) problem that minimizes the overall energy consumption of UAVs, subject to that every site is surveyed by a certain number of UAVs during a given time window, and all UAVs successfully return to the depot. Considering that this problem is NP-hard, we present two sub-optimal solutions. The first solution orders the surveillance tasks according to the starting times of their time windows. Then, starting from the earliest one, it assigns the tasks one by one to UAVs. The second solution breaks the tasks into small non-overlapping groups. It then assigns tasks to UAVs group by group. The former solution quickly addresses the assignment problem, but it lacks the overall management of UAV resources. The latter improves this by assigning a group of tasks simultaneously, and it can control the computation complexity by limiting the group size. The comparison with the brute force method shows that the proposed solutions can achieve competitive performance in a reasonable time. Note to Practitioners—Unmanned aerial vehicles (UAVs) have been widely used in surveillance missions. However, one challenge practitioners often meet is the limited flight duration. Commercial UAVs are in general powered by the onboard battery. Due to the restriction of payload, the battery capacity is constrained, which limits the UAVs’ operation time. In this paper, we present the approach exploiting public transportation vehicles (PTVs). In our design, a UAV can take a public transportation vehicles such as buses, trams and trains on the roof and transfer between vehicles when necessary. With this UAV-PTV collaboration scheme, we consider how to efficiently assign surveillance tasks to UAVs. Due to the NP-hardness of the considered problem, two suboptimal algorithms are presented.