Flight Maneuvers Research Articles

UDE-Based Dynamic Surface Control for Quadrotor Drone Attitude Tracking under Non-Ideal Actuators

Quadrotor drone attitude tracking is inevitably affected by the combination of model uncertainties, external disturbances, and non-ideal actuator dynamics during stable flight and complex maneuvers. In order to achieve precise attitude control in these situations, a cascade-structured dynamic surface control (DSC) strategy is proposed based on an uncertainty and disturbance estimator (UDE), considering the actuator dynamics as represented by a first-order plus time-delay model. The DSC scheme is used to transform the original attitude dynamics system into a set of interconnected subsystems. On the one hand, the mismatched disturbances in the attitude kinematics and dynamics loops are converted into matched disturbances to accommodate the structural constraints of the UDE so that these disturbances, as well as the non-ideality caused by the actuator time delay, are estimated and compensated for by the approach. On the other hand, the “complexity explosion” problem is addressed by the first-order filter employed by DSC. The ultimate boundedness of the closed-loop system is proven while the parameter design constraints are provided. MATLAB Simulink simulations are conducted to demonstrate the desirability of considering actuator dynamics and to verify that the proposed control strategy can relax the constraints of the control parameters and enable a higher accuracy.

Dynamic CFD/CSD Coupling Research for Flexible Micro Aircraft

Bio-inspired flapping wing aircraft have made progress in recent years. Flying birds can fly in various low Reynolds numbers (103-105) with high flight stability and maneuvering ability by use of the flexible deformation of skeletal muscle structures or thin-film structure wings. Early studies mainly focused on the aerodynamics and kinematics of the flapping wings, with relatively little research on the flexible structure, and the aerodynamic structure coupling characteristics of micro flappings are still unclear. At present, the focus of research is to evaluate the impact of structural deformation on the aerodynamic characteristics of flexible micro-flapping wing. A CFD/CSD coupling solver are developed and several technical challenges related to the CFD/CSD interface are resolved in this study (CFD/CSD data exchange method and moving mesh generation). The aerodynamic characteristics of five flexible wings with different structural parameters are calculated and compared. The results show that structural parameters play an important role in aerodynamic performance, which also indicates that the potential aerodynamic performance can be improved by the optimal structural design.

Can morphological traits explain species-specific differences in meta-analyses? A case study of forest beetles.

Meta-analyses have become a valuable tool with which to synthesize effects across studies, but in ecology and evolution, they are often characterized by high heterogeneity, where effect sizes vary between studies. Much of this heterogeneity can be attributed to species-specific differences in responses to predictor variables. Here, we aimed to incorporate a novel trait-based approach to explain species-specific differences in a meta-analysis by testing the ability of morphological traits to explain why the effectiveness of flight-intercept trap design varies according to beetle species, a critical issue in forest pest management. An existing morphological trait database for forest beetles was supplemented, providing trait data for 97 species, while data from a previous meta-analysis on capture rates of bark or woodboring beetles according to different trap designs were updated. We combined these sources by including nine morphological traits as moderators in meta-analysis models, for five different components of trap design. Traits were selected based on theoretical hypotheses relating to beetle movement, maneuverability, and sensory perception. We compared the performance of morphological traits as moderators versus guild, taxonomic family, and null meta-analysis models. Morphological traits for the effect of trap type (panel vs. multiple-funnel) on beetle capture rates improved model fit (AICc ), reduced within-study variance (σ2 ), and explained more variation (McFadden's pseudo-R2 ) compared with null, guild, and taxonomic family models. For example, morphological trait models explained 10% more of the variance (pseudo-R2 ) when compared with a null model. However, using traits was less informative to explain how detailed elements of trap design such as surface treatment and color influence capture rates. The reduction of within-study variance when accounting for morphological traits demonstrates their potential value for explaining species-specific differences. Morphological traits associated with flight efficiency, maneuverability, and eye size were particularly informative for explaining the effectiveness of trap type. This could lead to improved predictability of optimal trap design according to species. Therefore, morphological traits could be a valuable tool for understanding species-specific differences in community ecology, but other causes of heterogeneity across studies, such as forest type and structure, require further investigation.

The influence of stimulus history on directional coding in the monarch butterfly brain.

The central complex is a brain region in the insect brain that houses a neural network specialized to encode directional information. Directional coding has traditionally been investigated with compass cues that revolve in full rotations and at constant angular velocities around the insect's head. However, these stimulus conditions do not fully simulate an insect's sensory perception of compass cues during navigation. In nature, an insect flight is characterized by abrupt changes in moving direction as well as constant changes in velocity. The influence of such varying cue dynamics on compass coding remains unclear. We performed long-term tetrode recordings from the brain of monarch butterflies to study how central complex neurons respond to different stimulus velocities and directions. As these butterflies derive directional information from the sun during migration, we measured the neural response to a virtual sun. The virtual sun was either presented as a spot that appeared at random angular positions or was rotated around the butterfly at different angular velocities and directions. By specifically manipulating the stimulus velocity and trajectory, we dissociated the influence of angular velocity and direction on compass coding. While the angular velocity substantially affected the tuning directedness, the stimulus trajectory influenced the shape of the angular tuning curve. Taken together, our results suggest that the central complex flexibly adjusts its directional coding to the current stimulus dynamics ensuring a precise compass even under highly demanding conditions such as during rapid flight maneuvers.

Design of an aircraft generator with radial force control.

With the increasing electrical energy demands in aviation propulsion systems, the increase in the onboard generators' power density is inevitable. During the flight, forces coming from the gearbox or gyroscopic forces generated by flight manoeuvres like take-off and landing can act on the generators' bearings, which can lead to wear and fatigue in the bearings. Utilizing the radial force control concept in the electrical machine can relieve loads from the bearings that not only minimize the bearing losses but also increase bearing life. The objective of the MAGLEV project (Measurement and Analysis of Generator bearing Loads and Efficiency with Validation) is to study, demonstrate, and test a new class of high-speed generators with radial force control. In this paper, design steps of this type of generator and its test rig are presented and the measurement methodology used for radial force control is explained. The concept is developed in an electrical machine and is validated on a test rig by measuring required parameters like shaft displacement, vibrations and bearing temperature. Additionally, the friction moment of each generator's bearings is measured and validated in a separate test rig under comparable conditions to the bearing loads in the generator. Therefore, a novel approach to determine precisely the bearing friction in a radial load unit, rotatably supported by an additional needle bearing is used, which shows a good agreement with the calculated friction. Furthermore, new calculation methods for the operating behavior of cylindrical roller bearings with clearance are presented, which are utilized in the generator test rig.

Thermal characteristics of latent heat sinks based on low melting point metal and topologically optimized fins under lateral hypergravity

With the increasing thermal load of optoelectronic equipment on aircraft, the method of using low melting point metals (LMPMs) instead of organic phase change materials (PCMs) to construct latent heat sinks has immense potential to solve the thermal control problem. However, aircraft are usually under hypergravity during maneuvering flight, and the thermal characteristics of latent heat sinks are likely to be different from those under normal gravity. Hence, the dynamic thermal characteristics of a latent heat sink with bismuth-based LMPM and topologically optimized fins under lateral hypergravity (0–6 g) were investigated with heat fluxes of 10–50 kW/m2. Compared with n-docosane, LMPM decreases the heating wall temperature by over 10 °C, and the holding time below specified temperatures (50, 60, and 70 °C) is prolonged by more than 50 %. Compared with the pin fin, the topologically optimized fin reduces the heating wall temperature by more than 4 °C maximum. The effect of hypergravity on the thermal performances of the heat sink with LMPM and topologically optimized fins is connected with the melting stage. It is negligible in the solid conduction stage and the initial stage of latent melting. It makes the heating wall temperature first increase and then decrease but always higher than that under normal gravity in the rest stage of latent melting. It causes the heating wall temperature to monotonically decrease with hypergravity in the liquid convection stage. The largest difference in heating wall temperature under various gravity occurs between 2 g and 0 g. It is 5.2 °C and its percentage is 7.6 % for 50 kW/m2. In addition, the effect of heat flux on thermal performances is not related to hypergravity.

Flight risk evaluation based on flight state deep clustering network

Flight risk evaluation based on data-driven approach is an essential topic of aviation safety management. Existing risk analysis methods ignore the coupling and time-variant characteristics of flight parameters, and cannot accurately establish the mapping relationship between flight state and loss-of-control risk. To deal with the problem, a flight state deep clustering network (FSDCN) model was proposed to mine latent loss-of-control risk information implicating in raw flight parameters. FSDCN integrates the feature extraction and clustering into an end-to-end deep hybrid network to extract latent risk features from multivariate time-series flight parameters and cluster them. In the FSDCN model, a sequential multi-attention encoder–decoder network is designed to extract embedded risk features, and the feature clustering layer is designed to iteratively refine clustering effects and feature extraction. Besides, a loss-of-control classifier is added to optimize the risk feature vector expression and ensure sufficient dividing feature for facilitate clustering. The multi-task joint learning strategy is adopted to improve the clustering performance of the model further. According to extracted risk features and similarity metrics, the optimal clusters number of flight states is set as 5. Comparative experiments show that FSDCN significantly performs better than other clustering models with performance percentage error below 6%. Through statistical analysis of clustering results, the risk level is quantified for each cluster. Three high-difficulty maneuver cases are presented to demonstrate FSDCN for flight risk evaluation. The flight parameter sequences of the maneuver cases are input into the well-trained FSDCN to obtain the risk prediction results. The spatiotemporal distribution characteristics of the risk-quantized results are consistent with flight parameters over-limit situations, which demonstrates the effectiveness of FSDCN on clustering flight states. The experimental results on flight maneuver cases show that FSDCN can find potential loss-of-control risk features according to multivariate time-series flight data and provide support for in-flight risk warnings.

The Las Hoyas Lagerstätte: a palaeontological view of an Early Cretaceous wetland

Las Hoyas (Cuenca, Spain) represents a unique Early Cretaceous (Barremian) fossil biota of a wetland. The site has yielded a particularly diverse assemblage of >20 000 plant and animal fossils, many of which present unprecedented soft tissue preservation, including microstructural details. Among the most significant discoveries are the oldest angiosperms, the smallest species of chondrichtians and squamates, new theropod dinosaurs, including several enantiornithine birds, the first European tapejarid pterosaur and the most complete eutriconodont mammal. Such discoveries have produced data on important aspects related to plant and animal evolution, such as the first steps in flower development by plants, insights into unknown anatomical and diet specializations in theropod dinosaurs, the development of flight manoeuvrability in early birds, the unexpected global distribution of tapejarid dinosaurs and ground-breaking data on early mammalian hair development. There are many more discoveries to unveil and new research is now linking the immense wealth of palaeobiological information with mathematical procedures to study the ecological structure of the wetland. Supplementary material: Taxonomic structure of the Las Hoyas diversity and systematic list of unearthed taxa are available at https://doi.org/10.6084/m9.figshare.c.6336914

An Improved Feedforward-Robust Algorithm for Active Vibration Control of Helicopter Maneuver Flight

To solve the problem of secondary path mutation and external disturbance abrupt changes during helicopter maneuver flight, the previous research proposed a hybrid active vibration control law. To improve the engineering applicability, the original algorithm is ameliorated to the least mean square-input-output-based robust (LMS-IOBR) algorithm. The system model within the target frequency band can be identified through the input-output data to avoid constructing complex state observers. In addition, the output form of the feedback controller is constructed by an autoregressive moving average model with extra input, which is beneficial to improve operational efficiency. Numerical simulations demonstrate that compared with the original algorithm, controller real-time computation can be reduced by 52% with control effects guaranteed at the same time. Furthermore, to verify the effectiveness and adaptability of LMS-IOBR, multi-input multioutput vibration control experiments are carried out on a specially developed simple platform for simulating helicopter maneuver states. Comparative tests in various typical states are performed between the LMS-IOBR and the multichannel least mean square algorithm. Under the complex circumstances of simulating continuous subduction uplift, the peak response of closed-loop system attenuates by 80% and 70%, and the vibration of two points is reduced to 15% and 20%, respectively, within 3 s. The experimental results demonstrate that the proposed LMS-IOBR algorithm shows stronger transient adaptability and robustness against external disturbance excitation and secondary channel mutation in helicopter maneuver flight.

Multi-UAV Formation Control in Complex Conditions Based on Improved Consistency Algorithm

Formation control is a prerequisite for the formation to complete specified tasks safely and efficiently. Considering non-symmetrical communication interference and network congestion, this article aims to design a control protocol by studying the formation model with communication delay and switching topology. Based on the requirements during the flight and the features of the motion model, the three-degrees-of-freedom kinematics equation of the UAV is given by using the autopilot model of longitudinal and lateral decoupling. Acceleration, velocity, and angular velocity constraints in all directions are defined according to the requirements of flight performance and maneuverability. The control protocol is adjusted according to the constraints. The results show that the improved control protocol can quickly converge the UAV formation state to the specified value and maintain the specified formation with communication delay and switching topology.

Through Hawks’ Eyes: Synthetically Reconstructing the Visual Field of a Bird in Flight

Birds of prey rely on vision to execute flight manoeuvres that are key to their survival, such as intercepting fast-moving targets or navigating through clutter. A better understanding of the role played by vision during these manoeuvres is not only relevant within the field of animal behaviour, but could also have applications for autonomous drones. In this paper, we present a novel method that uses computer vision tools to analyse the role of active vision in bird flight, and demonstrate its use to answer behavioural questions. Combining motion capture data from Harris’ hawks with a hybrid 3D model of the environment, we render RGB images, semantic maps, depth information and optic flow outputs that characterise the visual experience of the bird in flight. In contrast with previous approaches, our method allows us to consider different camera models and alternative gaze strategies for the purposes of hypothesis testing, allows us to consider visual input over the complete visual field of the bird, and is not limited by the technical specifications and performance of a head-mounted camera light enough to attach to a bird’s head in flight. We present pilot data from three sample flights: a pursuit flight, in which a hawk intercepts a moving target, and two obstacle avoidance flights. With this approach, we provide a reproducible method that facilitates the collection of large volumes of data across many individuals, opening up new avenues for data-driven models of animal behaviour.

Vibroacoustic Helicopter Impact on Elevated Helipad

Abstract A helicopter landing and taking off on an elevated helipad is a source of noise that affects the environment and causes vibrations of the landing pad or the building infrastructure. Vibrations are also excited by the air stream flowing through the main rotor and transferred to the landing pad by contact of the helicopter chassis. Vibrations are transferred to the building through the structure of the helipad. Depending on the damping properties of the structure and the vibro-isolating elements used, vibrations can be felt in rooms used by people and also transmitted to devices located in the building. The subject of the study described in this paper is the vibroacoustic effects of an EC-135 helicopter on an elevated landing pad during landing, standstill with the propulsion system engaged and take-off. Measurements of vibrations and noise were made at points located both on the landing pad and in the building. The paper presents selected results of measurements in various phases of flight and helicopter manoeuvres. The frequency analyses of the fragment of the measurement data for the flight phase, in which the highest levels of impact were recorded, were also performed and included. The results are presented as graphs and annotated.

Motion Control System Design for a Novel Water-Powered Aerial System for Firefighting with Flow-Regulating Actuators

Flying water-jet propulsion devices, such as jet boards, jet packs, and jet bikes, can execute complex flight maneuvers. However, they require the direct involvement of trained operators to control, and their applications are very limited. In this study, we design an effective controller for a novel water-powered aerial system that aims for autonomous firefighting missions, especially at or in bodies water. Unlike existing water-powered systems, an assembly of flow-regulating actuators is proposed to fully operate the system in three-dimensional space. The paper first formulates the system dynamics by coupled partial ordinary differential equations. Then, the nonlinear controller is designed to ensure the desired system motion and stability. The design takes distinct characteristics of the system, such as coupling, under actuation, and effects of the hose conveying the water, into consideration so that the system is stabilized and uniform ultimate boundedness is achieved. Computational studies in comparison with previous control methods validated the superiority and feasibility of the proposed control system.

Flight performance and wing morphology in the bat Carollia perspicillata: biophysical models and energetics.

Studies on functional performance are important to understand the processes responsible for the evolution of diversity. Morphological trait variation within species influences the energetic cost of locomotion and impacts life history traits, with ecological and evolutionary consequences. This study examined wing morphology correlates of flight performance measured by energetic expenditure in the Seba's short-tailed bat, Carollia perspicillata. In the flight experiments, nature caught bats (59 females, 57 males) were allowed to fly for 3 min in a room. After each flight, thermographic images were taken to measure body temperature, and biophysical models were used to calculate sensible heat loss as a measure of energetic expenditure. Wing morphological traits were measured for each individual and associated with heat loss and power required to fly on performance surfaces. Wing morphological traits explained 7-10% of flight energetic cost, and morphologies with the best performance would save the energy equivalent to 9-30% of total daily requirements. The optimal performance areas within the C. perspicillata morphospace were consistent with predicted selection trends from the literature. A trade-off between demands for flight speed and maneuverability was observed. Wing loading and camber presented sexual dimorphism. These morphological differences are likely associated with more economical but less maneuverable flight in females, leading them to fly more often in open areas along the forest edge. Our findings demonstrate how small scale changes in wing morphology can affect life history strategies and fitness.

Generalized Design, Modeling and Control Methodology for a Snake-like Aerial Robot.

Snake-like robots have been developing in recent decades, and various bio-inspired ideas are deployed in both the mechanical and locomotion aspects. In recent years, several studies have proposed state-of-the-art snake-like aerial robots, which are beyond bio-inspiration. The achievement of snake-like aerial robots benefits both aerial maneuvering and manipulation, thereby having importance in various fields, such as industry surveillance and disaster rescue. In this work, we introduce our development of the modular aerial robot which can be considered a snake-like robot with high maneuverability in flight. To achieve such flight, we first proposed a unique thrust vectoring apparatus equipped with dual rotors to enable three-dimensional thrust force. Then, a generalized modeling method based on dynamics approximation is proposed to allocate the wrench in the center-of-gravity (CoG) frame to thrust forces and vectoring angles. We further developed a generalized control framework that can handle both under-actuated and fully actuated models. Finally, we show the experimental results with two different platforms to evaluate the flight stability of the proposed snake-like aerial robot. We believe that the proposed generalized methods can provide a solid foundation for the snake-like aerial robot and its applications regarding maneuvering and manipulation in midair.

High-dynamic intelligent maneuvering guidance strategy via deep reinforcement learning

Aiming at the coordination between maneuvering penetration and high-precision guidance under complex flight missions of high-velocity vehicle, the manuscript studies a three-dimensional high-dynamic intelligent maneuvering guidance strategy based on optimal control and deep reinforcement learning (DRL). A three-dimensional attack–defense model is established, and maneuver guidance mission is decomposed into longitudinal and lateral directions. In the longitudinal direction, maneuvering model with the instantaneous miss distance as the control variable is constructed, and the maximum value principle is employed to obtain the optimal maneuver duration and start timing. In the lateral direction, Markov decision process model of maneuver guidance is proposed by synthesizing the guidance error and miss distance of encounter point, and the reward function is designed by considering maneuver and guidance performance. The DRL method is used to learn and train the maneuver strategy, and the training process is improved as well. The simulation results show that the intelligent maneuvering guidance strategy can improve the penetration performance, reduce influence of maneuver flight on the guidance accuracy, and ensure the adaptability under changeable flight missions.

A Novel Actuation Strategy for an Agile Bioinspired FWAV Performing a Morphing-Coupled Wingbeat Pattern

Flying vertebrates exhibit sophisticated wingbeat kinematics. Their specialized forelimbs allow for the wing morphing motion to couple with the flapping motion during their level flight, Previous flyable bionic platforms have successfully applied bio-inspired wing morphing but cannot yet be propelled by the morphing-coupled wingbeat pattern. Spurred by this, we develop a bio-inspired flapping-wing aerial vehicle (FWAV) entitled RoboFalcon, which is equipped with a novel mechanism to drive the bat-style morphing wings, performs a morphing-coupled wingbeat pattern, and overall manages an appealing flight. The novel mechanism of RoboFalcon allows coupling the morphing and flapping during level flight and decoupling these when maneuvering is required, producing a bilateral asymmetric downstroke affording high rolling agility. The bat-style morphing wing is designed with a tilted mounting angle around the radius at the wrist joint to mimic the wrist supination and pronation effect of flying vertebrates' forelimbs. The agility of RoboFalcon is assessed through several rolling maneuver flight tests, and we demonstrate its well-performing agility capability compared to flying creatures and current flapping-wing platforms. Wind tunnel tests indicate that the roll moment of the asymmetric downstroke is correlated with the flapping frequency, and the wrist mounting angle can be used for tuning the angle of attack and lift-thrust configuration of the equilibrium flight state. We believe that this work yields a well-performing bionic platform and provides a new actuation strategy for the morphing-coupled flapping flight.

Basic flight maneuver generation of fixed-wing plane based on proximal policy optimization

Basic flight maneuver generation of fixed-wing plane based on proximal policy optimization

Internal Aerodynamic Performance Enhancement for Aircraft with High Maneuver by Designing a Distributed Submerged Inlet

Submerged inlet has been widely used in UAVs and cruise missiles due to its good stealth characteristics, but it also brings the disadvantage of poor aerodynamic characteristics. Especially in large maneuvering flight, the flow field near the fuselage has a strong unsteady effect, and the total pressure recovery coefficient and distortion characteristics have deteriorated sharply. In order to investigate the steady and transient aerodynamic characteristics of the submerged inlet in large maneuver flight and improve its maneuver envelope, a design scheme of a distributed submerged inlet for large maneuver flight is proposed in this paper. Taking a cruise missile as the research object, the steady and transient analysis of the conventional submerged inlet and the distributed submerged inlet is carried out using CFD numerical method. The results show that the distributed submerged inlet can significantly improve the inlet performance and enhance the sideslip limit of the submerged inlet during large sideslip maneuver flight. When the sideslip angle is 30°, compared with the conventional submerged inlet configuration, the outlet total pressure recovery coefficient of the distributed submerged inlet configuration is increased by 44.2%, and the total pressure distortion index is reduced by 66.3%.

Quadrotor Trajectory-Tracking Control with Actuator Saturation

As a very serious problem for control systems, actuator saturation often leads to an unstable system. The maneuvering flight of quadrotors may lead to actuator saturation, which commonly affects the flight quality, including trajectory-tracking accuracy. Quadrotors usually adopt double-closed-loop control, of which the outer loop is the position control used to calculate the desired attitude angle and the inner loop is the attitude control used to generate control actions for the vehicle. To address actuator saturation during the maneuvering flight of quadrotors, an attitude controller based on the conditioned super-twisting algorithm (CSTA) was designed. The sign functions in CSTA were replaced by a hyperbolic tangent function, which suppresses the chattering of CSTA. In order to improve the rapidity of the improved controller, the tanh-CSTA (TCSTA), a gain adjustment factor was utilized. The rapidity and smoothness of the controller can be satisfied by adjusting the gain factor. Additionally, a sliding surface was designed according to the characteristics of the quadrotor control structure, so that the TCSTA controller can be applied to the second-order system. The performances of the designed improved controller were simulated using MATLAB, and the results showed that the designed controller is more robust than the PID controller. Moreover, compared with the CSTA controller, the chattering of the designed controller was obviously suppressed without reducing the control accuracy.