Hover Flight Modes Research Articles

Determining the Efficiency of Small-Scale Propellers via Slipstream Monitoring

A large part of small-sized UAVs that are used for surface scanning, video- and photography, or other similar applications are of the multirotor type. These small aircraft perform mainly in hovering or nearly hovering flight mode, and the endurance of these vehicles depends greatly on the efficiency of their motors and the aerodynamic efficiency of their thrust-generating systems, including propellers, ducted fans, etc. Propellers may therefore work in different regimes: in a regime where the propeller performs work to move the vehicle through the air, and the static or hovering regime, in which standing air is accelerated. In both cases, the concept of efficiency can be used to describe the propeller’s performance. There have been several previous studies on static and advancing propellers’ performances. In these studies, when determining the efficiency of a static propeller, the thrust and power coefficients are most commonly compared to evaluate the propeller’s performance. Sometimes, the inducted velocities are calculated via the momentum theory. As small-scale propellers work on very low Reynolds (Re) numbers below 500,000, the flow type transition and boundary layer separation make it very hard to predict the actual efficiency of the propellers in static mode. Therefore, the aim of this paper is to introduce a method to determine the static efficiency of small-scale propellers directly and empirically via a comparison between the output and input power, wherein the output power is determined via the measured thrust and mean induced velocity. The used method combines thrust, torque, and angular velocity measurements with slipstream monitoring. The performed tests showed a decrease in efficiency, with the Re number rising in spite of the rising values of the thrust coefficient. This study led to two main conclusions: thrust and power coefficients are not always the key parameters to determine the efficiency of a propeller; the role of the Re number in the propeller’s efficiency is not yet clear and requires further investigation. The presence of Re number effects has been proven in numerous works, but the impact of those effects seems to not be as trivial as the claim that the lower the Re number, the weaker the propeller’s performance.

Design of a PEM fuel cell powered autonomous quadcopter

The purpose of this paper is to design a PID controller for a detailed nonlinear model of a custom-made quadcopter and utilise the power requirements in designing a proton exchange membrane (PEM) fuel cell system. The first principles methodology to commence with unmanned aerial vehicle architecture is delineated. The empirical actuator response of the brushless DC (BLDC) is obtained which further adds accuracy to the mathematical model of the system. The paper also presents simulations for nonlinear open loop and closed loop feedback with PID controller. The controller gains are obtained from the simulations for hover flight mode. The experimental implementation of battery powered quadcopter is validated with simulation results of PID control design. Finally, for the designed quadcopter, a mathematical model of a PEM fuel cell system to replace battery-specific power requirements is obtained. The key limitation of this paper is the absence of experimental data for fuel cell model due their high cost and low-availability.

A novel [formula omitted] adaptive-hybrid control with guaranteed stability for a class of uncertain nonlinear systems: A case study on SA330 Puma

The helicopter is a highly unstable nonlinear non-minimum phase multiple-input multiple-output (MIMO) system with strong coupling between degrees of freedom. Therefore, its modeling will cause many problems such as control complexity. In addition, hover and forward flight modes are one of the most widely used helicopter flight modes used in many operations. To achieve and stay in these situations, you need very precise settings and timely manual control of the bird. This paper seeks to provide an L1 adaptive-hybrid control method to solve helicopter control problems in the Koppler system. In this regard, three channels in the coupler system are considered for the design of this controller. The proposed controller also proves the stability of the system during switching between channels. The helicopter that is modeled in this research and its data is used to implement and simulate the Coupler system control is the SA330 Puma helicopter, which is a medium-sized twin-engine support helicopter, in the category of 6 tons, built by Eurocopter France (ECF), and is in service several domestic operators and the armed forces, including the British Air Force. This device is a completely unstable dynamic system. In addition to the inherent instability of this bird, by adding an external load hanging to this system, the challenge of controlling this system is doubled hence, it is necessary to maintain its stability by using a suitable control system. In the meantime, the modeling of the hanging load should be done in three dimensions and two planes, and like most of the work done, only the movement of the plane should not be considered. For this purpose, an L1 adaptive-hybrid control method is proposed and fully developed in the paper, then it is properly designed for the Coupler system, which contains three channels: Pitch, Roll, and Collective, taking into account the load hanging on the helicopter. Finally, by simulating the results, it can be seen that the main goals, even in the presence of various disturbances, have the desired, efficient, and very good performance.

Auditory detection probability of propeller noise in hover flight in presence of ambient soundscape.

Unmanned aerial vehicles are rapidly advancing and becoming ubiquitous in an unlimited number of applications, from parcel delivery to people transportation. As unmanned aerial vehicle (UAV) markets expand, the increased acoustic nuisance on population becomes a more acute problem. Previous aircraft noise assessments have highlighted the necessity of a psychoacoustic metric for quantification of human audio perception. This study presents a framework for estimating propeller-based UAV auditory detection probability on the ground for a listener in a real-life scenario. The detection probability is derived by using its free-field measured acoustic background and estimating the UAV threshold according to a physiological model of the auditory pathway. The method is presented via results of an exemplar measurement in an anechoic environment with a single two- and five-bladed propeller. It was found that the auditory detection probability is primarily affected by the background noise level, whereas the number of blades is a less significant parameter. The significance of the proposed method lies in providing a quantitative evaluation of auditory detection probability of the UAV on the ground in the presence of a given soundscape. The results of this work are of practical significance since the method can aid anyone who plans a hovering flight mode.

Modeling and control of a quadrotor tail-sitter unmanned aerial vehicles

The tail-sitter unmanned aerial vehicles have the advantages of multi-rotors and fixed-wing aircrafts, such as vertical takeoff and landing, long endurance and high-speed cruise. These make the tail-sitter unmanned aerial vehicle capable for special tasks in complex environments. In this article, we present the modeling and the control system design for a quadrotor tail-sitter unmanned aerial vehicle whose main structure consists of a traditional quadrotor with four wings fixed on the four rotor arms. The key point of the control system is the transition process between hover flight mode and level flight mode. However, the normal Euler angle representation cannot tackle both of the hover and level flight modes because of the singularity when pitch angle tends to [Formula: see text]. The dual-Euler method using two Euler-angle representations in two body-fixed coordinate frames is presented to couple with this problem, which gives continuous attitude representation throughout the whole flight envelope. The control system is divided into hover and level controllers to adapt to the two different flight modes. The nonlinear dynamic inverse method is employed to realize fuselage rotation and attitude stabilization. In guidance control, the vector field method is used in level flight guidance logic, and the quadrotor guidance method is used in hover flight mode. The framework of the whole system is established by MATLAB and Simulink, and the effectiveness of the guidance and control algorithms are verified by simulation. Finally, the flight test of the prototype shows the feasibility of the whole system.

Design, Development, and Testing of Package Delivery Quadrotor Biplane Tail-Sitter

This Paper explores the development of a novel hybrid air vehicle for package delivery called the quadrotor biplane tail-sitter. This vehicle uses differential thrust to effect body attitude changes like a traditional quadrotor, ensuring full transitional control between hover and forward flight modes. This method of control also allows the vehicle to remain mechanically simple. A vehicle was designed with a 1 lb (0.45 kg) payload, resulting in an 8 lb (3.63 kg) gross takeoff weight. The vehicle can hover using 15 in. (0.381 m) diameter proprotors and has two wings that span 3.35 ft (1.03 m), which provide lift in forward flight. Sensors were implemented onboard the vehicle to monitor individual dc brushless motor revolutions per minute, body attitude angles, electrical power consumption, and airspeed relative to wind. Stable hover was demonstrated with package delivery, and it was found that 18% less power was used when hovering with no payload compared to full payload. Package delivery was also successfully demonstrated after transitioning from hover to forward flight and back. In forward flight mode with no payload, the power consumption at a forward flight speed of () was seen to be 50% less than the power consumed in hover.

Mid-fidelity approach to aerodynamic simulations of unconventional VTOL aircraft configurations

A new flexible medium-fidelity open source computational tool was developed with the purpose of obtaining fast and reliable aerodynamic simulations of unconventional Vertical Take-Off and Landing (VTOL) aircraft configurations, such as the emerging category of eVTOLs. This tool, called DUST, ensures quick simulations and provides reasonably accurate results when the need for numerous evaluations rules out an extensive use of CFD due to its high computational cost, while maintaining robustness in the complex interactional aerodynamic phenomena typical of the novel eVTOL configurations. The paper first presents the analytical formulation of the tool, based on different potential boundary elements and vortex particles wake integrated in a common formulation. Then, the results obtained with the novel code are compared with experimental data and CFD results of a half-span tiltwing tiltrotor model and an eVTOL multi-rotor tiltwing aircraft, both in hover and forward flight mode. The comparisons show that DUST produces results that are as accurate as the results obtained with CFD, except for massively separated conditions, at a computational cost orders of magnitude lower. The results highlight the effectiveness of this approach for the preliminary design of a vehicle and for the preliminary study of the flow physics related to the aerodynamic interactions between rotor wakes and solid bodies as wings.

Longitudinal modeling and control for the convertible unmanned aerial vehicle: Theory and experiments

The field of unmanned aerial vehicles (UAVs) has grown in the last years, showing its utility in broader applications. For instance, in surveillance, precision agriculture, pack delivery, among others. The UAVs characteristics demand more suitable configurations for increasing their flight time, maneuverability, stability, and reliability for attending a growing quantity of services. One of the UAV configurations that has gained popularity in the last years is the Convertible Unmanned Aerial Vehicle (CUAV). This paper aims to provide a control strategy to stabilize the CUAV in all the flight modes: hover, cruise, and transition mode, in which the CUAV changes between hover and cruise flight mode. For that, we propose longitudinal modeling that considers realistic aerodynamics and even disturbances. This model presents a precise balance between complexity and practicality for control implementations. The control algorithm design is based on the Lyapunov stability theory and uses saturation functions intending not to saturate the actuators. Besides, the control algorithm does not include any switching function, is easy-to-implement, and demands the usually available feedback in the vast majority of low-cost commercial autopilots. The control allocation problem for this control is also solved. A mathematical proof based on Lyapunov theory demonstrates that the proposed controller performs the closed-loop system globally exponentially stable. Simulation and real flight experiments conducted with the CUAV demonstrate the effectiveness of theoretical results. Moreover, we present several comparative studies with the state of the art that demonstrate the paper’s contribution to the field of convertible aerial vehicles.

Numerical investigation of wing–wing interaction and its effect on the aerodynamic force of a hovering dragonfly

The present research focuses on the timing of wing–wing interaction that benefits the aerodynamic force of a dragonfly in hovering flight at Reynolds number 1350. A 3-D numerical simulation method, called the system coupling, was utilised by implementing a two-way coupling between the transient structural and flow analysis. We further explore the aerodynamic forces produced at different phase angles on the forewing and hindwing during the hovering flight condition of a dragonfly. A pair of dragonfly wings is simulated to obtain the force generated during flapping at a 60° inclination stroke plane angle with respect to the horizontal. The hovering flight is simulated by varying the phase angle and the inter-distance between the two wings. We observe a significant enhancement in the lift (16%) of the hindwing when it flaps in-phase with the forewing and closer to the forewing, maintaining an inter-wing distance of 1.2 cm (where cm is the mean chord length). However, for the same condition, the lift of the hindwing reduces by 9% when the wings are out of phase/counterstroke flapping. These benefits and drawbacks are dependent on the timing of the interactions between the forewing and hindwing. The time of interaction of wake capture, wing–wing interaction, dipole structure and development of root vortex are examined by 2-D vorticity of the flow field and isosurface of the 3-D model dragonfly. From the isosurface, we found that the root vortex elicited at the root of the hindwing in counter-flapping creates an obstacle for the shedding of wake vortices, which results in reduction of vertical lift during the upstroke of flapping. Hence, at the supination stage, a dragonfly uses a high rotation angle for the hovering flight mode. It is observed that the system coupling method was found to be more efficient and exhibited better performance. The present numerical methodology shows a very close match to the previously reported results.

Conceptual Sizing of Vertical Lift Package Delivery Platforms

Conceptual sizing and performance estimation of four vertical takeoff and landing (VTOL) configurations for a package delivery mission is presented in this Paper. The multifidelity VTOL design framework HYDRA is used to size a notional quadrotor, hexarotor, quadrotor biplane tailsitter (QBiT), and a lift-augmented tricopter for weight classes of 10, 15, 20, and 25 kg. Sizing is performed using a combination of physics-based empty weight models for the airframe, rotor blades, and wings, along with statistical models for predicting motor and battery weights. A gradient-based optimization methodology was implemented to identify the best designs for each configuration under each weight class. An optimization-based longitudinal trim methodology was used to identify the appropriate shaft power settings for each vehicle at various trimmed flight conditions along the mission profile. Representative payload delivery and return scenarios were constructed from different cruise speeds and ranges to identity a vehicle design in each configuration that can complete the highest number of payload drop missions successfully. The hexarotor performed better than the quadrotor in terms of requiring lower installed power and deliver heavier payload packages for a given radius of action. Wing-borne designs such as the QBiT and tricopter are capable of delivering packages in a short time owing to full/partial conversion to airplane mode during cruise flight but may require careful fine-tuning of the trimline and flight control system to successfully transition between hover and cruise flight modes.

Flight envelope estimation for helicopters under icing conditions via the zonotopic reachability analysis

This paper presents a new approach to estimating a flight envelope for a helicopter flying under clean and icing conditions based on a zonotopic reachability analysis. The helicopter is stabilized with a state-feedback linear controller to maintain its attitude around a trim point. Given the sets of possible initial conditions and disturbance inputs, and control effectiveness indices, this analysis results in reachable sets of state variables of the helicopter for a finite time interval. The reachability analysis is thus useful for predicting whether or not the helicopter evolves into an unsafe flight condition when it undergoes degraded control effectiveness ensued from the icing condition. The merit of this approach is shown through a case study about the Raptor-90 unmanned helicopter stabilized with either the linear quadratic regulator (LQR) or the H∞ controller in a hover-flight mode. This helicopter is considered to be affected by both symmetric and asymmetric icing conditions. The case study shows that the H∞ controller outperforms the LQR controller as the former is able to cope with greater loss of control effectiveness caused by the icing conditions. Moreover, as compared to the longitudinal control input, the lateral and directional control inputs are more susceptible to adverse effects of the icing conditions. These results verify not only the effects of ice contamination upon the helicopter dynamics and control, but also the capability of the proposed approach for flight envelope estimation.

Comparison of the Noise Directivity Pattern of the Main Rotor of a Helicopter for Flight and Hover Modes

The noise of the main rotor of a helicopter in hover and horizontal flight modes is numerically simulated. To calculate the acoustic characteristics caused by the nonstationary load on the blades, a software package is used, validated with experimental data in hover mode. A hybrid calculation method is used, according to which the near field is calculated first, followed by the acoustic characteristics in the far field. In the near field, the values of the field parameters near the rotating blade are found by direct solution of the unsteady Euler equations in a noninertial coordinate system. To calculate the far field, the integral Ffowcs Williams–Hawkings method is applied using permeable control surfaces enclosing the blade.

Design and development of FOLLY: A self-foldable and self-deployable quadcopter

New progress in the computational power of the flight controller industry drives quadcopters to be more preferable in various real-world applications. On the other hand, for different assignments, conventional quadcopter designs lack the ability to alter their configuration to satisfy the need to adapt to the requirements of the mission. In order to be entirely applicable to various kinds of assignments; being portable and transportable, having a low-volume is vital which is one of the main challenges in the design of quadcopters. This necessity, brings up a new research topic, namely morphologic quadcopters that are unique due to their nature of self-arm management feature. As morphologic quadcopters have self-arm management, they are capable of autonomously fold and deploy their arms which increases their functionally significantly. In this paper, we will present a self-foldable and self-deployable autonomous quadcopter, named as Folly. Folly is deployable to autonomous systems effortlessly as it is close-packed, mobile and has a self-arm management. In the design of self-arm management, we utilized a four-bar crank-rocker mechanism that is actuated by a single servo motor and coupled with spur gears that allow Folly to automatically fold and deploy its arms in a short period time, 0.6 s. The crank-rocker mechanism employed is scrutinized for position, velocity and acceleration kinematics to establish an efficient design. In addition, torque characteristics of the mechanism are analyzed numerically and collated with dynamic simulation to ensure desirable power transmission rates. Moreover, as a new approach, to deal with vibration effects in morphologic quadcopters, the frame material of Folly is selected to be acrylic. Furthermore, Folly has two flight modes which are the hover flight mode for horizontal flight patterns, and the object-tracking mode that enables indoor usage by preventing collision and increasing functionality. Various real-time experiments are performed to show the efficiency of the design of Folly.

Simulation-based Assessment of Quadrotor Linear Control Schemes

This work aims at finding the most suited control scheme for a typical quad-rotor. Selecting the appropriate controller is essential to achieve system stability. The most common control schemes are compared in terms of their performance in hovering mode. The quad-rotor propellers are modeled based on both momentum theory and blade element theory. The model describing the six-degrees of freedom system is used to develop a control strategy using different types of controllers such as PID, Fuzzy, Optimal, LQ), as well as LQR controller. The current work is confined to linear control schemes in hovering flight mode, where the comparison is based on achieving stable attitude in hovering. The simulation results show that the LQR controller is the most efficient control method to minimize the steady-state error.

Flight Time Estimation for Continuous Surveillance Missions Using a Multirotor UAV

To achieve the continuous surveillance capable multirotor type solar-powered unmanned aerial vehicle (UAV), we develop the photovoltaic power management system (PPMS) which manages power from photovoltaic (PV) modules and a battery pack to support the power of the UAV. To estimate the possible flight time of the UAV, we use the concept of state of charge (SOC) estimation based on the extended Kalman filter (EKF) and complementary filter (CF) and then calculate the possible flight time by using the slope of the SOC graph during hovering flight mode. According to the results, estimated flight time increases up to 54.14 min at 11:00 a.m. and decreases down to 6.70 min at 18:00 p.m.

Numerical Investigations of Aerodynamics Characteristics of Main Rotors in Helicopter UAV Used for Pesticide Spraying in Agriculture

In the last several decades past, Helicopters UAVs (Unmanned Aerial Vehicles) have quickly developed and day by day, they play an important role in human life. As it is well-known, helicopters UAV make some outstanding characteristics such as light weight, flexibility and particularly automatically controlled. By applying these characteristics, we research and manufacture Helicopter UAV using for spraying pesticide in agriculture. One of the most important components is main rotor because main rotor generated thrust, drag and momentum. Helicopters UAV efficient changed depending on main rotor. The research works focus on aerodynamics characterization of main rotor in helicopter UAV. This work uses CFD tool in ANSYS CFX software to calculate the aerodynamics parameters generated by main rotor using in UAV. The aim is to characterize the aerodynamics characteristics such as thrust, drag, pressure, aerodynamics quality on the different flight modes (hover, vertical and forward flight). Firstly, the simulations are carried out in hover flight mode with different blade pitch angles. The results are compared to experiment date in another research to validate numerical results. Then, the simulations are carried out in vertical flight mode and forward flight mode. The results showed that thrust and drag coefficient creased with increasing blade pitch angle. When blade pitch angle started from 1800, thrust coefficient decreased but drag coefficient increased sharply. The rotor performance was measured by aerodynamics quality and numerical results showed that the best rotor performance was at 900. In the vertical flight mode, the thrust and drag coefficient decreased with increasing vertical velocity but rotor performance increased slightly. The best vertical velocity for vertical flight is around 2 m/s and 3 m/s. Finally, in forward flight mode, the aerodynamics characterizations of rotors depended on azimuthal angular position of blade or time. Our helicopter operates in environment with light gust. The results showed the change of aerodynamics coefficient to time. Both thrust and drag coefficient changed but the rotor performance did not change much.

Vortex filamentation and fragmentation phenomena in flapping motion and effect of aspect ratio and frequency on global strain, rotation, and enstrophy

In the present study, flow field around rigid flat plate wings executing main flapping motion has been studied using phase-locked two-dimensional particle image velocimetry measurements. Experiments have been conducted in water as a fluid medium for an asymmetric upper–lower stroke single degree of freedom main flapping motion. Two different aspect ratio (1.5 and 1.0) rectangular wings at 1.5 and 2.0 Hz flapping frequency in hovering flight mode (advance ratio, J = 0), zero wing pitch angle, and chord-based Reynolds number of the order of 104 have been studied. Velocity field and vorticity field with λ2 criterion information have been obtained for the complete stroke in great detail to reveal the minute aspects of flow dynamics. The flow features during the downstroke and upstroke have been observed to be consistent for all four cases investigated. The predominant characteristic of the flow during downstroke and upstroke has been referred to as vortex filamentation and fragmentation phenomena. Quantities such as circulation, rate of strain, rate of rotation, and enstrophy have been studied to identity the effect of minor change in aspect ratio and flapping frequency. It is found that for higher aspect ratio wing hyperbolic behavior is predominant except for end of downstroke and beginning of upstroke where elliptic behavior is observed. For lower aspect ratio, wing elliptic behavior is predominant except for end of upstroke and beginning of downstroke where hyperbolic behavior is seen. The hyperbolic behavior became stronger at higher frequency. From enstrophy distribution it is evident that higher frequencies play a more dominant role than aspect ratio in determining the budget.

Coherent structures in the flow field generated by rigid flapping wing in hovering flight mode

Galilean invariant vortex identification methods and proper orthogonal decomposition (POD) are used to capture the coherent structures (CS) in the flow field generated by rigid wing in main flapping motion. Experiments are conducted for a square rigid wing at a flapping frequency f = 1.5 Hz. Tests are performed in water as a fluid medium in hover mode. The main flapping mechanism executes asymmetric lower-upper stroke of 1:3 ratio single degree of freedom motion. Two dimensional particle image velocimetry (PIV) technique is used to generate the phase locked velocity field at each discrete flapping angle by illuminating the mid chord plane of the wing. Three different Galilean invariant methods namely λ2 criterion, Q criterion and Δ criterion are used for vortex identification. These methods were found to be consistent in detecting swirling vortices or coherent structures (CS). Proper orthogonal decomposition is used to exhibit the most energetic modes of the flow field. The captured modes were identified to be in-connect with vortex identification methods. The combination of these tools were found to be more effective in comparison with velocity field data for achieving a deeper understanding of the complex flow produced by the flapping wing.

Optimization of lift force for a bio-inspired flapping wing model in hovering flight

The lift force is an important component that affects the aerodynamic performance of bio-inspired flapping-wing micro aerial vehicles. However, there is a lack of endeavors in the optimization of the flapping wing parameters that affect the lift force of micro aerial vehicles. This research is therefore to establish a methodology that combines computational fluid dynamic simulation for the evaluation of the lift generation and wing parameters. The Taguchi’s framework for design of experiments, combined with the computational fluid dynamics simulations, is performed on a simplified robotic fly wing model used in the experiment found in Dickinson et al. (1999), under the hovering flight mode, to identify the most influential parameters on the lift generation of micro aerial vehicles. A commercial computational fluid dynamics code, ANSYS/FLUENT, along with a three-dimensional Navier–Stokes solver is used to simulate the unsteady flow field. With the optimization of the time-averaged lift force as the optimization objective, five typical parameters (flapping frequency, maximum angle of attacks during the upstroke and downstroke motions, stroke amplitude, and rotation type) in the flapping trajectory equation are selected as the input factors with each having four levels. Specific computational fluid dynamics cases are simulated in accordance with the chosen orthogonal arrays. By conducting statistical analyses with analyses of means and variance, the flapping frequency and the stroke amplitude are determined to be the two most influential parameters. The response surface of the time-averaged lift force and the power consumption contour are constructed with respect to these two parameters to determine the optimal combination for the generation of lift forces under a specific power constrain and provide a guideline for bio-inspired micro aerial vehicle designs.

Approximate analysis for main rotor flapping dynamics of a model-scaled helicopter with Bell–Hiller stabilizing bar in hovering and vertical flights

In this paper, the effects of the rotor flapping dynamics in the control design for the model-scaled autonomous helicopter are analyzed in detail. The analysis is based on a specific model-scaled helicopter equipped with a Bell–Hiller stabilizing bar. A simplified analytic model for the flapping dynamics in hovering flight mode is derived and then expanded to the vertical flight mode. Eigenvalues of the approximated linear system indicate that flapping dynamics in both flight modes is comparatively fast and asymptotically stable. Effects of the rotor dynamics with Bell–Hiller stabilizing bar are assessed with both simulation and experimental results, indicating that static approximation of the rotor dynamics in control design is acceptable.