Rotary Aircraft Research Articles

Delayed-Onset Arterial Gas Embolism After Underwater Egress Training

BACKGROUND: Arterial gas embolism (AGE) may occur while breathing compressed air and failing to exhale during ascent to compensate for gas expansion as pressure decreases. Trauma to the lungs from over-pressurization may result in air bubbles entering the pulmonary veins and subsequently the systemic circulation, causing obstructed blood flow and inflammatory cascades. AGEs are known to always manifest within 10 min of surfacing from depth. In underwater egress training (UET), which is mandatory for U.S. Marines, service members learn to escape from a tilt-wing or rotor aircraft after it submerges and inverts in water. CASE REPORT: We report a case of cerebral AGE in which the victim experienced neurological symptoms more than 1 h after completing UET at a depth between only 3.28–6.56 ft (1–2 m). The patient was treated with a U.S. Navy Treatment Table 6 and experienced complete resolution of symptoms. DISCUSSION: This case is one of only two AGEs reported with symptom onset occurring after 10 min of surfacing from depth to be published. AGE at depths between 1–2 m has only been reported on three other occasions, and dysbarism injuries during UET are also exceedingly rare. This case demonstrates a situation in which all three events occurred, highlighting the need for increased awareness and clinical consideration of delayed AGE in similar scenarios despite the commonly held belief that AGEs do not occur outside of 10 min of surfacing. Harvey SE, Reynolds RP, Fisher JF. Delayed-onset arterial gas embolism after underwater egress training. Aerosp Med Hum Perform. 2024; 95(11):867–870.

Autoimmune Thyroid Disease: An Unusual Cause or Confounder of Vertigo.

Over the last decade, the published literature investigating the association between thyroid function and recurrent or persistent vertigo has become more robust. We present an interesting case of persistent vertigo in a healthy 31-year-old active duty Navy pilot who was restricted from operating single-pilot rotary aircraft because of the severity of her symptoms. During her work-up, she was newly diagnosed with autoimmune thyroid disease and started on thyroid hormone supplementation. Adequately treating her underlying thyroid disease was associated with resolution of dizzy symptoms and she was granted a waiver to return to flying. This case highlights the importance of autoimmune thyroid disease as a less common but important diagnosis to consider in the broad differential for vertigo. This is especially relevant to the military population since dizziness contributes to spatial disorientation for aviators and can be highly debilitating for warfighters. Astutely diagnosing and treating underlying causes of dizziness may allow service members to return to physically demanding and mentally arduous duties, improving overall military readiness.

High-fidelity computational study of aerodynamic noise of side-by-side rotor in full configuration

This paper presents a numerical study of side-by-side rotor aircraft in full configuration during hover using high-fidelity computational fluid dynamics (CFD) and aeroacoustic simulations. CFD simulations are performed using HPCMP CREATE™-AV Helios, while acoustic calculations are conducted with PSU-WOPWOP. Overset structured grids are applied using the SA-DES turbulence model along with adaptive mesh refinement in the near- and off-body meshes. Four overlap cases at a specific collective pitch angle of 8° are considered. Results reveal a substantial influence of the fuselage on rotor performance, with improvement in the figure of merit being observed for each overlap configuration due to a partial ground effect. There is considerable increase in blade sectional thrust, pressure fluctuations, and noise levels seen in the 0% overlap configuration compared to the 25% overlap configuration. This increase is primarily due to the absence of rotor overlap, resulting in a lower induced velocity allowing for flow to travel upward, and reaching the rotor disk plane. The acoustic spectrum appears at all harmonics of the blade passing frequency for the 0% and 5% overlap configurations. In contrast, the acoustic spectrum is distinctly present only at even harmonics for the 15% and 25% overlap cases. A noise reduction benefit of 3-5 dBA is noticed in the full configuration cases having rotor overlap compared to the 0% overlap configuration. Acoustic destructive interference is observed in the directivity plot only for the 15% and 25% overlap configurations. Overall, this paper reveals that the fuselage has a significant impact on the performance, aerodynamics, and aeroacoustics of the side-by-side UAM vehicle in hover.

Mechanism analysis of the vortex ring and its effects on an axial descending rotor

A vortex ring is a flow phenomenon involving a complex toroidal vortex system. When a rotor is in descending flight, it may enter the vortex ring state (VRS), which will affect the rotor’s aerodynamic characteristics and even endanger it. In this paper, to clarify the aerodynamic mechanism by which the vortex ring exerts its effects on an axial descending rotor, an unsteady numerical simulation method for the rotor integrated with structured moving overset grids is proposed and validated using experimental data. This numerical simulation method is then applied to analyze the aerodynamic characteristics of the rotor in descending flight. The variations of the aerodynamic forces and the flow characteristics in the slipstream are analyzed to elucidate the physical mechanisms responsible for the relationships between the aerodynamic loads, flow field, and vortices when the rotor is in the VRS. The effects of the VRS cause a sharp drop in the average aerodynamic forces, which directly affects the safety and reliability of a rotor aircraft. In the slipstream of the descending rotor, a distinct vortex ring forms and moves upward as the velocity of descent increases. The most severe VRS occurs at a nondimensional velocity of descent of 1.13 when the center of the highly unsteady vortex ring is right at the blade tip, and this can be used as an indicator of the VRS. The physical mechanism by which the VRS exerts its effects can be attributed to the low pressure induced by strong vortices. The VRS decreases the pressure on the lower surface of the blade and increases the pressure on the upper surface, resulting in a reduction in the aerodynamic loads. In comparison with the hovering state, the VRS results in a much larger vortex strength and possesses a different vortex structure.

Enhancing strategic deployment of baiting transects for invasive species control – a case study for feral pig baiting in north-eastern Australia

Context Baits are used to deliver lethal or other substances in wildlife management programs across the globe. Successful baiting campaigns are contingent upon the availability of baits to target animals. Bait density is often increased in an attempt to improve bait encounter probabilities. However, this comes with a concomitant increase in cost and may result in significant bait wastage if deployed in areas of low target species activity. Aims The aim of this study was to assess the effectiveness, efficiency and cost of different bait transect methods in intersecting home and core ranges of feral pigs as a case study to determine optimal spacing and placement of baiting transects. Methods The authors simulated a variety of systematically spaced aerial transects, watercourse-aligned aerial transects and ground transects along property boundaries and farm tracks, and compared them with home and core ranges of feral pigs, at two study sites in Queensland, Australia. Transect effectiveness at intersecting pig ranges was determined through beta-regression and estimated marginal means (emmeans); efficiency was considered as emmeans per unit of transect length. Key results The study found that systematically spaced aerial transects at 4 km intervals were the most efficient means of intersecting both home and core ranges of feral pigs. Additionally, no alternate transect method, either aerial or ground, provided significantly greater effectiveness at intersecting feral pig home and core ranges at these study sites. Ground transects along farm tracks and property boundaries were also between 113% and 192% more expensive than aerial transects at 4 km spaced intervals for either fixed-wing or rotary aircraft. Conclusion Systematically spaced aerial transects at 4 km intervals are among the most effective and are the most efficient means of intersecting feral pig ranges at the study sites examined. Implications Our methodology offers a blueprint for both vaccination and toxin baiting programs to assess and compare bait transect placements. More specifically for feral pig control, aerial transects with 4 km systematic spacing provide an effective and efficient means for intersecting feral pig ranges. Furthermore, additional data on bait encounter and interaction probabilities are required to determine transect effectiveness at bait uptake by the target species.

Bird strike analysis of new composite inlet for tilt rotor aircraft

Bird strikes are an important phenomenon to consider when designing and servicing aircraft structures. Most major bird strike incidents result in aircraft propulsion damage. Because an engine is the sole thrust-providing system of an aircraft, the effect of bird strikes on engine inlets and systems must be investigated and mitigated to the maximum extent. Especially in the case of (vertical take-off and landing) VTOL aircraft, such as an aircraft with tilting rotors, this effect is critical from the point of view of the operation, from the point of view of flight mechanics and the overall control of the aircraft. This work aims to propose the proof of resistance of a new composite air inlet for a new tilting rotor aircraft, which is experimentally verified and supported by numerical simulations performed on flat and simple curved test panels. The new, very effective method was used to calibrate the composite material model, which is further used in the following numerical simulations.

Analysis and Research on Aerodynamic Characteristics of Quad Tilt Rotor Aircraft

Analysis and Research on Aerodynamic Characteristics of Quad Tilt Rotor Aircraft

The Latest Development of Turboshaft Engines

As the main power of rotor aircraft, the turboshaft engine has always been the focus of scientific and engineering research and has achieved rich research results. This paper reviews and summarizes the research results at home and abroad in the past 10 years from the aspects of control systems, oil-electric mixing, pollutant emission and compressor internal flow field optimization. High altitude and low temperature is the best condition for turboshaft engine operation. Pre-mission fuel estimation is good for low emissions. Oil-electric mixing engines can effectively improve efficiency, but reducing weight and cost is a problem that needs to be solved. The interaction between the leakage vortex and the excitation wave in the compressor increases the total pressure loss in the vortex core downstream of the excitation wave. The modes associated with wheezing can be stabilised by feeding back small-amplitude perturbations. The universality of the surge suppression of transonic centrifugal compressors and the stability of most of the compressor surges by small disturbance feedback are the next research focus.

A simulation model for the electrical rotary-wing aircraft (eVTOL) performance estimation for the urban air mobility purposes

The present paper presents a simulation model description developed for the aircraft performance estimation of the most popular electric vertical takeoff and landing aircraft (eVTOL) aerodynamic configurations with the electric (hybrid) power plant for the urban air mobility purposes. It focuses on the quadcopter-type eVTOL aircraft aerodynamic configurations using the unshrouded-propellers or ducted fans driven by electric motors. The aircraft performance analysis for aerodynamic configurations of the quadcopter and tilt rotor-quadcopters with the tilt rotors and wing with the all-electric (EP) or hybrid power plant (HP) is given. To compare aircraft performance, the estimation results for a conventional single-rotor helicopter with EP or HP are given. Based on the numerical solution equation of the aircraft existence, feasible structural components mass distributions for various types of eVTOL configurations were obtained. eVTOL aircraft performance, including the estimation of apparent and drag power for the airspeed range, from hovering to the maximum airspeed, as well as for the transition modes (tilt rotor aircraft and quadcopters) were estimated. The eVTOL aircraft flight range and duration with EP and HP at the straight and level flight mode were calculated. Specific mass characteristics of EP and HP components (batteries, generators, electric motors, etc.) to ensure acceptable eVTOL aircraft performance were identified. A comparative evaluation of considered eVTOL configurations for the purpose of their efficiency was performed. Aerodynamic calculations were carried out based on the known analytical techniques of the lifting propeller momentum theory with the data correction capability according to test results. The simulation model, obtained in this paper, can be considered in the phase of the preliminary choice as the first approach of structural parameters and aerodynamic configurations of prospective electric (hybrid) eVTOLs designed for the use as an urban air taxi.

Design of Quadrotor Aircraft Control System Using PID Method

In order to realize the precise control of the dynamic performance of the four rotor aircraft, a PID based controller design method for the four rotor aircraft is proposed in this paper. Firstly, the mathematical model of the four rotor aircraft is established; Then, the control algorithm and parameters are simulated based on PID control method, and the control rules and controller parameters are designed. The simulation results verify the effectiveness of this method.

A Dynamic RCS and Noise Prediction and Reduction Method of Coaxial Tilt-Rotor Aircraft Based on Phase Modulation.

For tilt-rotor aircraft with coaxial rotors (coaxial rotor aircraft), reduction of radar cross section as well as acoustic noise can be essential for stealth design, and the rotation of the coaxial rotors can have an influence on noise and dynamic radar cross section (RCS) characteristics. In this paper, an approach to the prediction of both the sound pressure level (SPL) of noise and the dynamic RCS of coaxial-tilt aircraft is carried out, based on the theories of the FW-H equation, the physics optics method (PO) and the physical theory of diffraction (PTD) method. In order to deal with the rotating parts (mainly including coaxial rotors), a generated rotation matrix (GRM) is raised, aiming at giving a universal formula for the time-domain grid coordinate transformation of all kinds of rotation parts with arbitrary rotation centers and rotation axis directions. Moreover, a compass-scissors model (CSM) reflecting the phase characteristics of coaxial rotors is established, and a method of noise reduction and RCS reduction based on the phase modulation method is put forward in this paper. The simulation results show that with proper CSM parameter combinations, the reduction of noise SPL can reach approximately 3~15 dB and the reduction of dynamic RCS can reach 1.6 dBsm at most. The dynamic RCS and noise prediction and reduction method can be meaningful for the radar-acoustic stealth design of coaxial tilt-rotor aircrafts.

Modeling and PID control of quadrotor UAV based on machine learning

Abstract The aim of this article was to discuss the modeling and control method of quadrotor unmanned aerial vehicle (UAV). In the process of modeling, mechanism modeling and experimental testing are combined, especially the motor and propeller are modeled in detail. Through the understanding of the body structure and flight principle of the quadrotor UAV, the Newton–Euler method is used to analyze the dynamics of the quadrotor UAV, and the mathematical model of the UAV is established under the small angle rotation. Process identifier (PID) is used to control it. First, the attitude angle of the model is controlled by PID, and based on this, the speed in each direction is controlled by PID. Then, the PID control of the four rotor aircraft with the center of gravity offset is simulated by MATLAB. The results show that the pitch angle and roll angle can be controlled by 5 degrees together without center of gravity deviation, and the PID can effectively control the control quantity and achieve the desired effect in a short time. Classical BP algorithm, classical GA-BP algorithm, and improved GA-BP algorithm were trained, respectively, with a total of 150 sets of training data, training function uses Levenberg-Marquardt (trainlm), and performance function uses mean squared error (MSE). In the background of the same noise, the improved GA-BP algorithm has the highest detection rate, classical GA-BP algorithm is the second, and classical BP algorithm is the worst. The simulation results show that the PID control law can effectively control the attitude angle and speed of the rotor UAV in the case of center of gravity deviation.

An optimization for alleviating pilot workload during tilt rotor aircraft conversion and reconversion maneuvers

This work was focused on the conversion and reconversion maneuvers of XV-15 tilt rotor aircraft between helicopter and airplane modes. To alleviate pilot workload and improve safety, we proposed a multi-objective optimization method. Firstly, an augmented dynamics model has been developed and validated. Then, the transition maneuver was formulated as a proper optimization problem. The cost function consisted of several factors including transitional time, pilot workload, the power required, control allocation and pitch attitude. The constraints included not only the trajectory constraints and control rate limits, but also safety conditions of the conversion corridor and flight height. Finally, we analyzed the optimization results of two typical nacelle tilting schedules for both maneuvers using the wavelet analysis method to compare the pilot workload. Based on the results, in order to alleviate the pilot workload, it was recommended that during the conversion maneuver nacelles should initially tilt with much slower rate before aircraft reaches a certain forward speed at which the nacelle can tilt with normal rate. While during the reconversion maneuver nacelles were recommended to tilt under a normal rate. The nacelle tilting schedules in both maneuvers should be restricted inside the conversion corridors. As a result, the presented optimization method could identify the pros and cons between the two typical nacelle tilting schedules successfully. The obtained results could be used to provide a better reference for pilots and automatic conversion control systems.

Design of four rotor aircraft with obstacle avoidance

The system uses TM4C123G as the core of quadrotor autonomous vehicle control, which consists of flight control module, power supply module, motor speed control module, optical flow sensing module, and target tracking identification module. The flight control module includes angle sensor, gyroscope, and TLS1401-LF module. The flight control processes the collected data through the chip (TM4C123G), and processes the data with PID control algorithm, while solving the PWM increment and decrement needed for the corresponding motor, adjusting the motor in time and adjusting the flight attitude. The binocular camera identifies the color of the pole tower and measures the distance, so that the distance between the aircraft and the nearest point of the pole tower is kept within 50±10cm. After detecting the red (green) tower as the center, fly around the tower clockwise (counter) for one week (top view). Finally, the OV7725 camera is used to identify the solid black circle mark of the landing point and land smoothly and accurately in the target area, thus realizing an efficient robot around the barrier.

The Control Algorithm and Experimentation of Coaxial Rotor Aircraft Trajectory Tracking Based on Backstepping Sliding Mode

In view of the uncertainty of model parameters, the influence of external disturbances and sensor noise on the flight of coaxial rotor aircraft during autonomous flight, a robust backstepping sliding mode control algorithm for the position and attitude feedback control system is studied to solve the trajectory tracking problem of an aircraft in the case of unknown external interference. In this study, a non-linear dynamic model based on a disturbed coaxial rotor aircraft was established for an unknown flight. Then, a non-linear robust backstepping sliding mode controller was designed, which was divided into two sub-controllers: the attitude controller and the position controller of the coaxial rotor aircraft. In the controller, virtual control was introduced to construct the Lyapunov function to ensure the stability of each subsystem. The effectiveness of the proposed controller was verified through numerical simulation. Finally, the effectiveness of the backstepping sliding mode control algorithm was verified by flight experiments.

Study of RCS characteristics of tilt-rotor aircraft based on dynamic calculation approach

To study the Radar Cross-Section (RCS) characteristics of the tilt-rotor aircraft, a dynamic calculation approach that takes into account rotor rotation and nacelle tilt is presented. Physical optics and physical theory of diffraction are used to deal with the instantaneous electromagnetic scattering of the target. The RCS of the aircraft in the helicopter mode, fixed-wing mode and transition mode is analyzed. The results show that in the fixed-wing mode, the blade has a weaker deflection effect on the head incident wave in the horizontal plane. The helicopter mode improves the scattering of the rotor in the horizontal plane, while it increases the scattering source on the surface of the nacelle. At a fixed tilt angle, the RCS of the aircraft under a given azimuth angle still shows obvious dynamic characteristics. Dynamic tilting significantly changes the scattering effects of blades, hubs, nacelles and wingtips. The proposed approach is shown to be feasible and effective to learn the electromagnetic scattering characteristics of the tilt rotor aircraft.

Crashworthiness of a Composite Bladder Fuel Tank for a Tilt Rotor Aircraft

The fulfilment of the crash is a demanding requirement for a Tiltrotor. Indeed, such a kind of aircraft, being a hybrid between an airplane and a helicopter, inherits the requirements mainly from helicopters (EASA CS 29) due to its hovering ability. In particular, the fuel storage system must be designed in such a manner that it is crash resistant, under prescribed airworthiness requirements, in order to avoid the fuel leakage during such an event, preventing fire and, thus, increasing the survival chances of the crew and the passengers. The present work deals with the evaluation of crashworthiness of the fuel storage system of a Tiltrotor (bladder tank), and, in particular, it aims at describing the adopted numerical approach and some specific results. Crash resistance requirements are considered from the earliest design stages, and for this reason they are mainly addressed from a numerical point of view and by simulations that treat both single components and small/medium size assemblies. The developed numerical models include all the main parts needed for simulating the structural behavior of the investigated wing section: the tank, the structural components of the wing, the fuel sub-systems (fuel lines, probes, etc.) and the fuel itself. During the crash event there are several parts inside the tanks that can come into contact with the tank structure; therefore, it is necessary to evaluate which of these parts can be a damage source for the tank itself and could generate fuel loss. The SPH approach has been adopted to discretise fuel and to estimate the interaction forces with respect to the tank structure. Experimental data were used to calibrate the fuel tank and foam material models and to define the acceleration time-history to be applied. Thanks to the optimized foam’s configuration, the amount of dissipated impact energy is remarkable, and the evaluation of tanks/fuel system stress distribution allows estimating any undesired failure due to a survivable crash event.

Technical Configurations of a Helicopter Type Unmanned Aerial System for Pesticide and Fertilizer Application

It was noted that when forming the configurations of an unmanned aerial system for pesticide and fertilizer application, it is necessary to take into account the interdependence of unmanned and ground-based aerial systems. (Research purpose) To develop the configurations of an unmanned aerial system for pesticide and fertilizer application. (Materials and methods) The authors used Methodological recommendations on the use of chemicals in the precision farming system (VIM), regulatory and technical documentation for unmanned aerial systems. (Results and discussion) The authors developed a flowchart of the algorithm for forming the configurations of a helicopter type unmanned aerial system for fertilizer and pesticide application, including the formation of both unmanned and ground-based aerial systems. The authors calculated the aerodynamic characteristics of an unmanned coaxial rotor aircraft with a take-off weight of 280 kilograms and a payload of 100 kilograms. A modular-designed sprayer was offered. The authors substantiated the structure of the ground-based aerial complex in the form of a mobile transporter-tanker with a basic transport platform, lifting and transporting and refueling modules, and a universal ground control panel for the pilot-operator. (Conclusions) The authors formed reasonable configurations of a helicopter type unmanned aerial system for pesticide and fertilizer differentiated application in the precision farming system. Aircraft performance limitations were identified for the application of fertilizers and pesticides by a helicopter type unmanned aerial vehicle: the payload of at least 100 kilograms, the operating altitude of 1.0-1.5 meters when bypassing the agricultural field topography and avoiding possible obstacles, the operating airspeed kept below 60 kilometers per hour, automatic take-off and landing on a limited area, autoflight at the speed of 60 kilometers per hour at a one meter altitude in a tacking mode. It was showed that the static ceiling margin, without taking the earth influence into account, with a 280-kilogram flight mass, is 1300 meters, which allows flying in mountainous areas, for example, for the treatment of vineyards with pesticides.

Research on a combinatorial control method for coaxial rotor aircraft based on sliding mode

Aiming at the position and attitude tracking of coaxial rotor aircraft (CRA), this paper proposes a combinatorial control method of sliding mode control (SMC) coupled with proportional-integral-derivative control (PIDC). Considering the complete description of flight dynamics, aerodynamics and airflow interference, the dynamical model of CRA is established. The dynamical model is simplified according to the actual flight, then the simplified dynamical model is divided into two subsystems: a fully-actuated subsystem and an under-actuated subsystem. The controller of the fully-actuated subsystem consists of a SMC controller coupled with a rate bounded PIDC controller, while the controller of the under-actuated subsystem is composed of a SMC controller. The sliding manifold is defined by combining the position and velocity tracking errors of the state variables for each subsystem. Lyapunov stability theory is used to verify the stability of the sliding mode controller, which ensures that all state trajectories of the system can reach and stay on the sliding mode surface, the uncertainty and external interference of the model are compensated. Simulation and experiment compared with the conventional PIDC are carried out, the results demonstrate the effectiveness and the robustness of the proposed control method of this paper.

Manoeuvring control of an underactuated single rotor aircraft

Manoeuvring control of an underactuated single rotor aircraft