Rotary Wing Aircraft Research Articles

Characterising crack growth in commercially pure titanium

One of the challenges in aircraft sustainment is to develop additively manufactured (AM) replacement parts for legacy aircraft. This is particularly important for fixed and rotary wing aircraft that operate in in aggressive environments, i.e. off carriers, in a marine environment, etc. On the other hand the United States Air Force (USAF) have now adopted the concept of using AM to rapidly field limited-life unmanned air platforms. Whilst the temptation is to use AM Ti-6Al-4 V for these purposes, Ti-6Al-4 V powder is both costly and its supply is somewhat restricted. This paper reveals that the yield and ultimate strengths, the strain to failure of commercially pure (CP) Titanium, which is highly corrosion resistant, and it’s resistance to crack growth is superior to that of the commonly used aluminium ally AA7050-T7451, which is used in the F/A-18 Hornet, Super Hornet and F-35 (Joint Strike Fighter). Interestingly, when allowance is made for these improved properties then, if the crack growth rate da/dN is expressed as per the Hartman-Schijve crack growth equation, the resultant crack growth curves for Grade 2, 3 and 4 Titanium, and AA7050-T7451 all fall onto (essentially) the same master curve. It is also shown that the effect of different aggressive environments on Grade 3 Titanium is merely to change the fatigue threshold and that, when allowance is made for this, the crack growth curves associated with these different environments also fall onto the same master curve determined for CP Titanium and AA7050-T7451 tested in a laboratory air environment. Consequently, the damage tolerance and durability analyses presented in this paper suggest that CP Titanium may be attractive both for use as replacement parts for many aircraft parts, and for unmanned aerial vehicles (UAV’s).

CHARACTERIZATION AND EFFICACY OF VECTOBAC ® WDG APPLICATIONS TARGETING CONTAINER-INHABITING MOSQUITOES USING AN UNMANNED AERIAL VEHICLE

Application of Bacillus thuringiensis israelensis (Bti)-based liquid larvicide for the control of container inhabiting mosquito species, such as Aedes aegypti, is typically performed through the use of portable sprayers, truck-mounted mist systems, or manned fixed and rotary-wing aircraft. Recently, unmanned aerial vehicles (UAV) have provided a new avenue for control material applications. Here we report the characterization and efficacy of Wide Area Larvicide Sprays (WALS™) applications of Vectobac® WDG using UAV technology. Collier Mosquito Control District’s PrecisionVision 13 UAV was outfitted with the PrecisionVision Liquid Application System using four flat-fan TeeJet nozzles capable of producing fine/extra fine droplets for WALS applications of Vectobac WDG at a rate of 0.5 lb/A. Droplet characterization and mortality assays indicated that we achieved nearly 100% efficacy within 30-40 ft swaths. Furthermore, semi-field tests indicated delivery of the control material with six to seven adjacent swaths of 30 ft to open bioassay containers at the desired application rate within a 1 A treatment block, which was supported by reduction of natural populations of container inhabiting mosquitoes in the treatment area.

Recent developments in the aeroelasticity of morphing aircraft

This paper presents an extensive review of the developments in the aeroelasticity of morphing aircraft that occurred in the last decade (from 2009 to 2020). It focuses mainly on fixed-wing aircraft and highlights some representative examples from rotary-wing aircraft. Morphing wings are usually associated with significant changes in the aerodynamic loads, structural/elastic properties, and inertial properties and hence the aeroelastic behavior. Changes in aeroelastic behavior can also affect the flight dynamics, stability, and control of air-vehicles. The main motivation for this paper is the fact that it is not fully possible to assess and quantify the benefits of morphing technologies without accounting for aeroelastic effects. The literature on the aeroelasticity of morphing aircraft can be split into two main themes: Aeroelastic Stability and Aeroelastic Control. The first theme (Aeroelastic Stability) includes studies conducted on morphing concepts to ensure that they satisfy certain aeroelastic requirements/constraints and that such requirements/constraints do not limit the potential benefits of morphing. The second theme (Aeroelastic Control) includes studies that utilized morphing technologies to improve aeroelastic characteristics and/or control flight loads. It is evident that in both themes, the aeroelasticity of morphing aircraft has been analyzed using analytical, numerical, and/or computational tools with a very limited number of wind-tunnel and/or flight tests. In this paper, research activities and studies are categorized according to the morphing degree of freedom they address. For each degree of freedom, research activities are arranged according to the theme they fit under. Aeroelastic frameworks developed for generic morphing applications are also reviewed. In addition, the aeroelastic models used are highlighted and discussed. Finally, trends and research gaps are identified and discussed and main conclusions are drawn.

Multi-physics simulation of in-flight ice shedding

In-flight ice accretion may possibly jeopardise the safety of fixed-and rotary-wing aircraft. Icing can possibly occur if supercooled water droplets in clouds impinge on the aircraft surfaces and freeze upon impact. A major issue related to ice accretion is the possibility of ice shedding from the main body and impacting other parts of the aircraft or being ingested by the engines. A multi-physics framework is presented to simulate ice accretion and shedding from wings and engine nacelles due to aerodynamic forces. The aerodynamics is computed using the open-source tool-kit SU2. Cloud droplet trajectories are computed using the arbitrary-precision Lagrangian in-house solver PoliDrop. Then, the in-house ice accretion tool-kit PoliMIce is used to determine the ice layer. A FEM structural analysis is performed on the accreted ice shape by means of the open-source code MoFEM. Internal stresses within the ice geometry due to aerodynamic forces are computed. The possibility of the occurrence of cracks in the ice layer is assessed and its propagation is determined numerically. Two-dimensional ice accretion simulations are performed to check the validity of the present approach and compare fairly well with available results.

Generalized Energy-Based Flight Vehicle Sizing and Performance Analysis Methodology

Air vehicle sizing requires the ability to estimate the propulsive power and energy requirements of a flight vehicle as well as its weight. Existing tools and methods for aircraft sizing typically focus on a specific air vehicle category, generally assume a conventional fuel-burning propulsion system architecture, and employ a point-mass performance model. These shortcomings limit or preclude their applicability to novel concepts that differ from conventional fixed- or rotary-wing aircraft in configuration, employ all-electric or hybrid-electric propulsion systems, transition between different modes of flight, use propulsors in the dual role of control effectors, and/or offset weight in flight with a time-varying combination of aerodynamic lift, buoyant lift, and thrust. This paper demonstrates a methodology whereby flight performance, mission analysis, and energy sizing concepts are generalized and combined with explicit consideration of vehicle trim and geometry parameterization within a vehicle sizing and performance analysis framework intended for novel vehicle configurations and propulsion system architectures. The general applicability of the proposed methodology and developed framework is demonstrated through sizing and performance analyses of three dissimilar vehicle concepts: 1) a conventional twin-engine general aviation aircraft, 2) an all-electric vertical takeoff and landing lift-plus-cruise configuration, and 3) a hybrid lift airship.

Performance simulation of multi-stage axial-flow compressor of turbo-shaft engine with account for erosive wear nonlinearity of its blades

The construction and useful practice of gas-turbine engine diagnosis systems depend largely on the availability of the engine mathematical models and its certain components in their structure. Utilization of multi-stage axial flow compressor performance with account for erosive wear of its parts during the operation fundamentally raises possibilities of such systems as erosive wear of flow channel, blade rings of impellers and vane rings of multi-stage compressor is a common cause of preschedule gas-turbine engine detaching from an aircraft. As evidenced by various contributions presented in the article, special emphasis on abrasive wear impact assessment on axial flow compressor performance is placed upon rotor-wing turbo-shaft engine due to their particular operating conditions. One of the main tasks in the process of mathematic simulation of an axial flow compressor blade ring is consideration of its wear type that again has a nonlinear distribution along the level of the blade. In addition, wear rate at entry and exit blade edges often have different principles. Detecting of these principles and their consideration when constructing the compressor mathematical model is a crucial task in diagnostic assessment and integrity monitoring of rotor-wing turbo-shaft engine in operation. The article represents a concept to an estimate nonlinear erosive wear effect of axial flow compressor blades on its performance based on the three-dimensional flow approach in the gas-air flow duct of compressor with a formulation of the blade rings. This approach renders possible to take into account the nonlinearity of the compressor blades wear during their operation. Through the example of the inlet compressor stage of a rotor-wing aircraft gas-turbine engine, the engine pump properties predictions with different kind of rotor blade wear have been presented.

Assessing Aircraft Performance in a Warming Climate

AbstractIncreases in maximum and minimum air temperatures resulting from anthropogenic climate change will present challenges to aircraft performance. Elevated density altitude (DA) reduces aircraft and engine performance and has a direct impact on operational capabilities. The frequency of higher DA will increase with the combination of higher air temperatures and higher dewpoint temperatures. The inclusion of dewpoint temperature in DA projections will become increasingly critical as minimum air temperatures rise. High DA impacts aircraft performance in the following ways: reduction in power because the engine takes in less air; reduction in thrust because a propeller is less efficient in less dense air; reduction in lift because less dense air exerts less force on the airfoils. For fixed-wing aircraft, the performance impacts include decreased maximum takeoff weight and increased true airspeed, which results in longer takeoff and landing distance. For rotary-wing aircraft, the performance impacts include reduced power margin, reduced maximum gross weight, reduced hover ceiling, and reduced rate of climb. In this research, downscaled and bias-corrected maximum and minimum air temperatures for future time periods are collected and analyzed for a selected site: Little Rock Air Force Base, Arkansas. Impacts corresponding to DA thresholds are identified and integrated into risk probability matrices enabling quantifiable comparisons. As the magnitude and frequency of high DA occurrences are projected to increase as a result of climate change, it is imperative for military mission planners and acquisition officers to comprehend and utilize these projections in their decision-making processes.

Response to comment on “Flying by the Sun only: The Solarcopter prototype”, Aerosp. Sci. Technol. 45 (2015) 209-214

The Solarcopter proof of concept demonstrated the world's first purely solar-powered rotary-wing aircraft to fly, highlighting the feasibility of powering a rotary-wing unmanned aerial vehicle (UAV) exclusively by solar power. Absolutely no form of energy storage was utilised on this UAV prototype in any way. The novelties of the presented prototype include the exclusion of energy storage, utilising the central surface area of a quadrotor setup to maximise solar panel performance, and employing an ultra-lightweight, rigid, space frame structure. These key factors enabled the thrust-to-weight ratio of the presented prototype to be substantially greater than unity making the concept capable of continuous flight beyond the ground effect, provided sufficient solar energy is available. The presented concept and design was successfully validated with flight tests conducted in real-world conditions. The calculations and conclusions presented in the comments regarding the flight capability of the Solarcopter are premised on use of the Medusa 4000 rather than the Turnigy 800 motor that was implemented on the Solarcopter prototype. It is therefore unsurprising that the authors of the comments were unable to replicate the results presented for the Solarcopter.

A new robust adaptive mixing control for trajectory tracking with improved forward flight of a tilt-rotor UAV

A new robust adaptive mixing control (RAMC) is proposed in order to accomplish trajectory tracking of a tilt-rotor unmanned aerial vehicle (UAV) configuration. This kind of system is a hybrid aerial vehicle that combines advantages of rotary-wing aircraft, like hovering flight and vertical take-off and landing (VTOL), and those of fixed-wing aircraft, as improved forward flight. Although the VTOL and cruise flight regimes present different dynamic behaviors, in this work a unified, highly coupled, nonlinear model is developed to cope with the considered tilt-rotor UAV full flight envelope, that is, the axial flight, hovering, transition/cruise and turning flight. The modeling is performed via Euler–Lagrange formulation considering the tilt-rotor UAV as a multi-body system and taking into account aerodynamic effects and the dynamics of the tilting servomotors. Accordingly, in order to comply with the trajectory tracking requirements and improve the tilt-rotor UAV forward flight, this paper presents a novel robust adaptive mixing controller which is formulated to deal with linear parameter-varying (LPV) systems dependent on not known a priori large parameters but measured or estimated online, and also to provide robustness against unknown disturbances. Additionally, a rigorous closed-loop stability analysis is performed. The controller performance is validated with numerical experiments conducted using a high fidelity simulator developed on Gazebo and Robot Operating System (ROS) platforms.

Physical aspects of CMAS particle dynamics and deposition in turboshaft engines

Abstract

Crew-Friendly Countermeasures Against Musculoskeletal Injuries in Aviation and Spaceflight.

Aviation and space medicine face many common musculoskeletal challenges that manifest in crew of rotary-wing aircraft (RWA), high-performance jet aircraft (HPJA), and spacecraft. Furthermore, many astronauts are former pilots of RWA or HPJA. Flight crew are exposed to recurrent musculoskeletal risk relating to the extreme environments in which they operate, including high-gravitational force equivalents (g-forces), altered gravitational vectors, vibratory loading, and interaction with equipment. Several countermeasures have been implemented or are currently under development to reduce the magnitude and frequency of these injuries. Cervical and lumbar spine, as well as extremity injuries, are common to aviators and astronauts, and occur in training and operational environments. Stress on the spinal column secondary to gravitational loading and unloading, ± vibration are implicated in the development of pain syndromes and intervertebral disk pathology. While necessary for operation in extreme environments, crew-support equipment can contribute to musculoskeletal strain or trauma. Crew-focused injury prevention measures such as stretching, exercise, and conditioning programs have demonstrated the potential to prevent pre-flight, in-flight, and post-flight injuries. Equipment countermeasures, especially those addressing helmet mass and center of gravity and spacesuit ergonomics, are also key in injury prevention. Furthermore, behavioral and training interventions are required to ensure that crew are prepared to safely operate when faced with these exposures. The common operational exposures and risk factors between RWA and HPJA pilots and astronauts lend themselves to collaborative studies to develop and improve countermeasures. Countermeasures require time and resources, and careful consideration is warranted to ensure that crew have access to equipment and expertise necessary to implement them. Further investigation is required to demonstrate long-term success of these interventions and inform flight surgeon decision-making about individualized treatment. Lessons learned from each population must be applied to the others to mitigate adverse effects on crew health and well-being and mission readiness.

Integration of aeromedicine in the response to the COVID-19 pandemic.

There is limited guidance on the use of helicopter medical personnel to facilitate care of critically ill COVID‐19 patients. This manuscript describes the emergence of this novel virus, its mode of transmission, and the potential impacts on patient care in the unique environment of rotor wing aircraft. It details the development of clinical and operational guidelines for flight crew members. This allows other out‐of‐hospital clinicians to utilize our framework to augment or supplement their own for the current response effort to COVID‐19. It further serves as a road map for future response to the care of high consequence infectious disease patients.

Monitoring During Transport.

Transport of critically ill patients within and between hospitals is a common undertaking in an effort to improve patient outcomes. Intrahospital transports are frequently conducted to aid in diagnosis through advanced imaging techniques or to allow image-guided procedures. Interhospital transport is most frequently conducted to bring patients to specialized care, including centers of excellence for cardiac, trauma, transplant, and respiratory failure. Transport outside the hospital can be accomplished by ground or air, the latter including fixed-wing and rotor-wing aircraft. Often overlooked, transport of patients from the scene of an accident or illness to the hospital by emergency medical services is less sophisticated but more common than the other methods combined. Patients are also routinely transported to and from the operating room, a form of transport not commonly studied. Risks are inherent to transport, and an analysis of risks and benefits must be part of any risk-mitigation strategy. Monitoring the patient during transport by attendants and equipment is a key component of risk mitigation. Quicker transport times and specialized transport teams are associated with improved outcomes, whereas severity of illness is a harbinger of untoward complications. The type of monitoring during transport varies widely with the environment, the skill of the attendants, and the severity of patient illness. Standards for patient monitoring during transport are available, but they are predominantly based on expert opinion. This paper reviews guidelines and the risks of transport as a template for required monitoring, and it discusses common mishaps associated with transport and how these can be avoided with appropriate monitoring.

Adaptive attitude controller design for tail-sitter unmanned aerial vehicles

Tail-sitter unmanned aerial vehicles have two flight modes: they can fly long distances at high cruising speeds as fixed-wing aircrafts; or hover, take off, and land vertically as rotary-wing aircrafts. The tail-sitter dynamics involves serious nonlinearities and high uncertainties, especially in the two flight mode transitions. In this article, an adaptive control approach is proposed for a class of tail-sitter unmanned aerial vehicles to achieve the robustness properties. The control torque allocation problem is addressed based on the dynamic pressure in the transition flight. The proposed control method does not need to switch the coordinate system, the controller structure, or the controller parameters in different flight modes. It is proven that the attitude tracking errors can converge into a given neighborhood of the origin in finite time. Simulation results are presented to show the advantages of the proposed adaptive control method.

Low-Noise Flapping Wings with Tensed Membrane

Micro air vehicles with flapping wings have the potential to be both more efficient and maneuverable than similar-sized fixed- or rotary-wing aircraft. Reducing the perceived noise produced by flapping wings without compromising or possibly enhancing their aerodynamic performance would be crucial in surveillance and military applications. To this aim, flapping wings have been designed and fabricated for which the supporting stiffeners tense the Mylar membrane to which they are bonded. The sound produced by these wings at different flapping frequencies has been recorded in an anechoic chamber simultaneously to the upward thrust they create. Comparing their characteristics and performance with those of flapping wings of conventional design suggests that tensing the wing’s membrane can increase the thrust while decreasing the typical rustling noise of the flapping wings.

Viscoelastic haemostatic assays in aeromedical transport.

To assess the feasibility of using rotational thromboelastometry (ROTEM®)-sigma and thromboelastography (TEG®)-6s viscoelastic point-of-care assays during rotary wing aeromedical transport, and to determine the reliability of the results obtained. A single centre, prospective, observational, non-interventional feasibility study performed at Gold Coast University Hospital intensive care unit, and in a LifeFlight Retrieval Medicine operated Leonardo AW139 helicopter. Blood was collected from eight healthy volunteers on 18 April 2019 and all testing was performed on that day. Functions measured were ROTEM-sigma extrinsically activated thromboelastometry (EXTEM) clotting time (CT), EXTEM amplitude at 5 min after CT (A5) and fibrin-based extrinsically activated thromboelastometry (FIBTEM) A5, and TEG-6s Kaolin (CK) reaction time (R), functional fibrinogen (CFF) maximal amplitude (MA) and CFF amplitude at 10 min after R (A10). Differences between the results obtained in the helicopter and control results at Gold Coast University Hospital during flight and after flight, and also differences in control results over time up to 3 h were analysed. During flight both the ROTEM-sigma and TEG-6s devices failed to give reliable results. Post flight, the helicopter and control samples correlated well. Repeat testing of control samples at 1 and 3 h also revealed good correlation over time. It is feasible to reliably run tests on both the ROTEM-sigma and TEG-6s after the devices have been flown in a rotary wing aircraft. However, testing cannot be performed while in flight conditions. It is also possible to run blood samples collected up to 3 h prior and acquire results which correlate well with initial testing.

Coherent track‐before‐detect with micro‐Doppler signature estimation in array radars

In this work, the authors consider joint micro-Doppler signature estimation and track-before-detect for detecting and classifying manoeuvring and small rotary-wing aircraft with a phased array radar receiver. Such aircraft induce low signal-to-noise ratio reflections which complicates their detection. These difficulties are exacerbated by the high manoeuvrability of such aircraft which results with resolution cell migrations in conventional detectors. The authors propose a novel track-before-detect algorithm which jointly estimates the micro-Doppler signature, dominant reflectivity and kinematic trajectory of an object before the decision on its existence is made. These quantities are used in a Neyman-Pearson test against a constant false alarm rate threshold which is equivalent to evaluating a coherent long time integration value. The authors demonstrate the efficacy of the proposed scheme in a real data experiment and compare it with conventional techniques.

Patient, Paramedic and Institutional Factors Associated with Delays in Interfacility Transport of Injured Patients by Air Ambulance

Background: Air ambulance services are commonly used to expedite interfacility transport of injured patients to trauma centers. There is a lack of evidence surrounding risk factors for delays in interfacility transport of these patients. The purpose of this study was to examine patient, paramedic, and institutional-related characteristics for delay and identify specific causes of delays in interfacility transfers by air ambulance. Methods: This was a retrospective cohort study of injured patients undergoing interfacility transfer to a trauma center who were transported by air ambulance. Quantile regression was used to evaluate the impact of patient, paramedic and institutional characteristics on various time intervals of the interfacility transport process. Results: There are three key findings in our study. First, the use of rotor-wing aircraft and hospital-based helipads had substantially lower transport times. Second, transports from academic centers take longer compared to sending facilities with fewer resources. Third, interfacility transport times are heavily skewed and delays disproportionately affect longer patient transports. Conclusions: Ventilator dependence, paramedic level of care, classification of sending facility and helipad availability are associated with delays to interfacility transport of injured patients. Efforts can be made at both the air ambulance and institutional levels to ensure timely and efficient transports.

Spatial Disorientation Survey Among Military Pilots.

BACKGROUND: Spatial disorientation (SD) remains a significant cause of accidents and near accidents. A variety of training methods have been used to assist pilots to anticipate the SD problem. The value of such training in the prevention of disorientation has been difficult to assess.METHODS: To study transfer of SD awareness training, we related reported incidents to the content and frequency of SD awareness training received. The questionnaire was completed by 368 out of 495 pilots; 189 currently flying fixed-wing, and 150 flying rotary-wing aircraft. On average, their age was 38, and they had 2466 flight hours on-type.RESULTS: Respondents gave high ratings for the importance of SD training and their awareness of SD, the latter being one of the training objectives. The amount of SD training received by respondents was positively correlated with ratings for appreciation and importance. Self-rated awareness was positively correlated with the number of reported SD experiences. Although the correlations were below 0.50, the results provide an indication that SD training is effective. In total, respondents reported 5773 SD experiences, 195 of them resulting in a serious risk for flight safety. Narratives of these serious events show that, in many cases, pilots managed their SD by carefully checking the flight instruments, and also by good crew coordination.DISCUSSION: The results of the survey provide some evidence, although based on subjective reports, for transfer of SD training. The results of the SD experiences can be used to improve the SD training in terms of content and frequency.Pennings HJM, Oprins EAPB, Wittenberg H, Houben MMJ, Groen EL. Spatial disorientation survey among military pilots. Aerosp Med Hum Perform. 2020; 91(1):4-10.

Principal component analysis: The path ahead for aircrew-aircraft compatibility at the Institute of Aerospace Medicine

Introduction: The Institute of Aerospace Medicine provides design consultancy on aircraft-aircrew compatibility on a number of fixed-wing as well as rotary-wing aircrafts during various stages of development. Till date, the cockpit compatibility of aircrew has been determined based on the percentile concept. Percentiles, though useful when dealing with a single parameter, pose major design and fitment problems when considering multiple parameters simultaneously as in aircraft cockpit design. The concept of multivariate analysis has been the solution which the aviation industry the world over has accepted in overcoming this problem. This paper presents the Institute of Aerospace Medicine initial foray into the field of multivariate analysis, specifically principal component analysis (PCA) to achieve desired aircrew fitment in the aircraft cockpit right from the design stage. Materials and Methods: The fighter aircraft of the near future is being designed using the anthropometric parameters available in the IAF aircrew anthropometry survey 2013. Of the 57 parameters available, six parameters critical to the design of the cockpit were subject to PCA to derive three principal components. About 96% confidence ellipse was drawn on the plot of the principal components. From this, along the different axes, 21 boundary individuals were identified defining the extreme individuals in various combinations of the six parameters. Discussion: The use of more than 2 parameters is not amenable to sequential use of percentiles. As the number of parameters considered increases, it leads to reduced fitment percentage. The use of PCA allows consideration of critical parameters together at one go. The design aim is changed from the 3rd to 97th percentile to an overall aim of fitting 96% of the target population in the cockpit. The boundary individual’s entire anthropometry data are used to create boundary manikins for use in computer-aided design models. The fitment of these boundary individuals ensures that if these individuals fit, all others would fit in the cockpit. This concept brings about a paradigm shift in the aircrew-aircraft compatibility in the aviation industry in India.