Faster-than-realtime inverse simulation method for tiltrotor handling qualities investigation

The tiltrotor aircraft has unique flight dynamics characteristics because of the extensive aerodynamic interference and the unique control strategy. Inverse simulation offers an opportunity to study a vehicle's performance during manoeuvring flights. In this paper, an improved inverse simulation method is developed with an Automatic Differentiation (AD) approach embedded in the code based on the verified flight dynamics model of the tiltrotor aircraft. The AD algorithm would accelerate the computational rate of the inverse simulation process and make it achieve faster-than-realtime capability. Then, the XV-15 tiltrotor's control inputs and flight states encountered during a pop-up manoeuvre are investigated using this AD-augmented inverse simulation method, and the real-time capability of this method is also evaluated. The results indicate that the proposed method guarantees both accuracy and faster-than-realtime calculation performance. Lastly, the tiltrotor's manoeuvrability is assessed by executing this manoeuvre in different flight states and manoeuvre settings. Lastly, an envelope involving the velocity and nacelle incidence angle is calculated to indicate the safety region to achieve this pop-up manoeuvre

NASA Heavy Lift Rotorcraft Systems Investigation

The NASA Heavy Lift Rotorcraft Systems Investigation examined in depth several rotorcraft configurations for large civil transport, designed to meet the technology goals of the NASA Vehicle Systems Program. The investigation identified the Large Civil Tiltrotor as the configuration with the best potential to meet the technology goals. The design presented was economically competitive, with the potential for substantial impact on the air transportation system. The keys to achieving a competitive aircraft were low drag airframe and low disk loading rotors; structural weight reduction, for both airframe and rotors; drive system weight reduction; improved engine efficiency; low maintenance design; and manufacturing cost comparable to fixed-wing aircraft. Risk reduction plans were developed to provide the strategic direction to support a heavy-lift rotorcraft development. The following high risk areas were identified for heavy lift rotorcraft: high torque, light weight drive system; high performance, structurally efficient rotor/wing system; low noise aircraft; and super-integrated vehicle management system

A Summary of NASA Rotary Wing Research: Circa 20082018

The general public may not know that the first A in NASA stands for Aeronautics. If they do know, they will very likely be surprised that in addition to airplanes, the A includes research in helicopters, tiltrotors, and other vehicles adorned with rotors. There is, arguably, no subsonic air vehicle more difficult to accurately analyze than a vehicle with lift-producing rotors. No wonder that NASA has conducted rotary wing research since the days of the NACA and has partnered, since 1965, with the U.S. Army in order to overcome some of the most challenging obstacles to understanding the behavior of these vehicles. Since 2006, NASA rotary wing research has been performed under several different project names [Gorton et al., 2015]: Subsonic Rotary Wing (SRW) (20062012), Rotary Wing (RW) (20122014), and Revolutionary Vertical Lift Technology (RVLT) (2014present). In 2009, the SRW Project published a report that assessed the status of NASA rotorcraft research; in particular, the predictive capability of NASA rotorcraft tools was addressed for a number of technical disciplines. A brief history of NASA rotorcraft research through 2009 was also provided [Yamauchi and Young, 2009]. Gorton et al. [2015] describes the system studies during 20092011 that informed the SRW/RW/RVLT project investment prioritization and organization. The authors also provided the status of research in the RW Project in engines, drive systems, aeromechanics, and impact dynamics as related to structural dynamics of vertical lift vehicles. Since 2009, the focus of research has shifted from large civil VTOL transports, to environmentally clean aircraft, to electrified VTOL aircraft for the urban air mobility (UAM) market. The changing focus of rotorcraft research has been a reflection of the evolving strategic direction of the NASA Aeronautics Research Mission Directorate (ARMD). By 2014, the project had been renamed the Revolutionary Vertical Lift Technology Project. In response to the 2014 NASA Strategic Plan, ARMD developed six Strategic Thrusts. Strategic Thrust 3B was defined as the Ultra-Efficient Commercial VehiclesVertical Lift Aircraft. Hochstetler et al. [2017] uses Thrust 3B as an example for developing metrics usable by ARMD to measure the effectiveness of each of the Strategic Thrusts. The authors provide near-, mid-, and long-term outcomes for Thrust 3B with corresponding benefits and capabilities. The importance of VTOL research, especially with the rapidly expanding UAM market, eventually resulted in a new Strategic Thrust (to begin in 2020): Thrust 4Safe, Quiet, and Affordable Vertical Lift Air Vehicles. The underlying rotary wing analysis tools used by NASA are still applicable to traditional rotorcraft and have been expanded in capability to accommodate the growing number of VTOL configurations designed for UAM. The top-level goal of the RVLT Project remains unchanged since 2006: Develop and validate tools, technologies and concepts to overcome key barriers for vertical lift vehicles. In 2019, NASA rotary wing/VTOL research has never been more important for supporting new aircraft and advancements in technology. 2 A decade is a reasonable interval to pause and take stock of progress and accomplishments. In 10 years, digital technology has propelled progress in computational efficiency by orders of magnitude and expanded capabilities in measurement techniques. The purpose of this report is to provide a compilation of the NASA rotary wing research from ~2008 to ~2018. Brief summaries of publications from NASA, NASA-funded, and NASA-supported research are provided in 12 chapters: Acoustics, Aeromechanics, Computational Fluid Dynamics (External Flow), Experimental Methods, Flight Dynamics and Control, Drive Systems, Engines, Crashworthiness, Icing, Structures and Materials, Conceptual Design and System Analysis, and Mars Helicopter. We hope this report serves as a useful reference for future NASA vertical lift researchers

Technology Assessment of eVTOL Personal Air Transportation System

This thesis intended to provide a holistic vision on the potential consequences of the introduction of emerging electrical Vertical Takeoff and Landing (e VTOL) Personal Air Transportation System (PATS) to contribute to the forming of public and policy opinion, and to assess the impacts and the feasibility of that. Instead of looking from a detailed vehicle design viewpoint, we tried to understand the need, the impacts, and the perceptions and the concerns of stakeholders. Thus, it was set a framework and methodology starting with a technology assessment point of view in the light of transportation system analysis. Limitations of the current ground and airline transportation systems, increasing congestion, poor block speed, combined with expanding population and demand for affordable on- demand mobility are driving the development of future transportation technology and policy. The third wave of aeronautics might be the answer and could bring about great new capabilities for society that would bring aviation into a new age of being relevant in daily lives since eVTOL PATS is envisioned as the next logical step in the natural progression in the history of disruptive transportation system innovations. However, there are a lot of questions. Although there was difficulty since the system was an emerging air transportation mode, an interdisciplinary study has been conducted to assess the impacts of developing such a capability. The research questions were determined to address the research objectives. What is the current state of mobility and eVTOL air transportation mode? What are the potential benefits of eVTOL air transportation mode for user and society? What are the perceptions of service providers, regulator, and user? What are the main challenges including technology, regulation, operation, social and environment aspects to enable the system? What are the enabling technologies? Nevertheless, with the results obtained lately from the research activities, revolutionary technologies and regulations are bringing us closer to eVTOL PATS reality every day. It can be argued that a new socio-technical transition will come about like the transition from horse drawn carriers to cars. Even if it is still a long way to go, it seems rather likely that the time has been arriving in the next decade. Their existence and operation would therefore need to be taken into consideration for today’s planning considerations and construction projects to be able to have this emerging air transportation mode available in the future. As the technology underlying eVTOL PATS evolves, wider eVTOL adoption across various markets is likely to be supported further if a set of key challenges such as safety and security, ease of use and autonomy, noise, infrastructure, and air traffic management are overcome. Achieving drastic improvements in ease of use, safety and community acceptable noise are the most critical steps towards the future feasibility of this market. Multi-use demos and demonstrating successful operation with early vehicles, namely eVTOL PATS prototype field operations, will create public acceptance and understanding of potentials in emerging air transportation mode for public good, use and learn in multiple applications. The overall perception of the user, service provider and regulator are positive, and the support is high. Shortly, a successful implementation and sustainable transition will depend on overcoming technological hurdles, regulatory frameworks, operational safety, cost competitiveness, and sensibilities of the affected communities. There is a need to enable people and goods to have the convenience of on-demand, point-to-point safe travel, further, anywhere in less travel time, through a network of pocket airports/vertiports, and there is a significant potential benefit so that policy makers, regulators and metropoles’ transportation planning departments should consider an inclusion of eVTOL air transportation mode into the scenarios and policies of the future.Esta tese pretende fornecer uma visão holística sobre as potenciais consequências da introdução do Sistema de Transporte Aéreo Pessoal (PATS) de Decolagem e Pouso Vertical elétrico emergente (e VTOL) para contribuir para a formação de opinião pública e política, e para avaliar os impactos e a viabilidade disso. Em vez de olhar de um ponto de vista detalhado o projeto do veículo, tentamos entender a necessidade, os impactos, as percepções e as preocupações das partes interessadas. Assim, foi definido um quadro e uma metodologia partindo de um ponto de vista de avaliação de tecnologia à luz da análise do sistema de transporte. As limitações dos atuais sistemas de transporte terrestre e aéreo, o aumento do congestionamento, a baixa velocidade do tráfego, combinados com a expansão da população e a mobilidade com procura acessível estão impulsionando o desenvolvimento de futuras tecnologias e políticas de transporte. A terceira onda da aeronáutica pode ser a resposta e pode trazer grandes novas capacidades para a sociedade que trariam a aviação para uma nova era de ser relevante na vida cotidiana, uma vez que o VTOL PATS é visto como o próximo passo lógico na progressão natural na história das inovações disruptivas do sistema de transporte. No entanto, há muitas perguntas. Embora tenha havido dificuldade por se tratar de um modo de transporte aéreo emergente, um estudo interdisciplinar foi realizado para avaliar os impactos do desenvolvimento de tal capacidade. As questões de investigação foram determinadas para atender aos objetivos do projeto. Qual é o estado atual da mobilidade e do modo de transporte aéreo eVTOL? Quais são os benefícios potenciais do modo de transporte aéreo eVTOL para o utilizador e a sociedade? Quais são as percepções dos provedores de serviços, regulador e utilizador? Quais são os principais desafios, incluindo tecnologia, regulamentação, operação, aspectos sociais e ambientais para habilitar o sistema? Quais são as tecnologias facilitadoras? No entanto, com os resultados obtidos ultimamente nas atividades de pesquisa, tecnologias e regulamentações revolucionárias estão nos aproximando cada dia mais da realidade do VTOL PATS. Pode-se argumentar que uma nova transição sócio-técnica ocorrerá como a transição de carruagens puxadas por cavalos para automóveis. Mesmo que ainda seja um longo caminho a percorrer, parece bastante provável que a hora esteja chegando na próxima década. A sua existência e operação, portanto, precisam ser levadas em consideração para as questões de planeamento e projetos de construção de hoje para poder ter esse modo de transporte aéreo emergente disponível no futuro. À medida que a tecnologia subjacente ao eVTOL PATS evolui, é provável que a adoção mais ampla do eVTOL em vários mercados seja ainda mais apoiada se um conjunto de desafios importantes, como segurança e proteção, facilidade de uso e autonomia, ruído, infraestrutura e gestão de tráfego aéreo forem superados. Alcançar melhorias drásticas na facilidade de uso, segurança e ruído aceitável pela comunidade são os passos mais críticos para a viabilidade futura deste mercado. Demonstrações multi-uso e demonstração de operação bem- sucedida com veículos iniciais, ou seja, operações de campo do protótipo eVTOL PATS, criarão aceitação pública e compreensão dos potenciais no modo de transporte aéreo emergente para o bem público, uso e aprendizado em várias aplicações. A percepção geral do utilizador, prestador de serviço e regulador é positiva, e o suporte é alto. Uma implementação bem-sucedida e uma transição sustentável dependerá da superação de obstáculos tecnológicos, estruturas regulatórias, segurança operacional, competitividade de custos e sensibilidade das comunidades afetadas. Há uma necessidade de permitir que pessoas e mercadorias tenham a conveniência de viagens seguras de que necessitam, ponto a ponto, e além disso, em qualquer lugar em menos tempo de viagem. Isso pode ser feito por meio de uma rede de aeroportos/vertiports, e há um benefício potencial significativo para que os formuladores de políticas, reguladores e departamentos de planeamento de transporte das grandes metrópoles considerem a inclusão do modo de transporte aéreo eVTOL nos cenários e políticas do futuro

A Status of NASA Rotorcraft Research

In 2006, NASA rotorcraft research was refocused to emphasize high-fidelity first-principles predictive tool development and validation. As part of this new emphasis, documenting the status of NASA rotorcraft research and defining the state-of-the-art in rotorcraft predictive capability were undertaken. This report is the result of this two-year effort. Contributors to this work encompass a wide range of expertise covering the technical disciplines of aeromechanics, acoustics, computational fluid dynamics (CFD), flight dynamics and control, experimental capabilities, propulsion, structures and materials, and multi-disciplinary analysis

Performance and Loads of Variable Tip Speed Rotorcraft at High Advance Ratios

This dissertation presents a lifting-line, comprehensive approach to predicting the performance and loads of high advance ratio rotorcraft. At high advance ratios, the reverse flow region is large and its unique aerodynamics impacts the rotor performance and dynamics more than at conventional airspeeds where they are often ignored. The analysis is refined and augmented with improved modeling of the nearwake in reverse flow, a new aerodynamic model of the fuselage and the root cutout region and corrections to the airfoil properties for highly yawed flow. The analysis is correlated and evaluated against a full-scale UH-60A rotor test to an advance ratio of 1.0 and against an in-house Mach-scaled rotor to an advance ratio of 1.2. High advance ratio performance is predicted satisfactorily for both tests, including predicting the onset of thrust reversal. Despite the high advance ratio, correctly modeling the wake is most important for predicting airloads and the resulting blade bending loads, while yawed flow, nearwake inflow and the fuselage flow disturbances are important for predicting high advance ratio thrust and power. The validated analysis is used to investigate the effect of reverse flow stall, blade twist, root cut-out and shaft angle on high advance ratio performance