Browse Topic: Transportation Systems
This paper presents an efficient numerical framework for prediction of broadband noise scattering through time-domain synthesis and propagation. For efficient scattering of broadband noise sources, a time-domain boundary element method is applied to propagate all frequencies together in a single computation. To obtain a time-resolved incident field without high-fidelity aerodynamic simulation, a stochastic broadband noise synthesis method is developed based on a semi-analytical airfoil broadband noise modeling approach. The framework is validated for airfoil trailing edge noise prediction, and the correspondence of the time-domain broadband noise synthesis method to existing semi-analytical broadband noise models is demonstrated. The framework is then applied to predict fuselage scattering of rotor tonal and broadband noise for a full-size urban air mobility concept vehicle. Significant differences are observed between the scattering effects in the tonal and broadband contributions.
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The recent discovery of glacier remains in Noctis Labyrinthus, the "Maze of the Night" near Mars' equator sheds new light on the history of water on Mars, the evolution of the planet’s climate and geology, and the possibility of life. It also opens the possibility for massive amounts of clean glacier ice to be accessed by astronauts at low latitudes on Mars, alleviating the need to operate in more frigid higher latitudes. Further reconnaissance of the site requires a robotic vehicle capable of traversing rough, salt-crusted glacier surfaces and leaping across crevasse fields. To address this need, we propose a conceptual hybrid aerial/ground vehicle, LILI (Long-term Ice-field Levitating Investigator). LILI combines episodic rotary-wing flight with ground mobility as a propeller-driven sled through an arrangement of skis/runners, wheels, and tilting proprotors. A high-level look at the Noctis Labyrinthus "relict glacier" site is presented, along with a notional LILI mission traverse concept designed to ensure critical scientific measurements are captured. The NASA Design and Analysis of Rotorcraft (NDARC) software is utilized to ensure that mission requirements and sizing constraints are met. Furthermore, future work considers guidance, navigation, and control requirements to satisfy mission objectives, and an initial construction for a simplified LILI small-scale prototype.
NASA is conducting investigations in Advanced Air Mobility (AAM) aircraft and operations, including the development of Urban Air Mobility (UAM) aircraft designs that can be used to focus and guide research activities in support of AAM. This report is an investigation of the impact of technology and mission variations on several of the NASA AAM concept aircraft: quadrotor, quiet single main rotor, side-by-side, and tiltrotor configurations, with turboshaft and electric propulsion variants for each. First, the mission and aircraft models of the baseline designs were reassessed and updated, including rotor geometry optimization, update of the rotor performance models, and disk loading optimization. For these eight designs, technology and mission excursions were performed. Relative to the calibration cases that can be considered examples of good design practice, the impact of the weight technology factors is significant. For the electric aircraft, there is a very large impact of battery specific energy (Wh/kg), and correspondingly a very large impact of mission range. The vision of Advanced Air Mobility is driven by missions that will enable new transportation capabilities. Hence it is appropriate to compare Concept Vehicles of different lift and propulsive architectures, all designed to accomplish the same UAM mission. It is also useful however to consider specific missions that can take advantage of the strengths of individual aircraft configurations. So alternate designs were also developed for the concept vehicles: for turboshaft aircraft, longer unrefueled range, including faster cruise speed for the tiltrotor; for electric aircraft, shorter range and more realistic battery weight.
Urban Air Mobility (UAM) concepts require multidisciplinary analyses across multiple modes of operation and often involve discrete architectural differences such as propulsion type, rotor configuration, and mission context. Existing optimization and workflow frameworks support continuous design variables but provide limited mechanisms for handling discrete variants, multi-modal vehicle definitions, and vehicle management for UAM vehicles. This paper presents uam4x, an open-source Python framework that addresses these challenges through a structured problem definition representation, a plugin-based execution engine, integrated version control, and a function-based branching script mechanism for constructing analysis scenarios. The framework provides integration of existing tools including Open Vehicle Sketch Pad (OpenVSP), NASA Design and Analysis of Rotorcraft (NDARC), M4 Structures Studio (M4SS), and Intelligent Cross Section Generator (IXGEN) through unified plugin interfaces. Parameter sweeps, nested analyses, and optimization via OpenMDAO are supported within the same architecture. This paper also presents demonstrations that were created to illustrate the various capabilities and integration efforts of the framework.
Vertical Take-Off and Landing (VTOL) aircraft introduce complex monitoring challenges due to distributed propulsion, lightweight structures, and variable operating conditions. This paper presents advanced Frequency and Orders domain techniques that repurpose existing flight control, propulsion, and structural sensor data to enhance observability without additional instrumentation. By transforming vibration, acoustic, and electrical signals into frequency and order domains, the approach enables detection of harmonics, resonance, and fault signatures tied to rotor dynamics, supporting adaptive control and predictive maintenance. Beyond rotor systems, these techniques are equally effective for monitoring electric motor health, gearbox wear, bearing degradation, and structural coupling effects in composite airframes. They also provide insight into power electronics and thermal management systems by identifying spectral anomalies linked to electrical imbalance or cooling inefficiencies. Aggregated fleet data strengthens prognostic capabilities, enabling early detection of systemic issues and trend analysis. Applications include mitigating ground resonance and modal instabilities, as well as improving reliability of propulsion and structural subsystems. Integration into avionics emphasizes computational efficiency, scalability, and compliance with standards such as DO-160 [1], DO-178 [2], ARP4761 [3] and ARP4764 [4]. Simulation and bench testing confirm feasibility, demonstrating potential to enhance safety, reliability, and lifecycle cost for next-generation urban air mobility platforms.
This paper presents updates to The Rotorcraft Optimization Tools (RCOTools) package to streamline iterative rotorcraft comprehensive design. The work is presented in three parts. Part I. a brief introduction to our simplified API is shown, in addition to a new mission profile dashboard. Part II. demonstrates high-throughput using the embarrassingly parallel paradigm to produce large-scale datasets structured by simple design of experiments (DOE) as shown by our discussion on urban air mobility (UAM) emission minimization. Such datasets provide a necessary component for rapid database generation and supervised machine learning. Part III. the API is used to couple rotor performance and sizing optimization. A simple technique for ultra-fast hover calibration is given, as well as possible applications for neural network modeling in comprehensive design. These enhancements accelerate design workflows and enable data-driven approaches for next-generation urban air mobility and planetary rotorcraft concepts.
This paper discusses uncrewed aerial vehicles (UAVs) that can have additional applications beyond their respective civilian, industry, or military applications. The increasing popular electric UAVs in advanced air mobility (AAM) and urban air mobility (UAM) networks can be utilized to increase the efficiency and impact of emergency response in both urban and remote settings. The paper will explore the design considerations and requirements for these dual-use vehicles for specific public good missions, while presenting a survey of additional public good missions that could significantly benefit from additional ready-to-go drones. Additionally, this paper aims to explore the logistics required to implement a system for incorporating civilian, industrial, and military drones into a reserve fleet for emergency and disaster relief efforts.
With recent advancements in the field of Advanced Air Mobility (AAM), including Electric Vertical Takeoff and Landing (eVTOL), Remotely Piloted Aircraft Systems (RPAS), and Unmanned Aerial System (UAS), it is beneficial to understand the impact of complex flow features on operations in urban and shipboard environments. Testing methods for studying these impacts, including simulated environments such as wind-tunnel flows and engineered equivalence tests, will need to be adapted to prepare for when the vehicles of interest are too large for the available testing facilities, and to permit low-cost alternatives for industry and government. This work demonstrates a development process that can be used to ensure the complex-flow-environment phenomena can be studied. First, this work illustrates the development of downdraft and turbulence flow types in a wind tunnel setting, and assesses the response of an M600 RPAS to these flows. Then, the same parameters are compared for a Mission Task Element (MTE) that was designed to challenge the RPAS in the vertical direction. Comparison of the two data sets provides insight into both the behaviour of RPAS in complex flows and the challenges of developing engineered equivalence tests.
This study provides a comprehensive framework for establishing land use compatibility guidelines specific to vertiports serving electric Vertical Takeoff and Landing (eVTOL) aircraft within urban settings. Recognizing critical gaps in current regulatory standards, the research systematically integrates analyses of accident risk, noise propagation, and aerodynamic impacts—including downwash and outwash—to delineate compatibility zones around vertiports. Employing an artificial intelligence (AI) augmented system, the study conducted safety and hazard assessments, various quantitative analyses, and simulations to identify spatial constructs of operational risks and environmental impacts. Results indicated significant discrepancies between existing aviation infrastructure guidelines and the unique operational characteristics of eVTOLs, necessitating revised zoning parameters. The proposed multi-tiered safety zoning framework provides precise, evidencebased recommendations for urban planners, enhancing safety, minimizing noise impacts, and ensuring environmental sustainability. Ultimately, this research offers policymakers and stakeholders practical tools for integrating advanced air mobility infrastructure safely into complex urban landscapes.
With advanced air mobility (AAM) vehicles becoming an increasingly popular topic in aviation, the Eagle Flight Research Center (EFRC) at Embry-Riddle Aeronautical University continues to investigate control strategies that enhance aircraft resilience to total power unit failures. Utilizing a distributed electric propulsion (DEP) quad-heli test bed, the EFRC has explored a variety of control laws and hardware configurations to evaluate their effectiveness under failure conditions, including sustained flight with a completely inoperative rotor. The aircraft utilizes a fractional-order PID (FOPID) controller that has recently been developed and shown to outperform conventional PID controller used previously in both nominal and failure scenarios. The use of a FOPID controller offers improved stability and tracking performance. Another development is the implementation of a split-rotation rotor configuration—where the left-side rotors rotate clockwise and the right-side rotors rotate counterclockwise—which, when combined with a control law leveraging cyclic rotor inputs for yaw control, provides a robust alternative to conventional quadrotor designs. This configuration leverages the redundancy offered by equipping each of the aircraft's four rotors with full helicopter controls, enhancing the potential for sustained flight in the event of two rotor failures while preserving the maneuverability and controllability characteristic of the conventional configuration. Additionally, to support expanded testing and operational capability, the aircraft has been outfitted with a custom-designed landing gear system, designed and fabricated by the EFRC team.
Small, highly maneuverable Urban Air Mobility (UAM) air taxis might exhibit motions during hover and low-speed flight that are unfamiliar to many passengers, and for which there are no established guidelines to predict passenger comfort. Researchers performed a study in the Armstrong Virtual Reality Passenger Ride Quality Laboratory to identify relationships between sudden motion characteristics and UAM passenger comfort and acceptance. Twenty-three volunteer test subjects from the Armstrong workforce each completed a 15-minute experience as a passenger in a virtual air taxi simulation. Subjects evaluated a series of flight maneuvers with varying levels of sudden motion using a five-point rating scale and indicated which motion(s) they found uncomfortable. Researchers then administered a post-test questionnaire to relate the passengers’ ratings to their willingness to fly on a real air taxi with similar levels of motion. The study results relate peak heave acceleration and jerk to passenger acceptance.
A joint acoustic flight test was conducted by NASA Langley Research Center and the U.S. Army Combat Capabilities Development Command Aviation & Missile Center, with the goal of investigating new methods for acoustic data collection. The impetus for the effort is the anticipated growth of Urban Air Mobility and Future Vertical Lift vehicles. Many of these vehicles are expected to have distributed propulsion systems that may result in unsteady vehicle state conditions even during steady flight. This work examines the acoustic measurements collected during purposefully unsteady maneuvers performed by an MD530F helicopter. A snapshot microphone array design was deployed for this test to capture the acoustic signature on the ground from the helicopter under maneuver conditions. An analysis of the acoustic emissions indicated the presence of blade-vortex interactions, not only during the rolls towards the advancing side of the main rotor, but also rolls towards the retreating side and during pitch-up maneuvers. The strength of the interaction noise was found to be strongly dependent on the acceleration of the vehicle.
A multifidelity, multipoint aerodynamic blade shape optimization was conducted to design a realistic, full-sized proprotor, representative of recent industry tiltrotor and lift+cruise UAM vehicle designs. The proprotor was designed to achieve a disk loading of 8 psf in hover at sea level standard day and 1.9 psf in cruise at an altitude of 4000 ft above ground level with a multipoint efficiency optimization target. A low-fidelity optimization was first conducted using a differential evolution algorithm with CAMRAD II's uniform inflow model, followed by a mid-fidelity trim using CAMRAD II's nonuniform inflow and free-wake models, a high-fidelity verification using a hybrid RANS/LES approach in FUN3D, and finally a high-fidelity optimization on the low-fidelity optimized blade shape with a gradient-based method using a uRANS approach in FUN3D. The low-fidelity optimization resulted in a proprotor that achieved a hover figure of merit of 0.830 and a propulsive efficiency in cruise of 0.904. Results from the low-fidelity optimization, mid-fidelity trim, and high-fidelity verification were compared to highlight differences in predicted blade span loading and aerodynamic efficiency between the different aerodynamic solvers. It was shown that the low-fidelity solver compared least favorably with the high-fidelity aerodynamic solver. Lastly, the high-fidelity optimization further reduced the torque in cruise by approximately 75 ft-lb, with negligible changes in hover figure of merit and propulsive efficiency in cruise. Negligible blade shape differences were observed between the low-fidelity optimized design and the results from the sequential high-fidelity optimization with the largest difference being collective pitch in both hover and cruise, respectively.
The advanced air mobility (AAM) sector is using novel aircraft configurations and distributed electric propulsion to revolutionize aviation. These concepts require rotors that are efficient in vertical and forward flight. A concept that shows potential for this application is the slotted, natural-laminar-flow (SNLF) airfoil due to its high lift and low drag characteristics. This work explores the impacts of using an SNLF airfoil on an AAM rotor. Comparisons are made with blade element momentum theory (BEMT) method and computational fluid dynamics (CFD) to study the impact on the performance of an isolated rotor in hover. It is found that the rotational speed of the SNLF rotor can be reduced by 8% while still maintaining the necessary thrust for trim. A rotor broadband noise prediction shows that the slower SNLF rotor is 1-2dB quieter in terms of overall sound pressure level. Comparison of both rotors in forward flight indicates that the SNLF rotor consistently has a 1-2% higher propeller efficiency.
This study presents the development and application of a refined momentum source term methodology for synthetic turbulence generation in urban flow simulations. By embedding divergence-free, three-dimensional turbulence fields consistent with the von Kármán energy spectrum directly within the computational domain, the approach enables flexible and efficient turbulence generation with minimal sensitivity to grid stretching. The method is validated through Large Eddy Simulations (LES) of flow around a representative urban vertiport model under varying turbulence intensities (10%, 20%, and 30%). Results demonstrate that the generated synthetic turbulence significantly alters the flow field, reducing recirculation zones, promoting earlier shear-layer reattachment, and stabilizing the flow above the vertiport platform—key factors for safe eVTOL operations. Instantaneous flow analyses reveal that secondary tip vortices (STVs) persist even in the presence of strong inflow turbulence but lose their periodicity, explaining discrepancies with prior spectral analyses. Overall, the momentum source term approach offers a practical and effective tool for modeling atmospheric turbulence and gust conditions in urban air mobility and rotorcraft simulations.
Single microphone measurements lack the ability to separate nondeterministic noise sources on multipropulsor vehicles, limiting their usefulness to understand the dominant noise generation mechanisms. To advance the state-of-the-art for measuring multipropulsor aircraft in support of future Urban Air Mobility (UAM) and Future Vertical Lift (FVL) testing, a 117-channel phased array was deployed during an Army/NASA acoustic flight test of an MD530F helicopter. A time-domain beamforming algorithm, namely, the ROtating Source Identifier (ROSI), was utilized to track the aircraft's forward motion and main rotor rotation. This process isolates nondeterministic sources of the main rotor, effectively filtering out contributions of the tail rotor and other nonrotating components. Source maps are provided for low-speed forward flight and illustrate aeroacoustic sources near the main rotor blade tips over a broad frequency range. Particular emphasis is given on the benefits of flying at a lower altitude relative to the array to enhance source separation through increased spatial resolution. A coherence-based microphone weighting scheme was utilized to support component-based integrated spectral assessments. Total integrated levels over the rotating scan grid are provided, representing the contribution of the main rotor to the total aircraft levels. Although additional analysis is needed to gain confidence in the beamforming methods applied, results herein minimally indicate this to be a valuable technique for qualitative source ranking.
Electric Vertical Takeoff and Landing (eVTOL) vehicles undergoing advanced air mobility (AAM) operations feature increasingly autonomous systems (IAS) with non-traditional role allocations. Ensuring the safety of these operations and their novel human–machine teaming (HMT) paradigms requires an appropriate body of knowledge created through relevant, reproducible research. In this paper, we briefly examine the meaning of teaming; current regulation, standards, and guidance; and the knowledge required to build resilient HMTs before turning our attention to how this knowledge is being created by recent research and what conclusions or recommendations can be made. We identify the need for further research into the holistic performance of HMTs, the effect of novel allocations of roles between humans and machines, the ability of humans to provide resilience to unforeseen dangers when acting as a part of these teams; and the characteristics required for clear, timely, and accurate communication between the humans and machines. This work is done in the context of eVTOL aircraft with an indirect flight control system (IFCS) undergoing urban air mobility operations.
Urban Air Mobility (UAM) aircraft are highly susceptible to turbulent wind disturbances when operating near buildings in complex urban environments. Microscale wind phenomena, combined with the unconventional designs of UAM aircraft, increase the risk of performance deviation, the overall duration, and the cost of flight tests for certification. A way to overcome this would be through simulation-based flight tests. Therefore, this study simulates a UAM aircraft landing vertically behind an isolated tall building, considering four different wind scenarios: no wind, uniform wind fields at low and high spatial resolutions (assumed constant across the airframe), and non-uniform fields with spatially varying velocity profiles at individual rotor hubs. The resultant flight test data are then used to quantify the impact of microscale wind characteristics on landing performance by systematically analyzing the rotor performance, aerodynamics, control response, and trajectory deviation.
The complex and turbulent ship airwakes make shipboard rotorcraft launch and recovery difficult for even the most seasoned pilots. One of the main challenges to using flight simulation to train pilots is the real-time accurate prediction of the ship airwake. A real-time, accurate methodology that is able to operate on personal computers without computational meshing is being developed for Advanced Air Mobility (AAM) applications. The early success of this novel approach indicates that it may be well-suited to meet the challenge of dynamic interface (DI) applications as well. To explore this, a novel reduced-order model (ROM) to represent unsteady airwakes for shipboard operations is underway. This ROM will be integrated into an ocean-based representative environment model (REM) to close the gap in real-time simulations without significant computational investment. The ROM effort presented here specifically investigates which superstructure wake characteristics are dominant in different regions where flight operations are conducted. Canonical ship geometries that have been significantly studied experimentally and computationally provide the substantiation of this approach. Evaluation of the accuracy of the approach is presented, correlated with Lattice-Boltzmann simulations, theoretical and experimental data.
Urban Air Mobility (UAM) is quickly developing with the objective of transporting passengers and cargo in urban areas using electric vertical take-off and landing aircraft (EVTOLs). This paper presents the process developed to design and optimize the noise control treatment in EVTOLs. The process leverages CAE simulation models to predict the acoustic performance inside the aircraft due to the propellers acoustic noise sources and the turbulent flow around the fuselage during cruising. The model includes a representation of the noise control treatments modeled as multi-layer poro-elastic materials and allows performing multi-attribute optimization to balance the vibro-acoustic performance with the costs, weight, and packaging constraints. This process has been applied successfully to support the development of EVTOLS before physical prototypes become available, therefore reducing the development time and corresponding costs. A demonstrator model serves as an example to illustrate the proposed simulation process.
This paper presents a comprehensive evaluation of machine learning approaches for real-time operational/ flight parameter estimation in large electric vertical takeoff and landing (eVTOL) vehicles, addressing the challenges of time-varying payloads and atmospheric disturbances in Advanced Air Mobility (AAM) missions. Artificial Neural Networks (ANN), Gaussian Process Regression (GPR), and Support Vector Machines (SVM), are compared for their ability to estimate gross weight (GW), longitudinal center of gravity position (CGx), and airspeed (Ux) using readily available flight control inputs and aircraft attitudes. The models are tested on clean data, turbulence-affected data, and reduced training data to assess performance trade-offs between computational cost and prediction accuracy. Results demonstrate that GPR consistently achieves the highest accuracy across all prediction tasks with maximum errors below 0.3% of nominal values, though at significantly higher computational cost compared to ANN and SVM. Under turbulent conditions, ANN and GPR exhibit notable reductions in accuracy, resulting in all three models (ANN, GPR, and SVM) achieving similar levels of prediction performance. Data reduction analysis reveals that using the Multipoint Maximal Variance Retention (MMVR) algorithm allows an 85–90% reduction in training data while keeping errors below 3.5%, striking an optimal balance between accuracy and efficiency. These analyses demonstrate the feasibility of ML-based operational/flight parameter estimation for AAM operations where direct measurement systems are impractical or cost-prohibitive.
The operation of Urban Air Mobility Vehicles (UAMVs) presents significant technical and operational challenges, particularly in the areas of safety, training, and cost management. This paper explores how advanced simulation models and predictive algorithms can address these challenges. A digital transformation framework is developed and applied in an Urban Air Mobility (UAM) case study to illustrate the effectiveness of these tools. Through the development of simulation models, critical insights are provided on damage detection, impact analysis, and maintenance optimization. The application of predictive algorithms enables quick damage assessment, improving safety by facilitating timely maintenance and repair decisions. To help showcase the benefits of this research, a demonstration was designed and built that allows users to interact with the developed tools and get a better understanding through hands-on training.
Advanced Air Mobility (AAM) is an innovative concept that aims to revolutionize air transportation through electric and unmanned aircraft, enabling applications such as urban air taxis and medical transport. However, one of the key challenges to its widespread adoption is ensuring safety, particularly in collision avoidance. This study focuses on the development of a perception and guidance system for avoiding collisions with non-cooperative targets, which do not share their position or trajectory. To achieve this, a Frequency-Modulated Continuous Wave (FMCW) radar and an InfraRed(IR) camera are used. Compared to traditional pulsed or panel radars, FMCW radars offer higher resolution, better detection of small and slow-moving objects, and improved performance in cluttered environments. The IR camera enhances situational awareness by providing visual confirmation and additional tracking capability, making this sensor fusion approach particularly suitable for AAM applications. Our collision avoidance system follows ACAS Xu standards, which provide autonomous conflict detection and resolution for unmanned aerial vehicles. The maneuver selection process is based on precomputed lookup tables generated through a Markov Decision Process (MDP), optimizing responses based on risk and energy consumption. The entire system is tested in a simulation environment using Ansys AVxcelerate, a physics-based simulator capable of generating realistic sensor data. This approach allows for comprehensive testing of detection, tracking, and maneuver execution in a highly realistic scenario, ensuring the effectiveness of the proposed solution before real-world deployment.
Electric vertical take-off and landing vehicles are proposed as a viable solution for urban air mobility due to their potential for reducing carbon emissions, noise, and operational costs. However, the shift towards electrified aircraft introduces new thermal management issues due to the excess heat generated by electric motors and power electronics. This heat is challenging to dissipate during the mission, resulting in transient motor temperatures, especially during high-power mission segments. In addition, electrified aircraft also encounter design challenges associated with the fixed weight of electric motors and batteries. To address these challenges, this work presents a multifidelity framework for performing shape optimization of an electric motor subject to performance, geometric, and thermal transient constraints. A preliminary sizing of the electric motor is performed using a low fidelity Fourier series model. Next, the sizing is refined by utilizing a coupled electromagnetic-thermal finite element model of the the motor physics. To demonstrate the framework, a numerical optimization is performed for a hover hold mission with a relevant scale eVTOL vehicle, reducing the structural mass of the motor by 2.7kg while ensuring power and thermal constraints are satisfied.
Acoustic flight testing of rotorcraft often involves generating noise source hemispheres to gain an understanding about the aircraft's acoustic emissions. However, aerodynamically complex Urban Air Mobility and Future Vertical Lift vehicles may not maintain a steady aerodynamic state during flight, making source hemispheres measured using traditional linear arrays unreliable or difficult to interpret. To address this challenge, all emission angles need to be measured simultaneously. This has lead to the concept of the two dimensional 'snapshot' array layout. A mathematically defined microphone distribution was utilized to achieve uniform coverage on the source hemisphere. Within the chosen distribution, two lower microphone count distributions are embedded, allowing for a comparison of the effects of number of microphones. The array was deployed as part of a joint Army/NASA acoustic research flight test in July of 2024. Data were collected using an MD530F helicopter as the test vehicle, executing both steady and unsteady flight. Analysis of the array resolution is used to determine adequate channel count and spatially varying sensitivity to array density.
This paper aims to demonstrate the use of Simulation Driven Design and topology optimization for the conceptual design of an Advanced Air Mobility (AAM) airframe. Over the past few years, Altair has developed a streamlined process for automotive engineers to rapidly develop the main structure of a car body in white. This process relies on Altair Hypermesh® and Optistruct® to develop a concept level architecture and then refine it to a detailed design ready structure, while allowing full flexibility to explore different design ideas. With the emergence and rapid expansion of the AAM branch of the industry, many new aircraft concepts are competing to lead the industry into a new exciting phase. Because of the relative size of these concept and their complexity, they are very well suited to the kind of optimization Altair developed for the automotive industry. This paper explores the first phase of the Altair process, using a representative eVTOL fuselage as a reference. The work illustrates the capabilities, how the models are setup and suggests some best practices to help possible users get started. The work also shows how the results of such optimization can be interpreted.
Electric vertical takeoff and landing aircraft (eVTOL) have swiftly risen to prominence since the early 2000's due to their potential to serve as a sustainable and scalable improvement in urban air mobility. In edgewise forward flight, these aircraft can experience significant time-varying aerodynamic loads due to being variable RPM vehicles. Their fuselage, booms and auxiliary lifting surfaces are often very lightly damped, lightweight and highly stiff. Thus, multiple bending and torsional modes of vibration can be excited and result in unacceptably high stress levels. Particle impact dampers (PIDs) are an attractive vibration mitigation strategy as they can target more than one mode of vibration. The potential use of a PID to target a bending mode of vibration is experimentally and numerically studied within this work. Experimental forced response analysis shows a 53% attenuation in amplitude of vibrations at the cost of a 5% mass penalty. A reduced order model was developed in order to allow users to parametrically study the damper performance as a function of a variety of inputs. Initial numerical simulations of this reduced-order model show behavior observed in the experimental arrangement. Model parameters are set to match laboratory values, and agreement is found with experimental results. This publication, in tandem with the work presented at the Vertical Flight Society's 80th Annual Forum, by the same authors, sheds light on the potential multi-mode damping capacities of these devices.
Aircraft Certification is a mature and complex bureaucracy that has successfully ensured a very high degree of safety of aircraft design, construction, operation and maintenance. Outside of a very few doing the work, there is a general lack of knowledge of certification details. For novel technologies such as electric power, and innovative configurations such as multi-rotors, the rules are far less mature and still emerging and so also poorly understood. Within the Advanced Air Mobility (AAM) initiative, many new aircraft developments are underway using novel configurations, and the public announcements of regulatory progress toward FAA or EASA Type Certification capitalize on this ignorance by being vague or even misleading. Honeywell conceived the Regulatory Readiness Level (RRL) indicator as an objective measure of certification status to serve the AAM industry and ecosystem, with applicability across aviation. The released RRL Version 1 now enables credible, objective assessment of new aircraft progress toward FAA Type Certification, and Operational Approval for Part 135 operations, to allow consistent apples-to-apples comparisons with other aircraft in development. An emerging complementary version of the rubric for EASA Type Certification is ready for publication to enable RRL determination against the European Union criteria. Future releases will consider other Nation's regulatory authorities, supplemental types certifications (STCs), and risk-based airworthiness assessments such as the Specific Operations Risk Assessments (SORA).
A follow-on study to the 2024 paper by Kottapalli, Silva, and Boyd is presented with improved acoustics tools to examine whether the Vertical Aviation International (VAI) Fly Neighborly operational recommendations that are designed for single main rotor/tail rotor configurations will hold for non-conventional UAM rotorcraft with multiple rotors. The 6-occupant quadrotor concept vehicle designed under the NASA Revolutionary Vertical Lift Technology (RVLT) Project is studied. The tip speed is 550 ft/sec, with three blades per rotor. Predictions are made for three steady maneuvers: level turns, descending turns, and climbing turns. The RVLT Toolchain is exercised using CAMRAD II, pyaaron/AARON/ANOPP2 and AMAT (ANOPP2 Mission Analysis Tool). Quadrotor noise trends are analyzed using Sound Exposure Level (SEL) ground maps because it is anticipated that the upcoming updated Fly Neighborly recommendations will involve SEL maps. Importantly, unlike conventional helicopters with a single main rotor, quadrotor noise can increase in a direction opposite to the turn direction; this finding may need to be taken into consideration in formulating the upcoming updated Fly Neighborly recommendations. The recommendation Level turns are quieter than descending turns is followed by this quadrotor under the flight conditions examined. Turning away from the advancing blade … is quieter than turning into the advancing blade is not relevant for symmetric aircraft such as the quadrotor. Straight flight is quieter than turning flight is not predicted to be best for this quadrotor under the flight conditions examined – turning flight is quieter than straight flight for the quadrotor in this study.
In the context of developing new rotorcrafts dedicated to Advanced Air Mobility, aeroacoustic simulations of co-axial rotor systems have been conducted using the lattice Boltzmann method with the ProLB code. Eight configurations, spanning from co-rotating rotors to contra-rotating shrouded rotors, were analyzed in stationary conditions through comparisons with experimental data and flow field analysis. This investigation validates our numerical methodology, based on direct noise simulation, and enhances our understanding of noise generation and propagation of such propulsive systems. Our simulations successfully replicate all measured trends in global aerodynamic performance, average noise levels, and noise directivities. Maximum discrepancies were 1.5 N (9%) and 2.1 dB (averaged noise level on the considered microphones). Based on our analysis, the following observations have been made. The open co-rotating rotors is the quietest configuration due to reduced Blade-Vortex Interaction (BVI). A 30° leading rotor angle increases noise by inducing BVI and flow detachment on the downstream rotor. On the other hand, contra-rotation offers the best performance but generates high tonal noise. Finally, the shrouded configuration is the noisiest due to blade-flow interactions and detachments along the duct, resulting in reduced performance and additional noise sources primarily due to non-adapted blades and duct.
New forms of highly automated Advanced Air Mobility (AAM) aircraft, such as electric vertical take-off and landing (eVTOL) vehicles, could transform transportation, cargo delivery, and a variety of public services. The National Aeronautics and Space Administration (NASA) conducted a series of flight demonstrations in collaboration with the Defense Advanced Research Projects Agency (DARPA) and Sikorsky Aircraft (a Lockheed Martin company) to progressively evaluate autonomous technologies. The autoland flight test research is a first in series for investigating the world’s first procedural descending-decelerating automated landing with vertical guidance Instrument Flight Procedures (IFP). The Sikorsky Optionally Piloted Vehicle (OPV) experimental UH-60 Black Hawk was used to evaluate a flight path’s four-dimensional trajectory (4DT) management into primitive commands and then follow those commands to a Point-in-Space (PinS) landing to the ground. All flight procedures were manually flown to the ground at 12 degrees with a 20-knot tail wind to ensure flight safety before automation was engaged. New and novel high precision approach procedures could pave the way for all future VTOL operations.
This study investigates the aerodynamic behavior of lift rotors in a representative lift+cruise electric vertical takeoff and landing (eVTOL) configuration using high-fidelity Computational Fluid Dynamics (CFD) simulations. As lift+cruise concepts gain prominence for Urban Air Mobility (UAM) applications due to their operational simplicity, flight performance, and reduced cruise noise, a detailed understanding of rotor aerodynamics during transition and cruise is critical. CFD analysis was conducted for both slowed rotors at high advance ratios and fully stopped rotors, where traditional predictive tools become inaccurate. Results show that lift rotors operating at advance ratios approaching three exhibit quasi-steady behavior similar to stopped rotors. The influence of rotor lock orientation on aerodynamic loads was characterized, with a freestream-aligned lock angle minimizing drag and asymmetry. A rotor hub fairing was found to reduce blade root separation and drag, though at the cost of slightly increased hub moments. The sensitivity of axial loads to vehicle pitch angle was quantified, highlighting the need to account for effective angle of attack in cruise load predictions. These findings inform future modeling strategies, control system design, and airframe integration for advanced eVTOL vehicles concepts.
A hybrid RANS/LES simulation of the Ideally Twisted Rotor (ITR) in hover was interrogated to identify bluntness vortex shedding (BVS) and determine the contribution to the predicted rotor broadband self-noise. Three rotor blade stations were extracted to study spanwise variations in the BVS shedding frequency and amplitude. Corresponding 2-D airfoil simulations were performed to evaluate a simplified modeling approach that effectively isolates BVS. The BVS shedding frequencies predicted by the 2-D airfoil simulations differed by less than 2% from the corresponding rotor stations in the 3-D simulation. The increased computational cost incurred by performing 3-D airfoil simulations did not lead to a worthwhile increase in simulation fidelity. Farfield noise was predicted for the three rotor stations and the 2-D airfoil simulations, and trends in frequency agreed well. The 2-D approach overpredicted the 3-D peak amplitudes by 5 - 10 dB. This work demonstrates that 2-D hybrid RANS/LES airfoil simulations can be used to investigate BVS noise trends on the ITR.
Vertical lift technologies present a promising solution for civil transportation between separated metropolitan and urban regions. This paper introduces the University of California Air transportation Link (UCAirLink), an electric vertical takeoff and landing (eVTOL)-based air transportation system for reducing overall commute times between regions. By leveraging flight operations in the National Airspace System (NAS), the UCAirLink connects the four northernmost University of California (UC) or the Center for Information Technology Research in the Interest of Society and the Banatao Institute (CITRIS) campuses. The UCAirLink addresses key aspects of urban air mobility (UAM) including optimal vehicle selection, infrastructure design, and flight route planning given regulations from the Federal Aviation Administration (FAA). A detailed trade study is presented for the selection of an optimal eVTOL aircraft. The eVTOL's flight routes cruise primarily in Class E and G airspaces to adhere to FAA flight regulations and ensure safe passenger-operations. Preliminary analysis shows a threefold reduction in overall travel time compared to traditional ground-based transportation modes, with selected eVTOL completing flight routes in less than 40 minutes.
The emerging Advanced Air Mobility (AAM) market is an increasingly important area of research and development within vertical lift. AAM operations will be characterized by short- to mid-range flight that will include urban and suburban corridors and high utilization business models such as on-demand ride-share and package delivery operations. AAM operations also have an enhanced need for durability of vehicle components with respect to impact and fatigue within unsteady environments such as urban canyons. Further business model constraints include the minimization of scheduled maintenance, while maintaining safety levels. A university leadership initiative (ULI), Innovative Manufacturing, Operation, and Certification of Advanced Structures for Civil Vertical Lift Vehicles (IMOCAS), combined research and software development to address these operational aspects. Another major focus of the ULI was the development of processes to integrate new advanced composite materials into AAM designs. These new composites, such as thermosets and thermoplastics, offer equal or enhanced performance at lower weights than traditional aviation materials. This paper provides an overview of the outcomes of the ULI, introducing new software, processes, and data available to the community for the AAM market, crosscutting large passenger operations and smaller medical or commercial cargo operations.
A novel multirotor concept is proposed for airlifting the emergency medical personnel without the use of a rescue helicopter (designed for patient transport) during the first line emergency services. Based on this concept, two configurations are designed and introduced, comprising a common quadrotor system with single and dual pusher propellers, respectively. An initial flight performance assessment is conducted for the introduced configurations by means of trim calculations in two distinctive flight modes across the entire designated flight speed range, initially without rotor-rotor interactions, and subsequently, with their inclusion. For this purpose, an existing mid-fidelity rotor-rotor interaction method is extended to capture the interactions in all three directions between the rotors that are arbitrarily positioned and oriented to each other. The trim calculations including rotor-rotor interactions show a 10% increase in the vehicle power at the maximum flight speed. The interactions between the pusher propellers and the lifting rotor wakes result in sudden increases up to 100% in the induced inflow of the propellers at low-speed regimes. The paper presents the two conceptual configurations along with their model syntheses and the results of the trim calculations. The influences of the rotor-rotor interactions on the trim results are discussed both at the rotor and the vehicle level.
Piloted evaluations form a critical part of Handling Qualities (HQ) testing. Military rotorcraft standard ADS-33 outlines the widely accepted approach to perform HQ testing, including both methods to determine predicted and assigned HQs (Ref. 1). Recently, ADS-33 has been replaced with MIL-DTL-32742, which includes updates to previously defined criteria and tasks (Ref. 2). Assigned HQs are awarded using short-look tasks, so-called Mission Task Elements (MTEs), stylized to represent mission requirements. Test courses focus on external visual cues, used by the pilot to judge position. Setting up external courses is usually expensive and may not be feasibly possible. The MCRUER (Means of Compliance Requirements for UAM Evaluations and Ratings) system intends to support HQ evaluations, replacing physical test courses using virtual displays. Four MTEs were successfully demonstrated in flight by three pilots using a variable stability rotorcraft. HQ evaluations were performed both using physical courses (live) and the MCRUER virtual courses. Handling Qualities Ratings (HQRs) were found to be consistent across both live and virtual courses with identifiable trends. Differences observed between the two cueing environments are described. Overall, virtual displays were found to improve pilot adherence to task specifications, even exceeding live-courses for a specific tasks.
Advanced Air Mobility (AAM) faces operational challenges because a significant portion of AAM flight operations are likely to occur within the atmospheric boundary layer (ABL). In particular, terminal flight paths within the ABL roughness sublayer will involve flying through building wakes that will likely result in a considerable increase in significant dynamic and vibratory loads on the vehicle, affecting flight safety and ride quality. A new representative environmental method (REM) has been developed that provides real-time estimates of the unsteady wind environments, including the roughness sublayer. The approach has numerous advantages over computational fluid dynamics solutions of any fidelity, as no meshing is required and it can easily be modified to evaluate the sensitivity of different environmental factors on operations or design. This approach is explained, verified, and validated using computational and experimental data.
The emergence of electric Vertical Takeoff and Landing (eVTOL) air vehicles is transforming how people and freight are moved in short distances. This transformation has a profound impact on surrounding infrastructure necessary to provide Aircraft On Ground support for eVTOLs. The hover capabilities of eVTOLs have similar operating characteristics within terminal and uncontrolled airspace. However, the need to conserve battery energy via rapid approaches and departures affects terminal airspace management. To attract eVTOL operators, existing airports, landing zones, and vertiports are modifying their infrastructure to include fixed electric charging stations, additional taxiways, upgraded fire suppression systems, separate hangers, and capable MRO facilities. Augusta Regional Airport (KAGS) is the base airport for the annual Masters Golf Tournament which experiences five times the normal airport traffic and some 40,000 commuting patrons. eVTOLs can offset land traffic issues associated with commuters and supplies. Since KAGS is centroid to 32,000 square miles of territory void of major highways, basing eVTOLs can offer expedited transit services for people and goods which will have a profound impact on the economic viability and quality of life in the area.
In the last years, new rotorcraft configurations have increased the attention among industries, through which the tiltrotor one due to its capability of combining both rotorcraft and aircraft advantages. However, there are situations where the vertical take-off mode could be enhanced in hard environmental and flight conditions. Therefore, to address this challenge, this work aims to develop a methodology to characterize a roll take-off model for a general tiltrotor configuration in such situations. By combining the integration of the equation of motion and geometrical assumptions, the runway distance is determined for an acceptable range of nacelle tilting angles. The process is developed by meeting the requirements defined by the regulations, combining the aircraft certification standards (CS23 and CS25) with the available tiltrotor certification basis from the FAA project #TC3419RC-R. Following the Nominal application, a sensitivity analysis is carried out, which studies the main effects on the results by varying one variable at a time in terms of weight, wing-loading, and disk-loading.
This study investigates the effects of chord-to-radius ratio (c/R) and blade count on the aerodynamic and aeroacoustic performance of cyclorotors through experimental testing and a low-fidelity streamtube model. Cyclorotors with c/R ratios between 0.3 to 0.75 and blade counts ranging from 5 to 9 were tested across pitch amplitudes up to 51°. For a 5-bladed configuration, the pitch amplitude that maximizes the force-to-power coefficient (CF/CP) increases with c/R from approximately 32° at low c/R to around 51° at high c/R. However, the peak attainable CF/CP decreases with increasing c/R, indicating a trade-off between optimal pitch amplitude and aerodynamic efficiency. Increasing blade count enhances the generated force but reduces efficiency in all cases except for the lowest c/R configuration (0.3). Aeroacoustic analysis shows that tonal noise is primarily driven by pitch amplitude and intensifies with increasing c/R, while additional blades effectively mitigate it. In contrast, broadband noise is less sensitive to variations in pitch amplitude, c/R, and blade count. The streamtube model captures key aerodynamic trends, particularly at moderate pitch amplitudes. Scaling studies identify optimal configurations for a given disk loading, balancing power consumption and noise levels and highlighting key trade-offs critical to urban air mobility applications.
In support of research and development for Urban Air Mobility (UAM) operations, the National Aeronautics and Space Administration (NASA) is developing a fleet of Vertical Takeoff and Landing (VTOL) concept vehicles. These vehicles aim to identify key areas for technological growth and provide reference data to the UAM community. A six-passenger Tiltwing concept recently added to the fleet offers new opportunities to explore the UAM design space through trade studies of the power and propulsion systems. In this paper, a turboelectric powertrain is designed and analyzed using the Numerical Propulsion System Simulation (NPSS) tool, the NPSS Power System Library, and a motor drivetrain optimization tool. Direct and geared motor drivetrains are designed and compared across a UAM design mission. Sensitivity of the Tiltwing maximum takeoff weight to motor drivetrain weights and efficiencies is estimated and used to inform optimal motor and gearbox selection. Results indicate that direct-drive and geared-drive configurations are comparable for this vehicle, with slight advantages to direct-drive when the radius of the drivetrain is unconstrained. When the drivetrain radius is constrained, a geared-drive system becomes more optimal.
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