Browse Topic: Urban air mobility (UAM)
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Advanced and Urban Air Mobility aircraft development is revolutionizing the aerospace industry by providing a realizable path towards affordable on-demand passenger-carrying operations in metropolitan areas. Many aircraft concepts are in development, and as they start to mature, there is a need for higher fidelity design and analysis tools that have improved modeling of component-wake interactions. Unfortunately, the current generation of CFD-based high fidelity tools is unsuitable for many daily design and analysis applications due to computational cost, expertise and setup requirements. Conversely, current design tools often rely on empirical relationships to represent many interactional effects, or become increasingly inaccurate in regions where the wakes trailed and shed from aerodynamic component becomes highly distorted. This paper describes recent work by Continuum Dynamics, Inc. to develop a mid-fidelity analysis tool, embedded within the CHARM analysis package, which brings CFD-class interactional aerodynamics analysis capabilities to aspects of the design cycle without the cost and expertise requirements of contemporary CFD-based analysis.
In recent years, the electrically powered Urban Air Mobility (UAM) market has witnessed significant growth, fueled by advances in electric motor and high-power-density lithium battery technologies. This surge of interest has prompted an exploration into the design and functionality of electric vertical take-off and landing (eVTOL) vehicles, particularly those with multi-tilt-rotor configurations. These eVTOL vehicles, capable of operating at higher RPMs than traditional helicopters, face unique challenges, especially under adverse environmental conditions such as icing. Aircraft airframe icing is known to severely compromise the operational efficiency and safety of aerodynamic surfaces, posing a significant threat to the operational capabilities of eVTOL vehicles. This paper presents the development and testing of a full-scale eVTOL rotor test stand that was designed to assess the impact of icing on these novel vehicles. The study focuses on evaluating eVTOL configurations under specific atmospheric conditions outlined in the Federal Aviation Regulation (FAR) Appendix C. The research aims to provide insights into the dangers imposed by icing and to collect experimental ice shapes in these unique configurations. This comprehensive data will aid in validating icing models and could help contribute to the formulation of eVTOL icing rules and regulations, improving the safety and viability of these vehicles in commercial airspace. A full-scale eVTOL rotor test stand was developed and tested in the Rail Tec Arsenal icing wind tunnel. In total 23 experimental conditions yielding 62 reference points were analyzed. The samples were compared to current state of the art 2D modified LEWICE prediction software based on maximum leading edge thickness and horn height. Of the 13 rime cases, 100% were within ±30% of the experimental results. 73.9% of mixed cases were within these bounds and 34.6% of glaze cases satisfied this criteria. Only a single horn out of 23 cases (4%) was within these bounds. Horn structures and other large features were unable to be successfully captured by 2D prediction models. Current 2D modeling software is sufficient at predicting leading edge ice thickness at temperatures at or lower than −10oC. Accuracy decreased as temperature increased, and other factors like SLDs negatively affected the prediction accuracy. It was empirically determined that there was no observable spanwise LWC variation during testing that could account for model uncertainty. Additionally, LWC changes through the rotor plane were also measured. A comparison between full and truncated blades was also performed. Straight-cut, truncated tips have a negative effect on ice shape development that is unaccounted for in 2D ice accretion models. Finally, it was determined that for an eVTOL trying to land after accreting ice in cruise, there would be an approximately 15%-30% additional power requirement (RPM held constant), dependent on icing conditions. The overarching goal of this work was to showcase the implications of icing on eVTOLs, with the ultimate goal of ensuring their operational integrity in diverse climatic conditions. This research represents a necessary step towards establishing eVTOLs icing testing, for efficient, and reliable urban air mobility.
NASA has previously designed and described set of concept aircraft to serve as reference vehicles for Urban Air Mobility (UAM), to encourage public discussion and research. These vehicles are used in this paper to quantify how suitable UAM aircraft might be for missions other than their primary commercial design missions. A set of representative public good missions are described, along with design requirements and equipage. For two of these missions, the additional weight, power, and cost to facilitate a basic vehicle which may be built or configured with the ability to perform these missions is quantified. Special layout and other considerations which may impact vehicle design are described. For aircraft designed to the NASA UAM reference mission, the addition of some meaningful public good missions causes less than 10% growth in weight and power for fossil-fueled aircraft; advanced battery-electric powered aircraft grow by a significantly larger amount and may only be possible with relaxed requirements. Meaningful public good missions with UAM vehicles are feasible, provided that public good mission requirements are considered and incorporated in the conceptual design stage of development.
Flight mechanics modeling and real-time simulation of rotorcraft have many challenges including the aerodynamics and dynamics of the rotor system, rotor inflow, and wake-airframe interactions. Furthermore, interactional aerodynamic effects are difficult to characterize, in particular during early configuration down-selection. Rotorcraft configurations under consideration for advanced air mobility applications are trending toward designs with coaxial rotor systems and multiple distributed propellers / rotors in close-proximity with one another and the airframe. This proximity leads to strong coupling between the rotor inflow and lifting surfaces (e.g., tiltwing and lift+cruise urban air mobility concepts). This paper describes recent work toward the development of a general-purpose modeling framework for flight mechanics analysis and simulation of rotorcraft and aircraft configurations proposed for advanced air mobility applications. This modeling framework was developed for assessment of aircraft ride qualities during urban flight operations; however, the focus of this paper is on the modeling framework development and application. Model validation with experimental data is another focus, examining scaled model data and flight test results.
Hazard assessment is an engineering activity that produces insight into which states of thing being engineered might be hazardous. In aviation contexts, it is often performed for certification credit at both the aircraft and system levels during the early design phase of the system's lifecycle. However, novel aircraft paradigms such as urban air mobility (UAM) operations might either violate assumptions on which traditional aviation hazard assessment is based or simply possess attributes that would make other approaches more effective. In this paper, we define the key concepts underpinning hazard assessment and identify the limitations and assumptions inherent in hazard analysis. We analyze popular techniques to show how they embody these key concepts. We identify ways in which hazard assessment may be scoped and tailored to an application. And, using worked examples, we discuss how, where, and why such tailoring might be needed, especially in novel contexts.
The paper presents a novel strategy for minimum energy consumption in automatic conversion control of tiltrotor eVTOL aircraft, exemplified by the Aston Martin Volante Vision model. We introduce a tilt schedule methodology that strategically balances conversion and reconversion performance with climb, descent, and cruise phases to minimize overall energy expenditure. Our approach accounts for critical factors such as blade loading, operation handling qualities, and passenger ride comfort within a predefined conversion corridor. The optimized trajectories approximate the minimum energy pathway, essential for operational efficiency in urban air mobility. Analytical results demonstrate that our proposed conversion and reconversion phase profiles significantly reduce energy consumption, contributing to the sustainability of tiltrotor flight operations. This research not only enhances understanding of tiltrotor dynamics but also serves as a pivotal step toward achieving globally optimized energy usage, marking a significant advancement in autonomous flight technology for advanced air mobility systems.
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To aid in the development of electric Vertical Take-off and Landing (eVTOL) technology, the National Aeronautics and Space Administration has undertaken research initiatives to evaluate and optimize design features of eVTOL aircraft. One such initiative has been to develop energy attenuating design mechanisms to improve eVTOL vehicle crashworthiness. In this study, crashworthiness design mechanisms, implemented within a six-passenger lift plus cruise (LPC) eVTOL concept vehicle, were evaluated under multi-axis dynamic loading conditions. This work builds upon crashworthiness design concepts previously optimized within a simplified vehicle-loading environment. The results of this study found the effectiveness of energy attenuating design mechanisms to be dependent on the complexity of load environment in which they were employed. An increase in off-axis loading resulted in a decrease in occupant protective capability. These results indicate the necessity for evaluating vehicle design across the range of possible dynamic impact conditions to characterize crashworthiness. This work provides preliminary methodology for implementing energy attenuating design mechanisms and evaluating crashworthiness for future UAM markets.
In November 2019, NASA completed the first wind tunnel test entry of the Multirotor Test Bed (MTB), a new test capability for advanced VTOL rotorcraft configurations. The MTB had been under development since 2017 when the need arose for an easily reconfigurable test stand for multirotor aircraft configurations. With the wide-ranging assortment of aircraft currently targeted at Urban Air Mobility and Unmanned Aircraft System applications, there is a need for validation data that will increase confidence in the computational modeling tools being used to develop these platforms. The MTB fills this need. This paper describes the key features of the MTB as well as its first wind tunnel test entry. A selection of results from the test is presented here, demonstrating the flexible configuration of the MTB and the types of data researchers can generate using this new test capability.
Many electric vertical take-off and landing (eVTOL) aircraft intended for the urban air mobility (UAM) market are currently being designed with multirotor configurations using variable speed fixed-pitch, rigid rotors for lift. These types of rotors, which are similar in construction to general aviation airplane propellers, are simpler than helicopter rotors and have no moving parts in the rotating frame. This paper discusses wind-tunnel testing of a full-scale, UAM multirotor size, fixed-pitch, rigid rotor with a focus on vibratory blade loads and on the ability to predict these loads with comprehensive analysis. Test results show that vibratory loads are very high, with peak-to-peak magnitudes up to three times greater than the steady component. Correlation of test data to comprehensive analysis using geometrically exact composite beam structural elements and dynamic inflow wake modeling captures the trends in the steady and vibratory loads, but under-predicts the magnitudes by up to 50%. The paper also discusses the physical sources of the observed vibratory loads and suggests potential options for mitigating their magnitude.
Modern system identification techniques were used to identify a linear model based on a nonlinear simulation of a concept Urban Air Mobility quadcopter, and compared to a perturbation-based model. These models were used to develop feedback controllers for both variable-pitch and variable-RPM variants of the quadcopter, with the handling qualities requirements determining current requirements for the electric motors. To have sufficient stability margins and bandwidth, the motor time constant for the variable-RPM system must be no greater than 0.122s. Both variable- RPM and variable-pitch systems were limited by the yaw axis, which relies on differential motor torque for control. The introduction of rotor cant alleviated this problem for the variable-pitch vehicle, allowing a 47% reduction in motor weight, relative to the uncanted variable-pitch system.
The present study endeavors to consider the most popular eVTOL (electric vertical takeoff and landing) aerodynamic concepts employed nowadays. This research gives a theoretical evaluation of the possible eVTOL design with different electric or hybrid power plant configurations. Conventional helicopter, quadcopter and tiltrotor quadcopter with ducted fans or open rotors have been considered. Relationship between eVTOL mass parameters and available power of the power plant is calculated. Performance of the eVTOL with full electric and hybrid power plants in forward flight mode is estimated. Available and required power needs for speed envelope in hover and maximal speed modes are calculated. Optimal specific parameters (batteries, generators, electric motors) of fully electric and hybrid power plant elements are defined to provide acceptable eVTOL flight performance.
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