Browse Topic: Electric vertical take-off and landing (EVTOL)
Emerging technologies in the field of electrified propulsion systems offer a promising solution to reduce the dependence on fossil fuels and improve efficiency. However, the design of high-power density electric machines introduces new challenges, including limited passive cooling potential and the issue of the weight of electric motors. To address these challenges, this paper considers analysis and design methods for high torque-to-weight ratio axial flux motors. A magnetic equivalent circuit model coupled with a lumped parameter thermal network is developed for design space exploration and optimization. This inexpensive analytical model predicts the performance of a single-stator dual-rotor axial flux motor based on geometry, loading condition, and slot and pole pair combination. To enable comparisons against real-world data, the optimization study was demonstrated using the hover mission requirements from the Research Aircraft for eVTOL Enabling techNologies (RAVEN) vehicle to minimize the mass of the motor. In tandem with the analytical model, a higher-fidelity finite element model was also developed, and good agreement between predicted power and efficiency was demonstrated across a range of axial flux motor designs. The lightest weight design that satisfied the hover mission requirements was the 12 pole pair 27 slot (12PP 27S) configuration with a fixed weight of 9.28 kg. The analytic model undersized the output power of the electric motor by approximately 9% across a range of slot and pole pair combinations.
Advanced Air Mobility (AAM) air vehicles with electric vertical takeoff and landing capability come in a wide variety of configurations and are often equipped with many lift and propulsion devices. Lift rotors of AAM configurations often have high disk loading which produce strong downwash and outwash (DWOW) at low speed and hover close to the ground. Recent outwash surveys of AAM aircraft have confirmed the presence of strong DWOW produced by various aircraft configurations [1]. The capability to predict the DWOW characteristics produced by these aircraft can aid in deriving requirements for vertiport design, ground operation, and landing/takeoff flight safety procedures. This paper investigates the sensitivity of selected aircraft design and operation parameters on the overall DWOW. This includes rotor horizontal and vertical separation distances, and near ground flight maneuvers. The focus in this paper is on the DWOW profile near the aircraft to help inform design and operational decisions. Moreover, transient approach/departure simulation for an AAM aircraft are conducted for an understanding of the complex flow field during unsteady flight maneuvers. The Viscous Vortex Particle Method (VVPM) is used to estimate the aircraft DWOW characteristics.
This paper presents an initial handling qualities analysis of an Electric Vertical Take-Off and Landing (eVTOL) hexacopter. The analysis uses the Distributed Electric Propulsion Simulation (DEPSim), developed by Penn State University (PSU) and the Comprehensive Hierarchical Aeromechanics Rotorcraft Model (CHARM), developed by Continuum Dynamics, Inc. (CDI). The study focuses on evaluating a generic AAM hexacopter performing Handling Qualities Task Elements (HQTE) as defined by the DOT / FAA. A trajectory controller was developed to enable simulation of prescribed flight paths, allowing automated simulation of four HQTEs: Heliport Approach, Hovering Turn and Hold, Pirouette, Lateral Reposition and Hold. Design modifications incorporating lateral mast tilt and Direct Side Force Control (DSFC) were implemented to enhance yaw control and ride qualities. Piloted simulations were conducted at the PSU rotorcraft flight simulation facility using DEPSim, employing an Attitude Command Attitude Hold (ACAH) architecture with mode switching to Translational Rate Command / Position Hold (TRC / PH) and TRC plus DSFC modes. Two of the four HQTEs were tested in piloted simulations. Though formal ratings were not collected at this time, pilot commands and performance indicated that TRC / PH and TRC plus DSFC modes enhance handling qualities over ACAH mode. The DSFC control law was found to have substantially reduced roll attitude, which could potentially enhance visual cueing, pilot comfort, and pilot-perceived handling qualities.
This study presents a comprehensive analysis of single-rotor failure tolerance for a classical octocopter configuration, examining both hover and forward flight at the best range speed. Using a state-of-the-art eVTOL comprehensive analysis to retrim the octocopter post-failure, the redistribution of rotor thrust, torque, and power following individual rotor failures was quantified, along with resulting aircraft-level power penalties. In hover, orthogonal rotors to the failed rotor provide primary lift compensation, the opposing rotor operates mostly unchanged, and the four opposite spinning rotors primarily provide pitch/roll moment compensation. This results in a total aircraft level power increase of approximately 10.4%, roughly half that of comparable hexacopters. In forward flight, at best range cruise speed, load redistributions were again calculated for various individual rotor failures. In the worst case, a maximum individual rotor torque increase of 62% and power increase of 108% was observed, while total aircraft power requirements increased between 7-12%. These results demonstrate the fault-tolerant capabilities of octocopters and provide practical guidance for propulsion system sizing, energy management, and failure-case assessment on classical octocopters.
This paper presents a comprehensive evaluation of data-driven machine learning (ML) frameworks for the estimation of critical operational parameters, gross weight (GW), longitudinal center-of-gravity (CGx ), and airspeed (Ux ) for a UAM-scale Lift plus Cruise eVTOL aircraft. Artificial Neural Networks (ANN), Gaussian Process Regression (GPR), and Support Vector Machines (SVM) are compared for their ability to track these dynamic parameters across both low-speed rotor-borne and high-speed wing-borne flight regimes. The models are rigorously tested on steady-state clean data and stochastic atmospheric turbulence data sets to assess performance trade-offs between computational cost, noise robustness, and predictive accuracy. Results demonstrate that GPR consistently achieves the highest accuracy on clean data, particularly for GW and CGx estimation, though it exhibits the highest sensitivity to stochastic noise. Conversely, SVM demonstrates the greatest relative robustness under turbulent conditions and superior computational efficiency, identifying it as a practical candidate for resource-constrained onboard flight computers. Furthermore, a dynamic continuous-time analysis reveals a critical trade-off between responsiveness and accuracy. Instantaneous predictions are shown to suffer from severe transient error spikes during maneuvers, whereas a moving average filtering strategy effectively mitigates these errors at the cost of response latency. These analyses demonstrate the feasibility of ML-based parameter estimation for UAM operations and highlight the necessity of adaptive temporal filtering to balance agility with resilience in turbulent environments.
During conceptual presizing of electric vertical takeoff and landing aircraft, it is critically important to predict the weight and efficiency of powertrain subsystems as accurately as possible, since these components usually represent a large fraction of the vehicle design gross weight. This paper compares the electric powertrain weight and efficiency models implemented in three aircraft conceptual design and performance estimation tools: HYDRA, NDARC, and CREATION. Using a common lift plus cruise vehicle configuration and mission, this paper investigates the effects of motor, electronic speed controller, battery, and other powertrain subsystem models on vehicle sizing. Results for both operating conditions with all rotors operational and cases accounting for the failure of one or two lifting rotors are presented. Results show that differences in powertrain subsystem models - particularly in motor scaling laws and battery sizing assumptions—lead to large variations in vehicle design gross weight, an effect that is exacerbated when sizing for motor/rotor failures. While HYDRA and CREATION predicted similar battery system weights for all cases, NDARC estimated lower battery weights but higher motor/ESC weights at lower power and torque, with convergence closer to the other two codes at higher power and torque requirements. This paper presents a comparison of methodologies from modern conceptual presizing codes, and proposes areas of improvement where full vehicle sizing accuracy can be improved.
This paper discusses the design of a 2000-lb manned eVTOL aircraft propelled by a novel cycloidal rotor propulsion system. To systematically evaluate the performance of the proposed configuration, a coupled trim model was developed to quantitatively evaluate the performance of the configuration across a range of forward flight speeds. The trim framework integrates an efficient physics-guided neural-network-based aerodynamic model for cycloidal rotor performance with a vehicle-level dynamic response model. This framework is used to conduct a systematic parametric study to identify key cycloidal rotor and airframe design parameters. The selected configuration is verified using high-fidelity CFD simulations, and a detailed structural design, powertrain design, and CAD model of the aircraft is developed. In addition to CFD validation, the proposed cycloidal rotor underwent structural optimization to confirm the validity of such a concept at this scale. The results demonstrate that the cycloidal rotors provide a viable propulsion alternative for eVTOL aircraft with strong potential to overcome limitations of existing configurations.
This paper presents the design, development, and subscale flight testing of an optionally-autonomous lift-plus-cruise (LPC) eVTOL aircraft for emergency response missions that bridges the gap between existing aerial capabilities and the needs of first responders. A 4+1 LPC configuration consisting of four vertical lift propellers and a single pusher propeller was selected to balance hover performance and cruise efficiency. The vehicle is sized around a 600 lbs gross takeoff weight with a 125 lbs payload capacity. VTOL and Pusher propeller blades were optimized using parametric studies, resulting in a high Figure of Merit and propulsive efficiency. Trim analysis demonstrates efficient hover to cruise transition, lift-to-drag ratios of 10-11 between 70-90 knots, and propulsive efficiency exceeding 0.9 at the cruise speed of 100 knots. The subscale configuration utilized a simulation framework for trim and optimization of flight control laws, which were subsequently implemented on a 1/3-scale subscale demonstrator. Subscale flight tests showed stable hover and robust trajectory tracking under wind disturbances throughout the flight envelope, which demonstrates the feasibility of the proposed LPC architecture.
This paper details comprehensive analysis modeling and analysis supporting the development of the Research Aircraft for eVTOL Enabling techNologies (RAVEN). An isolated rotor model was developed in CAMRAD II, and predictions of rotor performance and rotor aeroelastic stability were generated. The rotor stability predictions are part of assessing airworthiness of the RAVEN vehicle. The performance predictions were used to calibrate the surrogate model for the NASA Design of Rotorcraft (NDARC).
This study investigates the performance and vibration characteristics of representative lift rotors for a notional lift+cruise electric vertical takeoff and landing (eVTOL) configuration. As new eVTOL concepts continue to be developed and others progress towards FAA certification, it is crucial to understand the performance and vibratory considerations associated with different lift rotor design choices, including the number of blades and the method of thrust control (e.g., variable blade pitch/fixed RPM vs. fixed blade pitch/variable RPM). The NASA Revolutionary Vertical Lift Technology (RVLT) Lift+Cruise configuration was chosen as the baseline vehicle for this analysis (Ref 1). The investigation includes the evaluation of multiple lift rotors with 2-, 3-, and 4-bladed configurations as well as variable- vs. fixed-pitch designs. Both isolated rotor and full vehicle simulations were assessed to demonstrate some of the design variables applicable to the full vehicle performance and vibratory content. Industry-standard rotorcraft comprehensive analysis software, the Rotorcraft Comprehensive Analysis System (RCAS) (Ref 3), was used to evaluate and compare each configuration for performance and vibratory loads at key points in the rotors and in the fuselage
Recent flight tests and simulations have suggested that the outwash from eVTOL air-taxis could be larger than conventional helicopters of equal weight and thus pose greater safety issues for their operation than previously anticipated. This has prompted interest in the analytical and experimental study of the aerodynamics related to multi-rotor aircraft outwash. This paper will describe work investigating some of the related issues, specifically (1) how wake models and wake model parameters impact outwash predictions in comprehensive rotorcraft analyses and (2) considerations when scaling results from model scale to full scale. This work will also compare outwash predictions for conventional and multi-rotor VTOL aircraft obtained with a Lagrangian free-vortex wake model and with an Eulerian velocity-vorticity grid based wake model.
Winged electric vertical takeoff and landing (eVTOL) aircraft commonly employ multiple lift rotors mounted on underwing booms to enable efficient cruise while retaining vertical flight capabilities, making resilience to rotor failure a critical consideration in design and certification. While prior studies have primarily assessed fault tolerance through control feasibility and allocation strategies, the physical consequences of rotor failure on individual motor loading and overall aircraft power requirements remain relatively unexplored. This paper investigates the effects of single-rotor failure on an eVTOL aircraft with eight rotors on four underwing booms in hover using a physics-based comprehensive rotorcraft model. Three rotor spin configurations are examined, including the baseline NASA Lift plus Cruise arrangement and two alternate configurations inspired by emerging industry designs. Post-failure trim solutions are obtained using both power-optimal and intuitive paired-rotor shutdown strategies. Results quantify changes in rotor thrust, torque, and power, revealing that rotor spin configuration strongly influences load redistribution and peak motor demands despite similar increases in total aircraft power. These findings highlight the importance of incorporating physical motor loading considerations alongside control feasibility in fault-tolerant eVTOL design.
A high-fidelity computational study is conducted to investigate the aerodynamic behavior and flight response of an electric Vertical Take-Off and Landing (eVTOL) multirotor configuration using unsteady computational fluid dynamics (CFD) framework. Four simulation cases are considered to examine the vehicle aerodynamics under both prescribed and fully coupled conditions. Prescribed hover and forward-flight cases isolate rotor aerodynamics and rotor-airframe interactions under constrained kinematics. Six-degree-of-freedom (6-DoF) free-flight maneuvering simulations capture the coupled evolution of aerodynamic loads, vehicle attitude, and translational motion. The results demonstrate that the high-fidelity unsteady CFD framework, coupled with rigid-body dynamics, effectively resolves the tightly coupled aerodynamic–dynamic interactions inherent to eVTOL configurations. This work provides a foundation for future investigations into trim strategies, control modeling, and expanded flight envelopes.
NASA Airspace Operations and Safety Program is researching the utility of electric vertical takeoff and land (eVTOL) advanced air mobility (AAM) instrument flight procedures. The result will be dynamic and tailored procedures that align to the following modus operandi: maximize safety, optimize efficiency, support passenger comfort and minimize acoustics. This is achieved through dynamic airspace procedure design, which is a modular approach to create an airspace construct that customizes procedures to vehicle design and configuration, operation, and environmental conditions. The test plan supports different eVTOL platforms and envisioned operations for flight test or simulation and may be leveraged by AAM aircraft manufacturers and operators for any given aircraft, location and operation. This white paper is a reduced subset of the flight test plan; the full publication can be found on the NASA Technical Research Server (NTRS), https://ntrs.nasa.gov/citations/20240002788.
Researchers at the National Aeronautics and Space Administration (NASA) have conducted a series of module-level 50-ft dynamic drop tests on electric Vertical Take-off and Landing (eVTOL) Energy Storage Systems (ESS) for the generation of dynamic impact data to support standards developments. The tests were conducted on zero-state-of-charge Electric Power Systems (EPS) Electric Propulsion Ion Core (EPIC) modules at the National Institute for Aviation Research (NIAR), utilizing the NIAR outdoor drop test setup and conducted by NIAR test personnel. Four total tests were conducted on modules oriented in four different orientations. During initial post-test inspections at the drop facility, it was observed that the modules experienced varying amounts of damage in various locations and forms. The damage was quantified to the maximum extent possible via photogrammetric methods such as digital image correlation and marker tracking. Post-test modules were then disassembled, and forensics were conducted, which involved inspections into various containment structures and the cells themselves. A scoring rubric was developed in order to utilize a common methodology to quantitatively assess the damage incurred into each module as way of determining the least and most amount of damage present. Results in the form of post-test inspections, digital image correlation deformations, and scoring rubric values will be all presented, along with proposed paths forward for future work.
Electric aviation is advancing rapidly, with aircraft from manufacturers like Joby and Archer well on their way to certification, aircraft electrification will continue and begin to apply to larger aircraft. To support larger electrified rotorcraft, rotors will need to grow if disc-loading and hover efficiency are to be maintained. A consequence of this is the need to reduce rotor speed to maintain an acceptable acoustic signature, especially for operation in urban environments. Most current applications utilize radial flux motors, sometimes with a reduction gearbox. Gearboxes can improve overall propulsion system power density by enabling higher motor speeds but are generally not preferred as they introduce additional potential failure modes and maintenance schedules. In this paper a holistic approach is used to understand the trade-offs between rotor and motor and their consequences on propulsion system power density.
This paper presents the development, verification, and validation results of an electrical Vertical Take-off and Landing (eVTOL) powertrain model. To better understand the potential impact of powertrain limitations on eVTOL aircraft handling qualities, a powertrain model was developed, integrated into revolutionary vertical lift technology (RVLT) reference vehicle designs, and tested in the National Aeronautics and Space Administration (NASA) Ames Vertical Motion Simulator (VMS). The high computational complexity required to capture the relevant powertrain physics may conflict with the ability to execute the simulation models in real time. In this paper, the authors present models and modeling decisions related to motors, batteries, and interconnections. Physics-based models and empirical models are used in tandem to support the modeling effort. Simulated motor-data comparisons are made to data collected from the NASA Scaled Power ElEctrified Drivetrain (SPEED) and Advanced Reconfigurable Electrified Aircraft Lab (AREAL) testbeds. The empirical battery model is compared to experimental 18650 battery data.
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) 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.
A piloted simulation study in the Vertical Motion Simulator at NASA Ames Research Center will investigate the handling and ride qualities of eVTOL configurations (lift-plus-cruise and tiltwing) for both civilian and military applications. The flight dynamics models were developed in the FLIGHTLAB modeling and analysis software environment, while explicit model-following control laws and high-fidelity powertrain models were developed in Simulink. The Joint Input-Output method was used to generate frequency responses for linear model verification, as the control effectors are highly correlated for these types of vehicles. The linear models were verified for the frequency range of interest for handling qualities. Once verified and tested individually, the three parts (flight dynamics model, control laws, and powertrain) will be integrated into the Vertical Motion Simulator for piloted simulation evaluations.
This paper presents an overview of the comprehensive aerodynamic framework developed at ERC for the analysis and simulation of electric vertical takeoff and landing (eVTOL) aircraft. Addressing the challenges inherent to distributed propulsion architectures and the complex transition between hover and forward flight, the methodology integrates multi-fidelity simulation tools ranging from analytical models and low-fidelity simulation to fully-resolved transient CFD. The framework addresses all phases of aircraft design and validation, and includes dedicated insight into aeroacoustics, aeroelasticity, and interactional aerodynamics problems. A modular approach is adopted, where individual phenomena are first studied in isolation before being synthesized into an aircraft model. Experimental validation through wind tunnel testing, full-scale static thrust test stand measurements, and scaled model flight tests is essential to ensuring model accuracy and validity. The paper concludes with an outlook to further enhance data generation, simulation efficiency, and fidelity in future eVTOL development programs.
Gaussian Process Regression (GPR) is a flexible, non-parametric machine learning method well-suited for regression tasks. In the context of modeling aerodynamic propellers, GPR significantly reduces the amount of computationally expensive training data needed compared to simpler interpolation or curve-fitting approaches for the same level of accuracy. This work explores several strategies for building a surrogate model of an isolated propeller for the Joby Aviation tilt-propeller electric vertical take-off and landing (eVTOL) aircraft. To better capture sharp local variations in output quantities of interest and accommodate unevenly spaced training data, a novel delta-layer GPR approach is introduced. This method builds on the traditional single-layer GPR method by fitting to the error between the training data and the first layer fit. In parallel, a multi-fidelity GPR model is developed, using lower-fidelity data to achieve better prediction of the underlying mean function while incorporating high-fidelity CFD data for precision. This approach is further extended by integrating a third source of high-fidelity wind tunnel data, resulting in a smooth and accurate surrogate model across the entire flight envelope.
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.
Active vibration damping by rotor torque modulation has been demonstrated for vibratory modes in the rotor disk plane. In this study, we introduce a simple, first-principles model, which includes kinematic coupling between lag movement and blade pitch, in order to extend damping authority to strut vibratory modes normal to the rotor disk plane. Using a medium-sized (12kg) quadcopter drone model, we demonstrate the capability to excite strut vibrations normal to the rotor disk plane, indicating control authority for vibration damping. For this vehicle model, a steady state strut deflection of over 12% is obtained using a 15% voltage perturbation, with under 2% rotor speed change. Redesign of the vehicle to have lower and/or co-located lag and structural frequencies increases the control authority of rotor torque actuation with pitch-lag coupling.
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.
This paper outlines observations from an FAA-sponsored research project that examined aviation Fly-By-Wire (FBW) accidents. The goal was to identify risk areas that will help guide a focus for FAA certification testing. Part of this study specifically focused on current powered-lift tiltrotors, identifying six general categories of causal factors for accidents, which will be discussed in detail regarding how they influenced flight control designs. The results of this survey, along with extrapolation to current designs, will be discussed and will illustrate why manufacturers are moving toward state-based flight control designs. In a state-based flight control scheme, the pilot does not have direct control over aircraft attitudes and motor tilt angles. Instead, the pilot requests a speed and or flight path with inceptor input, and the commanded attitudes and motor tilts are scheduled by the flight control computer. Additionally, recent lessons learned from electric Vertical Takeoff and Landing (eVTOL) aircraft accidents will be discussed, along with a comparison of powered-lift causal factors to accidents in the transport category FBW fixed-wing aircraft. From this analysis, broad observations will be offered about the trend of how accident-causal factors may evolve with greater maturity in aircraft design. This accident survey will be detailed further as part of an upcoming FAA Research Report.
In 2023, Joby Aviation conducted a test of a prototype propeller for an electric vertical takeoff and landing (eVTOL) tilt-propeller aircraft in the 40- by 80-Foot Wind Tunnel at the National Full-Scale Aerodynamics Complex (NFAC). The propeller differed from rotors found on typical helicopters and tiltrotors in having rigid blades and no cyclic pitch variation, and from airplane propellers in operating in an edgewise flow environment. This wind tunnel test was intended to study the behavior of the propeller in the transition regime experienced during conversion from thrust-borne, through semi-thrust-borne, to wing-borne flight and back. There were three objectives of the test: measuring 1) propeller performance, 2) dynamic blade loads, particularly in resonance, and 3) aeroacoustics. The propeller was instrumented with rotating-frame blade load sensors and mounted to a fixed-frame balance. Testing was performed at a range of wind speed, propeller angle of attack, propeller speed, and collective blade pitch points. Sample results are provided in the paper, including a look at the high propeller pitch and roll moments in edgewise flight, a demonstration of blade resonance due to variable RPM operation, and a comparison of overall sound pressure levels showing expected increases in noise with high propeller angles of attack and high tip speeds. This paper is part of a trio, with companion papers cited in the text presenting detailed analysis of measurements and comparisons to analytical predictions of performance, loads, and aeroacoustics.
This paper presents a novel approach for bearing spall detection and Remaining Useful Life (RUL) prediction in electric vertical takeoff and landing (eVTOL) aircraft. By leveraging vibration-based signals and an operational binning methodology, a robust Health Index (HI) is developed using angular resampling-based order analysis. This HI accounts for varying operational conditions, providing a reliable indicator of bearing degradation. A piecewise Bayesian degradation model is then applied to predict RUL, facilitating effective predictive maintenance and enhancing eVTOL operations.
This paper describes the dynamic modeling and flight control software development efforts for a subscale tiltrotor electric vertical takeoff and landing (eVTOL) aircraft built at NASA Langley Research Center. The vehicle, referred to as the Research Aircraft for eVTOL Enabling techNologies (RAVEN) SubscaleWind-Tunnel and Flight Test (SWFT) model, serves as a flight dynamics and controls research testbed to foster advances in eVTOL aircraft technology. After fabricating the vehicle, wind-tunnel testing was conducted to identify a high-fidelity aero-propulsive model for use in a flight dynamics simulation enabling flight control system development. The RAVEN-SWFT aircraft subsequently underwent flight-test risk reduction steps and then free flight testing employing custom research flight control software. The flight control software, which can be efficiently updated and tested on the vehicle, includes a robust model-based control algorithm and an extensive programmed test input injection capability. The progress of RAVEN-SWFT research activities will be summarized alongside the associated modeling and flight control software development aspects, including the flight dynamics simulation, flight control system architecture, vehicle integration, and testing approaches.
The performance and acoustics of a scaled propeller designed for an eVTOL vehicle were investigated in axial and edgewise flight. The measured performance compared well with BEMT predictions in axial flight conditions. The noise produced by the propeller is dominated by broadband noise sources, where there is evidence of contributions from blade wake interaction noise, turbulent boundary layer trailing edge noise, and laminar boundary layer vortex shedding noise. The directivity of the noise was found to be dependent on the advance ratio. Beamform maps also identified changes in the dominant noise source at different observer locations as a function of advance ratio.
This paper describes the design, development, and testing of a full-scale eVTOL propulsor optimized for quiet and efficient operation. To design the propulsor, a design tool was developed for predicting the aerodynamic and acoustic performance of eVTOL propellers and rotors. The design tool consists of an aerodynamic prediction code, AMP (Aerodynamic Modeling of Propulsor), and an acoustics prediction code, OpenCOPTER, coupled with an acoustics propogator, PSU-WOPWOP, which can receive inputs from either an acoustic solver or high-fidelity CFD. The tool was used to design a coaxial eVTOL propulsor, and both subscale and full-scale blades were manufactured. The aerodynamic and acoustic performance of the subscale propulsor was tested in hover and edgewise flight in an anechoic wind tunnel. A custom test stand was developed and used to measure the aerodynamic and acoustic performance of the 8-ft diameter full-scale propeller in hover. The experimental results were used to validate the design tool.
This paper presents insights into a comparative approach to down-select on the most suitable pilot control schemes for eVTOL and powered-lift aircraft. The investigation examines three main areas: (1) experimental flight test performance, (2) flight control analysis, and (3) Human-Machine Interface (HMI) factors. Experiments were conducted to evaluate how various inceptor control schemes were perceived by people of various experience levels, ranging from manned aviation pilots with experience in flying F-16 jets, AH-64D helicopters and high-performance turboprop trainers, to unmanned aviation pilots of various backgrounds, such as with remote control (RC) rotorcraft and RC fixed-wing aircraft, and finally to participants with zero experience with either of these. In this experimental surveying study, all participants were briefed on a standardized mission profile and tasked to fly a VTOL drone and a computer based flight simulator using various flight control schemes. Videos were recorded for each test and reviewed for in-depth flight performance and controls scoring and analysis. At the end, feedback on key Human Machine Interface (HMI) factors for each flight control method is obtained. These results in totality provided insights, strengths and weaknesses for each flight control scheme. Upon identification of the most optimal control methodology, a novel energy-based control method to unify both multirotor drone and fixed wing aircraft control logics was developed, future testing will involve incorporating the 3+1 control inceptor scheme with the energy-based control method for further testing and optimization in a simulation environment. The goal of this study is providing a design framework to help eVTOL and powered-lift aircraft designers optimize their pilot control methodology; to become more instinctive, easier to operate, safer and more cost-effective to train new eVTOL and powered-lift pilots and operators.
This paper presents handling qualities (HQs) research findings for electrical Vertical Take-off and Landing vehicles. Testing in the Vertical Motion Simulator (VMS) investigated handling qualities of vehicle configurations having a degraded powertrain. Powertrain components, including batteries and electric motors, can degrade as the vehicle is flown. This paper investigates the impact of low battery charge and high motor temperature degradations on the pilot's ability to execute precise maneuvers. Pilot comments and ratings that were collected from four rotorcraft test pilots in VMS testing are used to quantify the effects that powertrain degradations had on the HQs of the vehicle.
This paper describes an ongoing aircraft system identification effort for an industry prototype electric vertical takeoff and landing (eVTOL) vehicle. Building on previous eVTOL aircraft system identification developments in windtunnel testing and flight simulations, an approach to modeling from flight-test data is formulated for the AIBOT 500 aircraft. The full system identification process is presented, including the experiment design, flight data collection, and model identification steps. Orthogonal phase-optimized multisine programmed test inputs are integrated into the flight control system and are applied to each control surface and propulsor simultaneously to efficiently collect informative flight data for model identification. Initial modeling results are given in hover, where an aero-propulsive model is identified using the equation-error method in the frequency domain. The presented results demonstrate the utility of the modeling approach and are compared to FLIGHTLAB® predictions executed using a dynamic wake model made prior to conducting flight testing. Practical techniques and recommended improvements are discussed to inform future flight-test system identification efforts for eVTOL aircraft.
This study experimentally explores the behavior of an isolated propeller of an electric vertical takeoff and landing (eVTOL) aircraft, a next-generation type of vehicle that combines the operational capabilities of both helicopters and airplanes, in vortex ring state (VRS). VRS is a hazardous aerodynamic phenomenon that occurs when a propeller in vertical descent interacts with its own wake, forming a vortex ring around the propeller disk. Depending on the inflow and operating conditions of the propeller, VRS can lead to a significant loss of thrust, making it a critical flight condition for helicopters, tiltrotors, and eVTOL aircraft. Despite its importance, VRS has not yet been extensively studied in the context of eVTOL systems. This research study, carried out under the collaboration between Archer Aviation and the Department of Aerospace Science and Technology of Politecnico di Milano, focuses on characterizing the performance of a propeller of an eVTOL vehicle during vertical descent and analysing the flow field around the propeller blades in VRS. Experimental tests were conducted at the "S. De Ponte" wind tunnel of Politecnico di Milano using a 1:4 scaled model of one of the tilting propellers of Archer Aviation eVTOL Maker vehicle.
This paper presents the development and implementation of a complete flight control architecture for a 200kg-class tilt-wing eVTOL aircraft, designed and tested by Dufour Aerospace. The system enables fully automated flight across all regimes, including hover, transition, and cruise. A modular control architecture is described, incorporating a unified vehicle controller, envelope protection, and a guidance system. The control design leverages classical and modern techniques, including model-based synthesis, control allocation, and gain scheduling. A structured software development and validation pipeline is outlined, combining simulation, software- and hardware- in-the-loop testing, and flight testing on both subscale and full-scale platforms. Results from recent autonomous flight trials of the Aero2 aircraft demonstrate precise trajectory tracking and robust performance. The presented approach highlights the feasibility of rapid development cycles while maintaining high standards of safety and reliability for certifiable eVTOL platforms.
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.
Researchers at the National Aeronautics and Space Administration (NASA) have conducted a series of module-level tests on electric Vertical Take-off and Landing (eVTOL) Energy Storage Systems (ESS) for the generation of dynamic impact data to support standards developments. The tests were conducted on zero-state-of-charge Electric Power Systems (EPS) Electric Propulsion Ion Core (EPIC) modules at the National Institute for Aviation Research (NIAR), utilizing the NIAR outdoor drop test setup and personnel. Four total tests were conducted. For each test, the module was dropped at a specific orientation from a height of 50 feet while connected to a guided trolley in order to assess the effects of a 50-foot drop test on the ESS. The test velocities ranged between 46.9 and 52.8 ft/s with impact angles ranging between a flat, zero-degree impact and 18 degrees. Data were recorded in the form of temperatures, cell-level voltage, module level acceleration and digital image correlation from the tests. Accelerations were in the range of 1,500 g for a few millisecond duration, which were indicative of a shock type loading condition. No modules entered thermal runaway, and post-test inspections revealed a variety of internal deformations and damage present in the various modules tested, with specific damage occurring for specific orientations. The modules were ranked according to a custom developed scoring rubric developed by utilizing the test and post-test inspection results. The results were compiled, reported, and will be used to guide future ESS testing. Part 1 discusses the loading environments in the modules, while Part 2 will discuss the deformation and damage in the modules.
Large eddy simulations (LES) of the Joby Aviation S4 propeller at the NFAC tunnel are performed with a GPUaccelerated low-Mach (Helmholtz) solver, and compared with experimental data provided by Joby at two flow conditions of hover and pure edgewise flow of 10 m/s. Accurate prediction of the laminar-turbulent transition was seen to be critical to the prediction of the noise sources for hover condition, with additional prominent noise sources found to be near the trailing edge and tip of the propeller. The dominant edgewise noise sources were seen to be from the dynamic outboard flow separation and reattachment from advancing to retreating side of the blade azimuth as well as the convective amplification of the acoustic waves from the 10 m/s flow. The far-field noise at the target set of microphone locations are predicted using the frequency-domain Ffowcs Williams-Hawking (FW-H) formulation. The A-weighted 1/3rd octave band results showed a good prediction of the noise compared with the experiments.
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 advent of electric propulsion technology has led to a paradigm shift in aircraft design over the past few decades. This shift has expanded the possibilities for design and optimization processes more than at any previous time. To support these advancements, efficient flight dynamics simulation models that can be employed in iterative optimization and design processes are essential. Among the modules of a typical flight dynamics framework—namely, control, flight dynamics, and aerodynamics—the aerodynamics module, which includes the rotor performance model, generally demands the most computational effort, thereby limiting simulation efficiency. In this study, a novel machine learning (ML)-assisted flight dynamics framework is developed, incorporating a Neural Network Blade Element Theory (NN-BET) model as the rotor performance module. The results show a 7- to 8-fold reduction in computational time compared to fast, physics-based frameworks utilizing efficient Blade Element Momentum Theory (BEMT) models, without compromising predictive accuracy. Furthermore, the modular architecture of the framework allows for easy adaptation to a wide range of practical applications by replacing modules with functionally equivalent alternatives. The demonstrated accuracy and computational efficiency of the proposed flight dynamics framework make it a highly promising candidate for optimization and design applications.
In 2023, Joby Aviation conducted a test of a prototype propeller for an electric vertical takeoff and landing (eVTOL) tilt-propeller aircraft in the 40- by 80-Foot Wind Tunnel at the National Full-Scale Aerodynamics Complex (NFAC). There were three objectives of the test: measuring 1) propeller performance, 2) dynamic blade loads, particularly in resonance, and 3) aeroacoustics. This paper is part of a trio and is focused on performance and blade loads measurements and validation; two companion papers cited in the text present an overview of the test and provide details on aeroacoustics analysis, respectively. Test measurements are compared to predictions generated by a CFD-trained model called AeroRef, the comprehensive analysis code RCAS with a finite state dynamic wake model, the Helios ROAM mid-fidelity blade loads solver coupled to RCAS, and OVERFLOW CFD coupled to RCAS. For performance, the AeroRef model and CFD were able to accurately predict thrust and rolling and pitching moments. RCAS was able to accurately predict structural dynamic modes and resonance crossings, but test measurements showed stronger modal responses than the dynamic inflow model was able to excite. Coupling RCAS with OVERFLOW resulted in excellent predictions of dynamic blade loads but at high computational cost; ROAM-RCAS coupling provided conservative predictions with a more efficient solver, demonstrating itself as a good option for eVTOL design studies.
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.
This paper demonstrates methods of aircraft sizing, flight dynamics modeling, and performance analysis using a lift+cruise concept vehicle with an electric powertrain and variable-speed rotors. The central focus is the development of methods to relate the aircraft design sizing constraints to achievable maneuverability and predicted handling qualities. A toolchain is demonstrated that performs aircraft sizing, mass moment of inertia estimation, powertrain modeling, trim optimization, dynamics linearization, handling qualities prediction, and quantification of achievable maneuverability under both nominal conditions and control effector failures. A convex optimization problem framework is introduced to compute agility bound estimates without requiring control system design or control allocation, potentially supporting rapid design iteration as well as early detection of deficiencies and undesirable operating conditions. This analysis is supplemented with more conventional methods of analysis to provide additional perspective and observations. Overall, the results suggest that each modeling and analysis element in the demonstrated toolchain adds significant value, with the combined approach supporting a more efficient and comprehensive exploration of trade-offs within the design space.
To document noise characteristics and provide validation data for acoustic modeling of rotor systems appropriate for eVTOL/UAM aircraft, the authors performed an outdoor static test of a subscale 5-blade proprotor. The testing was carried out as part of a program to demonstrate feasibility and overall performance of a quiet proprotor system in support of the eVTOL industry. The authors designed a low-tip speed proprotor to approximate performance required by a 4-5 passenger UAM vehicle. A driving design feature was low-tip speed operation (Mtip ˜0.27) at system disk loadings of 7 to 8 psf (˜3.7 N/m2). The test article was designed as a ground adjustable pitch 5-blade proprotor, with aerodynamic and acoustic data collected in outdoor static hover testing. The test article diameter of 3 feet (0.91 m) represented a scale factor of approximately 30% to 40% compared to vehicles currently in operation or development. The aerodynamic performance in hover was consistent with other rotor systems tested in the past by the authors (Figure of Merit ˜0.72-0.75), and the effects of naturally occurring turbulence on rotor acoustics were measured using a 180-deg arc array of ground plane microphones at the Virginia Tech Drone Park test facility. The paper closes with a prop diameter scaling investigation using lattice-Boltzmann method CAA with and without atmospheric turbulence.
This paper identifies key considerations necessary to perform a fire risk assessment for electric vertical takeoff and landing (eVTOL) operations at heliports. Fire and life safety goals, objectives, and performance (i.e., acceptance) criteria are postulated for heliport structures designed to accommodate vertical takeoff and landing of eVTOL aircraft. Quantitative techniques used to assess performance criteria, such as design fire development and fire modeling, are discussed for localized and large-scale fire events. Select heliport design elements that support fire and life safety are identified. The paper concludes with recommendations for future fire safety research efforts related to eVTOL operations at heliports.
eVTOL aircraft are a stable part of nowadays rotorcraft industry, gathering attention and investments throughout all geographies. The challenge of designing such a vehicle is the necessity to combine transformative flight and distributed lifting systems. This paper presents a methodology developed within Leonardo Helicopters Division (LHD) to perform the preliminary design of eVTOLs, following an approach that starts from hovering flight, investigating the design permutations able to satisfy certain criteria of performance, maneuverability, and safety.
The transition phase of eVTOL aircraft poses a challenge in balancing energy efficiency and stability. This study presents the development and evaluation of an automatic flight control system for eVTOL transition phases, focusing on minimizing energy consumption while ensuring robust performance. The control architecture implements a hybrid response type combining Translational Rate Command below 5 knots and Acceleration Command Speed Hold above 5 knots, with control allocation dynamically adjusted based on airspeed and rotor shaft angle. Stability analysis reveals surge mode instability at high shaft angles due to negative speed stability derivatives, stabilized through carefully tuned feedback control. The system demonstrates Level 1 handling qualities against bandwidth, quickness, and disturbance rejection criteria when evaluated against MIL-DTL-32742 and MIL-STD-1797B standards. Simulation results verify the control system's ability to maintain precise acceleration/deceleration rates and attitude control while ensuring passenger comfort through limited pitch excursions. The control strategy achieves minimum energy transitions by locking rotor shaft angles to optimal schedules while avoiding excessive hub moments. Flight test maneuvers developed specifically for conversion phases confirm the system's capability to execute efficient transitions within defined performance boundaries. This research establishes a framework for certifiable eVTOL flight control systems that balance energy efficiency with robust performance across diverse flight regimes.
Developing and operating an advanced air mobility service is challenging in many ways. The technical complexity of the task, the lack of available supporting infrastructure, the regulatory environment, and the necessity of collaboration among all stakeholders are barriers to a wide-spread implementation. Digital tools are now available to the whole industry to tackle those challenges, one of them being the virtual twin experience technology. The virtual twin experience is generated by the digital twin technology applied to a certain domain of application. It is a system of systems designed to provide users with a unique and immersive experience of reality, without physically being present in the real-world environment. It offers capabilities that go beyond traditional means, enabling organizations and users to achieve tasks and insights that were previously not possible. This paper describes how the virtual twin experience is adopted within the advanced air mobility ecosystem, that is comprised of the aircraft manufacturer, the vertiport provider and the operator. It reviews the different business processes on electric vertical take-off and landing (eVTOL) vehicle design and manufacturing, vertiport design, and operations, and highlights the associated benefits of such approach. Through these processes, we will see how the virtual twin experiences shape the future of product design, manufacturing, and operations. It changes the way in which stakeholders collaborate in a complex system of systems context. The paper concludes on the ways that the virtual twin experience provides organizations enhanced visualization and understanding, expanded trade-space exploration, and improved decision-making, and how it enables innovators and enterprises alike with greater visibility, efficiency, flexibility, and compliance.
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