Browse Topic: Vertical take-off and landing (VTOL)
This paper presents the design, implementation, and validation of an aerial-launch FPV (First-Person View) drone system that was developed to provide a complex environment with flexible deployment and precise delivery capabilities. The integrated system is composed of a hybrid VTOL carrier aircraft, a number of FPV drones, and an aerial mounting / release equipment. Using the AYK-250 platform, the carrier has a vertical take-off and landing function and long-time endurance. In terms of the FPV drones, it is built upon the high performance MARK4 5-inch frame that has high agility and high payload. The release module uses a single-hook point structure with a limit stop. The FPV drones are released stably, and the separation is reliable in flight. Comprehensive flight tests proved all workflows completely, involving carrier take-off, cruise with drones mounted, sequential aerial launch, and subsequent autonomous attitude recovery and route tracking by the FPV drones. The test results confirm the system’s capability for reliable launch from an aerial platform coupled with precise guidance, establishing a credible technical solution for expanding the practical applications of FPV drones in distributed tasks. Results show that our system can be launched via an aerial platform with an accurate guide and is a viable technological solution to spread FPF Drones for operational strategies in a more distributed way.
With the rapid development of China’s logistics and transportation industry, how to reasonably and efficiently use drones to carry out logistics and distribution business under the background of UAM has become a focus of attention for social enterprises. It is urgent to propose a feasible logistics drone take-off and landing sites layout planning method based on reality. The article first explains the principles and connotations of the layout of logistics unmanned aerial vehicle take-off and landing sites, dividing logistics distribution scenarios into three sub scenarios: urban end of pipe distribution, medical material distribution, and short distance logistics transportation. Then, based on strong constraint conditions, preliminary site selection is carried out for each sub scenario. The HRW-Kmedoids algorithm is used to optimize the site selection points for each sub scenario, and the final site selection and alternative points are obtained. The Huangpu District of Guangzhou is taken as a case study for field application. The results show that compared with the traditional method, this method can effectively avoid the actual undeployable area, and it is helpful to reasonably plan the location of the vertical take-off and landing field according to the actual demand, so as to provide some reference for the future vertical take-off and landing field layout.
To examine the unsteady aerodynamic environment surrounding vertiports, this research performs high-fidelity Large-Eddy Simulations of two full-scale square cylinders with aspect ratios of 2 and 1, representing prospective urban and vertiport configurations. To ensure realistic conditions, a volumetric momentum-source term is utilized to generate atmospheric turbulence internally within the computational domain. Numerical results reveal severely disturbed flows, with total turbulence intensities reaching a peak of 38% near the first vertiport structure. While the downstream vertiport benefited from a 40% reduction in maximum turbulence intensity due to the sheltering effect of the upstream building wake, the flow in its vicinity still maintains a powerful content. To evaluate operational safety conditions, multiple flight trajectories were analyzed approaching two distinct end-points located 4m and 11m above the center of each vertiport model from three directions: aligned with the wind, against the wind, and sidewise. Based on the evaluation of transient velocity components across these trajectories, and following the Federal Aviation Administration compliant 8:1 approach slopes, this study proposes a robust operational strategy centered on lateral approaches followed by vertical descents from higher altitudes. This maneuver sequence is designed to avoid the severe and sudden gust-induced disturbances prevalent in the immediate vicinity of the vertiport.
This paper develops an engineering concept and research framework showing how Cherokee MC2 (Mobile Command Center) and MVP (Mobile Vertipad Platform) can individually, and then as a combined system, resolve key operational and infrastructure challenges facing rotorcraft, eVTOL, VTOL, and UAS missions across civil, commercial, and military contexts. The investigation synthesizes current vertiport / vertipad design guidance, UAM and UTM operational architectures, and recent research on rotor downwash and degraded visual environment hazards to derive a deployable "vertiport node" architecture for austere and time-critical operations. MC2 is treated as the digital and procedural core enabling command, control, communications, data fusion, and manned–unmanned teaming, while MVP is treated as the physical landing interface enabling rapid, load-bearing, illuminated vertical-lift operations without fixed infrastructure. The primary contribution is a traceable topic-to-capability mapping supported by standards and research, plus a modeling, simulation, and optimization workflow to validate safety zones, capacity, scheduling, and resilience. Conclusions identify practical deployment pathways and research gaps for certification-aligned operations.
This paper presents the development, optimization, and flight test validation of a Trajectory Control System (TCS)-based flight control system for a tiltwing unmanned aerial vehicle. The TCS is a configuration-independent middle-loop longitudinal controller for vertical takeoff and landing aircraft and is integrated here with explicit model following inner-loop controllers, inverse propulsor models, and a tiltwing-specific control allocation scheme. The resulting flight control system provides coordinated control across vertical flight mode, hybrid flight mode, transition flight mode, and forward flight mode while relying on a concise feedback set and requiring only airspeed from the air data system. The control laws are obtained using a formal constrained optimization framework and transferred directly from simulation to flight without additional on-site retuning. Flight test results from piloted, semi-autonomous, and fully autonomous operations demonstrate stable and predictable behavior throughout the flight envelope, including tight hover performance, simultaneous climb rate and speed tracking in hybrid flight, and successful departure and arrival transitions at multiple speeds. Selected simulation-versus-flight comparisons further show that the nonlinear model captures the dominant trends in the measured response while also identifying specific aerodynamic and transition regime effects that warrant further refinement. Overall, the results demonstrate that the TCS + EMF architecture provides a practical and effective control solution for tiltwing VTOL aircraft.
The effects of hover operations near a partial boundary structure were assessed for a free-flying quadrotor platform under both wind-off and wind-on conditions. The partial boundary structure was selected to replicate a building facade or urban vertiport environment, providing a realistic operational context for these free-flight tests. Test points were chosen to investigate operations near the partial boundary wall and edge, and across a range of partial ground effect conditions to capture the progressive onset of ground effect characteristics. Regions of degraded vehicle performance, quantified primarily by rotor thrust coefficient (CT ) and power requirements, emerged near the partial boundary edge. These performance trends were attributed to localized changes in rotor inflow profile, characterized by near-field rotor pressure measurements. Partial ground effect was found to not resemble full ground effect until much of the vehicle had traversed over the partial boundary, with the vehicle airframe and fuselage serving as the primary factor driving the onset and development of ground effect characteristics. Under wind-on conditions, the interaction between the wind freestream and the partial boundary structure significantly shaped vehicle performance and handling qualities. The most adverse handling qualities coincided with regions of peak flow vorticity, highly unsteady flow, and large velocity gradients at the shear layer above the partial boundary.
The United Kingdom's convertible rotorcraft studies of the 1960s and early 1970s represent a systematic effort to combine vertical take-off and landing capability of helicopters with the speed and efficiency of fixed-wing transport aircraft. Conducted primarily by Westland Helicopters under the Short Range Transport (SRT) programme, these investigations explored both tiltrotor and tiltwing configurations for civil and military applications. Early work focused on the WE-01 tiltrotor, conceived as a research and demonstrator aircraft to investigate transition aerodynamics, control integration, and rotor–wing interactions, and subsequently scaled to the larger WE-02, intended for intercity and tactical transport missions. In parallel, Westland pursued the more ambitious WG.22 tiltwing, a 100-seat intercity VTOL transport incorporating high-incidence stall wing technology, large prop-rotors, and mechanically scheduled flight controls to ensure benign handling through transition. Although none of these aircraft were built, the studies addressed aerodynamics, structures, propulsion, flight controls, noise, and socio-economic viability with exceptional depth. Shaping the future through the past, this paper revisits Westland's early involvement in tiltrotor and tiltwing research, with the aim of assessing the technical maturity of these configurations and evaluating their lasting relevance to contemporary vertical lift aircraft design.
This study develops an efficient framework coupling the Lattice Boltzmann Method with the Actuator Line Method to evaluate the unsteady downwash/outwash of eVTOL aircraft. By incorporating a modified Prandtl loss function with geometric smearing correction, the framework accurately predicts velocity profiles and preserves unsteady vortices at lower computational costs than conventional RANS-based simulations. Analyzing three distinct eVTOL configurations sized for identical payload missions reveals that higher disk loading and multi-rotor interactions generate highly asymmetric, localized jet-like outwash structures, contrasting with the symmetric ground-level footprint of single rotor designs. Utilizing a 95th percentile velocity metric, transient peak hazards breach the regulated vertiport Safety Area boundary, extending up to 1.65 times the prescribed baseline limit. These findings demonstrate that time-averaged metrics underestimate physical hazards, highlighting the necessity for future guidelines to mandate configuration specific evaluations utilizing high-resolution unsteady flow data and robust statistical processing.
In November 2024, Blue Ridge Research and Consulting and Archer Aviation performed acoustic flight tests of the pre-production version of Midnight, Archer Aviation’s full-scale, multirotor electric vertical takeoff and landing (eVTOL) aircraft. The flight tests included concurrent community noise and cabin noise measurements of Midnight across a range of flight conditions. This paper describes the flight test design, measurement instrumentation, and empirical analysis methods used to assess steadiness and repeatability, develop acoustic hemispheres, and identify aeroacoustic sources on Midnight. The acoustic measurements reveal that tonal noise from the propellers is dominant during hover, broadband noise from the propellers and airframe is dominant during cruise, and both tonal and broadband noise components are important during transition. The geometric arrangement of Midnight's propellers influences the acoustic directivity. Source separation using the Vold-Kalman filter reveals that the rear propellers produce higher tonal sound levels than the forward propellers, but broadband noise is the dominant contributor to the overall sound level in forward flight. The paper concludes with lessons learned and recommendations for future acoustic flight tests.
This paper presents several methods for measuring large flow fields in the wake of a helicopter, including wind vanes ("flags"), tufts, BOS (Background Oriented Schlieren), and BOS-velocimetry. The motivation is to develop methods that can map the outwash distribution of VTOL aircraft with strongly asymmetric wakes and identify jets that can be particularly dangerous for bystanders. Each measurement technique is shown to have specific advantages, and the resulting flow fields are demonstrated for the BO105 helicopter in hovering flight in ground effect above a tarmac.
Electric Vertical Take-Off and Landing (eVTOL) vehicles are emerging as solutions for urban air mobility, but their operation can encounter hazardous aerodynamic conditions such as the Vortex Ring State (VRS), which causes thrust loss and intense vibrations. This study investigates VRS for the Archer Maker tilter propeller by combining numerical simulations using the mid-fidelity solver DUST and the high-fidelity solver OVERFLOW with prior experimental observations. Propeller performance is evaluated through thrust and torque evolution under various descent conditions, while flow fields in the propeller wake at different descent ratios around VRS conditions are evaluated and compared via 2D visualizations. A comparison of results reveals that both numerical approaches are capable of evaluating the performance degradation in correlation with vortex ring formation within specific descent regimes, showing slight discrepancies particularly regarding the descent ratio regime where VRS occurs. A flow field comparison with experimental data validates the multi-fidelity numerical approach, showing the capabilities of both numerical approaches to capture the flow physics mechanisms that lead to the generation of the vortex ring around the propeller disk.
Rainwater accumulation and management are critical to the safety and reliability of drones and emerging eVTOL aircraft. Current industry practice relies on physical rain testing, such as RTCA DO-160, which defines rainfall conditions for environmental qualification but is costly and difficult to apply during early design stages. This work presents a virtual rainwater assessment framework using Smoothed Particle Hydrodynamics (SPH) simulation in PreonLab. Using an early-stage APELEON cargo drone as a reference case, the method predicts rain impingement, surface runoff, pooling, and ingress under representative rainfall conditions. The meshless SPH approach enables direct simulation of complex geometries and transient interactions without mesh generation, while also supporting rotating components and arbitrary orientations. Results identify key mechanisms governing water transport, including geometry-driven runoff, hinge-related ingress, and droplet deflection from nearby structures. While the total water accumulated on the aircraft can reach on the order of several hundred grams, the amount entering the cargo space remain small. Localized moisture exposure highlights potential durability risks. The framework enables early design evaluation, parametric studies, and rapid assessment of mitigation strategies, supporting simulation-driven development and certification preparation for advanced air mobility systems.
Urban air mobility with electric Vertical Take-Off and Landing (eVTOL) aircraft faces critical micro-weather and infrastructure readiness challenges. This paper proposes a novel socio-technical solution: a tokenized gamification platform that crowdsources hyper-local wind and weather data to enhance operational resilience. We outline the safety gap left by traditional aviation weather systems (METAR, AWOS, ASOS) in urban environments, and leverage community engagement to fill it. The proposed system integrates with Unmanned Traffic Management (UTM) and Safety Management Systems (SMS) to validate user-contributed micro-weather observations, incentivize accurate reporting through tokens and skill-level progression, and feed data into AI-driven forecasts. Early proof-of-concept results indicate improved wind hazard detection and robust user participation. By aligning with emerging regulations (FAA, EASA, DGCA) and test frameworks, this crowdsourced micro-weather ecosystem shows potential to uplift eVTOL safety, build public trust, and support city-scale planning for advanced air mobility.
This paper presents the design, development, and successful demonstration of the first-ever ballistically tube-launched tailsitter unmanned aerial system. The vehicle expands upon the capabilities of existing tube-launched systems by simultaneously integrating the hovering capability of a rotary-wing aircraft with the efficiency and speed of a fixed-wing aircraft. To achieve this, the platform's design incorporates a novel coaxial thrust-vectoring propeller system for control in vertical flight and a unique foldable wing design for ultra-compact storage in the launch tube. The aeromechanics of the foldable wings during deployment are studied through a combination of wind tunnel experiments and flight dynamics model simulations, and the results are used to formulate a methodology for executing the ballistic launch. Simulations are also performed to characterize the robustness of the system against asynchronous deployment of the left and right wings. Experimental data, collected from flying a prototype in vertical, horizontal, and transitioning flight, demonstrate the aircraft’s flying performance. The study ultimately culminates with a demonstration of the prototype being rapidly launched from a tube at 25 m/s (56 mph) and autonomously unfolding, stabilizing, and transitioning into self-powered cruising flight.
A methodology was developed and validated to predict total noise from a 1/5th scale eVTOL rotor in hover by coupling 2D-RANS airfoil simulations with the comprehensive code, CHARM, for rotor loading, the acoustic code, PSU-WOPWOP, for tonal noise, and the broadband noise code, UCD-QuietFly, for broadband noise prediction. Improved sectional 2D aerodynamic inputs obtained from 2D-RANS simulations were used throughout the framework, replacing XFOIL-derived inputs to enhance the prediction accuracy of low Reynolds-number effects such as transition and laminar separation bubbles. Predictions were validated against measurements at Virginia Tech. Results indicate that turbulence model selection influences local boundary-layer development and sectional aerodynamic loading, producing modest differences in tonal noise at 4000 RPM (first BPF) and spectral differences of approximately 4 dB in broadband noise, while integrated OASPL shows slight sensitivity to turbulence model choice. At 2000 RPM, broadband noise dominates the total SPL, with transitional models predicting thinner boundary layers and reduced high-frequency trailing-edge noise. In addition, high-fidelity 3D-DDES simulations performed in OpenFOAM capture the mid-frequency noise content that is underpredicted by CHARM. Overall, the combined mid-fidelity broadband noise results and high-fidelity mid-frequency range noise results provide improved agreement with experimental spectra and demonstrate an effective approach for eVTOL rotor noise prediction.
Urban Air Mobility (UAM) represents a paradigm shift in metropolitan transportation, introducing electric vertical takeoff and landing (eVTOL) aircraft into dense urban ecosystems. This transformation is driven by advances in electrification, digital infrastructure, and integrated airspace management. According to the U.S. Department of Transportation's Advanced Air Mobility National Strategy 2025, UAM is expected to become a cornerstone of multimodal urban transport, with commercial operations projected in multiple U.S. cities before 2030 [1].
Fuel cell systems have achieved a significant level of technological maturity in ground-based mobility over the past two decades. In particular, commercially available fuel cell propulsion systems are now in serial production for passenger cars and city buses, and are already in regular commercial operation. In the segment of heavy-duty vehicles - such as trucks and other long-haul applications - small-series production and technology demonstrators are currently available and are on the verge of entering the mainstream market. These developments have resulted in well-proven system architectures, sophisticated balance-of-plant components, and established supply chains. In contrast, the utilization of fuel cell propulsion in aviation is still at a very early stage. At present, only a handful of individual prototypes and technology demonstrators - mostly for small aircraft - exist, while serial production remains far in the future. Particularly in the field of lightweight, small, electrical vertical take-off and landing (eVTOL) aircraft there is a unique opportunity to leverage the proven fuel cell systems developed for ground vehicles, adapt them, and further develop them to meet aviation-specific requirements. Such an approach can shorten development timelines and reduce technical risks. Transferring existing fuel cell technologies into aviation, however, is far from a straightforward process. One decisive difference lies in the required specific power density. Aircraft - especially eVTOL - demand significantly higher power densities than those delivered by current commercial fuel cell systems from the automotive sector. This requires a direct adjustment of the stack design and system architecture. Likewise, thermal management poses particular challenges. Whereas piston engines and gas turbines discharge a large portion of their waste heat via exhaust gases, fuel cells must remove all waste heat directly through their cooling systems. This requires efficient radiators capable of transferring heat from the coolant to ambient air. Larger radiator surfaces, however, increase both total aircraft mass and aerodynamic drag, making compact radiator designs essential for aviation applications.
Advanced air mobility (AAM) seeks to develop a large-scale transportation system to revolutionize how people live and work, with electric vertical take-off and landing (eVTOL) aircraft serving a central role due to reduced emissions and noise impact. An important aspect for eVTOL aircraft certification is safe urban operations, which require understanding of the response due to aerodynamic disturbances. Experimental data are required to support eVTOL aircraft development with respect to flight dynamics and controllability, as well as design specification development. While flight testing of the full-sized air vehicle will be necessary as part of the certification process, subscale testing offers many advantages with respect to cost and flexibility, in addition to examining operational conditions that one would be reluctant to test in flight at full scale such as emergency conditions. These advantages only may be seen if the underlying scaling principles of flight dynamics / control, aerodynamic interactions, and propulsion-airframe integration are understood. This paper describes initial work towards development of a general subscale testing methodology for eVTOL aircraft flight dynamics and disturbance response characteristics including limited degree of freedom (DOF) and free flight testing. An overview of the initial development work is provided, including discussion of scaling relationships, subscale air vehicle model development, and testing activities focusing on flying qualities and stability / control characteristics.
This paper introduces a novel concept for an AI-powered system designed to manage vertiport takeoffs and landings by proactively addressing the safety-critical issues of downwash and outwash. The proposed system utilizes a stream of live feedback from on-site sensors, combined with a robust predictive modeling engine, to generate optimal, aircraft-specific approach and landing trajectories in real-time. By leveraging a comprehensive database of pre-computed downwash/outwash scenarios for a multitude of UAM aircraft configurations, the AI can accurately predict the unique outwash operational footprint for each individual landing operation, based on the approaching aircraft and under the prevailing conditions. This powerful predictive capability allows the system to calculate and assign an optimal approach vector that actively minimizes risk by directing hazardous airflows away from personnel, active walkways, and other sensitive ground assets. This represents a paradigm shift from static, reactive safety measures to a proactive, intelligent, and performance-based operational model; thereby paving the way for the safe, efficient, and large-scale implementation of UAM aircraft and air taxi operations.
Newly designed eVTOL aircraft utilize propellers that operate with a large range of propeller rotation rates. Traditional nomenclature uses nondimensionalization based on the blade tip speed, and input reduction based on a similarity assumption under constant advance ratios. In this study, we explore the validity of this similarity assumption in the context of hover and descent scenarios for a variable pitch eVTOL propeller with rotation rates ranging from 54%-100% of the maximum value. In hover, the relative Reynolds number and Mach number effects are found to be relatively minor. As the axial descent ratio increases, prior to the onset of vortex ring state, the similarity assumption breaks down, and the mean thrust coefficient varies up to ±10% under different rotation rates. A similar breakdown is observed for descent conditions with higher edgewise flow. A detailed exploration shows that the effect is primarily due to relative Mach number effects, which alters the tip vortex wake interaction at the disk, and to a lesser extent changes the loading along the blade. Since the breakdown in the similarity assumption is isolated to a small region of the propeller operating envelope, a surrogate model is developed to preserve the reduced input dimensionality while accounting for the relative tip speed effects in the affected region of the envelope. This is achieved by first generating the surrogate over the full domain, assuming validity of the similarity assumption. A separate high-RPM surrogate correction layer is then built to capture the worst-case tip speed effects in the descent region of the envelope.
This paper develops and tests a feature-based autonomous landing system for vertical lift aircraft on stochastically moving ship decks, under degraded visual conditions. The system is tested with a custom-built quadrotor on a six-degree-of-freedom 1.5-ton Stewart platform reproducing stochastic motions up to Sea State typical of DDG-51-class ships. Experiments began with nominal conditions, followed by a stepwise degradation of deck features through occlusion, low illumination, water distortion, and glare. The vision algorithm tracked the platform and achieved landing across all scenarios, with tracking errors of up to 14% of the vehicle footprint, and up to 2.2° of pitch and roll. Overall, it demonstrated the ability to land in a GPS/Lidar-denied, difficult environment with on-board vision alone, achieving deterministic, repeatable results.
This work describes the flight control system architecture of the VSDDL VT-03-s Shadow, a cost-effective subscale aircraft used as a testbed for novel flight control schemes. The highlight is the Maneuver Control System comprising the Trajectory Control System, which facilitates Simplified Vehicle Operations, and the Tactical Maneuvering System, which permits more aggressive maneuvering. The control laws permit the selection of both vertical takeoff and landing and conventional takeoff and landing modes of operation. Flight test results shown include transitions between vertical and forward flight modes performed using both Trajectory Control System and Tactical Maneuvering System, limited aerobatic maneuvering performed using the Tactical Maneuvering System, and demonstration of some of the automatic flight functions and capabilities.
This study evaluates the predictive accuracy and computational efficiency of a mid-fidelity Lattice-Boltzmann Method (LBM) framework in simulating the complex aerodynamic interactions of a tilting proprotor–wing configuration. The analysis focuses on the tiltrotor conversion maneuver, investigating a range of proprotor tilt angles from forward towards edgewise and vertical flight. To resolve the interactional flow physics, the LBM framework was integrated with two distinct proprotor modeling approaches, an Actuator Line Method (ALM) and an unsteady Actuator Disk Method (ADM), and two wall model boundary conditions, the explicit power-law and Reichardt’s log-law. The computational models were compared with experimental wind tunnel measurements and high-fidelity computational fluid dynamics (CFD) simulations. The ALM significantly outperformed the ADM in capturing discrete tip vortices and wake turbulence, which were critical for resolving the complex flow fields and wing surface pressure distributions. Reichardt’s log-law wall model demonstrated greater physical accuracy over the power-law model by correctly preserving proprotor wake alignment and improving surface pressure predictions. Modifications to the wall models and co-locating both the proprotor and the wing within the finest mesh refinement level enabled the LBM to accurately capture lift coefficient trends and magnitudes across the conversion maneuver. While limitations were identified in resolving leading edge flow attachment at high tilt angles and resolution-sensitive wing drag, this study demonstrated that the LBM-ALM approach with log-law wall model is a highly effective tool for rapid and accurate aerodynamic analysis of tilting proprotor-wing systems.
This paper demonstrates the sizing and optimization of a hybrid-electric multi-tilt rotor configuration of both conventional and vertical takeoff and landing capabilities. The study uses Parametric Energy-Based Aircraft Configuration Evaluator to design and optimize the aircraft. To explore the design space comprising both discrete and continuous design variables, a genetic algorithm is used for optimization. The design variables are not limited to conventional aero-propulsive parameters such as wing loading, aspect ratio, and disk loading. Battery-related parameters such as the maximum permissible depth of discharge, maximum permissible discharge rate, and the number of parallel strings in a battery pack are also considered in this work to study their impact on aircraft gross weight and fuel consumption. The Non-dominated Sorting Genetic Algorithm-II (NSGA-II) optimization framework is used to solve the multi-objective optimization problem, with objectives to minimize the maximum take-off mass and fuel weight. The sensitivity studies showed that higher wing-loading and lower-aspect-ratio designs resulted in lower gross weight. A higher permissible depth of discharge led to lower fuel consumption, despite a slight increase in gross weight. But increasing the number of parallel strings in a battery pack increased gross weight with negligible change in fuel consumption.
Electric Vertical Take-Off and Landing (eVTOL) aircraft are poised to transform urban and regional mobility by offering zero-emission, congestion-free transportation. As regulatory frameworks evolve and advanced air mobility (AAM) gains traction, manufacturers are exploring propulsion strategies that improve range, power delivery, and overall system efficiency. A key challenge in eVTOL development is balancing range with payload capacity. While larger battery packs can extend range, they also increase system weight, reduce payload, and prolong charging times, limiting operational flexibility and turnaround time. Hydrogen fuel cells, supported by liquid hydrogen (LHâ‚‚) present a promising alternative for eVTOL propulsion. This study proposes a methodology for optimizing fuel cell propulsion systems tailored to eVTOL applications. A multi-physics modeling framework for eVTOL flight dynamics and propulsion system was developed, representing the target eVTOL configuration. For a defined flight path including vertical takeoff, hover, cruise, and landing, a Genetic Algorithm (GA) based optimization was conducted on propulsion system. The algorithm down-selected battery size, fuel cell stack specifications, and hydrogen tank capacity to meet mission requirements while minimizing propulsion system weight. The modeling framework was also used to evaluate trade-offs between payload and performance as functions of component sizing, battery chemistry and energy distribution strategy.
The outwash flow of a VTOL aircraft in near-ground operation is a serious risk for surrounding objects or personnel, and has been investigated for a long time. The current paper contributes to this topic by revisiting quantitative outwash measurement techniques and evaluation strategies suitable for full-scale flight experiments. An array of purpose-built ultrasonic anemometers, a pitot tube rake, and fiber-film sensors were applied during outwash tests with a hovering Eurocopter EC135, complemented by accompanying numerical simulations with the Vorticity Transport Model (VTM). A focus is set on an analysis of the flow unsteadiness, revealing large fluctuations at low frequencies which require careful data post-processing. The fluctuations limit the application of pitot tubes to measure the mean flow due to their angular sensitivity, and ultrasonic anemometers are recommended as a particularly suitable and convenient measurement method with a sufficient frequency response. Furthermore, the experimental and numerical results are compared to semi-empirical outwash models, and the importance of simultaneous measurements of the ambient wind conditions is demonstrated.
Electric vertical takeoff and landing (eVTOL) aircraft have rapidly emerged as a potential promising solution for sustainable and scalable urban air mobility. These vehicles are at a crucial stage of development, with sub-scale and full-scale flight test campaigns already underway. In forward flight, critical structural components of these variable RPM rotary wing aircraft can experience strong time varying aerodynamic loads. These components are lightweight, stiff, and often have very little intrinsic damping. Thus, from a life-cycle perspective, vibratory strains are of significant concern. This work investigates the use of Impact Dampers (IDs) in attenuating the bending and torsional response of a characteristic eVTOL boom. A computational reduced order model of an ID is developed using the Hunt-Crossley nonlinear contact model and linear beam finite elements. Predicted damper performance is compared with prior experimental measurements. Parametric studies are performed by varying key damper design variables, and predicted trends are shown to be consistent with experimentally observed behavior. The IDs attenuated the system structural response at resonance by 60.7% in bending and 52.1% in torsion, for a 5% mass penalty. Building on works presented at the 80th and 81st Vertical Flight Society Annual Forums, this publication is a next step towards establishing IDs as a viable multi-modal passive vibration control device in variable RPM multirotor vehicles.
This study investigates the acoustic performance of a single rotor representative of those seen on multi-passenger UAM-sized vehicles, focusing on the effects of blade count, disk loading, solidity, and tip Mach number in both hover and propeller operating conditions. Using PSU-WOPWOP and ANOPP2, unweighted and A-weighted overall sound pressure levels (OASPL) are computed in-plane for 2- and 5-bladed rotors across a range of design parameters and operating conditions. Unweighted results show that reducing blade count significantly increases total noise levels (14.1 dB on average) and reduces sensitivity to design parameters. In contrast, A-weighted results demonstrate that broadband noise dominates perceived acoustic performance and shows a decreased sensitivity to blade count (1.9 dBA average difference). Minimum noise levels occur at tip Mach numbers ranging from 0.35-0.45 for unweighted results and 0.4-0.5 for A-weighted results, and are primarily governed by broadband noise sensitivity to disk loading and solidity. The rotor in propeller mode, with axial flow and reduced disk loading, showed less sensitivity to variation in disk loading and solidity than the rotor in hover, indicating weaker acoustic dependence in cruise conditions.
The growing demand for high-performance vertical take-off and landing aircraft is driving the development of configurations capable of surpassing the speed and range limitations of conventional helicopters. Among these, tiltrotor architectures represent a promising solution for achieving high cruise efficiency. Building on decades of experience gained through major tiltrotor programs -- including Leonardo AW609 tiltrotor, and Next Generation Civil Tiltrotor -- Leonardo has recently investigated an innovative configuration known as the Advanced Tiltrotor Aircraft (ATA). This paper presents a preliminary aerodynamic assessment of a variant of the ATA concept aimed at improving overall aerodynamic efficiency. Early-stage Computational Fluid Dynamics (CFD) analyses were conducted to evaluate the configuration's aerodynamic behavior and estimate potential efficiency gains. To validate the numerical predictions, two dedicated wind-tunnel campaigns were performed on scaled models: a low-speed test at Politecnico di Milano and a high-speed campaign at Centro Italiano Ricerche Aerospaziali, covering Mach numbers up to 0.6. Experimental datasets were processed through a validated in-house toolchain including wind-tunnel corrections and Reynolds/Mach scaling to full-scale conditions. Experimental results show strong agreement with the CFD predictions and indicate a significant improvement in aerodynamic efficiency, supporting further development of the ATA concept and demonstrating the effectiveness of the combined CFD-experimental methodology for innovative tiltrotor design.
A high-fidelity computational study investigates the aerodynamic behavior, flight response, and control effectiveness of a multirotor electric Vertical Take-Off and Landing (eVTOL) configuration. The investigation is organized into two parts. Part I employs an unsteady computational fluid dynamics (CFD) framework coupled with a six-degree-of-freedom (6-DoF) rigid-body dynamics module. Simulations for isolated coaxial rotors and a complete eVTOL isolate rotor aerodynamics and rotor–airframe interactions under constrained kinematics, quantifying lift capability, fuselage download, and a residual nose-up pitching moment arising from fore-aft rotor lift imbalance. Fully coupled 6-DoF free-flight simulations capture the transient vehicle response to a motor failure and recovery sequence during hover. Part II assesses flight control response through a cascade Proportional-Derivative (PD) controller implemented in MATLAB/Simulink across two maneuver cases: hover stabilization and climb rate tracking, which are parameterized using aerodynamic data extracted from the isolated rotor CFD simulation. This decoupled approach enables systematic gain tuning and controller assessment without the computational overhead of fully coupled closed-loop CFD simulations. The results confirm that the CFD–6-DOF framework effectively resolves tightly coupled aerodynamic-dynamic interactions inherent to distributed electric propulsion configurations, and that the cascade PD architecture provides initial control authority assessment across the primary flight axes. These findings establish a foundation for trim strategy development, advanced control law design, and future integration toward robust flight control for urban air mobility operations.
The University of Maryland undergraduate team presents Draco in response to the 42nd Student design Competition RFP "Pioneering Hydrogen-Electric VTOL". Draco uses a simple, effective configuration: a single main rotor helicopter with compounded wings. Through calculations and trade studies, the team was able to design a rotorcraft capable of performing the prescribed mission with maximized loiter endurance, while meeting all design constraints and requirements.
The increasing use and development of electric vertical takeoff and landing (eVTOL) aircraft and unmanned aerial systems (UAS) for logistics and urban mobility requires acoustic assessment methods that better correlate with human perception and community acceptance than the conventional SPL-based metrics alone. This study presents field-based psychoacoustic measurements of repeated tilt-Octorotor delivery flight operations using a binaural Head and Torso Simulator (HATS). Event segments including lateral approach, takeoff, hover, departure and landing were analyzed using A-weighted SPL, loudness, tonality, fluctuation strength, sharpness, and roughness. Results show strong repeatability across runs and event-dependent signatures within the analysis. Landing produced the highest average loudness (11.65 soneHMS) and sharpness (3.06 acum), while hovering exhibited the highest peak roughness (1.12 asper) and strong tonal persistence. Lateral approach events showed high tonality and sharpness highlighting the directional cues. These findings demonstrate that psychoacoustic metrics provide an improved interpretation of perceived annoyance and support validation workflows for future eVTOL/UAS acoustic design and certification.
This study evaluates the impact of range extension on gross takeoff weight (GTOW) and energy cost for the NASA Lift+Cruise eVTOL configuration under present and near-term battery technology limitations. A baseline 8,210 lb, 6-passenger vehicle, originally designed for a 75-mile mission at 400 Wh/kg battery energy density, is shown to achieve only 15 miles at a more realistic 200 Wh/kg, largely due to the 20-minute SFAR reserve, which accounts for 64% of total onboard energy. To quantify the penalties of range extension, three sizing strategies are examined: fixed GTOW with payload trade-offs, fixed-geometry overloading, and fully co-scaled vehicle resizing. The co-scaled configurations reveal a strong nonlinear GTOW growth driven by an "adding battery to carry battery" effect, in which increases in GTOW necessitate heavier structure and propulsion, leading to a practical feasibility ceiling near 45 miles. Energy cost per payload-mile is found to be non-monotonic, reaching a minimum near 20-25 miles before increasing due to compounding weight penalties, contrary to trends predicted by fixed-weight analyses. Significant off-design penalties are also observed; operating a 40-mile aircraft on a 10-mile mission incurs a 72% energy cost increase relative to a co-scaled vehicle for 10 miles. Increasing battery energy density by 22.5% (to 245 Wh/kg) reduces the 6-passenger 40-mile design GTOW by 33% (from 13,712 lb to 9,187 lb) and shifts the optimal energy cost point outward to 30 miles. Ultimately, battery energy density is identified as the dominant parameter dictating the vehicle size, weight, performance, and the fundamental operational feasibility of UAM eVTOLs.
This paper presents the design and simulation-based evaluation of a configuration-independent Trajectory Control System (TCS) for multiple vertical takeoff and landing (VTOL) vehicles. The TCS provides a unified, middle-loop longitudinal control system applicable to lift-plus-cruise, tiltwing, and vectored-thrust configurations. Developed under the Simplified Vehicle Operations (SVO) paradigm, the TCS computes thrust-to-weight commands from normalized vertical and horizontal acceleration using inertial frame force-balance relationships and allocates the resulting trajectory requirements across the available propulsors. The governing TCS equations, propulsor-share framework, and mode structure remain common across configurations, while configuration-specific effects enter only through mode thresholds, inverse propulsor models, and control allocation. The control laws require only attitude, angular rate, fore-aft acceleration, and vertical velocity feedback. Subscale simulation comparisons across three dissimilar VTOL vehicles demonstrate closely grouped longitudinal response characteristics together with broadly comparable departure and arrival transition behavior, supporting the predicted configuration-independent formulation and its suitability for pilot-intuitive operation. These results establish a scalable longitudinal control approach for next-generation VTOL vehicles. The simulation-based findings are further supported by the broader flight test progression of the three configurations reported in prior work.
A method for evaluation of control derivatives is introduced for the purpose of rapid design evaluation of an electric, fixed-pitch multirotor aircraft during the conceptual pre-design phase. This explicit linearization methodology allows rapid co-design of the vehicle configuration and control allocation using the pseudo-inverse method. A multi-objective design analysis is conducted for a 12 rotor lift + cruise eVTOL configuration subject to hover power requirements, controllability, and tolerance to failure conditions. Generalizable design guidelines are found and presented for the cant and rotor spin direction of the lift + cruise aircraft. The benefits shown include the addition of direct lateral force control derivative, a major increase in yaw control derivative, and reconfiguration to accommodate any Two Engine Inoperative failure conditions. These are achieved through mixing anhedral and dihedral rotor cant within each quadrant of the wing, setting the spin direction so the component of thrust in the yaw axis is additive with the motor reaction torque, and having larger cant angles inboard and closer to the center of gravity. Additional analyses of stability characteristics are performed using DynaPyVTOL, a medium-fidelity flight dynamics analysis tool for any configuration.
In response to the 42nd (2025) Annual VFS Student Design Competition, the Graduate Student Design Team from the University of Maryland introduces Wyvern, a novel hydrogen-powered electric compound rotor-craft engineered for maximum loiter and operational safety. Named after a mythical dragon that defies convention by not breathing fire, Wyvern only breathes water vapor by forgoing hydrocarbon combustion in favor of the quiet and clean power of hydrogen. This design reflects not only an aeronautical solution to an engineering challenge but a greater aspiration to reshaping how practical and clean vertical flight can be achieved.
In September 2025 a test was conducted at the NASA Ames Research Center's Outdoor Aerodynamics Research Facility to characterize the outwash flow from a hovering rotor. The studied configurations included variations in rotor height above the ground plane as well as variations in rotor speed, thrust, and trim state. Outwash flow was measured using a rake of hot-film anemometers mounted to a semi-autonomous instrumentation cart. Flow measurements were conducted for a single rotor azimuth at distances between 0.6 and 4.0 diameters from the rotor center. In addition to hot-film anemometry, additional flow data was captured using a Background Oriented Schlieren Velocimetry technique that provides a detailed measurement over time of flow velocity in an image plane upstream of the hot-film sensors. The downwash and outwash produced by a lifting rotor in the presence of a ground plane can pose significant risks to life and property in the area of operations. Rotor wake interactions exhibited by modern, multi-rotor aircraft designs can amplify these flows and increase the risk. The rotorcraft community is therefore motivated to better understand rotor downwash and outwash to establish safe operating limits in the vertiport environment.
Urban Air Mobility (UAM) vertical takeoff and landing (VTOL) air taxis might exhibit flight motions that are unfamiliar to many passengers. Researchers at the NASA Armstrong Flight Research Center performed a study to identify relationships between rotational flight motion and passenger comfort and acceptance. Fifty test subjects each completed a 20-min passenger experience in a virtual air taxi simulation. Subjects evaluated flight maneuvers with varying levels of rotational motion and indicated their comfort level and willingness to take a real flight with the motion they experienced. Study factors included yaw rate, pitch rate, and roll rate. Participants evaluated four levels of each study factor. The study found linear relationships for each study factor showing a decrease in passenger comfort and acceptance with increased motion. Statistical significance of the results, the possible influence of participants’ backgrounds and experiences, and other potential sources of bias in the study population are discussed.
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