Technical Papers - SAE Mobilus
SAE Technical Papers are written and peer-reviewed by experts in the automotive, aerospace, and commercial vehicle industries and provide the latest advances in technical research and applied technical engineering information.
ABSTRACT Over time, the National Institute of Standards and Technology (NIST) has refined the 4Dimension / Real-time Control System (4D/RCS) architecture for use in Unmanned Ground Vehicles (UGVs). This architecture, when applied to a fully autonomous vehicle designed for missions in urban environments, can greatly assist in the process of saving time and lives by creating a more intelligent vehicle that acts in a safer and more efficient manner. Southwest Research Institute (SwRI®) has undertaken the Southwest Safe Transport Initiative (SSTI) aimed at investigating the development and commercialization of vehicle autonomy as well as vehicle-based telemetry systems to improve active safety systems and autonomy. This paper will discuss the implementation of the 4D/RCS architecture to the SSTI autonomous vehicle, a 2006 Ford Explorer.
This organizational process survey provides insight into the technical aspects of approved airworthy aircraft modifications applied in government organization vertical lift flight test. The publication reviews processes applied by the National Research Council of Canada's Flight Research Laboratory (NRC-FRL) and its Airworthiness Control System to enable research flight testing. Dominated by the need for integrating experimental payloads, the NRC-FRL embeds a Design and Fabrication Service organization for modification of internal and external client projects and flight test aircraft. In context of experimental flight testing, this work reviews technical information on process, facilities, and methodology for airworthy integration of flight test payloads. Information is used to synthesize recommendations in experimental vertical lift flight testing that satisfy both formal (regulated compliance) and informal (compliance intent) airworthiness requirements.
This paper shares the complete process and recommendations on how an eVTOL (electric vertical take-off and landing) aircraft is planned, conceptualized, designed, built and tested. The recommendations draw on extensive experience gained from designing multiple eVTOL aircraft and working within the rotorcraft industry. A Lift + Cruise eVTOL aircraft with a wingspan of 8-meter (26.3 ft) is used as a case study to illustrate the whole process.
Deep Reinforcement Learning (DRL) for quadrotor flight control typically relies on Domain Randomization (DR) for sim-to-real transfer, resulting in overly conservative policies that struggle with dynamic disturbances. To overcome this, we propose a novel adaptive control architecture that actively perceives and reacts to instantaneous perturbations. First, we train an optimal outer-loop policy, then replace its reliance on ground-truth disturbance data with a Residual Dynamics Predictor (RDP). The RDP estimates the external forces and moments acting on the aircraft in flight online using only the history of states and control actions. For seamless hardware transfer, we introduce a data-efficient linear calibration bridge and an online thrust correction mechanism that align the simulated latent space with reality using mere seconds of flight data. Real-world validations on a Crazyflie micro-quadrotor demonstrate that our adaptive controller significantly outperforms baselines
This paper introduces an eigenvalue-based whirl flutter prediction method accounting for aerodynamic interactions between a wing and propeller. The linearized unsteady vortex lattice method was utilized to model fixed-wing aerodynamics while the linearized viscous vortex particle method was utilized to model rotary-wing aerodynamics. The complete aerodynamics model was then coupled with computational structural models to demonstrate the capabilities of the model to predict whirl flutter using an eigenvalue-based method. Two computational structural models were used: the first being an analytical propeller model affixed to a rigid wing via root springs and dampers, and the second being the University of Michigan's Nonlinear Aeroelastic Simulation Toolbox. These models demonstrate the capabilities of the linearized aerodynamics model in predicting instability with structural models of different fidelities, both considering and not considering aerodynamic interactions. The linearized
This paper investigates the impact of aerodynamic interactions on the whirl flutter boundary of wing-twin-propeller configurations. A coupled wing-pylon-propeller model is developed in the Rotorcraft Comprehensive Analysis System (RCAS), where the wing is modeled using uniform inflow and the propeller wake is modeled using the viscous vortex particle method (VVPM). The study examines the effects of spanwise propeller placement and rotation direction by first analyzing a single-propeller configuration and subsequently extending the analysis to twin-propeller configurations. The analyses are performed for both rigid and flexible wings, with the latter designed such that whirl flutter governs the instability boundary. Results show that spanwise propeller placement strongly influences whirl flutter stability, with outboard locations exhibiting higher flutter speeds. Aerodynamic interactions between the wing and the propeller are found to be generally destabilizing, reducing the whirl
This paper presents an efficient numerical framework for prediction of broadband noise scattering through time-domain synthesis and propagation. For efficient scattering of broadband noise sources, a time-domain boundary element method is applied to propagate all frequencies together in a single computation. To obtain a time-resolved incident field without high-fidelity aerodynamic simulation, a stochastic broadband noise synthesis method is developed based on a semi-analytical airfoil broadband noise modeling approach. The framework is validated for airfoil trailing edge noise prediction, and the correspondence of the time-domain broadband noise synthesis method to existing semi-analytical broadband noise models is demonstrated. The framework is then applied to predict fuselage scattering of rotor tonal and broadband noise for a full-size urban air mobility concept vehicle. Significant differences are observed between the scattering effects in the tonal and broadband contributions.
This work presents the development of an interconnected gearbox drive system for a tandem rotor unmanned aerial vehicle (UAV) designed for a power rating of 20 kW per rotor. Development of the facility for dynamic testing of the interconnecting drive system is also presented. Tandem rotor configurations offer superior payload capacity and aerodynamic efficiency but pose challenges in transmission design due to the need for synchronized power distribution between counter-rotating rotors. The proposed gearbox employs a simple two-stage reduction system combining bevel and planetary gears to achieve compactness, high torque transmission, and ease of fabrication. A dedicated test rig is concurrently being developed to evaluate gearbox performance under variable torque and speed conditions for the first stage with the mechanical interconnection. The test set-up integrates a variable-speed drive, torque and vibration sensors, and a data acquisition system to measure efficiency, losses, and
When surveying the current landscape of Deterministic Ethernet avionics solutions in the aerospace industry, the three main technologies in the market are ARINC 664 part 7 rate-constrained Ethernet (commonly known by its trademark name "AFDX®"), TTEthernet (which combines ARINC 664 part 7 with Best-Effort Ethernet, while adding a new class of synchronous determinism defined in SAE AS6802 [Time-Triggered Ethernet]), and IEEE 802.1 Time-Sensitive Networking (TSN). No single deterministic Ethernet technology optimally satisfies certification, MOSA, and lifecycle goals across all avionics domains. Instead, successful digital backbones require intentional partitioning of responsibilities across technologies. This paper will seek to identify a number of those considerations and provide guidance on which technologies offer the best fit. After first opening with an explanation of the market forces driving the trends towards these technologies, this paper will delve into a short outline of each
This paper presents a wind tunnel investigation on the interactional aerodynamics of a slowed-rotor lift- and thrust-compounded helicopter model in high-speed forward flight. A systematic configuration study was conducted to isolate the aerodynamic contributions of the main rotor, wings, fuselage, and pusher propeller to the aft flowfield, measured using phase-resolved 2D-3C particle image velocimetry. Measurements were acquired at an advance ratio of 0.5 across multiple rotor thrust levels, lift offset trim states, and propeller rotational speeds. The fuselage induces a streamwise velocity deficit of nearly 50% of the freestream near the tail boom due to oncoming flow blockage. This deficit is modulated by the main rotor and wing configurations. The rotor slipstream partially alleviates the deficit by convecting high-speed freestream flow downwards. Lift offset in the asymmetric half-wing configuration suppresses the rotor wake influence, deepening the velocity deficit relative to a
A wind tunnel investigation to assess the impact of rotor-fuselage spacing on the development of the Vortex Ring State and flow topology is presented. Particle Image Velocimetry was utilised to investigate flow mechanisms across a range of rotor-fuselage spacings and descent ratios, which were compared to that of an isolated rotor configuration. Mean flow data was used to identify coherent flow structures, whilst flow unsteadiness was investigated through statistical analysis of the velocity fluctuations. It was found at cases of Vortex Ring State onset, the presence of the fuselage delays the development of the Vortex Ring State for all rotor-fuselage separation distances tested. Furthermore, certain cases of rotor-fuselage spacings display a rotor-fuselage aerodynamic interaction that results in an increased effective descent ratio.
OverFlight is an in-development graphical user interface (GUI) that implements a state-of-the-art rotorcraft maneuvering noise model using a source noise hemisphere approach coupled with the Aircraft NOise Prediction Program 2 (ANOPP2). This GUI stems from a demand for easy-to-use mission planning and community impact acoustic tools that can model the maneuvering flight of a rotary-wing vehicle. This paper covers the models used for the development of OverFlight and model validation efforts. Data from a joint NASA/Army flight test of an MD530F aircraft are used both for source noise hemispheres as well as maneuvering flight data. Analysis of the predicted maneuvering noise shows better agreement that traditional methods currently employed, while also demonstrating maneuvers where the underlying assumptions fail to hold.
Shrouded rotor configurations provide aerodynamic efficiency benefits that are valuable for aerial vehicles requiring high endurance in hovering flight. The effect of the shroud on the loads produced by a vehicle in response to cyclic pitch are not well known in literature. This paper aims to understand the magnitude and phasing of the steady hub loads produced by shrouded coaxial hingeless rotors in hover due to cyclic pitch. A shrouded coaxial rotor vehicle weighing 0.934 kg and with a rotor radius 0.138 m is used as the test platform. The rotors are operated at a tip Reynolds number of 70,000 and a tip Mach number of 0.18. First, the origins of steady hub loads due to cyclic pitch on a hingeless rotor are described using theory. To quantify the effect of the shroud, different configurations of rotors were tested by giving cyclic pitch to only one rotor. For the open hingeless rotor, cyclic variation in drag force at blade sections contributed to 55% of the steady lateral force. In
This work presents the development and application of a methodology for predicting fatigue life, implemented within the modern progressive failure analysis software tool CDMat, developed at the Advanced Materials and Structures Laboratory of the University of Texas at Arlington. CDMat is designed as an extension to the general-purpose finite element analysis program ABAQUS/Explicit. The set of user-defined subroutines for describing material behavior can be expanded by adding new subroutines. A recent development in CDMat is a computational model capable of predicting delamination crack growth under quasi-static and fatigue loading, based on a fracture mechanics approach using the J-integral. The J-integral is calculated by integrating stresses and displacements along a line defined by the negative gradient of displacements in the cohesive interface. Due to the large integration path, the J-integral allows for a highly accurate estimation of the energy release rate, which makes it
The rapid expansion of electric aviation and eVTOL operations introduces tightly coupled challenges related to energy‑constrained aircraft design, battery and thermal management, mission planning, and the generation of certification‑relevant evidence. This paper presents an integrated simulation workflow developed by AVL, Unisphere, and blueflite that combines high‑fidelity electric powertrain and battery models with a guidance‑level, digital‑twin‑based 4‑D trajectory simulation driven by historical weather and operational constraints. At each mission time step, the trajectory layer provides time‑resolved environmental and routing conditions, while the system‑level models compute instantaneous power demand, state‑of‑charge evolution, and thermal response, enabling mission feasibility assessment under realistic wind, temperature, and airspace effects. The workflow is calibrated and validated using flight telemetry from blueflite's active eVTOL cargo aircraft development, ensuring
The safe integration of Unmanned Aerial Vehicles (UAVs) into shared airspace necessitates robust conflict detection and avoid (DAA) methods that scale effectively with multiple dynamic intruders. Geometric methods, such as those in the DO-365 standard, are provably safe for pairwise encounters but become intractable in dense environments. Conversely, applying kinodynamic motion planners designed for static obstacles to dynamic scenarios leads to unstable behavior, characterized by excessive re-planning and oscillatory motion, as they lack a predictive model of intruder trajectories. This paper introduces a closed-loop planning framework based on the Closed-Loop Rapidly-exploring Random Tree* (CL-RRT*) algorithm to prevent Loss of Well-Clear (LoWC) in multi-intruder scenarios. Our approach integrates a closed-loop dynamics model to guarantee dynamically feasible trajectories and incorporates a spatiotemporal planning strategy. A time-to-come metric is propagated from the tree root to
The impact of ship airwake on helicopter operations to rear flight decks has been a topic of much research over the past three decades. While generic ships have been developed over the years to enable analysis tool and knowledge development, actual ships can vary significantly, resulting in different airwake features. The study of variations in ship geometry is important both to understand how differences may impact operations, but also to understand the level of geometrical fidelity that is required on ship models undergoing analysis. In Canada, the newly launched (2018) Harry DeWolf-class Arctic Offshore Patrol Ships (AOPS) have unique features that have been studied for their impact on airwake characteristics. This paper explores different geometrical characteristics from the perspective of their operational impacts and also considering their importance for inclusion in simulation. The paper shows that turbulence level is the parameter most affected by the minor variations that were
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
Hybrid bearings, which pair traditional bearing-steel raceways with ceramic rolling elements, can offer improved performance over full-metal bearings, particularly in aerospace applications. Because rolling-element bearings are critical components, effective condition monitoring is essential to prevent in-flight failures and support proactive maintenance strategies. Wear-debris monitoring is widely used in these applications to detect and diagnose bearing fault modes. To compare degradation behavior and monitoring signatures, bearing life tests were conducted on hybrid and full-metal bearings under matched Hertzian stress conditions. The results showed that differences in degradation curves between the two bearing types were small relative to the overall variability in bearing life. Additionally, hybrid bearings that develop rolling-element pitting were observed to progress toward raceway spall formation. This paper was presented at ERF Forum 51 but has been updated with new findings
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].
The aeromechanics of a full-wing lift-compounded slowed-rotor rotorcraft were investigated experimentally at the Glenn L. Martin Wind Tunnel, characterizing the effects of rotor shaft tilt, wing configuration, and advance ratio on performance, blade structural loads, and hub vibratory loads. Measurements were obtained across advance ratios up to μ=0.7, three shaft tilt angles (-4°, 0°, and 4°), and three wing configurations, including an asymmetric wing arrangement. The results were used to validate the University of Maryland Advanced Rotorcraft Code (UMARC) coupled rotor-wing analysis. Rearward shaft tilt and increased wing lift sharing improved lift-to-drag ratio, reduced blade structural loads, and decreased hub vibratory loads due to the rotor being placed in a descent state and being partially unloaded. Rearward shaft tilt alone yielded a 5% improvement in lift-to-drag ratio and a 32% reduction in steady rotor flap bending moment relative to the forward tilt configuration at an
An aspect of the ship-helicopter dynamic interface (DI) is the highly unsteady flow environment generated by ship-rotor aerodynamic interactions, which challenges safe launch and recovery operations. To investigate these interactions without the constraints of conventional rotor scaling, a novel airflow-and-blade-frequency (ABF) system was developed, decoupling rotor thrust from blade-passing frequency and enabling independent control of disk loading and periodic excitation. Mean-flow superposition and spectral analyses were used to assess the validity of linear-superposition approaches for DI modeling. While superposition reproduced portions of the interacting mean flow, it failed to capture key features such as superstructure sheltering. Spectral results showed that momentum injection and blade-passing frequency modified the interacting flow through distinct mechanisms. Across all operating conditions, the interacting flow exhibited elevated turbulent kinetic energy at pilot-relevant
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.
The present study aims to investigate the dynamic behavior of composite drive shafts operating in the supercritical rotational speed regime, with a particular focus on the mode crossing and the potential emergence of vibratory instabilities. Composite shafts offer significant advantages in terms of mass reduction and mechanical properties, making them attractive for high-performance transmission systems such as helicopter drive lines. However, their operation beyond the first critical speed raises specific challenges related to stability, damping, and sensitivity to mechanical and operational parameters. To address these issues, an experimental and analytical framework was developed to explore a wide design space involving parameters that are known or suspected to influence supercritical behavior. These parameters include unbalance levels, support characteristics, flexible coupling properties, tightening conditions of the damper, and rotational speed. Particular attention was given to
A 5.5-ft diameter dynamically-scaled hingeless rotor was tested at high advance ratios (μ) up to 1.4, representing the first aeroelastic stability characterization of a hingeless rotor at high-μ. This paper describes the wind tunnel test setup, hover and forward flight stability data, and comprehensive analysis predictions. A novel rotating frame piezoelectric actuator-based perturbation system located in-line with the pitch links is developed to excite the blade pitch. Damping is identified via the matrix pencil method, which is shown to outperform the moving block method for the highly damped flap mode. Hover data shows constant flap damping until stall onset, where a drop in damping is observed and captured by the University of Maryland Advanced Rotorcraft Code (UMARC). UMARC has been modified to solve for elastic blade stability using linearized perturbation equations in conjunction with Floquet transition matrix theory. Elastic blade modeling is shown to be required for accurate
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
A challenge in establishing rotor performance map for sizing tool during design cycle is the rotor performance uncertainty for full vehicle. Sometimes, simplified tests at different setup/scale are conducted to guide performance map, but this introduces another uncertainty due to configuration difference from full vehicle. To aid insights, validated computational fluid dynamics simulations (using CREATE-AV™ Helios) were carried out to examine hovering rotor performance prediction variations at different design stages, or different modeling/testing setup with identical blade design. Quantitative rotor figure of merit differences has been demonstrated along with descriptions of underlying physical reasons. The examined model setup includes isolated rigid blades with and without flapping, elastic blades, model-scale blades, whirl-tower conditions, blades installed on fuselage, and full-vehicle including tail rotor. Both fully turbulent flow and laminar-turbulence transition flow
This study investigates the use of the Overset mesh method for propeller simulations in OpenFOAM and compares it with the Arbitrary Mesh Interface (AMI) approach. While AMI is well validated for rotor aeroacoustics, it is limited in handling large relative motions and complex component interactions. In contrast, the Overset method enables flexible simulation of transition kinematics using overlapping grids, though its aeroacoustic capability in OpenFOAM has not been well established. A comparative analysis was conducted on a Joby-scale five-bladed propeller at an 80° tilt angle without a fairing, representing a transition-flight condition. Aerodynamic and acoustic predictions were obtained using hybrid DDES coupled with the Ffowcs Williams–Hawkings method. Results show that the Overset method provides improved agreement with experimental thrust and torque and captures stronger leading-edge vortices than AMI. Both methods resolve blade-vortex and blade-wake interactions. However, the
Previous computational aeroacoustics studies of a hovering ideally twisted rotor demonstrated the presence of new broadband noise sources, trailing-edge vortex shedding (TE-VS) noise and blade secondary vortex interaction (BSVI) noise, yielding high-frequency and mid-frequency noise respectively. Past research has demonstrated and explained the capabilities of implementing a serrated trailing edge to reduce broadband noise for rotary-wing applications, but its effect on TE-VS has not been investigated fully and explained thoroughly. In this work, we employ high-fidelity computational fluid dynamics (CFD) simulations to demonstrate how trailing-edge serrations and modulated airfoil thickness can suppress TE-VS noise with the trade-off of an increase in BSVI noise due to enhanced local three-dimensional flow effects. Ongoing work aims to evaluate the impact of various leading-edge and trailing-edge serration geometries to minimize the overall rotor broadband noise and identify an optimal
This paper presents the results of a flight test effort examining fully autonomous shipboard operations for small unmanned aerial vehicles (UAVs). Experiments were conducted at the Maneuvering and Seakeeping Basin (MASK) located at the Naval Surface Warfare Center, Carderock Division using custom-built quadrotor UAVs landing on an unmanned surface vessel (USV). These tests build upon previous ship landing algorithm testing in order to expand the envelope of operations and be more representative of a real-world mission. Several new flight modes were implemented, including takeoff and pattern flying, and a finite state machine was developed to allow smooth and autonomous transition between the different flight modes. The results from testing show smoothly executed missions both in still water and in the presence of waves. However, it was found that the initial conditions for the command filters in the position controller needed to be carefully selected. Without the correct initial
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.
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
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
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
This paper presents control and estimation approaches for multiple vehicles to cooperatively sample atmospheric variables, with a focus on wind estimation, in complex environments. The technology is encapsulated in the WINDSENSE system. The collected data could be used to initialize weather models for nowcasting or forecasting, assess the fidelity of a meteorological model, assist in understanding plume dynamics or tracking plumes, provide real-time data for fire controls or wildfire fighting, or locate the source of a chemical, biological, radiological, or nuclear (CBRN) source. The wind estimation approach utilizes a Bayesian formulation with a process model found using system identification techniques. The model structure of the identified dynamics builds on prior work by the authors and combines first-principles and experimental data collection to generate a model that is valid over a wide range of the flight envelope. This enables the wind estimator to also be viable over the
This paper presents the integration of a state-space viscous vortex particle method (SS-VVPM) into rotorcraft flight dynamics simulations. More specifically, the near wake is modeled using a near-wake vortex-lattice method, while the far wake is represented by viscous vortex particles. The VVPM equations are formulated as a nonlinear, time-varying system in first-order form, allowing the wake dynamics to augment those of the rigid body and rotors. This formulation enables the coupled vehicle, rotor, and wake dynamics to be trimmed and linearized for use in stability analysis and flight control design. Different strategies for coupling the near wake to the particle wake are investigated, and a tip-edge shedding approach is identified as the best compromise between computational cost and accuracy. Verification is carried out for a generic utility-helicopter rotor in hover and forward flight through comparisons with previously validated free-vortex wake methods. Results show good
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
The Enhanced Tiltrotor blade, also known as the RGF3 blade, represents a major milestone in Leonardo Helicopters Division's pursuit of advanced rotorcraft technology. Developed at the Yeovil facility in the United Kingdom as part of a dedicated program and in collaboration with the European Clean Sky 2 initiative, it is a key enabler for the Next Generation Civil Tiltrotor Technology Demonstrator. Leveraging the AW609 airframe, the NGCTR integrates a new lateral rotor control system and a V-tail with ruddervators to expand maneuverability and control authority. The RGF3 blade combines aerodynamic efficiency with manufacturability, cost effectiveness, and certification readiness. Innovations include advanced airfoil families, highly swept anhedral tips, dual-redundant anti-ice systems, and full compatibility with legacy components. A comprehensive test campaign—covering structural loads, lightning and bird strikes, icing, and wind tunnel validation—confirmed its robustness and
Battery energy awareness is an important aspect of tasking Unmanned Aerial Systems (UAS) safely and efficiently. By considering energy expenditure during mission planning, flight plans are assigned to the UAS only if there is sufficient energy onboard to complete the mission. In this work, several methods are developed for predicting the energy consumed during a flight, and their accuracy is assessed. Three simulation-based models derived from momentum-theory, blade-element theory, and computational fluid dynamics (CFD) are considered in addition to two data-driven models derived from flight test data (linear regression and Kriging), and four multi-fidelity models (Optimized Kirchstein, Hover-corrected, Additive Bridge, and Predictor-Corrector). Each model is used to predict the energy consumption of a representative mission and their predictions are compared to the measured energy consumption. From this analysis, it is found that a linear regression model trained on flight test data
Atmospheric turbulence is a major source of uncertainty for unmanned rotorcraft operating in confined or disturbed environments, where robust trajectory planning requires reliable bounds on vehicle response. High-fidelity turbulence models are typically too computationally demanding for onboard use and difficult to integrate into planning frameworks. This paper presents a Control Equivalent Turbulence Input (CETI)–based approach to characterize turbulence effects on the inner-loop dynamics of a small unmanned helicopter and to derive disturbance-induced state deviation bounds suitable for robust planning. CETI models are identified from manually piloted hover flight tests of the unmanned research helicopter midiARTIS using a linear bare-airframe model and a Kalman filter for disturbance estimation. CETI transfer functions are fitted to averaged power spectral densities of the extracted disturbance inputs. The resulting model is validated by reproducing the identified transfer functions
Developing high-integrity software is a complex process that involves meeting strict standards across various industries. For instance, in the avionics sector, the DO-178C Design Assurance Level A (DAL-A) sets the highest level of rigor, requiring comprehensive evidence that the software will perform its intended safety functions. Modern avionics systems are made up of hardware and software from different vendors, all integrated by prime contractors. By achieving modularity in these systems, we can reduce interface complexity, manage version control, address supply chain vulnerabilities, and significantly lower recertification costs. To support a high degree of integration and software reuse in avionics systems, certain architectural elements are necessary. These include a certified Real-Time Operating System (RTOS), open standards consortia like FACE® and MOSA, multicore partitioning strategies, deterministic networking, and hypervisor-based virtualization. The role of a certified
This study addresses the integrated plant-controller design problem for sizing a VTOL air vehicle. An Explicit Model Following control architecture is employed, where the reference model is formulated according to selected ADS-33 handling qualities criteria, and parametrized to introduce design flexibility within the optimization framework. An iterative algorithm is developed based on the Linear Matrix Inequalities formulation of the H∞ synthesis problem, enabling sequential optimization of the controller, the parameters of the vehicle's linear parametric model, and the parameters defined for the design objectives. The proposed approach is evaluated using a simplified design scenario. The results indicate that the design objectives are improved without compromising the closed-loop system performance.
Low situational awareness (SA) during low-altitude rotorcraft operations near terrain and obstacles increases flight risk by reducing the time available for pilot response. To address this problem, a Tau-theory-based obstacle avoidance methodology has been developed to support real-time trajectory adjustment and improve safety and efficiency in obstacle-dense and degraded visual environments (DVE). The method uses 3D conformal visual cueing presented on a head-up display (HUD) to support a heads-up, eyes-out interaction strategy. The present study provides a quantitative pilot-in-the-loop evaluation of this guidance framework. During the simulations, pilots interact with the visual cues in real time and assess the intuitiveness, responsiveness, and overall effectiveness of the system. The objective is to evaluate whether the framework can support safe obstacle avoidance, smooth maneuver transitions, and effective pilot-system interaction. Pilot feedback is also used to guide further
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
A novel airfoil was designed at a Reynolds number (Re) of 50,000 using a multi-objective, multi-fidelity framework based on unsteady Reynolds-averaged Navier-Stokes (URANS) simulations and a gradient-free optimization approach, and compared with the DEA-11 airfoil. Aerodynamic performance and flow physics were investigated through water tunnel experiments, two-dimensional and three-dimensional URANS simulations, and microscopic particle image velocimetry (Micro-PIV), with numerical results validated against experimental data. At Re = 50,000, the optimized airfoil achieves approximately 60% drag reduction at matched lift coefficient, a reduced extent of flow separation, lower pitching moment, with comparable maximum lift coefficient relative to the DAE-11 baseline. In the three-dimensional setting, a classical aspect ratio correction recovers the finite-wing lift closely, while three-dimensional URANS consistently under-predicts drag at positive angles of attack. Measurements and
An advanced coupling framework was leveraged to assemble analytic sensitivities of lifting line theory aerodynamic loads with respect to externally-defined blade geometry parameters for optimization of main rotor performance of conventional helicopter configurations. Three vehicle weights and two flat-plate-equivalent drag configurations were examined across the flight envelope from hover to an advance ratio of 0.3. Two types of twist controls were investigated: quasi-static and fully active. Power savings were strongly correlated to the forward flight to hover power, ranging between 1.5 and 3.5% for quasi-static geometries and 2.0 and 4.5% for fully active controls when the installed power is twice of that required in hover. Blade twists optimized at higher power ratios were observed to favor high shaft tilt angles. Optimal twist deformation relative to hover-optimized designs is nonlinear across the blade span. Minimal penalties to aerodynamic vibrations were incurred through the use
Integrating safety standards across domains offers significant opportunities to enhance the safety coverage of vertical takeoff and landing (VTOL) aircraft. By integrating various frameworks with advanced digital engineering practices, stakeholders can leverage the strengths of each approach to build a more comprehensive and resilient safety strategy. This paper demonstrates how such integration, particularly within electrical and electronic (E/E) domain, supports robust certification processes and promotes the development of safer, more adaptable VTOL platforms for both civil and defense applications.
This historical paper explores the development of vertical lift. Beginning with Leonardo's aerial screw, a profound conceptual leap, which was a helical device intended to compress air beneath it and rise vertically. Though never constructed or flown, it represents the first recorded articulation of rotary lift. The idea of rising directly upward would echo through the dirigible era of the early twentieth century, the helicopter age of the mid-century, and the emerging era of Advanced Air Mobility (AAM). This study traces that intellectual lineage and explores the technological and social forces that shaped the destiny of vertical passenger flight.
This paper examines the documented evolution of Kaman Aircraft Corporation's early helicopter development, specifically the progression from the K-225 evaluation aircraft to the groundbreaking HTK-1K drone helicopter. Through analysis of primary and secondary sources, this study establishes the technical and operational foundations that enabled the world's first remotely controlled helicopter. Additionally, this paper critically examines a hypothesis suggesting that 1st Lt. Donald M. Thompson may have been involved in preliminary remote-control helicopter experiments prior to the officially recognized HTK-1K program. While initially appearing speculative, this hypothesis gains substantial support from the discovery of a 1944 Army Air Forces memorandum documenting Thompson's position as Chief of Special Weapons Unit at Wright Field, with explicit responsibility for developing radio-controlled aircraft systems. This primary source evidence establishes Thompson as a documented historical
This paper presents the flight-test evaluation of a velocity-aided navigation solution that integrates inertial measurements with line-of-sight (LOS) Doppler velocity observations from the Psionic Navigation Doppler Lidar (PNDL) prototype to support navigation in GPS-denied environments. LOS velocity measurements collected during a helicopter flight-test campaign were first compared with velocities derived from an Applanix reference navigation system to assess measurement accuracy. The navigation solution was then developed and evaluated under simulated GPS-denied conditions by removing GPS aiding and continuing operation using LOS velocity measurements alone for extended periods. Results show that Doppler lidar velocity aiding effectively constrains inertial navigation error growth and maintains a stable navigation solution during prolonged GPS outages. These flight-test results demonstrate the utility of FMCW Doppler lidar velocity measurements as an enabling technology for Assured
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