bluuebunny/crossref_metadata_2025 huggingface dataset:
Electromechanical Modeling and Testing of a Phase-Controlled Stacked Rotor
Authors:   University of Texas at Austin, Asper Matthew ,   LaunchPoint EPS, Brewer Jack , Sirohi Jayant , Ricci Michael
Published: September 2022

Electric power has enabled unique propulsion architectures to improve eVTOL performance. This paper discusses independently-controlled electric motors to enable active phase angle maneuvers for thrust variation of stacked, corotating rotors. This can potentially increase the bandwidth of thrust control compared to varying rotor speed. A two-meter diameter phase-controlled stacked rotor system with independent electric drives was tested. Both isolated rotor and stacked rotor tests were performed actively varying the position, or phase angle of the rotors. Blade collective pitch was set to 11° and rotor speed was set to 950 RPM. Dynamic and steady state performance was predicted with an electromechanical model incorporating blade element momentum theory, field oriented control logic, and equations of motion. Tests evaluated the performance of varying both the magnitude of the phase change as well as the rate of the phase change. Isolated rotor tests showed good agreement with the model, with lower phase changes modelled better. For an isolated single rotor at a blade loading CT/σ=0.1175, changing the rotor phase by−5° at a rate of 50°/s could be completed in 0.11 seconds, or less than 2 rotor revolutions, with an additional 49.7% of nominal rotor torque. Stacked rotor testing showed that there is significant coupling during phase angle changes, which limited the total phase angle achieved. At an axial spacing of 0.7 chord, thrust changes of up to 16.5% in 0.4 seconds were observed with an increase in power required by 44.6% for a phase change rate of 25°/s. Faster rates had comparable thrust changes, but increased the power required. Future work will include designing a control architecture to account for the aerodynamic coupling between rotors during angle changes and mitigate the drift each rotor experiences.
Drag Performance Degradation Due to Icing of eVTOL (Paper 1202)
Authors:   Pennsylvania State University, Karli Geoffrey ,   Continuum Dynamics Inc., McKillip Robert , Yan Sihong , Palacios Jose
Published: September 2022

An empirical model was developed to estimate the liquid water content (LWC) and mean volume diameter (MVD) of super-cooled water droplets of an icing cloud based on the torque variation of a single rotor. The model was developed for eVTOL configurations that can actively monitor on-board torque via an electric speed controller (ESC). Experimental data was collected in the Penn State Adverse Environment Rotor Test Stand chamber under various icing conditions. From experimental data, a relationship between torque degradation and LWC was developed. This LWCis coupled to the FAR Appendix C Icing Envelopes to determine an MVD range of possible values. The range discrepancy is resolved by running Blade Element Momentum Theory (BEMT) and the Han-Palacios Correlation (HPC) for a given set of condition and finding the results that best match with the recorded torque. This process is repeated over the flying duration, using the actively incoming torque information from the ESC. Through the coupling of BEMT and HPC, torque degradation due to blade icing can be modeled and predicted. Being able to predict torque degradation means that the time until a critical torque is reached can also be estimated. This estimated time is then relayed to the vehicle as the available flying time in the current cloud environment. The proposed model was verified by comparing experimental data to the predicted values. The BEMT prediction deviated from the constant measured torque value by 6.0%. For HPC verification, 11 experimental cases were compared to estimated results. On average HPC deviated from the experimental cases by 14.8% at 20 MVD and 16.6% at 40 MVD. With the model verified, a blind study was performed using this method. A case that emulates possible flying conditions in a realistic environment was chosen. Torque data was acquired during the icing event. Within 90 seconds of data available during testing, the MVD and LWC were predicted within 1.39% and 20% respectively. Every 10 seconds the prediction for 10 more seconds into the future was compared to the 'blind' experimental data. On average, the prediction overestimated the torque by 6.5%. Based on the final calculations it was determined that 5.25 minutes of flying time was available to this particular rotor operating within this cloud environment. The presented effort introduces and verifies the capability to determine icing cloud conditions and available flight time available based on the proposed approach.
Experimental Evaluation of Panel-Method-Based Path Planning for eVTOL in A Scaled Urban Environment
Authors:   Middle East Technical University, Bilgin Zeynep ,   ENAC, Bronz Murat , Yavrucuk Ilkay
Published: September 2022

In this study, previously proposed panel method based path planning for electric vertical take off and landing vehicles in urban environments is tested in a high fidelity simulation environment and with real-life drones in an indoor flight arena. Panel method is a numerical tool, borrowed form fluid dynamics domain, that can generate collision free paths for multiple vehicles in environments with arbitrarily shaped obstacles while guaranteeing obstacle avoidance and convergence to global minima with little computational load. In this study, panel method based path planning is further improved with introduction of novel safety source element that enables a safety perimeter around obstacles without losing convergence guarantee. Furthermore, path planning capability of panel method for electric vertical take off and landing vehicles in urban environments is demonstrated with hardware experiments in a scaled urban environment. Experiment results indicate that panel method is a promising tool for path planning in urban environments.
High-Fidelity Analysis of Six-Passenger Quadrotor Air Taxi Concept
Authors:   NASA Langley Research Center, Druyor(Jr.) Cameron , Wang Li
Published: September 2022

A code-to-code comparison has been performed for high-fidelity simulations of NASA's six-passenger quadrotor air taxi concept vehicle. The multidisciplinary simulations combine comprehensive rotorcraft dynamics with high-fidelity fluid dynamics obtained from an unsteady Navier-Stokes computational fluid dynamics code. An internal overset-grid assembler, Yoga, developed at the NASA Langley Research Center, is employed to efficiently handle the communications between component grids particularly for the present large-scale, unstructured-grid systems. The simulation results are then compared with those in the literature. A quantitative comparison of converged trim angles has been performed and normal force, chord force, and pitching moment coefficients are presented for qualitative comparison. Workflow changes to meet the unique demands of multirotor vehicle analysis are also discussed.
Parametric Investigation of Flow over a Rotor-Blown Wing using High-fidelity Simulations
Authors:   Rensselaer Polytechnic Institute, Hebbar Ullhas , Gandhi Farhan , Sahni Onkar
Published: September 2022

This study models an infinite rotor-wing unit based on the CRC-20 quad-rotor bi-plane at an angle of attack of 8° and rotor modeled using the actuator line method (ALM). Parametric variations to the rotor-wing geometry are considered. These include rotor-wing chordwise separation, rotor-wing vertical offset and rotor-rotor spanwise separation. Large eddy simulation (LES) and delayed detached eddy simulation (DDES) approaches with and without the transition model are used to analyze the baseline configuration. DDES with the transition model is found to compare well with LES and is selected for the parametric study to balance the computational cost. Compared to isolated wing and rotor cases, baseline rotor-wing case shows 5.46% lower power loading, 14.42% higher lift and 4.45% higher L/D ratio. From the parametric study, varying the rotor-wing chordwise spacing did not significantly influence rotor power loading but placing rotor further from the wing improved L/D ratio by 7.64% compared to baseline due to reduction in sectional drag. The rotor-wing vertical offset cases show that placing the rotor below the wing significantly reduces the L/D ratio while placing it above yields similar L/D ratio to baseline but lowers the power loading by 6.69%. Finally, the spanwise rotor-rotor separation cases show that higher separation yields a 5.66% improvement to L/D ratio with no effect on the rotor power loading, again due to reduction in sectional drag.
Advanced Thermal Analysis Methodologies to Support eVTOL Propulsion System Optimization
Authors:   Drive System Design, Rogers Lee , Holdstock Thomas
Published: September 2022

eVTOL vehicles have seen rapid advancements in electric propulsion technologies supported by complex high-fidelity simulations that allow subsystem performance to be maximized. Optimizing subsystem performance can improve propulsion system power density, especially through improved cooling. However, current work on holistic system level approach to eVTOL propulsion system designs [1,2] can benefit from earlier consideration of the interactions between inverter, motor, transmission, and thermal management systems. This can give a better understanding of the trade-offs between increasing power density and more complex, active cooling systems. These trade-offs must be understood as active cooling elements can lead to additional redundancy and certification requirements, which can increase the time-to-market in a highly competitive environment. This paper proposes an approach that quantifies these trade-offs early in the design process, so that the right propulsion system can be brought to market in the right timeframe.
Handling Qualities Considerations in Control Allocation for Multicopters
Authors:   University of Portland, Ivler Christina ,   NASA Ames Research Center, Malpica Carlos , Hunter Will , Russell Kate , Vo Emily , Withrow-Maser Shannah
Published: September 2022

Due to multicopters' role in advanced air mobility, there has been an increasing interest in their handling qualities. This paper investigates the effect of rotor speed control allocation of multicopters on handling qualities. Typically, multicopter aircraft are trimmed with equal speed on each rotor. The force generated by each rotor can be modeled, where thrust and torque of the rotor are related to the square of the rotor speed. The dynamic equations indicate that trimming pairs of motors at higher speeds results in an increase of control effectiveness in the associated axis, improving bandwidth and disturbance rejection. A tradeoff occurs where power usage is no longer minimal at trim, but handling qualities are improved in that control axis. A blade element model for multicopter, RMAC, was used to simulate how this off-nominal control allocation would affect the dynamics of a multicopter. System identification flight tests were used to validate the trends seen in RMAC. Control systems were optimized to provide improved disturbance rejection bandwidth in the axis associated with increased rotor speed. Unmanned mission task elements were performed in flight test, showing improved tracking in the lateral axis by using off-nominal mixing to increase trim speed on the rolling motors. The method was also investigated on a full-sale UAM hexacopter, which showed similar trends, but only small changes in the dynamics were achievable because of significantly smaller power margin as compared to the small scale hexacopter.
Load Alleviation Control vs. Load Limiting Control: Pros and Cons.
Authors:   Georgia Institute of Technology, Mballo Chams , Prasad J.V.R
Published: September 2022

The development of life extending control schemes is important to ensure the longevity of critical helicopter components. Perhaps, equally important is the ability to choose the appropriate component life extension scheme for a specific application. In this paper, the benefits and drawbacks associated with two control schemes for component life extension are discussed: namely Load Alleviation Control (LAC) and Load Limiting Control (LLC). Understanding such benefits and drawbacks can help to not only motivate future research that will improve these schemes but also in the selection of a suitable scheme for a specific application.
Rotor Fault Detection and Identification on Multicopter based on Statistical Data-driven Methods: Experimental Assessment via Flight Tests
Authors:   Rensselaer Polytechnic Institute, Dutta Airin , Wang Jianxi , Kopsaftopoulos Fotis , Gandhi Farhan
Published: September 2022

A robust framework for fault detection and identification of rotor faults in multicopters is validated with data from experiments with a quadcopter and a hexacopter. The rotor fault detection and identification methods employed in this study are based on excitation-response signals of the aircraft under atmospheric disturbances. A concise overview of the development of the statistical time series model for healthy aircraft using the aircraft attitudes as the output and controller commands as the input is presented. This model is utilized to extract quality features for training a simple neural network to perform effective online rotor fault detection and identification. A proper justification of choosing the method of time-series assisted neural network has been given. It is shown a statistical time-series assisted neural network employed for online monitoring in the quadcopter and hexacopter achieves accuracy over 96% and 95%, respectively. It is effective under gusts and experimental variability encountered during outdoor flight and is sensitive to even partial loss of rotor thrust.
Exploring Transmission System Vibration monitoring using an Optical Fiber FabryPerot Bragg Grating Cavity
Authors:   University of Southampton, Washak James ,   GE Aviation Systems, Dunning Paul ,   National Center for Advanced Tribology (nCATS), Wang Ling , Holmes Christopher
Published: September 2022

This paper presents a Fabry-Perot cavity Bragg grating (FP-FBG) technique for vibration monitoring. The FP-FBG is created by placing two identical and uniform Fibre Bragg Grating (FBG) with the same Bragg wavelength to produce a Fabry-Perot (FP) cavity between them. This has the effect of enhancing the vibration monitoring through tailorable enhancement of the spectral response, which scales proportionately with relative grating spacing. In this work, a single fibre containing four FPFBG of varying cavity sizes (4mm-72mm) was fabricated and tested on both a square meatal plate mounted on a mechanical shaker and bearing test rig to test the overall sensitivity of FP-FBG. The cavity size of the FP-FBG and physical positioning was investigated. The findings so far indicate that overall, FP-FBGs are effective at vibration monitoring, and initial tests are shown to detect the shaft rotation speed from a ball bearing with no faults. Future work shall look at FP-FBG capability to detect faulty bearing conditions and design parameter further.
Ernst Otto Schmidt 1872-1938: Passionate Helicopter Inventor
Authors:   German Aerospace Center (DLR), VanDerWall Berend ,   Retiree, Schmidt Gert
Published: September 2022

Ernst Otto Schmidt is practically unknown in the row of aeronautical and especially helicopter pioneers. This is because his profession was a decoration painter and he earned good reputation at the time. However, he also was fascinated by the idea to vertically take off and land with a machine, experimented more than half of his life with models and held two patents for his designs (issued 1924 and 1939). Oral reports state that one demonstration flight was performed in 1929 and a U.S. businessman offered funding that Schmidt denied. Schmidt was afraid of being laughed at and kept his experiments secret for a long time. Without a wealthy sponsor his designs never came to fruition, partly because he also lacked any aeronautical engineering education. However, some ideas he had were realized by others at much later times. A book about Ernst Otto Schmidt was published by his grandson, the co-author of this paper. Additional personal correspondence from his family archive and further material found by the author are provided here for the first time.
Paint Scheme and Markings Digital Transformation
Authors:   Sikorsky Aircraft a Lockheed Martin Company, DaSilva Mary
Published: September 2022

The emergence of new and more powerful tools and processes associated with digital transformation has provided the aircraft design engineer with improved and more efficient ways to define and apply paint schemes and markings to our aircraft. This technology reach affects; visually defining paint schemes, foreseeing material quantities, utilizing Virtual Reality (VR), robotic paint booths, projection systems and all coming down to customer satisfaction with the benefit of savings to schedule time and costs.
Computational Analysis of a Model Coaxial Rotor Hub Wake
Authors:   University of Tennessee, Mobley Forrest , Coder James
Published: September 2022

A model counter-rotating coaxial rotor hub in free-air was simulated using computational fluid dynamics as a comparison against experimental results. The simulation is performed using NASA's OVERFLOW 2.3d Reynolds averaged Navier-Stokes solver, and flow conditions are based on experiments performed in the 12-inch diameter water tunnel at ARL Penn State. Surface forces were examined, and harmonics in this data were computed and analyzed. The turbulent wake of the rotor hub was analyzed using frequency content as well as turbulent quantities related to the production and transport of turbulent kinetic energy. The lift spectrum showed different dominant frequencies for each counter-rotating hub, and the drag spectrum showed the expected dominant frequency for both parts of the hub. Frequency content of the velocity components in the wake showed positional biases towards the advancing side of each hub, opposing the results from past analyses of similar single rotor hubs. Reynolds stresses showed similar positional biases, and were also consistently concentrated in relatively small areas within the wake. The individual wakes of the hubs did not show signs of interaction until the far wake.
Sikorsky Seal Leakage Criteria and Prevention Methods
Authors:   Sikorsky a Lockheed Martin Company, Hashim Altayeb , Buzzeo Joseph , Donecker Cody , Chory Anthony
Published: September 2022

Helicopter gearbox seals typically exhibit a zero-leakage condition, especially on new helicopters. Improved lip seal materials and molding techniques, special attention to grinding seal liners, application of break-in grease, and smooth lead-in chamfers to prevent assembly damage have all contributed to excellent seal performance. Operational leakage criteria, especially for military aircraft is established for completion of missions and exceeds what is expected by operators of new helicopters or by crew chiefs and pilots who are accustomed to zero leakage or minor seal wetness. There are, on occasion, conditions where wetness or drips occur that are questioned by operators because a norm has been established. There are also occurrences where miniscule scratches in seal liners barely visible by the naked eye or microscopic nicks in seal rubber can allow minor seepage. Seal replacement can result in removal of rotors or shafting, requiring reservicing with all new lubricants and serviceability inspections, which can cause mission or delivery delays and put an extra burden on maintenance crews. This paper describes methods to eliminate leakage and provides recommended leakage criteria for safe and reliable operation.
Evaluation of Simulator Cueing Fidelity for Rotorcraft Certification by Simulation
Authors:   German Aerospace Center (DLR), Podzus Philipp ,   Royal Netherlands Aerospace Centre (NLR), Crijnen Jur , Jones Michael , van'tHoff Stefan , Breed Paul
Published: September 2022

Before their entry into service, newly developed rotorcraft must go through an extensive certification process in order to receive a type certificate from the certification authority. A vital and long-lasting phase of this process is the compliance demonstration. This phase involves a large amount of flight testing, which leads to high expenses for the rotorcraft manufacturer and can be considered as high-risk when it comes to rotorcraft safety, especially for scenarios including control system or engine failures, as in the case of a category-A rejected take-off (CAT-A RTO). The Rotorcraft Certification by Simulation (RoCS) CleanSky2 research project aims to reduce the amount of flight testing required for compliance demonstration by using flight simulation, to achieve an increase in safety (less hazardous situations) and effectiveness, and a reduction in certification duration and costs. Within the project, pilot-in-the-loop simulator test campaigns were conducted at DLR and NLR, investigating the visual cueing fidelity required for performing a CAT-A RTO scenario. Emphasis was put on varying the available field of view (FoV) for the pilot and investigating the suitability of virtual reality (VR) devices. Subjective and objective results from these simulator campaigns, as well as pilot comments are presented in this paper.
Physics and Improved Simulations for Computational Modeling of Synthetic Jets
Authors:   Georgia Institute of Technology, Crawford Aaron , Smith Marilyn
Published: September 2022

With the rise of active flow control techniques several approaches of flow reattachment have been studied, including the use of direct momentum injection through a zero-net mass flow synthetic jet. The focus of this paper is to further understand the role of turbulence in the physics of synthetic jets and the sensitivity of external crossflow on the prediction of the jet and its downstream behavior while in cross flow. Computational results are correlated with recent experimental data obtained by the U.S. Army. The full actuator geometry is computationally modeled and to develop unsteady and phase-averaged boundary conditions at the jet/outer mold line interface at the relevant spatial and temporal levels. This study also considers the effect of turbulence model, as well as the associated turbulent quantities, and their influence in the prediction of the local synthetic jet flowfield in cross flow. Results indicate that turbulent fluctuations in three-dimensional flows with large eddy simulation wakes are required to predict the jet interactional effects. The external crossflow has a significant impact on the magnitude of the turbulent characteristics, but the trends observed in experiments are captured with the additional of turbulence in the jet.
A Comparative Assessment of the NATO-GD and SFS2 Ship Airwakes and their Influence upon Helicopter Aerodynamic Loading
Authors:   University of Liverpool, Fernandez Nicholas , Watson Neale , Owen Ieuan , White Mark
Published: September 2022

The purpose of this study was to assess and compare the airwakes of two generic ship models, the NATO-GD and the SFS2, and their impact upon helicopter aerodynamic loading in operations over a ship's deck. Airwakes were computed using Delayed Detached Eddy Simulation, a time accurate CFD approach, for each ship model in a headwind and a Green 30 wind. The CFD airwakes were then integrated with a helicopter flight dynamics model, representative of an SH-60B Seahawk. The helicopter model was held stationary at a number of points along a lateral traverse profile over the flight deck of each ship, and the unsteady aerodynamic loads on the fixed-position helicopter were recorded and compared for the two ships. It was seen that the NATO-GD airwake created higher levels of turbulence and greater unsteady loads on the helicopter model than did the SFS2 airwake, implying greater workload for a pilot.
The Effect of Lift Position on Helicopter Recovery to a Twin-Island Aircraft Carrier
Authors:   University of Liverpool, Watson Neale ,   QinetiQ, Lynn Richard , Owen Ieuan , White Mark
Published: September 2022

This paper describes an investigation of the air flow over the flight deck of a twin-island aircraft carrier with the ship's lifts in a raised and lowered position, and the subsequent change in the aerodynamic loads on a helicopter in hover over the deck. The unsteady flow over the flight deck was simulated using Computational Fluid Dynamics for a 40 kt wind from 60◦ off the starboard. The turbulence intensity and velocity flow field produced over the flight deck for each lift configuration was analyzed and compared. An experimental study was conducted in which the mean and unsteady f low over a 1:200 scale model the aircraft carrier submerged in a large recirculating water channel was measured with the lifts in the raised and lowered position. The CFD prediction of the flow over the full-scale aircraft carrier was compared to the experimental velocity data. To analyze the effect of the two airwakes on a helicopter in hover, a technique known as the Virtual AirDyn was used to quantify the unsteady forces and moments acting on the aircraft. Thirty seconds of time-varying velocity data simulated for each lift configuration was integrated with a flight dynamics model of a helicopter representative of a Seahawk SH-60B. The helicopter was fixed in hover positions over the flight deck and subjected to each unsteady airwake. The resultant unsteady aerodynamic loads acting on the aircraft were analyzed to assess the effect of the lift positions on the helicopter in hover. The results show that for the conditions considered, while the lifts' positions do affect the air flow and the aerodynamic loading, there will only be a limited impact on a recovering helicopter.
Design and Integration of a Tilt-Rotor Flight Simulation Platform
Authors:   Politecnico di Torino, Primatesta Stefano ,   ZHAW, Capone Pierluigi , Barra Federico , Guglieri Giorgio
Published: September 2022

This paper introduces a tilt-rotor flight simulation platform for research and teaching purposes implementing a real-time simulation of the Bell XV-15 aircraft. The mathematical model of the XV-15 aircraft has been implemented including simplified models for the aerodynamics of the whole aircraft, rotors, and engine dynamics. Hence, the simulation is performed in a graphic environment to reproduce the simulated flight and to interact with it using commands given by the pilot. The simulation platform is implemented using MATLAB/Simulink®, while the input commands are set using USB peripherals, i.e., a flight stick and a pedal board. Instead, the visualization environment is performed using FlightGear, an open-source and cross-platform software that is widely used in research. The result is a portable tilt-rotor simulator to be executed on a commercial pc, while ensuring real-time performance. The tilt-rotor flight simulator is also validated by a licensed helicopter pilot returning positive feedback regarding the flight experience.
The Bambi Bucket: Evolution of the Most Versatile Aerial Firefighting Tool
Authors:   Columbia Helicopters Inc., Roedts(II) Robert
Published: September 2022

From humble beginnings in the 1940s, helicopters have become an integral part of managing and fighting wildfires throughout the world. Starting in the 1950s and over the next several decades, various government agencies increased the utilization of helicopters in their management of wildfires across the US and deployed new technologies. One of the most impactful technologies developed was using a slung bucket to dump water. Initially using repurposed construction and agricultural equipment, these early generation buckets were dipped in sources of water and released using a simple mechanical gate system. In parallel with these early generation buckets, the technique of long-line operations were being perfected that allowed flight crews to increase separation from terrain and increased control of the external load. Over the next several decades, these buckets were steadily improved and incorporated into firefighting operations across the work. In addition, the use of long lines for external loads allowed the use of remote water sources and increased precision water drops. In 1982, Don Arney developed the ubiquitous "Bambi Bucket." This bucket was innovative in many ways: easily scalable, lightweight, collapsible, stowable, and reduced drag. Today, helicopters have become the main aerial resource to fight wildfires across the world. Furthermore, helicopters outfitted with Bambi Buckets account for 90% of all firefighting operations.
SmartHangars and SAE International Aircraft Charging Standard
Authors:   Electro.Aero Pty Ltd, Portlock Joshua , Watson Richard
Published: September 2022

Electro.Aero has been supporting the emerging electric aviation industry for nearly a decade, including the development of chargers, electrical management systems, battery management systems and electric propulsion systems to numerous electric aircraft development projects. During that time, it was identified that the industry needed standardization, especially regarding the charging coupler, so the SAE AE-7D committee was founded by Joshua Portlock in 2018 to help standardize electric aircraft charging and energy management. The AS6968 standard for light conductive charging of electric aircraft was the first standard the committee worked on and is now approaching completion through this year. Furthermore, while the charging coupler standard was proving to be of high priority to the industry, there has also been a noticeable trend that typical airport hangars don't have sufficient electrical power to charge the growing power demands of future electric vertical take-off and landing (eVTOL) aircraft. Therefore, SmartHangar technology was developed, whereby the limited grid connectivity is supplemented by solar and stationary battery energy storage systems to help deliver the peak power demands of electric aviation charging, whilst also helping airports and vertiports transition to more self-sufficient sustainable energy.
Impact of Transformative Air Vehicle Operations on Logistic Supply Chains
Authors:   LogistiWerx Inc., Stanzione Kaydon ,   Georgia Institute of Technology, Schrage Daniel ,   Nodein Autonomy Inc., Kannan Suresh , Ruff Richard
Published: September 2022

Global supply chains have reached critical capacity, resulting in escalating prices, long delivery times, and has had a crippling effect on manufacturing, health care, agriculture, and commerce in general. In addition, the cascading effects of the COVID-19 pandemic as well as other intra-supply chain problems have resulted in a 40-year high inflation and degradations in quality of life, employment, GNP, and personal and national security. During the pandemic, shortages in the workforce and all transportation carrier modes forced the acceleration of digitally powered solutions for capacity improvements. At the same time, emerging technologies in autonomy, electrification, fuel cells, and low carbon powerplants are pushing the envelope of OEM development for over-the-road trucks, aircraft, and maritime vessels. These new transportation modes offer clean, low noise, and high safety operations, which promise to move people and goods faster, cleaner, and ultimately more affordably between origin and destination. This paper provides an overview of general logistics issues that can assist VTOL designers and operators in determining critical configuration parameters, location demographics, flight operations, and emerging Aircraft On Ground (AOG) technologies to maximize near-term ROI for transformative VTOL aircraft.
Scenario-based Study of using Civilian Cargo eVTOL Aerial System for Counter Catastrophic-Disaster Mission
Authors:   Yamato Transport Co. Ltd., Tsuge Haruki , Ito Yu
Published: September 2022

In recent years, the use of Unmanned Aerial Vehicles (UAVs) in natural disaster situations such as earthquakes or heavy rain has attracted a great deal of attention. The flight and safety performance of UAVs continues to evolve over the years. Because UAVs are more maneuverable than helicopters and other manned aircraft, they are being used to quickly assess damage at the scene after an actual natural disaster has happened. UAVs are also expected to be used for transporting relief supplies in the event of a disaster. Therefore, test flights and demonstration tests are being conducted across Japan to transport relief supplies in the event of a disaster. However, there have not been many studies on UAV logistics during large-scale disasters. This paper analyzes the effectiveness of eVTOL aircraft that is expected to perform a role as a next-generation parcel delivery service in normal operations for relief supplies transportation in a large-scale natural disaster, which is likely to occur within a few decades. Based on the results of the analysis, this paper proposes an operational model for eVTOL aircraft for logistics in large-scale natural disasters
CFD Modeling Framework Development for Robust Rotorcraft Design
Authors:   Sikorsky a Lockheed Martin Company, Neerarambam Shyam , Alexander Michael , Berezin Charles , Birtwell Nolan , Coleman Dustin , Cotton Rebecca , Frydman Jonathan , Lamb Donald
Published: September 2022

Reducing development cycles, developing advanced capabilities at reduced technical risk, and containing overall program development costs are key goals of next generation rotorcraft development programs. Achieving these goals requires a significant investment in digital transformation in all phases of the aircraft development; design, test, manufacturing, and certification. CFD tools have traditionally been used to shape and influence various aspects of rotorcraft design. However, workflow inefficiencies typically limit use of CFD to key flight conditions of the rotorcraft flight envelope. Robust design requires analytical design assessments across a very broad range of environmental conditions - ambient temperature, wind, gross weight etc., across a very broad range of rotorcraft mission spectra. Development of a CFD modeling framework and streamlining/automating all building blocks for rotorcraft CFD analysis is essential to enabling robust analysis driven design. This paper provides an overview of the digital transformation efforts on CFD modeling framework development for rotorcraft design and productivity improvement realized on practical use cases with ongoing work.
Design Concepts to Meet EASA SC-VTOL-01 Single Failure Criteria
Authors:   The Boeing Company, Darmstadt Patarick ,   NASA Glenn Research Center, Krantz Timothy , Pathak Sheevangi , Valco Mark
Published: September 2022

The objective of the current work is to discuss European Union Aviation Safety Agency (EASA) SC-VTOL-01 single failure criteria, VTOL.2250(c). VTOL.2250(c) increases safety metrics compared to existing Vertical Takeoff and Landing (VTOL) regulations, creating new engineering challenges that must be addressed. Additionally, research and development targeting compliance against VTOL.2250(c) will more broadly benefit the VTOL industry, providing guidance for safer system designs. Prior studies have developed concept distributed propulsion and flight control (DPFC) system architectures and found they comply with EASA SC-VTOL-01 probabilistic failure criteria, VTOL.2510(a). Prior work developed two all-electric DPFC systems utilized in a quadrotor concept aircraft developed by the National Aeronautics and Space Administration (NASA); one uses interconnecting shafts and gearboxes to interconnect redundant motors with each rotor system and the other uses gearboxes to connect redundant motors locally, near each rotor. Common between the two electric DPFC systems were rotor shafts, epicyclic systems, and motors. The current work explores Category I failures in drive systems, relevant research to support fail-safe design practices for gear systems, research and adjacent industry trends in motor fail-safety and reliability, and proposed design concepts to comply with VTOL.2250(c). Continued research in fail-safe design concepts and design guidance will benefit eVTOL and conventional rotorcraft, alike. Continued research in these areas will benefit eVTOL certification against SC-VTOL-01, and could optimistically translate to more widespread adoption of similar fail-safe design concepts into new rotorcraft designs certified against CS-29.
Safety Considerations on the Operation of Electric Vertical and Takeoff Landing (VTOL) Aircraft at Airports and Vertiports
Authors:   WSP USA, Le Bris Gaël , Nguyen Loup-Giang
Published: September 2022

Design innovation for electric vertical takeoff and landing (eVTOL) aircraft is accelerating rapidly. By 2025, eVTOL aircraft might be operating commercial flights. Aviation facilities may have to distribute new energy vectors used by eVTOLs. Accommodating these aircraft will require careful planning, as well as design features, standards, and operational procedures to ensure aviation safety. Indeed, these new technologies cannot be turned into a viable air transportation system if they cannot be integrated into existing and future aviation facilities. With the first eVTOL certification on the horizon, a study of potential airside integration issues is timely. This paper identifies and analyzes potential aviation safety hazards and risks specific to the introduction of eVTOL aircraft and hydrogen technologies at airports and vertiports. A review of existing industry standards and ongoing standardization tasks suggests ways to further reduce the most prominent risks through industry standards and practices promoting operational flexibility and interoperability.
The Safety of Advanced Air Mobility and The Effects of Wind in the Urban Canyon
Authors:   RWDI, Schajnoha Sharon ,   National Research Council Canada, Barber Hali , Larose Guy , Al-Labbad Maryam , Wall Alanna
Published: September 2022

The safe integration of vertical takeoff and landing aircraft (VTOLs) into an urban setting requires careful consideration of the effects of the wind flows through the urban canyon, which are complex and cannot be predicted with the reliability level necessary to enable safe operations. The assessment of wind in the urban canyon is critical to the siting and design of vertiports and safe operations of VTOLs.

Vertiport design guidance related to the effects of wind flows in the urban canyon is limited and draws from helipad design guidance. The guidance recommends that wind conditions be assessed across a vertiport, but the guidance does not suggest how the study should be conducted nor does it provide design thresholds for wind.

RWDI, the National Research Council Canada and Transport Canada have joined forces to identify and study the wind characteristics that would be important for the aerodynamic performance of VTOL and how these characteristics would be influenced by buildings and structures in the urban environment. In the framework of this research effort, an experimental approach was developed, centered on several sites in Canadian cities, representing a range of urban densities and surrounding topographies, as wind conditions are highly dependent on the built environment, including building footprint, building features, combinations of buildings and the local climatology.

The work involved a quantitative approach in which physical models of several urban sites were built, instrumented and tested in boundary layer wind tunnels. In the wind tunnel experiments, "red flag" wind conditions were identified and measured. Detailed data capturing these flow features were collected around roof tops of lower and taller buildings, representing prospective vertiport locations and along prospective flight paths.

This paper provides the details of the wind tunnel testing conducted for one of the urban sites; a site with an existing helipad at a hospital and a low-rise parking garage. The wind tunnel measurements were compared to published helipad design thresholds and combined with long term meteorological conditions representative of the site to determine how often vertiport operations will be limited by unfavourable urban wind conditions on an annual basis and by season. The wind tunnel study provides a case study and demonstrates how to evaluate the safety of a vertiport now, based on limited availability of VTOL aerodynamic performance capabilities and into the future as more information becomes available on VTOL performance in turbulent winds.
Physics-Based Detection of the Proximity to Loss of Tail Rotor Effectiveness Within the Helicopter Flight Data Monitoring Program
Authors:   FAA William J. Hughes Technical Center, Zanella Paola ,   Georgia Institute of Technology, Mavris Dimitri , Johnson Charles , Prasad J.V.R.
Published: September 2022

Loss of tail rotor effectiveness (LTE) is a critical helicopter flight characteristic and a major factor in numerous fatal accidents. To support LTE risk mitigation, the Helicopter Flight Data Monitoring (HFDM) program provides pilots with constant flight evaluation reports. Nevertheless, the existing LTE safety metric used within the HFDM environment presents several pitfalls that hinder the reliability of the results, contributing to a misleading pilot's training and low LTE awareness during flights. This paper is part of a larger ongoing effort that aims to develop an expanded safety metric to enhance the detection of proximity to LTE within the HFDM program. While LTE has been defined to include different complex flight conditions, this work focuses on the phenomenon of running out of pedal (tail rotor collective) for trim, a critical event that may lead to LTE behavior. A parametric surrogate model for the detection of proximity to running out of pedal events is formulated by combining results from physics-based simulations with machine learning techniques. The new safety metric allows for operator fine-tuning of proximity to critical boundaries, and hence, it provides flexibility in risk management from post-flight analyses. The results confirm the accurate prediction of running out of pedal for trim, providing an improved detection of the proximity to LTE within flight data. This aims to promote better awareness of LTE within the pilot community and support the proactive mitigation of LTE accidents.
The Application of Sandwich Technology to the Airframe Structure of Helicopters
Authors:   Airbus Helicopters, Arelt Rainer , Arent Jan-Christoph , Goerlich Stefan , Hailer Benjamin , Dambaur Mathias
Published: September 2022

The H160-B is the latest helicopter design from AIRBUS HELICOPTERS with the extensive use of sandwich technology in the airframe. A sandwich with face sheets from CFRP and honeycomb cores is a robust outer skin of a helicopter. Furthermore it shows a very good tolerance to impact damages and a very good reparability. At Airbus Helicopters great experience is available which is required to understand and to control all manufacturing parameters, that are driving the quality of such parts. Powerful inspection technologies are in place to maintain the high level of manufacturing quality. In this paper an overview of the parts on this Helicopter made with sandwich technology will be given. These are cowlings and structural parts as well as principal structural elements (PSE) on main load paths. The respective certification requirements and related means of compliance demonstrations will be explained in detail. Special attention is paid to the applied methods for the damage tolerance demonstration of sandwich. The design and strength analysis was done with a combination of FEM analysis and analytical method, using basic allowable derived and validated by tests.
Comparison of Helicopter Component Fatigue Test Results to Analysis
Authors:   Bell Textron Inc., Michael James , Altman Leigh , Green Nathan
Published: September 2022

The safe-life fatigue methodology approach, combined with fatigue testing, is used throughout the industry to qualify helicopter components. In the early stages of helicopter development, limited component fatigue test results are available. As a result, component designs risk failure in down-stream testing. Alternatively, an over-designed component risks adding unnecessary weight to the aircraft. This paper discusses an analytical approach for fatigue evaluation with the purpose of minimizing these risks. The approach, applied to a flight-critical metallic component, utilizes finite element modeling and coupon fatigue test data to assess the component's design early-on. Analytically predicted component fatigue strength is assessed and compared to measured component fatigue test results to draw conclusions regarding the validity of the analytical approach. In summary, the analytical method compares favorably to the component test data.
Fifty Years of Innovation in Performance Limit Indicator: A Success Story of Airbus Helicopters Contribution, to Helicopter Fleet Safety by Simplifying Piloting and Reducing Workload
Authors:   Airbus Helicopters, Germanetti Serge
Published: September 2022

Since their invention, helicopters were typical flying object that requested very specific competencies to control their flight. The control of the rotors power, delivered by the engine, was subject to multiple indicators that were installed in the cockpit. Depending on the various technologies, engine temperature, turbine rotation speed, and torque are measured; main gearbox torque, or free turbine speed are monitored. The pilot has the responsibility to ensure that none of them are at their limit, depending on the environmental conditions mainly outside temperature and atmospheric pressure.
Thermodynamic Modeling for the Analysis of Non-Stabilized Flight Test Temperature Data
Authors:   Airbus Helicopters Inc., Hamel Denis , Cooper Thomas , Merkel James , Allgood Carson , Kolarich Alexander
Published: September 2022

Temperature is the result of underlying thermodynamically independent heat transfer modes of conduction, convection and radiation. Flight test methods have evolved to collect targeted data in support of most engineering disciplines - flight mechanics, aerodynamics, performance, dynamics - but little has changed in the field of thermal analysis, which relies mainly on stabilized temperature data requiring extended ground and flight test conditions. Traditional methods are time consuming and may result in imprecise extrapolation of steady-state temperatures. Temperature response is an exponential time decay function with time constant and asymptotic values defined by material properties, compartment volume, and heat transfer mode. A generalized heat transfer block diagram and matrix state space model presents each heat transfer mode in a multi-zonal system of helicopter compartments. The model is defined via system identification tests that isolate the heat transfer effects - electrical heating, passive cooling, solar radiation, and airspeed effects. The resultant model can be used with time-variant standardized hot day solar radiation and ambient temperature profiles to yield temperature versus time profiles for direct comparison with equipment qualification criteria. This methodology is the basis for more efficient and more accurate results than current evaluation techniques.
eVTOL Component Testing for Supporting Algorithmic Icing Detection
Authors:   Continuum Dynamics Inc., McKillip(Jr.) Robert
Published: September 2022

Component testing in support of the development of a model-based algorithmic Icing Detection Filter (IDF) for use on eVTOL aircraft is described. The IDF represents an extension of prior work on holistic aircraft icing detection where data from individual electric motor controllers is monitored to track performance degradation effects due to accreted icing on rotating components. Icing accretion tests were conducted at a variety of conditions on representative components from a Lift+Cruise eVTOL configuration in both an icing hover chamber and an icing wind tunnel. Several different simulation tools were used to assess their capability to predict observed trends from the test data, and while icing accretion on rotating components was modeled sufficiently, non-rotating components appeared to accumulate ice more uniformly than suggested from the droplet trajectory analysis used.