bluuebunny/crossref_metadata_2025 huggingface dataset:
Reconfigurable Discrete Event Simulation of Rotorcraft Maintenance and Operations for Technology Assessment and Tradeoff
Authors:   Georgia Institute of Technology, Armstrong Ryan ,   US Army Research Laboratory, Spero Eric , Ernst Zachary , Collins Kyle , Mavris Dimitri
Published: October 2024

is used to model the operational lifecycle of a fleet of rotorcraft. Vehicles are modeled as a container of parts, each of which accrue damage through normal fatigue during flight. Many different vehicle configurations can be represented through the use of different parts. Incorporation of technology factors allows exploration of technology effects on operational availability, vehicle loss rate, operations and support costs, and maintenance metrics. Initial model verification on a UH-60M baseline demonstrated expected trends in availability as well as the ability to model technologies which impact O&S costs, such as HUMS.
Closing the Gap between Capability and Affordability for System Upgrades and Major-Modifications
Authors:   Georgia Institute of Technology, Ashok Sylvester , Sirirojvisuth Apinut , Smith Andrew
Published: October 2024

The helicopter community and the US Army are constantly looking to expand the horizon of capability for future fleet. The Future Vertical Lift (FVL) program looks to use new technology, advanced materials, and designs to deliver a system that can fly faster, farther, carrying more payload, and that is more available, dependable, and affordable. Until FVL completely replaces the current fleet, the military will depend on block upgrades and some major modifications to existing fleet of Apaches, Black-Hawks, and Chinooks. The need to maintain military capabilities in the near team poses a significant challenge to the design community to engineer more performance out of the older platforms. The problem is further aggravated by the limited time and cost margin to design, build, and certify these new designs. As a solution to this problem, we propose a Development Assurance (DA) method for design trade-off and Value Based Acquisition (VBA).
Effort sponsored by the US Government under Other Transaction number W15QKN-10-9-0003 between Vertical Lift Consortium, Inc. and the Government. The US Government is authorized to reproduce and distribute reprints for Governmental purposes notwithstanding any copyright notation thereon.
The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of the US Government.
Rotorcraft Turbine Engine Applications of Environetix's Wireless High Temperature Surface Acoustic Wave (SAW) Micro-Electromechanical Machines (MEM) Sensor System
Authors:   US Army AATD, Moffatt John ,   Environetix Technologies Corporation, Lad Robert , Pereia Maurice
Published: October 2024

The purpose of this paper is to explain the benefits, value, and achievements of Environetix's Surface Acoustic Wave (SAW) Micro-Electromechanical Machine (MEM) sensor technology, developed under the Army Small Business Innovative Research (SBIR) program, as an enabler for advanced monitoring of aircraft components for future Army sustainment efforts. Details will be provided to demonstrate how the SAW sensor system, with its micro-size, minimal weight, non-obtrusive characteristics, battery-free operation, and wireless transmission capabilities, can enable the autonomous monitoring of components/systems on Army rotorcraft. The details of the design, fabrication, and temperature sensing on an actual turbine engine compressor section will be presented. Finally, this paper recommends refining this technology and preparing it for validation/qualification testing in multiple Army turbine engines and other critical rotorcraft components.
Establishing Rotorcraft Component Fatigue Lives using SUMS Data and a Partial Usage Spectrum Approach for the MH-47G Chinook
Authors:   Vencore Inc, Finckenor Jeff ,   US Army, Baker Terry ,   PeopleTec, Wallace Christopher , Chandler Michael , Engelmeyer Scott
Published: October 2024

Lives of fatigue critical components for Army aircraft are typically established based on component strength from ground test, loads for each regime from flight test, and aircraft usage in each regime from engineering and aircrew judgement. This paper documents the first time that an Army platform has had component fatigue lives defined with usage monitored by the Structural Usage Monitoring System (SUMS). SUMS uses aircraft parameters to identify the regime at any given time. The time in recognized regimes is summed up to generate a spectrum of time spent in each regime. The Partial Regime Recognition Spectrum used here identified specific regimes that had a significant effect on part life and concentrated on identifying only those regimes. Time in other 'unrecognized' regimes was prorated based on the legacy spectrum. The SUMS system is validated using scripted flights, as well as by cross checking against a spectrum generated via pilot interviews. Six components were addressed with life changes of -1.5%, +24%, +33%, +44%, +45% and +124%, with an annual return of $1M as well as reduced maintenance burden and increased readiness.
Improving Gear Fault Detection by Reducing Tachometer Jitter
Authors:   GPMS Inc., Bechhoefer Eric ,   University of Illinois at Chicago, He David
Published: October 2024

Much research has been published on gear fault analysis techniques, almost all based on the time synchronous average (TSA). These include and are not limited to: residual analysis, energy operator, energy ratio, amplitude modulation, frequency modulation, sideband index, zero-order figure of merit, etc. Because the TSA is based on tachometer zero cross times, the performance of these analyses is dependent on the quality of the tachometer data. The tachometer signal always has jitter, due to electrical noise, magnetic noise, or manufacturing spacing error of the tachometer target (e.g. gear tooth spacing). By implementing a novel zero phase filter to reduce tachometer jitter, large improvements in the fault detection were observed. For a known gear fault, the separability, related to fault detection, increased from 10 to 25%.
Tip Displacement Estimation Using Fiber Optic Sensors for X2 Technology Rotor Blades
Authors:   Sikorsky Aircraft Corporation, Geiger Derek ,   United Technologies Research Center, Kim Seung , Bowles Patrick , Matalanis Claude , Wake Brian
Published: October 2024

Rotor-state feedback will be important to realize the full capability of next generation high speed, highly efficient rotorcraft with attributes such as X2 Technology™. Being able to sense and regulate rotor tip clearance on an X2 Technology™ rotorcraft will maximize its capability while maintaining safety of flight without requiring an overly conservative deisgn. One concept for acquiring rotor tip clearance is to use a strain-displacement transformation to indirectly estimate blade tip displacement. This strain-displacement transformation relates on-blade strain measurements, acquired from fiber optic sensors, to blade deformation using a minimum number of sensors and the measured or estimated blade structural properties. Testing on a simple cantilever beam and on a model-scale rotor operated in the UTRC Pilot Wind Tunnel demonstrated feasibility of the concept. Even in the presence of airflow and centrifugal load, the tip displacement estimation did not exceed 7% deviation from reference sensor readings. The performance and endurance of the fiber optic sensors and sensing hardware were also studied during the tests.
S-92 Main Rotor Blade Life Extension
Authors:   Sikorsky Aircraft, Jr. Raymond , Davis Mark , Kloda Jared , Templeton David
Published: October 2024

Rotorcraft structural methodology has traditionally relied upon the use of three sources of conservatism for design and fatigue substantiation of rotorcraft dynamic components: fatigue strength, flight loads, and the aircraft usage spectrum. In contrast to the thousands of engineering hours typically spent quantifying component strength and loads through full scale laboratory and flight testing, definition of the usage spectrum has traditionally relied on legacy specifications, pilot surveys, and rotorcraft original equipment manufacturer (OEM) historical knowledge of rotorcraft usage. Significant and largely untapped value lies in the application of HUMS recorded flight parameter data and regime recognition (RR) algorithms to monitor fleet wide usage metrics and to support development of a data driven usage spectrum that maintains the intended conservatism of the original usage spectrum. This paper presents the methods and tools that were used to determine actual fleet usage rates for one very significant and easy to detect damaging regime for the S-92® main rotor blade using 700,000 flight hours of S-92® rotorcraft fleet HUMS data. The calculated retirement time (CRT) based on this updated usage demonstrated that the main rotor blade can be safely extended from a retirement time of 22,000 to >30,000 hours.
A Modified Tukey Boxplot for Threshold Analysis: Upper Quartile Parameterization
Authors:   QTEC, Watson Matthew
Published: October 2024

Current thresholds for condition indicators may be estimated by calculating sample means and then adding a determined number of standard deviations. This approach is based off of a normal distribution which in reality very rarely occurs with the condition indicators of interest. Instead the data follows other distributions that tend to be heavily right skewed with long tails. This approach is also highly susceptible to inflation caused by an unpredictable number of faulted points within the data set. Tukey's boxplot method of adding multiples of the interquartile range to the third quartile is far more robust but fails to adequately characterize distributions with very long tails. A parameter can be developed, however, to account for the increased tail length by dividing the range of the distribution between the 75th and 97.5th percentiles by the range of the data between the 25th and 75th percentiles. Adding this parameter to Tukey's boxplot method extends the inner and outer fences proportionally to the tail length with a very low likelihood of any corruption from faulted data that may exist within the data set. This method can provide an analyst a way to quickly calculate initial threshold values for large data sets without any knowledge of the nature of the distribution.
A Comprehensive Approach for Tracking Helicopter Transmission Power Usage
Authors:   ACR Inc., Chin Harrison ,   Bristow U.S. LLC, Barnett Richard ,   Bell Helicopter, Macedo Marco ,   Starmark Corp., Green David
Published: October 2024

This paper describes the development and implementation of a power usage metric designed to accurately track the usage of rotorcraft power train systems. Utilization of this power usage metric is believed to be more accurate than the traditional approach that uses flight time for scheduling the overhaul of rotorcraft transmissions. As such, the result of this study may help the industry develop engineering processes that include a power usage algorithm for establishing the intervals between inspections of transmissions in helicopter powertrains. The feasibility of this metric was subjected to a two-year operator's demonstration program. The results of this program showed that the rate of power usage for each aircraft could be tracked accurately and reliably. Furthermore, it showed that this power usage algorithm could be combined with mechanical diagnostic indicators to form a reliable prognostic model.
Rotor Durability Advanced Technology Demonstration
Authors:   Sikorsky a Lockheed Martin Co., Harris William ,   US Army Aviation Development Directorate, Centolanza Louis
Published: October 2024

Rotor Durability Advanced Technology Demonstration, a co-funded effort between the Aviation Applied Technology Directorate and Sikorsky Aircraft, demonstrated technologies leading to increased blade durability to support current and future Army Aviation platforms. Milestones for this program included demonstration of improved main and tail rotor environmental durability, repair-ability, and performance. This paper summarizes the work the Army and Sikorsky conducted to accomplish this objective, providing a means for significantly increased aircraft availability rate supporting an increased OPTEMPO for the baseline UH-60L aircraft and the UH-60M. The approaches proposed are expected to reduce life-cycle costs through an improvement-by-spares upgrade concept for the current fleet, as well as new blade designs for next generation aircraft.
Application of Casting Technologies to Sikorsky Development Programs
Authors:   Sikorsky Aircraft, Woodworth Heather ,   Aviation Applied Technology Directorate, Fetty Jason , Baker Treven
Published: October 2024

Sikorsky Aircraft Corporation recently demonstrated new casting technologies in two if its latest development programs, the S-97 RAIDER™ aircraft and Future Advanced Rotorcraft Drive System (FARDS), to improve casting quality and speed to market. The development of new sand castings for rotorcraft gearbox housings can frequently take years to complete. Using modeling and simulation, additive manufacturing of the mold, and low pressure casting, Sikorsky has shown that the lead time and number of pours to yield a usable casting has been reduced by at least ten times compared to using traditional casting methods. These technologies also reduce the amount of weld repair required. Ultimately this will allow for new and improved gearbox designs with better speed to the market.
A Simple Analytical Model for Investigation of Fuselage-Rotor Interference
Authors:   German Aerospace Center - DLR, van Berend ,   Iowa State University, Rajagopalan Ganesh ,   Konkuk University, Jung Sung , Wentrup Marc , Yin Jianping
Published: October 2024

A simple analytical model to account for fuselage-induced velocities at rotor blade elements and at rotor wake nodes is described. The method is applied to four different fuselage configurations: two rotor test rig bodies used in the NASA Ames Full-Scale Aerodynamics Complex and two test rigs used by the DLR (German Aerospace Center) in the Large Low-speed Facility of the German-Dutch Wind tunnels in the Netherlands. The fuselage-induced flow fields in the volume of rotor operation above the respective fuselages are modeled in the range of angle of attack and sideslip applicable in the respective wind tunnel of their usage. Results for the effect of the fuselage, relative to the isolated rotor, on trim controls and rotor thrust are estimated using the blade element/momentum theory, and are compared to results obtained with a comprehensive rotor code. It is found that in forward flight fuselage effects mainly affect the lateral control, strongly depending on angle of attack. The rotor thrust can be varied by the presence of the fuselage, depending on its angle of attack, and the fuselage influence generally increases with flight speed. In sideslip conditions, the fuselage influence on cyclic controls shifts from mainly lateral control in forward flight to mainly longitudinal control in quartering flight. Significant differences in results emerge from the method of data generation, depending on the representation of separated flow (Navier-Stokes code) or not (Panel code).
Modeling the Aerodynamic Interaction of Multiple Rotor Vehicles and Compound Rotorcraft with Viscous Vortex Particle Method
Authors:   Advanced Rotorcraft Technology Inc., He Chengjian
Published: October 2024

This paper presents an efficient and high fidelity aerodynamic interaction modeling method for effective simulation and analysis of compound rotorcraft as well as aircraft configured with multiple rotors. The methodology is the first-principle based viscous Vortex Particle Method (VPM) whose rotor wake modeling accuracy has been validated through extensive simulation. This research extends the modeling methodology to address modern multiple rotor systems and compound rotorcraft and emphasizes the mutual interaction between the rotors, wings, fuselage, and aerodynamic surfaces of a full rotorcraft. The developed methodology aims to provide an effective modeling tool to support the design and analysis of next generation vertical lift vehicles. In this paper, the mutual aerodynamic interaction between major components of modern rotorcraft configurations (such as the rotor/rotor, the rotor/wing, the rotor/propeller, the rotor/empennage, and interactions) and its impact on the vehicle performance is studied. The simulation results are compared with available measurements and a good correlation with the measurements is obtained for the representative cases evaluated.
Free-Wake Based Dynamic Inflow Model for Hover, Forward and Maneuvering Flight
Authors:   Technion - Israel Institute of Technology, Rand Omri , Khromov Vladimir
Published: October 2024

The paper describes a methodology to extract linearized state-space dynamic inflow model from a generic and high fidelity aerodynamic analysis for single and coaxial helicopter rotor systems. Both hover and forward flight are studied including maneuvering and the results are demonstrated by a free-wake analysis. The proposed methodology which is founded on a Single Frequency Analysis is computationally efficient and provide the entire frequency-domain behavior of the wake inflow states. Besides being able to incorporate any advanced computational tool, the present methodology takes advantage of exact wake states and thus adequately encompasses high frequency responses. The paper also extends the methodology to the case where states of higher harmonics are required and to the case of heaving, rolling and pitching rotor disc. For a single rotor system the results resemble the well known classical dynamic inflow model. For coaxial rotor system in hover, the high mutual couplings between the rotors are clearly demonstrated and affect the resulting system matrices. An important feature of the present methodology lays in the fact that the entire formulation is non-dimensional and the in-flow analysis is completely separated from the loads analysis, which enables a consistent generalization of the results.
Towards Real-Time Fully Coupled Flight Dynamics and CFD Simulations of the Helicopter/Ship Dynamic Interface
Authors:   Penn State University, Oruc Ilker ,   CRAFT Tech, Shenoy Rajiv , Horn Joseph , Shipman Jeremy
Published: October 2024

This study represents the ongoing efforts of a project whose ultimate goal is real-time virtual dynamic interface modeling and simulation with fully coupled Navier-Stokes CFD with a helicopter flight dynamics simulation. The coupling between GENHEL-PSU/CRUNCH CFD has been developed in a recent work and successful results of fully coupled flight dynamics and CFD simulations of rotorcraft/ship dynamic interface were presented. In the coupled simulations, the flight dynamics model is free to move within a computational domain, where the main rotor forces are converted to source terms in the momentum equations of the CFD solution. Simultaneously, the CFD solver calculates induced velocities that are fed back to the simulation and affect the aerodynamic loads in the flight dynamics. The CFD solver models the inflow, ground effect, and interactional aerodynamics in the flight dynamics simulation. An actuator disk model was used to map rotor blade loads into the computational domain. In order to enhance stability and efficiency of the CFD solution, rotor source terms are applied onto vertically stacked planes with a 1D Gaussian distribution. In this work, the simulation framework for fully coupled piloted flight dynamics/CFD is demonstrated for a simplified shedding wake example. Improvements to the coupling interface are described that allow the simulation to run at real-time execution speeds on currently available computing platforms, demonstrating a simulation framework for pilot-in-the-loop CFD (PILCFD) flight simulation.
Improving System Identification Results: Combining a Physics-Based Stitched Model with Transfer Function Models Obtained Through Inverse Simulation
Authors:   German Aerospace Center - DLR, Greiser Steffen , Grünhagen Wolfgang
Published: October 2024

It is state-of-the-art to model helicopter dynamics by low-order equivalent linear systems at certain speed-dependent operating points for the flight envelope of interest. These models are obtained from flight test data by system identification. Based on the linear models, it is desired to simulate maneuvering flight such as acceleration and deceleration between hover and high forward-speed. Additionally, the identified operating point model should consist of a high modeling accuracy. Thus, the two modeling and simulation goals are: generation of a full-envelope simulation by embedding all linear models and improvement of the modeling accuracy at each operating point. These two goals stimulate the application of two techniques: model stitching and inverse simulation. Model stitching allows to implement a full-envelope quasi-nonlinear helicopter simulation whereas inverse simulation allows to analyze and model additional non-physical transfer functions that improve the linear model accuracy at a certain operating point. These transfer functions describe the remnants that are originally not considered by the system identification results. This paper presents the combination of the two techniques model stitching and inverse simulation as well as their application. Finally, the paper assesses the modeling accuracy for ACT/FHS flight test data.
Flight Simulation and Control of a Helicopter Undergoing Rotor Chord Extension Morphing
Authors:   Rensselaer Polytechnic Institute, Krishnamurthi Jayanth , Gandhi Farhan
Published: October 2024

The current study focuses on flight simulation and control of a helicopter undergoing rotor chord morphing. A model-following dynamic inversion controller with inner and outer loop control laws (CLAWS) is implemented and chord extension is introduced as an additional feedforward component to the inner loop CLAW. Simulation results based on a chord-morphing variant of the UH-60A Black Hawk helicopter at 20,000 lbs gross weight are presented. From the baseline rotor blade, the chord is increased from 63% to 83% of the rotor span by means of a trailing-edge plate (TEP) extension at a deployment angle of 2 degrees. Chord morphing at sea-level and hot-and-high conditions are considered. The controller is shown to regulate the operating state of the aircraft well over the nominal morphing duration of 60 seconds and also for reduced durations down to 15 seconds. Differences between baseline and morphed states are discussed. In addition, the performance of the controller with respect to rate of morphing is evaluated and the effect of asynchronous morphing is also considered.
Flight Dynamics and Control Modeling with System Identification Validation of the Sikorsky X2 Technology Demonstrator
Authors:   Sikorsky Aircraft Corporation, Fegely Cody ,   US Army Aviation Development Directorate (ADD), Tischler Mark ,   San Jose State University and US Army Aviation Development Directorate (ADD), Juhasz Ondrej , Xin Hong
Published: October 2024

Physics-based flight dynamic models are vital to the aircraft design process and are used for design loads prediction, flight control development, handling qualities evaluation, and in support of design and vehicle layout trade studies. These models must be validated with flight-data whenever available to increase confidence in model fidelity and to help determine model deficiencies. This paper presents the validation of coaxial compound helicopter flight dynamics models developed in GenHel and HeliUM by correlating with the X2TD flight test data. GenHel is the flight dynamics model used by Sikorsky and HeliUM is used at the U.S. Army ADD. Both modeling tools are modular in architecture, include flexible rotor blade models, and allow for complete free-flight analysis. Both tools have been extensively correlated against a variety of single-main-rotor flight test data. When applied to the X2TD configuration, both models show good correlation to flight data for steady-state and dynamic responses. The models accurately predict the bare-airframe X2TD frequency response from 0.2 to 1.0 Hz. Key modeling parameters are determined using an analytical model of the coupled rotor and fuselage, and then identified from flight data using system identification. When propagated back into the HeliUM model, the fidelity was increased to a larger frequency range and approached the response obtained from GenHel. The broken-loop and closed-loop behavior of the X2TD are also analyzed and match well with flight data.
Towards Generalized Certification of Slung Load Flight Envelopes
Authors:   Georgia Institute of Technology, Motahari Nicholas , Hiremath Nandeesh , Komerath Narayanan
Published: October 2024

An alternative is sought to individual full-scale flight testing in order to certify the safe flight envelope for every combination of helicopter and slung load. The major uncertainty has been the difficulty in obtaining reliable aerodynamic load maps for use in dynamic simulation. The possibility of reliable certification based on an iterative process is discussed. Knowledge bases with parametric variation of canonical shapes are now feasible using the Continuous Rotation method. The test case of an empty engine canister is considered. An initial estimate of dynamics based on interpolation from a canonical knowledge base shows surprising accuracy, when the initial level of perturbation is adjusted. This is followed with scale model experimental data at different levels of detail, compared to estimates from knowledge of the geometry and inertia. It is shown that initial perturbation level changes the amplification path, but the eventual divergence speed is uncertain to less than 10 percent. Higher perturbation levels cause lower divergence speed as expected. Intermediate amplification behavior is also captured.
A Python-based Framework for Real-time Simulation using Comprehensive Analysis
Authors:   University of Maryland, Rubenstein Greg , Sridharan Ananth , Moy David , Chopra Inderjit
Published: October 2024

This paper describes an open-source framework to use a rotorcraft comprehensive analysis with elastic blades and free wake for real-time simulation. Several acceleration strategies are combined with load-balanced parallelization algorithms to achieve this goal. Up to 24 times speed-up for trim, and 33 times speed-up for time marching were demonstrated for a single rotor system with 4 blades, allowing for 5 deg azimuthal time steps. Heterogeneous computing for accelerated analysis with free wake was also explored as a preliminary step towards real-time wake modeling. 23 times/29 times speed-ups were obtained with a GPU for a single rotor and coaxial rotor, respectively, compared to serial execution on CPUs. Lag-free communication between the analysis and a pilot interface is provided by a Python framework.
Performance Evaluation and Comparison of Dynamic Inflow Models for Rotorcraft Simulation
Authors:   Middle East Technical University, Guner Feyyaz , Gursoy Gonenc , Yavrucuk Ilkay
Published: October 2024

In this paper, well-known inflow models commonly used in rotorcraft simulations are applied to a blade element rotor model and compared with the isolated rotor wind tunnel tests of the main rotor of the S-76 helicopter in trimmed conditions. The paper provides side-by-side comparisons of steady state power estimations, collective blade angles, lateral cyclic, longitudinal cyclic inputs and coning angles in hover and forward flight trim conditions, when uniform inflow, linearly distributed inflow with Payne's coefficient, Pitt-Peters inflow model and Peters-He inflow model with higher harmonics are used. In addition, the differences in side and drag forces are shown in forward flight, when different inflow models are used. Inflow and angle of attack distributions over the rotor disk are compared at various flight conditions. Concluding remarks on the observed differences are given.
Humanitarian Operation Packaged Essentials From an Underslung Load
Authors:   US Army (NSRDEC), Tardiff Marc
Published: October 2024

Disasters, both natural and man-made, occur every year and can significantly impact a population near the disaster site. In some disasters, ground lines of communication and transportation may be damaged or destroyed making it impossible to quickly deliver aid via traditional methods. Aerial delivery provides humanitarian aid response within hours following a disaster. The currently utilized solutions present significant risk of injury to the underlying population from the descending items. Delivering a substantial volume of aid in a single container also raises concerns that the strong or weapon-wielding population will take control of the container and ration out the aid as they see fit. The goal of this paper is to document the design, development and testing of a helicopter delivery system that will deliver food and water over a population and significantly reduce the risk of injury from dispersed aid items over the population.
Development of the Multiple Bundle Sling Load System
Authors:   US Army (NSRDEC), Tardiff Marc , Matook George , Nyren Daniel
Published: October 2024

Airdrop is a process where a payload is released from an aircraft and allowed to fall to the ground, typically suspended under one or more parachutes. A challenge with conventional airdrop is the inability to maneuver payloads within the aircraft easily to be more flexible to mission needs. Rotary wing aircraft provide an additional challenge since they tend to fill the cargo compartment before they utilize the lift capacity of the helicopter. This paper documents the steps taken by the US Army Natick Soldier Research, Development and Engineering Center to create a materiel solution. The tests conducted at the Aberdeen Test Center demonstrated the feasibility of conducting multiple bundle airdrops from the cargo hook of a helicopter. Over 100 payloads of varying size, weight, parachute system, altitude, and drop configuration were demonstrated from rotary wing aircraft.
HH-60G Airframe Service Life via Multi-Element Damage Monte Carlo Risk Analysis
Authors:   Mercer Engineering Research Center (MERC), Branch Nathan ,   Tom Brussat Engineering LLC, Brussat Thomas , Wood Gregory
Published: October 2024

The United States Air Force (USAF) HH-60G Pave Hawk helicopter did not have a defined structural service life since it was originally designed for crash-survivability and economic replacement of all critical parts. To quantify the service life of HH-60G due to the onset of Widespread Fatigue Damage (WFD), the Mercer Engineering Research Center (MERC) created new Multi-Element Damage (MED) Monte Carlo risk analysis methods that utilize the available data provided by the HH-60G's Aircraft Structural Integrity Program (ASIP). The Single Flight Probability of Failure (SFPOF) calculated by the Monte Carlo programs show that the current maintenance strategy of annual visual inspections is not sufficient to reach a 20,000 Equivalent Flight Hour (EFH) target service life. This is due to the poor crack-detectability of visual inspections combined with the fast crack growth observed at hot spots on flight-safety critical structure. The risk analysis demonstrates that improving the quality and frequency of inspections reduces the SFPOF to acceptable levels and achieves the target service life of the aircraft.
A Training and Educational Demonstration for Improving Maintenance Practices
Authors:   University of South Carolina, Edwards Travis , McCaslin Rhea , Bell Eddie , Bayoumi Abdel , Eisner Lester
Published: October 2024

Improper and unnecessary maintenance actions can result in a waste of resources, time, and money. Training and education play a vital role in maintenance implementation and can be used to prevent improper maintenance procedures. The Center for Predictive Maintenance (CPM) has developed a demonstration framework and tool that can be used to educate and train users extending from maintainers to leadership on the maintenance process from fault to maintenance action. This demonstration tool will walk an audience through the maintenance process starting with the collection of sensor and historical data, and how it is then integrated to create predictive models. Finally, the data and results are displayed in unique dashboards that provide personnel with the information needed to make educated decisions on the condition and maintenance of their system.
Evaluation of Future Helicopter Powertrain Concepts Regarding Flight Mission and Operational Aspects
Authors:   Technische Universitaet Muenchen, Kerler Martin , Erhard Wolfgang , Heibel Yvonne
Published: October 2024

Environmental and operational requirements will get more and more challenging in the future. Helicopter and power plant manufacturers face this with new helicopter and powertrain concepts. Currently, more electric and all-electric aircrafts are investigated. Research has shown that an all-electric helicopter is not feasible right now. But hybrid concepts may be possible. In a retrospective view, new technologies and improvements rarely find application at the forecasted time. Because of that, four different future helicopter powertrain concepts are discussed with a technology level achievable in 15 to 20 years. The powertrain concepts are compared to a baseline powertrain with two conventional gas turbines at a future technology level. The powertrains are combined with three different generic helicopters of two weight classes. The helicopters represent an expectable technology level of the year 2030. The masses of the powertrains are evaluated and compared. Challenges of realization are identified. With a helicopter performance tool the helicopters and powertrains are simulated with respect to payload range capabilities and mission related performance. The results are discussed. Hybrid powertrain concepts are only feasible for lighter helicopters. Diesel engines are too heavy for high power requirements. Also batteries have to get lighter and more powerful to meet aviation requirements. An intermediate step can be the further development and improvement of gas turbines for power supply.
Bringing Direct Bolt Preload Measurement to the Aerospace Industry
Authors:   Bell Helicopter Textron Inc, Chavez Andrea ,   Aviation Development Directorate - Aviation Applied Technology Directorate, Fetty Jason ,   Intellifast, Meisterling Jesse , Baker Treven
Published: October 2024

Many helicopter components are held together with fastened joints that include threaded bolts. Bolt preload is important for keeping fastened joints from loosening or sliding. In the aerospace industry, bolt preload is typically set by applying a specified torque. Common procedures for clamping a joint include the use of a calibrated torque wrench to apply the specified torque. While a torque wrench will display the torque applied to a clamped bolt assembly, the preload (or bolt tension) must be inferred. However, a significant factor relating applied torque to the acquired bolt tension is the friction between the bolt threads and joint interface. Tension measurement techniques are available in the aerospace industry, but they are not common. A small amount of contamination or lubricant can significantly alter the torque-tension relationship. Under the Future Advanced Rotorcraft Drive Systems (FARDS) agreement, Bell Helicopter, IntellifastTM, and the Army Aviation Development Directorate (ADD) - Aviation Applied Technology Directorate (AATD) developed and tested a technology that directly measures the tension in the bolted flexure joints of a KAFLEX drive shaft coupling. The main purpose of testing was to validate bolt tension measurement to demonstrate the Technology Readiness Level (TRL) suitable for flight test. Testing performed under the FARDS agreement for this new technology included measuring the variation in bolt preload when set to a specific torque and then dynamically testing the joint to simulate flight time. Correlation was obtained between joint movement and the reduction in bolt preload. This paper summarizes the test results and shows the importance of directly measuring bolt preload in a fastened assembly to ensure joint integrity.
A Physics-based Tribology Model and Parametric Assessments of Loss-of-Lubrication Using Reduced-Order System Level Analysis
Authors:   The Pennsylvania State University, Yu Qingtao , McIntyre Sean , Kunz Robert , Chang Liming , Bill Robert
Published: October 2024

A newly-developed tribology model is integrated with a reduced-order heat transfer model to construct a simulation platform which is used to conduct system-level simulation of transient multi-physics loss-of-lubrication (LoL) operation of a high-speed gearbox. In the simulations, the processes of increasing gear bulk temperature and of oil depletion are transient. The former is captured by the reduced-order heat transfer model, and the latter is studied parametrically. A nominal problem is studied based on LoL tests of involute spur gears by NASA Glenn. The simulation results qualitatively capture the trend and scale of the "thermal run-away" observed in the experiments. Parametric analyses are carried out to demonstrate the capability of the simulation platform to guide design optimizations in various aspects, including gear configurations, material considerations and secondary emergency lubrication systems.
Implementation of the Product Equipment List to Further Enhance Safety on Commercial Rotorcraft
Authors:   Sikorsky Aircraft Corp., Hepner Stephen , Bufort Jessica
Published: October 2024

This paper will discuss how Sikorsky's Aviation and Product Safety (A&PS) Organization is actively promoting a recently developed initiative known as the Product Equipment List (PEL) to enhance safety on their commercial aircraft models. The PEL initiative is managed by a committee of individuals with extensive experience in areas of rotorcraft system safety, accident investigation, pilot operations, engineering design and development, marketing and sales, litigation management, and customer support. The committee oversees a classification tool that separates optional and regulatory safety equipment for customers during final aircraft purchase. Sikorsky takes the initiative to ensure the customer fully understands the potential consequences of removing optional safety equipment from the final purchase configuration.
Standardization of Rotorcraft Guidelines for Quantitative Risk Assessment
Authors:   Sikorsky Aircraft, Braman Gary , Hewitt John
Published: October 2024

Sikorsky Aircraft Corporation (SAC) uses Quantitative Risk Assessment (QRA) to accurately predict future risk by first analyzing the risk without corrective action (uncorrected risk), and then analyzing the risk with specific mitigating actions implemented (corrected risk). However, Sikorsky and the aviation industry do not have standard QRA Guidelines for predicting future risk. In an attempt to resolve this issue, SAC sponsored a Benchmarking event to document the basis of the established QRA guidelines used internally at SAC and at the same time develop and implement standard QRA guidelines for use in the rotary wing aircraft industry. The benchmarking event was conducted through a series of meetings where current industry and FAA guidelines were discussed with new guidelines being developed. The benchmarking process resulted in the significant milestone of industry/government agreement on uniform definitions and risk guidelines for all rotorcraft and for engines installed on multi engine rotorcraft. The new guidelines were adopted by the group and have been incorporated into the FAA Rotorcraft Risk Analysis Handbook for application in the rotary wing aircraft industry.
Alternate Characterizations of Fatigue Load Spectra
Authors:   US Army Aviation Engineering Directorate, E. Robert , Howell Stephen
Published: October 2024

This paper improves prior efforts to provide a framework for fair, early, and meaningful assessment of rotorcraft fatigue durability. The authors provide methods to determine fatigue damage accumulation in accordance with piecewise exponential density functions, which represent the load spectra in a manner that is more manageable to the reader than prior efforts. The particular load spectra under consideration are for a conventional rotorcraft performing a scout mission. New formula are derived to calculate exceedances and cumulative damage fraction. Normalized critical endurance limits are determined for the range of expected fatigue curve shape parameters, and charts compare results to allow readers to obtain a sense of the sensitivity to selected curve-fit basis functions. A traditional curve-fit metric (the standard error of the fit) is used to determine and control the quality of the parameterization. Prior results are confirmed by application of the newly derived and independent method.
Tribological Testing of PEEK for Aerospace Applications
Authors:   SKF Aeroengine North America, Allison Bryan
Published: October 2024

Polyetheretherketone (PEEK) is a popular material for high performance bearing cages. It is now being considered for aerospace drive train applications due to the 80% weight savings compared to steel, but gaps remain in the understanding of PEEK's tribological performance. In this study, wear testing was performed to investigate the tribological performance of fiber reinforced PEEK under conditions that were representative of a typical aerospace drivetrain application. It was found that the processing conditions used can have a significant effect on the wear resistance. Further, it was found that both of the optimized PEEK materials tested experienced significantly less wear than the silver plated steel used as a baseline. Finally, it was determined that the friction loss of a PEEK bearing cage is expected to be higher than that of a silver plated steel one, but is still quite low with a coefficient of friction of approximately 0.02-0.03.
Very-High Cycle Fatigue Testing Under Spectrum Loading for Endurance Limit Structural Design
Authors:   NAVAIR SYSCOM, Rusk David , Taylor Robert , Pregger Bruce , Sanchez Luis
Published: October 2024

A program has recently concluded that generated fatigue test data for the influence of a rotorcraft main rotor blade root bending spectrum (Helix) on the crack nucleation mechanisms in 7075-T651 aluminum. High frequency tests were performed that generated spectrum fatigue failures out to nearly 10⁹ cycles. Fractographic examination showed a distinct change in crack nucleation from slip initiated to inclusion initiated cracking as the spectrum peak stress level was increased. Spectrum life predictions were made using three different baseline constant-amplitude S-N curves, one using a traditional rotorcraft OEM fitting methodology, one using the HCF portion of a strain-life curve, and one that was fit to S-N data with test lives out to 3x10⁸ cycles. The spectrum life prediction using the S-N curve that properly modeled material behavior in the Very High-Cycle Fatigue (VHCF) regime provided a good correlation to the spectrum fatigue test data. Predictions using the other S-N curves were highly conservative.
Use of Global and Local Finite Element Analyses to Investigate Peak Stress in Fastened Joints, Validate Structural Repairs, and Design Preventative Structural Modifications
Authors:   Columbia Helicopters Inc., Solem Courtney , Pilkington Larry , Royce Anna
Published: October 2024

Columbia Helicopters, Inc. (CHI) has created the Fuselage Fatigue Assessment Program as a tool to evaluate the stress distribution of an airframe, design structural modifications, and predict the life of a part. This program uses an airframe FEM to analyze and determine the stress distribution in the airframe. The results from the airframe FEA will reveal areas of peak stress in the airframe. Local FEMs of the areas showing peak stress are built and analyzed to detail the stress distributions to specific parts and/or fasteners and define an effective stress concentration factor which is used to predict the life of the part. A preventative structural modification can be designed to lessen the peak stress. Finally, the designed modification is validated back to the local and global FEMs to verify the stress has been appropriately distributed to the rest of the airframe.
Dual-Use Structures: Composite Wing with Structural Antenna Aperture
Authors:   The Boeing Company, Tyrell Stacey ,   US Army AMRDEC ADD, Robeson Mark , Kube Courtney , McCarthy Dennis , Lavin Ronald
Published: October 2024

Many modern aircraft, including rotorcraft, require conformal antennas and fairings to reduce wind drag, ice accretion, lightning strikes, and impact damage. An innovative composite wing configuration with a structural Ultra High Frequency (UHF) antenna window "aperture" has been developed. The wing is based on variants of lightweight X-Cor® sandwich core technology for durability and damage tolerance, with tailored electromagnetic properties in the aperture region of the wing. This paper presents a brief introduction to helicopter wings, a summary of recent research at Boeing and Army leading to this design, and the development approach used for this project. Structural and electromagnetic analyses are provided, and measurement results of an early prototype are summarized. The emphasis of this paper is on the wing configuration details surrounding the antenna aperture. The approach can be replicated on almost any current or future aircraft or rotorcraft.
Design and Flight Test of an Adaptive Vehicle Management System on an AH-64 Helicopter Demonstrator
Authors:   The Boeing Company, Klein Gary , Kashawlic Bryan , Enns Russell
Published: October 2024

The three and a half year Adaptive Vehicle Management System (AVMS) Phase II program developed technologies in the areas of tactile-cueing based carefree maneuvering, maneuver aiding, and mission aiding. It also flight tested these technologies on three platforms, an H-6 Little Bird technology demonstrator, MH-47G Chinook, and AH-64 Apache. This paper focuses primarily on the results from testing the AVMS technologies on the AH-64 Apache helicopter. In summary, the results show a significant improvement in mission productivity, workload, performance, and handling qualities. These results substantiate the hypothesis that the AVMS technologies provide significant, positive impacts on attack helicopter platforms and it proves AVMS technologies can improve multiple metrics simultaneously without the expense of impacting the other metrics.
The 525 Transmission Development Test Stand
Authors:   Bell Helicopter Textron, Elliott David
Published: October 2024

Testing of high speed / high power helicopter transmissions is required to meet regulatory requirements and promote product safety. Transmission development testing typically ranges from 18 months to two years and involves tests that include; Oil Management, Gear Tooth Pattern Development, Gear Tooth Bending Fatigue, Endurance and Loss of Lubricant Testing. To accomplish these goals for the Bell 525, Bell Helicopter has developed new electrically regenerative test stands that both deliver and absorb power in the drive path. These new test stands provide a means to test the transmissions of other helicopter models with minimal changes, resulting in lower development costs. The transmission test system utilizes electric motors on the input side of the drive system and a generator on the output. While full power is passed through the drive system, the regenerative cycle means that net power consumed is limited to just the electrical and drive system losses - a small fraction of the drive system power. This paper reviews the design approach of the 525's electrically regenerative test stand and compares this system to prior mechanically regenerative test stand designs. The new approach, allows Bell Helicopter to achieve enhanced test efficiency resulting in faster development cycles and direct savings to the customer.