Browse Topic: Test facilities
This organizational process survey provides insight into the technical aspects of approved airworthy aircraft modifications applied in government organization vertical lift flight test. The publication reviews processes applied by the National Research Council of Canada's Flight Research Laboratory (NRC-FRL) and its Airworthiness Control System to enable research flight testing. Dominated by the need for integrating experimental payloads, the NRC-FRL embeds a Design and Fabrication Service organization for modification of internal and external client projects and flight test aircraft. In context of experimental flight testing, this work reviews technical information on process, facilities, and methodology for airworthy integration of flight test payloads. Information is used to synthesize recommendations in experimental vertical lift flight testing that satisfy both formal (regulated compliance) and informal (compliance intent) airworthiness requirements.
This study examines the capability of medium-fidelity comprehensive analysis models to predict the acoustics for manned and unmanned rotorcraft configurations. Using the automated tool NDARC2RCAS developed at DEVCOM Army Research Laboratory, multiple configurations including a single main rotor, tilt rotor, coaxial and pusher, quadcopter, and hexacopter are evaluated at various mission segments including hover, advancing climb, and forward flight. Each configuration and condition is evaluated using a range of aerodynamic models from lower to higher fidelity, including uniform inflow, dynamic inflow, prescribed wake, free wake, and viscous vortex particle method (VVPM). These evaluations are then used with another automated tool, RCAS Acoustics, to predict noise on a Voronoi observer sphere. A comparison of the results for the single main showed good agreement between all of the aerodynamic models except VVPM. For the tilt rotor in forward flight, the higher-fidelity models produced changes in rotor loads due to the interaction with the wing. With prescribed and free wake models, this change in load is sharp and causes noise increases of up to 40 dB in front of and behind the vehicle, while the VVPM model produced a smoother change that results in a smaller, 20 dB increase in noise. The quadcopter and hexacopter show similar in-plane noise levels for all models, with alternating cancellation and amplification patterns due to rotor phasing, while out-of-plane noise is increased on the hexacopter when using the higher fidelity models.
With recent advancements in the field of Advanced Air Mobility (AAM), including Electric Vertical Takeoff and Landing (eVTOL), Remotely Piloted Aircraft Systems (RPAS), and Unmanned Aerial System (UAS), it is beneficial to understand the impact of complex flow features on operations in urban and shipboard environments. Testing methods for studying these impacts, including simulated environments such as wind-tunnel flows and engineered equivalence tests, will need to be adapted to prepare for when the vehicles of interest are too large for the available testing facilities, and to permit low-cost alternatives for industry and government. This work demonstrates a development process that can be used to ensure the complex-flow-environment phenomena can be studied. First, this work illustrates the development of downdraft and turbulence flow types in a wind tunnel setting, and assesses the response of an M600 RPAS to these flows. Then, the same parameters are compared for a Mission Task Element (MTE) that was designed to challenge the RPAS in the vertical direction. Comparison of the two data sets provides insight into both the behaviour of RPAS in complex flows and the challenges of developing engineered equivalence tests.
Future military missions for Agile Combat Employment (ACE) and next generation Special Operations Forces need an aircraft with effective hover and the ability to operate in transonic cruise. Hover requires significant power that can only be mitigated by larger diameter rotors, but large diameter rotors become a detriment to achieving transonic flight. The stop-fold rotor configuration can “make the rotor disappear” in cruise and stands out as the most viable option for meeting these next-generation air vehicle requirements. This paper discusses the progress Bell has made in developing enabling technologies for a practical and scalable high-speed VTOL (HSVTOL) based on the stop-fold configuration. To this end, a unique Track-Guided Test Vehicle (TGTV) was developed at Bell and tested at the 10-mile High Speed Test Track at Holloman Air Force Base. The test vehicle integrates all subsystems required to demonstrate the key technologies in a representative environment, including multi-mode propulsion, folding proprotors, and fly-by-wire transition controls to automatically manage each step of the prop-to-jet (and reverse) process. The TGTV demonstration validated the stop-fold technical approach and generated critical data to substantiate engineering models. Test results provide confidence that each step in the stop-fold transition process is thoroughly understood and that engineering tools can be used confidently for future aircraft design efforts. This paper documents the first known powered prop-to-jet and jet-to-prop transition and represents a significant milestone in vertical flight technology development.
Helicopter pilots are exposed to a wide range of vibration frequencies, primarily generated by engine and rotor dynamics. These vibrations, particularly within the 0.5–80 Hz range, pose significant risks to pilot health, including musculoskeletal injuries and fatigue. To mitigate these effects, vibration isolators are employed, with passive and active isolation systems offering different advantages. This study investigates the initial design and performance of a novel metal additive manufactured vibration isolator, optimized for placement under the pilot's seat in a rotorcraft simulator. The isolator was designed with key structural parameters including stiffness, coil dimensions, and material properties while maintaining a lightweight and durable form, with a primary goal of validating the additive manufacturing of a metallic isolator. Experimental corroboration was conducted by incorporating modifications to the Gannon Biomechanics Flight Simulator test stand (GBFS), comparing the novel isolator to an elastomeric isolator. Results demonstrate the successful fabrication of the initial additive isolator design. The additive isolator displayed a similar performance to the rubber isolator after being installed in the GBFS, though limitations on the current test rig and sensing configuration did not allow accurate characterization of the transmissibility. This research sets the groundwork for further development of a novel additive isolator and test facility.
This study presents computational analyses of coaxial rotor hub flows and validation against experimental data obtained from the fifth Rotor Hub Flow Prediction Workshop. Experiments were conducted in a 12-inch diameter water tunnel at Pennsylvania State Applied Research Laboratory, employing tomographic particle-image velocimetry (Tomo-PIV) and precise hub drag measurements. Three CFD codes (UMD Mercury, CREATETM-AV Helios, and OVERFLOW) utilizing hybrid Reynolds-Averaged Navier-Stokes (RANS) / Large Eddy Simulation (LES) modeling based on Spalart–Allmaras turbulence model, were applied to replicate and analyze hub flows. Counter-rotating coaxial rotor hubs under free-air condition was simulated as the simplest case and the hub drags are compared between the three CFD codes. The full water tunnel configuration, consisting of two hubs, a fairing, and shafts, was also simulated and compared to experimental results, with a focus on hub drag, wake velocity fields, and turbulence quantities. Results demonstrated that the computational frameworks effectively captured key flow physics, although some discrepancies in drag harmonics, wake velocity and turbulence intensity magnitudes were observed. Additionally, the study highlighted the impact of rotor hub geometry and installation of sail-fairing on drag and wake structures. These findings contribute to improve computational predictions, essential for designing high-speed rotor hub configurations.
Design modifications to a 3lb variant of DEVCOM Army Research Laboratory's Common Research Configuration (CRC-3) are assessed using simulation tools. To identify areas for improvement, the baseline CRC-3 is analyzed in hover and forward flight, and contributors to overall power consumption are identified, with the rotor drag consuming the greatest amount of power, due to the high rotational speeds required to maintain thrust in the face of the freestream velocity. Potential areas for improvement are identified as: wing airfoil, rotor blade pitch, and rotor orientation. Changing the airfoil has little to no measurable effect on the overall power consumption. Increasing the blade pitch improves cruise performance considerably, but at the cost of hover efficiency, for an overall range improvement of up to 28%. Changing the rotor orientation improves rotor efficiency as well, without substantial cost to hover power consumption, increasing the range by 37% but will require a redesign of the CRC-3 supporting structure to avoid the blades striking the structure. Experimentally determined trim sweeps of pitch and power requirement are shown for the quadrotor, tailsitter, and three different wing incidence angles (10◦, 20◦, and 40◦), showing up to 28% reductions in minimum power.
A computational study is conducted on a coaxial rotor hub and sail fairing configuration to analyze hub surface forces and the characteristics of its downstream wake. The flow conditions and grids are based on experimental tests performed at the Penn State Applied Research Lab (ARL) Water Tunnel at a baseline Reynolds number. Grid development for the rotor hubs and sail fairing is done using Pointwise v18.04R1 and Chimera Grid Tools (version 2.2). Simulations are performed using NASA's OVERFLOW2.4b Reynolds Averaged Navier-Stokes solver. The drag forces on the rotor hubs are computed and compared to standalone drag data to analyze the effects of interactional aerodynamics. Flow features, frequency content and Reynolds stresses of the wake are analyzed. Frequency content and Reynolds stresses show clear spatial bias. The anisotropy of the Reynolds stresses is computed and used to determine the character of the wake turbulence.
ABSTRACT A full-scale Reynolds number water tunnel experiment was performed to generate a data set used to analyze the effects of helicopter rotor hub wake impingement on a canonical horizontal stabilizer. The experiment was designed and performed in the Pennsylvania State University Applied Research Laboratory Garfield Thomas Water Tunnel, where a 10.5 inch constant chord stabilizer was placed in the 48-inch diameter test section downstream of a 1/4 scale helicopter hub. Two rotor hubs were tested, a baseline configuration and a low-drag model. The stabilizer was mounted in the long-age wake. Lift, pitching moments, and unsteady pressures were measured on the horizontal stabilizer at a Reynolds number of 0:9x10⁶, 1:8x10⁶ and 2:7x10⁶, corresponding to hub diameter-based Reynolds numbers of 2:2x10⁶, 4:3x10⁶, 6:5x10⁶ and rotor advance ratios of 0.1, 0.2, and 0.3. The hub-wake interaction results were compared to a baseline airfoil test, which was performed without a hub upstream. Pressure sensors were used to evaluate wake unsteadiness impinging on the horizontal stabilizer. The horizontal stabilizer in clean flow exhibited lift and pitching moment in agreement with XFOIL predictions. With the low-drag hub upstream it measured lift fluctuations at a frequency of 2/rev, 4/rev, 8/rev and 12/rev. Downstream velocity and pressure fluctuations of 2/rev 4/rev and notably 6/rev were measured with the baseline hub upstream. Drag reduction on the low-drag hub was measured to be >25% compared to the baseline hub at full-scale Reynolds number. Both drag and wake harmonics measured at the hub and downstream on the stabilizer were found to be dependent on the upstream hub geometry. Pressure frequencies taken on the horizontal stabilizer yielded similar results and were consistent with those measured via the force balance.
The paper presents recent and ongoing activities of the German Aerospace Center (DLR) focusing on experimental icing investigations within the nationally funded project InTEnt-H (2018-2022) and progressive activities in continuing internal DLR projects. The aim of InTEnt-H was to investigate innovative de-icing and anti-icing technologies for small and medium-weight helicopters, for which no rotor de-icing technologies exist to date, and to demonstrate the effectiveness of these systems in a suitable test facility. For this purpose, the whirl tower test facility of the DLR in Braunschweig has been converted into an icing test facility that is unique in Europe and will allow for the generation of atmospheric icing conditions. In this facility, de-icing and anti-icing systems for rotor blades can be tested under centrifugal loads and various icing conditions. The paper starts with a short presentation of the retrofitting works at the DLR whirl tower test facility and its major components. Then, the progress of the first test campaigns of the projects are reported. The main focus is on the design and test of the de-icing rotor system, carrying different antiicing/ de-icing technologies. The paper closes with an outlook on the upcoming activities planned to satisfy and verify EASA CS-29 Appendix C icing conditions in the frame of the DLR internal project SAFER2.
ABSTRACT Pressure Sensitive Paint (PSP) rotor hover predictions are obtained using computational fluid dynamics simulations. Laminar-turbulent transitional modeling predictions are made with the OVERFLOW 2.2 compressible flow solver on structured, overset grids. Solutions are generated based on a tip Mach number of 0.58 for varying collective pitch angles. In addition to isolated rotor predictions, results are generated for rotor-fuselage interactions using the PSP rotor and Rotor Body Interaction (ROBIN) fuselage. Hover performance is assessed and compared to available measurements obtained in the NASA Langley Research Center Rotor Test Cell (RTC). Grid generation techniques and computational methods for both cases are described. Rotor flow field behavior and transition locations are discussed for both cases along with the impact of transition modeling.
This paper presents activities performed in the frame of MOTUS, a DGAC-funded research project, to better understand and reduce annoyance of helicopter operations. It focuses on the operational context of La Réunion island where local authorities intend to define concrete measures to answer multiple complaints from the population. In parallel with ongoing research towards a better understanding of short- and long-term annoyance thanks to both laboratory and field studies, the paper presents an in-depth analysis of helicopter operations in the area. Furthermore, specific recommendations on low noise operations are proposed to local operators in order to reduce their noise footprint and improve helicopter acceptance.
This paper describes the methodology, involving testing and simulation activities, to assess malfunction conditions of complex systems installed on fly-by-wire vehicles, including the evaluation of their effects. This paper provides also a description about how the system malfunction tests are designed, driven by input requirements and systems capability and behavior. With respect to prior publications, this paper includes some practical test examples, based on systems monitoring, logics and alerting functions. The case study described here comes from a portion of multiple laboratory certification tests done for AW609 Tiltrotor, focused on Avionics System malfunctions. These tests and simulations are a valuable Means of Compliance with respect to applicable airworthiness rules, and a suitable means to verify the design safety requirements. Three relevant examples are presented, grouped by input requirement and safety conditions. The effect of such malfunctions is evaluated, with respect to the Avionics System output produced to keep adequate flightcrew awareness about the vehicle status.
This study models the interaction of a two-bladed 14" propeller with the ground under different configurations using actuator disk method (ADM) where the rotor is modeled using unsteady momentum sources distributed over the entire disk. While ADM has been extensively used for standard rotorcraft analysis, it's performance in unconventional operating conditions remains an open question. Exhaustive experiments conducted at DEVCOM Army Research Laboratory are compared with ADM to evaluate the inexpensive method's ability to predict rotor loads for parametric variations in rotor-ground interaction scenarios. Partial ground effect (part of the rotor operating IGE), side-by-side rotors in ground effect and variation in IGE pitch attitude are specifically considered in this study. ADM generally predicts the thrust increase in partial ground effect (PGE) as the rotor goes from OGE to IGE although the increase is somewhat earlier and milder than measured in experiments. Side-by-side rotors in ground effect are predicted remarkably well by ADM which captures the fountaining flow between the rotor wakes as well as reduction in thrust seen compared to IGE in experiments. Finally, pitch attitude variation cases showed reasonably good agreement in trend at lower angles although ADM shows a more gradual drop in thrust at higher angles (beyond 15◦) compared to the sharper drop seen in experiments.
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This SAE standard establishes the requirement for suppliers to plan a reliability program that satisfies the following three requirements: a The supplier shall ascertain customer requirements b The supplier shall meet customer requirements c The supplier shall assure that customer requirements have been met
This paper reports on the current state of experimentation and deployment of the PMM method within the Design Office of Airbus Helicopters (AH). It shows that it is possible to efficiently carry out a system engineering process based on modeling and simulation (MS4SE). It is based on simulation tools that are widely available and known to engineers in the practice of their disciplines. The PMM method has not yet been used at AH on a complete helicopter program. This is owed in part to the too recent emergence of PMM. However, PMM has gone through several qualification stages in the form of Proofs of Concept (POCs) and pilot projects conducted directly in relation with operational teams and engineering disciplines interested to PMM for the greatest benefit of end users. The paper presents results for each stage of the development cycle paying a particular attention on both ends of this cycle: from the development of the operational concept and the validation of the top-level specification to the final verification of a helicopter function on an integrated helicopter test laboratory.
Unsteady boundary layer transition predictions are performed on a four-bladed rotor in hover using a computational fluid dynamics approach. Simulations are performed using the NASA OVERFLOW 2.3 solver with hybrid RANS/LES and laminar-turbulent transition modeling. Solutions are based on a hover tip Mach number of 0.143 with prescribed dynamic pitching conditions. The configuration is based on experiments performed at the German Aerospace Center (DLR)in the 1.6-mx3.4-m wind tunnel in the rotor test facility (RTG). Computational methods and grid generation are described. The rotor flowfield is analyzed and the effect of transition modeling on unsteady boundary layer transition prediction is assessed. Laminar-turbulent transition predictions and rotor performance are compared to experimental measurements obtained at the DLR RTG.
The objective of the joint National Research Council of Canada (NRC) and The Boeing Company Technology Development Program (TDP) entitled 'Canadian Vertical Lift Autonomy Demonstration' (CVLAD) is to evaluate automated and supervised autonomous flight systems on NRC Bell 412 Advanced Systems Research Aircraft (ASRA) and Royal Canadian Air Force Boeing CH-147F Chinook demonstrators. Boeing technologies such as Degraded Visual Environment Pilotage System and Advanced Vehicle Management System form the foundation of an autonomy solution that aims to satisfy Royal Canadian Air Force, US Army, and other Armed Service branch end-use objectives for force multiplication, tactical advantage, pilot assistance, reduced crew operations, and enhanced fleet productivity. The Boeing Company engaged NRC under a Cooperative Research Agreement since 2016 as part of a number of strategies to upgrade Medium-Heavy Lift H-47 Chinook capabilities prior to long-term aircraft replacement in the 2030 to 2060 timeframe. A recent achievement of the CVLAD TDP by its Boeing Phantom Works, Boeing Chinook Program, Aurora Flight Sciences, and NRC Flight Research Laboratory team was the development of Automated Flight Guidance methods addressing system safety and performance. Design and evaluation activities occurred in Boeing Software-/Hardware in-loop facilities as well as on the NRC Bell 412 ASRA. The CVLAD team is using a blend of traditional Systems Engineering 'V-Shaped' Life Cycle Model, System of Systems, and Model-Based processes to develop a cyber-physical system that aims to meet end-user concept of operations and requirements. Significant benefits of virtual development tools such as component-vehicle digital twins and surrogate inflight simulation facilities are achieved as they promote effective collaboration, efficient design, and relevant verification/validation methodologies. Business models can be made more robust by phasing the introduction of technology where effective automation provides users with near-term benefits, while providing a foundation for safe, reliable, and trusted autonomous capabilities for long-term production.
Washington State University researchers have developed a technology that is more than 30 times more sensitive than current lab-based tests in finding early stage cancer biomarkers in blood.
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