Browse Topic: Test equipment and instrumentation
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.
While known and largely studied, the Vortex-Ring-State (VRS) phenomenon remains the cause of numerous accidents every year and many questions are still open. In order to better understand the VRS phenomenon on different kinds of helicopters and to evaluate the effectiveness of recovery manoeuvres such as the one proposed by Capt. Vuichard, the European Union Aviation Safety Agency (EASA) launched the Helicopter Vortex-Ring-State Experimental Research project (EASA.2022.C11). Both objectives required to set-up flight test campaigns on two helicopter types, with a total of eight flights performed during the project. In addition to the description of the procedures that such flights required, the paper presents the Flight Test Instrumentation used and the analyses of the flight test data, including vibration measurements. Thus, flight conditions at which the VRS starts to develop, main parameters that influence and contribute to VRS symptoms and effects, or the effectiveness of the recovery techniques currently applied are presented and discussed in this paper.
A cooperative flight test campaign between the US Army and NASA was performed. This test sought to characterize the acoustic emissions of a fully instrumented MD530F helicopter using a snapshot array and a phased array of microphones. The snapshot array of microphones aimed to provide even coverage across the surface of a hemisphere, providing an acoustic emission hemisphere in a single 'snapshot' of time. The phased array of microphones was designed to provide enough resolution to determine noise sources from each individual blade as well as perform source separation from main rotor and tail rotor emissions. Test conditions for the characterization effort were chosen using a traditional one-factor-at-a-time approach as well as three design of experiment approaches. Characterization conditions included constant speed level flight, descent, and ascent conditions. Transient maneuver conditions were also captured over the snapshot array. The vehicle instrumentation included measurements of pilot controls, optical sensors to measure blade azimuth locations, pitch link loads, along with strain gauges to measure structural loads, blades and fuselage. This report will provide an overview of the test, document the data acquired, and provide some initial results.
This paper will present the use of a licensed open-source software application based on commercially available off-the-shelf hardware for the control and data acquisition of aerospace system integration test rigs. System integration test rigs are complex systems requiring real-time deterministic control and high-speed data acquisition. Various aircraft flight systems and subsystems can be tested to see if they interact as they would on the aircraft without an airframe. These systems are critical to ensure interoperability during the development phase and facilitate the interchangeability of actual flight hardware, prototypes, and simulation models throughout the development cycle. Deploying open, flexible, and highly configurable real-time control and data acquisition systems ensures that development milestones will be achieved cost-effectively, whether using actual flight hardware or working with a simulation. This is because, as the prototype hardware is developed, the remaining aircraft systems can still be tested by interacting with the model.
AAM concepts use multiple distributed electric motors driving propellers and rotors to augment or directly generate lift and propulsive forces. Several current concepts incorporate separate drive systems for providing vertical lift, for takeoff and landing, and propulsive thrust for wing-borne cruising flight. Measurement of loads and performance on these rotating systems is very important in both the design and development stage, as well as for certification use and ultimately supporting HUMS monitoring. However, providing instrumentation in the rotating frame and extracting their associated measurements is often problematical, as it requires some means for both power and signals to bridge the rotating interface between the blade of the rotor/propeller and the fixed frame (fuselage) system. This paper describes work conducted to leverage prior CDI development of a novel optical telemetry/instrumentation system to create a prototype unit that can support ground and flight tests, allowing for multiple installations on the many rotors that constitute current AAM configurations. The resulting hardware was designed to expand the capabilities developed previously in types and rates of data collected, on-board processing, and user configuration options, supporting NASA and commercial organizations in their testing activities.
Aircraft with small speed-controlled propellers are becoming increasingly popular. This is conspicuous in the commercial sector, but also evident in the defense sector. Proof of the latter is the Army's Air Launched Effects (ALE) program, which aims to develop foldable, tube-launched Unmanned Aerial Systems (UAS). Such aircraft will likely use small speed-controlled folding propellers, which have unique geometry and limited publicly available data making it difficult to characterize their performance. This paper concerns performance testing of a small speed-controlled folding propeller in the U.S Army's 7- by 10-foot Wind Tunnel at NASA Ames Research Center, utilizing a new test rig that aerodynamically isolates a propeller's blades. The results of the test are presented, which include thrust and efficiency measured at various pitch angles, rotational speeds and wind speeds. Useful and expected trends are identified in the data, such as the peak efficiencies increasing with increased RPM, wind speed and blade pitch.
Mercer Engineering Research Center (MERC) is supporting Naval Air Systems Command (NAVAIR) in the determination of external airframe loading requirements and test rig design support for an MH-60 full scale fatigue test demonstrator project being conducted in collaboration with the Australian Defence Science and Technology Group (DST Group). The analyses included determination of loads for quasistatic and vibratory flight conditions, sensitivity of the structural response to the loads, displacements at actuators across the MH-60R usage spectrum, and feasibility of driving aircraft vibrations at frequencies lower than those measured in flight - specifically, obtaining vibration levels measured at 17.2 Hz by imposing forces at only 2.15 Hz. The studies also addressed the minimum number and locations of actuators required for static and vibratory loading.
This paper reports an overview of the experimental and analytical activities carried out in relation to the identification of the more severe limit load conditions for the AW169 Main Rotor components, with particular attention to the Main Rotor Tension Link. The entire interdisciplinary process involving the set up as well as the validation of the aeroelastic software used, the setup of the validated FE Model of the Tension Link related to both the helicopter installation and the Test Rig, the definition of the criterion used to select the more severe limit conditions will be extensively described. Particularly, the definition of a simple criterion able to restrict the number and the typologies of conditions to be simulated proved to be very useful in reducing the computational time involved in the simulation of several dozen conditions. The approach described here, although related to a specific part with specific characteristics, can be generalized to any other complex part loaded by multiple forces and tested in a Test Rig which, due to implementation constraints, cannot fully represent the real helicopter installation.
This paper describes the features, specifications, and instrumentation of a new tiltrotor test rig at the University of Maryland, the Maryland Tiltrotor Rig (MTR). The MTR is a semi-span, floor-mounted, optionally-powered rig with a static rotor tilt mechanism, capable of testing proprotors of up to 4.75-ft diameter in the Glenn L. Martin wind tunnel (7.75- by 11-ft section with 200 kt maximum speed). It supports interchangeable hubs (gimballed and hingeless), interchangeable blades (straight and swept tip), and interchangeable spars, to allow a systematic variation of components important for tiltrotor flutter and loads. The baseline rig dimensions are 1/5.26 scale XV-15 or 1/8 scale V-22. The principal objectives are to measure tiltrotor instabilities in cruise and vibratory loads in conversion. Additional objectives are airloads, drive system loads, rotor-wing aerodynamic interactions, and closed-loop control of loads and instabilities. The baseline rig is a gimballed hub. It is complete, all components fabricated (Calspan), parts assembled, sensors integrated, and statically calibrated. The objective of this paper is to describe this baseline rig. The vision behind the rig is to conduct research on future high-speed tiltrotors with an envisioned flutter-free cruise up to 400 kt, enabled by thin wings, and light-weight, low-vibration, high-performance rotors. the features, specifications, and instrumentation of this rig. The purpose of the MTR is to provide a testbed for 1 Introduction basic research on aeromechanics of high-speed tiltrotors. A vision for the next generation of these aircraft is 400 kt A new tiltrotor test facility at the University flutter-free cruise with a turboprop-like thin wing (14% of Maryland has continued to make progress on the thickness to chord ratio) and a lightweight, low-vibration, Maryland Tiltrotor Rig (MTR). The design of the rig high-performance proprotor. The objective of MTR was outlined in Ref. [1]. The fabrication of the baseline is to enable this vision through systematic parametric gimballed hub rig is now complete. This paper describes variation of blades, hub, and wing spar. MTR is a research rig, not a scaled-down version of a particular
A full-scale isolated proprotor test was recently conducted in the USAF National Full-Scale Aerodynamics Complex (NFAC) at NASA Ames Research Center. The test article was a 3-bladed research rotor derived from the right-hand rotor of the AW609. For this test, the NASA Tiltrotor Test Rig (TTR) and rotor were installed in the 40- by 80-foot test section. This paper presents initial correlations between data and predictions of rotor performance and blade moments using the newly acquired test data and the comprehensive analysis CAMRAD II. Four low-speed conditions were studied, including hover (actually, low speed vertical climb), cruise (airplane mode), conversion, and helicopter mode. Mean and 1⁄2 peak-to-peak quantities (hpp) are correlated; time-history correlation for the helicopter condition is also included. The hover calculations proved useful in providing reality checks on the test hardware. The correlation is reasonable. The mean midspan flap banding moments are predicted very well. The trends (with CT/σ) are largely captured, with some overprediction or underprediction (details in the paper). The time-history correlations (helicopter mode) show that, compared to the rolled-up wake (RW) model, the multiple-trailer wake model improves the correlation slightly; the collective is predicted well by the RW model, the lateral cyclic correlation is not good, and the longitudinal cyclic correlation is reasonable; the flap moment correlation is reasonable; the pitch link load and lag moment are underpredicted; and the torsion moment correlation is poor and needs further study.
This paper presents measurements of the efficiency of NASA's 2nd magnetic gear prototype. A detailed discussion of the test rig used to make these measurements was presented, including a thorough uncertainty analysis. The reported uncertainties are 95% confidence intervals that include the effects of temperature and parasitic loads. The prototype's response was measured at output speeds between 124 rpm and 744 rpm for a controlled output torque of 10 Nm (8% of the prototype's maximum torque). After correcting for tare losses, the prototype's efficiency was found to decrease from 90.0% to 83.0% as speed increased. If the efficiency is extrapolated to a typical operating condition (85% of maximum torque) using the good assumption that energy loss is approximately independent of the transmitted torque, the expected efficiency would be 99.0% to 98.4%, which exceeds the state of the art for these speeds.
The Tiltrotor Test Rig (TTR) was tested in the National Full-Scale Aerodynamics Complex (NFAC) 40- by 80-Foot Wind Tunnel from 2017 to 2018. The primary goal of the test was to understand the operational capabilities of the TTR, while also acquiring research data, including acoustic data. Four microphones were placed around the TTR: two on the wind tunnel floor and two on struts. Acoustic measurements of the TTR rotor were acquired to 1) understand the acoustic testing capabilities of the TTR in the NFAC 40- by 80-FootWind Tunnel, 2) compare to previous XV-15 rotor acoustic data acquired in the NFAC 80- by 120-Foot Wind Tunnel, and 3) provide data for future validation studies. A data quality study revealed that the NFAC 40- by 80-Foot Wind Tunnel is an adequate acoustic environment to test the TTR rotor. For a given thrust and advance ratio, a shaft angle sweep was performed and acoustic measurements were compared against 1996 and 1999 XV-15 data in the NFAC 80- by 120-Foot Wind Tunnel; differences between the three tests are discussed.
The Tiltrotor Test Rig (TTR) is a NASA project, joint with the U.S. Army and Air Force, to develop a new, large-scale proprotor test system for the National Full-Scale Aerodynamics Complex (NFAC). The first wind-tunnel entry was completed in November 2018 with a modern, 26-ft diameter proprotor. The primary purpose was to complete the development of the TTR, including systems integration with the NFAC. The TTR and rotor were tested up to 273 knots in axial flow. This is the highest airspeed ever achieved by a full-scale proprotor in any wind tunnel. Extensive conversion-mode data were also acquired, and hover/climb conditions were explored. Additional testing included aerodynamic tares, motor tests, thermal tests, modal vibration tests, and other checkout activities. This paper summarizes the results of the test, including examples of the most significant data.
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