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NASA NTRS2016

Photogrammetric Deflection Measurements for the Tiltrotor Test Rig (TTR) Multi-Component Rotor Balance Calibration

Calibrating the internal, multi-component balance mounted in the Tiltrotor Test Rig (TTR) required photogrammetric measurements to determine the location and orientation of forces applied to the balance. The TTR, with the balance and calibration hardware attached, was mounted in a custom calibration stand. Calibration loads were applied using eleven hydraulic actuators, operating in tension only, that were attached to the forward frame of the calibration stand and the TTR calibration hardware via linkages with in-line load cells. Before the linkages were installed, photogrammetry was used to determine the location of the linkage attachment points on the forward frame and on the TTR calibration hardware. Photogrammetric measurements were used to determine the displacement of the linkage attachment points on the TTR due to deflection of the hardware under applied loads. These measurements represent the first photogrammetric deflection measurements to be made to support 6-component rotor balance calibration. This paper describes the design of the TTR and the calibration hardware, and presents the development, set-up and use of the photogrammetry system, along with some selected measurement results.

Calibration↗

NASA NTRS2016

Photogrammetric Deflection Measurements for the Tiltrotor Test Rig (TTR) Multi-Component Rotor Balance Calibration

Calibration↗

NASA NTRS1990

Geodetic positioning of the Aerospace Electronics Research Lab (ERL) Osborne Time Transfer Receiver (TTR) using the GPS NAVSTAR Block I satellites

Aerospace has routinely processed the Osborne Time Transfer Receiver (TTR) data for the purpose of monitoring the performance of ground and GPS atomic clocks in near real-time with on-line residual displays and characterizing clock stability with Allan Variance calculations. Recently, Aerospace added the ability to estimate the TTR's location by differentially correcting the TTR's location in the WGS84 reference system. This new feature is exercised on a set of TTR clock phase data and Sub-meter accurate station location estimates of the TTR at the Aerospace Electronic Research Lab (ERL) are obtained.

Liu, Anthony S.↗

NASA NTRS1994

The use of the AOA TTR-4P GPS receiver in operation at the BIPM for real-time restitution of GPS time

The Global Positioning System is an outstanding tool for the dissemination of time. Using mono-channel C/A-code GPS time receivers, the restitution of GPS time through the satellite constellation presents a peak-to-peak discrepancy of several tens of nanoseconds without SA but may be as high as several hundreds of nanoseconds with SA. As a consequence, civil users are more and more interested in implementing hardware and software methods for efficient restitution of GPS time, especially in the framework of the project of a real-time prediction of UTC (UTCp) which could be available in the form of time differences (UTCp - GPS time). Previous work, for improving the real-time restitution of GPS time with SA, to the level obtained without SA, focused on the implementation of a Kalman filter based on past data and updated at each new observation. An alternative solution relies upon the statistical features of the noise brought about by SA; it has already been shown that the SA noise is efficiently reduced by averaging data from numerous satellites observed simultaneously over a sufficiently long time. This method was successfully applied to data from a GPS time receiver, model AOA TTR-4P, connected to the cesium clock kept at the BIPM. This device, a multi-channel, dual frequency, P-code GPS time receiver, is one of the first TTR-4P units in operation in a civil laboratory. Preliminary comparative studies of this new equipment with conventional GPS time receivers are described in this paper. The results of an experimental restitution of GPS time, obtained in June 1993, are also detailed: 3 to 6 satellites were observed simultaneously with a sample interval of 15 s, an efficient smoothing of SA noise was realized by averaging data on all observed satellites over more than 1 hour. When the GPS system is complete in 1994, 8 satellites will be observable continuously from anywhere in the world and the same level of uncertainty will be obtained using a shorter averaging time.

Thomas, Claudine↗

NASA NTRS2020

Acoustic Testing of the Bell 699 Rotor on the Tiltrotor Test Rig (TTR) in the National Full-Scale Aerodynamics Complex 40- by 80- Foot Wind Tunnel in Conversion and Airplane Configuration

The Tiltrotor Test Rig (TTR) provides new proprotor testing capabilities to the National Aeronautics and Space Administration (NASA) and the Department of Defense (DoD). A checkout test for the TTR with the 699 proprotor was performed in the National Full-Scale Aerodynamics Complex (NFAC) 40- by 80 Foot Wind Tunnel from 2017 to 2018. Four microphones were placed around the rotor to capture acoustic data. Revolution based acoustic data processing techniques are evaluated for appropriateness in both helicopter and airplane configurations. This paper presents the acoustic data acquired for the rotor in conversion and airplane configuration.

Shelts, Kelly↗

NASA NTRS2019

Acoustic Testing of the Tiltrotor Test Rig in the National Full-Scale Aerodynamics Complex 40- by 80-Foot Wind Tunnel

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.

40- by 80-FootWind Tunnel↗

NASA NTRS2019

Aeroelastic Stability Analysis of a Full-Scale Isolated Proprotor on the Tiltrotor Test Rig

A full-scale isolated proprotor test was recently conducted in the USAF National Full-Scale Aerodynamics Complex (NFAC) 40- by 80-Foot Wind Tunnel at NASA Ames. 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 Wind Tunnel. This paper covers the analyses and testing done to prepare for a safe entry. Included are brief descriptions of the following: NASTRAN models of the TTR, ground vibration tests of the TTR (and resulting modal data), loads analyses, and stability predictions using the comprehensive analysis CAMRAD II. The evolution of these analyses from early in the TTR program until the initiation of actual testing is also discussed. The intent is to show how all of these efforts were integrated to ensure a successful test. This paper includes stability predictions based on NASTRAN modal data and worst-case damping test data. The stability predictions covered all test conditions: hover, cruise (airplane mode), conversion, and helicopter mode. The predictions showed that the TTR and rotor are stable within the test envelope.

Full-Scale Isolated Proprotor↗

NASA NTRS2019

Acoustic Testing of the Tiltrotor Test Rig in the National Full-Scale Aerodynamics Complex 40- by 80-Foot Wind Tunnel

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 rotor system can be configured in airplane mode, with the rotor plane perpendicular to the wind flow, and in helicopter mode, with the rotor plane parallel to the wind flow. Four microphones were placed around the TTR: two on the wind tunnel floor and two on struts. The primary goal of the test was to understand the operational capabilities of the TTR, while also acquiring research data as available. Limited measurements of the blade vortex interaction (BVI) noise of the TTR rotor were taken to not only understand the acoustic testing capabilities of the TTR in the NFAC 40- by 80-Foot Wind Tunnel, but to also compare to previous tests and to be used for future validation studies. In particular, data will be compared to measurements of an XV-15 rotor previously acquired in the NFAC 80- by 120-Foot Wind Tunnel.

Tiltrotor Test Rig↗

NASA NTRS2019

Correlation of Full-Scale Isolated Proprotor Performance and Loads

A full-scale isolated proprotor test is currently being conducted in the USAF National Full-Scale Aerodynamics Complex (NFAC) 40- by 80-Foot Wind Tunnel at NASA Ames. The test article is a 3-bladed research rotor derived from the right-hand rotor of the AW609; this rotor was manufactured by Bell Helicopter under contract to NASA. In this paper, this research rotor is referred to as "699". The test, nearly completed, is an integral part of the initial checkout test of the newly developed Tiltrotor Test Rig (TTR), whose purpose is to test advanced, full-scale proprotors in the NFAC. Figure 1 shows the TTR/699 installed in the 40- by 80-Foot test section. The TTR rotor axis is horizontal and the rig rotates in yaw on the wind tunnel turntable for conversion (transition) and helicopter mode testing. To date, a substantial amount of wind tunnel test data has already been acquired. The completed operational conditions include hover, airplane mode (cruise, wind tunnel airspeed V=61 to 267 knots), and the helicopter and conversion conditions (with a comprehensive sweep of the TTR yaw angle ranging, to date, from 90-deg yaw helicopter mode to 30-deg yaw conversion mode, at varying airspeeds). This 699 proprotor performance and loads correlation study uses these newly acquired wind tunnel test data. This paper represents the third analytical study, coming after two earlier analytical studies on the TTR/699; that is, a 2018 paper on pre-test predictions of 699 performance and loads, Ref. 1, and an upcoming January 2019 paper on aeroelastic stability analysis of the TTR/699 installed in the 40- by 80-Foot Wind Tunnel, Ref. 2. Reference 8 will present an overview of the entire TTR/699 test program. For completeness, Ref. 3 addresses the development and initial testing of the TTR. Background information on the TTR effort at NASA Ames can be found at the Aeromechanics website: https://rotorcraft.arc.nasa.gov/Research/Facilities/ttr.html. To the authors' knowledge, the full-scale results presented in this paper are the first of their kind. A literature survey brought up several existing correlation studies, but these were either based on small-scale test data (for example, the studies performed by the University of Maryland) or full-scale aircraft flight test data (for example, flight tests conducted by Bell Helicopter). Separately, the 2009 NASA study involving the JVX rotor is relevant (see Ref.4). The JVX is closely similar to the 699 in size and aerodynamics, and is accordingly a good reference for performance calculations. In Ref. 1 (as mentioned above), pre-test reality checks of the current analytical model were made by comparing JVX and 699 predictions in hover and forward flight (airplane mode).

Isolated Proprotor Performance↗

NASA NTRS2022

Wind Tunnel Performance Tests of a Full-Scale Proprotor on the Tiltrotor Test Rig

The Tiltrotor Test Rig (TTR) is a new, large-scale proprotor test system for the National Full-Scale Aerodynamics Complex (NFAC). The TTR was jointly developed by NASA, the U. S. Army and the U. S. Air Force. 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, which is the highest airspeed ever achieved by a full-scale proprotor in any wind tunnel. The entry constitutes the first full-scale wind-tunnel test of a gimballed, coning-flexure rotor. 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 report summarizes the results of the test, including examples of the most significant data.

Tiltrotor Test Rig↗

NASA NTRS2018

Development and Initial Testing of the Tiltrotor Test Rig

The NASA Tiltrotor Test Rig (TTR) is a new, large-scale proprotor test system, developed jointly 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 TTR is designed to test advanced proprotors up to 26 feet in diameter at speeds up to 300 knots, and even larger rotors at lower airspeeds. This combination of size and speed is unprecedented and is necessary for research into 21st-century tiltrotors and other advanced rotorcraft concepts. The TTR will provide critical data for validation of state-of-the-art design and analysis tools.

Proprotor↗

NASA NTRS2015

Wind Tunnel Interference Effects on Tilt Rotor Testing Using Computational Fluid Dynamics

Experimental techniques to measure rotorcraft aerodynamic performance are widely used. However, most of them are either unable to capture interference effects from bodies, or require an extremely large computational budget. The objective of the present research is to develop an XV-15 Tilt Rotor Research Aircraft rotor model for investigation of wind tunnel wall interference using a novel Computational Fluid Dynamics (CFD) solver for rotorcraft, RotCFD. In RotCFD, a mid-fidelity URANS solver is used with an incompressible flow model and a realizable k-ε turbulence model. The rotor is, however, not modeled using a computationally expensive, unsteady viscous body-fitted grid, but is instead modeled using a blade element model with a momentum source approach. Various flight modes of the XV-15 isolated rotor, including hover, tilt and airplane mode, have been simulated and correlated to existing experimental and theoretical data. The rotor model is subsequently used for wind tunnel wall interference simulations in the National Full-Scale Aerodynamics Complex (NFAC) at NASA Ames Research Center in California. The results from the validation of the isolated rotor performance showed good correlation with experimental and theoretical data. The results were on par with known theoretical analyses. In RotCFD the setup, grid generation and running of cases is faster than many CFD codes, which makes it a useful engineering tool. Performance predictions need not be as accurate as high-fidelity CFD codes, as long as wall effects can be properly simulated. For both test sections of the NFAC wall interference was examined by simulating the XV-15 rotor in the test section of the wind tunnel and with an identical grid but extended boundaries in free field. Both cases were also examined with an isolated rotor or with the rotor mounted on the modeled geometry of the Tiltrotor Test Rig (TTR). A 'quasi linear trim' was used to trim the thrust for the rotor to compare the power as a unique variable. Power differences between free field and wind tunnel cases were found from -7 % to 0 % in the 80- by 120-Foot Wind Tunnel test section and -1.6 % to 4.8 % in the 40- by 80-Foot Wind Tunnel, depending on the TTR orientation, tunnel velocity and blade setting. The TTR will be used in 2016 to test the Bell 609 rotor in a similar fashion to the research in this report.

CFD↗

NASA NTRS2016

Wind Tunnel Interference Effects on Tilt Rotor Testing Using Computational Fluid Dynamics

Experimental techniques to measure rotorcraft aerodynamic performance are widely used. However, most of them are either unable to capture interference effects from bodies, or require an extremely large computational budget. The objective of the present research is to develop an XV-15 Tiltrotor Research Aircraft rotor model for investigation of wind tunnel wall interference using a novel Computational Fluid Dynamics (CFD) solver for rotorcraft, RotCFD. In RotCFD, a mid-fidelity Unsteady Reynolds Averaged Navier-Stokes (URANS) solver is used with an incompressible flow model and a realizable k-ε turbulence model. The rotor is, however, not modeled using a computationally expensive, unsteady viscous body-fitted grid, but is instead modeled using a blade-element model (BEM) with a momentum source approach. Various flight modes of the XV-15 isolated rotor, including hover, tilt, and airplane mode, have been simulated and correlated to existing experimental and theoretical data. The rotor model is subsequently used for wind tunnel wall interference simulations in the National Full-Scale Aerodynamics Complex (NFAC) at Ames Research Center in California. The results from the validation of the isolated rotor performance showed good correlation with experimental and theoretical data. The results were on par with known theoretical analyses. In RotCFD the setup, grid generation, and running of cases is faster than many CFD codes, which makes it a useful engineering tool. Performance predictions need not be as accurate as high-fidelity CFD codes, as long as wall effects can be properly simulated. For both test sections of the NFAC wall, interference was examined by simulating the XV-15 rotor in the test section of the wind tunnel and with an identical grid but extended boundaries in free field. Both cases were also examined with an isolated rotor or with the rotor mounted on the modeled geometry of the Tiltrotor Test Rig (TTR). A "quasi linear trim" was used to trim the thrust for the rotor to compare the power as a unique variable. Power differences between free field and wind tunnel cases were found from -7 to 0 percent in the 80- by 120-Foot Wind Tunnel and -1.6 to 4.8 percent in the 40- by 80-Foot Wind Tunnel, depending on the TTR orientation, tunnel velocity, and blade setting. The TTR will be used in 2016 to test the Bell 609 rotor in a similar fashion to the research in this report.

CFD↗

NASA NTRS2019

High-Speed Wind Tunnel Tests of a Full-Scale Proprotor on the Tiltrotor Test Rig

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.

Wind Tunnel Tests↗

NASA NTRS2020

Loads Correlation of a Full-Scale Proprotor on the Tiltrotor Test Rig

In 2018, a full-scale isolated proprotor test was conducted in the USAF National Full-Scale Aerodynamics Complex (NFAC) at NASA Ames. The test article was the 3-bladed Bell 699 research rotor derived from the AW609 rotor. For this test, the NASA Tiltrotor Test Rig (TTR) and rotor were installed in the 40- by 80-foot test section. Correlations between the 2018 test data and predictions from the comprehensive analysis CAMRAD II for blade and yoke (flexbeam) loads and rotor torque are presented. The full range of conversion to helicopter modes is covered: conversion 30-, 45-, and 60-deg TTR yaw, and helicopter 75- and 90-deg TTR yaw. The flap moment correlation is reasonable to good; the pitch link load and torsion moment are uniformly underpredicted. The measured 2P lag moment and 2P torque are not captured by the analysis. The inability to predict the 2P component is currently attributed to the analytical assumption of a perfect gimbal, whereas the actual test gimbal may be operating imperfectly and thus introducing the 2P harmonic. A new analytical model that accounts for non-ideal gimbal operation is needed.

Kottapalli, Sesi↗

NASA NTRS2022

Tiltrotor Test Rig Aerodynamic Tares

The Tiltrotor Test Rig (TTR) is a NASA facility designed to test full-scale proprotors in the National Full-Scale Aerodynamics Facility (NFAC). The first wind-tunnel entry included measurements of aerodynamic loads (tares) on the spinner without a rotor. The TTR has an onboard balance for direct measurement of rotor loads, so these tares comprise only spinner loads. Spinner tares also affect shaft loads measured independently of the balance. The results show that in axial flow, spinner drag is a linear function of dynamic pressure as expected, but at other flow angles, spinner loads include substantial lift and drag. Furthermore, there is a pronounced Magnus effect when the spinner is sideways to the flow. There is a sharp change in aerodynamic load at 90-deg yaw angle, indicating separation. Equations were developed to characterize the spinner tares at any arbitrary combination of yaw angle and airspeed.

TTR↗

NASA NTRS2024

Tiltrotor Test Rig Wind-Tunnel Test Data Catalog

The Tiltrotor Test Rig (TTR) is a 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 rotor tested was the Bell Model 699, an AW609 rotor modified specifically for wind-tunnel testing. The primary purpose was to complete the development of the TTR, including systems integration with the NFAC. Testing included axial flow up to 273 knots, conversion mode from 30 to 100 deg nacelle angle, and hover/vertical climb conditions. Additional testing included aerodynamic tares, motor tests, thermal tests, modal vibration tests, and other checkout activities. This report lists the test conditions achieved and the types of data acquired and saved in the database.

NFAC↗

NASA NTRS1990

Advanced Rotorcraft Transmission program - A status report

The work being conducted under the first phase of the joint Army/NASA Advanced Rotorcraft Transmission program is reviewed. The work includes the selection of the Tactical Tilt Rotor (TTR) system and the development plans for assessing advanced component technologies. The TTR drive-system arrangement is outlined, and the comparisons and trade studies of self-aligning bearingless planetary, split torque, and conventional single-stage planetary configurations are presented. The effects of transmission improvements are evaluated, and component development testing is discussed, including noise reduction by active force cancellation, hybrid bidirectional tapered roller bearings, and precision net forged spur gears.

Drago, Raymond J.↗