: A full-scale wind tunnel test of the UH-60A airloads rotor was recently completed in the National Full-Scale Aerodynamics Complex 40- by 80-Foot Wind Tunnel The rotor was the same one tested during the landmark 1993 NASA/Army UH-60A Airloads flight test and included a highly pressure-instrumented blade to measure rotor airloads This paper provides an overview of the wind tunnel test, including detailed descriptions of the hardware, instrumentation, and data acquisition and reduction systems In addition, the data validation process, the test objectives and approach, and some sample results are presented The test has produced unique data not available from the flight test, including data from new measurements as well as data acquired at conditions outside the conventional flight envelope The new measurements included rotor balance forces and moments, oscillatory hub loads, blade displacements and deformations, and rotor wake measurements using largefield Particle Image Velocimetry and Retro-reflective Background Oriented Schlieren The new flight conditions included 1- g flight simulations up to advance ratios of 040, parametric sweeps at non-standard conditions, including multiple sweeps into stall, and slowed rotor simulations up to advance ratios of 10 These new data should provide an excellent resource for validating new and emerging predictive tools

Full-Scale Wind Tunnel Test of the UH-60A Airloads Rotor

: A full-scale four-bladed UH-60 rotor system was tested in the NASA Ames 80- by 120-Foot Wind Tunnel. A quality data set at low forward speed, 0 to 80 knots, has been obtained to support future rotor developments and analysis improvements. To evaluate the NASA Ames 80- by 120- Foot Wind Tunnel as a hover testing facility, rotor performance data were compared with predictions, UH-60 aircraft flight test data, and UH-60 model-scale data from other test facilities. Results indicate that valid hover data for this size rotor can be obtained from this facility at low to medium thrust conditions. Comparisons with flight test and model-scale data demonstrate the variability between existing data sets. Predictions show good agreement with full-scale data. To evaluate the analytical modeling in the 0 to 80 knot speed range, forward flight rotor performance data were acquired and compared with predictions. Comparisons were also made with existing model-scale and flight test data. Power calculations show fair to good agreement with full-scale wind tunnel data at advance ratios between 0.10 to 0.19 and poor agreement at advance ratios below 0.10. Comparisons with flight test and model-scale data show good agreement at all advance ratios tested. Propulsive force calculations show good correlation with full-scale wind tunnel data at advance ratios of 0.10 to 0.19.

https://rotorcraft.arc.nasa.gov/publications/files/Shinoda_AHSF02.pdf

Rotor Performance of a UH-60 Rotor System in the NASA Ames 80- by 120-Foot Wind Tunnel

The control system stiffness of an UH–60A helicopter was measured. A description of the measurement and the results is provided. The measured control system stiffness values were used within a comprehensive analysis, CAMRAD II, to establish a baseline calculation of the rotor system during an extreme thrust condition causing dynamic stall on the rotor. The baseline CAMRAD II model is compared to measured blade shake test data and level flight, high thrust, flight test data also showing dynamic stall from the UH–60A Airloads Program to validate the baseline calculations. An evaluation of the sensitivity of the rotor system response to different control system stiffness models was made. The calculated results show that the rotor system response is significantly improved using an accurate control system model when dynamic stall is present.

https://rotorcraft.arc.nasa.gov/publications/files/Kufeld_JAHS2000.pdf

The Effects of Control System Stiffness Models on the Dynamic Stall Behavior of a Helicopter

In this paper, helicopter rotor blades are analysed in hover using computational fluid dynamics (CFD) coupled with a structural model. The method relies on a mesh deformation algorithm that allows for exchange of forces and deformations between a beam-based finite-element model and the fluid flow volume mesh. The method is demonstrated against experimental data, and the aerodynamic predictions appear to improve when the aeroelastic model is used. For all employed cases the flexibility of the method allows the CFD mesh deformation to be spread over the computational domain in a controlled fashion. The influence of the aeroelastic deformations on the blade loads was limited yet evident on the rotor performance. The lack of adequate test cases and experiments for validation of CFD/CSD methods is also highlighted.

Hovering rotor computations using an aeroelastic blade model

The flight test phase of the Nasa-Army UH-60A Airloads Program was completed in February 1994. The objective of the project was to measure the airloads in flight on an UH-60A Black Hawk using 221 blade pressure transducers installed in nine radial arrays. In addition, 21 transducers were installed along the blade leading edge to better identify blade-vortex interaction phenomena. This paper briefly describes the program's background and history, instrumentation, and data acquisition. Airloads data are presented for two test conditions with different levels of complexity: steady, level flight and a diving turn. These flight data provide useful information of relatively simple and complex nonlinear flow for the validation of theoretical analyses. Evidence of shock waves, reverse flow, dynamic stall and blade vortex interactions are presented.

UH-60A helicopter rotor airloads measured in flight

The dynamic characteristics of instrumented and production UH-60A Black Hawk main rotor blades were measured, and the results were validated with NASTRAN finite element models. The blades tested included pressure and strain-gage instrumented blades, which are part of the NASA Airloads Flight Research Phase of the Modern Technology Rotor Program. The dynamic similarity of the blades was required for accurate data collection in this program. Therefore, a nonrotating blade modal analysis was performed on the first 10 free-free modes to measure blade similarities. The results showed small differences between the modal frequencies of instrumented and production blades and a close correlation with the NASTRAN models. This type of modal testing and analysis is recommended as a standard procedure for future instrumented blade flight testing.

/pdf/modal-analysis-of-uh-60a-instrumented-rotor-blades-3tfiye9dnb.pdf

Karen S. Hamade

Papers

Modal analysis of UH 60A instrumented rotor blades