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Bousman, William G.

Publications and source records attributed to Bousman, William G..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2014

Rotorcraft Airloads Measurements-Extraordinary Costs, Extraordinary Benefits

The first airloads measurements were made in the 1950s at NACA Langley on a 15.3-foot model rotor, stimulated by the invention of miniaturized pressure transducers. The inability to predict higher harmonic loads in those early years led the U. S. Army to fund airloads measurements on the CH-34 and the UH-1A aircraft. Nine additional comprehensive airloads tests have been done since that early work, including the recent test of an instrumented UH-60A rotor in the 40- by 80-Foot Wind Tunnel at NASA Ames. This historical narrative discusses the twelve airloads tests and how the results were integrated with analytical efforts. The recent history of the UH-60A Airloads Workshops is presented and it is shown that new developments in analytical methods have transformed our capability to predict airloads that are critical for design.

Extraordinary Costs↗
NASA NTRS2009

UH-60 Airloads Program Tutorial

From the fall of 1993 to late winter of 1994, NASA Ames and the U.S. Army flew a flight test program using a UH-60A helicopter with extensive instrumentation on the rotor and blades, including 242 pressure transducers. Over this period, approximately 30 flights were made, and data were obtained in level flight, maneuver, ascents, and descents. Coordinated acoustic measurements were obtained with a ground-acoustic array in cooperation with NASA Langley, and in-flight acoustic measurements with a YO-3A aircraft. NASA has sponsored the creation of a "tutorial' which covers the depth and breadth of the flight test program with a mixture of text and graphics. The primary purpose of this tutorial is to introduce the student to what is known about rotor aerodynamics based on the UH-60A measurements. The tutorial will also be useful to anyone interested in helicopters who would like to have more detailed knowledge about helicopter aerodynamics.

Bousman, William G.↗
NASA NTRS2003

Aerodynamic Characteristics of SC1095 and SC1094 R8 Airfoils

Two airfoils are used on the main rotor blade of the UH-60A helicopter, the SC1095 and the SC1094 R8. Measurements of the section lift, drag, and pitching moment have been obtained in ten wind tunnel tests for the SC1095 airfoil, and in five of these tests, measurements have also been obtained for the SC1094 R8. The ten wind tunnel tests are characterized and described in the present study. A number of fundamental parameters measured in these tests are compared and an assessment is made of the adequacy of the test data for use in look-up tables required by lifting-line calculation methods.

Bousman, William G.↗
NASA NTRS2003

Airfoil Design and Rotorcraft Performance

The relationship between global performance of a typical helicopter and the airfoil environment, as represented by the airfoil angles of attack and Mach number, has been examined using the comprehensive analysis CAMRAD II. A general correspondence is observed between global performance parameters, such as rotor L/D, and airfoil performance parameters, such as airfoil L/D, the drag bucket boundaries, and the divergence Mach number. Effects of design parameters such as blade twist and rotor speed variation have been examined and, in most cases, improvements observed in global performance are also observed in terms of airfoil performance. The relations observed between global Performance and the airfoil environment suggests that the emphasis in airfoil design should be for good L/D, while the maximum lift coefficient performance is less important.

Bousman, William G.↗
NASA NTRS2002

Power Measurement Errors on a Utility Aircraft

Extensive flight test data obtained from two recent performance tests of a UH 60A aircraft are reviewed. A power difference is calculated from the power balance equation and is used to examine power measurement errors. It is shown that the baseline measurement errors are highly non-Gaussian in their frequency distribution and are therefore influenced by additional, unquantified variables. Linear regression is used to examine the influence of other variables and it is shown that a substantial portion of the variance depends upon measurements of atmospheric parameters. Correcting for temperature dependence, although reducing the variance in the measurement errors, still leaves unquantified effects. Examination of the power difference over individual test runs indicates significant errors from drift, although it is unclear how these may be corrected. In an idealized case, where the drift is correctable, it is shown that the power measurement errors are significantly reduced and the error distribution is Gaussian. A new flight test program is recommended that will quantify the thermal environment for all torque measurements on the UH 60. Subsequently, the torque measurement systems will be recalibrated based on the measured thermal environment and a new power measurement assessment performed.

Bousman, William G.↗
NASA NTRS2000

Airfoil Dynamic Stall and Rotorcraft Maneuverability

The loading of an airfoil during dynamic stall is examined in terms of the augmented lift and the associated penalties in pitching moment and drag. It is shown that once stall occurs and a leading-edge vortex is shed from the airfoil there is a unique relationship between the augmented lift, the negative pitching moment, and the increase in drag. This relationship, referred to here as the dynamic stall function, shows limited sensitivity to effects such as the airfoil section profile and Mach number, and appears to be independent of such parameters as Reynolds number, reduced frequency, and blade sweep. For single-element airfoils there is little that can be done to improve rotorcraft maneuverability except to provide good static C(l(max)) characteristics and the chord or blade number that is required to provide the necessary rotor thrust. However, multi-element airfoils or airfoils with variable geometry features can provide augmented lift in some cases that exceeds that available from a single-element airfoil. The dynamic stall function is shown to be a useful tool for the evaluation of both measured and calculated dynamic stall characteristics of single element, multi-element, and variable geometry airfoils.

Bousman, William G.↗
NASA NTRS2000

Putting the Aero Back into Aeroelasticity

The lack of progress in understanding the physics of rotorcraft loads and vibration over the last 30 years is addressed in this paper. As befits this extraordinarily difficult problem, the reasons for the lack of progress are complicated and difficult to ascertain. It is proposed here that the difficulty lies within at least three areas: 1) a loss of perspective as to what are the key factors in rotor loads and vibration, 2) the overlooking of serious unsolved problems in the field, and 3) cultural barriers that impede progress. Some criteria are suggested for future research to provide a more concentrated focus on the problem.

Bousman, William G.↗
NASA NTRS2000

Evaluation of Airfoil Dynamic Stall Characteristics for Maneuverability

In severe maneuvers, out of necessity for a military aircraft or inadvertently for a civil aircraft, a helicopter airfoil will stall in a dynamic manner and provide lift beyond what would be calculated based on static airfoil tests. The augmented lift that occurs in dynamic stall is related to a vortex that is shed near the leading edge of the airfoil. However, directly related to the augmented lift that results from the dynamic stall vortex are significant penalties in pitching moment and drag. An understanding of the relationship between the augmented lift in dynamic stall and the associated moment and drag penalties is the purpose of this paper. This relationship is characterized using data obtained in two-dimensional wind tunnel tests and related to the problem of helicopter maneuverability.

Bousman, William G.↗
NASA NTRS1999

Putting the Aero Back Into Aeroelasticity

The lack of progress in understanding the physics of rotorcraft loads and vibration over the last 30 years is addressed in this paper. As befits this extraordinarily difficult problem, the reasons for the lack of progress are complicated and difficult to ascertain. It is proposed here that the difficulty lies within at least three areas: 1) a loss of perspective as to what are the key factors in rotor loads and vibration, 2) the overlooking of serious unsolved problems in the field, and 3) cultural barriers that impede progress. Some criteria are suggested for future research to provide a more concentrated focus on the problem.

Bousman, William G.↗
NASA NTRS1996

A Comparison of Lifting-Line and CFD Methods with Flight Test Data from a Research Puma Helicopter

Four lifting-line methods were compared with flight test data from a research Puma helicopter and the accuracy assessed over a wide range of flight speeds. Hybrid Computational Fluid Dynamics (CFD) methods were also examined for two high-speed conditions. A parallel analytical effort was performed with the lifting-line methods to assess the effects of modeling assumptions and this provided insight into the adequacy of these methods for load predictions.

Bousman, William G.↗
NASA NTRS1996

Aerodynamic Limitations of the UH-60A Rotor

High quality airloads data have been obtained on an instrumented UH-60A in flight and these data provide insight into the aerodynamic limiting behavior of the rotor. At moderate weight coefficients and high advance ratio limiting performance is largely caused by high drag near the blade tip on the advancing side of the rotor as supercritical flow develops on the rotor with moderate to strong, shocks on both surfaces of the blade. Drag divergence data from two-dimensional airfoil tests show good agreement with the development of the supercritical flow regions. Large aerodynamic pitching moments are observed at high advance ratio, as well, and these pitching moments are the source of high torsional moments on the blade and control system loads. These loads occur on the advancing side of the disk and are not related to blade stall which does not occur for these weight coefficients. At high weight coefficients aerodynamic and structural limits are related to dynamic stall cycles that begin on the retreating side of the blade and, for the most severe conditions, carry around to the advancing side of the blade at the presumed first frequency of the blade/control system.

Coleman, Colin P.↗
NASA NTRS1995

Research and technology 1994

Selected research and technology activities at Ames Research Center are summarized. These activities exemplify the Center's varied and productive research efforts for 1994.

Bousman, William G.↗
NASA NTRS1994

Unsteady Aerodynamic Behavior Measured in Hovering Flight

A highly-instrumented UH-60A aircraft was tested at NASA-Ames Research Center from August 1993 to February 1994 obtaining an extensive data base for level flight, maneuvers, acoustics (both with respect to ground microphone arrays and inflight microphones), and flight dynamics. A majority of the data obtained are now in an electronic data base, however, only a small fraction of the data have been examined. The proposed paper will examine the issue of hovering steadiness in more detail. In particular, a single set of data obtained during ground acoustic testing may provide considerable insight as the wind speeds were measured at a hover height of 250 feet and the aircraft was positioned in 15 deg. steps in heading from 0 to 180 deg. Also, hover housekeeping data were obtained for many of the 31 flights and these will also allow a characterization of the unsteadiness. The variation in section lift will be examined in terms of the induced flow angle variation and this will be related to possible physical explanations.

Bousman, William G.↗
NASA NTRS1993

An examination of the aerodynamic moment on rotor blade tips using flight test data and analysis

The analysis CAMRAD/JA is used to model two aircraft, a Puma with a swept-tip blade and a UH-60A Black Hawk. The accuracy of the analysis in predicting the torsion loads is assessed by comparing the predicted loads with measurements from flight tests. The influence of assumptions in the analytical model is examined by varying model parameters and comparing the predicted results to baseline values for the torsion loads. Flight test data from a research Puma are used to identify the source of torsion loads. These data indicate that the aerodynamic section moment in the region of the blade tip dominates torsion loading in high-speed flight. Both the aerodynamic section moment at the blade tip and the pitch-link loads are characterized by large positive (nose-up) moments in the first quadrant with rapid reversal of load so that the moment is negative in the second quadrant. Both the character and magnitude of this loading are missed by the CAMRAD/JA analysis.

Maier, Thomas H.↗
NASA NTRS1990

The effects of structural flap-lag and pitch-lag coupling on soft inplane hingeless rotor stability in hover

A 1.62-m-diameter rotor model was tested in hover to examine the effects of structural flap-lag and pitch-lag coupling on isolated rotor blade lead-lag stability. Flap-lag coupling was introduced by inclining the principal axes of the blade structure up to 60 degrees. Pitch-lag coupling was obtained either alone or in combination with flap-lag coupling through the use of skewed flexural hinges. The principal results confirm the predictions of theory, and show that both structural flap-lag and pitch-lag coupling when used separately are beneficial to blade stability. Moreover, when the couplings are combined, the lead-lag damping is significantly greater than it would be if the individual contributions were superimposed. Pitch-flap coupling is shown to have only a minor effect on blade lead-lag damping. Differences between theory and experiment observed at zero blade pitch and flexure angles during the initial testing were determined in a second test to be caused by stand flexibility. Other differences between theory and experiment warrant further investigation.

Bousman, William G.↗
NASA NTRS1989

Correlation of Puma airloads: Lifting-line and wake calculation

A cooperative program undertaken by organizations in the United States, England, France, and Australia has assessed the strengths and weaknesses of four lifting-line/wake methods and three CFD methods by comparing their predictions with the data obtained in flight trials of a research Puma. The Puma was tested in two configurations: a mixed bladed rotor with instrumented rectangular tip blades, and a configuration with four identical swept tip blades. The results are examined of the lifting-line predictions. The better lifting-line methods show good agreement with lift at the blade tip for the configuration with four swept tips; the moment is well predicted at 0.92 R, but deteriorates outboard. The predictions for the mixed bladed rotor configuration range from fair to good. The lift prediction is better for the swept tip blade than for the rectangular tip blade, but the reasons for this cannot be determined because of the unmodeled effects of the mixed bladed rotor.

Bousman, William G.↗
NASA NTRS1989

The response of helicopter rotors to vibratory airload

The problems of oscillatory and vibratory loading are examined from the perspective of the rotor's structural response. Blade flap, chord, and torsion responses, from flight or wind tunnel tests of eight full-scale rotors are examined and compared for high-speed flight conditions in the absence of blade stall or maneuvers. Some important similarities and differences between rotors are considered, and it is pointed out that these observations are useful in determining the appropriate tests for development of theoretical prediction methods. Among other things, major similarities were found in the dominant flapping vibratory response which occurs at 3/rev, and the root oscillatory chord bending for the CH-34, the SA 349/2, and the UH-60A; differences noted include vibratory chord bending-moment behavior of the rotors, a difference in the damper-induced behavior of CH-53A root oscillatory chord bending, and unique torsion and pitch link loading behavior exhibited by the AH1-G articulated rotor.

Bousman, William G.↗