BUFFET TESTS OF AN ATTACK-AIRPLANE MODEL WITH EMPHASIS ON ANALYSIS OF DATA FROM WIND-TUNNEL TESTS
Buffeting tests of attack aircraft model at transonic speeds
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Subsonic wind tunnel investigation of a twin-engine attack airplane model having nonmetric powered nacelles
A 1/10-scale powered model of a twin-engine attack airplane was investigated in the Langley high-speed 7- by 10-foot tunnel. The study was made at several Mach numbers between 0.225 and 0.75 which correspond to Reynolds numbers, based on the mean aerodynamic chord, of 1.35 million and 3.34 million. Unheated compressed air was used for jet simulation in the nonmetric engine nacelles which were located ahead of and above the horizontal stabilizer.
Lockwood, V. E.↗
Interference effects of aft reaction-control yaw jets on the aerodynamic characteristics of a space shuttle orbiter model at supersonic speeds
A wind tunnel investigation of the interference effects of aft reaction control system yaw jet plumes on a 0.0125 scale Space Shuttle orbiter model was conducted at Mach numbers from 2.50 to 4.50. Test variables included model angle of attack, model angle of sideslip, jet to free stream mass flow ratio, and number and position of operating jets. The aft reaction control jet plume creates a blockage above and behind the wing on the side in which the jet exhausts and results in flow separation on the wing upper surface and fuselage side. Positive pitching moment and side force increments and negative yawing moment and rolling moment increments due to the flow separations are incurred for left side firing jets, primarily at angles of attack above 10 deg. The yawing moment interference increments are favorable and result in a small jet thrust amplification. As a result of this investigation, the aft reaction control system was certified for operation at supersonic Mach numbers prior to the first flight of the space transportation system (STS-1).
Covell, P. F.↗
Acoustic measurements of the X-wing rotor
Noise measurements of a stoppable X-wing rotor system model, tested in the Ames 40- by 80-foot wind tunnel, are summarized. Performance, control system stability, and noise of the model were investigated at various forward speeds, tip speeds, collective blade angles, jet blowing velocities, and model attack angles. The model was tested in the rotating wing helicopter configuration, in the fixed wing configuration, and in wing configurations between the two. Noise data obtained in the helicopter configuration at the two highest tip speeds (Mach 0.44 and 0.47) and at wind tunnel speeds below 140 knots are reported. Test configuration and performance information are included. General acoustic measurements (dB, dBA, and PNdB) at six microphone locations are presented for all conditions under which the background noise was below the model noise. More specific measurements (1/3-octave and blade passage frequency harmonic levels) are presented for selected conditions. Graphs of dBA and 1/3-octave spectra, which show the noise trends as functions of operating condition, are included. The noise depends mainly on the jet blowing velocity. The noise levels were highest at moderate jet blowing velocities, less at the highest velocity, and lowest with no blowing at all.
Mosher, M.↗
Creep fatigue life prediction for engine hot section materials (ISOTROPIC)
The specific activities summarized include: verification experiments (base program); thermomechanical cycling model; multiaxial stress state model; cumulative loading model; screening of potential environmental and protective coating models; and environmental attack model.
Nelson, R. S.↗
Toward more environmentally resistant gas turbines: Progress in NASA-Lewis programs
A wide range of programs are being conducted for improving the environmental resistance to oxidation and hot corrosion of gas turbine and power system materials. They range from fundamental efforts to delineate attack mechanisms, allow attack modeling and permit life prediction, to more applied efforts to develop potentially more resistant alloys and coatings. Oxidation life prediction efforts have resulted in a computer program which provides an initial method for predicting long time metal loss using short time oxidation data by means of a paralinear attack model. Efforts in alloy development have centered on oxide-dispersion strengthened alloys based on the Ni-Cr-Al system. Compositions have been identified which are compromises between oxidation and thermal fatigue resistance. Fundamental studies of hot corrosion mechanisms include thermodynamic studies of sodium sulfate formation during turbine combustion. Information concerning species formed during the vaporization of Na2SO4 has been developed using high temperature mass spectrometry.
Lowell, C. E.↗
Buffet Tests of an Attack-airplane Model with Emphasis on Analysis of Data from Wind-tunnel Tests
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Davis, Don D , Jr↗
A Generic T-Tail Transport Airplane Simulation for High-Angle-Of-Attack Dynamics Modeling Investigations
A preliminary simulation of a generic T-tail transport airplane configuration has been developed at the National Aeronautics and Space Administration Langley Research Center. The primary purpose of this piloted simulation is to assess aerodynamic model fidelity requirements for training airline pilots to recognize and recover from full-stall flight conditions in a T-tail airplane. As a result, significant flexibility has been designed into the flight dynamics model. The flight dynamics model is based on newly acquired static and dynamic stability and control data from sources that include: wind tunnel, water tunnel, and computational fluid dynamics. Preliminary results for initial stall show an unstable stall pitch break (if the stick pusher is inhibited), un-commanded motions due to stall asymmetries, significantly reduced dynamic roll stability, and decreased control effectiveness. Preliminary studies indicated an insensitivity to the fidelity of the pitch damping model.
Cunningham, Kevin↗
The 12-foot pressure wind tunnel restoration project model support systems
The 12 Foot Pressure Wind Tunnel is a variable density, low turbulence wind tunnel that operates at subsonic speeds, and up to six atmospheres total pressure. The restoration of this facility is of critical importance to the future of the U.S. aerospace industry. As part of this project, several state of the art model support systems are furnished to provide an optimal balance between aerodynamic and operational efficiency parameters. Two model support systems, the Rear Strut Model Support, and the High Angle of Attack Model Support are discussed. This paper covers design parameters, constraints, development, description, and component selection.
Sasaki, Glen E.↗
Supersonic Aerodynamic Characteristics of a Space Shuttle Orbiter Model at Angles of Attack from 20 Deg to 90 Deg
Space Shuttle Orbiter aerodynamic characteristics have been determined in the angle-of-attack range from 20 to 90 degrees and Mach numbers from 4.60 to 1.80 at Reynolds numbers, based on body length, of 2.15 x 10 to the 6th and 4.30 x 10 to the 6th power. Emphasis is on vehicle stability, control, and trim characteristics above a 60 degree angle of attack. The model used was a 0.986 percent scale Orbiter, having a blade-mounted support system entering the model in the region of the vertical tail. Elevon deflections of 0, -10, -20, and -40 degrees and body-flap deflections of 0, +6 and -12 degrees were investigated individually and in combination. Schlieren photographs are also presented for selected configurations and Mach numbers. The Orbiter was found to be longitudinally stable and trimmable in the angle-of-attack range from approximately 60 to 80 degrees. Both the elevon and body flap provided positive pitch control-effectiveness at angles of attack from 60 to 80 degrees and the Mach numbers of this study. For the range of neutral to stable trim in the angle-of-attack range above about 55 degrees, the deflected elevon/body-flap combination provided positive trimmed lift and lift/drag ratios.
Spencer, Bernard, Jr.↗
Spin-tunnel investigation of a 1/30-scale model of a subsonic attack airplane
Spin and recovery characteristics of 1/30 scale subsonic attack aircraft model determined in wind tunnel tests
Lee, H. A.↗
Nonlinear Analysis of a Two-Parachute System Undergoing Pendulum Motion
Motion resembling that of a pendulum undergoing large-amplitude limit cycle oscillation was observed during a series of flight tests of an unoccupied Orion Capsule Parachute Assembly System (CPAS) comprised of two parachutes and a capsule payload. Large excursions away from vertical by the capsule could cause it to strike the ground or ocean at a large angle with respect to vertical, or at a large horizontal speed. These conditions are undesirable because they would endanger the occupants of the capsule in an actual mission. A simplified planar dynamics model in conjunction with a nonlinear normal force coefficient vs. angle of attack model serves as the basis of an analytical investigation of the fundamental dynamics of this pendulum motion. Output error methodology from system identification theory was used to identify the parameters of the nonlinear aerodynamics model. The identified model yielded excellent comparison with portions of flight test data where the pendulum motion occurred. Due to the inherent nonlinear nature of the pendulum motion limit cycle, traditional nonlinear analysis techniques were applied to gain further insight into the system. Lyapunov’s direct method provided mathematical proof in the absolute stability of the pendulum mode. Describing Function method was used to predict the amplitude and frequency of the limit cycle oscillation. Finally, phase plane analysis allowed easy visualization on the size and shape of the limit cycle with respect to variations in key aerodynamic parameters.
Pei, Jing↗
Toward more environmentally resistant gas turbines - Progress in NASA-Lewis programs
The paper surveys programs for improving the environmental resistance of gas turbine and power system materials to oxidation and hot corrosion. A computer program Corest has been produced which provides an initial method for predicting long-time metal loss using short-time oxidation data. The role of the coefficient of thermal expansion mismatch on oxide spallation is being studied. A paralinear oxidation attack model in conjunction with regression analysis of weight change data has been applied to the study of oxidation and hot corrosion attack of some Ni-Cr-Al system alloys. Oxide-dispersion strengthened alloys based on the Ni-Cr-Al system are being developed. Sodium sulfate formation during turbine combustion is being investigated from a thermodynamic viewpoint.
Lowell, C. E.↗
Rapid Calculations of Three-Dimensional Inlet/Fan Interaction
Two computational fluid dynamics codes have been merged to permit rapid calculations of inlet/fan interaction. Inlets are modeled using the WIND-US Navier-Stokes code. Fans are modeled using a new three-dimensional Euler code called CSTALL that solves the flow through the entire compression system but models blade rows using body forces for turning and loss. The body force model is described and it is shown how unknown terms in the model can be estimated from other Navier-Stokes solutions of the blade rows run separately. The inlet and fan calculations are run simultaneously and are coupled at an interface plane using a third code called SYNCEX that is described briefly. Results are shown for an axisymmetric nacelle at high angle of attack modeled both as an isolated inlet and coupled to a single stage fan. The isolated inlet calculations are unrealistic after the flow separates but the coupled codes can model large regions of separated flow extending from the lower lip of the nacelle into the fan rotor.
Chima, Rodrick V.↗
Forced Oscillation Wind Tunnel Testing for FASER Flight Research Aircraft
As unmanned air vehicles (UAVs) continue to expand their flight envelopes into areas of high angular rate and high angle of attack, modeling the complex unsteady aerodynamics for simulation in these regimes has become more difficult using traditional methods. The goal of this experiment was to improve the current six degree-of-freedom aerodynamic model of a small UAV by replacing the analytically derived damping derivatives with experimentally derived values. The UAV is named the Free-flying Aircraft for Sub-scale Experimental Research, FASER, and was tested in the NASA Langley Research Center 12- Foot Low-Speed Tunnel. The forced oscillation wind tunnel test technique was used to measure damping in the roll and yaw axes. By imparting a variety of sinusoidal motions, the effects of non-dimensional angular rate and reduced frequency were examined over a large range of angle of attack and side-slip combinations. Tests were performed at angles of attack from -5 to 40 degrees, sideslip angles of -30 to 30 degrees, oscillation amplitudes from 5 to 30 degrees, and reduced frequencies from 0.010 to 0.133. Additionally, the effect of aileron or elevator deflection on the damping coefficients was examined. Comparisons are made of two different data reduction methods used to obtain the damping derivatives. The results show that the damping derivatives are mainly a function of angle of attack and have dependence on the non-dimensional rate and reduced frequency only in the stall/post-stall regime
Hoe, Garrison↗
Optical methods for model angle of attack and transition measurement
A novel laser-based sensor for the in situ measurement of wind tunnel model angle of attack is described and the results of a successful demonstration in the NASA Ames 9 x 7-ft. Supersonic wind tunnel are presented. The design concepts of a scanning laser-based turbulence detector, which will enable nonintrusive, microscopic studies of the onset and extent of transition on wind tunnel test models, is also described.
Owen, F. K.↗
Study of optical techniques for the Ames unitary wind tunnel, part 7
A summary of optical techniques for the Ames Unitary Plan wind tunnels are discussed. Six optical techniques were studied: Schlieren, light sheet and laser vapor screen, angle of attack, model deformation, infrared imagery, and digital image processing. The study includes surveys and reviews of wind tunnel optical techniques, some conceptual designs, and recommendations for use of optical methods in the Ames Unitary Plan wind tunnels. Particular emphasis was placed on searching for systems developed for wind tunnel use and on commercial systems which could be readily adapted for wind tunnels. This final report is to summarize the major results and recommendations.
Lee, George↗
Evaluation of electrolytic tilt sensors for measuring model angle of attack in wind tunnel tests
The results of a laboratory evaluation of electrolytic tilt sensors as potential candidates for measuring model attitude or angle of attack in wind tunnel tests are presented. The performance of eight electrolytic tilt sensors was compared with that of typical servo accelerometers used for angle-of-attack measurements. The areas evaluated included linearity, hysteresis, repeatability, temperature characteristics, roll-on-pitch interaction, sensitivity to lead-wire resistance, step response time, and rectification. Among the sensors being evaluated, the Spectron model RG-37 electrolytic tilt sensors have the highest overall accuracy in terms of linearity, hysteresis, repeatability, temperature sensitivity, and roll sensitivity. A comparison of the sensors with the servo accelerometers revealed that the accuracy of the RG-37 sensors was on the average about one order of magnitude worse. Even though a comparison indicates that the cost of each tilt sensor is about one-third the cost of each servo accelerometer, the sensors are considered unsuitable for angle-of-attack measurements. However, the potential exists for other applications such as wind tunnel wall-attitude measurements where the errors resulting from roll interaction, vibration, and response time are less and sensor temperature can be controlled.
Wong, Douglas T.↗