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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Preliminary results from an airdata enhancement algorithm with application to high-angle-of-attack flight

A technique has been developed to improve the fidelity of airdata measurements during dynamic maneuvering. This technique is particularly useful for airdata measured during flight at high angular rates and high angles of attack. To support this research, flight tests using the F-18 high alpha research vehicle were conducted at the NASA Ames Research Center Dryden Flight Research Facility. A Kalman filter was used to combine information from research airdata, linear accelerometers, angular rate gyros, and attitude gyros to determine better estimates of airdata quantities such as angle of attack, angle of sideslip, airspeed, and altitude. This paper briefly develops the state and observation equations used by the Kalman filter and shows how the state and measurement covariance matrices were determined from flight data.

Moes, Timothy R.↗
NASA NTRS1991

An experimental study of the effects of aft blowing on a 3.0 caliber tangent ogive body at high angles of attack

An experimental study of the effects of aft blowing on the forebody vortex asymmetry over a 3.0 caliber tangent ogive body at high angles of attack was conducted. The tip of the ogive body was equipped with a single blowing nozzle whose position could be adjusted. The tests were conducted in a subsonic wind tunnel at laminar flow conditions. The effects of model roll, angle of attack, blowing coefficient, and blowing nozzle axial position were independently studied. Surface pressure measurements and flow visualization results were obtained. Aft blowing was observed to alleviate the degree of vortex asymmetry at all angles of attack. The blowing was found to be more effective at the higher angles of attack. However, proportional control of the degree of vortex asymmetry was not observed, because the initial flowfield was highly asymmetric.

Gittner, Nathan M.↗
NASA NTRS1986

Low Aspect Ratio Wings at High Angles of Attack

A comprehensive evaluation is made of experimental data compiled to date for the flowfields and aerodynamic forces that occur at high angles of attack for low aspect ratio wings with delta, rectangular, clipped delta, and strake/wing planform geometries. Attention is given to wing leading edge-generated vortex breakdown, aspect ratio and compressibility effects, and strake vortex effects on main wing areas. Although the nonlinear effects created by a wing-body combination significantly alter wing-alone aerodynamics, the wing-alone data presented are vital to the development of prediction methodologies for large angle of attack aerodynamics.

R L Stallings Jr.↗
NASA NTRS1991

A numerical and experimental study of tangential jet blowing applied to bodies at high angles of attack

The effects of tangential jet blowing on the vortical structures developing about the fuselage of a missile or aircraft at high angle of attack are investigated numerically and experimentally. Computations are carried out for fully laminar and fully turbulent flows, and the results are compared with flow visualization data. It is shown that turbulent computations are more accurate in describing the flow behavior. The actuator plane method is shown to be sufficiently accurate in modeling the essential flow physics of a tangential jet.

Font, G. I.↗
NASA NTRS1994

X-31 high angle of attack control system performance

The design goals for the X-31 flight control system were: (1) level 1 handling qualities during post-stall maneuvering (30 to 70 degrees angle-of-attack); (2) thrust vectoring to enhance performance across the flight envelope; and (3) adequate pitch-down authority at high angle-of-attack. Additional performance goals are discussed. A description of the flight control system is presented, highlighting flight control system features in the pitch and roll axes and X-31 thrust vectoring characteristics. The high angle-of-attack envelope clearance approach will be described, including a brief explanation of analysis techniques and tools. Also, problems encountered during envelope expansion will be discussed. This presentation emphasizes control system solutions to problems encountered in envelope expansion. An essentially 'care free' envelope was cleared for the close-in-combat demonstrator phase. High angle-of-attack flying qualities maneuvers are currently being flown and evaluated. These results are compared with pilot opinions expressed during the close-in-combat program and with results obtained from the F-18 HARV for identical maneuvers. The status and preliminary results of these tests are discussed.

Huber, Peter↗
NASA NTRS1990

Preliminary results from a subsonic high-angle-of-attack flush airdata sensing (HI-FADS) system - Design, calibration, algorithm development, and flight test evaluation

A nonintrusive high angle-of-attack flush airdata sensing (HI-FADS) system was installed and flight-tested on the F-18 high alpha research vehicle. This paper discusses the airdata algorithm development and composite results expressed as airdata parameter estimates and describes the HI-FADS system hardware, calibration techniques, and algorithm development. An independent empirical verification was performed over a large portion of the subsonic flight envelope. Test points were obtained for Mach numbers from 0.15 to 0.94 and angles of attack from -8.0 to 55.0 deg. Angles of sideslip ranged from -15.0 to 15.0 deg, and test altitudes ranged from 18,000 to 40,000 ft. The HI-FADS system gave excellent results over the entire subsonic Mach number range up to 55 deg angle of attack. The internal pneumatic frequency response of the system is accurate to beyond 10 Hz.

Whitmore, Stephen A.↗
NASA NTRS1985

Recent experiences of unsteady aerodynamic effects on aircraft flight dynamics at high angle of attack

Recent research is highlighted which was conducted at the NASA Langley Research Center on two high angle-of-attack flight dynamic phenomena which are dominated by unsteady aerodynamic effects: wing rock and tumbling. Studies of wing rock induced by strong vortical flows and tumbling characteristics observed on an advanced configuration are reviewed. Results of wind tunnel experiments are summarized and the aerodynamic mechanisms involved in the phenomena were discussed.

Nguyen, L. T.↗
NASA NTRS1990

Development of non-conventional control methods for high angle of attack flight using vortex manipulation

Methods of manipulating the forebody vortices on a generic fighter model to produce controlled yawing moments at high angles of attack were investigated. Forces and moments were measured on the complete configuration and on the isolated forebody. Two schemes for vortex control on the forebody were evaluated: individually-controlled tip strakes and individually-controlled blowing ports. The effectiveness of the forebody strakes in controlling forebody side forces was strongly dependent on the size and location of the strakes. A yawing moment can be produced by deploying the forebody strakes asymmetrically, or can be eliminated by deploying the strakes symmetrically. The most effective strake position was found to be near the primary separation point, between 105 and 120 deg from windward. Blowing on the surface of the model was also shown to have a strong effect on the yawing moment. Blowing either forward or aft tangential to the surface appears to be more effective than blowing normal to the surface. The most effective method to control the yawing moment on the forebody was to minimize the natural asymmetry with a pair of small symmetrically mounted tip strakes and to perturb the vortex system away from the symmetric condition with asymmetric blowing.

Malcolm, Gerald N.↗
NASA NTRS1992

Wind-tunnel static and free-flight investigation of high-angle-of-attack stability and control characteristics of a model of the EA-6B airplane

An investigation was conducted in the Langley 30- by 60-Foot Tunnel and the Langley 12-Foot Low-Speed Tunnel to identify factors contributing to a directional divergence at high angles of attack for the EA-6B airplane. The study consisted of static wind-tunnel tests, smoke and tuft flow-visualization tests, and free-flight tests of a 1/8.5-scale model of the airplane. The results of the investigation indicate that the directional divergence of the airplane is brought about by a loss of directional stability and effective dihedral at high angles of attack. Several modifications were tested that significantly alleviate the stability problem. The results of the free-flight study show that the modified configuration exhibits good dynamic stability characteristics and could be flown at angles of attack significantly higher than those of the unmodified configuration.

Jordan, Frank L., Jr.↗
NASA NTRS1992

Experimental investigation of the effects of aft blowing with various nozzle exit geometries on a 3.0 caliber tangent ogive at high angles of attack: Forebody pressure distributions

An experimental study of the effects of aft blowing on the asymmetric vortex flow of a slender, axisymmetric body at high angles of attack was conducted. A 3.0 caliber tangent ogive body fitted with a cylindrical afterbody was tested in a wind tunnel under subsonic, laminar flow test conditions. Asymmetric blowing from both a single nozzle and a double nozzle configuration, positioned near the body apex, was studied. Aft blowing was observed to alter the vortex asymmetry by moving the blowing-side vortex closer to the body surface while moving the non-blowing-side vortex further away from the body. The effect of increasing the blowing coefficient was to move the blowing-side vortex closer to the body surface at a more upstream location. The data also showed that blowing was more effective in altering the initial vortex asymmetry at the higher angles of attack than at the lower. The effects of changing the nozzle exit geometry were studied and it was observed that blowing from a nozzle with a low, broad exit geometry was more effective in reducing the vortex asymmetry than blowing from a high, narrow exit geometry.

Chokani, Ndaona↗
NASA NTRS1992

Low aspect ratio wings at high angles of attack

A survey is conducted of the results of investigations into the flowfields and aerodynamic forces associated with low aspect ratio wings at high angles of attack. Attention is given to criteria for the cataloging of these flowfields, the phenomenon of vortex breakdown, with varying wing incidence and Mach number, and the effects of aspect ratio and compressibility. The planforms treated are of rectangular, clipped-delta, and strake-wing combination geometries. Extensive graphic representations of performance trends with varying parameters are furnished.

Stallings, Robert L., Jr.↗
NASA NTRS1987

Exploratory studies of actuated forebody strakes for yaw control at high angles of attack

Wind-tunnel studies have been conducted to evaluate the potential of actuated forebody strakes to provide increased levels of yaw control on fighter aircraft at extremely high angles of attack where conventional aerodynamic controls are ineffective. The studies involved low-speed wind-tunnel tests of actuated forebody strake concepts applied to a generic fighter model and included circumferential pressure and flow visualization surveys on an isolated forebody. Results showed that the actuated forebody strake concept can provide high levels of yaw control over wide ranges of angle-of-attack and sideslip. However, when lifting surfaces were placed in close proximity to the forebody/strake combination, significant interaction effects occurred which reduced the yaw control effectiveness of the strakes and induced coupled rolling and pitching moments.

Murri, Daniel G.↗
NASA NTRS1993

Actuator and aerodynamic modeling for high-angle-of-attack aeroservoelasticity

Accurate prediction of airframe/actuation coupling is required by the imposing demands of modern flight control systems. In particular, for agility enhancement at high angle of attack and low dynamic pressure, structural integration characteristics such as hinge moments, effective actuator stiffness, and airframe/control surface damping can have a significant effect on stability predictions. Actuator responses are customarily represented with low-order transfer functions matched to actuator test data, and control surface stiffness is often modeled as a linear spring. The inclusion of the physical properties of actuation and its installation on the airframe is therefore addressed using detailed actuator models which consider the physical, electrical, and mechanical elements of actuation. The aeroservoelastic analysis procedure is described in which the actuators are modeled as detailed high-order transfer functions and as approximate low-order transfer functions. The impacts of unsteady aerodynamic modeling on aeroservoelastic stability are also investigated by varying the order of approximation, or number of aerodynamic lag states, in the analysis. Test data from a thrust-vectoring configuration of an F/A-l8 aircraft are compared to predictions to determine the effects on accuracy as a function of modeling complexity.

Brenner, Martin J.↗
NASA NTRS1993

Actuator and aerodynamic modeling for high-angle-of-attack aeroservoelasticity

Accurate prediction of airframe/actuation coupling is required by the imposing demands of modern flight control systems. In particular, for agility enhancement at high angle of attack and low dynamic pressure, structural integration characteristics such as hinge moments, effective actuator stiffness, and airframe/control surface damping can have a significant effect on stability predictions. Actuator responses are customarily represented with low-order transfer functions matched to actuator test data, and control surface stiffness is often modeled as a linear spring. The inclusion of the physical properties of actuation and its installation on the airframe is therefore addressed in this paper using detailed actuator models which consider the physical, electrical, and mechanical elements of actuation. The aeroservoelastic analysis procedure is described in which the actuators are modeled as detailed high-order transfer functions and as approximate low-order transfer functions. The impacts of unsteady aerodynamic modeling on aeroservoelastic stability are also investigated in this paper by varying the order of approximation, or number of aerodynamic lag states, in the analysis. Test data from a thrust-vectoring configuration of an F/A-18 aircraft are compared to predictions to determine the effects on accuracy as a function of modeling complexity.

Brenner, Martin J.↗
NASA NTRS1989

Flutter Clearance of the F-18 High-angle-of-attack Research Vehicle with Experimental Wingtip Instrumentation Pods

An F-18 aircraft was modified with wingtip instrumentation pods for use in NASA's high-angle-of-attack research program. Ground vibration and flight flutter testing were performed to clear an acceptable flight envelope for the aircraft. Flight test utilized atmospheric turbulence for structural excitation; the aircraft displayed no adverse aeroelastic trends within the envelope tested. The data presented in this report include mode shapes from the ground vibration and estimates of frequency and damping as a function of Mach number.

Freudinger, Lawrence C.↗
NASA NTRS1992

Pitch Control Margin at High Angle of Attack - Quantitative Requirements (Flight Test Correlation With Simulation Predictions)

Aircraft designs that employ relaxed static stability (RSS) have the following problem: reduced pitching moments associated with RSS at high angle of attack (AOA) require a minimum pitch recovery moment or margin to guarantee a safe return from high AOA maneuvers at the most aft center of gravity (CG) encountered during a mission. Recent incidents and mishaps on Class IV aircraft have demonstrated a need for establishing quantitative longitudinal high AOA pitch control margin design guidelines for future aircraft. The Naval Air Warfare Center - Aircraft Division (NA WC-AD) is currently supporting an effort in conjunction with NASA Langley Research Center (NASA LaRC) to quantify such requirements. NASA LaRC has conducted a series of extensive simulation evaluations to define these design guidelines. The purpose of flight tests were to validate the overall research test methodology by comparing pilot comments, pilot ratings, and aircraft response characteristics gathered during inflight recoveries from high AOA conditions to those gathered during the fixed-base simulation sessions. Tests were completed on an F/A-18A in six flights for a total of 9.8 flight hours using an AOA and CG buildup sequence. Flight test results have validated the simulation studies in that pilot rating of high AOA nose-down recoveries were based on the short-term response interval in the forms of pitch acceleration and rate. In addition, flight test has demonstrated that high AOA pitch control margin can be evaluated using a stabilized pushover method.

Flight Testing↗
NASA NTRS1992

A High Angle of Attack Inviscid Shuttle Orbiter Computation

An accurate description of the aerothermal environment is required to minimize the weight of the Thermal Protection System required on the leeside of winged reentry vehicles. The inability of ground-test facilities to reproduce the high enthalpy, separated flow present during reentry flight conditions, coupled with the prohibitive expense of flight tests, leads to the use of an analytical method - namely Computational Fluid Dynamics (CFD) - to describe the flow. While the ultimate goal of this work is to accurately predict the leeside flow and its associated thermal environment, an essential and reasonable first step towards that goal is a comparison of pressure predictions by a code with wind-tunnel data. Until such CFD pressure predictions agree with wind-tunnel test cases, there is little hope of accurately predicting the thermal environment at flight conditions. Thus, the objective of this study is to compare the pressure distributions predicted by inviscid, perfect gas CFD to Shuttle Orbiter wind-tunnel data and to address any significant issues encountered during the computation. While flight data is available for the Shuttle Orbiter, a wind-tunnel case is chosen for this study to allow a tractable problem for preliminary investigation. A wind-tunnel case allows the perfect gas assumption for the flow chemistry. This provides a significant computational savings over a several species finite-rate chemistry model which would be necessary if high-temperature effects present at flight conditions were to be included. In addition, by concentrating on the surface pressures, the analysis need only consider inviscid flow for general evaluation of the code capability. This further reduces the computational expense due to the absence of viscous terms and the associated decrease in the number of points required for the computational grid. Previous computational efforts (such as STEIN and HALIS) have been directed toward the windward surface quantities, primarily due to restrictions in treating either the winged geometry or its associated subsonic regions at high angle of attack. The code used for this study, the LAURA (Langley Aerothermodynamic Upwind Relaxation Algorithm) code of Gnoffo, represents a state-of-the-art code for computing the flow over complex configurations at hypersonic speeds. In the study, the LAURA code is applied to a wind-tunnel condition to initiate the assessment of the code's ability to predict the flow over a relatively complex hypersonic vehicle at high angles of attack. This presentation is used to highlight the pertinent results of a more detailed investigation of the inviscid calculation over the Shuttle Orbiter with the LAURA code.

William L. Kleb↗