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At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Progress towards large wind tunnel magnetic suspension and balance systems

Recent developments and current research efforts leading towards realization of a large scale production wind tunnel Magnetic Suspension and Balance facility are reviewed. Progress has been made in the areas of model roll control, high angle-of-attack testing, digital system control, high magnetic moment superconducting solenoid model cores, and system failure tolerance. Formal design studies of large scale facilities have commenced and are continuing.

Britcher, C. P.↗
NASA NTRS1985

Programming for Pioneer 12

Background on Pioneer probes 6 to 11 is given as well as an overview of the Pioneer Venus mission. A computer program was written in C language for analyzing radio signals from the Pioneer Venus orbiter. A second program was written to facilitate high gain antenna commands to move the antenna itself, to set the simulated spin period, and to set the attitude control system angle.

Shem, B. C.↗
NASA NTRS1985

Small-signal model for the series resonant converter

The results of a previous discrete-time model of the series resonant dc-dc converter are reviewed and from these a small signal dynamic model is derived. This model is valid for low frequencies and is based on the modulation of the diode conduction angle for control. The basic converter is modeled separately from its output filter to facilitate the use of these results for design purposes. Experimental results are presented.

King, R. J.↗
NASA NTRS1988

Penetration landing guidance trajectories in the presence of windshear

Flight trajectory guidance in the presence of windshear is considered with reference to flight in a vertical plane. Both horizontal shear and the presence of a downdraft are assumed. The optimal trajectory is first determined by minimizing a performance index which is subject to touchdown constraints, under the assumption of control via angle of attack and power setting. It is shown that the coupling relation between the angle of attack and the power setting can be ignored. A guidance scheme is constructed in which the angle of attack is determined by the windshear intensity, the absolute path inclination, and the glide slope angle, while the power setting is determined by the windshear intensity and the velocity. Particular attention is given to low-altitude penetration landing.

Miele, A.↗
NASA NTRS1990

Delivery performance of conventional aircraft by terminal-area, time-based air traffic control: A real-time simulation evaluation

A description and results are presented of a study to measure the performance and reaction of airline flight crews, in a full workload DC-9 cockpit, flying in a real-time simulation of an air traffic control (ATC) concept called Traffic Intelligence for the Management of Efficient Runway-scheduling (TIMER). Experimental objectives were to verify earlier fast-time TIMER time-delivery precision results and obtain data for the validation or refinement of existing computer models of pilot/airborne performance. Experimental data indicated a runway threshold, interarrival-time-error standard deviation in the range of 10.4 to 14.1 seconds. Other real-time system performance parameters measured include approach speeds, response time to controller turn instructions, bank angles employed, and ATC controller message delivery-time errors.

Credeur, Leonard↗
NASA NTRS1992

Flight Testing and Simulation of an F-15 Airplane Using Throttles for Flight Control

Flight tests and simulation studies using the throttles of an F-15 airplane for emergency flight control have been conducted at the NASA Dryden Flight Research Facility. The airplane and the simulation are capable of extended up-and-away flight, using only throttles for flightpath control. Initial simulation results showed that runway landings using manual throttles only control were difficult, but possible with practice. Manual approaches flown in the airplane were much more difficult, indicating a significant discrepancy between flight and simulation. Analysis of flight data and development of improved simulation models that resolve the discrepancy are discussed. An augmented throttles-only control system that controls bank angle and flightpath with appropriate feedback parameters has also been developed, evaluated in simulations, and is planned for flight in the F-15.

Flight Testing↗
NASA NTRS1993

Prediction of active control of subsonic centrifugal compressor rotating stall

A mathematical model is developed to predict the suppression of rotating stall in a centrifugal compressor with a vaned diffuser. This model is based on the employment of a control vortical waveform generated upstream of the impeller inlet to damp weak potential disturbances that are the early stages of rotating stall. The control system is analyzed by matching the perturbation pressure in the compressor inlet and exit flow fields with a model for the unsteady behavior of the compressor. The model was effective at predicting the stalling behavior of the Purdue Low Speed Centrifugal Compressor for two distinctly different stall patterns. Predictions made for the effect of a controlled inlet vorticity wave on the stability of the compressor show that for minimum control wave magnitudes, on the order of the total inlet disturbance magnitude, significant damping of the instability can be achieved. For control waves of sufficient amplitude, the control phase angle appears to be the most important factor in maintaining a stable condition in the compressor.

Lawless, Patrick B.↗
NASA NTRS1992

X-29 vortex flow control tests

A joint Air Force/NASA X-29 aircraft program to improve yaw control at high angle of attack using vortex flow control (VFC) is described. Directional VFC blowing proved to a be a powerful yaw moment generator and was very effective in overriding natural asymmetries, but was essentially ineffective in suppressing wing rock. Symmetric aft blowing also had little effect on suppressing wing rock.

Hancock, Regis↗
NASA NTRS1936

Notes on the technique of landing airplanes equipped with wing flaps

The proper landing of airplanes equipped with flaps, although probably no more difficult than landing without them, requires a different technique. The effects of flaps on the aerodynamics characteristics of a wing are given and, with the aid of figures and diagrams, a detailed comparison of the glide and landing of an airplane with and without flaps is made. The dangers attending improper execution and the importance of such factors as air speed fuselage attitude, glide-path angle, and control manipulation, upon all of which a pilot bases his judgement, are emphasized. Of most importance in connection with the use of flaps are: the maintenance of a sufficient margin of speed above the stall; a decisive use of the controls at the proper time; more cautious use of power during the approach glide; and, above all, the willingness to accept the steep nose-down attitude necessary in the glide resulting from the use of flaps.

Gough, Melvin N↗
NASA NTRS1993

Aeroelastic response and stability of tiltrotors with elastically-coupled composite rotor blades

There is a potential for improving the performance and aeroelastic stability of tiltrotors through the use of elastically-coupled composite rotor blades. To study the characteristics of tiltrotors with these types of rotor blades it is necessary to formulate a new analysis which has the capabilities of modeling both a tiltrotor configuration and an anisotropic rotor blade. Background for these formulations is established in two preliminary investigations. In the first, the influence of several system design parameters on tiltrotor aeroelastic stability is examined for the high-speed axial flight mode using a newly-developed rigid-blade analysis with an elastic wing finite element model. The second preliminary investigation addresses the accuracy of using a one-dimensional beam analysis to predict frequencies of elastically-coupled highly-twisted rotor blades. Important aspects of the new aeroelastic formulations are the inclusion of a large steady pylon angle which controls tilt of the rotor system with respect to the airflow, the inclusion of elastic pitch-lag coupling terms related to rotor precone, the inclusion of hub-related degrees of freedom which enable modeling of a gimballed rotor system and engine drive-train dynamics, and additional elastic coupling terms which enable modeling of the anisotropic features for both the rotor blades and the tiltrotor wing. Accuracy of the new tiltrotor analysis is demonstrated by a comparison of the results produced for a baseline case with analytical and experimental results reported in the open literature. Two investigations of elastically tailored blades on a baseline tiltrotor are then conducted. One investigation shows that elastic bending-twist coupling of the rotor blade is a very effective means for increasing the flutter velocity of a tiltrotor, and the magnitude of coupling required does not have an adverse effect on performance or blade loads. The second investigation shows that passive blade twist control via elastic extension-twist coupling of the rotor blade has the capability of significantly improving tiltrotor aerodynamic performance. This concept, however, is shown to have, in general, a negative impact on stability characteristics.

Nixon, Mark W.↗
NASA NTRS1994

Dynamic-stall and structural-modeling effects on helicopter blade stability with experimental correlation

The effects of blade and root-flexure elasticity and dynamic stall on the stability of hingeless rotor blades are investigated. The dynamic stall description is based on the ONERA models of lift, drag, and pitching moment. The structural analysis is based on three blade models that range from a rigid flap-lag model to two elastic flap-lag-torsion models, which differ in representing root-flexure elasticity. The predictions are correlated with the measured lag damping of an experimental isolated three-blade rotor; the correlation covers rotor operations from near-zero-thrust conditions in hover to highly stalled, high-thrust conditions in foward flight. That correlation shows sensitivity of lag-damping predictions to structural refinements in blade and root-flexure modeling. Moreover, this sensitivity increases with increasing control pitch angle and advance ratio. For high-advance-ratio and high-thrust conditions, inclusion of dynamic stall generally improves the correlation.

Barwey, D.↗
NASA NTRS1961

Study of the Use of a Terminal Controller Technique for Reentry Guidance of a Capsule-Type Vehicle

A study has been made of the use o f a terminal controller technique i n the guidance of a high-drag, variable-lift reentry vehicle to a desired landing point. The technique uses linearized equations of motion attained by the perturbation of the dependent variables from those of a reference trajectory. The guidance system continuously predicts the terminal range error and uses this error to control the angle of attack of the vehicle in an on-off manner until the predicted range error is within +-O.1 degrees of the required arc or +-6.9 miles.

Foudriat, Edwin C.↗
NASA NTRS1961

Aerodynamic Characteristics in Pitch of a Series of Cruciform-Wing Missiles with Canard Controls at a Mach Number of 2.01

An investigation has been conducted in the Langley 4- by 4-foot supersonic pressure tunnel at a Mach number of 2.01 to determine the static longitudinal stability and control characteristics of a series of missile configurations with canard controls at angles of attack up to about 28 deg. The missiles had cruciform wings and canard surfaces of delta plan form with 70 deg.swept leading edges. Five bodies having fineness ratios of 19.1, 17.7, 16.7, 15.7, and 14.8 were investigated. The results of the investigation indicated a large nonlinear variation of pitching moment with angle of attack for the body of largest fineness ratio that was progressively reduced by decreasing the fineness ratio until it was essentially eliminated for a body of fineness ratio 14.8. The increased linearity of the moment curve would make it possible to reduce the margin of stability so that, for a given canard size and deflection, a higher trim angle of attack might be obtained for the shortest missile than for the longest missile. The pitching-moment results indicated that methods of prediction which assumed linear variations with angle of attack for the wing-alone and wing-plus-interference characteristics were adequate for angles of attack up to about 12 deg. At higher angles of attack it was evident that the characteristics of these components were nonlinear and that more refined methods would be required for adequate prediction.

Spearman, M. Leroy↗
NASA NTRS2007

Dryden Flight Research Center Overview

This viewgraph document presents a overview of the Dryden Flight Research Center's facilities. Dryden's mission is to advancing technology and science through flight. The mission elements are: perform flight research and technology integration to revolutionize aviation and pioneer aerospace technology, validate space exploration concepts, conduct airborne remote sensing and science observations, and support operations of the Space Shuttle and the ISS for NASA and the Nation. It reviews some of the recent research projects that Dryden has been involved in, such as autonomous aerial refueling, the"Quiet Spike" demonstration on supersonic F-15, intelligent flight controls, high angle of attack research on blended wing body configuration, and Orion launch abort tests.

Meyer, Robert R., Jr.↗
NASA NTRS2010

A Computational Study of BVI Noise Reduction Using Active Twist Control

The results of a computational study examining the effects of active-twist control on blade-vortex interaction (BVI) noise using the Apache Active Twist Rotor are presented. The primary goal of this activity is to reduce BVI noise during a low-speed descent flight condition using active-twist control. Rotor aeroelastic behavior was modeled using the Comprehensive Analytical Model of Rotorcraft Aerodynamics and Dynamics code and the rotor noise was predicted using the acoustics code PSU-WOPWOP. The accuracy of the analysis was validated through comparisons with experimental acoustic data for the first generation Active Twist Rotor at an advance ratio of mu=0.14. The application of active-twist to the main rotor blade system consisted of harmonic actuation frequencies ranging from 2P to 5P, control phase angles from 0' to 360 , and tip-twist amplitudes ranging from 0.5 to 4.0 . The acoustic analysis was conducted for a single low-speed flight condition of advance ratio =0.14 and shaft angle-of-attack, c^=+6 , with BVI noise levels predicted on a flat plane of observers located 1.1 rotor diameters beneath the rotor. The results indicated reductions of up to 11dB in BVI noise using 1.25 tip-twist amplitude with negligible effects on 4P vertical hub shear.

Fogarty, David E.↗
NASA NTRS1994

Comment on 'Guidance for an Aerocapture Maneuver

It is stated that the aerodynamic forces on the vehicle being aerocaptured are controlled by "altering the angle of attack" and thereby controlling the lift coefficient. Furthermore, the resulting variation of drag coefficient with angle of attack was ignored. The purpose of this Comment is to point out that an aerodynamic control method that is much more effective than the pitch modulation has been studied and utilized during entries for many years. During aerocapture, it is desirable to have a large range of lift coefficients available, while keeping the vehicle's ballistic coefficients constant. This is accomplished by modulating the vehicle's bank angle, i.e., by rolling the vehicle about its velocity vector. By this method, the angle of attack can be held constant (at the trim angle, if desired), and the C(sub D) and the ballistic coefficient remain constant. Furthermore, the vertical component of the normal force vector (essentially the lift) can be varied over its entire range, from maximum positive to maximum negative values. Reaction controls, rather than aerodynamic ones, are usually utilized to change the bank angle of the vehicle, thus requiring the use of fuel. However, the fuel expenditure that is required to change the bank angle is far less than the amount that would have to be used to continuously hold the vehicle at pitch angles that differ significantly from its trim angle of attack. Also, it has been shown that bank angle modulation to vary the lift can enlarge the entry corridor by increasing the entry angle for the undershoot boundary, where both the heating rate and deceleration reach a maximum. Finally, the crew's deceleration tolerance can be increased somewhat when the bank angle is varied, as opposed to the pitch angle. For bank modulation, the deceleration force vector can be kept at a constant angle with respect to the occupants whose tolerance to g loads is highest when the force is applied in a direction normal to the upper torso. The advantages of bank angle variation to modulate the lift vector were recognized long ago, and this method of control was used successfully on the Apollo command module during lunar return' and, more recently, for the Space Shuttle Orbiter.

Tauber, Michael E.↗