Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “angle control”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Simulation comparison of a decoupled longitudinal control system and a velocity vector control wheel steering system during landings in wind shear

A simulator comparison of the velocity vector control wheel steering (VCWS) system and a decoupled longitudinal control system is presented. The piloting task was to use the electronic attitude direction indicator (EADI) to capture and maintain a 3 degree glide slope in the presence of wind shear and to complete the landing using the perspective runway included on the EADI. The decoupled control system used constant prefilter and feedback gains to provide steady state decoupling of flight path angle, pitch angle, and forward velocity. The decoupled control system improved the pilots' ability to control airspeed and flight path angle during the final stages of an approach made in severe wind shear. The system also improved their ability to complete safe landings. The pilots preferred the decoupled control system in severe winds and, on a pilot rating scale, rated the approach and landing task with the decoupled control system as much as 3 to 4 increments better than use of the VCWS system.

Kimball, G., Jr.↗
NASA NTRS1953

Flight Investigation of the Stability and Control Characteristics of a 0.13-Scale Model of the Convair XFY-1 Vertically Rising Airplane During Constant-Altitude Transitions, TED No. NACA DE 368

An investigation is being conducted to determine the dynamic stability and control characteristics of a 0.13-scale flying model of the Convair XFY-1 vertically rising airplane. This paper presents the results of flight tests to determine the stability and control characteristics of the model during constant-altitude slow transitions from hovering to normal unstalled forward flight. The tests indicated that the airplane can be flown through the transition range fairly easily although some difficulty will probably encountered in controlling the yawing motions at angles of attack between about 60 and 40. An increase in the size of the vertical tail will not materially improve the controllability of the yawing motions in this range of angle of attack but the use of a yaw damper will make the yawing motions easy to control throughout the entire transitional flight range. The tests also indicated that the airplane can probably be flown sideways satisfactorily at speeds up to approximately 33 knots (full scale) with the normal control system and up to approximately 37 knots (full scale) with both elevons and rudders rigged to move differentially for roll control. At sideways speeds above these values, the airplane will have a strong tendency to diverge uncontrollably in roll.

Lovell, Powell M., Jr.↗
NASA NTRS2010

Mode Tracker for Mode-Hop-Free Operation of a Laser

A mode-tracking system that includes a mode-controlling subsystem has been incorporated into an external-cavity (EC) quantum cascade laser that operates in a mid-infrared wavelength range. The mode-tracking system makes it possible to perform mode-hop-free wavelength scans, as needed for high-resolution spectroscopy and detection of trace gases. The laser includes a gain chip, a beam-collimating lens, and a diffraction grating. The grating is mounted on a platform, the position of which can be varied to effect independent control of the EC length and the grating angle. The position actuators include a piezoelectric stage for translation control and a motorized stage for coarse rotation control equipped with a piezoelectric actuator for fine rotation control. Together, these actuators enable control of the EC length over a range of about 90 m with a resolution of 0.9 nm, and control of the grating angle over a coarse-tuning range of +/-6.3deg and a fine-tuning range of +/-520 microrad with a resolution of 10 nrad. A mirror mounted on the platform with the grating assures always the same direction of the output laser beam.

Wysocki, Gerard↗
NASA NTRS1975

Entry reaction control system propellant analysis. Flight control integration

The effects of winds, sideslip angle feedback, and the data reference (air or inertial) on the Reaction Control System (RCS) propellant requirements during entry were investigated. It was determined that in the presence of a 3 sigma crosswind an addition 188 pounds of RCS propellant was required for entry control which is within the present 200 pound allotment for winds. The absence of air data information does result in slightly higher RCS propellant demands.

Devall, O. R.↗
NASA NTRS1983

A study of helicopter gust response alleviation by automatic control

Two control schemes designed to alleviate gust-induced vibration are analytically investigated for a helicopter with four articulated blades. One is an individual blade pitch control scheme. The other is an adaptive blade pitch control algorithm based on linear optimal control theory. In both controllers, control inputs to alleviate gust response are superimposed on the conventional control inputs required to maintain the trim condition. A sinusoidal vertical gust model and a step gust model are used. The individual blade pitch control, in this research, is composed of sensors and a pitch control actuator for each blade. Each sensor can detect flapwise (or lead-lag or torsionwise) deflection of the respective blade. The acturator controls the blade pitch angle for gust alleviation. Theoretical calculations to predict the performance of this feedback system have been conducted by means of the harmonic method. The adaptive blade pitch control system is composed of a set of measurements (oscillatory hub forces and moments), an identification system using a Kalman filter, and a control system based on the minimization of the quadratic performance function.

Saito, S.↗
NASA NTRS1986

An experimental investigation of the flap-lag-torsion aeroelastic stability of a small-scale hingeless helicopter rotor in hover

A small scale, 1.92 m diam, torsionally soft, hingeless helicopter rotor was investigated in hover to determine isolated rotor stability characteristics. The two-bladed, untwisted rotor was tested on a rigid test stand at tip speeds up to 101 m/sec. The rotor mode of interest is the lightly damped lead-lag mode. The dimensionless lead-lag frequency of the mode is approximately 1.5 at the highest tip speed. The hub was designed to allow variation in precone, blade droop, pitch control stiffness, and blade pitch angle. Measurements of modal frequency and damping were obtained for several combinations of these hub parameters at several values of rotor speed. Steady blade bending moments were also measured. The lead-lag damping measurements were found to agree well with theoretical predictions for low values of blade pitch angle. The test data confirmed the predicted effects of precone, droop, and pitch control stiffness parameters on lead-lag damping. The correlation between theory and experiment was found to be poor for the mid-to-high range of pitch angles where the theory substantially overpredicted the experimental lead-lag damping. The poor correlation in the mid-to-high blade pitch angle range is attributed to low Reynolds number nonlinear aerodynamics effects not included in the theory. The experimental results also revealed an asymmetry in lead-lag damping between positive and negative thrust conditions.

Sharpe, David L.↗
NASA NTRSDate not supplied

Pterodactyl: 6-DOF Integration of Guidance and Control Algorithms in Genesis

The NASA-funded Pterodactyl project seeks to advance the current state-of-the-art for entry vehicles by developing novel guidance and control technologies for Deployable Entry Vehicles. This paper builds upon the Pterodactyl architecture that employed eight individually articulating flaps with two options for guidance, bank angle modulation with the Fully Numerical Predictor Corrector Entry Guidance (FNPEG) technique and angle of attack and sideslip modulation with FNPEG uncoupled range control. These, with a linear quadratic regulator controller, have previously been presented in separate 3-DOF trajectory simulations, one for translational motion and another for rotational dynamics. This work will show results for integrated 6-DOF simulations, leveraging recent advancements in trajectory simulation tools, namely the Julia-based Genesis package. Results show similar performance for both schemes when compared to the previously presented 3-DOF results once the controllers were adequately tuned. Angle of attack and sideslip modulation necessitated a controller designed at high dynamic pressure conditions, and bank angle modulation necessitated a controller designed at lower dynamic pressure conditions. Notably, angle of attack and sideslip modulation could not achieve the parachute deploy point target Mach number of 2, when only tuning the controller gains, thus future work will be needed to tune guidance specific parameters to achieve acceptable range targeting and guidance command tracking.

DEV↗
NASA NTRS1995

Universal Controller For Supersonic Engine Inlet

Engine-demand airflow used as primary control parameter. Optimum inlet angle depends on such other variables as mach number, altitude, and ambient temperature. Function of these variables approximated by schedule ("inlet ramp schedule") of digitized values implemented by digital control system.

Yonke, William A.↗
NASA NTRS1994

Active control of fan noise from a turbofan engine

A three-channel active control system is applied to an operational turbofan engine to reduce tonal noise produced by both the fan and the high-pressure compressor. The control approach is the feedforward filtered-x least-mean-square algorithm implemented on a digital signal processing board. Reference transducers mounted on the engine case provide blade passing and harmonics frequency information to the controller. Error information is provided by large area microphones placed in the acoustic far field. To minimize the error signal, the controller actuates loudspeakers mounted on the inlet to produce destructive interference. The sound pressure level of the fundamental tone of the fan was reduced using the three-channel controller by up to 16 dB over a +/- 30-deg angle about the engine axis. A single-channel controller could produce reduction over a +/- 15-deg angle. The experimental results show the control to be robust. Outside of the areas contolled, the levels of the tone actually increased due to the generation of radial modes by the control sources. Simultaneous control of two tones is achieved with parallel controllers. The fundamental and the first harmonic tones of the fan were controlled simultaneously with reductions of 12 and 5 dBA, respectively, measured on the engine axis. Simultaneous control was also demonstrated for the fan fundamental and the high-pressure compressor fundamental tones.

Thomas, Russell H.↗
NASA NTRS1931

The Steady Spin

With the object of further clarifying the problem of spinning, the equilibrium of the forces and moments acting on an airplane is discussed in light of the most recent test data. Convinced that in a spin the flight attitude by only small angles of yaw is more or less completely steady, the study is primarily devoted to an investigation of steady spin with no side slip. At small angles, wholly arbitrary and perfectly steady spins may be forced, depending on the type of control displacements. But at large angles only very steep and only "approaching steady" spins are possible, no matter what the control displacements.

Fuchs, Richard↗
NASA NTRS1979

Precision controllability of the F-15 airplane

A flying qualities evaluation conducted on a preproduction F-15 airplane permitted an assessment to be made of its precision controllability in the high subsonic and low transonic flight regime over the allowable angle of attack range. Precision controllability, or gunsight tracking, studies were conducted in windup turn maneuvers with the gunsight in the caged pipper mode and depressed 70 mils. This evaluation showed the F-15 airplane to experience severe buffet and mild-to-moderate wing rock at the higher angles of attack. It showed the F-15 airplane radial tracking precision to vary from approximately 6 to 20 mils over the load factor range tested. Tracking in the presence of wing rock essentially doubled the radial tracking error generated at the lower angles of attack. The stability augmentation system affected the tracking precision of the F-15 airplane more than it did that of previous aircraft studied.

Sisk, T. R.↗
NASA NTRS1995

Performance of an aerodynamic yaw controller mounted on the space shuttle orbiter body flap at Mach 10

A wind-tunnel investigation of the effectiveness of an aerodynamic yaw controller mounted on the lower surface of a shuttle orbiter model body flap was conducted in the Langley 31-Inch Mach 10 Tunnel. The controller consisted of a 60 deg delta fin mounted perpendicular to the body flap lower surface and yawed 30 deg to the free stream direction. The control was tested at angles of attack from 20 deg to 40 deg at zero sideslip for a Reynolds number based on wing mean aerodynamic chord of 0.66 x 10(exp 6). The aerodynamic and control effectiveness characteristics are presented along with an analysis of the effectiveness of the controller in making a bank maneuver for Mach 18 flight conditions. The controller was effective in yaw and produced a favorable rolling moment. The analysis showed that the controller was as effective as the reaction control system in making the bank maneuver. These results warrant further studies of the aerodynamic/aerothermodynamic characteristics of the control concept for application to future transportation vehicles.

Scallion, W. I.↗
NASA NTRS1985

Preliminary design study of a lateral-directional control system using thrust vectoring

A preliminary design of a lateral-directional control system for a fighter airplane capable of controlled operation at extreme angles of attack is developed. The subject airplane is representative of a modern twin-engine high-performance jet fighter, is equipped with ailerons, rudder, and independent horizontal-tail surfaces. Idealized bidirectional thrust-vectoring engine nozzles are appended to the mathematic model of the airplane to provide additional control moments. Optimal schedules for lateral and directional pseudo control variables are calculated. Use of pseudo controls results in coordinated operation of the aerodynamic and thrust-vectoring controls with minimum coupling between the lateral and directional airplane dynamics. Linear quadratic regulator designs are used to specify a preliminary flight control system to improve the stability and response characteristics of the airplane. Simulated responses to step pilot control inputs are stable and well behaved. For lateral stick deflections, peak stability axis roll rates are between 1.25 and 1.60 rad/sec over an angle-of-attack range of 10 deg to 70 deg. For rudder pedal deflections, the roll rates accompanying the sideslip responses can be arrested by small lateral stick motions.

Lallman, F. J.↗
NASA NTRS1992

The F-18 High Alpha Research Vehicle - A high-angle-of-attack testbed aircraft

The F-18 High Alpha Research Vehicle is the first thrust-vectoring testbed aircraft used to study the aerodynamics and maneuvering available in the poststall flight regime and to provide the data for validating ground prediction techniques. The aircraft includes a flexible research flight control system and full research instrumentation. The capability to control the vehicle at angles of attack up to 70 degrees is also included. This aircraft was modified by adding a pitch and yaw thrust-vectoring system. No significant problems occurred during the envelope expansion phase of the program.

Regenie, Victoria↗
NASA NTRS1935

Development of the NACA slot-lip aileron

An investigation of the undesirable delayed action, or lag, of the spoiler-type lateral control device led to the development of the NACA slot-lip aileron. The tests were made in the 7- by 10-foot wind tunnel with a 4- by 8-foot wing hinged at the tunnel jet boundary and taken of the motion of the control device under test and of the resulting wing motion. First, the lag, as affected by the fore-and-aft location of retractable ailerons or spoilers was determined. The lag was found to increase regularly as the spoiler was moved from the rear of the wing toward the front. Then a combination of spoilers and fixed slot was developed that, with the spoiler retracting into the forward part of the slot, reduced the time lag to a negligible value. In addition, an arrangement was developed using a hinged aileron-type flap as the upper portion, or lip, of a slot through the wing. This arrangement appears to be usable as a form of lateral control device that shows promise of giving improved control and stability at the high angles of attack through stall, with negligible lag, low control forces, and relatively simple construction.

Weick, Fred E↗
NASA NTRS1994

High angle of attack flying qualities criteria for longitudinal rate command systems

This study was designed to investigate flying qualities requirements of alternate pitch command systems for fighter aircraft at high angle of attack. Flying qualities design guidelines have already been developed for angle of attack command systems at 30, 45, and 60 degrees angle of attack, so this research fills a similar need for rate command systems. Flying qualities tasks that require post-stall maneuvering were tested during piloted simulations in the McDonnell Douglas Aerospace Manned Air Combat Simulation facility. A generic fighter aircraft model was used to test angle of attack rate and pitch rate command systems for longitudinal gross acquisition and tracking tasks at high angle of attack. A wide range of longitudinal dynamic variations were tested at 30, 45, and 60 degrees angle of attack. Pilot comments, Cooper-Harper ratings, and pilot induced oscillation ratings were taken from five pilots from NASA, USN, CAF, and McDonnell Douglas Aerospace. This data was used to form longitudinal design guidelines for rate command systems at high angle of attack. These criteria provide control law design guidance for fighter aircraft at high angle of attack, low speed flight conditions. Additional time history analyses were conducted using the longitudinal gross acquisition data to look at potential agility measures of merit and correlate agility usage to flying qualities boundaries. This paper presents an overview of this research.

Wilson, David J.↗
NASA NTRS1973

Experimental investigation of hypersonic buzz on a high cross-range shuttle configuration.

An experimental study confirming the existence of hypersonic buzz in the separated region of a space shuttle's downward deflected control surface is described. Wind tunnel tests in helium on a 1:100 scale model of a shuttle type configuration at M = 17.5 clearly demonstrated the occurrence of large scale pressure oscillations throughout a substantial range of angles of attack and control surface deflections. Measurements of surface pressure fluctuations along with high speed schlieren photography served to delineate the boundaries of the phenomenon and to identify the physical parameters necessary for the onset of a buzz condition. Prominent spectral energy peaks were also observed in the surface pressures that could be directly correlated with the instability. These conditions were found to be strongly dependent on the presence of multiple shock interactions and the position of these interactions relative to the location of a reattaching shear layer.

Goldman, R. L.↗