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  • Aircraft Stability and Control
  • 1995-1999  (13)
  • 1965-1969
  • 1950-1954
  • 1995  (13)
  • 1
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    A fresh view of the fly-by-light/power-by-wire program (1995)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: NASA has been funding a focused program to promote the development of optical signaling and electrical actuation for civil transports. This program is reviewed in the context of other government and private sector initiatives. It is concluded that significant resources have and continue to be expended to develop these technologies. A second goal of the program is to develop certification methods for aircraft that implement these new technologies. It is concluded that there is a significant need for this effort and that NASA in cooperation with the FAA are well suited to do satisfy the need. Electrical actuation is not new but has recently been made feasible for a broader array of high power applications than previously because of developments in power switching technologies, motors, and computers. This development has been well explored by the Air Force and the private sector and requires little more government attention. Light signal and sensor technology has been developing under public and private funding and has reached a level of maturity such that some companies are using optical signal carriers for flight control on private jets. Several issues remain unresolved but centrally focused government effort is not an effective way to pursue the variety of issues that persist. Certification of aircraft for flight is a government activity. The poor preparedness of the FAA to certify fault tolerant digital flight control systems against electromagnetic effects coupled with the increasing number of electromagnetic emitters constitutes an impediment for development of this technology. The complete lack of preparation to certify optical components is currently causing concern for a general aviation supplier who is having difficulty certify their system. NASA with the FAA should work to develop clear, reasonable, and cost effective ways of certifying the reliability of fault tolerant digital and optical flight control components and systems.
    Keywords: Aircraft Stability and Control
    Type: The 1995 NASA-ODU American Society for Engineering Education (ASEE) Summer Faculty Fellowship Program; 111; NASA-CR-198210
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  • 2
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    Electromagnetic compatibility and the all-electric airplane (1995)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: NASA is studying the feasibility of installing 'all-electric' controls in future commercial aircraft, replacing the current hydraulic and pneumatic systems. Planes utilizing such equipment should weigh less and be cheaper to maintain, but might also be susceptible to interference from undesired external electromagnetic fields. Possible sources of these extraneous signals include radio and television broadcasters, two-way communications stations, and radar installations of all kinds. One way to reduce the hazard would be to use fiber-optic cables to carry signals from the cockpit to the various points of use, a concept known as 'fly-by-light' or FBL. However, electrical circuits (PBW, or 'power-by-wire') would still be required at both ends of the cables to perform control functions, so the possibility of harmful interference would remain. Computer models for two different antennas were created in order to find the magnitude of the electric fields which would be generated in the airspace around them while in the transmit mode. The first antenna was a horizontal 'rhombic' used by the Voice of America (VOA) for long-distance short-wave broadcasting. The second antenna was a multi-element 'log-periodic dipole array' (LPDA) of a type often used for two-way radio communications. For each case, a specified amount of power was applied in the computer model, and the resulting electric field intensity was predicted at a variety of locations surrounding the antenna. This information will then be used to calculate the levels of interference which could occur inside an airplane flying in the vicinity of these radiation emitters.
    Keywords: Aircraft Stability and Control
    Type: The 1995 NASA-ODU American Society for Engineering Education (ASEE) Summer Faculty Fellowship Program; 68; NASA-CR-198210
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  • 3
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    Free-Flight Evaluation of Forebody Blowing for Yaw Control at High Angels of Attack (1995)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Forebody blowing is a concept developed to provide yaw control for aircraft flying at high angles of attack where a conventional rudder becomes ineffective. The basic concept is fairly simple. A small jet of air is forced out of the nose of the aircraft. This jet causes a repositioning of the forebody vortices in an asymmetrical fashion. The asymmetric forebody vortex flows develop a side force on the forebody which results in substantial yawing moments at high angles of attack. The purpose of this project was to demonstrate the use of forebody blowing as a control device through free-flight evaluation. This unique type of testing was performed at the NASA-Langley 30- by 60-foot tunnel. From these tests, it could then be shown that forebody blowing is an effective method of maintaining yaw control at high angles of attack.
    Keywords: Aircraft Stability and Control
    Type: Technical Reports: Langley Aerospace Research Summer Scholars; Part 1; 373-378; NASA-CR-202463
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  • 4
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    Roll-Yaw control at high angle of attack by forebody tangential blowing (1995)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The feasibility of using forebody tangential blowing to control the roll-yaw motion of a wind tunnel model is experimentally demonstrated. An unsteady model of the aerodynamics is developed based on the fundamental physics of the flow. Data from dynamic experiments is used to validate the aerodynamic model. A unique apparatus is designed and built that allows the wind tunnel model two degrees of freedom, roll and yaw. Dynamic experiments conducted at 45 degrees angle of attack reveal the system to be unstable. The natural motion is divergent. The aerodynamic model is incorporated into the equations of motion of the system and used for the design of closed loop control laws that make the system stable. These laws are proven through dynamic experiments in the wind tunnel using blowing as the only actuator. It is shown that asymmetric blowing is a highly non-linear effector that can be linearized by superimposing symmetric blowing. The effects of forebody tangential blowing and roll and yaw angles on the flow structure are determined through flow visualization experiments. The transient response of roll and yaw moments to a step input blowing are determined. Differences on the roll and yaw moment dependence on blowing are explained based on the physics of the phenomena.
    Keywords: Aircraft Stability and Control
    Type: NASA-CR-201844 , NAS 1.26:201844 , JIAA-TR-113
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  • 5
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    Pilot-Induced Oscillations and Human Dynamic Behavior (1995)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: This is an in-depth survey and study of pilot-induced oscillations (PIO's) as interactions between human pilot and vehicle dynamics; it includes a broad and comprehensive theory of PIO's. A historical perspective provides examples of the diversity of PIO's in terms of control axes and oscillation frequencies. The constituents involved in PIO phenomena, including effective aircraft dynamics, human pilot dynamic behavior patterns, and triggering precursor events, are examined in detail as the structural elements interacting to produce severe pilot-induced oscillations. The great diversity of human pilot response patterns, excessive lags and/or inappropriate gain in effective aircraft dynamics, and transitions in either the human or effective aircraft dynamics are among the key sources implicated as factors in severe PIO's. The great variety of interactions which may result in severe PIO's is illustrated by examples drawn from famous PIO's. These are generalized under a pilot-behavior-theory-based set of categories proposed as a classification scheme pertinent to a theory of PIO's. Finally, a series of interim prescriptions to avoid PIO is provided.
    Keywords: Aircraft Stability and Control
    Type: NASA-CR-4683 , H-2042 , NAS 1.26:4683 , TR-2494-1
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  • 6
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    Rotorcraft flight control design using quantitative feedback theory and dynamic crossfeeds (1995)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A multi-input, multi-output controls design with robust crossfeeds is presented for a rotorcraft in near-hovering flight using quantitative feedback theory (QFT). Decoupling criteria are developed for dynamic crossfeed design and implementation. Frequency dependent performance metrics focusing on piloted flight are developed and tested on 23 flight configurations. The metrics show that the resulting design is superior to alternative control system designs using conventional fixed-gain crossfeeds and to feedback-only designs which rely on high gains to suppress undesired off-axis responses. The use of dynamic, robust crossfeeds prior to the QFT design reduces the magnitude of required feedback gain and results in performance that meets current handling qualities specifications relative to the decoupling of off-axis responses. The combined effect of the QFT feedback design following the implementation of low-order, dynamic crossfeed compensator successfully decouples ten of twelve off-axis channels. For the other two channels it was not possible to find a single, low-order crossfeed that was effective.
    Keywords: Aircraft Stability and Control
    Type: NASA-CR-200066 , NAS 1.26:200066
    Format: application/pdf
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  • 7
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    Parametric Investigation of The Aeromechanic Stability of Bearingless Rotors (1995)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: The objective of this investigation is to conduct a parametric investigation on the aeromechanic stability of modern bearingless rotors. To ensure aeromechanic stability, modem bearingless; rotors use elastomeric dampers to augment the blade inplane damping. The augmented dampers are necessary to avoid aeromechanic instabilities such as air and ground resonance on soft-inplane rotors. The prevention of air and ground resonance depends largely on the damping level of the rotor-fuselage system during the critical frequency-crossing between the rotor and the fuselage inplane motions. The blade inplane damping, critical in ensuring aeromechanic stability of a rotor, depends not only on the damper sizes but also on the aeroelastic properties of the rotor blade. The results of this investigation provide insight into the source of inplane damping. The parametric study is carried out analytically using the University of Maryland Advanced Rotorcraft Code, or UMARC.
    Keywords: Aircraft Stability and Control
    Type: National Specialist Meeting; Oct 04, 1995 - Oct 05, 1995; CT; United States
    Format: text
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  • 8
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    An Advanced Fly-By-Wire Flight Control System for the RASCAL Research Rotorcraft: Concept to Reality (1995)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: Design features of a new fly-by-wire flight control system for the Rotorcraft-Aircrew Systems Concepts Airborne Laboratory (RASCAL) are described. Using a UH-60A Black Hawk helicopter as a baseline vehicle, the RASCAL will be a flying laboratory capable of supporting the research requirements of major NASA and Army guidance, control, and display research programs. The paper describes the research facility requirements of these pro-rams and the design implementation of the research flight control system (RFCS), with emphasis on safety-of-flight, adaptability to multiple requirements and performance considerations.
    Keywords: Aircraft Stability and Control
    Type: 14th DASC Digital Systems Conference and Technical Display Conference; Nov 05, 1995 - Nov 09, 1995; Cambridge, MA; United States
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  • 9
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    An investigation of the effects of pitch-roll (de)-coupling on helicopter handling qualities (1995)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: An investigation of the effects of pitch-roll coupling on helicopter handling qualities was performed by the US Army and DLR, using a NASA ground-based and a DLR inflight simulator. Over 90 different coupling configurations were evaluated using a roll-axis tracking task. The results show that although the current ADS-33C coupling criterion discriminates against those types of coupling typical of conventionally controlled helicopters, it not always suited for the prediction of handling qualities of helicopters with modern control systems. Based on the observation that high frequency inputs during tracking are used to alleviate coupling, a frequency domain pitch-roll coupling criterion that uses the average coupling ratio between the bandwidth and neutral stability frequency is formulated. This criterion provides a more comprehensive coverage with respect to the different types of coupling and shows excellent consistency.
    Keywords: Aircraft Stability and Control
    Type: DLR-FB-95-08 , (ISSN 0939-2963)
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  • 10
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    Interactive flutter analysis and parametric study for conceptual wing design (1995)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: An interactive computer program was developed for wing flutter analysis in the conceptual design stage. The objective was to estimate the flutter instability boundary of a flexible cantilever wing, when well defined structural and aerodynamic data are not available, and then study the effect of change in Mach number, dynamic pressure, torsional frequency, sweep, mass ratio, aspect ratio, taper ratio, center of gravity, and pitch inertia, to guide the development of the concept. The software was developed on MathCad (trademark) platform for Macintosh, with integrated documentation, graphics, database and symbolic mathematics. The analysis method was based on nondimensional parametric plots of two primary flutter parameters, namely Regier number and Flutter number, with normalization factors based on torsional stiffness, sweep, mass ratio, aspect ratio, center of gravity location and pitch inertia radius of gyration. The plots were compiled in a Vaught Corporation report from a vast database of past experiments and wind tunnel tests. The computer program was utilized for flutter analysis of the outer wing of a Blended Wing Body concept, proposed by McDonnell Douglas Corporation. Using a set of assumed data, preliminary flutter boundary and flutter dynamic pressure variation with altitude, Mach number and torsional stiffness were determined.
    Keywords: Aircraft Stability and Control
    Type: NASA-TM-111260 , AIAA Paper 95-3943 , NAS 1.15:111260 , 1st AIAA Aircraft Engineering, Technology and Operations Congress; Sep 19, 1995 - Sep 21, 1995; Los Angeles, CA; United States
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  • 11
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    Nonlinear Stability of Supersonic Jets (1995)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This paper presents stability calculations made for a shock-free supersonic jet using the model based on parabolized stability equations. In this analysis the large-scale structures, which play a dominant role in the mixing as well as the noise radiated, are modeled as instability waves. This model takes into consideration non-parallel flow effects and also nonlinear interaction of the instability waves. The stability calculations have been performed for different frequencies and mode numbers over a range of jet operating temperatures. Comparisons are made, where appropriate, with the solutions to Rayleigh's equation (linear, inviscid analysis with the assumption of parallel flow). The comparison of the solutions obtained using the two approaches show very good agreement.
    Keywords: Aircraft Stability and Control
    Type: NASA-TM-111928 , NAS 1.15:111928 , AIAA Paper 95-089 , Aeroacoustics; Jun 12, 1995 - Jun 15, 1995; Munich; Germany
    Format: application/pdf
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  • 12
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    Ground-to-Flight Handling Qualities Comparisons for a High Performance Airplane (1995)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A flight test program was conducted in conjunction with a ground-based piloted simulation study to enable a comparison of handling qualities ratings for a variety of maneuvers between flight and simulation of a modern high performance airplane. Specific objectives included an evaluation of pilot-induced oscillation (PIO) tendencies and a determination of maneuver types which result in either good or poor ground-to-flight pilot handling qualities ratings. A General Dynamics F-16XL aircraft was used for the flight evaluations, and the NASA Langley Differential Maneuvering Simulator was employed for the ground based evaluations. Two NASA research pilots evaluated both the airplane and simulator characteristics using tasks developed in the simulator. Simulator and flight tests were all conducted within approximately a one month time frame. Maneuvers included numerous fine tracking evaluations at various angles of attack, load factors and speed ranges, gross acquisitions involving longitudinal and lateral maneuvering, roll angle captures, and an ILS task with a sidestep to landing. Overall results showed generally good correlation between ground and flight for PIO tendencies and general handling qualities comments. Differences in pilot technique used in simulator evaluations and effects of airplane accelerations and motions are illustrated.
    Keywords: Aircraft Stability and Control
    Type: NASA-TM-111925 , NAS 1.15:111925 , AIAA Paper 95-3457 , Atmospheric Flight Mechanics; Aug 07, 1995 - Aug 09, 1995; Baltimore, MD; United States
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  • 13
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    Three Dimensional Solution of Pneumatic Active Control of Forebody Vortex Asymmetry (1995)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Pneumatic active control of asymmetric vortical flows around a slender pointed forebody is investigated using the three dimensional solution for the compressible thin-layer Navier-Stokes equation. The computational applications cover the normal and tangential injection control of asymmetric flows around a 5 degree semi-apex angle cone at a 40 degree angle of attack, 1.4 freestream Mach number and 6 x 10(exp 6) freestream Reynolds number (based on the cone length). The effective tangential angle range of 67.5 approaches minus 67.5 degrees is used for both normal and tangential ports of injection. The effective axial length of injection is varied from 0.03 to 0.05. The computational solver uses the implicit, upwind, flux difference splitting finite volume scheme, and the grid consists of 161 x 55 x 65 points in the wrap around, normal and axial directions, respectively. The results show that tangential injection is more effective than normal injection.
    Keywords: Aircraft Stability and Control
    Type: NASA-CR-203089 , NAS 1.26:203089 , AIAA Paper 95-0101 , Aerospace Sciences; Jan 09, 1995 - Jan 12, 1995; Reno, NV; United States
    Format: application/pdf
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