One-Dimensional Scanning Approach to Shock Sensing

Measurement tools for high speed air flow are sought both in industry and academia. Particular interest is shown in air flows that exhibit aerodynamic shocks. Shocks are accompanied by sudden changes in density, pressure, and temperature. Optical detection and characterization of such shocks can be difficult because the medium is normally transparent air. A variety of techniques to analyze these flows are available, but they often require large windows and optical components as in the case of Schlieren measurements and/or large operating powers which precludes their use for in-flight monitoring and applications. The one-dimensional scanning approach in this work is a compact low power technique that can be used to non-intrusively detect shocks. The shock is detected by analyzing the optical pattern generated by a small diameter laser beam as it passes through the shock. The optical properties of a shock result in diffraction and spreading of the beam as well as interference fringes. To investigate the feasibility of this technique a shock is simulated by a 426 m diameter optical fiber. Analysis of results revealed a direct correlation between the optical fiber or shock location and the beam s diffraction pattern. A plot of the width of the diffraction pattern vs. optical fiber location reveals that the width of the diffraction pattern was maximized when the laser beam is directed at the center of the optical fiber. This work indicates that the one-dimensional scanning approach may be able to determine the location of an actual shock. Near and far field effects associated with a small diameter laser beam striking an optical fiber used as a simulated shock are investigated allowing a proper one-dimensional scanning beam technique

Wind Tunnel Testing of a One-Dimensional Laser Beam Scanning and Laser Sheet Approach to Shock Sensing

A 15- by 15-cm supersonic wind tunnel application of a one-dimensional laser beam scanning approach to shock sensing is presented. The measurement system design allowed easy switching between a focused beam and a laser sheet mode for comparison purposes. The scanning results were compared to images from the tunnel Schlieren imaging system. The tests revealed detectable changes in the laser beam in the presence of shocks. The results lend support to the use of the one-dimensional scanning beam approach for detecting and locating shocks in a flow, but some issues must be addressed in regards to noise and other limitations of the system

High-speed civil transport issues and technology program

A strawman program plan is presented, consisting of technology developments and demonstrations required to support the construction of a high-speed civil transport. The plan includes a compilation of technology issues related to the development of a transport. The issues represent technical areas in which research and development are required to allow airframe manufacturers to pursue an HSCT development. The vast majority of technical issues presented require flight demonstrated and validated solutions before a transport development will be undertaken by the industry. The author believes that NASA is the agency best suited to address flight demonstration issues in a concentrated effort. The new Integrated Test Facility at NASA Dryden Flight Research Facility is considered ideally suited to the task of supporting ground validations of proof-of-concept and prototype system demonstrations before night demonstrations. An elaborate ground hardware-in-the-loop (iron bird) simulation supported in this facility provides a viable alternative to developing an expensive fill-scale prototype transport technology demonstrator. Drygen's SR-71 assets, modified appropriately, are a suitable test-bed for supporting flight demonstrations and validations of certain transport technology solutions. A subscale, manned or unmanned flight demonstrator is suitable for flight validation of transport technology solutions, if appropriate structural similarity relationships can be established. The author contends that developing a full-scale prototype transport technology demonstrator is the best alternative to ensuring that a positive decision to develop a transport is reached by the United States aerospace industry

Optimal Aeroelastic Vehicle Sensor Placement for Root Migration Flight Control Applications

An important step in control design for elastic systems is the determination of the number and location of control system components, namely sensors. The number and placement of sensors can be critical to the robust functioning of active control systems, especially when the system of interest is a large high-speed aeroelastic vehicle. The position of the sensors affects not only system stability, but also the performance of the closed-loop system. In this dissertation, a new approach for sensor placement in the integrated rigid and vibrational control of flexible aircraft structures is developed. Traditional rigid-body augmentation objectives are addressed indirectly through input-output pair and compensation selection. Aeroelastic control suppression objectives are addressed directly through sensor placement. A nonlinear programming problem is posed to minimize a cost function with specified constraints, where the cost function terms are multiplied by appropriate weighting factors. Cost function criteria are based on complex frequency domain geometric pole-zero structures in order to gain stabilize or phase stabilize the aeroelastic modes. Specifically, these criteria are based on dipole magnitude and complementary departure angle. In turn, the control design approach utilizes one of the classical methods known as Evans root migration to exploit the pole-zero structures resulting from sensor placement. Desirable complementary departure angles can lead to significant aeroelastic damping improvement as loop gain is increased, while favorable dipole magnitudes can virtually eliminate the effects of aeroelastics in a feedback loop. Appropriate constraints include minimum phase aeroelastic zeros to avoid common problems associated with right-half plane zeros. To achieve desirable flight control system characteristics via optimal sensor locations, different kinds of blending filters for multiple sensors are investigated. Static filters, as well as dynamic filters with fixed or variable parameters and fixed or variable compensator parameters, are considered. For every cost function, there are several local minima indicating many distributions of the sensors are available. By evaluating the cost for each minimum, the global optimum can then be found

Life-Extending Control for a Highly Maneuverable Flight Vehicle

This dissertation investigates the feasibility and potential of life extension control logic for reducing fatigue within aerospace vehicle structural components. A key underpinning of this control logic is to exploit nonintuitive, optimal loading conditions which minimize nonlinear crack growth behavior, as predicted by analytical fatigue models with experimentally validated behavior. A major simplification in the development of life extension control logic is the observation and justification that optimal stress loading conditions, as described by overload magnitude ratio and application interval, are primarily independent of crack length and therefore, component age. This weak relationship between optimal stress loading and structural age implies the life extension control logic does not require tight integration with real-time health monitoring systems performing crack state estimation from measurement and model simulation. At a fundamental level, the life extension control logic conducts load alleviation and/or amplification tailoring of external and internal excitations to optimally exploit nonlinear crack retardation phenomenon. The life extension control logic is designed to be a simple, practical modification applied to an existing flight control system. A nonlinear autopilot for the nonlinear F-16 dynamics, coupled with a separate flexible F-16 wing model and a state space crack growth model, are used to demonstrate the life extension control concept. Results indicate that significant structural life savings is obtained by integrating life extending control logic dedicated for critical structural components to the existing flight control system. On the other hand, some components under life extending control showed minor reductions of structural life, particularly when the components are located in a low stress region where fatigue damage is of lower concern. Further, to achieve enhanced long-term structural integrity with life extending control, tradeoffs with flight system stability and performance may be required. Careful consideration is thus necessary when applying life extending logic to the aircraft flight control system. Although life extending control appears feasible with significant potential, full implementation of the concept requires further study

Six Decades of Flight Research: An Annotated Bibliography of Technical Publications of NASA Dryden Flight Research Center, 1946-2006

Titles, authors, report numbers, and abstracts are given for nearly 2900 unclassified and unrestricted technical reports and papers published from September 1946 to December 2006 by the NASA Dryden Flight Research Center and its predecessor organizations. These technical reports and papers describe and give the results of 60 years of flight research performed by the NACA and NASA, from the X-1 and other early X-airplanes, to the X-15, Space Shuttle, X-29 Forward Swept Wing, X-31, and X-43 aircraft. Some of the other research airplanes tested were the D-558, phase 1 and 2; M-2, HL-10 and X-24 lifting bodies; Digital Fly-By-Wire and Supercritical Wing F-8; XB-70; YF-12; AFTI F-111 TACT and MAW; F-15 HiDEC; F-18 High Alpha Research Vehicle, F-18 Systems Research Aircraft and the NASA Landing Systems Research aircraft. The citations of reports and papers are listed in chronological order, with author and aircraft indices. In addition, in the appendices, citations of 270 contractor reports, more than 200 UCLA Flight System Research Center reports, nearly 200 Tech Briefs, 30 Dryden Historical Publications, and over 30 videotapes are included