Store Configuration Research Articles

Parametric Studies of Transonic Aeroelastic Effects of an Aircraft Wing/Tip Store

This research investigates the effect of store parameters variation on store-induced flutter and limit-cycle oscillation phenomena of an aircraft wing in the transonic regime. The primary store parameters were its mass and the chordwise location of its center of gravity. The effect of including store aerodynamics on the wing/tip store configuration was also investigated. The tip store center of gravity (c.g.) was varied and positioned at three different locations: 32.5, 40, and 50%, with respect to aerodynamic tip chord. Automated Structural Optimization System and Computational Aeroelasticity Program‐Transonic Small Disturbance were used in the linear and nonlinear region to perform this research. Studies showed that flutter speed increases as the store c.g. was moved forward toward the leading edge. This gives an indication that store c.g. must be placed as far forward as possible with respect to the elastic axis to delay the occurrence of flutter, while satisfying other design constraints. It was observed that the increase in tip store mass significantly reduced the flight operating speed range of the aircraft. The effect of inclusion of store aerodynamics for different wing/store configurations was found to be insignificant compared to their corresponding mass-only models in the transonic regime. The limit-cycle oscillation (LCO) onset speed was found to be sensitive to both store mass and store c.g. parameters and varied significantly for different store mass configurations. The LCO onset speed decreased significantly with increase in store mass and aft movement of store c.g.

Nonlinear Analysis of Store-Induced Limit Cycle Oscillations

Flight tests of modern high-performance fighter aircraft reveal the presence of limit cycle oscillation (LCO) responses for aircraft with certain external store configurations. Conventional linear aeroelastic analysis predicts flutter for conditions well beyond the operational envelope, yet these store-induced LCO responses occur at flight conditions within the flight envelope. Several nonlinear sources may be present, including aerodynamic effects such as flow separation and shock-boundary layer interaction and structural effects such as stiffening, damping, and system kinematics. No complete theory has been forwarded to accurately explain the mechanisms responsible. This research examines a two degree-of-freedom aeroelastic system which possesses kinematic nonlinearities and a strong nonlinearity in pitch stiffness. Nonlinear analysis techniques are used to gain insight into the characteristics of the behavior of the system. Numerical simulation is used to verify and validate the analysis. It is found that when system damping is low, the system clearly exhibits nonlinear interaction between aeroelastic modes. It is also shown that although certain applied forcing conditions may appear negligible, these same forces produce large amplitude LCOs under specific realizable circumstances.

Stimulus generalization in two associative learning processes.

Recent studies involving nonlinear discrimination problems suggest that stimuli in human associative learning are represented configurally with narrow generalization, such that presentation of stimuli that are even slightly dissimilar to stored configurations weakly activate these configurations. The authors note that another well-known set of findings in human associative learning, cue-interaction phenomena, suggest relatively broad generalization. Three experiments show that current models of human associative learning, which try to model both nonlinear discrimination and cue interaction as the result of 1 process, fail because they cannot simultaneously account for narrow and broad generalization. Results suggest that human associative learning involves (a) an exemplar-based process with configural stimulus representation and narrow generalization and (b) an adaptive learning process characterized by broad generalization and cue interaction.

The DAQ system with a RACEway switch for the PHOBOS experiment at RHIC

The PHOBOS data acquisition system based on a RACEway switching network is described. Occupying a single VME crate, the system utilizes 22 PPC750 CPUs working in parallel to compress data from 135 168 silicon pad detectors and an UltraSPARC VME host for event building and data storage. Lossless Huffman coding is used for compression; this reduces the event size fourfold. The two-host disk array is used to stage data before sending them over Gigabit Ethernet to the Relativistic Heavy Ion Collider (RHIC) central computing facility. All trigger and control logic is formed using universal programmable logic VME modules, which can be programmed in situ, even when the system is running. The event building and run control software is written using the ROOT framework. The slow control and configuration makes use of an Oracle database to store configuration and monitoring parameters. The system has been taking data from the PHOBOS experiment at RHIC since June 2000. The achieved data-taking rate is 280 events/s or 28 MB/s, with additional disk arrays it can potentially reach 80 MB/s.

'India Shopping': Indian Grocery Stores and Transnational Configurations of Belonging

How do representations of 'India' shape the lives of members of a diasporic community, the identities they forge, and the politics they negotiate? This paper examines how grocery stores in the San Francisco Bay Area enable the construction of India and Indian culture, and argues that (1) Indian grocery storesin the diaspora form a crucial node in the transnational circulation of texts, images, and commodities between India and the diaspora; (2) the objects sold in these stores create varying regimes of value in different contexts; (3) gender (as it intersects with class and race) offers an important lens to examine the kinds of social practices facilitated by these stores. Throughout, the author wishes to foreground the on-going and contested construction of a transnational set of images, discourses, and institutions that engender what different people mean by 'India.'

Out-of-equilibrium dynamics of the hopfield model in its spin-glass phase

In this paper, we study numerically the out-of-equilibrium dynamics of the Hopfield model for associative memory inside its spin-glass phase. Aside from its interest as a neural network model, it can also be considered as a prototype of a fully connected magnetic system with randomness and frustration. By adjusting the ratio between the number of stored configurations p and the total number of neurons N, one can control the phase-space structure, whose complexity can vary between the simple mean-field ferromagnet (when p=1) and that of the Sherrington Kirkpatrick spin-glass model (for a properly taken limit of an infinite number of patterns). In particular, little attention has been devoted to the spin-glass phase of this model. In this paper, we analyze the two-time autocorrelation function, the decay of the magnetization and the distribution of overlaps between states. The results show that within the spin-glass phase of the model, the dynamics exhibits aging phenomena and presents features that suggest a non trivial breaking of replica symmetry.

Limit Cycle Oscillation Flight Test Results of a Fighter with External Stores

Oscillatory wing response data were measured on an F-16A aircraft during flutter tests of several external store configurations. Previous testing had shown the F-16 to exhibit limit cycle oscillations (LCO) in the transonic regime, During the present tests, LCO were encountered as well as the sudden onset of high-amplitude oscillations. This sudden high-amplitude response closely resembled that of classical flutter. In all, three distinct categories of response behavior were seen during these tests: classical flutter, typical LCO, and nontypical LCO. These categories are representative of the broad spectrum of aeroelastic responses encountered by fighter aircraft with external stores. Theoretical flutter analyses are shown to adequately identify flutter- or LCO-sensitive store configurations and their instability oscillation frequencies. In addition, a strong correlation between the flight test response and the modal composition of the analytical flutter mechanism is evident. However, the linear analysis fails to provide insight into the oscillation amplitude or onset velocity, which are of primary importance for external store certification on fighter aircraft. Flutter analysis results are presented along with details of the analytical model, the store configurations, and the store mass properties for use as realistic check cases for the validation of nonlinear flutter analysis methods.

Active Control of Store-Induced Flutter in Incompressible Flow

An active method for enhancing the performance and improving the robustness of a decoupler pylon-mounted store flutter suppression system is presented. The proposed active decoupler pylon involves the use of a piezoceramic wafer strut as an actuator that acts as a soft spring between the wing and the store. A two degree-of-freedom typical section of an airfoil is used to represent the structural model of the wing. The circulatory component of the incompressible aerodynamic loads is modeled using an approximation to the Theodorsen function. The GBU-8/B store configuration of an F-16 aircraft is used for the analysis. A classical robust control algorithm called the loop transfer recovery method is applied to design a controller for the linear wing/store model. Some simulations are presented using singular-value Bode plots for robust stability and nominal performance analysis.

Aerodynamic characteristics of external store configurations at low speeds

Aerodynamic characteristics of external store configurations used on interceptor aircraft were investigated experimentally and computationally. Balance measurements, flow visualization, and static pressure measure- ments were made in a low-speed wind tunnel. The experimental and computational data revealed the global structure of the flow around a basic configuration. Six groups of models were used in the present study. This article discusses the results for the first and second group of models. The incompressible flow over a limited number of models was computed by solving the Navier-Stokes equations. The solution method is based on the Galerkin finite element discretization of space and the fractional step discretization of time. Reasonably good agreement was observed between the experimental and computational static pressure distributions on a basic geometry. The computational data, which revealed details of reverse flow regions, supported and supplemented the experimental data. using the code employed in the present study are presented in Refs. 5-7. The scope of the study was limited to the aero- dynamic characteristics of the isolated carriage, i.e., inter- ference with the aircraft body was not investigated. The experimental and computational data revealed the global structure of the flow around the carriage. Balance measure- ments showed that aerodynamically more suitable forms of the carriage geometry could be obtained by modifying its major drag-producing features. Surface flow visualization in- dicated locations of vortical flow regions whose existence was also supported by contour plots of the measured static pres- sure. Despite differences in the Reynolds numbers of the computed and measured flows, reasonably good agreement was observed between the experimental and computational static pressure distributions on the basic carriage geometry. The computations also exhibited details of reverse flow re- gions and, thus, both supported and supplemented the ex- perimental data that did not include velocity measurements. The geometry of the basic carriage used in the present study is not axisymmetric. There is a lack of data in the literature on studies of external stores that have nonaxisymmetric ge- ometries. References 8 and 9 present data for bodies having square and rectangular cross sections. Studies of the flow around axisymmetric bodies show that there exist four char- acteristic flow regimes1012: vortex-free, symmetric vor- tex, asymmetric vortex, and wake-like flow regimes are observed with increasing angle of attack. Crossflow separation of the boundary layer on an axisymmetric body gives rise to formation of vortices on the lee side. Reference 10 states that the nonlinear lift force due to these vortices can be much larger than the lift predicted by the linear (small perturbation) theory. References 13-15 describe studies that investigate the effect of afterbody modifications on the drag of axisymmetric bodies. Interference between the flowfields of stores and air- craft bodies is investigated by Refs. 1 and 2.

Unstructured grid solutions to a wing/pylon/store configuration

The purpose of this article is to validate an inviscid flow solution package based on a new unstructured grid methodology using experimental data on a wing/pylon/finned store configuration. The solution package consists of an advancing front grid generator, VGRID, and an efficient Euler equation solver, USM3D. Comparisons of computed data vs experimental data are made for two freestream Mach numbers at five store locations relative to the wing. Both rigid body aerodynamics and mutual interference effects are explored. A very good agreement is observed between computed and wind-tunnel data.

Flight loads test of the indigenous defensive fighter

Flight loads test is a primary structural verification test in fighter aircraft development. The indigenous defensive fighter flight loads test is the first complete flight loads test executed in Taiwan, Republic of China. The basic configuration part of the flight test, including flight loads survey and structural demonstration, was accomplished in 42 flights with external store configurations to follow. Results give both similarity and deviation compared to predictions, and numerous valuable experiences were accumulated from ground calibration test and flight test. One significant improvement in flight test, the automatic roll capability, was introduced to greatly improve maneuver quality during testing and resulted in safe and efficient flight test. HE indigenous defensive fighter (IDF) program was started in the mid-1980s by Aero Industry Development Center (AIDC) in Taiwan, Republic of China. The purpose of the program is to develop and manufacture a lightweight, high- maneuverability fighter aircraft to obtain defensive air su- periority over the Taiwan Strait. m The basic configuration flight loads test of the IDF was executed from February 1990 to April 1991 at CCK AFB, Taiwan, R.O.C. The external store configuration flight loads test is planned to be conducted in the near future. The purpose of the flight loads test was to obtain data for determination of the structural adequacy of the IDF aircraft for the condi- tions determined critical through analysis and review of test data. The test employed buildup to, and demonstration of, the design limit conditions for the parameters determined to be critical. Test results will also be used to improve analysis methods or for advanced versions of the production airplane if needed (Fig. 1). In this article, a brief description of the test article is given first, including a detailed discussion of the multifunctional test aid. Next is the introduction of loads and aircraft response measuring instrumentation; also mentioned are the test data recording equipment and the real time monitor facility. For the ground calibration test, the calibration methods, hardware setup, and the calibration results are described. The flight loads test objectives, test maneuvers, and test sequence are also depicted. Finally, the flight loads test results are pre- sented with different component's load trends. Test Article Description The IDF is a lightweight, twin-engine, high-maneuverabil- ity fighter aircraft with midmounted, moderately swept wing. Highly swept strake and well-designed fuselage geometry blend the wing and fuselage into a lifting body. The leading-edge flaps deflect according to a preset angle of attack (AOA)- related schedule for optimal lift-to-drag ratio. The IDF is controlled by a digital fly-by-wire flight control system that consists of three independent sets of sensors, three channels of digital flight control computer, one channel of analog backup flight control computer, and electrically sig-

Unsteady subsonic aerodynamics for bodies and wings with external stores including wake effect

An unsteady subsonic method has been developed for aerodynamic computations of any elastic or rigid aricraft with external stores. The method consists of two integral parts: a body surface panel method (SPM) and a constant-pressure lifting surface method, which is the subsonic parallel of the HGM (or the ZONA51 code) for unsteady supersonics. The body considered can be flat-based or close-ended and its geometry input is amenable to any given fuselage or store configuration. The present method is considered an advancement over the past development at least in three aspects: (1) correct unsteady boundary condition on body, (2) a new wake model to account for the body/wake effect and (3) improved accuracy in wingbody interference. Various AGARD iifting surfaces, truncated blunt and pointed bodies and a number of NLR wing-storetiptank combinations were studied for method validation. The present method has shown substantial improvement in the pressures, stability derivatives and airloads on these configurations. For all cases considered, the present results, with or without the wake model, have consistently shown closest agreement with all measured data among existing methods. Therefore, we believe that an accurate and effective method is finally at hand for subsonic aeroelastic applications.

Cavity door effects on aerodynamic loads of stores separating from cavities

A wind-tunnel investigation was conducted to determine the effects of cavity doors on the aerodynamic characteristics of compressed-ca rriage store configurations during separation from a shallow box cavity. The tests were conducted in the NASA Langley Unitary Plan Wind Tunnel at freestream Mach numbers of 1.70,2.00, and 2.65 for a constant Reynolds number/ft of 2.00X106. Results are summarized to show the effects of door opening angles and vertical height, folded and unfolded tail fins, and Mach number on the near-field aerodynamic separation characteristics of a single missile-type store with in-line cruciform wings and tail fins.

Verified Accurate Performance Simulation Model of Direct Thermosyphon Solar Energy Water Heaters

A detailed analysis of the heat transfers and fluid flows within direct thermosyphonic solar energy water heaters has been undertaken. The collector energy equations were cast in a two-dimensional form in order that the heat transfer and thermal capacitance effects can be simulated accurately at the small flow rates encountered commonly in these buoyancy-driven systems. The use of an appropriate nonisothermal friction factor correlation when calculating energy losses in the collector’s riser pipes, produced predicted flow rates which were corroborated to within 2 percent by the values measured under steady flow conditions. For the laminar flow rates and the store configuration investigated, relaxation of the thermocline was shown to be dominated by axial conduction in the store walls. An indoor test facility, monitored and controlled by a microcomputer, enabled “real” operating conditions to be simulated. The predicted responses of the system to identical conditions showed good agreement with the corresponding experimental observations, the predicted heat delivery being within 2.8 percent of that measured.

A case study in using two-level control stores

A two-level control store can reduce storage requirements of microprograms without affecting microprogrammability, which is important for a processor programmed directly in microcode. This paper presents a case study investigating how to use a two-level control store effectively. The study is based on Warp cell, a high-performance, microprogrammable processor used in a systolic array computer called Warp. Warp cell is programmed directly in microcode by an optimizing compiler and uses wide horizontal microinstructions with over 200 bits.Two methods which can increase the effectiveness of using a two-level control store have been considered. First, control store configuration can be adjusted so that the storage of an instruction can be partitioned among microstore and one or more nanostores to maximize storage efficiency. Second, it is possible to increase storage reduction of microprograms by exploiting insignificant and symmetric fields in instructions in mapping microprograms to the control store. It has been found that the average storage reduction for Warp cell programs can be increased from 41% in a straightforward two-level control store implementation to 72% by using these methods.

Efficient vibration mode analysis of aircraft with multiple externalstore configurations

A coupling method for efficient vibration mode analysis of aircraft with multiple external store configurations is presented. A set of low-frequency vibration modes, including rigid-body modes, represent the aircraft. Each external store is represented by its vibration modes with clamped boundary conditions, and by its rigid-body inertial properties. The aircraft modes are obtained from a finite-element model loaded by dummy rigid external stores with fictitious masses. The coupling procedure unloads the dummy stores and loads the actual stores instead. The analytical development is presented, the effects of the fictitious mass magnitudes are discussed, and a numerical example is given for a combat aircraft with external wing stores. Comparison with vibration modes obtained by a direct (full-size) eigensolution shows very accurate coupling results. Once the aircraft and stores data bases are constructed, the computer time for analyzing any external store configuration is two to three orders of magnitude less than that of a direct solution.

Study of multibody aerodynamic interference at transonic Mach numbers

A wind tunnel experiment involving single, double, and triple combinations of mutually interfering generic, unfinned aircraft stores has been conducted. Each combination of stores was tested at Mach numbers from 0.60 to 1.20 and at angles of attack from 0 to 25 deg for the single store and from 0 to 6 deg for the double and triple store configurations. Extensive axial and circumferential pressure and flow visualization data at each store location were obtained. Euler solutions for each configuration at 0 deg incidence have been generated and compared with experimental data. This comparison indicates an Euler flow solver can yield accurate predictions of the location and magnitude of multibody interference provided an appropriate grid is used and the viscous effects associated with these configurations remain small. The data indicate multibody interference in the transonic region increases as the freestream Mach number approaches 1 from either direction, and subsides as the Mach number moves away from sonic conditions. This interference is characterized by a large, localized reduction in pressure on the inboard surfaces of the bodies which results in forces that draw the configuration closer together.

F-16 Flutter Suppression System Investigation Feasibility Study and Wind Tunnel Tests

A study was conducted to determine the feasibility of employing active controls on the F-16 to suppress wing- store flutter for several external store configurations. It was determined that the existing flaperons, with modifications to the integrated servoactuators, were effective in suppressing flutter. The F-16 flutter model was tested with active flaperons. Open-loop frequency response functions (FRF's) were successfully measured in the wind tunnel environment both with the feedback loop physically opened and with the loop closed. These measurements provided guidance in the selection of sensor locations and feedback control laws to suppress flutter. Control law variations were made to obtain the desired FRF characteristics. A 100% increase in dynamic pressure above the flutter dynamic pressure was demonstrated. IGHTER aircraft are required to carry a very large number of external store configurations. The probability is high that at least a small subset of these configurations will flutter within the desired operational envelope of the airplane. This probability is further increased as new stores are added to the operational airplane inventory. When wing-store flutter problems occur, the solution requires a modification of the airplane (usually a change in stiffness and weight) and/or a speed restriction which reduces the operational envelope of the airplane. Flutter suppression with active controls is another solution which has been investigated in recent years. Several approaches have been taken to design these sys- tems.1-3 One of the more promising approaches to the design of calibrated active control systems is the frequency response method. This approach is attractive because of the state of development of methods for computing oscillatory aerodynamic pressure distributions, because frequency response functions (FRF's) are experimentally measurable, and because the military specification for the stability of aeroservoelastic systems is based on the Nyquist criteria. This method was applied in a flutter suppression system (FSS) feasibility study4 for the F-4. The results of this study indicate that the milder flutter modes and the lower flutter frequencies associated with wing-store configurations could be relatively easily suppressed with active controls. The initial design approach for the active control system for the YF-17 semispan flutter model was the root locus method.5 However, a modified Nyquist approach was subsequently used.6 The Nyquist stability criteria has been applied extensively by Turner.7 The Nyquist criteria was employed as the principal design tool in the F-16 FSS investigations. For the system with negative feedback shown in Fig. 1, the transfer function for the closed loop system is

Computational and Simplified Analytical Treatment of Transonic Wing/Fuselage/Pylon/Store Interactions

Transonic modified small-disturbance has been employed to numerically model the flowfield around wing/fuselage/pylon/store configurations. A fine grid region enclosing the wing/pylon/store is embedded within a global crude grid and a successive crude-fine relaxation is performed. Using an image point concept, the store and the pylon are introduced into an existing wing/fuselage program, thus avoiding excessive additional computer memory requirements. Comparison of results with experiments on the F-5 wing with a pylon/store arrangement is presented showing good agreement. A study of the roles of pylon height, store diameter, pylon span mount location, angle of attack, and Mach number relative to the achievement of optimum LID from beneficial nonlinear interference is presented. In addition, a simplified analytical approach to compute the loading on the store using an immersion theory is indicated and validated against experiments.

Prediction of critical Mach number for store configurations

A numerical method is described and applied to the prediction of the critical Mach number of store configurations. A finite volume integral method is used to solve the full nonlinear potential equation in conservation of mass form. With the density held constant, the entire potential flowfield is solved by matrix iteration. The density field is then relaxed using the new potential values. The use of central differences for the velocity everywhere in the field is made possible by special treatment of the density terms in the coefficient matrix. The finite volume concept allows the boundary conditions to be treated in a simple and exact manner, without the use of a mapping scheme. Results are obtained for configurations that range from very thin pointed bodies to hemispherically blunt bodies. Excellent agreement is obtained for the pressure distribution over each body, even in supercritical flows, and the critical Mach number is easily and accurately computed. Finally, the computational advantages and capabilities of the numerical method are discussed and compared with other existing codes.