Showing papers in "Journal of Aircraft in 2000"

Low Reynolds Number Aerodynamics of Low-Aspect-Ratio, Thin/Flat/Cambered-Plate Wings

Abstract: The design of micro aerial vehicles requires a better understanding of the aerodynamics of small low-aspect-ratio wings An experimental investigation has focused on measuring the lift, drag, and pitching moment about the quarter chord on a series of thin flat plates and cambered plates at chord Reynolds numbers varying between 60,000 and 200,000 Results show that the cambered plates offer better aerodynamic characteristics and performance It also appears that the trailing-edge geometry of the wings and the turbulence intensity in the wind tunnel do not have a strong effect on the lift and drag for thin wings at low Reynolds numbers Moreover, the results did not show the presence of any hysteresis, which is usually observed with thick airfoils/wings

Active Aeroelastic Wing Flight Research Program: Technical Program and Model Analytical Development

Abstract: The Active Aeroelastic Wing (AAW) Flight Research Program's (Pendleton, E., Griffin, K., Kehoe, M., and Perry, B., A Flight Research Program for Active Aeroelastic Wing Technology, AIAA Paper 96-1574, April 1996 and Pendleton, E., Bessette, D., Field, P., Miller, G., and Griffin, K., The Active Aeroelastic Wing Flight Research Program, AIAA Paper 98-1972, April 1998) technical content is presented and analytical model development is summarized. Goals of the AAW flight research program are to demonstrate, in full scale, key AAW parameters and to measure the aerodynamic, structural, and flight control characteristics associated with AAW. Design guidance, derived from the results of this benchmark flight program, will be provided for implementation on future aircraft designs.

Modern Adaptation of Prandtl's Classic Lifting-Line Theory

Abstract: The classical solution to Prandtl's well-known lifting-line theory applies only to a single lifting surface with no sweep and no dihedral. However, Prandtl's original model of a finite lifting surface has much broader applicability. A general numerical lifting-line method based on Prandtl's model is presented. Whereas classical lifting-line theory is based on applying the two-dimensional Kutta-Joukowski law to a three-dimensional flow, the present method is based on a fully three-dimensional vortex lifting law. The method can be used for systems of lifting surfaces with arbitrary camber, sweep, and dihedral. The accuracy realized from this method is shown to be comparable to that obtained from numerical panel methods and inviscid computational fluid dynamics solutions, but at a small fraction of the computational cost

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

Abstract: 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.

Aerodynamics of Gurney Flaps on a Single-Element High-Lift Wing

Abstract: The trailing-edge region of a single-element wing fitted with Gurney flaps has been studied. Measurements include surface pressure, force, and velocity by laser Doppler anemometry (LDA). The mean-velocity vectors and streamlines suggest a twin vortex structure downstream of the Gurney flap. Spectral analysis of the LDA data indicates that the wake consists of a von Karman vortex street of alternately shed vortices, and this flow structure is confirmed by smoke visualization of the flow downstreamof the Gurney flap. The vortex shedding increases the trailing-edge suction of the aerofoil, whereas the upstream face of the device decelerates the flow at the trailing edge of the pressure surface. These two changes result in a pressure difference acting across the trailing edge, and it is this that generates the increase in circulation.

Aerodynamics of a Single Element Wing in Ground Effect

Abstract: A study was performed of a cambered, double-element, high-lift wing operating in ground effect. The effect of ground proximity and flap setting has been quantified in terms of aerodynamic performance and off-surface flowfield characteristics. Measurements include surface pressure taps, force, surface streaklines, and laser doppier anemometry (LDA). It was found from the Haw visualization that the flow is three-dimensional (3D) towards the wing tip with the main element generating most of the downforce, but retains quasi-2D features near the centre of the wing. However, at large heights the downforce increases asymptotically with a reduction in height, Then there is either a plateau, in the case of a low flap angle, or a reduction in down-force, in the case of a large flap angle. The downforce then increases again until it reaches a maximum, and then reduces at a height near the ground. The maximum downforce is dictated by gains in downforce from lower surface suction increases and losses in downforce due to upper surface pressure losses and lower surface suction losses, with a reduction in height. For the high flap angle, there is a sharp reduction just beyond the maximum, due to the boundary layer separating, and a resultant loss of circulation on. the main element.

Nonlinear Aeroelastic Analysis of Complete Aircraft in Subsonic Flow

Abstract: Aeroelastic instabilities are among the factors that may constrain the flight envelope of aircraft and, thus, must be considered during design. As future aircraft designs reduce weight and raise performance levels using directional material, thus leading to an increasingly flexible aircraft, there is a need for reliable analysis that models all of the important characteristics of the fluid-structure interaction problem. Such a model would be used in preliminary design and control synthesis. A theoretical basis has been established for a consistent analysis that takes into account 1) material anisotropy, 2) geometrical nonlinearities of the structure, 3) unsteady flow behavior, and 4) dynamic stall for the complete aircraft. Such a formulation for aeroelastic analysis of a complete aircraft in subsonic flow is described. Linear results are presented and validated for the Goland wing (Goland, M., The Flutter of a Uniform Cantilever Wing, Journal of Applied Mechanics, Vol. 12, No. 4, 1945, pp. A197-A208). Further results have been obtained that highlight the effects of structural and aerodynamic nonlinearities on the trim solution, flutter speed, and amplitude of limit-cycle oscillations. These results give insight into various nonlinear aeroelastic phenomena of interest: 1) the effect of steady-state lift and accompanying deformation on the speed at which instabilities occur, 2) the effect on nonlinearities in limiting the amplitude of oscillations once an instability is encountered, and 3) the destabilizing effects of nonlinearities for finite disturbances at stable conditions.

Evaluation of computational algorithms suitable for fluid-structure interactions

Abstract: The objective was to identify and mathematically evaluate suitable methods to transfer information between nonlinear computational fluid dynamics (CFD) and computational structural dynamics (CSD) grids. This data transfer is vital in the field of computational aeroelasticity, where the interpolation method between the two grids can easily be the limiting factor in the accuracy of an aeroelastic simulation. The data to be transferred can include a variety of field variables, such as deflections, loads, pressure, and temperature. For a method to be suitable, it is important that it provide a smooth, yet accurate transfer of data for a wide variety of functional forms that the data may represent. An extensive literature survey was completed that identified current algorithms in use, as well as other candidate algorithms from different implementations, such as mapping and CAD/CAM. The performance of the various methods was assessed on a number of analytical functions, followed by a series of applications that have been or are currently being studied using nonlinear CFD methods coupled with linear representations of the CSD equations (equivalent plate/shell mode shapes and influence coefficient matrices). Two methods, multiquadric-biharmonic and thin-plate spline, are shown to be the most robust, cost-effective, and accurate of all of the methods tested.

Computational Study of Flapping Airfoil Aerodynamics

Abstract: Unsteady, viscous, low-speed e ows over a NACA 0012 airfoil oscillated in plungeand/orpitch at various reduced frequency,amplitude, andphaseshift arecomputed. Vortical wakeformations, boundary-layere owsat theleading edge, the formation of leading-edge vortices and their downstream convection are presented in terms of unsteady particletraces.Flowseparationcharacteristicsandthrust-producingwakeproe lesareidentie ed.Computedresults compare well with water tunnel e ow visualization and force data and other computational data. The maximum propulsive efe ciency is obtained for cases where the e ow remains mostly attached over the airfoil oscillated in a combined pitch and plunge.

New Model for Vortex Decay in the Atmosphere

Abstract: A new vortex decay model for the prediction of the descent of aircraft trailing vortices subjected to realistic environmental conditions (stratie cation, turbulence, crosswind, headwind, shear effects, and ground effect ) is presented, and the model is applied to e eld data obtained with Lidar in Memphis and Dallas ‐Fort Worth airports. Although the model has not yet been fully optimized, the predictions and e eld data compare reasonably well. Some e ights, particularly in unstable environments, exhibit behavior unexplainable in terms of the assumed, measured, and/or indirectly calculated input parameters, for example, vortex separation, uncertainties in Lidar measurements, stratie cation, shear, gravity currents, head- and crosswinds, turbulent kinetic energy, and/or the eddy dissipation rate.

Development of a Shallow-Water Icing Model in FENSAP-ICE

Abstract: As part of a modern comprehensive in-flight icing simulation code (FENSAP-ICE), a new thermodynamic model for ice accretion is developed (the Shallow-Water Icing Model or SWIM). SWIM is based on a system of partial differential equations (PDEs) and thus is thought to be superior to a control volume (no PDE) approach used in current icing codes. Flexibility in the physical modeling and flexibility in numerical algorithm selection make SWIM an attractive icing model. The complete model, numerical algorithms used, and results are presented

Recent Turbulence Model Advances Applied to Multi-Element Airfoil Computations

Abstract: A one-equation linear turbulence model and two-equation nonlinear explicit algebraic stress model (EASM) are applied to the flow over a multielement airfoil. The effect of the K-epsilon and K-omega forms of the two-equation model are explored, and the K-epsilon form is shown to be deficient in the wall-bounded regions of adverse pressure gradient flows. A new K-omega form of EASM is introduced. Nonlinear terms present in EASM are shown to improve predictions of turbulent shear stress behind the trailing edge of the main element and near midflap. Curvature corrections are applied to both the one- and two-equation turbulence models and yield only relatively small local differences in the flap region, where the flow field undergoes the greatest curvature. Predictions of maximum lifts are essentially unaffected by the turbulence model variations studied.

Three-Dimensional Eulerian Approach to Droplet Impingement Simulation Using FENSAP-ICE, Part 1: Model, Algorithm, and Validation

Abstract: To realistically compute three-dimensional droplet impingement on aircraft and engines, an Eulerian model for diphasic aire ows containing water droplets is proposed as an alternative to the traditional Lagrangian particle tracking approach. The partial differential equations-based model is presented, together with details on the numerical methods and its algorithmic implementation in three dimensions within the e nite element Navier ‐Stokes analysis package for icing. Code validations in two and three dimensions are presented in comparison with published NASA experimental impingement results, and numerical accuracy requirements are discussed.

Linking Riveting Process Parameters to the Fatigue Performance of Riveted Aircraft Structures

Abstract: The onset of widespread fatigue damage in riveted aircraft structure has been linked to sharp gradients of stress arising from contact between rivets and rivet holes. In addition, the mechanics of load transfer in lap joint structure (and resulting damage) is influenced by the through-thickness restraint offered by the installed rivet. Finally, the propagation of fatigue cracks at and around the rivet/hole interface is tied to the residual stress field induced during the riveting process. In light of the influence that rivet installation has on the fatigue performance of riveted joints, the aim was to link details of a quasi-static, squeeze force-controlled riveting process as provided by finite element modeling to the resulting residual stress field in a single-lap joint structure. Supporting experiments provide insight into the inelastic response of the rivet material and validation of the model results. These results from the model reveal both a strong through-thickness gradient in residual stresses and a change in the distribution of residual hoop stress near the rivet/hole interface with squeeze force. Comments are also made regarding the relationship between riveting process parameters and trends in observed fatigue failures of riveted lap joint test articles.

Aerodynamic and Aeroacoustic Optimization of Rotorcraft Airfoils via a Parallel Genetic Algorithm

Abstract: A parallel genetic algorithm (GA) methodology was developed to generate a family of two-dimensional airfoil designs that address rotorcraft aerodynamic and aeroacoustic concerns The GA operated on 20 design variables, whichconstitutedthecontrolpointsforasplinerepresentingtheairfoilsurfaceTheGAtookadvantageofavailable computer resources by operating in either serial mode, where the GA and function evaluations were run on the same processor or “ manager/worker” parallel mode, where the GA runs on the manager processor and function evaluations areconducted independently on separate workerprocessors The multiple objectives of this work were to minimizethedrag and overall noiseof the airfoil Constraintswereplaced on liftcoefe cient, moment coefe cient, andboundary-layerconvergenceTheaerodynamicanalysiscodeXFOILprovidedpressureandsheardistributions in addition to liftand drag predictions Theaeroacousticanalysis code, WOPWOP, provided thicknessand loading noise predictions The airfoils comprising the resulting Pareto-optimal set exhibited favorable performance when compared with typical rotorcraft airfoils under identical design conditions using the same analysis routines The relationship between the quality of results and the analyses used in the optimization is also discussed The new airfoil shapes could provide starting points for further investigation

Conceptual Design Studies of a Strut-Braced Wing Transonic Transport

Abstract: Recent transonic airliner designs have generally converged upon a common cantilever low-wing configuration. It is unlikely that further large strides in performance are possible without a significant departure from the present design paradigm. One such alternative configuration is the strut-braced wing (SBW), which uses a strut for wing-bending load alleviation, allowing increased aspect ratio and reduced wing thickness to increase the lift to drag ratio. The thinner wing has less transonic wave drag, permitting the wing to unsweep for increased areas of natural laminar flow and further structural weight savings. High aerodynamic efficiency translates into smaller, quieter, less expensive engines and less pollution. A multidisciplinary design optimization (MDO) approach is essential to realize the full potential of this synergistic configuration caused by the strong interdependence of structures, aerodynamics, and propulsion. NASA defined a need for a 325-passenger transport capable of flying 7500 n miles at Mach 0.85 for a 2010 service entry date

Equations of motion of a vehicle in a moving fluid

Abstract: Dife culties with the differing sets of equations used for submersibles, airships, and airplanes are removed by treating the effects of the inertial and added masses as separate functions of the inertial and relative velocities. The equations of motion of a rigid vehicle moving in a perfect e uid are then derived for the case where the e uid mass is accelerating and contains velocity gradients. The classic perfect e uid moments and forces for straight, curved, and convergent e ows arerecovered. It is shown that the differing sets of equations normally used for submersibles, airships, and aircraft can also be recovered as special cases, but in an augmented form that includes the effects of e uid motion and velocity gradients. In addition, it is shown how the resultant perfect e uid equations may be augmented to include viscous forces and moments derived from other theoretical or experimental sources.

Transonic flutter simulations using an implicit aeroelastic solver

Abstract: Flutter computations are presented for the AGARD 445.6 standard aeroelastic wing configuration using a fully implicit, aeroelastic Navier-Stokes solver coupled to a general, linear, second-order structural solver. This solution technique realizes implicit coupling between the fluids and structures using a subiteration approach. Results are presented for two Mach numbers, M∞ = 0.96 and 1.141. The computed flutter predictions are compared with experimental data and with previous Navier-Stokes computations for the same case. Predictions of the flutter point for the M∞ = 0.96 case agree well with experimental data. At the higher Mach number, M∞ = 1.141, the present computations overpredict the flutter point but are consistent with other computations for the same case. The sensitivity of computed solutions to grid resolution, the number of modes used in the structural solver, and transition location is investigated. A comparison of computations using a standard second-order accurate central-difference scheme and a third-order upwind-biased scheme is also made.

Flutterometer: An On-Line Tool to Predict Robust Flutter Margins

Abstract: Robust eutter margins can be computed for an aeroelastic model with respect to an associated uncertainty descriptionthatdescribes modelingerrors. Anon-lineimplementationtocomputetheserobustmarginsisconsidered. The on-line approach generates uncertainty descriptions at test points and can account for time-varying errors in themodel.A eutterometer isintroduced as an on-linetool toindicateameasure ofdistancetoe utterduringaeight e utter test. Suchatool is formulated based on robust euttermargin analysis. A e ight test of an F/A-18 is simulated todemonstrate theperformance ofthee utterometer.Thistool isclearly more informativethantraditional tracking of dampingtrends and provides accurate information about the true eutter margin throughout the e ight test. The simulation demonstrates characteristics of the eutterometer that could improve eight test efe ciency by increasing safety and reducing eight time for envelope expansion.

Aerodynamic Design of a Flying Wing Using Response Surface Methodology

Abstract: The design of a subsonic e ying wing with maximized lift is considered. A novel method of surface generation, known as the partial differential equation (PDE) method, is used to parameterize the e ying wing. Because this method is able to parameterize complex geometries in terms of a small number of shape parameters, the computational costs that are normally associated with optimal aerodynamic design are dramatically reduced. The lift data, which are estimated using a low-order potential e ow panel method, are subject to numerical noise and yield, therefore, a design space that contains many spurious noise-induced local maxima. Standard methods of local optimization are severely hampered by this noise and may converge prematurely in nonoptimal plateau regions where the variation of the lift is small relative to that of the noise. To combat this inefe ciency, techniques from response surface methodology (RSM) are used to construct smooth analytic approximations of the noisy lift data, which can be optimized successfully. This combination of the PDE method and RSM results in a design approach that is both efe cient and robust. Three e ying-wing design problems areinvestigated, and the results are presented.

Hypersonic Flow Predictions Using Linear and Nonlinear Turbulence Closures

Abstract: Two- and three-dimensional hypersonic flow cases are computed using linear one-equation closures and a nonlinear two-equation model, where the anisotropy tensor is modeled as a cubic function of mean strain and vorticity tensors. The latter is found to excel in predicting bypass transition, whereas the one-equation R t model is very good at heat-transfer prediction. Both closures excel in predicting pressure distributions; however, the nonlinear model is found to overpredict heat-transfer. This suggests that in separated flow regions with simultaneously low mean-flow kinetic energy (and therefore low strain magnitude) and high temperature gradients, overpredicted levels of turbulence length scale can lead to rather small errors in the turbulent shear stress, while at the same time leading to a large overprediction of the turbulent heat fluxes

Small Disturbance Euler Equations: Efficient and Accurate Tool for Unsteady Load Prediction

Abstract: It is well known that the time-accurate solutions of the unsteady Euler equations are a reasonable but computationally expensive and time-consuming approach. Concerning aeroelastic applications, there is a need for efficient and accurate tools to determine the unsteady aerodynamic loads due to a variety of parameters. A numerical method based on an alternative approach, namely, on the solution of the small disturbance Euler equations (SDEu), is presented. These equations provide the following advantages: The unsteady problem is reduced to a steady-state problem for the perturbation part. The unsteady loads can be evaluated directly. Assuming harmonic behavior of unsteadiness, tire use of well-proven modal methods in aeroelastic analysis is supported. By application of this method, a substantial reduction of computational time is achieved. Results are presented for several airfoils and wings in pitching motion at subsonic, transonic, and supersonic Mach numbers. It is shown that for the most critical region, namely, the transonic region, the SDEu provide an excellent and fast means for the prediction of unsteady forces. The only remarkable differences between the nonlinear Euler solution and the SDEu solution can be observed in the pressure distribution in the vicinity of a shock, which is shown to have negligible influence on the integral contribution of the shock impulse to the generalized forces.

Variable Stiffness Spar Approach for Aircraft Maneuver Enhancement Using ASTROS

Abstract: An innovative variable stiffness spar (VSS) approach is studied for improving aircraft roll performance. In this concept some of the existing wing spars are replaced by the adaptive-structure VSS to control the stiffness as a function of Mach number and altitude. The VSS stiffness scheduling is designed to maximize the roll rate while satisfying flutter, control surface hinge moment, and maximum deflection constraints. The VSS mechanism consists of segmented spar having articulated joints at the connections with wing ribs and an electrical actuator capable of rotating the spar. The wing stiffness provided by the spar varies sinusoidally as a function of the rotation angle. The objective of the present study is to explore when and how to best apply this concept and assess its payoffs in terms of performance gains. The F/A-18 pre-roll-modification aircraft was selected as the baseline aircraft for its low torsional wing stiffness and available flight data. The multidisciplinary design optimization software ASTROS * was used tier performing the analyses in the Mach number range of M = 0.8-1.2 at altitudes up to 35,000 ft (40,668 m). Results show that VSS can amplify the aeroelastic forces and significantly enhance roll performance of aireraft.

Computation of Viscous Flow for a Boeing 777 Aircraft in Landing Configuration

Abstract: A series of Navier-Stokes simulations of a complete Boeing 777-200 aircraft configured for landing is obtained using a structured overset grid process and the OVERFLOW CFD code. At approach conditions, the computed forces for the 777 computation are within 1.5% of experimental data for lift, and within 4% for drag. The computed lift is lower than the experiment at maximum-lift conditions, but shows closer agreement at post-stall conditions. The effect of sealing a span-wise gap between leading edge elements, and adding a chine onto the nacelle is computed at a high angle of attack. These additions make a significant difference in the flow over the wing near these elements. Detailed comparisons between computed and experimental surface pressures are shown. Good agreement is demonstrated at lower angles of attack, including a prediction of separated flow on the outboard flap.

Wake Vortices in Convective Boundary Layer and Their Influence on Following Aircraft

Abstract: The decay of three wake vortex pairs of a B-747 aircraft in an evolving and convectively driven atmospheric boundary layer is investigated by means of large-eddy simulations (LES). Convective boundary layers are considered hazardousbecausetheupdraft velocitiesofa thermalmay compensatetheinduceddescent speed ofthevortex pair such that the vortices stall in the e ight path. The LES results illustrate that 1 )the primary rectilinear vortices are rapidly deformed on the scale of alternating updraft and downdraft regions; 2 ) parts of the vortices stay on e ight level but are quickly eroded by the turbulence of the updraft; 3 )the longest living sections of the vortices are foundinregionsofrelativelycalmdownwarde ow,which augmentstheirdescent.Striptheory calculationsareused to illustrate the temporal and spatial development of lift and rolling moments experienced by a following medium weight class B-737 aircraft. Characteristics of the respective distributions are analyzed. Initially, the maximum rolling moments slightly exceed theavailableroll controloftheB-737. After60 sthe probability ofrolling moments exceeding 50% of the roll control has decreased to 0.009% in a safety corridor around the glide path. Nomenclature b = aircraft span b0 = initial vortex spacing c = section chord cl = section lift coefe cient dP = probability difference g = gravitational acceleration k = wave number

Validation of a Rotorcraft Mathematical Model for Autogyro Simulation

Abstract: Results are presented from a study undertaken to validate a rotorcraft mathematical model for simulation of autogyro e ight. Although this class of rotary-wing aircraft has found limited application in areas other than sport or recreational e ying, commercial interest is increasing. A sparsecontemporary literature on autogyro e ight emphasizes the timeliness of this work, which takes advantage of e ight experiments using a fully instrumented autogyro.Validationisbasedoncomparisonsoftrim,linearizedsix-degree-of-freedomderivatives,andtimehistory response of the full nonlinear model to control inputs. The validation process is a vital ingredient in dee ning the applicability of a mathematical model as an engineering tool for supporting studies into aircraft stability, control, andhandlingqualities.Themodelisofgeneric,nonlinear,individualblade/bladeelementtype,anditscone guration as an autogyro is described. It is concluded that simulation of autogyro e ight presents no particular dife culties for a generic rotorcraft model. Limitations in predictive capability are clearly delineated, although in general comparisons between e ight and theory are good.

Systems Analysis of Noise Abatement Procedures Enabled by Advanced Flight Guidance Technology

Abstract: Advanced flight guidance technologies such as area navigation utilizing the global positioning system offer the potential to reduce the impact of aircraft noise on communities surrounding airports by enabling more flexible approach and departure procedures that reduce noise exposure to the most sensitive areas. A systems analysis is presented of noise abatement procedures enabled by these technologies. NOISIM, the primary systems analysis tool, combines a flight simulator, a noise model, and a geographic information system to create a unique rapid prototyping environment in which the user can simulate an aircraft's operation in existing and potential guidance and navigation environments, while simultaneously evaluating the aircraft's noise impact. The analysis included generic and site specific studies of approach and departure procedures using 737-200 noise estimates. The results of the generic study of approach procedures indicate that a 3-deg decelerating approach provides significant noise reductions in comparison to the baseline instrument landing system (ILS) approach and is preferred by pilots to the more complex vertically segmented approach. In a study of approaches to runway 13L at Kennedy Airport, a 3-deg decelerating approach reduced the population impacted by noise greater than 60 dBA from over 250,000 in the ILS approach to less than 70,000. The results of the generic study of departure procedures indicate that the benefits of noise abatement departures are site specific. In a study of departures from runway 4R at Logan Airport, a noise abatement departure that combined a targeted thrust cutback with a dual turn lateral trajectory reduced the population impacted by peak noise greater than 60 dBA by over 15%.

Database tomography applied to an aircraft science and technology investment strategy

Abstract: : Data Base Tomography (DT) is a textual data base analysis system consisting of two major components: (1) algorithms for extracting multiword phrase frequencies and phrase proximities (physical closeness of the multiword technical phrases) from any type of large textual data base, and (2) applying interpretative capabilities of the expert human analyst. DT was used to obtain technical intelligence from aircraft data bases derived from the Science Citation Index and the Engineering Compendex. Phrase frequency analysis by the technical domain expert provided the pervasive technical themes of the aircraft data bases, and the phrase proximity analysis provided the relationships among the pervasive technical themes. Bibliometric analysis of the aircraft literature supplemented the DT results with author/journal/institution publication and citation data. Comparisons of the aircraft data base results with past analyses of similarly structured near-earth space, chemistry, and hypersonic/supersonic flow data bases are made.