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At least 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Three dimensional steady and unsteady asymmetric flow past wings of arbitrary planforms

The nonlinear discrete vortex method is extended to treat the problem of asymmetric flows past a wing with leading edge separation, including steady and unsteady flows. The problem is formulated in terms of a body fixed frame of reference and the nonlinear-discrete vortex method is modified accordingly. Although the method is general, only examples of flows past delta wings are presented due to the availability of experimental data as well as approximate theories. Comparison of results with experimental results for a delta wing undergoing a steady rolling motion at zero angle of attack demonstrate the superiority of the present method over existing approximate theories in obtaining highly accurate loads. Numerical results for yawed wings at large angles of attack are also presented. In all cases, total load coefficients, pressure distributions, and shapes of the free vortex sheets are shown.

Kandil, O. A.↗
NASA NTRS1998

History of Research on Lift-Generated Vortices

A theoretical and experimental program on the structure and possible modification of lift-generated vortices shed by subsonic aircraft has been underway at NASA Ames Research Center since the late 1960's. The objectives of the program were to first obtain a better understanding of the hazard posed by the vortex wakes of subsonic transports, and then to develop methods on how to modify or design the wake-generating aircraft in order to make the vortices less hazardous. Some effort was also expended on the development of methods to avoid vortex wakes. The seminar will present a brief history of the research program beginning with the nature of vortex wakes and their relationship to the span loading on the wake-generating wing. Examples will then be presented to show how span-loading changes were used to influence the dynamics of the vortex wakes shed by subsonic transport aircraft. Video tape segments will be shown to illustrate the dynamics of vortex wakes and the flight tests carried out by NASA to find out how configurations developed in wind tunnels would perform on flight vehicles. The presentation will then summarize some recent results obtained in the 80- by 120-Foot Wind Tunnel at NASA Ames Research Center on the vortex wakes that trail from 0.03 scale models of a B-747 and of a DC-10 at downstream distances of 81 ft and 162 ft behind the wake-generating model; i.e., at scale distances of 0.5 and 1.0 mile. Lastly, a proposed vortex avoidance scheme based on the Global Positioning System will be described. All of the material to be presented is publically available in technical journals.

Rossow, Vernon J.↗
NASA NTRS1961

Aerodynamic Loads at Mach Numbers from 0.70 to 2.22 on a Airplane Model Having a Wing and Canard of Triangular Plan Form and Either Single or Twin Vertical Tails

Results of an investigation of the aerodynamic loads on a canard airplane model are presented without detailed analysis for the Mach number range of 0.70 t o 2.22. The model consisted of a triangular wing and canard of aspect ratio 2 mounted on a Sears-Haack body of fineness ratio 12.5 and either a single body-mounted vertical tail or twin wing mounted vertical tails of low aspect ratio and sweptback plan form. The body, right wing panel, single vertical tail, and left twin vertical tail were instrumented for measuring pressures. Data were obtained for angles of attack ranging from -4 degrees to +16 degrees, nominal canard deflection angles of 0 degrees and 10 degrees, and angles of sideslip of 0 degrees and 5.3 degrees. The Reynolds number was 2.9 x 10(exp 6) based on the wing mean aerodynamic chord. Selected portions of the data are presented in graphical form and attention is directed to some of the results of the investigation. All of the experimental results have been tabulated in the form of pressure coefficients and integrations of the pressure coefficients and are available as supplements to this paper. A brief summary of the contents of the tabular material is given.

Peterson, Victor L.↗
NASA NTRS1989

Some aerodynamic characteristics of the scissor wing configuration

A scissor wing configuration, consisting of four adjustable wing surfaces, is compared with a comparable fixed wing baseline configuration. Wave drag, induced drag, viscous drag, thrust required, and gust loading are calculated for both configurations. The scissor wing is shown to have lower zero lift wave drag and higher total lift to drag ratios than the baseline. It is demonstrated that the scissor configurations' sweep can be programmed to keep the static margin fixed. Thrust required for both the fixed static margin case and a constant sweep angle case are presented with the scissor configuration requiring lower thrust levels. The gust loading ratio of the scissor wing to the baseline is also shown to be significantly less than 1.0 for sweep angles greater than 20 degrees.

Selberg, Bruce P.↗
NASA NTRS2018

LEAPTech/HEIST Experiment Test and Evaluation Summary

The Leading Edge Asynchronous Propeller Technology (LEAPTech) project tested the Hybrid-Electric Integrated Systems Testbed (HEIST) and was intended for a general aviation sized aircraft with Distributed Electric Propulsion (DEP) to show large improvements with regards to efficiency, emissions, safety and operating costs. The wing was designed for high loading to improve ride quality and show improved takeoff and landing characteristics. The full-scale test article wing had a 31-foot-span, had integrated electric motors, was mounted on a truck 20 ft. above ground and driven in a simulated flight test environment at various velocities up to 70 miles per hour. The simulated flight test varied primarily angle of attack and flap settings. These tests were conducted to obtain data and verify blown wing performance primarily with regards to lift. The experimental test results are presented.

electric propulsion↗
NASA NTRS2019

Structural Analysis and Performance-Based Validation of a Composite Wing Spar

Electric-motor powered aircraft possess the ability to operate with efficient energy delivery, but lack the operational range of internal combustion engine powered aircraft. This range limitation requires the use of high aspect ratio, thin-chord wings to minimize aerodynamic drag losses, which results in highly loaded composite spar structures. High aspect ratio wings are required to increase mission durations for a NASA-developed experimental multi-rotor electric powered aircraft denoted as the Scalable Convergent Electric Propulsion Technology and Operations Research (SCEPTOR) or “X-57”. This paper examines the structural performance of the composite main wing spars to validate spar strength using ply-based laminate finite element methods. Geometric scaling of a main spar test-section was initially proposed for proof-testing but sacrificed stability. Ply-based structures modeling with local structural features was implemented as a risk-reduction methodology. Ply-based modeling was selected to augment the conventional “building block” approach to reduce risk, and leverage a “performance-based” approval processes encouraged in Federal Aviation Administration (FAA) design guidance. Therefore, ply-based laminate modeling of the full-scale main spar and forward spar shear-web attachments were subsequently undertaken to determine load path complexity with predicted flight loads. Ply-based modeling included stress concentrations and interlaminate behavior at interface locations that can be obscured in traditional finite element sizing models. Analysis of the wing spar laminate ply-based models compared with bearing test coupon performance was used to reduce future wing assembly proof-testing burden and facilitate performance-based flight hardware safety for the X-57 experimental aircraft.

Moore, James B.↗
NASA NTRS1990

The aerodynamic design of the oblique flying wing supersonic transport

The aerodynamic design of a supersonic oblique flying wing is strongly influenced by the requirement that passengers must be accommodated inside the wing. It was revealed that thick oblique wings of very high sweep angle can be efficient at supersonic speeds when transonic normal Mach numbers are allowed on the upper surface of the wing. The goals were motivated by the ability to design a maximum thickness, minimum size oblique flying wing. A 2-D Navier-Stokes solver was used to design airfoils up to 16 percent thickness with specified lift, drag and pitching moment. A new method was developed to calculate the required pressure distribution on the wing based on the airfoil loading, normal Mach number distribution and theoretical knowledge of the minimum drag of oblique configurations at supersonic speeds. The wing mean surface for this pressure distribution was calculated using an inverse potential flow solver. The lift to drag ratio of this wing was significantly higher than that of a comparable delta wing for cruise speeds up to Mach 2.

Vandervelden, Alexander J. M.↗
NASA NTRS1968

Modified Multhopp mean camber computer program

Computer program which determines the mean camber surface required to support a given set of loadings on a composite wing in subsonic compressible flow has been developed.

Lamar, J. E.↗
NASA NTRS1973

V/STOL tilt rotor aircraft study: Wind tunnel tests of a full scale hingeless prop/rotor designed for the Boeing Model 222 tilt rotor aircraft

The rotor system designed for the Boeing Model 222 tilt rotor aircraft is a soft-in-plane hingeless rotor design, 26 feet in diameter. This rotor has completed two test programs in the NASA Ames 40' X 80' wind tunnel. The first test was a windmilling rotor test on two dynamic wing test stands. The rotor was tested up to an advance ratio equivalence of 400 knots. The second test used the NASA powered propeller test rig and data were obtained in hover, transition and low speed cruise flight. Test data were obtained in the areas of wing-rotor dynamics, rotor loads, stability and control, feedback controls, and performance to meet the test objectives. These data are presented.

Magee, J. P.↗
NASA NTRS1974

Far-field wake-vortex characteristics of wings

Velocity measurements have been made in the wake of wings that were being towed underwater. As the wake aged, measurements of the tangential and axial velocity profiles were made with a two-dimensional scanning laser velocimeter at downstream distances of 5 to 200 span lengths behind wings with different span loadings. The results identify two characteristic flow regions for the dependence of vortex maximum tangential velocity on downstream distance. The first, a region with little, if any, change in maximum tangential velocity, extends from wake rollup to downstream distances as great as 100 span lengths, depending on span loading and angle of attack. This is followed by a decay region in which the maximum tangential velocity decreases with downstream distance at rates nominally proportional to the inverse one-half power.

Ciffone, D. L.↗
NASA NTRS1975

Application of an advanced computerized structural design system to an arrow-wing supersonic cruise aircraft

A structural design study of an arrow-wing supersonic cruise aircraft has been made using the integrated design system, ATLAS, and a relatively large analytical finite-element model containing 8500 degrees of freedom. This paper focuses on structural design methods developed and used in support of the study with emphasis on aeroelasticity. The use of ATLAS permitted (1) automatic resizing of the wing structure for multiple load conditions, (2) rapid evaluation of aeroelastic effects, and (3) an iterative approach to the correction of flutter deficiencies. The significant results of the study are discussed along with the advantages derived from the use of an advanced structural design system in preliminary design studies.

Robinson, J. C.↗
NASA NTRS1976

Optimization of multi-constrained structures based on optimality criteria

A weight-reduction algorithm is developed for the optimal design of structures subject to several multibehavioral inequality constraints. The structural weight is considered to depend linearly on the design variables. The algorithm incorporates a simple recursion formula derived from the Kuhn-Tucker necessary conditions for optimality, associated with a procedure to delete nonactive constraints based on the Gauss-Seidel iterative method for linear systems. A number of example problems is studied, including typical truss structures and simplified wings subject to static loads and with constraints imposed on stresses and displacements. For one of the latter structures, constraints on the fundamental natural frequency and flutter speed are also imposed. The results obtained show that the method is fast, efficient, and general when compared to other competing techniques. Extensions to the generality of the method to include equality constraints and nonlinear merit functions is discussed.

Rizzi, P.↗
NASA NTRS1980

Graphite-epoxy panel compression strength reduction due to local impact

A review of results from on-going research to investigate the effects of low-velocity impact on the compressive strength of graphite-epoxy structures is presented. Extensive tests have been conducted on sandwich beams, laminated plates and stiffened panels. Conditions for failures were investigated by impact tests on statically loaded test specimens. The effects of compression load intensity were such that lightly loaded graphite structures (such as aircraft secondary structure) were insensitive to impact damage. In more heavily loaded structures, (such as wing panels), however, appreciable reductions in compressive strength occurred. The implications of the tests for structural design are discussed by comparing panel masses for designs where ultimate strains have been reduced due to impact considerations with the masses of designs with higher ultimate strains. Finally, preliminary test data is presented to show the possibility of improvements in damage tolerance achievable by using an alternate matrix material.

Card, M. P.↗
NASA NTRS1980

Graphite-epoxy panel compression strength reduction due to local impact

The effects of low velocity impact on the compressive strength of graphite/epoxy structures are reviewed. Extensive tests were conducted on sandwich beams, laminated plates and stiffened panels. Conditions for failures were investigated by impact tests on statically loaded test specimens. Lightly loaded graphite structures (such as aircraft secondary structure) were insensitive to impact damage. In more heavily loaded structures, (such as wing panels), appreciable reductions in compressive strength occurred. The implications of the tests for structural design are discussed by comparing panel masses for designs where ultimate strains were reduced due to impact considerations with the masses of designs with higher ultimate strains. Preliminary test data are presented to show the possibility of improvements in damage to tolerance achievable by using an alternate matrix material.

Card, M. F.↗
NASA NTRS1981

Development of a nonlinear vortex method

Progress is reported in the development of reliable nonlinear vortex methods for predicting the steady and unsteady aerodynamic loads of highly sweptback wings at large angles of attack. Abstracts of the papers, talks, and theses produced through this research are included. The modified nonlinear discrete vortex method and the nonlinear hybrid vortex method are highlighted.

Kandil, O. A.↗
NASA NTRS1980

Integrative application of active controls (IAAC) technology to an advanced subsonic transport project. Initial act configuration design study

The performance and economic benefits of a constrained application of Active Controls Technology (ACT) are identified, and the approach to airplane design is established for subsequent steps leading to the development of a less constrained final ACT configuration. The active controls configurations are measured against a conventional baseline configuration, a state-of-the-art transport, to determine whether the performance and economic changes resulting from ACT merit proceeding with the project. The technology established by the conventional baseline configuration was held constant except for the addition of ACT. The wing, with the same planform, was moved forward on the initial ACT configuration to move the loading range aft relative to the wing mean aerodynamic chord. Wing trailing-edge surfaces and surface controls also were reconfigured for load alleviation and structural stabilization.

Source record↗
NASA NTRS1982

Recent advances in applying Free Vortex Sheet theory to the estimation of vortex flow aerodynamics

Free Vortex Sheet theory has been applied to a variety of configurations for the estimation of three-dimensional pressure distributions for wings developing separation-induced leading-edge vortex flows. Correlations with experiment show reasonable estimates for the effects of compressibility, side-slip, side edges, swept-wing blast-induced loads, and leading-edge vortex flaps. Theoretical studies expand upon these correlations to show general aerodynamic trends. Consideration is also given to simple, yet effective techniques which expedite convergence and therefore reduce computational expense.

Luckring, J. M.↗