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Study of Two Dimensional Panel Flutter and Panel Divergence in Subsonic Flow (III) - Experimental Studies of Two Dimensional and Three Dimensional Panels in Low Speed Wind Tunnel
Two-dimensional panel flutter and panel divergence in subsonic flow - wind tunnel testing of two and three-dimensional panels
Experimental Studies of Flutter of Buckled Rectangular Panels at Mach Numbers from 1.2 to 3.0 Including Effects of Pressure Differential and of Panel Width-Length Ratio
Experimental panel flutter data have been obtained at Mach numbers from 1.2 to 3.0 for buckled rectangular panels and the effect of a pressure differential has been determined. Increasing the pressure differential was effective in eliminating flutter on most of the panels tested. The effects of the variables in the panel flutter parameter ((square root of m(exp 2) -1) * (E/q))(exp 1/3) t/l (where M is the Mach number, q is the dynamic pressure, E is Young's modulus, and t and l are the panel thickness and length, respectively) were investigated for buckled panels clamped on the front and rear edges and a critical value of this parameter of 0.44 is indicated at zero pressure differential when the panel width-length ratio is 0.69. An estimated flutter boundary is presented for buckled panels clamped on four edges, with width-length ratios of 0.21 to 4.0. This boundary shows that the panel width is more significant than the panel length when the ratio of width to length is less than approximately 0.5. Panels clamped on four edges and buckled in two half waves in the direction of flow were found to be particularly susceptible to flutter. The results of limited tests on panels with applied damping, curvature, and lengthwise stiffeners are also presented and discussed.
The effect of oblique angle of sound incidence, realistic edge conditions, curvature and in-plane panel stresses on the noise reduction characteristics of general aviation type panels
Experiments and a theoretical analysis were conducted to predict the noise reduction of inclined and curved panels. These predictions are compared to the experimental results with reasonable agreement between theory and experiment for panels under an oblique angle of sound incidence. Theoretical as well as experimental results indicate a big increase in noise reduction when a flat test panel is curved. Further curving the panel slightly decreases the noise reduction. Riveted flat panels are shown to give a higher noise reduction in the stiffness-controlled frequency region, while bonded panels are superior in this region when the test panel is curved. Experimentally measured noise reduction characteristics of flat aluminum panels with uniaxial in-plane stresses are presented and discussed. These test results indicate an important improvement in the noise reduction of these panels in the frequency range below the fundamental panel/cavity frequency.
Investigation of forming curved ablative panels from flat panels for space shuttle
The purpose of this study was to determine the feasibility of reforming flat ablative panels to a curved configuration. The study indicated that if the panels could be shaped to a radius of 2.54 m (100 in.) then 88.7% of the surface area of the orbiter could be covered, and that if they could be shaped to a radius of 3.81 m (150 in.) then 77.2% of the surface could be covered. Two basic approaches were followed to determine the best method for forming the flat panels to a curved shape. The first was to determine if partially cured panels could be formed, allowing the forming heat cycle to complete the curing of the ablator. The second method was to form fully cured flat panels into the desired curvature through a secondary heat cycle. Measurements made on the panels during storage indicated that they continued to straighten out over time. This was attributed to residual stresses locked into the panels that had not been fully relaxed by the heat cycle.
Supersonic Panel Flutter Test Results for Flat Fiber-Glass Sandwich Panels with Foamed Cores
Flutter tests have been made on flat panels having a 1/4 inch-thick plastic-foam core covered with thin fiber-glass laminates. The testing was done in the Langley Unitary Plan wind tunnel at Mach numbers from 1.76 t o 2.87. The flutter boundary for these panels was found to be near the flutter boundary of thin metal panels when compared on the basis of an equivalent panel stiffness. The results also demonstrated that the depth of the cavity behind the panel has a pronounced influence on flutter. Changing the cavity depth from 1 1/2 inches to 1/2 inch reduced the dynamic pressure at start of flutter by 40 percent. No flutter was obtained when the spacers on the back of the panel were against the bottom of the cavity.
Optical monitor panel provides flexible test panel configurations
Optical monitor panel projects a chosen panel configuration upon a translucent screen by using a master projector and appropriate slide to project panel board nomenclature and a series of smaller individual projectors to superimpose monitor indicators upon the projected panel board.
A general panel sizing computer code and its application to composite structural panels
A computer code for obtaining the dimensions of optimum (least mass) stiffened composite structural panels is described. The procedure, which is based on nonlinear mathematical programming and a rigorous buckling analysis, is applicable to general cross sections under general loading conditions causing buckling. A simplified method of accounting for bow-type imperfections is also included. Design studies in the form of structural efficiency charts for axial compression loading are made with the code for blade and hat stiffened panels. The effects on panel mass of imperfections, material strength limitations, and panel stiffness requirements are also examined. Comparisons with previously published experimental data show that accounting for imperfections improves correlation between theory and experiment.
Study of noise reduction characteristics of composite fiber-reinforced panels, interior panel configurations, and the application of the tuned damper concept
The application of fiber reinforced composite materials, such as graphite epoxy and Kevlar, for secondary or primary structures developing in the commercial airplane industry was investigated. A composite panel program was initiated to study the effects of some of the parameters that affect noise reduction of these panels. The fiber materials and the ply orientation were chosen to be variables in the test program. It was found that increasing the damping characteristics of a structural panel will reduce the vibration amplitudes at resonant frequencies with attendant reductions in sound reduction. Test results for a dynamic absorber, a tuned damper, are presented and evaluated.
EXPERIMENTAL PANEL FLUTTER RESULTS FOR SOME FLAT AND CURVED TITANIUM SKIN PANELS AT SUPERSONIC SPEEDS
Panel flutter results for flat and curved titanium skin panels at supersonic speed
Flutter at Mach 3 of thermally stressed panels and comparison with theory for panels with edge rotational restraint
Flutter at Mach 3 of thermally stressed flat isotropic panels
Research study to provide concepts of panel attachment mechanisms suitable for refurbishable panel application
Panel attachment mechanism for replaceable heat shield system of manned lifting entry vehicle
Panel flutter studies of boost-vehicle full-scale flight insulation panels
Supersonic wind tunnel tests on flutter resistance of Centaur flight insulation panels
A method for predicting the panel flutter fatigue life of Saturn 5 panels
Development of method for predicting fatigue life of panels under flutter conditions with application to Saturn 5 launch vehicle structures
Annual Report to the NASA Administrator by the Aerospace Safety Advisory Panel on the Space Shuttle Program. Part 2: Summary of Information Developed in the Panel's Fact-Finding Activities
The panel focused its attention on those areas that are considered most significant for flight success and safety. Elements required for the Approach and Landing Test Program, the Orbital Flight Test Program, and those management systems and their implementation which directly affect safety, reliability, and quality control, were investigated. Ground facilities and the training programs for the ground and flight crews were studied. Of special interest was the orbiter thermal protection subsystems.
Recommendations of the panels: Panel on in-flight measurements
The attenuation factor for aircraft other than the B-747 in reducing the ambient ozone concentrations which enter the cabin is obtained. The need to continue NASA Global Air Sampling Program measurements was expressed for three main purposes; testing new filters, correlation of complaints with ozone levels, and ambient ozone data. The need to continue cooperation between NASA and industry is indicated. Concern with regard to the correlation of ozone levels and complaints was given. The need to measure the variability of ozone within the aircraft cabin was investigated. The requirement for an onboard ozone monitor on all aircraft is discussed.
Recommendations of the panels: Panel on flight planning to avoid high ozone
Flights planned or accomplished during certain months of the year at the higher latitudes and altitudes at or above the tropopause are discussed. Cabin ozone level limitations are established, and additional information is required for more accurate and qualtitative forecasting and design data base for operational utilization. Better tropopause heights, ozone concentration and corresponding meteorological data along selected flight routes, and meteorological data were investigated.
Recommendations of the panels: Panel on ozone destruction techniques
Catalyst materials to reduce weight, size, and cost of the ozone removal device were developed. Catalyst bed lifetime, competitive reactivity contaminants in the inlet air on the catalyst bed efficiency for ozone removal, and the kinetics and mechanism by which ozone is destroyed on selected catalysts were studied.