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At least 1,729 records · Page 96

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NASA NTRS1957

Loads Due to Controls at Transonic and Low Supersonic Speeds

Some results of recent experimental investigations at supersonic and transonic speeds are presented to show the present status in the estimation of load distributions on controls and adjacent wing surfaces resulting from the deflection of flap controls and spoiler controls. The results indicate that the development of methods for predicting loads associated with controls has not kept pace with the acquisition of experimental data. At low supersonic speeds sweeping the hinge line induces strong three-dimensional-flow characteristics which cannot be treated by the simplified methods previously developed for controls without sweep. At transonic speeds the estimation of loads associated with controls must usually be dependent upon experimental information inasmuch as the latest attempts to predict chordwise and spanwise loadings have met with only limited success.

West, F. E, Jr↗

NASA NTRS1950

The application of the statistical theory of extreme values to gust-load problems

An analysis is presented which indicates that the statistical theory of extreme values is applicable to the problems of predicting the frequency of encountering the larger gust loads and gust velocities for both specific test conditions as well as commercial transport operations. The extreme-value theory provides an analytic form for the distributions of maximum values of gust load and velocity. Methods of fitting the distribution are given along with a method of estimating the reliability of the predictions. The theory of extreme values is applied to available load data from commercial transport operations. The results indicate that the estimates of the frequency of encountering the larger loads are more consistent with the data and more reliable than those obtained in previous analyses. (author)

Press, Harry↗

NASA NTRS1954

A revised gust-load formula and a re-evaluation of v-g data taken on civil transport airplanes from 1933 to 1950

A revised gust-load formula with a new gust factor is derived to replace the gust-load formula and alleviation factor widely used in gust studies. The revised formula utilizes the same principles and retains the same simple form of the original formula but provides a more appropriate and acceptable basis for gust-load calculations. The gust factor is calculated on the basis of a one-minus-cosine gust shape and is presented as a function of a mass-ratio parameter in contrast to the ramp gust shape and wing loading, respectively, used for the alleviation factor. A summary of gust-velocity data from v-g records taken on civil transport airplanes from 1933 to 1950, reevaluated by the revised formula, is also presented.

Pratt, Kermit G↗

NASA NTRS1957

Induced Velocities Near a Lifting Rotor with Nonuniform Disk Loading

A method is given for converting known uniformly loaded rotor induced velocities to correspond with arbitrary axisymmetric nonuniform disk load distributions. Numerical results for two specific distributions are given in chart form. Symmetry relations and relations between radial disk loading and wake velocities are developed. Experimental flow measurements are presented and compared with theory. Reasonable agreement is shown in the forward part of the flow when nonuniform loading is assumed, but far behind the rotor the flow is more like that of a wing.

Heyson, Harry H↗

NASA NTRS1946

Consideration of dynamic loads on the vertical tail by the theory of flat yawing maneuvers

Dynamic yawing effects on vertical-tail loads are considered by a theory of flat yawing maneuvers. A comparison is shown between computed loads and the loads measured in flight on a fighter airplane. The dynamic effects were investigated on a large flying boat for both an abrupt rudder deflection and sinusoidal rudder deflection. Only a moderate amount of control deflection was found to be necessary to attain the ultimate design load on the tail. In order to take into account dynamic effects in design, specifications of yawing maneuverability or control movement are needed.

Boshar, John↗

NASA NTRS1948

Theoretical symmetric span loading at subsonic speeds for wings having arbitrary plan form

A method is shown by which the symmetric span loading for a certain class of wings can be simply found. The geometry of these wings is limited only to the extent that they must have symmetry about the root chord, must have a straight quarter-chord line over the semispan, and must have no discontinuities in twist. A procedure is shown for finding the lift-curve slope, pitching moment, center of lift, and induced drag from the span load distribution. A method of accounting for the effects of Mach number and for changes in section lift-curve slope is also given. Charts are presented which give directly the characteristics of many wings. Other charts are presented which reduce the problem of finding the symmetric loading on all wings falling within the prescribed limits to the solution of not more than four simultaneous equations. The loadings and wing characteristics predicted by the theory are compared to those given by other theories and by experiment. It is concluded that the results given by the subject theory are satisfactory. The theory is applied to a number of wings to exhibit the effects of such variables as sweep, aspect ratio, taper, and twist. The results are compared and conclusions drawn as to the relative effects of these variables.

Deyoung, John↗

NASA NTRS1953

Theory and procedure for determining loads and motions in chine-immersed hydrodynamic impacts of prismatic bodies

A theoretical method is derived for the determination of the motions and loads during chine-immersed water landings of prismatic bodies. This method makes use of a variation of two-dimensional deflected water mass over the complete range of immersion, modified by a correction for three-dimensional flow. Equations are simplified through omission of the term proportional to the acceleration of the deflected mass for use in calculation of loads on hulls having moderate and heavy beam loading. The effects of water rise at the keel are included in these equations. In order to make a direct comparison of theory with experiment, a modification of the equations was made to include the effect of finite test-carriage mass. A simple method of computation which can be applied without reading the body of this report is presented as an appendix along with the required theoretical plots for determination of loads and motions in chine-immersed landings.

Schnitzer, Emanuel↗

NASA NTRS1956

Low-speed cascade investigation of loaded leading-edge compressor blades

Six percent thick NACA 63-series compressor-blade sections having a loaded leading-edge A4K6 mean line have been investigated systematically in a two-dimensional porous-wall cascade over a range of Reynolds numbers from 160,000 to 385,000. Blades cambered to have isolated-airfoil lift coefficients of 0.6, 1.2, 1.8, and 2.4 were tested over the usable angle-of-attack range at inlet-air angles of 30 degrees, 45 degrees, and 60 degrees and solidities of 1.0 and 1.5. A comparison with data of NACA RM L51G31, shows that the angle-of-attack operating range is 2 degrees to 4 degrees less than the range for the uniformly loaded section; however, the wake losses near design angle of attack are slightly lower than those for the uniformly loaded section. Except for highly cambered blades at high inlet angles, the 63-(C s oA4K6)06 compressor-blade sections are capable of more efficient operation for moderate-speed subsonic compressors at design angle of attack than are the 65-(C s oa10)10 or the 65-(c s oA2I8b)10 compressor-blade sections. In contrast to the other sections, the loaded leading-edge sections are capable of operating efficiently at the lower Reynolds numbers.

Emery, James C↗

NASA NTRS1955

Aerodynamic Loads on an External Store Adjacent to a 45 Degree Sweptback Wing at Mach Numbers from 0.70 to 1.96, Including an Evaluation of Techniques Used

Aerodynamic forces and moments have been obtained in the Langley 9- by 12-inch blowdown tunnel on an external store and on a 45 degree swept-back wing-body combination measured separately at Mach numbers from 0.70 to 1.96. The wing was cantilevered and had an aspect ratio of 4.0; the store was independently sting-mounted and had a Douglas Aircraft Co. (DAC) store shape. The angle of attack range was from -3 degrees to 12 degrees and the Reynolds number (based on wing mean aerodynamic chord) varied from 1.2 x10(6) to 1.7 x 10(6). Wing-body transonic forces and moments have been compared with data of a geometrically similar full-scale model tested in the Langley 16-foot and 8-foot transonic tunnels in order to aid in the evaluation of transonic-tunnel interference. The principal effect of the store, for the position tested, was that of delaying the wing-fuselage pitch-up tendency to higher angles of attack at Mach numbers from 0.70 to 0.90 in a manner similar to that of a wing chord extension. The most critical loading condition on the store was that due to side force, not only because the loads were of large magnitude but also because they were in the direction of least structural strength of the supporting pylon. These side loads were greatest at high angles of attack in the supersonic speed range. Removal of the supporting pylon (or increasing the gap between the store and wing) reduced the values of the variation of side-force coefficientwith angle of attack by about 50 percent at all test Mach numbers, indicating that important reductions in store side force may be realized by proper design or location of the necessary supporting pylon. A change of the store skew angle (nose inboard) was found to relieve the excessive store side loads throughout the Mach number range. It was also determined that the relative position of the fuselage nose to the store can appreciably affect the store side forces at supersonic speeds.

Guy, Lawrence D↗

NASA NTRS1931

Load assumptions for the landing impact of seaplanes

The formula for the impact of floats must include the enlargement factor itself as well as the type of enlargement. The latter is preferably characterized by the change in surface loading. It is shown that the enlargement of a small seaplane generally results in a changed float (or boat) loading as well as wing loading. The conditions of starting stipulate the retention of the float loading when changing from single-float (boat) to twin-float arrangement. This contingency is followed by an increased impact factor in the twin-float type against the otherwise equivalent single-float type.

Taub, Josef↗

NASA NTRS1930

Load assumptions for calculating the strength of airplanes

The following load assumptions shall be taken as the basis of the strength calculations. Certain definite load conditions (e.g. of flight, control, landing and transport) shall be assumed. The loads shall be assumed to be safe loads, constant or only slowly variable, and the inertia forces due to elastic deformation are accordingly disregarded. The external forces, the force of gravity and the inertia forces on the whole airplane shall produce a condition of equilibrium.

Source record↗

NASA NTRS1993

Improvements to a method for the geometrically nonlinear analysis of compressively loaded stiffened composite panels

The NLPAN computer code uses a finite-strip approach to the analysis of thin-walled prismatic composite structures such as stiffened panels. The code can model in-plane axial loading, transverse pressure loading, and constant through-the-thickness thermal loading, and can account for shape imperfections. The NLPAN code represents an attempt to extend the buckling analysis of the VIPASA computer code into the geometrically nonlinear regime. Buckling mode shapes generated using VIPASA are used in NLPAN as global functions for representing displacements in the nonlinear regime. While the NLPAN analysis is approximate in nature, it is computationally economical in comparison with finite-element analysis, and is thus suitable for use in preliminary design and design optimization. A comprehensive description of the theoretical approach of NLPAN is provided. A discussion of some operational considerations for the NLPAN code is included. NLPAN is applied to several test problems in order to demonstrate new program capabilities, and to assess the accuracy of the code in modeling various types of loading and response. User instructions for the NLPAN computer program are provided, including a detailed description of the input requirements and example input files for two stiffened-panel configurations.

Stoll, Frederick↗

NASA NTRS1993

A parametric study of harmonic rotor hub loads

A parametric study of vibratory rotor hub loads in a nonrotating system is presented. The study is based on a CAMRAD/JA model constructed for the GBH (Growth Version of Blackhawk Helicopter) Mach-scaled wind tunnel rotor model with high blade twist (-16 deg). The theoretical hub load predictions are validated by correlation with available measured data. Effects of various blade aeroelastic design changes on the harmonic nonrotating frame hub loads at both low and high forward flight speeds are investigated. The study aims to illustrate some of the physical mechanisms for change in the harmonic rotor hub loads due to blade design variations.

He, Chengjian↗

NASA NTRS1993

Population-based learning of load balancing policies for a distributed computer system

Effective load-balancing policies use dynamic resource information to schedule tasks in a distributed computer system. We present a novel method for automatically learning such policies. At each site in our system, we use a comparator neural network to predict the relative speedup of an incoming task using only the resource-utilization patterns obtained prior to the task's arrival. Outputs of these comparator networks are broadcast periodically over the distributed system, and the resource schedulers at each site use these values to determine the best site for executing an incoming task. The delays incurred in propagating workload information and tasks from one site to another, as well as the dynamic and unpredictable nature of workloads in multiprogrammed multiprocessors, may cause the workload pattern at the time of execution to differ from patterns prevailing at the times of load-index computation and decision making. Our load-balancing policy accommodates this uncertainty by using certain tunable parameters. We present a population-based machine-learning algorithm that adjusts these parameters in order to achieve high average speedups with respect to local execution. Our results show that our load-balancing policy, when combined with the comparator neural network for workload characterization, is effective in exploiting idle resources in a distributed computer system.

Mehra, Pankaj↗

NASA NTRS1994

Method of determining load in anisotropic non-crystalline materials using energy flux deviation

An ultrasonic wave is applied to an anisotropic sample material in an initial direction and the intensity of the ultrasonic wave is measured on an opposite surface of the sample material by two adjacent receiving points located in an array of receiving points. A ratio is determined between the measured intensities of two adjacent receiving points, the ratio being indicative of an angle of flux deviation from the initial direction caused by an unknown applied load. This determined ratio is then compared to a plurality of ratios of a similarly tested, similar anisotropic reference material under a plurality of respective, known load conditions, whereby the load applied to the particular anisotropic sample material is determined. A related method is disclosed for determining the fiber orientation from known loads and a determined flux shift.

Prosser, William H.↗

NASA NTRS1994

Recent advances in the modelling of crack growth under fatigue loading conditions

Fatigue crack growth associated with cyclic (secondary) plastic flow near a crack front is modelled using an incremental formulation. A new description of threshold behaviour under small load cycles is included. Quasi-static crack extension under high load excursions is described using an incremental formulation of the R-(crack growth resistance)- curve concept. The integration of the equations is discussed. For constant amplitude load cycles the results will be compared with existing crack growth laws. It will be shown that the model also properly describes interaction effects of fatigue crack growth and quasi-static crack extension. To evaluate the more general applicability the model is included in the NASGRO computer code for damage tolerance analysis. For this purpose the NASGRO program was provided with the CORPUS and the STRIP-YIELD models for computation of the crack opening load levels. The implementation is discussed and recent results of the verification are presented.

Dekoning, A. U.↗

NASA NTRS1995

Transient and Steady-state Tests of the Space Power Research Engine with Resistive and Motor Loads

The NASA Lewis Research Center (LeRC) has been testing free-piston Stirling engine/linear alternators (FPSE/LA) to develop advanced power convertors for space-based electrical power generation. Tests reported herein were performed to evaluate the interaction and transient behavior of FPSE/LA-based power systems with typical user loads. Both resistive and small induction motor loads were tested with the space power research engine (SPRE) power system. Tests showed that the control system could maintain constant long term voltage and stable periodic operation over a large range of engine operating parameters and loads. Modest resistive load changes were shown to cause relatively large voltage and, therefore, piston and displacer amplitude excursions. Starting a typical small induction motor was shown to cause large and, in some cases, deleterious voltage transients. The tests identified the need for more effective controls, if FPSE/LAs are to be used for stand-alone power systems. The tests also generated a large body of transient dynamic data useful for analysis code validation.

Rauch, Jeffrey S.↗

NASA NTRS1995

Comparison of measured and calculated dynamic loads for the Mod-2 2.5 mW wind turbine system

The Boeing Company, under contract to the Electric Power Research Institute (EPRI), has completed a test program on the Mod-2 wind turbines at Goodnoe Hills, Washington. The objectives were to update fatigue load spectra, discern site and machine differences, measure vortex generator effects, and to evaluate rotational sampling techniques. This paper shows the test setup and loads instrumentation, loads data comparisons and test/analysis correlations. Test data are correlated with DYLOSAT predictions using both the NASA interim turbulence model and rotationally sampled winds as inputs. The latter is demonstrated to have the potential to improve the test/analysis correlations. The paper concludes with an assessment of the importance of vortex generators, site dependence, and machine differences on fatigue loads. The adequacy of prediction techniques used are evaluated and recommendations are made for improvements to the methodology.

Zimmerman, D. K.↗