Design and manufacture of parasitic load resistors for Brayton power conversion system Final report
Design, manufacture, and testing of parasitic load resistors for Brayton power conversion system
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Energy efficient engine, low-pressure turbine boundary layer program
A study was conducted to investigate development of boundary layers under the influence of velocity distributions simulating the suction side of two state-of-the-art turbine airfoils: a forward loaded airfoil (squared-off design) and an aft loaded airfoil (aft-loaded design). These velocity distributions were simulated in a boundary layer wind tunnel. Detailed measurements of boundary layer mean velocity and turbulence intensity profiles were obtained for an inlet turbulence level of 2.4 percent and an exit Reynolds number of 800,000. Flush-mounted hot film probes identified the boundary layer transition regimes in the adverse pressure gradient regions for both velocity distributions. Wall intermittency data showed good agreement with the correlations of Dhawan and Narasimha for the intermittency factor distribution in transitional flow regimes.
Gardner, W. B.↗
PMR Graphite Engine Duct Development
The objective was to demonstrate the cost and weight advantages that could be obtained by utilizing the graphite/PMR15 material system to replace titanium in selected turbofan engine applications. The first component to be selected as a basis for evaluation was the outer bypass duct of the General Electric F404 engine. The operating environment of this duct was defined and then an extensive mechanical and physical property test program was conducted using material made by processing techniques which were also established by this program. Based on these properties, design concepts to fabricate a composite version of the duct were established and two complete ducts fabricated. One of these ducts was proof pressure tested and then run successfully on a factory test engine for over 1900 hours. The second duct was static tested to 210 percent design limit load without failure. An improved design was then developed which utilized integral composite end flanges. A complete duct was fabricated and successfully proof pressure tested. The net results of this effort showed that a composite version of the outer duct would be 14 percent lighter and 30 percent less expensive that the titanium duct. The other type of structure chosen for investigation was the F404 fan stator assembly, including the fan stator vanes. It was concluded that it was feasible to utilize composite materials for this type structure but that the requirements imposed by replacing an existing metal design resulted in an inefficient composite design. It was concluded that if composites were to be effectively used in this type structure, the design must be tailored for composite application from the outset.
Stotler, C. L.↗
Detailed analysis and test correlation of a stiffened composite wing panel
New finite element analysis methods are examined by application to a complicated composite wing panel from the V-22 rotorcraft. A detailed FEM model with a relatively coarse mesh of 9-node elements was generated, and linear and nonlinear stress analyses, first-ply failure analyses, and buckling analyses were conducted. At low values of applied load, i.e., up to the design ultimate load of the panel, the linear stress analysis accurately predicted the strains and structural response characteristics of the panel.
Davis, D. D., Jr.↗
Recent experiments with large seaplanes
This report covers the following aspects of large seaplane design and construction: heavy wing loading; propeller design; how the motion of the airplane is affected by increasing the dihedral angle; power plants; floats; and the hull.
SEAPLANES - DESIGN↗
Design of Launch Vehicle Flight Control Systems Using Ascent Vehicle Stability Analysis Tool
A launch vehicle represents a complicated flex-body structural environment for flight control system design. The Ascent-vehicle Stability Analysis Tool (ASAT) is developed to address the complicity in design and analysis of a launch vehicle. The design objective for the flight control system of a launch vehicle is to best follow guidance commands while robustly maintaining system stability. A constrained optimization approach takes the advantage of modern computational control techniques to simultaneously design multiple control systems in compliance with required design specs. "Tower Clearance" and "Load Relief" designs have been achieved for liftoff and max dynamic pressure flight regions, respectively, in the presence of large wind disturbances. The robustness of the flight control system designs has been verified in the frequency domain Monte Carlo analysis using ASAT.
Jang, Jiann-Woei↗
Highly Loaded Low Pressure Turbine (LPT)
The goal of this study is to evaluate aspirated and non-aspirated aerodynamics on highly loaded LPT design. The objective is to increase stage loading by 30 to 50 percent without loss of efficiency for an existing low pressure turbine design. A study conducted on a NASA highly loaded multistage fan drive turbine (NASA CR-1964) indicated that end-wall bleed at the hub is a more significant parameter compared to aspirated airfoil. Based on this study, a 3-stage LPT is redesigned to 2-stage LIT with and without end-wall bleed. Both aerodynamic design and mechanical design are completed. In addition to end-wall bleed, exit guide vanes are designed with aspirated airfoils to reduce the losses. The LPT is redesigned with all constraints necessary for practical application. The benefit of the high-performance, highly loaded LPT shows up in reduced stage and part count, reduced size and weight, and reduced cost.
Ortiz, Milt↗
An improved method for optimum design of mechanically and thermally loaded structures
The problem of obtaining the minimum-mass design of mechanically and thermally loaded structures is presented. The special nature of thermal stresses with regard to their response to resizing of structural members is discussed. It is shown that conventional resizing procedures which are based on driving the total stress to its allowable value may be inefficient when the thermal stress in an element makes up a significant fraction of the total stress. An improved algorithm for resizing of structures subjected to thermal stresses is treated. In this algorithm the mechanical portions of the stresses were driven to their maximum allowable values. The thermal stresses were used to adjust the allowable values of the mechanical stresses. The new algorithm was exercised for a number of truss structures of varying complexity and compared with ordinary fully stressed design.
Adelman, H. M.↗
Loads Combination Research at Marshall Space Flight Center
This is the result of a study conducted by the Structural Dynamics Division of the Marshall Space Flight Center concerning the combination of low- and high-frequency dynamic loads for spacecraft design. Low-frequency transient loads are combined with high frequency acoustically induced loads to arrive at a limit load, for design purposes. Different methods are used for combining the loads which can lead to considerable variation in limit loads, depending on which NASA Center did the calculation. This study investigates several different combination methods and compares the combination methods with Spacelab 1 flight data. In addition, the relative timing of low- and high-frequency loads is examined.
Ferebee, R.↗
Loads Combination Research at Marshall Space Flight Center
This is the result of a study conducted by the Structural Dynamics Division of the Marshall Space Flight Center concerning the combination of low- and high-frequency dynamic loads for spacecraft design. Low-frequency transient loads are combined with high frequency acoustically induced loads to arrive at a limit load, for design purposes. Different methods are used for combining the loads which can lead to considerable variation in limit loads, depending on which NASA Center did the calculation. This study investigates several different combination methods and compares the combination methods with Spacelab 1 flight data. In addition, the relative timing of low- and high-frequency loads is examined.
Ferebee, R.↗
Design curves for non-linear analysis of simply-supported, uniformly-loaded rectangular plates
Design curves for the non-linear analysis of simply-supported rectangular plates subjected to uniform normal pressure loads have been developed. These curves yield the center deflection, center stress and corner stress in non-dimensionalized form plotted against a dimensionless parameter describing the load intensity. The results presented are based on extensive non-linear finite element analysis employing the ARGUS structural analysis program. Plates with length to width ratios of 1, 1.5, 2, 3 and 4 are included. The load range considered extends to 1000 times the load at which the behavior of the plate becomes significantly non-linear. Over the load range considered, the analysis shows that the ratio of center deflection to plate thickness for a square plate is less than 16 to 1, whereas linear theory would predict a center deflection 400 times the plate thickness. Likewise, the stress is markedly lower than would be predicted by linear theory. The present results are shown to be in excellent agreement with the classical linear theory up to a central deflection to plate thickness ratio of about one-half. In the non-linear regime the present results for deflection and stress are in very good agreement with the analytical and experimental work of other investigators.
Moore, D.↗
Structural Sizing of the EDIN0620 Body Components Using the APAS Structural Synthesis Computer Program
The use of a structural synthesis computer program to design components for a heavy lift launch vehicle is defined. A loads program was used to determine the vehicle shears, bending moments, and axial loads at two design loading conditions. A comparison was made between results from the structures program and the results of a weight estimating program which used historical data in determining component weights.
Nolte, W. E.↗
Modal MAC Launch Loads for SMAP Structural Design
No abstract available
Mass Acceleration Curve (MAC)↗
Extension-twist coupling of composite circular tubes with application to tilt rotor blade design
This investigation was conducted to determine if twist deformation required for the design of full-scale extension-twist-coupled tilt-rotor blades can be achieved within material design limit loads, and to demonstrate the accuracy of a coupled-beam analysis in predicting twist deformations. Two extension-twist-coupled tilt-rotor blade designs were developed based on theoretically optimum aerodynamic twist distributions. The designs indicated a twist rate requirement of between .216 and .333 deg/in. Agreement between axial tests and analytical predictions was within 10 percent at design limit loads. Agreement between the torsion tests and predictions was within 11 percent.
Nixon, Mark W.↗
Deformed Shape Calculation of a Full-Scale Wing Using Fiber Optic Strain Data from a Ground Loads Test
A ground loads test of a full-scale wing (175-ft span) was conducted using a fiber optic strain-sensing system to obtain distributed surface strain data. These data were input into previously developed deformed shape equations to calculate the wing s bending and twist deformation. A photogrammetry system measured actual shape deformation. The wing deflections reached 100 percent of the positive design limit load (equivalent to 3 g) and 97 percent of the negative design limit load (equivalent to -1 g). The calculated wing bending results were in excellent agreement with the actual bending; tip deflections were within +/- 2.7 in. (out of 155-in. max deflection) for 91 percent of the load steps. Experimental testing revealed valuable opportunities for improving the deformed shape equations robustness to real world (not perfect) strain data, which previous analytical testing did not detect. These improvements, which include filtering methods developed in this work, minimize errors due to numerical anomalies discovered in the remaining 9 percent of the load steps. As a result, all load steps attained +/- 2.7 in. accuracy. Wing twist results were very sensitive to errors in bending and require further development. A sensitivity analysis and recommendations for fiber implementation practices, along with, effective filtering methods are included
Jutte, Christine V.↗
Improved Benchmarking of Cohesive Elements in Abaqus Standard for Predicting Disbond and Delamination in Composite Structures
Traditional approaches for aircraft certification require the assumption of an initial flaw condition, either represented as barely visible impact damage (BVID) or through inclusion of a Teflon insert to serve as surrogate damage. Based on the initial composite damage state, the structure must be shown to demonstrate structural durability and damage tolerance (DaDT) according to the following criteria: a. Damage displays no detrimental growth under cyclic loading. The structure is able to sustain design limit load (DLL). Currently, the only available manner for validating structural performance is through test. Since damage can occur over a wide variety of areas within a structure, this approach has proven to be increasingly expensive and time consuming for composite airframes and acreage structure within the design-test-certification building block. A further complicating factor is the requirement to accurately capture the most critical damage morphologies as a starting condition. To understand the severity of the damage, it is either required to experimentally determine the most critical areas at tremendous expense or rely on legacy data of similar structural testing, which limits design space expansion. A preferred solution is to use advanced analysis to provide improved understanding of load margins for critical locations based on a wide variety of potential starting damage conditions.
Eric M. Roberts↗
Preliminary analysis of the span-distributed-load concept for cargo aircraft design
A simplified computer analysis of the span-distributed-load airplane (in which payload is placed within the wing structure) has shown that the span-distributed-load concept has high potential for application to future air cargo transport design. Significant increases in payload fraction over current wide-bodied freighters are shown for gross weights in excess of 0.5 Gg (1,000,000 lb). A cruise-matching calculation shows that the trend toward higher aspect ratio improves overall efficiency; that is, less thrust and fuel are required. The optimal aspect ratio probably is not determined by structural limitations. Terminal-area constraints and increasing design-payload density, however, tend to limit aspect ratio.
Whitehead, A. H., Jr.↗
Cold-air investigation of a 31/2-stage fan-drive turbine with a stage loading factor of 4 designed for an integral lift engine. 2: Performance of 2-, 3- and 3 1/2-stage configurations
The stage work distribution among the three stages was very close to the design value. The specific work output-mass flow characteristics of the three stages were closely matched. The efficiency of the 3 1/2 stage turbine at design specific work output and design speed was within 0.008 of the estimated value, and this agreement was felt to demonstrate the adequacy of the prediction method in the high stage loading factor regime.
Whitney, W. J.↗