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The abolition of military qualifications gives free scope to new technical possibilities in the development of transport airplanes. This report notes the various considerations that must be made when designing aircraft to meet the needs of commercial passengers. Comfort and safety must be emphasized.
Since aircraft design is tending toward all-metal construction, the strong heat-treatable light aluminum alloy, duralumin (a generic name for a class of heat-treatable alloys containing Cu, Mg, Mn, and Si), is finding increasing application. Doubt has been expressed concerning the reliability and permanence of these materials. Information is given on the effect of corrosion on the tensile properties of 14-gauge sheet duralumin, heat treated by quenching in hot water after being heated for 15 minutes in a fused nitrate bath at 500 to 510 C. Intercrystalline corrosion and practical aspects of intercrystalline embrittlement are discussed with respect to duralumin.
Strength values of various woods for aircraft design for a 15 per cent moisture condition of material and a 3-second duration of stress are presented, and also a discussion of the various factors affecting the values. The toughness-test method of selecting wood is discussed, and a table of acceptance values for several species is given.
The topics are presented in viewgraph form and include the following: basic system structure and user interface; quasi-procedural method; knowledge-based system; and application to aircraft design.
This is one of a series of reports on the lessons learned from past research related to lift-fan aircraft concepts. An extensive review is presented of the many lift-fan aircraft design studies conducted by both government and industry over the past 45 years. Mission applications and design integration including discussions on manifolding hot gas generators, hot gas dusting, and energy transfer control are addressed. Past lift-fan evaluations of the Avrocar are discussed. Lessons learned from these past efforts are identified.
The need for regional aircraft stems from the problem of hub airport congestion. Regional travel will allow a passenger to commute from one spoke city to another spoke city without entering the congested hub airport. In addition, those people traveling longer routes may begin the flight at home instead of traveling to the hub airport. At this time, there is no American aerospace company that produces a regional transport for under 100 passengers. The intention of the Developmental Advanced Regional Transport (DART-75) is to fill this void with a modern, efficient regional aircraft. This design achieves the efficiency through a number of advanced features including three lifting surfaces, partial composite construction, and an advanced engine design. Efficiency is not the only consideration. Structural integrity, fatigue life, ease of maintenance, passenger comfort and convenience, and environmental aspects must all be considered. These factors force the design team to face many tradeoffs that are studied to find the best solution. The final consideration that cannot be overlooked is that of cost. The DART-75 is a 75-passenger medium-range regional transport intended for spoke-to-spoke, spoke-to-hub, and some hub-to-hub operations. Included are the general descriptions of the structures, weight and balance, stability and control, performance, and engine design.
The U.S. aerospace industry has a long history of federal support for research related to its needs. Since the establishment of the National Advisory Committee for Aeronautics (NACA) in 1915, the federal government has provided continuous research support related to flight and aircraft design. This research has contributed to the international preeminence of the U.S. aerospace industry. In this paper, we present a sociological analysis of aerospace engineers and scientists and how their attitudes and behaviors impact the flow of scientific and technical information (STI). We use a constructivist framework to explain the spotty dissemination of federally funded aerospace research. Our research is aimed towards providing federal policymakers with a clearer understanding of how and when federally funded aerospace research is used. This understanding will help policymakers design improved information transfer systems that will aid the competitiveness of the U.S. aerospace industry.
High surface temperatures and temperature gradients can affect the vibratory characteristics and stability of aircraft structures. Aircraft designers are relying more on finite-element model analysis methods to ensure sufficient vehicle structural dynamic stability throughout the desired flight envelope. Analysis codes that predict these thermal effects must be correlated and verified with experimental data. Experimental modal data for aluminum, titanium, and fiberglass plates heated at uniform, nonuniform, and transient heating conditions are presented. The data show the effect of heat on each plate's modal characteristics, a comparison of predicted and measured plate vibration frequencies, the measured modal damping, and the effect of modeling material property changes and thermal stresses on the accuracy of the analytical results at nonuniform and transient heating conditions.
General aviation is officially defined as all aviation except scheduled airlines and the military. It is the only air transportation to many communities throughout the world. In order to reverse the recent decline in general aviation aircraft produced in the United States, the Task Force recommends that NASA provide the expertise and facilities such as wind tunnels and computer codes for aircraft design. General aviation manufacturers are receptive to NASA's innovations and technological leadership and are expected to be effective users of NASA-generated technologies.
The accuracy and robustness of a two-dimensional smoothing methodology is examined for the problem of recovering accurate interlaminar shear stress distributions in laminated composite and sandwich plates. The smoothing methodology is based on a variational formulation which combines discrete least-squares and penalty-constraint functionals in a single variational form. The smoothing analysis utilizes optimal strains computed at discrete locations in a finite element analysis. These discrete strain data are smoothed with a smoothing element discretization, producing superior accuracy strains and their first gradients. The approach enables the resulting smooth strain field to be practically C1-continuous throughout the domain of smoothing, exhibiting superconvergent properties of the smoothed quantity. The continuous strain gradients are also obtained directly from the solution. The recovered strain gradients are subsequently employed in the integration o equilibrium equations to obtain accurate interlaminar shear stresses. The problem is a simply-supported rectangular plate under a doubly sinusoidal load. The problem has an exact analytic solution which serves as a measure of goodness of the recovered interlaminar shear stresses. The method has the versatility of being applicable to the analysis of rather general and complex structures built of distinct components and materials, such as found in aircraft design. For these types of structures, the smoothing is achieved with 'patches', each patch covering the domain in which the smoothed quantity is physically continuous.
The impact of advanced high lift systems on aircraft size, performance, direct operating cost and noise were evaluated for short-to-medium and medium-to-long range aircraft with high bypass ratio and very high bypass ratio engines. The benefit of advanced high lift systems in reducing noise was found to be less than 1 effective-perceived-noise decibel level (EPNdB) when the aircraft were sized to minimize takeoff gross weight. These aircraft did, however, have smaller wings and lower engine thrusts for the same mission than aircraft with conventional high lift systems. When the advanced high lift system was implemented without reducing wing size and simultaneously using lower flap angles that provide higher L/D at approach a cumulative noise reduction of as much as 4 EPNdB was obtained. Comparison of aircraft configurations that have similar approach speeds showed cumulative noise reduction of 2.6 EPNdB that is purely the result of incorporating advanced high lift system in the aircraft design.
Systematic approach to validation helps ensure good designs. Four-phase procedure devised to standardize and systematize assessment of performances of computational fluid dynamics (CFD) software used in designing aircraft, turbines, and other machines interacting with flows. Associated with procedure set of criteria by which one classifies given computer code and measures its ability to predict flows and flow-related quantities accurately.
This paper deals with nonplanar wing concepts -- their advantages and possible applications in a variety of aircraft designs. A brief review and assessment of several concepts from winglets to ring wings is followed by a more detailed look at two recent ideas: exploiting nonplanar wakes to reduce induced drag, and applying a 'C-wing' design to large commercial transports. Results suggest that potential efficiency gains may be significant, while several nonaerodynamic characteristics are particularly interesting.
Time exposure photography, sometimes coupled with strobe illumination, is an accepted method for motion analysis that bypasses frame by frame analysis and resynthesis of data. Garden variety video cameras can now exploit this technique using a unique frame buffer that is a non-integrating memory that compares incoming data with that already stored. The device continuously outputs an analog video signal of the stored contents which can then be redigitized and analyzed using conventional equipment. Historically, photographic time exposures have been used to record the displacement envelope of harmonically oscillating structures to show mode shape. Mode shape analysis is crucial, for example, in aeroelastic testing of wind tunnel models. Aerodynamic, inertial, and elastic forces can couple together leading to catastrophic failure of a poorly designed aircraft. This paper will explore the usefulness of the peak store device as a videometric tool and in particular discuss methods for analyzing a targeted vibrating plate using the 'peak store' in conjunction with calibration methods familiar to the close-range videometry community. Results for the first three normal modes will be presented.
As both computers and flow-analyzing equations have increased in sophistication, Computational Fluid Dynamics (CFD) has evolved into a fixture for advanced aircraft design. While CFD codes have improved in accuracy and efficiency, their ability to encompass viscous effects is lacking in certain areas. For example, current CFD codes cannot accurately predict or correct for the increased drag due to these viscous effects at some flow conditions. However, by analyzing an airfoil's turbulent boundary layer, one can predict not only flow separation via the shape factor parameter, but also viscous drag via the momentum thickness. Various codes have been written which can calculate turbulent boundary layer parameters. The goal of my research is to develop procedures for modifying an airfoil (via its local pressure distribution) to eliminate boundary layer separation and/or to reduce viscous drag. The modifications to the local pressure distribution necessary to achieve these objectives will be determined using a direct-iterative method installed into a turbulent boundary layer analyzer. Furthermore, the modifications should preserve the basic characteristics of the original airfoil.
As part of the NASA History Series, this report (NASA SP-4309) describes fifty years of aeronautical research at the NASA Dryden Flight Research Center. Starting with early efforts to exceed the speed of sound with the X-1 aircraft, and continuing through to the X-31 research aircraft, the report covers the flight activities of all of the major research aircraft and lifting bodies studied by NASA. Chapter One, 'A Place for Discovery', describes the facility itself and the surrounding Mojave Desert. Chapter Two, 'The Right Stuff', is about the people involved in the flight research programs. Chapter Three, 'Higher, Faster' summarizes the early years of transonic flight testing and the development of several lifting bodies. Chapter Four, 'Improving Efficiency, Maneuverability & Systems', outlines the development of aeronautical developments such as the supercritical wing, the mission adaptive wing, and various techniques for improving maneuverability fo winged aircraft. Chapter 5, 'Supporting National Efforts', shows how the research activities carried out at Dryden fit into NASA's programs across the country in supporting the space program, in safety and in problem solving related to aircraft design and aviation safety in general. Chapter Six, ' Future Directions' looks to future research building on the fifty year history of aeronautical research at the Dryden Flight Research Center. A glossary of acronyms and an appendix covering concepts and innovations are included. The report also contains many photographs providing a graphical perspective to the historical record.
A Dynamic Cell Structure (DCS) Neural Network was developed which learns topology representing networks (TRNS) of F-15 aircraft aerodynamic stability and control derivatives. The network is integrated into a direct adaptive tracking controller. The combination produces a robust adaptive architecture capable of handling multiple accident and off- nominal flight scenarios. This paper describes the DCS network and modifications to the parameter estimation procedure. The work represents one step towards an integrated real-time reconfiguration control architecture for rapid prototyping of new aircraft designs. Performance was evaluated using three off-line benchmarks and on-line nonlinear Virtual Reality simulation. Flight control was evaluated under scenarios including differential stabilator lock, soft sensor failure, control and stability derivative variations, and air turbulence.
Air-breathing propulsion engines play an important role in the development of both civil and military aircraft Design optimization of such engines can lead to higher power, or more thrust for less fuel consumption. A multimission propulsion engine design can be modeled mathematically as a multivariable global optimization problem, with a sequence of subproblems, which are specific to the mission events defined through Mach number, altitude, and power setting combinations.