Latest content added for UNT Digital Library Collection: National Advisory Committee for Aeronautics (NACA)http://digital.library.unt.edu/explore/collections/NACA/browse/?fq=str_title_serial:NACA+Technical+Reports&sort=default&fq=untl_institution:UNTGD2011-11-17T22:13:23-06:00UNT LibrariesThis is a custom feed for browsing UNT Digital Library Collection: National Advisory Committee for Aeronautics (NACA)The physical effects of detonation in a closed cylindrical chamber2011-11-17T22:13:23-06:00http://digital.library.unt.edu/ark:/67531/metadc66150/<p><a href="http://digital.library.unt.edu/ark:/67531/metadc66150/"><img alt="The physical effects of detonation in a closed cylindrical chamber" title="The physical effects of detonation in a closed cylindrical chamber" src="http://digital.library.unt.edu/ark:/67531/metadc66150/thumbnail/"/></a></p><p>Detonation in the internal-combustion engine is studied as a physical process. It is shown that detonation is accompanied by pressure waves within the cylinder charge. Sound theory is applied to the calculation of resonant pressure-wave frequencies. Apparatus is described for direct measurement of pressure-wave frequencies. Frequencies determined from two engines of different cylinder sizes are shown to agree with the values calculated from sound theory. An outline of the theoretically possible modes of vibration in a right circular cylinder with flat ends is included. An appendix by John P. Elting gives a method of calculating pressure in the sound wave following detonation.</p>General airplane performance2011-11-17T22:13:23-06:00http://digital.library.unt.edu/ark:/67531/metadc66312/<p><a href="http://digital.library.unt.edu/ark:/67531/metadc66312/"><img alt="General airplane performance" title="General airplane performance" src="http://digital.library.unt.edu/ark:/67531/metadc66312/thumbnail/"/></a></p><p>Equations have been developed for the analysis of the performance of the ideal airplane, leading to an approximate physical interpretation of the performance problem. The basic sea-level airplane parameters have been generalized to altitude parameters and a new parameter has been introduced and physically interpreted. The performance analysis for actual airplanes has been obtained in terms of the equivalent ideal airplane in order that the charts developed for use in practical calculations will for the most part apply to any type of engine-propeller combination and system of control, the only additional material required consisting of the actual engine and propeller curves for propulsion unit. Finally, a more exact method for the calculation of the climb characteristics for the constant-speed controllable propeller is presented in the appendix.</p>Elastic instability of members having sections common in aircraft construction2011-11-17T22:13:23-06:00http://digital.library.unt.edu/ark:/67531/metadc66038/<p><a href="http://digital.library.unt.edu/ark:/67531/metadc66038/"><img alt="Elastic instability of members having sections common in aircraft construction" title="Elastic instability of members having sections common in aircraft construction" src="http://digital.library.unt.edu/ark:/67531/metadc66038/thumbnail/"/></a></p><p>Two fundamental problems of elastic stability are discussed in this report. In part one formulas are given for calculating the critical stress at which a thin, outstanding flange of a compression member will either wrinkle into several waves or form into a single half wave and twist the member about its longitudinal axis. A mathematical study of the problem, which together with experimental work has led to these formulas, is given in an appendix. Results of test substantiating the recommended formulas are also presented. In part two the lateral buckling of beams is discussed. The results of a number of mathematical studies of this phenomenon have been published prior to this writing, but very little experimentally determined information relating to the problem has been available heretofore. Experimental verification of the mathematical deductions is supplied.</p>Air propellers in yaw2011-11-17T22:13:23-06:00http://digital.library.unt.edu/ark:/67531/metadc66255/<p><a href="http://digital.library.unt.edu/ark:/67531/metadc66255/"><img alt="Air propellers in yaw" title="Air propellers in yaw" src="http://digital.library.unt.edu/ark:/67531/metadc66255/thumbnail/"/></a></p><p>Report presents the results of tests conducted at Stanford University of a 3-foot model propeller at four pitch settings and at 0 degree, 10 degrees, 20 degrees, and 30 degrees yaw. In addition to the usual propeller coefficients, cross-wind and vertical forces and yawing, pitching, and rolling moments were determined about axes having their origin at the intersection of the blade axis and the axis of rotation. The tests showed that the maximum efficiency was reduced only slightly for angles of yaw up to 10 degrees but that at 30 degrees yaw the loss in efficiency was about 10 percent. In all cases the cross-wind force was found to be greater than the cross-wind component of the axial thrust. With a yawed propeller an appreciable thrust was found for v/nd for zero thrust at zero yaw. Yawing a propeller was found to induce a pitching moment that increased in magnitude with yaw.</p>Application of practical hydrodynamics to airship design2011-11-17T22:13:23-06:00http://digital.library.unt.edu/ark:/67531/metadc66062/<p><a href="http://digital.library.unt.edu/ark:/67531/metadc66062/"><img alt="Application of practical hydrodynamics to airship design" title="Application of practical hydrodynamics to airship design" src="http://digital.library.unt.edu/ark:/67531/metadc66062/thumbnail/"/></a></p><p>The purpose of the first two parts of this report is to present in concise format all the formulas required for computation of the hydrodynamic forces, so that they can be easily computed for either straight or curvilinear flight. Improved approximations are also introduced having a high degree of accuracy throughout the entire range of practical proportions. The remaining two parts of the report are devoted respectively to stability and skin friction, as functions of the same hydrodynamic forces.</p>A proof of the theorem regarding the distribution of lift over the span for minimum induced drag2011-11-17T22:13:23-06:00http://digital.library.unt.edu/ark:/67531/metadc66001/<p><a href="http://digital.library.unt.edu/ark:/67531/metadc66001/"><img alt="A proof of the theorem regarding the distribution of lift over the span for minimum induced drag" title="A proof of the theorem regarding the distribution of lift over the span for minimum induced drag" src="http://digital.library.unt.edu/ark:/67531/metadc66001/thumbnail/"/></a></p><p>The proof of the theorem that the elliptical distribution of lift over the span is that which will give rise to the minimum induced drag has been given in a variety of ways, generally speaking too difficult to be readily followed by the graduate of the average good technical school of the present day. In the form of proof this report makes an effort to bring the matter more readily within the grasp of this class of readers.</p>Aircraft woods: their properties, selection, and characteristics2011-11-17T22:13:23-06:00http://digital.library.unt.edu/ark:/67531/metadc66007/<p><a href="http://digital.library.unt.edu/ark:/67531/metadc66007/"><img alt="Aircraft woods: their properties, selection, and characteristics" title="Aircraft woods: their properties, selection, and characteristics" src="http://digital.library.unt.edu/ark:/67531/metadc66007/thumbnail/"/></a></p><p>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.</p>A method of calculating the ultimate strength of continuous beams2011-11-17T22:13:23-06:00http://digital.library.unt.edu/ark:/67531/metadc66000/<p><a href="http://digital.library.unt.edu/ark:/67531/metadc66000/"><img alt="A method of calculating the ultimate strength of continuous beams" title="A method of calculating the ultimate strength of continuous beams" src="http://digital.library.unt.edu/ark:/67531/metadc66000/thumbnail/"/></a></p><p>The purpose of this study was to investigate the strength of continuous beams after the elastic limit has been passed. As a result, a method of calculation, which is applicable to maximum load conditions, has been developed. The method is simpler than the methods now in use and it applies properly to conditions where the present methods fail to apply.</p>Stability of thin-walled tubes under torsion2011-11-17T22:13:23-06:00http://digital.library.unt.edu/ark:/67531/metadc66136/<p><a href="http://digital.library.unt.edu/ark:/67531/metadc66136/"><img alt="Stability of thin-walled tubes under torsion" title="Stability of thin-walled tubes under torsion" src="http://digital.library.unt.edu/ark:/67531/metadc66136/thumbnail/"/></a></p><p>In this report a theoretical solution is developed for the torsion on a round thin-walled tube for which the walls become unstable. The results of this theory are given by a few simple formulas and curves which cover all cases. The differential equations of equilibrium are derived in a simpler form than previously found, it being shown that many items can be neglected.</p>An extended theory of thin airfoils and its application to the biplane problem2011-11-17T22:13:23-06:00http://digital.library.unt.edu/ark:/67531/metadc66017/<p><a href="http://digital.library.unt.edu/ark:/67531/metadc66017/"><img alt="An extended theory of thin airfoils and its application to the biplane problem" title="An extended theory of thin airfoils and its application to the biplane problem" src="http://digital.library.unt.edu/ark:/67531/metadc66017/thumbnail/"/></a></p><p>The report presents a new treatment, due essentially to von Karman, of the problem of the thin airfoil. The standard formulae for the angle of zero lift and zero moment are first developed and the analysis is then extended to give the effect of disturbing or interference velocities, corresponding to an arbitrary potential flow, which are superimposed on a normal rectilinear flow over the airfoil. An approximate method is presented for obtaining the velocities induced by a 2-dimensional airfoil at a point some distance away. In certain cases this method has considerable advantage over the simple "lifting line" procedure usually adopted. The interference effects for a 2-dimensional biplane are considered in the light of the previous analysis. The results of the earlier sections are then applied to the general problem of the interference effects for a 3-dimensional biplane, and formulae and charts are given which permit the characteristics of the individual wings of an arbitrary biplane without sweepback or dihedral to be calculated. In the final section the conclusions drawn from the application of the theory to a considerable number of special cases are discussed, and curves are given illustrating certain of these conclusions and serving as examples to indicate the nature of the agreement between the theory and experiment.</p>