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278 AIRCRAFT ENGINEERING September, 1940 0·040 in. with extruded bulb-angle sections of 12 Technical Note No. 750. A Generalized U.S.A. shapes, spaced at 4 and 5 in. as stiffeners, were Vortex Theory of the Screw Propeller and its NATIONAL ADVISORY tested to obtain the buckling stress and the Application. By Hans Reissner. COMMITTEE FOR AERONAUTICS amplitud e of the maximum wave when buckled. TECHNICAL NOTES Th e vortex theory, as presented by the author Bulb angles from 3 to 27½ in. in length were tested in earlier papers, has been extended to permit the as pin-end columns. The experimental data are (Secretary, N.A.C.A., Washington) solution of the following problems. presented as stress-strain and column curves and in (i) The investigation of the relation between tabula r form. Some comparisons with theoretical Technical Note No. 746. The Frequencies thrus t and torque distribution and energy loss as results are presented. of Cantilever Wings in Beam and Torsional given by the induction of helical vortex sheets and Analytical methods are developed that make it Vibrations. By C. P. Burgess. by the parasite drag. possible for the designer to predict with reasonable Methods are described for calculating the period (ii) The checking of the theorem of Betz of the accuracy the buckling stress and the maximum- and frequency of vibration of cantilever wings and rigidly behaving helical vortex sheet of minimum wav e amplitude of the sheet in stiffened-panel similar structures in which the weight and moment induced energy loss. combinations. The scope of the tests was of inertia vary along the span. Both the beam and (iii) The extension of the theory of the screw insufficient to formulate general design criteria, torsional frequencies may be calculated by these propeller of minimum energy loss for the inclusion bu t the results are presented as a guide for design methods. The procedure is illustrated by examples. of parasite-drag distribution along the blades. an d an indication of the type of theoretical and I t is shown that a surprisingly close approxima A simple system of diagrams has been developed experimental work needed. tion to the beam frequency may be obtained by a t o systematize the design of airscrews for a wide ver y brief calculation in which the curvature of the rang e of practical application. Several typical TECHNICAL REPORTS wing in vibration is assumed to be constant. A diagram s are presented to illustrate the method. (Superintendent of Documents, Washington) somewhat longer computation permits taking accoun t of the true curvature of the beam by a (10 cents each, except where otherwise stated) Technical Note No. 751. Damping series of successive approximations which are shown Formulas and Experimental Values of Damping Report No. 672. Free-Spinning Wind- to be strongly convergent. in Flutter Models. By Robert P. Coleman. Analogous methods are applied to calculations of Tunnel Tests of a Low-Wing Monoplane with th e torsional frequency. For the first approxi Th e problem of determining values of structural Systematic Changes in Wings and Tails. matio n it is assumed that the angle of twist varies dampin g for use in flutter calculations is discussed. IV.—Effect of Centre-of-Gravity Location. linearly along the semispan. The true variation of Th e concept of equivalent viscous damping is By Oscar Seidman and A. I. Neihouse. th e twist is computed by successive approximations reviewed and its relation to the structural clamping which are strongly convergent, as in the case of coefficient g introduced in N.A.C.A. Technical Eigh t wings and three tails, covering a wide range beam vibrations. Repor t No. 6vS5 is shown. The theory of normal of aerodynamic characteristics, were independently modes is reviewed and a number of methods are ballasted so a s to be interchangeable with no change described for separating the motions associated in mass distribution. For each of the 24 resulting Technical Note No. 747. Propeller Rotation wit h different modes. Equations are developed wing-tail combinations, observations were made of Noise due to Torque and Thrust. By Arthur for use in evaluating the damping parameters from th e steady spin for four control settings and of F . Deming. experimental data. recoveries for five control manipulations. The results Sound pressures of the first four harmonics of Experimenta l results of measurements of damping ar e presented in the form of charts comparing the rotatio n noise from a full-scale two-bladed airscrew in several flutter models are presented. spin characteristics. The tests are part of a general were measured and are compared with values investigation being made in the N.A.C.A. free- calculated from theory. The comparison is made spinning tunnel to determine the effects of syste Report No. 671. A Theoretical Study of the (i) for the space distribution with constant tip mati c changes in wing and tail arrangement upon Moment on a Body in a Compressible Fluid. speed and (ii) for fixed space angles with variable th e steady spin and the recovery characteristics of a By Carl Kaplan. li p speed. conventional low-wing monoplane for various load A relation for rotation noise from an element of distributions. Th e extension to a compressible fluid of Lagally's radius developed by Gutin is extended to cover the Th e present tests are a continuation of the theorem on the moment on a body in an incom entire airscrew disc. Curves are given showing the investigation, the entire series of tests performed pressible fluid and Poggi's method of treating the effect of the number of blades on the rotation noise. for the basic loading being repeated with the centre flow of compressible fluids are employed for the of gravity 10 per cent forward and 10 per cent determinatio n of the effect of compressibility on the Technical Note No. 748. Principles, behind the normal location at 25 per cent of the momen t on an arbitrary body. Only th e case of the mean chord. The results are compared with those Practice and Progress of Noise Reduction in two-dimensional subsonic flow of an ideal compres for the basic loading condition. sible fluid is considered. Airplanes. By Albert London. Fo r all tail and wing arrangements there was a As examples of the application of the general The investigators in the field of aeroplane noise definite effect of centre-of-gravity location, the theory, two well-known systems of profiles are hav e had to consider many and divers topics. forward location giving steeper spins and faster treate d ; namely, the elliptic profile and the To name a few: the principal sources of noise recoveries and the rearward location giving flatter symmetrica l Joukowski profiles with sharp trailing in the aeroplane, and how they may be reduced spins and slower recoveries than the basic centre-of- edges. or eliminated; how to measure the noise; gravit y location. The spin coefficient Ωb/21 Th e effect of compressibility on the position of the relationship between the purely physical increased as the centre of gravity was moved forward th e centre of pressure is also discussed. In order to attribute s of noise and the physiological reaction an d decreased as the centre of gravity was moved determin e this effect, it is necessary t o calculate the of the ear to this stimulus ; how the filtration of back. In general, there was a tendency for the rate additional circulation induced by the compressi noise into the aeroplane cabin may be reduced by of descent to increase and for the sideslip t o become bilit y of the fluid for both the elliptic and the proper attention to constructional details and more outward as the centre of gravity was moved Joukowski profiles. For these two types of profile how this may be accomplished with a minimum forward. The wing of N.A.C.A. 6718 section, th e centres of pressure in the compressible and the of weight; the systematic procedure to be used however, generally gave more inward sideslip for incompressible fluids are found to coincide for a in carrying out this quieting process ; etc. th e forward centre-of-gravity location than for the definite and fairly small angle of incidence, which Th e purpose of this note is to review the body rearward location. The importance of centre-of- is essentially dependent on th e thickness coefficients. of knowledge which has been accumulated in this gravit y location, wing arrangement, and control Fo r angles of incidence less than this neutral angle, field. Special attention is paid to effective sound manipulation s increased as the effectiveness of the th e centre of pressure in the compressible fluid is proofing schemes and all the data available in tail unit decreased. farther from the nose and, for angles of incidence th e published literature on this subject is given. greate r than the neutral angle, nearer to the nose tha n the centre of pressure in the incompressible PROFESSIONAL PUBLICATIONS Technical Note No. 749. A New Method fluid. of Studying the Flow of the Water along Several numerical examples of both the elliptic Journa l of the Aeronautical Sciences an d the Joukowski profiles are given. The results the Bottom of a Model of a Flying-boat Vol 7, No. 9, July, 1940. show that , although the effect of compressibility on Hull. By Kenneth E. Ward. "Performance Dictates Design." R. H. Upson. th e moment and on the lift may be large, the effect "Coupled Oscillations of Aircraft Engine-Propeller Systems. A new method of studying the flow of the water M. A. Biot. on the centre of pressure for conventional profiles "Th e C.A.A. Instrument Landing System Installed at along the bottom of a model of a flying-boat hull is negligible. Thus, for a Joukowski profile, the Indianapolis." H. I. Metz. is described. In this method, the model is fitted maximu m thickness of which is equal t o 13 pe r cent "A n Instrument for Measuring Low Frequency Accelerations in with a transparent bottom and is divided down Flight." C S. Draper and W. Wrigley. of the chord, the centre of pressure moves toward "Streamline Visualization." C. Witoszynski. th e centre-line by a bulkhead. The flow is observed th e nose a distance equal to only 0·19 per cent "Th e Tensor Gage." W. B. Klempferer. and photographed through one-half of the model by of the chord, where the angle of incidence is 6 deg. means of the diffused illumination from a battery an d v /c = 0·70. Th e Journal of the Royal Aeronautical Society 0 0 of lamps contained in the other half of the model. Vol XLIV, No. 356, August, 1940. Photograph s of th e flow, particularly of th e changes "Some Aspects of the Aerial Warfare in the German-Polish Technical Note No. 752. An Investiga tha t occur when the step ventilates, are shown. Campaign." J. J . Dziewonski and S. Rogalski. tion of Sheet-Stiffener Panels Subjected to Th e results of the present investigation indicate " A Rational Definition of Yield Strength." W. R. Osgood. "Fir e Protection of Petrol Tanks." A. R. Weyl. tha t the method has considerable promise, chiefly Compression Loads with Particular Reference in connexion with motion-picture studies. to Torsionally Weak Stiffeners. By Louis G. S.A.E . Journal Dunn. "Production of Magnesium-Alloy Aircraft Parts." L. B. Grant. * Under this heading are published regularly abstracts of the " A New Method of Testing and Grading Fine Abrasives." A total of 183 pane l specimens of 24ST aluminium Reports and Notes issued by the aeronautical research institutions E. L. Hemingway. and bodies throughout the world. alloy with nominal thicknesses of 0·020, 0·025 and "Passenger Comfort in Commercial Aviation." W. W. Davies.
Aircraft Engineering and Aerospace Technology – Emerald Publishing
Published: Sep 1, 1940
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