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(d) Extrapolation of the data may be made with reasonable assurance to gust velocities of about 36 ft./sec. E.A.S., when it would be necessary to fly, on average, about 106 miles to meet such a gust intensity. Under this beading are published regularly abstracts of all Reports and Memoranda of the Aeronautical (e) Severe gusts are met more often in thunder Research Council, Reports and Technical Memoranda of the United States National Advisory Com storms (as given by the U.S. Thunderstorm Project), but heavy turbulence, by their stand mittee for Aeronautics and publications of other similar Research Bodies as issued ards, is sometimes encountered in clear air. Meteorological Aspects (a) Analysis of the possible causes pointed to the FRANCE pilot's over-corrections on the rudder. Nevertheless, presence of marked wind gradient in the vertical it was possible in some of the runs to evolve the re as the most likely cause. An indirect method of OFFICE NATIONALE D'ÉTUDES ET DE RE- sultant yawing moment from double differentiation checking this theory has yielded promising CHERCHES AÉRONAUTIQUES of the heading angles and where this could be done results, confirming that wind gradient in the 25 Avenue de la Division Leclerc, Chatillon-sous- successfully, good agreement was obtained between vertical, or more precisely, the Richardson Bagneaux (Seine) number, is of prime importance. this resultant moment and the summation of the NOTES TECHNIQUES estimated components. By integrating the summation (b) Evidence exists which suggests that the worst No. 19. Représentation des Vibration Libres d'une of the estimated yawing moments along a take-off turbulence is associated with jet streams, and run, which should be approximately zero, a further that turbulence often occurs near the tropo- Aile dans le Vent a L'Aide de la Notion de Mémoire check on the comparison of the flight and wind-tunnel pause. (Representation of the Free Vibrations of a Wing in yawing moments can be made. (c) No other simple factor, such as terrain, geo a Moving Air Stream by Use of the Memory concept.) graphical location, absolute wind speed, was R. Mazet. The results show very good agreement with the found to yield any consistent clue to the cause wind-tunnel tests. As runs have been made done under By using the 'linear mathematical matrix' and the of turbulence. various cross-wind conditions on the aerodrome 'global' method, the author derives approximate ex (i.e., different angles of sideslip) the order of each of Recommendations to Operators—Certain recom pressions for the instantaneous aerodynamic forces the aerodynamic components was verified. mendations can be made at this stage to operators which are convenient for use in calculations of the and particularly aircrews, although much more vibrations or lifting surfaces. Only one of the ex A method of evaluating the rudder angles required information is needed to establish a sound forecasting ponentially decreasing terms of the Muntz series are to trim is suggested, by solving the side-force and basis. These are: preserved, for representation of the generating func yawing-moment equations simultaneously, using the (a) Avoid flying in areas where jet streams or high tion of the Wagner effect. wind-tunnel measurements for the aerodynamic components and introducing the side force from the horizontal thermal gradients are known to exist. By extending the formulae to three-dimensional undercarriage, in terms of the crab angle of the wheels. (b) Avoid flying within 2,000ft. of the tropopause. cases, using the 'sections' treatment, a simple pro In the yawing-moment equation, the second-order (c) If heavy turbulence is encountered assume one cedure of 'scanning by velocity' is arrived at, in which is entering a jet stream and differential inertia term is neglected as the changes the presence of additional atmospheric parameters is (i) climb or descend until turbulence is reduced of angle in the theoretical calculations (representing compensated for by complete systematization of the and/or a straight take-off run) are very small. The effect of computations, whatever the speed. (ii) fly at right-angles to the local wind direction. the tail wheel has been disregarded as it is only in (d) Should it appear that wing oscillations are being operation during the initial stages of the run. PUBLICATIONS excited by the turbulence, alter speed as much Owing to considerable over-correction by the pilot, No. 67. Mesures Statistiques de la Corrélation as possible. it is desirable to design for a rudder range at least dans le Temps. Premières Applications a l'Etude des The Unit has now been disbanded, but certain 20 per cent in excess of that required to trim. Mouvements Turbulents en Soufflerie. (Statistical reporting procedures have been initiated whereby it measurements of time correlation Factors. First Ap is hoped that information from airline operators on plications to the Study of Turbulent Movements in R. & M. No. 2700. The Pressure Distribution, at turbulence encountered will become available for Wind-Tunnels.) A. Favre. Supersonic Speeds and Zero Lift, on some Swept-back analysis. Such information will help to provide data Two methods of measuring time correlations be Wings having Symmetrical Sections with Rounded concerning other areas of the globe, as the results tween two aleatory variables are described, yielding Leading Edges. By G. M. Roper. February 1949. given in the report were obtained over Western Europe satisfactorily accurate values of the time coefficient (5s. 6d.) and do not necessarily apply elsewhere. of correlation and the spectral curves.Measurements Formulae are found for the pressure distribution have been made of these functions for the turbulent at supersonic speeds and at zero incidence for certain motion downstream from a grid in a wind-tunnel, and symmetrical surfaces of small finite thickness, with of the effect of increase in velocity of the air-stream swept-back leading edges. the surfaces being set SWEDEN and subdivision of the grid, on them. symmetrically to the wind direction. The solutions FLYGTEKN1SKA FÖRSÖKSANSTALTEN (F.F.A.) are only valid if the surfaces lie wholly within the THE AERONAUTICAL RESEARCH INSTITUTE GREAT BRITAIN Mach cone of the apex. OF SWEDEN AERONAUTICAL RESEARCH COUNCIL Ulvsunda 1, Stockholm H.M. Stationery Office, London R. & M. No. 2737. An Investigation of High- Report No. 49. Theoretical and Experimental R. & M . No. 2655. Supersonic Theory for Oscil Altitude Clear-Air Turbulence over Europe using Investigations of Interference Effects of Delta Wing- lating Wings of Any Plan Form. By W. P. Jones. Mosquito Aircraft. By G. S. Hislopand D. M. Davies. Vertical Tail Combinations with Yaw. By Willi Jacobs. June 1948. (is. 6d.) June 1950. (10s. 6d.) Interference effects between vertical tail and delta A theory for thin wings of any plan form describing The British European Airways Clear-Air Gust wing with yaw are investigated theoretically and simple harmonic oscillations of small amplitude in Research Unit was formed, with the financial support experimentally. The experiments include force and a supersonic air stream is developed. It is based on of the Ministry of Supply, to investigate the problem pressure measurements with a delta wing with a 70 the use of the generalized Green's Theorem in con of clear-air turbulence at high altitude over Europe. deg. swept-back leading edge and three different junction with particular solutions which vanish over The aircraft were based at Cranfield, Bedfordshire, vertical tails, two single vertical tails with different the characteristic cone with vertex at any point in the and flights were made of roughly 1,000 miles radius sweep angles and a double vertical tail. The results field of flow. from that base. In the two years of its existence, the give considerable effects, which are especially pro- The theory can be used to calculate the aerodynamic two PR 34 Mosquito aircraft employed for the purpose nounccd for the rolling moment. The comparison forces acting on fluttering wings when the modes of covered 92,300 miles of research flying between the between theory and measurements shows that at small distortion are known. selected limits of 15,000 ft. and 37,000 ft. Statistically angles of attack, at which no flow separation occurs speaking this is a very small sample and must be at the wing, good agreement is obtained. R. & M. No. 2660. Flight Tests on Swinging during borne in mind when considering the results. Take-off on a Single-engined Fighter-bomber (Typhoon Some twenty areas of turbulence (defined as giving Report No. 50. Analysis of Thin Square Plates 1b). By W. Stewart. April 1948. ( 8s.) vertical acceleration increments greater than ±0·2g) under Normal Pressure and Provided with Edge Frames Flight tests have been carried out on a Typhoon were actually investigated, the greatest vertical gust of Finite Stiffness in the Plane of the Plates. By Sigge aircraft to compare the values of the aerodynamic velocity encountered being +26 ft./sec. E.A.S. Eggwertz and Artur Norr. side forces and yawing moments, during take-off, The results were examined from the passenger with the wind-tunnel measurements, and to compare The deformations and stresses of a thin, square comfort and structural aspect, and from the meteoro plate subjected to an evenly distributed normal pres various methods of estimating the rudder angles logical aspect. The main findings are: sure are studied. The edges of the plate are provided required to trim during a take-off run. Structural/Passenger Comfort with stiffeners which are supported along their whole The side forces can be checked fairly simply by (a) Clear-air turbulence occurs in isolated patches lengths to prevent deflexions perpendicular to the estimating the various component side forces acting of widely varying thickness and horizontal plane of the plate, while the edges are free to deflect at each instant during the run and comparing the extent and at widely varying altitudes; a repre in this plane. Using the energy method and neglecting summation with the resultant side force measured by sentative example is 50 to 100 miles long by bending of the plate, simple formulae are derived for an accelerometer. The aerodynamic side forces were about 3,000 ft. thick. It is characterized by the the deflexions and the membrane stresses, including evaluated from the wind-tunnel tests under the cor lack of warning of its presence and by its short the influence of the stiffness of the edge frame. A responding conditions and the side force from the sharp hammering nature resulting from the rough estimate is also made of the bending moments undercarriage was estimated from the load on the quick succession of positive and negative gusts. of the plate as well as of their share of the transmission wheels and the angle of crab of the wheels to their (b) The probability of meeting a gust of a given of the total load to the supports. Test values from instantaneous direction of motion. magnitude is roughly the same at any height within the range covered. plates of different thicknesses and with different It is more difficult to compare the yawing moments edge frames are presented in diagrams and compared (c) The probability of meeting a gust of moderate operating as there is no direct method, at present, of with the theoretical results. The coefficients of the intensity in clear air at high altitude is roughly measuring an angular acceleration. Angular accelera membrane theory equations are finally modified to the same as in clear air or cloud at low or tions are difficult to obtain by differentiation of the give curves in close agreement with the test results for moderate altitudes. Severe gusts almost certainly observed angular displacements of the aircraft, due comparatively large deflexions. occur much less frequently in clear air. to the rapid variations in angle produced by the 204 Aircraft Engineering
Aircraft Engineering and Aerospace Technology – Emerald Publishing
Published: Jun 1, 1954
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