166 A I R C R A F T E N G I N E E R I N G June, 1941 because of the fact that, in order to augment the JAPAN Report No. 201. November, 1940. Studies performance, thin metallic airscrews have been THE AERONAUTICAL RESEARCH on the Subsonic Flow of a Compressible Fluid substitute d for thick wooden ones, flutter is more INSTITUTE : TOKYO IMPERIAL past an Elliptic Cylinder. By Susumu Tomo- often experienced than formerly, resulting in fre UNIVERSITY tika and Ko Tamada. (In English.) (1.05 yen.) quen t airscrew failures. Consequently, the atten [Kôgyô Tosho Kabushiki Kaisha, Tokyo) I n this paper, the two-dimensional irrotational tion of investigators has recently been drawn to th e subsonic flow of a compressible fluid past an elliptic origin of th e phenomenon and to devising means for Report No. 200, October, 1940. Investiga cylinder placed at an arbitrary inclination to th e its prevention. Although a number of investiga tion on the Mechanism of the Cementation of direction of the undisturbed stream has been re tions, both theoretical and experimental, have Metals. (Molybdenum on Nickel.) By the investigated, with the special intention of studying alread y been published relating to vibrations of th e late Masaji Goto, Hirosi Asada and Tuneyosi th e manner in which the value of the so-called airscrew blade, those for airscrew flutter are very critical Mach number for th e elliptic cylinder varies meagre, one evidence of which is the fact that Okamoto. (In English.) (0.90 yen.) with th e angl e of incidence as well as wit h th e thick various writers do no t ye t seem to be agreed on th e Cementation is a method of coating th e surface of ness rati o of th e ellipse. The critical Mach numbe r is, definition of th e word "airscrew flutter". one metallic material with another metal, by which as is well known, the value of th e Mach number at I n the present experiment, the airscrew was the material to be coated is surrounded with the which the local speed of sound is first attained in th e coating material in powdered form, and th e vapour rotate d on the test-stand by means of a noiseless field of flow and, according to th e results of recent of the coating metal is diffused into the other electric motor, and the natur e of the characteristic experimental investigations, i t ha s a close connexion material. Within this definition come th e carburiz- sound tha t accompanies th e flutter investigated by wit h an important phenomenon called the com ing process, the nitriding process, etc., bu t it is a utilizing th e bes t possible modern methods of sound pressibility burble. investigation. question whether cementation can be effected per fectly when the vapour pressure of the material to Th e method of Poggi is employed, as in Kaplan's Th e vibration of the non-rotating airscrew was b e coated is far greater than that of the coating papers. Although Kaplan has confined his atten carefully determined by separate experiment, in tion chiefly to th e stat e of affairs on th e surface of metal, as in the case of applying molybdenum to which electrical means were also utilized ; thus, by th e elliptic cylinder, the analysis is here to some nickel. comparing the frequencies of the various modes of exten t generalized, by obtaining first the velocity This study of the mechanism of cementation vibratio n of the non-rotating airscrew with the potentia l at any point in th e field of flow and then frequencies of th e various partial tones tha t consti under the foregoing conditions was mad e to furnish proceeding to the discussion of th e state of affairs tut e flutter sound, an attemp t was mad e to clarify guidance for the coating of metals. Few data on the surface of the body. th e manner of vibration of th e blade when flutter have been published on test s of molybdenu m cemen Very laborious numerical calculations have been occurred, and thus find means for preventing air tation, the only available reports being those by carried out in detail and thus the values of the screw flutter. M. J . Laissus and Dr. Kase. critical Mach number M have been found as In the present experiment round bars of nickel In order to avoid the effect of other noises, these erit functions of both the angle of incidence and the studies in flutter were usually conducted in the surrounded by molybdenum powder were cemented thickness rati o of th e ellipse. The result s ar e shown evening, the airscrew being illuminated by electric unde r various conditions of heating temperature, graphically in Figs. 2, 3 and 4, where the ordinate light. In thi s case ; a distinct bright line was formed, heating period, heat treatment after cementation, gives th e vaules of M and th e abscissa gives the along a diameter of th e so-called airscrew disc, by diffusion agent, etc., bu t adequat e cementation could eri t thickness ratio t of th e ellipse. One of th e interest light reflected from the rotating airscrew blade so no t be effected. The test results were studied by ing results obtained is tha t when the angle of inci tha t th e intens e vibration of th e airscrew blade when means of microscopic examination and X-ray analysis in order to obtain some idea of th e mechan dence takes any value different from 0 deg. and flutter occurred was easily recognized by violent ism of cementation , and on th e basis of th e ide a thus 90 deg., the curve of the critical Mach number flickering of th e bright line. It was therefore soon obtained, a two-stage heating process was developed. plotte d against th e thickness ratio t ha s a maximum noticed that by obtaining a photograph of the a t a certain definite value of t. This point seems to The two-stage heating process must be employed flickering bright line, by such means as that of a b e worthy of special notice. to cement a molybdenu m coating on nickel by means high-speed cinema, it may be possible to estimate of the diffusion phenomenon and with the use of Also, th e momen t of th e fluid pressures acting on th e vibrating condition of the blade. However, in the present experiment no such optical method molybdenum powder. The amoun t of molybdenum th e surface of the elliptic cylinder with respect to was resorted to, th e stud y being purely acoustic. tha t is cemented on the nickel surface increases in th e centre of the ellipse are calculated, and, by proportion to th e rise of temperature, but above a performing various numerical calculations, the B y comparing the results of analysis of th e flutter certain critical temperature the vapour pressure of effect of compressibility upon the moment of the sound with th e period of natura l vibration of a non - nickel increases so greatly that a reverse pheno elliptic cylinder is discussed. It is found tha t when rotatin g airscrew, and also b y taking into account menon occurs, nickel being diffused on th e molyb th e value of th e angle of incidence is fixed, the value several examples of breaking blades, the modes of denum. When cementation is carried out below of the ratio M /M for a definite elliptic cylinder vibratio n that are excited when flutter occurs are c i th e critical temperature, the cemented layer be increases as the Mach number increases and also estimated to b e th e following three. comes saturated in about !) hours, before perfect tha t the value of M /M for a definite Mach number I t was moreove r confirmed tha t bending vibration c i cementation can be effected. increases slightly as th e angl e of incidence increases, scarcely appears, at any rat e when the airscrew is where M denotes the moment which an elliptic rotate d by means of an electric motor. The two-stage heating process is a method by cylinder experiences when placed in th e compressible Modes of vibration constituting the flutter which cementation is carried on for several hours a t fluid flow an d M the momen t which th e sam e elliptic a temperature below the critical temperature (for (1) Third mode of bendin g vibration, approximate cylinder experiences when placed, at th e same angle example a t 1,100 deg. C.),and then carried on again frequency = 115, of incidence, in th e incompressible fluid flow. above th e critical temperature. X-ray examination (2) First mode of torsional vibration, approximate of specimens thus treated reveals pur e molybdenum Further , the validit y of Glauert-Prandtl' s approx frcquency=315 , on the surface and molybdenum penetration to a imat e formula for th e rati o M /M is briefly discussed. (3) Second mode of torsional vibration, approxi c i depth of 0·22 mm. Thus perfect cementation can mat e frequency=590. Report No. 202. November, 1940. Acous be effected. In view of this, it is considered that tical Studies of the Flutter of an Airscrew. metals with a low vapour pressure can b e satisfac PROFESSIONA L PUBLICATIONS (Experiments with an Actual Airscrew.) (In torily cemented upon metals with higher vapour Under this heading are given each month the principal articles of vestigations of Airscrew Flutter. Part II.) pressures by means of th e two-stag e heating process. aeronautical interest appearing in the current issues of the Journals of the leading Professional institutions. Th e calculated value of resistance to hydrochloric By Jûichi Obata, Major Yuzo Matumura, Ryo Th e Journa l of th e Roya l Aeronautical Society acid of the molybdenum coatings which applied in Kanayama and Yahei Yosida. (In English.) this manner is comparatively great, because their Vol. XLV, No. 365, May 1941 (0.70 yen.) surface is very rough owing to th e adhering molyb "Th e Plow of a Perfect Fluid Through Cascades of Aerofoils." I n a previou s paper, Report No. 187 (see AIRCRAF T A. R. Collar. denum powder, and consequently the actual surface Library Catalogue. ENGINEERING , Vol. XII, July, 1940, p. 210), i.e. in area is almost infinitely great. Abstracts from the Scientific and Technical Press. Par t I of the writers' investigations of airscrew The addition of chromium, copper and iron to th e S.A.E . Journal flutter, the nature of the sound that is produced metal which is to be cemented is believed to raise b y flutter was fully described. Airscrew flutter Vol. 48, No. 4, April 1941 th e critical temperatur e t o a poin t above 1,200 deg. C. itself, excluding of accompanying sound, is of None of these elements, however, promotes cemen "Altitude Performance of High-Output Aircraft Engines." course, a phenomenon of very unusual character, R. N. Du Bois. tation . while the sound that is caused by it is no less "A n Instrument for Measuring the Ignition Quality of Diesel According to the results of X-ray examination, Fuels." W. H. Browne. characteristic, and as it seemed to be a novel th e layer which formed on th e specimen with 2 pe r "Aircraft Electricity as the Airline Operator Sees It." P. C exampl e of combination tones, it was made the Sandretto. cent chromium, contained only about 8 per cent subject of Par t I. In th e present paper, th e nature Abstracts of Papers Read at National Aeronautic Meeting. molybdenum a t th e surface, and so a perfect molyb of airscrew flutter itself is dealt with. Journa l of th e Aeronautica l Sciences denum coating could not be obtained. The layer As already stated in Par t I, the flutter of an air thu s formed, however, appears to be a ternar y alloy Vol. 8 No. 6, April 1941 screw is a phenomenon tha t is believed to b e a form which is resistant to hydrochloric acid, th e corrosion "Air-cooled vs. Liquid-cooled Aircraft," J. G. Lee, of severe vibration of the airscrew blade, easily ''Possibilities of the Two-Stroke Cycle for Small Aircraft Engines." rat e being of the order shown in Fig. 30. recognized by a sudden and remarkable increase in A. R. Rogowaki. th e sound emitted by th e airscrew. "Th e Technique of Forecasting Low Ceilings and Fog." * Under this heading are published abstracts of the Reports on J . J . George. Although the phenomenon has been known with research work undertaken by aeronautical research institutions " Flight Level Indicator." R. W. Knight. wooden airscrews for more tha n ten years, owing to and bodies throughout the world so far as these are, in wartime, "Uni t Method of Beam Analysis." F. R. Shanley and F . P. th e increase in engine power in recent years, and still being issued and made available. Cozzone.
Aircraft Engineering and Aerospace Technology – Emerald Publishing
Published: Jun 1, 1941
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