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Research Reports and Memoranda

Research Reports and Memoranda 44 AIRCRAF T ENGINEERING February, 1941 Report No. 193. August, 1940. Dynami­ Report No. 195. August, 1940. Some JAPAN cal Stability of a Column under Periodic Experiments on the Forced Vibration of THE AERONAUTICAL RESEARCH Longitudinal Forces. By Ikuo Utida and Varying Period. By Katsutada Sezawa and INSTITUTE: TOKYO IMPERIAL Katsutada Sezawa. (In English.) (0.80 yen.) Wataru Watanabe. (In English.) (0.30 yen.) UNIVERSITY (Kôgyô Tosho Kabushiki Kaisha, Tokyo) The present problem deals with the vibrational The resonance condition of an elastic bar condition of a column under periodic longi­ under forces with frequency increasing or Report No. 191, July, 1940. Measurement tudinal forces. The problem was examined in decreasing linearly with time, was investigated of the Period of Natural Vibration of an two ways : experimentally and mathematically. experimentally. The vibration of the same bar Airscrew Blade. By Jûichi Obata and Yahei was excited electromagnetically, the intensity The results show that the problem is dynamic­ Yosida. (In English.) (0.30 yen.) of the force being constant for every vibration ally that of instability in free transverse oscilla­ tion as well as tha t of resonance in forced longi­ through the whole range of the varying fre­ In Report No. 103 of the Aeronautical Re­ tudinal vibration. quency and also for any case of experiments. search Institute, will be found the results of A magnetic damper was added to the bar for Although there is a number of frequences at experiments in the electrical method of measur­ ascertaining the effect of viscous damping on th e which the vibration becomes unstable or reson­ ing small vibrations with the aid of a triode resonance amplitude in the case of varying ance-like, the mode of vibratio n of th e column is valve, together with its application s to th e meas­ frequency. of fundamental mode almost in any case; that urement of vibrations of airscrew blades. is to say, th e fundamental mode of vibration is Let dN/dt be the absolute speed of change of Recently, in connexion with the stud y of air­ excited by the periodic forces of different fre­ frequency and k the logarithmic decrement of screw flutter, the urgent need of accurate quencies. The conditions in which the vibration free vibration in the case of dN/dt being zero. measurements of bending as well as of torsional When k was not ver y large, the resonance ampli­ in question occurs, are such tha t the ratio s of th e vibrations of an airscrew blade was felt, result­ tud e diminished enormously with increase in natura l frequency to tha t of th e exciting forces ing in th e application of this electrical method are 1/2, 2/2, 3/2, 4/2, 5/2, . . . The greater the dN/dt. On the other hand, when k was fairly with very satisfactory results. At that time, ratio under consideration, the smaller the reson­ large, no appreciable change in resonance certain improvements and developments were ance amplitude and, also, the range of instabi­ amplitude occurred for different dN/d, the made on th e former method, and i t is t o describe lity. The condition in which the ratio becomes contribution from k having taken the important these that the present paper has been written. 1/2, corresponds to tha t called Melde's effect. par t of the problem. From the nature of things, although the resistance arising from At every resonance or unstable condition, the Report No. 192. August, 1940. Viscosity viscous damping was operative in forced vibra­ change of amplitude in th e stage of raising fre­ Characteristics of Lubricating Oils as Related tion as well as in free vibration, that due to quency is not the same as tha t in the stage of change of cycle manifested itself only in th e case to their Chemical Structure. By Bunnosuke decreasing frequency. In the stage of decreas­ of forced vibration. Furthermore, although Yamaguchi. (0.50 yen.) ing frequency the vibration amplitude augments the resonance amplitude was nearly the same, The author has shown that no clear definite increasingly for a relatively wide range until the provided the absolut e value of dN/dt were given, relation exists between the chemical structure limit is reached when the amplitude suddenly there was some time lag in reaching the maxi­ and the viscosity index or the "Viscositatpol- reduces to that taken in the stage of raising mu m amplitude in raising or diminishing the höhe " of high-molecular-weight hydrocarbons, frequency. In order to get the condition frequency. This feature was pronounced parti­ and has explained the reason. It has been theo­ corresponding to the stage of decreasing fre­ cularly in the case of large k. Finally, it was retically and experimentally evidenced that the quency even in th e stage of increasing frequency, possible to construct empirical formulae in­ viscosity-temperature coefficient at the same some artificial shock should be applied to the dicating the resonance amplitudes for any case viscosity of liquids is a unique function of their column. When there is a relatively small mass of dN/dt. Although, in this case, the existence chemical structure. For a number of synthetic a t an end of the column, there are some further of the term dN/dt was somewha t similar to tha t high-molccular-weight hydrocarbons, the vis­ complex relations between the vibration ampli­ of the term k, the coefficient of the term dN/dt cosity-temperature coefficients at their re­ tud e and th e frequency. was likely to change with difference in cases. spective temperatures having the same vis­ The mathematical interpretation of th e present Although the periodic vibration of th e column cosity of 100 centistokes, the values of results will be published in a forthcoming paper. in the unstable or resonance condition is almost —hav e been calculated by means of sine form, the same form tends to change v=100 c.s. increasingly with increase in the order of reson­ of Walther's viscosity-temperature equation, ance. It is likely that the wave form of the and it has been substantiated that the coeffici­ vibration of th e column in th e frequency inter­ ents thus calculated are always definitely cor­ mediate between two neighbouring unstable related with their chemical structure, with the conditions, contains bot h types of wave s in these PROFESSIONA L PUBLICATIONS conclusion that the greater the "entangling unstable conditions. degree " of molecules of a hydrocarbon, which Under this heading are given each month the principal articles of depends upon its molecular structure and is Experimental as well as mathematica l results aeronautical interest appearing in the current issues of the Journals of the leading professional institutions. decidable under an assumption by the size or show tha t the resonance or instability condition length of cyclic nuclei and paraffinic side chains depends on the magnitude of the vibrating The Journa l of th e Royal Aeronautical Society together with the size and allocation of branched forces applied. If the forces were not great, it Vol. XLV, No. 361, January, 1941. chains in the molecule, the smaller its value of would be impossible for the resonance or un­ "Som e Theoretical Considerations on Box Beams." Jean stable condition to occur, from which it follows Drymael. — or its "structure viscosity tha t the phenomena resemble those of reson­ Library Catalogue. ance with respect to the vibrational frequency Abstracts from the Scientific and Technical Press. and those of buckling with respect to the index," —+ 5] × 100. A criter- magnitude of th e applied forces. v=100c.s. S.A.E. Journal ion for grading the viscosity characteristics of Vol. 48, No. 1, January, 1941. hydrocarbons may be given by both the values " Fluid Transmission of Power." N. L. Alison. of viscosity and " structure viscosity index," Report No. 194. August, 1940. On the " Ground Form Finishing Hobs." Charles R. Staub. as for compounds of comparative viscosities "A n Instrument for Continuous Measurement of Piston Tem­ Subsonic Flow of a Compressible Fluid past the smaller the structure viscosity index, peratures." Arthur F. Underwood and A. A. Catlin. an Elliptic Cylinder. By Isao Imai and the more excellent the viscosity characteristics. "Th e C.U.E. Cooperative Universal Engine for Aviation Single- Takasi Aihara. (In English.) (0.45 yen.) From this point of view, it has been pointed out Cylinder Research " A. W. Pope, Jnr . what molecular structure to be required for a In this paper a new method of dealing with The Journa l of th e Aeronautica l Sciences hydrocarbon to have the best viscosity charac­ compressible fluid flow is presented . The meth­ teristics. It has been also shown that the vis­ Vol. 8, No. 2, December, 1940. od is essentially equivalent to the original cosity characteristics of commercial mineral "Wing Loading, Icing and Associated Aspects of Modern Trans­ Janzen-Rayleigh method, but makes it possible port Design." Clarence L. Johnson. and fatty lubricating oils and the effect of such t o obtain the result without recourse to the "Experimental Determination of Hydrodynamic Stability." an addition agent as paraton e can be reasonably infinite series expansion, thus making the Ernest G. Stout. explicated by the idea of structure viscosity analysis much simpler. As an example of its "Measurements on Detonation in Duchêne Apparatus." G. index. Broersma. application, subsonic flow of a compressible "A n Experimental Verification of the Isotropy of Turbulence fluid past an elliptic cylinder at an arbitrary Produced by a Grid." D. C. Macphail. * Under this heading are published regularly abstracts of the orientation, with any circulation round it, is " A Hidden Safety Factor in the Design of Metal Wings." H. W. Reports and Notes issued by the aeronautical research institutions considered. and bodies throughout the world. Sibert. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Aircraft Engineering and Aerospace Technology Emerald Publishing

Research Reports and Memoranda

Aircraft Engineering and Aerospace Technology , Volume 13 (2): 1 – Feb 1, 1941
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Publisher
Emerald Publishing
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Copyright © Emerald Group Publishing Limited
ISSN
0002-2667
DOI
10.1108/eb030740
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Abstract

44 AIRCRAF T ENGINEERING February, 1941 Report No. 193. August, 1940. Dynami­ Report No. 195. August, 1940. Some JAPAN cal Stability of a Column under Periodic Experiments on the Forced Vibration of THE AERONAUTICAL RESEARCH Longitudinal Forces. By Ikuo Utida and Varying Period. By Katsutada Sezawa and INSTITUTE: TOKYO IMPERIAL Katsutada Sezawa. (In English.) (0.80 yen.) Wataru Watanabe. (In English.) (0.30 yen.) UNIVERSITY (Kôgyô Tosho Kabushiki Kaisha, Tokyo) The present problem deals with the vibrational The resonance condition of an elastic bar condition of a column under periodic longi­ under forces with frequency increasing or Report No. 191, July, 1940. Measurement tudinal forces. The problem was examined in decreasing linearly with time, was investigated of the Period of Natural Vibration of an two ways : experimentally and mathematically. experimentally. The vibration of the same bar Airscrew Blade. By Jûichi Obata and Yahei was excited electromagnetically, the intensity The results show that the problem is dynamic­ Yosida. (In English.) (0.30 yen.) of the force being constant for every vibration ally that of instability in free transverse oscilla­ tion as well as tha t of resonance in forced longi­ through the whole range of the varying fre­ In Report No. 103 of the Aeronautical Re­ tudinal vibration. quency and also for any case of experiments. search Institute, will be found the results of A magnetic damper was added to the bar for Although there is a number of frequences at experiments in the electrical method of measur­ ascertaining the effect of viscous damping on th e which the vibration becomes unstable or reson­ ing small vibrations with the aid of a triode resonance amplitude in the case of varying ance-like, the mode of vibratio n of th e column is valve, together with its application s to th e meas­ frequency. of fundamental mode almost in any case; that urement of vibrations of airscrew blades. is to say, th e fundamental mode of vibration is Let dN/dt be the absolute speed of change of Recently, in connexion with the stud y of air­ excited by the periodic forces of different fre­ frequency and k the logarithmic decrement of screw flutter, the urgent need of accurate quencies. The conditions in which the vibration free vibration in the case of dN/dt being zero. measurements of bending as well as of torsional When k was not ver y large, the resonance ampli­ in question occurs, are such tha t the ratio s of th e vibrations of an airscrew blade was felt, result­ tud e diminished enormously with increase in natura l frequency to tha t of th e exciting forces ing in th e application of this electrical method are 1/2, 2/2, 3/2, 4/2, 5/2, . . . The greater the dN/dt. On the other hand, when k was fairly with very satisfactory results. At that time, ratio under consideration, the smaller the reson­ large, no appreciable change in resonance certain improvements and developments were ance amplitude and, also, the range of instabi­ amplitude occurred for different dN/d, the made on th e former method, and i t is t o describe lity. The condition in which the ratio becomes contribution from k having taken the important these that the present paper has been written. 1/2, corresponds to tha t called Melde's effect. par t of the problem. From the nature of things, although the resistance arising from At every resonance or unstable condition, the Report No. 192. August, 1940. Viscosity viscous damping was operative in forced vibra­ change of amplitude in th e stage of raising fre­ Characteristics of Lubricating Oils as Related tion as well as in free vibration, that due to quency is not the same as tha t in the stage of change of cycle manifested itself only in th e case to their Chemical Structure. By Bunnosuke decreasing frequency. In the stage of decreas­ of forced vibration. Furthermore, although Yamaguchi. (0.50 yen.) ing frequency the vibration amplitude augments the resonance amplitude was nearly the same, The author has shown that no clear definite increasingly for a relatively wide range until the provided the absolut e value of dN/dt were given, relation exists between the chemical structure limit is reached when the amplitude suddenly there was some time lag in reaching the maxi­ and the viscosity index or the "Viscositatpol- reduces to that taken in the stage of raising mu m amplitude in raising or diminishing the höhe " of high-molecular-weight hydrocarbons, frequency. In order to get the condition frequency. This feature was pronounced parti­ and has explained the reason. It has been theo­ corresponding to the stage of decreasing fre­ cularly in the case of large k. Finally, it was retically and experimentally evidenced that the quency even in th e stage of increasing frequency, possible to construct empirical formulae in­ viscosity-temperature coefficient at the same some artificial shock should be applied to the dicating the resonance amplitudes for any case viscosity of liquids is a unique function of their column. When there is a relatively small mass of dN/dt. Although, in this case, the existence chemical structure. For a number of synthetic a t an end of the column, there are some further of the term dN/dt was somewha t similar to tha t high-molccular-weight hydrocarbons, the vis­ complex relations between the vibration ampli­ of the term k, the coefficient of the term dN/dt cosity-temperature coefficients at their re­ tud e and th e frequency. was likely to change with difference in cases. spective temperatures having the same vis­ The mathematical interpretation of th e present Although the periodic vibration of th e column cosity of 100 centistokes, the values of results will be published in a forthcoming paper. in the unstable or resonance condition is almost —hav e been calculated by means of sine form, the same form tends to change v=100 c.s. increasingly with increase in the order of reson­ of Walther's viscosity-temperature equation, ance. It is likely that the wave form of the and it has been substantiated that the coeffici­ vibration of th e column in th e frequency inter­ ents thus calculated are always definitely cor­ mediate between two neighbouring unstable related with their chemical structure, with the conditions, contains bot h types of wave s in these PROFESSIONA L PUBLICATIONS conclusion that the greater the "entangling unstable conditions. degree " of molecules of a hydrocarbon, which Under this heading are given each month the principal articles of depends upon its molecular structure and is Experimental as well as mathematica l results aeronautical interest appearing in the current issues of the Journals of the leading professional institutions. decidable under an assumption by the size or show tha t the resonance or instability condition length of cyclic nuclei and paraffinic side chains depends on the magnitude of the vibrating The Journa l of th e Royal Aeronautical Society together with the size and allocation of branched forces applied. If the forces were not great, it Vol. XLV, No. 361, January, 1941. chains in the molecule, the smaller its value of would be impossible for the resonance or un­ "Som e Theoretical Considerations on Box Beams." Jean stable condition to occur, from which it follows Drymael. — or its "structure viscosity tha t the phenomena resemble those of reson­ Library Catalogue. ance with respect to the vibrational frequency Abstracts from the Scientific and Technical Press. and those of buckling with respect to the index," —+ 5] × 100. A criter- magnitude of th e applied forces. v=100c.s. S.A.E. Journal ion for grading the viscosity characteristics of Vol. 48, No. 1, January, 1941. hydrocarbons may be given by both the values " Fluid Transmission of Power." N. L. Alison. of viscosity and " structure viscosity index," Report No. 194. August, 1940. On the " Ground Form Finishing Hobs." Charles R. Staub. as for compounds of comparative viscosities "A n Instrument for Continuous Measurement of Piston Tem­ Subsonic Flow of a Compressible Fluid past the smaller the structure viscosity index, peratures." Arthur F. Underwood and A. A. Catlin. an Elliptic Cylinder. By Isao Imai and the more excellent the viscosity characteristics. "Th e C.U.E. Cooperative Universal Engine for Aviation Single- Takasi Aihara. (In English.) (0.45 yen.) From this point of view, it has been pointed out Cylinder Research " A. W. Pope, Jnr . what molecular structure to be required for a In this paper a new method of dealing with The Journa l of th e Aeronautica l Sciences hydrocarbon to have the best viscosity charac­ compressible fluid flow is presented . The meth­ teristics. It has been also shown that the vis­ Vol. 8, No. 2, December, 1940. od is essentially equivalent to the original cosity characteristics of commercial mineral "Wing Loading, Icing and Associated Aspects of Modern Trans­ Janzen-Rayleigh method, but makes it possible port Design." Clarence L. Johnson. and fatty lubricating oils and the effect of such t o obtain the result without recourse to the "Experimental Determination of Hydrodynamic Stability." an addition agent as paraton e can be reasonably infinite series expansion, thus making the Ernest G. Stout. explicated by the idea of structure viscosity analysis much simpler. As an example of its "Measurements on Detonation in Duchêne Apparatus." G. index. Broersma. application, subsonic flow of a compressible "A n Experimental Verification of the Isotropy of Turbulence fluid past an elliptic cylinder at an arbitrary Produced by a Grid." D. C. Macphail. * Under this heading are published regularly abstracts of the orientation, with any circulation round it, is " A Hidden Safety Factor in the Design of Metal Wings." H. W. Reports and Notes issued by the aeronautical research institutions considered. and bodies throughout the world. Sibert.

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Aircraft Engineering and Aerospace Technology – Emerald Publishing

Published: Feb 1, 1941

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