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Aviation History
1927
1927 - 0214.PDF
28 SUPPLEMENT TOFLIGHT MARCH 31. 1927 THE AIRCRAFT ENGINEER 2. Total maximum horse-power was reported in many eases higher and ina lew cases lower, than obtained in this report. 3. Propulsive coefficients at maximum speeds are in general lower than thereported values. Coefficient •• 0 " is constant and the propeller efficiency " E " is reduced as at maximum speed that the propulsive coefficient " K "falls off. 4. It was further noted that several ships of widely different designs hadnearly the same drag coefficient for the whole ship. However, this is looked upon as a coincidence in the cases where the type of hull, cars, and surfacesdiffered widely. 5. That in general an idling propeller was iound to have about ir> sq. ft.area of drag, while a stopped propeller had about 6 sq. ft. area of drag. This was found by working out the area of drag from the ship's performance andcomparing it with the area of drag as obtained on the deceleration test with either stopped or idling propellers as the case was reported. In some casesthis difference of area worked out to be 8 or 9 SIJ. ft. per propeller, but witli certain types of engines it is possible that all engines were not stopped butthat one or two were left idling during the deceleration tests. Applied values of principal data and results arc given in Table I and Fig. 3. T.N. No. 248 :—" THE DRAG OF AIRSHIPS, PART II." By Lieut. Clinton H. Havill, U.S.N. The extension of wind tunnel tests of models of airship hulls to full sealf-requires an extension from a VL of the order of less than 500 BIJ. ft./see., to the order of 80.000 sq. ft.'sec, where V = air speed, feet per second, L = lengthin feet of the particular form of hull. The reason for this research was fo furnish the. airship designer with a method for finding tiie VI, curve of anyconventional type of hull, using data obtained from actual performance of airships flown prior to 192(>. This digest, as given here in Part II. was begun in preliminary details inJune, 1922, and completed in April, 192(5. as it was necessary to complete Part I before Part II could be completed : the period between September.1923, and December, 1925, was devoted to work on Part 1. The outstanding results are as follows :1. An empirical method for finding the drag coefficient of any bare airship hull with its VL curve from 100,000 cub. ft. volume to (',,400.000 cub. ft.volume. 2. The derivation of an empirical shape coefficient that can be calculatedfrom the hull contour that defines the VL curve of any conventional airship shape within the limits placed on Figs. 7 and 8.3. (a) That the slope of each VL curve differs with each type of hull and that its slope is not quite constant. (ft) That CH = function of (VL)" and n is a variable at different values of VL. CII = drag coefficient of bare airship hull. Drag *-- Cn^(Volume)2'n'^. (c) That tho value of n varies slowly so that extrapolations beyond thatgiven by diagrams Figs. 7 and 6 of the' VL curves are not much in error, as requirement 3 of illustrative problem shows. 4. The region from model tests to a volume of 100,000 cub. ft. size indicatesthat in this region the most rapid change in the slope occurs with the conclusion ' that " The best model in the wind tunnel will probably be the best (lowestdrag) airship hull but not necessarily " as their VL curves may cross and again may re-cross at higher values of VL. In view of this as found by extrapolatingthe VL curves calibrated on performance back to wind tunnel values and extrapolating wind tunnel results to higher values of VL together with thefact that airship designers are not interested in airship hulls of less than 100,000 cub. ft. of volume, this part of these researches was left out. Thescale on diagrams at 0-3 cub. ft. volume calibrated on existing wind tunnel data is merely for general information. T.N. No. 249:—" EFFECT OF PROTRUDING GASOLINE TANKS UPON THE CHARACTERISTICS OF AN AIRFOIL." By Eastman N. Jacobs, Langley Memorial Aeronautical Laboratory. These tests were carried out in the variable-density wind tunnel, on a5 in. by 30 in. model. The tank was made to represent roughly that used on the de Havilland " Moth." The tests were made only at the highestvalue of the Reynolds Number at which the tunnel is ordinarily operated. With the tank on top there was a decrease in lift at large angles, althoughup to 10 degrees the decrease was not large. The drag was considerably increased throughout, most at large angles. Putting the tank below thecentre-section resulted in a decrease in drag, but the lift at large angles was not increased, in spite of the fact that with the tank in this position the airfoi!went to higher angles before burbling commenced. The wing section used in the experiments was the " Clark Y." T.N. No. 250:—" INFLUENCE OF THE ORIFICE ON MEASURED PRESSURES." By Paul E. Hemke, Langley Memorial Aeronautical Laboratory. The influence of different orifices on the result of measuring the samepressure distributions is the subject of this note. A circular cylinder is exposed to an air stream perpendicular to its axis and its pressure distributionis repeatedly determined. The pressure on the greater part of the upstream half of the cylinder apparently increases when the orifice size increases. Thepressures measured on the downstream half of the cylinder do not change for the orifice sizes used in the tests. Rounding the edge of an orifice hasthe same effect as increasing its size. The maximum value of the ratio of orifice diameter to radius of curvatureof the surface in the plane of motion, for which no measurable error was found, is given. Values of this ratio for orifices as used in aircraft and mode]airfoils were found to be much less than the maximum ratio. T.N. No. 251 :—" THE EFFECT OF TUBE LENGTH UPON THE RECORDED PRESSURES FROM A PAIR OF STATIC ORIFICES IK A WING PANEL." By T. Carroll and R. E. Mixon, Langley Memorial Aeronautical Laboratory. The differences in head caused by variations in the length of tubing aresmall, the lowest recorded being zero, and the highest 2-7 per cent. This difference is well within the experimental error. T.N. No. 252 :—" RESISTANCE OF A FIFTEEN-CENTIMETER DISK." By James M. Shoemaker, Langley Memorial Aeronautical Laboratory. The results of thfetest show that the dynamic scale has very little effect onthe drag coefficient of a disc over a wide range of Reynolds Number. A comparison of these results with those of tests made on a series of discs atGtSttmgen University furnishes a good check on the method of testing in this tunnel. T.N. No. 253:—" WIND TUNNEL STANDARDIZATION DISK DRAG." By Montgomery Knight, Langley Memorial Aeronautical Laboratory. This report deals with the resistance of a series of three similar discs placednormal to the wind as determined in the atmospheric wind tunnel of the National Advisory Committee for Aeronautics. This is the first of the stan-dardisation tests to be made in American wind tunnels using these particular discs. The curves of drag coefficient plotted against Reynolds Number forthis tunnel show discrepancies between overlapping values which are to be attributed to the presence of the tunnel walls. BERICHTE UND ABHANDLUNGEN. No. 14 of the " Berichte und Abhandlungen der Wissen- schaftlichen Gesellschaft fur Luftfahrt E. V. (W.G.L.),' published as a special issue of the Zeitschrift fur Flugtechnik und Motorluftschiffahrt, contains a number of lectures and papers of unusual interest. ]''irst comes a paper by Dr. E. Rumpler on •• The Trans-Oceanic Aero-plane," in which lie outline? his scheme for a huge multi-engined, multi-mill Hying - boat. The subject of seawortluness is dealt with at considerablelength, and during the discussion several speakers raised objections to the machine on account of the stresses that would be set up by the different hullsworking in a seaway. The machine is designed to have a high wing loadinsr. and it is estimated that the take-off speed would be about 130 km. (80 miles)per hour, so that considerable stresses may be expected. Dr. Rohrbach is represented by a paper entitled " Design and Problemsof Light Metal Construction." the paper being illustrated by photographs and drawings of Rohrbaoh constructional details. The subject of steel orlight metal is dealt with both in the paper and the discussion. A paper on " Photosrammetric Measurements of Starting and Landing."by Bruno Spieweck. explains how tho times for taking off and alighting may be measured by means of the cine camera and stop watch, the latter beimrphotographed on the film. The machine flies straight away from, or straight towards the camera, as the case may be. and when trie wing span is known,the distance from the camera at any moment can be calculated. A paper on the stresses and changes in form in airscrews is contributed byF. fcjeewald, and F. N. Seheubel, of Aachen, is represented by a paper on "Control Surface Flutter and its Prevention," a subject much to the forein this country at the moment. " The mutual Influence of Wings and Propellers " is the title of a paperby R. Seiferth, of frottingen. while Hanns Wcidinger contributes a paper on " Profile Drag Measurements of a Junkers Wing." making use of Betz'sProcedure in making comparisons between model and full scale flying tests. A paper by H. Herrmann (who was chief designer to the Udet Works atMunich) is entitled " Floats and Flying Boat Hulls," and gives the lines of a large number of hulls (many of them English), and their resistance.The book is of very considerable technical interest, and those of our readers who are able to read technical German will be well advised to obtain a copy.The price is 16 marks, and the report can be obtained from Verlag B. Olden- burg. 8, Gliickstrasse. Munich. SCHUTTE-LANZ AIRSHIP WORKS, 1909-1925. Another work recently published by Oldenburg, and obtainable from the same address (Price 15 Marks), is entitled " Der Luftschiffbau Schutte-Lanz, 1909-1925." The preface to this is by Dr.-Ing. Johann Schiitte, surviving partner of the Schlitte-Lanz Airship Company (Dr. Karl Lanz died in 1921—Ed.), and contains a brief history of the firm. The numerous sections into which the book is divided arc written byspecialists, most of whom have worked with the Schutte-Lanz Airship Com- pany in various capacities. The first chapter, by Dr.-Ing. Dietrich Riibl.deals with the peculiar Schiitte-Lauz plywood construction. Then follows a chapter by Dr. Ing. W. Bleistein on the influence of speed on the com-mercial economy in commercial airships. A chapter on the design and stress calculations of Sehntte-Lanz airships by members of the staff, editedand collated by Dipl.-Ing. Weiss and Dip].-Ing. Gcntzke, is naturally of a very highly technical character, and is elaborated by an appendix dealingwith some loading experiments. Another interesting section, by Dipl.-lns. Weiss, is entitled ' Contributions to ltiaid Airship Construction." Dipl-Ing. Fritz Gentzke contributes a section on the light-weight construction nf airships, treating in great detail upon metal ter-m plywood as materials forairship construction. The development of the electric installation in Schiitte-Lanz airships is ablydealt with by Ulrich Aschmaun. while Clem. Endras writes of the gas cell* and outer covering. Other sections of the, book deal with various subjects,including the general history of German airship work. Altogether this is a book which no one interested in airship constructioncan afford to be without. Although it deals to a considerable extent with the plywood construction adopted by the Sclv'itte-Lanz firm, and which in moderntimes probably nobody would be likely to take up, the book contains such a wealth of technical information on general airship subjects that it is of verymuch more than historical interest. The illustrations are well reproduced. and there are large insets of drawings, etc. SOME RECENT PAPERS AND LECTURES We have had quite a crop of papers and lectures in this country recently, most of which, unfortunately, have been of such a nature that they cannot usefully be summarised. At the Royal Aeronautical Society, Group-Capt. Flack read a paper on " Man and the Machine " on March 10. Mr. M. A. Giblett dealt with li Line-Squalls " on March 17, Maj. Wronsky with " Air Traffic in Germany" on March 24 (summary published in FLIGHT this week), and on March 31 a paper was read by F. G. Richardson entitled '" Recent Model Experiments in Aerodynamics.1' At the Institution of Aeronautical Engineers, Maj. Wylie read a paper on " Portable Hangars" on March 8, and Mr. Wingfield on " Aircraft Law "' on March 22. 188ft
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