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Aviation History
1928
1928 - 0136.PDF
20 SUPPLEMENT TO FLIGHT FEBRUABY 23, 1828 THE AIRCRAFT ENGINEER Fig. 6. 461-25 19-32 2 1 , a Area = —;— X —s— X 7 X i~7J = 41-25 sq. ft. The area of the load water plane is found by total of functions of areas multiplied by one-third the interval between stations, and this result multiplied by two for both sides of the float. As the ordinates used are measured in inches we then divide by 144 to bring the result to square feet. Finding the position of the load waterline is a matter of judgment and " trial and error." The first consideration is water-clearance for the airscrew, which fixes the position of the floats below the fuselage. The trim fore and aft depends upon the nature of the machine. 3. Centre of Flotation. For transverse inclinations the centre of flotation, which is defined as the centre of gravity of the water plane, is taken as on the centre line of machine, but the position of centre of flotation for inclinations fore and aft must be calculated. As we are dealing first with the transverse metacentric height we will leave this calculation for the moment and pass on to No. 4. 4. Moment on Inertia of Waterplane. This must be found:— (a) About the C.L. of float, (b) About the C.L. of machine. 4 (a) is tabulated as follows :— • . Then Io = I + (area of W.P. + \ track2) = 21-45 + f41-25 x 1. ^tlOI 12 Hi11 10 9 8 7 6 5 4 3 2 1 *0 2Semi-ords. l" in ft. 0-0 0-5 1-0 1-341-40 1-42 1-42 1-33 1-25 112 0-96 0-71 0-46 0-33 00 3Cube of Semi-ords. 0-0 0 125 1-0 2-4 2-74 2-85 2-85 2-35 1-95 1-400-88 0-35 0-09 0-036 0-0 4 Simpson's Multiplier. I 2 li4 2 4 2 4 2 4 2 4 2 i 5 Functions of Cubes. 0-0 0-25 1-50 9-605-48 11-40 5-70 9-40 3-90 5-601-76 1-40 0 135 0-072 0-0 56-197 Moment of inertia about centre line of float 56-2 1-725 3=21-54 X -z — The moment of inertia about the centre line of float is found by adding up the functions of cubes, multiplying this by one- third of the interval between stations, and multiplying the result by two-thirds. Let I = moment of inertia of W.P., about C.L. of float and let Io = moment of inertia of W.P., about C.L. of machine. = 856-8. Then Io for both floats = 2 x 856-8 = 1713-6. [To be concluded.) TECHNICAL LITERATURE. SUMMARIES OF AERONAUTICAL RESEARCH COMMITTEE REPORTS. A DISCUSSION OF THE LAW OF VARIATION OF ENGINE POWER WITH HEIGHT. By H. GLAUEBT, M.A. R. & M. No. 1099 (E. 25). (7 pages.) March, 1927. Price 4d. net. As a result of a long series of experiments at the Royal Aircraft Establishment, it appears that the power of an engine is a function of the pressure rather than of the density. Recently, Mr. Capon* has suggested that the law should be defined more precisely as a function of pressure to the two thirds and density to the one third power. Other investiga- tions at the R.A.E. have previously been published as R. & M. Nos. 462,t 960J, and 961§. The whole question of the variation of engine power with height has been reviewed, and the experimental results have been examined to find confirmation or otherwise of Mr. Capon's suggestion. The relative importance of pressure and density in deter- mining the power of an engine appears to vary with height, and different methods of experiment lead to slightly dis- cordant results. The simple pressure law is undoubtedly better than the simple density law, and for greater refinement Mr. Capon's suggestion should give a very close approximation to the truth. * R. & M. 1080.—The Reduction of Performance Tests to the StandardAtmosphere.—By R. S. Capon. t R. & M. 462.—The Variation of Engine Power with Height.—By Pinsentand Ben wick. J R. i M. 960.—Variation of Engine Power with Height.—By H. L.Stevens, B.A.E. § R. & M. 961—The Variation of Engine Power with Height.—By H. M.Garner and W. G. Jennings, R.A.E. These Reports are published by His Majesty's Stationery Office, London, and may be purchased directly from H.M. Stationery Office at the following addresses : Adastral House, Kingsway, W.C. 2; 28, Abingdon Street, London, S.W.I; York Street, Manchester; 1, St. Andrew's Crescent, Cardiff ; or 120, George Street, Edinburgh; or through any book- seller. AERODYNAMIC INTERFERENCE. We very much regret that Mr. Stanley H. Evans has been so busy recently in other directions that he has not been able to find the time to complete his second article on " The Problem of Aerodynamic Interference " in time for it to be included in the present issue. We are, however, promised an interesting instalment for next month.—ED. 116*
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