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Aviation History
1931
1931 - 1036.PDF
SUPPLEMENT TOFLIGHT 68 THE AIRCRAFT ENGINEER SEPTEMBER 25, 193; The analysis of the performance of these designs yields a drag coefficient of 0.000024 for the wing air- foil resistance, 0.00030 for the fuselage with cowled radial engine, and for the low-wing, 0.00012 additional to the resistance of the fuselage for wing interference. Wind Tunnel Wing aloneHigh wing High wingMidwing Low wingWing below N.P.L. Wind High wing High wingMidwing.. Low wing Effect of TABLE 3 fuselage and Wing interference Tests in Goettingen. Ergebnisse I. parasol fuselage . ky max. .. 0-00304 Tunnel Tests. K with fillets 0-003140-00311 0-003020-00300 0-00302 oyal Aeron. 0-00264 0-002610-00109 0-O0228 kx min. 0-00003480-0000486 0-00004170-0000417 0-00004430-0000537 Soc. Journal, 0•0000700 0-00007500-0000630 0-0000855 Ratio 87 65 74 7-2 68 56 1U30 37-7 35-231-5 27 The ratio of kymax, over kxmin. figure of merit for high speed indicates in both tests the better qualities of the high-wing type. In other tests the low-wing plane occasionally shows better lift characteristics than in these, and simultaneously increase drag. Usually the interference of the fuselage of the low-wing plane with the sensitive airflow on the upper surface of the wing results in increased form drag at low incidence and increased induced drag at high angles. TABLE 4 Power Economics of Burnelli and High-Speed Single-Engine Design Both planes carry equal power load; use the same wing section; havethe same landing speed ; equal propeller tip speed and are equipped with retractable landing gear and tail wheel Fuselage Resistance and Space Comparison RoundStreamline SingleEngine Wing SectionBurnelli Twin 0 0 28 42517-5 24-2135 314 •00016•00030 — 0-385 j>er cent. 88 1,20050 24 550 2-12 0-000220-00030 0-0020140 1-22 0-290 21 per cent. 46 low-wing plane, which is 0.6 sq. ft. flat plate, or 0.14 sq. ft. per 100 h.p.-engine power. This reduces tLs entire comparison to a consideration of the round streamline body and the airfoil section body with maximum fairing. The comparison is carried out in Table 5, which particularly illustrates the capacity of the Burnelli plane. The comparison of the percentage of power required by the fuselage at 190 m.p.h., 28 per cent, by the single-engined plane, and 21 per cent, by the Burnelli, indicates the greater speed possibilities of the latter. The following figures, which are based on established values, complete the comparison, and give the relative high speed of both types : — Hound Stream-line Single Engine Flat plate resistance per horse'power of— WingBody Tail areasOutriggers Fuselage-wing interference TotalHigh speed 0-00565 0-00385 0-00088 0-00140 Wing Fuselage,Burnelli 0-00565 0-00290 0-00088 0-00050 0-01178 204 m.p.h. 0•00993 216 m.p.h. Investigation of the figures employed in this article leads to the result that the all-wing trend of design affords immediate opportunity for transport design advancement by combining the speed efficiency of the finest single-engined design with the increased safety and capacity of the multi-engined type with other desirable safety and structural advantages. HorsepowerFrontal area of fuselage, sq. ft. H.P. per square foot of frontal areaCargo space, cubic feet .. H.P. per cubic foot of cargo spaceDray coeflk-ient of body ideally faired .. KJ Engine and cooling system .. .. KJ-Lift coefficient of body .. .. .. Ky Equivalent wing area saving, sq. ft. ,Equivalent resistance saving, flat plate Resulting comparative body resistance equiva-lent flat plate per 100-h.p. Percentage of engine power required by body at190 m.p.h. Engine power required at 190 m.p.h. per 100cub. ft. of cargo space The frontal area per h.p. is about equal, also the resistance coefficients with power plant installed; therefore, the resistance per h.p. The lift of the Burnelli wing section body as verified is allowed for by substracting the drag of the equivalent wing area replaced by the same. This results in 25 per cent, drag per h.p., and in the much lower power of 46 h.p. to fly 100 cub. ft. of cargo space at 190 m.p.h. A comparison of the power-area relations of a high- speed single-engined design with a Burnelli high-speed design is significant (Table 4). It is based on both planes having equal power load, landing speed, similar wing section and propeller tip speed, with retractable landing gear and tail wheel. The Burnelli plane is provided with 40 per cent, more tail area to support, the outriggers extending from the short-wing section fuselage. They add 0.6 sq. ft. flat plate resistance, or 0.05 per 100 h.p., which is neglected in the comparison to balance for the wing-fuselage interference of the ' . 970d HORSEPOWER AT SPEED OF SOUND. BY A. E. PARKER, B.SC. The Kinetic Theory of Gases states the following, and these assumptions will be made in this elementary theory:— (1) A gas consists of molecules which are moving about in all directions and colliding with each other, and, with the walls of the containing vessel, all molecules have same mass. (2) The molecules are considered to be perfectly elastic, that is, if they strike a body with a certain speed they rebound with the same speed. (3) The molecules are considered to be infinitely small. This assumption does not make any difference at ordinary pressures. F E. G y/ n s L uBC
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