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Aviation History
1925
1925 - 0673.PDF
OCTOBER 15, 1925 were reWH t ^ ynamiC StreSSCS °f the ^"^ntal surfaces meln, + 1° thC suPP°rting framework of the hull bv Sn OtrStrUCtUreS,Statlcally determined and easy of calcu- obtamed ?TTi y' * VCry Simple and h*ht structure wasficial S4enfn n g ltely "^ ^^ than th* s>'ste™ «* *»P«- Naturally, when drawing a comparison between the two systems one had to bear in mind that w.th the system of Z/H f^lffe"lnK a certal" volume of gas was lost ; but, on the other hand, as far as the stern was concerned we got a better utilisation of lift. In the new system, as in the old, the lower vertical fin and relative rudder were directly and rigidly joined to the ventral framing, whereas the upper fin, if any was merely supported by the envelope to which it was suitably braced by means of steel cables. Having designed the new structure of the tail end, big. Mobile said he did not deem it expedient, for obvious reasons, to apply it to dirigibles of medium or large volume without first experimenting with it, and so he decided to test it out on the " Mr.," a miniature airship of only 1 014 cubic metres (35,000 cubic ft.). The experiment was' highly successful. The peculiarity of this little dirigible was not so much What was really remarkable, he added, and gave a patent demonstration of the high degree of perfection reached in Italy in the technique of semi-rigid construction, was that they obtained a useful load which, proportionately to the small dimensions of the airship, was undeniably very high. In fact, in its own weight, notwithstanding the adoption of a rigid framing from prow to stern, was only 650 kg. (1,430 lbs.) and, consequently, the useful load was 516 kg. (1,135 lbs.). Thus, the coefficient of useful load was 51 per cent. From some characteristics of the " Mr." given—Volume (V) = 1,014 cub. m., speed (v) =- 72 k.p.h., h.p. (N) = 40— Sig. Nobile gave the value for aerodynamic efficiency as ——— = 935,000, which was very high considering the volume: for the index of actual efficiency:—0-51 x 935,000 x 72 = 106 x 34-3. To give an idea of the progress achieved, Sig. Nobile compared these values with those of the " S.C.A." dirigible, 1,500 cub. m. (53,500 cub. ft.), built in 1921, and which at that time was considered a great advance. " SCA " airship " Mr. " airship Coefficient of useful load .. 0-29 0-51 Aerodynamic efficiency . . S70,000 935,000 Index of actual efficiency .. 106x20-7 10« x 34 • 3 oooo oooo o o o o o o o o o o o o o o o o o The stern of the N.2 semi-rigid airship, showing the modified system of tail surfaces. oooo oooo and this, notwithstanding the inexorable law by which, on the volume decreasing, the percentage of useful load decreased more and more in proportion. from prow to stern consisted of elements which were rabbeted In view of the satisfactory results obtained with the " Mr " inste-ul of articulated with spherical knuckle joints, as was dirigible, the new supporting system of the tail surfaces was that it was the smallest semi-rigid in the world, but that it was the most rigid of all the others built up to the present. In fact, the triangular beam of steel tubing forming the keel instead l , the case with all previous construction. Spherical knuckles existed only in two transversal sections, in order to facilitate ._,,_, assembling, disassembling and transportation of the keel July, with considerable success. itself. Here Sig Nobile briefly described this small airship, but as full particulars of the " Mr." were published in FLIGHT for September 4, 1924, we need hardly repeat them here, d h t b f th, n y pHe state however, that in a great number of cases the " Mr " had' been flown single-handed ; its navigating qualities were'really remarkable, and it possessed great stability and exceptional manocuvrability-so much so that a number of successful landings had been made m a courtyard in the heart of the city of Rome. It had already made over the Appennme mountains several160 flights, crossing fitted to a dirigible of larger volume—the N.27,000 cub. m., which was built last winter, and made its first flights last ily, with considerable success. With the exception of the tail-stiffening, its general structure was substantially the sajne as that of the N.I type (18,500 cub. m.). The profile adopted for the hull was similar to that of the N.I, with the exception of a slight modification at the stern which, in this case, was conical instead of roundish. Furthermore, after the project had been completed, it was decided to somewhat increase the volume, and to simplify matters, a cylindrical trunk was inserted in correspondence with the main section, so that the elongation was slightly greater than that of the N.I. The author here gave some constructional details of the N.2, and again we would refer our readers to a description of this airship which was published in FLIGHT for September 10n1--*- .... ( imn,,rt,nrp tn note mls airsnip wnicn was puonsnea in i'LIGHT ior oeptemoer IU Continuing, Sig. Xobie saidjt wa> ^^^ last. From a specification of the N.2, given-from whichthat on nose S umg Sig. Xobile said it w pe'other hand, the rigidity and robustness o the h hd the compactness of theand on land, tne rigiunv a.m ^""-""T " ^ we quote the following :—Volume (V) = 7,100 cub. m. ;the other hand compactness; i e H = | = 47^with coefficieni envelope. q g () speed (v) = 110 k.p.h.; h.p. (N) =470—with a coefficient of useful load of 42 -5 per cent., for the aerodyanmic efficiency V°-i3v<> , , 366 x 1,331,000 , M. nnn ^ . , • a value of -=r- = 1,030,000, was obtained, and for the index of actual efficiency, a value of 0-425 X 1,035,000 x 110 = 10« x 48-5. §73
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