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Aviation History
1911
1911 - 0447.PDF
AIRSHIP The Navy " Airship No. 1." UPON the authority of Mr. McKenna, in the House of Commons, the total liability voted for the naval airship built at Barrow was for the hull and machinery ,£40,876 ; and for spare gear £681. The " Deutschland " Again Wrecked. THERE is something almost uncanny in the way in which the Zeppelin airships are persistently dogged by misfortune, and the disaster which overtook the reconstructed aerial liner " Deutsch- land," after being in use for little more than a month, must be very discouraging to those who have pinned their faith to this type of craft. Since April 7th the vessel has been stationed at Dusseldorf, and it was to have been transferred to Baden Baden on Wednesday. A satisfactory cruise had been carried out on Monday, and on Tuesday a number of passengers booked seats for a short aerial trip. At the time fixed for the start the wind, however, was blowing rather strongly. Nevertheless, after waiting for some time, those in charge of the airship decided to bring her out, which was done, but before she could be released from her human " anchor" of 120 men, she was struck by a squall and driven against the garage. The bows of the vessel rested on the roof, and the strain on the framework caused it to be twisted and damaged to such an extent that it will have to be entirely reconstructed, while several of the ballonels were * ® torn. The two cars, in which were four lady passengers as well as the crew, remained suspended in the air, and the occupants were eventually rescued by the Fire Brigade. Fortunately, no one was injured. It is proposed to reconstruct the airship at Dusseldorf, but this will take considerable time, and it is doubtful if she can be put into commission again this year. Another Dirigible for Holland. PILOTED by Count Henry de la Vaulx, the new /.odiacdirigible, which has been built for the Dutch Army, underwent a test of half- an-hour at the beginning of the week. It is claimed that the dirigible, which is named "Duindigt," is the smallest military dirigible in the world. The envelope has a capacity of 900 cubic metres, while the speed works out to between 35 and 40 k.p.h. The New Italian Dirigible. ON Thursday of last week a very satisfactory trial trip was carried out with the new Italian military dirigible, which belongs to the smaller series. Starting from the hangar, near Verona, with five persons on board, she cruised along the Mincio Valley, over Dossobuono, Villafranca, Nozzerone and Vallegio, afterwards returning to the starting point, a distance of about 65 kiloms. being covered in about an hour and 20 mins. The envelope of the airship is 63 metres in length, and holds 4,000 cubic metres of gas. ATMOSPHERIC FRICTION. By A. F. ZAHM. Continued from page 428.) IT should be remarked that the minimum resistance already given is such only for the symmetrical shapes in question, but not neces sarily a minimum for all possible shapes having the same major section. In fact, when a five-calibre bow, shown by the dotted line in Fig. 7, was combined with a 50-calibre stern, the resistance was much diminished, and it was found incidentally that the ratio of the resistance of a good model to that of its major section can be made less than one part in eight. What the ratio may be for the shape of least possible resistance has not been ascertained. Similar experiments were made with spindles having the outline shown in Fig. 8, and with like results. These are still unfinished ; but it may be mentioned, in passing, that the frictional effect is very manifest. The total resistance of a symmetrical spindle having such outline is again half friction, and has its minimum value in a model of about twelve calibres, for which the length is nearly seven times the major diameter—a relation given by Rankine for well-formed ships. A still less resistance is found when a two-calibre bow, shown dotted in Fig. 8, is combined with a twelve-calibre stern, in which case the length is about five times the major diameter. The Fig. 8.—Symmetrical ogival spindle of minimum resistance. ratio of the resistances of the spindle and its major section has been reduced to about one part in eight. What the smallest possible ratio may be for a given velocity has still to be ascertained, and may well form the object of a special research. The foregoing samples suffice to indicate the importance of the friction term in the general equations of aerodynamics. We may now notice its bearing on problems of transportation, and particu larly the cost of propulsion in aeronautics. Let us consider the soaring plane, first assuming it smooth, then frictional. Let A be the area of the plane, W its weight, v its velocity, a its angle of flight. A' its resistance, H the propulsive power, and s the density of the fluid in which it is moving. Then, if the plane is frictionless and steadily soaring on a horizontal course in still air, R = W tan a, (a) H= Rv, . . . . (b) ... 2ks Avl sin a cos a , , I + siwa. the last expression being the lift as given by Duchemin's formula, in which k is a constant of figure. The relations of these seven variables contain much that is ot interest in the theory of the aeroplane. For example, let us find the mileage cost and the propulsive power when the plane is just soaring. The mileage cost is proportional to the resistance divided by the load, and hence, as shown by equation (a), it is directly proportional to the tangent of the angle of flight. It may, therefore, have any value, from zero to infinity, according to the inclination of the plane, and if this be kept constant the mileage cost is the same for all velocities, for whatever extent of surface, and for all densities of the medium, from mountain air to sea water. In a similar way the mileage cost may be studied as a function <>t any of the other variables. Thus from equation (/) we obtain IV (l + sin*a) ... tan a= • . 3-5-7; • .. ., • • • (") 2 As Av- (I - sin -a) in which the ratio of the parenthetical factors is practically unity for small values of o. Hence, writing IV tan a = —. —-5, ...(d) 2ks ATF it is at once evident that the mileage cost is directly proportional to the load, and inversely proportional to the density of the medium, the area of the plane, and the square of its velocity. The propulsive power may be obtained directly from the last equa- W" tion. Thus, // = W;> tan a — , , . This shows that the power 2ks AT varies directly as the square of the load, and inversely as the density of the medium, the area and speed of the plane. This last relation, viz., that if IV, r, and A remain constant, S varies inversely as v, has been more emphasised than the other relations by the various writers on aeronautics. It was first proved, though in a different manner, by A. Du Roy de Bruignac,* and formally enunciated by him in '875, as follows: "Providing the angle of a heavy plane, moving in the air, be maintained at the minimum necessary to sustain its weight, the work of translation diminishes as the velocity increases." Mr. Curtist gives a different analytical proof, and Lord Rayleigh, in his interesting memoir on " The Mechanical Principles of Flight," demonstrates analytically that " if frictional forces can be neglected, a high speed is all that is required in order to glide without energy." Mr. ChanuteJ has »hown, by numerical computation, that De Bruignac's statement may be applied to birds and flying machines moving at limited speeds, say 30 to 40 miles an hour; and Professor Langley has concluded from his experiments that the propulsive power of a material soaring plane diminishes with the speed up to at least 66 ft. a second, if the edge resistance be left out of the account. Nearly identical with the expression for power is the equation for the speed of fall of a horizontal plane having lateral motion. If * " Kecherches sur la Navigation Aerienne.' t " Experiments in Aerodynamics," I.angley. J " Aerial Navigation." 449
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