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Aviation History
1913
1913 - 0301.PDF
MARCH 15, 1913. It will be observed that the majority of the machines attained their maximum speed between the two graphs representing lift coefficients* of o-3 and 0*2. The angle of incidence required to give a lift coefficient in the order of from -2 to *3 depends, of course, on the shape of the wing. For a series of similar wings tested at the N.P.L., all of which had flat under sides, the lift coefficient at a given angle of incidence below the critical angle increased with the height of the maximum ordinate. One of the profiles so tested, No. 4, had an upper surface corresponding to Eiffel No. 13 bis, which is also known as Bieriot No. 11 bis, and has been much used as a basis for the design of wings employed on other aeroplanes. A chart reproduced from the latest technical report of the Advisory Committee shows the lift coefficients for the No. 4 section throughout a range of angles, and it will be observed that a lift coefficient of o'2 obtains for an angle of incidence of about \°, while a lift coefficient of o-3 corresponds to an angle of incidence of 30. From the fact that these lift coefficients cover the range of maximum flight speeds, it is evident that the normal attitude corresponds to a somewhat coarser angle of attack. One ol the most interesting results associated with the particular series of tests to which reference has just been made was that the maximum aerodynamic efficiency, or ratio of lift to resistance, occurred always in the neighbourhood of 4° angle of incidence. It is apparent that for a one-speed machine, such as is now under consideration, it is desirable that the wings should normally fly in their attitude of maximum efficiency, and so far as this particular type of section is concerned the angle in question would be approxi mately 40, as is shown by the accompanying chart that illustrates the lift-resistance ratios. The " aerodynamic efficiency " for wing No. 4 at 40 is about 12J. The corresponding graphs for the wing sections used by Mr. * The lift coefficient is the numerical factor, C, in the expression Cpr*2, where P is the density of the air and v is the flight speed in feet per second. If 1 V- .„.,,, pig = then pv2 = ' where V is the flight speed in m.p.h. Thus, a lift coefficient o'2 gives the formula = as the ratio of wing loading to tt 200 loco * ° speed for the case in point. Similarly, the coefficient o 22 corresponds to Va -7- 900, while the coefficients 0*3 and o'35 are represented by Va -*- 670 and V2 •*• 570, respectively, on the chart. ® ® A Review of Aircraft IN connection with the visit of the Prince Regent of Bavaria to Berlin last week, a review of airships and aeroplanes was arranged at Johannislhal, and it had been hoped that the Kaiser would make a trip in the Naval Zeppelin. He, however, did not attend the review, but the Prince Regent of Bavaria spent a couple of hours inspecting the seven airships and sixty aeroplanes on parade. February at JohannisthaL DURING the month of February flying was possible at Johannisthal on 23 days, and the 69 pilots and 14 pupils on the ground made 2,373 flights, of a total duration of 254 hrs. 44 mins. I/Scafi Fales are not available. The sections tested by the N.P.L. have the position of their maximum ordinate much further from the leading edge, but among the flat-bottomed sections so tested there is one, No. 5, that has the height of the maximum ordinate approxi mately the same as that in the Fales' wing section, N0.13A, which is the section to which I have made particular reference. Although there is no reason to suppose that the characteristics for the f 'ales' wing would be similar to those of the N.P.L. series, the N.P.L. section, No. 5, is included, as a matter of interest, in the chart that also contains the N.P.L. wing No. 4, to which reference has previously l>een made. If the Fales' wing did possess a similar characteristic to that of the N.P.L. wing No. 4, then an angle of incidence of 4 would lie in the middle of its most stable region, as is shown by the slope of the graph in the chart showing the travel of th«- c.p. It would also give a lift coefficient of 0-35. which would serve to lift 4*4 lbs. per sq. ft. at 50 m.p.h. Other corresponding wing loadings for different speeds can be seen from the 0-35 graph on the speed chart. The graph of the Fales' wing on the chart showing the travel of the c.p. is prepared from a small portion of one of the curves drawn by Mr. Fales. It is on a much larger scale, however, so as to emphasise the movement of the c.p. in the flight region. An interesting feature of the Fales' wing is that it is unstable on berth sides of the flight region, i.e., from 2 to 10". On the same chart I have placed a graph taken from the latest technical report of the Advisory Committee showing the travel of the c.p. on a wing section corresponding to Eiffel 13 bis. It is interesting to observe that the instability of this wing is more pro nounced at angles Iwlow 2' than at angles aliove 2", which emphasises the inadvisability of forcing a wing section of this kind to fly at a very fine angle in a system that is designed for normal longitudinal stability at some coarser angle. When the angle becomes finer than 2" the travel of the centre of pressure towards the rear is very marked indeed, and might well endanger the control of the machine. For the sake of comparison I have also introduced a graph showing the travel of the centre of pressure on a flat plate, which is stable for all angles of incidence. One practical consideration of great importance is whether wing sections of the Fales kind would permit of a rear spar in their construction. ® ® Military Flying in Germany. ON the 4th inst. Lieut. Braun and Schulz, the latter with Major Siefert as passenger, left Metz, and following the Moselle Valley landed at the Carthaus Ground at Coblcntz after two hours' flying. After a short rest Lieut. Schulz went on to Cologne, his time for the 300 kiloms. from Metz to Cologne, including the stop al Coblentz being 5 hours. Turkey Orders Aeroplanes. IT is announced from Berlin that the Turkish Government has just placed with German firms orders for some 33 aeroplanes. THE BLERIOT MONOPLANE TRANSPORTER.—The top picture shows the transporter folded up and In tow on a pair of its own wheels behind a car; that on the left illustrates the transporter in action, carrying: a Bieriot tandem two- seater monoplane. An idea of its construction can be gathered from the right-hand photograph, which shows how the transporter, which can be towed by means of horses or automobile, can be driven over obstacles without upsetting; the balance of the monoplane on board. 307
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