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Aviation History
1923
1923 - 0169.PDF
MARCH 29, 1923 THE A.N.E.C. LIGHT AEROPLANE 20 H.P. Bristol "Cherub" Engine IN describing the Bristol " Cherub " engine (March 1, 1923)we stated that this low-powered engine promised really to "fill a long-felt want." We did not then anticipate theprompt attention which the engine would attract, and, conse- quently, it is the more gratifying to be able to record that theAir Navigation and Engineering Company, of Addlestone, Surrey, of which Mr. N Chereau is managing director, has gotout the complete designs for a small machine to take this «ngine. The designs are due to Mr. Shackleton, and, as theaccompanying general arrangement drawings will show, the new little machine, which, for want of a better term we,describe as a light aeroplane " (following motor-car practice of speaking of a light car), is of very pleasing lines indeed, andwith its small overall size, and particularly low height (less than 4 ft.) could scarcely fail to appeal to anyone interestedin aircraft. We have had the privilege of going through the performance figures with Mr. Shackleton, and we are frankly astonished at the excellence of the aerodynamic design. Mr. Shackleton has evolved for this machine a special wing section, which ceiling is attained. The machine would probably take some-thing like three hours to reach the ceiling. In external appearance the A.N.E.C. light aeroplane might,perhaps, be described as a Dornier built on a very much reduced scale. The high engine position, the parallel semi-cantileverwing, the short cantilever beams projecting from the floor of the fuselage and carrying the shock absorbers, and the generalappearance are suggestive of the Dornier " Komet." We axe not in any way accusing Mr. Shackleton of copying Dornier.It merely so happens that in combining the features which he has thought desirable he has arrived at much the samearrangement. Constructionally this small machine is, of course, entirely different. The new A.N.E.C. monoplane incorporates in its construc-tion several novel features, most important of which is, perhaps, the wing spar construction. In the past it has beencustomary to have two spars, placed a considerable distance apart. In the German gliders the single spar construction,strengthened by covering the entire leading edge with ply- wood, has gained much favour recently, as providing good THE A.N.E.C. LIGHT AEROPLANE : Part-section through fuselage in way of pilot's seat, looking forward. Note the aileron control and the cantilever undercarriage. in model form and not tested at a particularly high velocity,gave a maximum L/D of 22, while the maximum lift coefficient was somewhat above 0-65. By reducing external bracingand all extraneous parts to a minimum Mr. Shackleton has been able to bring the maximum L/D of the whole machineup to the very good figure of 16-5. The consequence is that, as the machine is light and lightly loaded very smallpower is required for horizontal flight, and the ceiling is correspondingly high. We mention this, not because a highceiling is of any particular value in a machine of this type, but because the characteristics which give a high ceiling arethe characteristics that are desired for other reasons in such a machine. It should not be assumed that because theceiling is high the machine has a rapid climb. (As a matter of fact, the climb is sufficiently good, but not nearly so astonish-ing as the ceiling. The estimated climb to 3,000 ft. is eight minutes.) This will be appreciated when it is rememberedthat rate of climb is mainly a matter of light loading per horse- power, while high ceiling is chiefly attained by having a goodexcess of horse-power available over horse-power required, even if the power loading is somewhat high. Thus, in thecase of this machine., the power loading (on 20 h.p.) is 22-9 ibs./h.p., which is a reasonably high figure, and yet the high resistance to torsion. Mr. Shackleton has, in a way, com- bined the two systems, with a touch of Junkers multi-spar construction, in the new monoplane, and as this form of spax is, of course, applicable to other machines as well, its con- struction wiil be dealt with at some length. Fundamentally the spar consists of three stringers, running across from wing tip to wing tip, and covered by three-ply wood. The apex of the triangle thus formed is at the top of the wing section, and the base at the lower surface. It might be objected that a better plan would have been to reverse the position, standing the triangle on its apex, and thus have got more material on the top of the spar, where, as regards the cantilever portion, the top is in compression. While this would be so the advantage would have been smaller than might be expected at first glance owing to the configuration of the usual wing section, i.e., approximately flat bottom and deeply cambered top surface. This would reduce the overall depth of the spar, and there might be little or no gain. On the other hand, the present arrangement has several practical advan- tages. Thus the flat bottom of the spar forms a very con- venient base for attachment to the fuselage. Writh the pilot placed where he is, the slope of the rear spar wall materially improves the view in a forward and upward direction. 169
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