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Aviation History
1920
1920 - 0031.PDF
JANUARY I, 1920 MODEL AEROPLANES NOTE.—All communications should be addressed to the Model Editor. •"•-'••• Revolutions of Airscrews •'- • THERE is a speed at which a given airscrew will give a maximum thrust and a minimum slip. If rotated beyond this speed it loses efficiency and slip increases, and it is therefore better to underpower the machine rather than overpower it, and gradually to work up to the correct amount. With single screw machines a tractor screw requires a slightly coarser pitch than a canard machine of similar weight, area, and dimensions, and generally requires more power. In those dim and hoary days of 1909, when tractors were avoided and the dictum was preached (very much an obiter dictum now, I fear) that tractors could never be consistent flyers, it was only the failure of model flyers to appreciate the principles and correlative functions of airscrews and aerofoils that was responsible for their meagre performances. The excellent results nowadays obtained are directly attributable to the cognisance of theoretical considerations. There are many clubs, even now, where the internecine conflict between the advocates of theory and practice continues. The point is that model flying for sport can only hold an ephemeral charm, whereas the study of aeronautics by this medium is absorbing in its interest. Three " Canard " Models Fig. 1 shows the model hydroplane built some time ago by the writer. It weighed complete about 11 oz. The mainspar was fretted out and covered with veneer, bracing wires being a great amount of tuning, and are seldom consistent flyers.It is essential that the swept-back wing should have a nega- tive angle on the tips for purposes of longitudinal stability.The stabilising vane is also essential on the nose of the machine. Houlberg's best recorded performance with thistype was 89 sees, (formerly the record). [To be continued.) Aero Models and Research Club MR. C. J. BURCHALL, the Acting Secretary of the aboveClub, writes :— " I wish to congratulate FLIGHT on its resumption of "articles on the ' Model' aspect of aeronautics. I know it has long been felt that aeromodellists have not received much attention, especially as regards ' up-to-date' machines. The old Finsbury Park Club (now known as the Aero Models and Research Club) managed to keep going through the War, although depleted in membership owing to many joining H.M. Forces. However, the few left carried on, and, I think, have, by keeping to one type of model, viz., the tractor mono, managed to interest themselves in the science of model aeronautics to some purpose. I have made a duration flight of slightly over 3 min. with a special ' high aspect ' 'bus, eventually losing it, for a week, it then being discovered at the top of a high tree right off the flying ground. A few general dimensions of this machine may be interesting. Length of spar, 31 in., which is of deep section very much like the body of a Fig. 1. Fig. 2. Fig. 3. necessary owing to its extreme lightness (4 ft. 3 ins. long, weight f oz.!). The flotational capacity was 33 oz.—three times the weight of the model, so that the floats were about one-third im- mersed. The capacity of hydroplane floats is calculated in the following manner: A cubic foot of water (1,728 cu. ins.) weighs approximately 1,000 oz. Therefore -—— X-~ = 19 cu. ins. to be displaced to float 11 oz., which is the weight of the machine. Now the floats would only just support the model if made with this minimum capacity, and since it is desirable that they should only be about one-third im- mersed, it follows that the flotational capacity should be three times as great = 3 X 19 = 57 cu. ins. The rule is that the constant 1-728 should be multiplied by three times the weight of the model to obtain the total cubic capacity of the floats. I think two front floats and one rear one are best for flotational stability. In designing the floats it is advantageous to make them at least support their own weight in the air. Floats of high aspect ratio and small depth have given good results. The hand-launched model biplane (Fig. 2) has obtained a duration of 100 sees. Most features of its design are manifest from the perspective drawing. Fig. 3 shows the so-called " tail behind " type, flown with great success by Houlberg. Such models require real machine (viewed in side elevation) except for its greater length ; span, 45 in., with a chord, central, of 3! in. tapering to 3 in. at tips ; tail of wire, 18 in. span, with a maximum chord of 3 in. Fin and rudder combined, of approximately 18 in. area, and fitted with a 12-in. four-bladed tractor screw, which has been used by the club with success for a time. The weight in flying order is 6 oz., and the machine is driven by six strands of average J-in. strip rubber. This machine is fitted with chassis and rises from the ground, but the greatest duration is obtained by hand-launching. Many other members can nearly equal this duration, a 60-sec. flight being quite a common thing. The remarkable thing about these models is their gliding range (we have had glides of 55 sec.) on quite small machines. Aero models still have a great hold of a section of the public quite as much as at any time prior to the War, and I think it only needs a little encouragement to enable it to come into its place as the most enjoyable and instructive of hobbies. Any enquiries from live aero-modellists regarding membership will be wel- comed. Our flying ground is still Parliament Hill, Hampstead. ' \ .>".'• -": Note ' ';• •'.' -; The model Editor would like to get into touch with the Model Aero Clubs, and also to receive their monthly reports for publication. Will they therefore write to him c/o FLIGHT ?
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