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Aviation History
1936
1936 - 0053.PDF
JANUARY 2, 1936. FLIGHT. 27 MODELS Autogiro Problems : Progress in Petrol Power Units By M. R. KNIGHT A Successful Autogiro ALTHOUGH a model Autogiro flew before a full-scale version did so, and, in fact, indicated the line along which success was to be obtained, the attendant difficulties and limitations have, until comparatively recently, resulted in the type being neglected by the model-maker. Foremost among the experimenters now at work is Mr. S. R. Crow, of the Blackheath Model Flying Club. His model, illustrated on this page, holds the British hand-launched Autogiro record with a flight of 37 sec. The average duration, however, is about 20 sec. Modest as these figures may sound to those familiar with the capabilities of the lightweight duration class of model, they represent a very real achievement. Even with the more orthodox type of model, such factors as the varying power output of the rubber motor, and the absence of a controlling hand during flight, complicate the problem of securing equally satisfactory power flight and natural glide. The Autogiro presents all the limitations of the ordinary model aeroplane in the highest degree, plus the problem of autorotation. As will be seen, the Crow Autogiro has a three-bladed rotor, and is wingless. It is a lightweight, constructed almost entirely of hard balsa wood, and covered with the thinnest of jap tissue, clear doped. The rotor differs from that of the full-scale machine in several ways. Very wide blades are used, their mid-spars of birch terminating in simple wire attachments to the rotor hub, and the flexibility of the structure being relied upon for such variations in blade incidence and coning as are entailed by sustained, stable flight. The rotor axis is tilted rearwards at a greater angle than in full-scale practice, and the blades are mounted at an angle negalive to the axis. The rotor pylon is built up out of 0.75 mm. three-ply, and can be slid along the fuselage, to which it is attached by thin rubber strip. This facilitates trimming, and is'Still more valuable as a shock- absorbing device. The lateral tilt necessary to offset rotor torque can be increased or decreased by varying the amount of packing beneath the base of the pylon. The blades have leading- and trailing-edge spars of balsa and balsa ribs, which are set farther apart towards the tips. The airscrew is given a considerable degree of down-thrust. The tail-plane lacks the upturned tips of the full scale machine. Normally the rotor revolves when the model is held level, facing the wind, but on a calm day, or indoors, the "pilot" walks forward until rotation is secured. In R.O.G. flights the blades commence to rotate as the model moves forward. The main dimensions arc as follows: rotor blade span, 7-lin. ; chord, 2jin. ; height of pylon above fuselage, 3|in. ;, height of fin above fuselage, ijin. ; tail plane span, i2iin. ; chord, 4H11. to 2jin. ; fuselage length, i5|in. ; wheclbase, 12111.; airscrew diameter, gin.: pitch, gin.; maximum blade width, lin. Petrol Power Progress /CONSIDERABLE interest having been expressed in the ^ Willis monoplane described in Flight of November 7, a brief outline of the progress of the petrol-engined model in this country will perhaps be welcomed. It will be news to many that a successful petrol model was produced as far back as 1908—by Mr. Q. Stanger. In April, 1914, he established a rise-off-ground record of 51 secontls with ft Canard biplane weighing io|lb., and powered by a 60 c.c. vee-twin-cylinder four-stroke weighing 2lb. 120Z. This engine ii still in exisience, though out of commission, and Mr. Stanger is still a member of one of our foremost model clubs. His record remained unchallenged for eighteen years, due to the War, the post-war slump in model aviation, and, doubtless, the inconveniently large size (and expense) of model necessi tated by the heavy engines of the period. fn May, 1932, Capt. C. E. Bow den raised the record to 71 seconds with his tractor biplane Kanga. This model had heavily staggered cantilever wings and was fitted with a modified model boat engine, a Wall single-cylinder 28 c.c. tour-stroke. This versatile enthusiast seems to have been the prune mover in the revival of the petrol model, and in secur- The Crow Autogiro : The rather wide divergence from scale has been found necessary in order to achieve success ; a previous model, exactly to scale, gave the constructor very disappointing results. ing the production of the really small and reliable I.C. engine which has led to the present popularity of the petrol model. He induced Mr. E T. Westbury to design the first of the modern engines, the 15 c.c. Atom Minor two-stroke, which was eventually modified and put into production by A. E. Jones, Ltd. With Blue Dragon, a Oft. span high-wing monoplane with a sharply tapered wing and fitted with an Atom Minor engine, Capt. Bowden established the present R.O.G. record of 12 min. 48 sec. The 6|lb. model took off from Fairey's Aerodrome after a run of about four feet, climbed steeply in a spiral and disappeared in cumulus cloud at about 2,000ft. It was found undamaged on a farm ten miles away. Capt Bowden's successful petrol models have included oiplanes, high-wing and low-wing monoplanes, an Autogiro, and a flying boat An inverted Atom Minor is also the- power unit in the Willis monoplane, the present holder of the Sir John Shelley cup for power models. Mr. J. W. Bishop's 10ft. span biplane Endeavour (30 c.c. two-stroke), the outstanding features of which are slow, steady flight and exemplary landings, flies consistently and often. Even scale modellists have succumbed to the attraction of the petrol engine. Mr. Bishop's initial effort was a Comper Swift, which, during its short and gay life, flew in interceptor fashion. More sedate is the 5ft-span Moth Corsicanfly, built by Messrs. J H. Collings, R. Bennett and J. A. Andrews, with which numerous flights have been obtained. The weight is 6|lb. The 15 c.c. two-stroke engine was designed and constructed by Mr. Andrews. Both these models corre spond very closely with the prototypes in the matter of main . proportions, the difficulties being less serious than in the case of rubber-driven scale models. A spectacular flight was made last July by a- high-wing monoplane fitted v\ith a Comet 18 c.c. two-stroke, both the work of Mr. A. E. Brooks, of Leicester. The model, which was of 6ft. span and weighed 8|lb., took off from a meeting of the Bournemouth Model Aircraft Society, at Cranborne, North Dorset, and in a few minutes was out of sight. Next day the crew of a coasting steamer retrieved it from the sea off Cowes, 35 miles away! S.M.A.E. Annual General Meeting THE annual general meeting of the Society of Model Aero nautical Engineers (the body appointed by the Royal Aero Club to govern model aeronautics in Great Britain) will be held in the drawing-room of the Y.M.C.A., Tottenham Court Road, W.C.i, on Januarv 16, at 7.30 p.m. All who are eligible to attend are urged to do so, as a reorganisation scheme, which may have a far-reaching effect, is to be voted upon.
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