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Aviation History
1920
1920 - 0485.PDF
APRIL 29, 1920 MODEL AEROPLANES NOTE.—^4W communications should be addressed to the Model Editor. WE wilTconsider this week the various applications of elasticrubber for the propulsion of model aeroplanes. As regards the motor itself, there can be no doubt that it is the simplestand at the same time for power developed the lightest obtain- able. There are, however, three great objections to it.In the first place it is extremely perishable, especially the purest kinds. This is noticeable by the rubber becomingdry on the outside, and cracking. Secondly, the power commences to drop gradually from the moment the motor isstarted ; and consequently there arises the third point, viz., the extremely limited time over which the power is spread. The simplest way in which rubber can be applied to drivean aeroplane is in skeins of cord after the manner shown in the models with which I commenced this series—viz., by a hookat the front of the machine and another on the end of the wire propeller spindle. There is only one objection to this—namely, the rather large amount of friction at the bearing when the rubber is fully wound, caused by the pull of the twistedrubber between the two points. The friction of course tends to retard the revolution of the propeller and reducejthe initialthrust and speed. When this arrangement is employed the bearing should be kept well lubricated with thick machineoil. Friction may be reduced by fitting a ball thrust bearing.Such a bearing may be considered only worth the fitting on fairly large machines, as they would be very fiddling tomake for tiny flyers. As an alternative, I give a dra^fing (Fig. 1) of an arrangement suggested by Mr. A. J. Hando— Sim flic G Ranee* Mofon , Fig. 1. in a letter to FLIGHT some time ago. It will be seen that two'*'skeins are used, both connected to a double-hooked spindle placed at the centre of the frame. Both rubbers should be of exactly the same length and strength, and if this is carefully attended to friction from the effects of rubberpull is quite eliminated, the tension on one skein being balanced by the pull of the other. It is true that the skeins are of only half the length of anordinary skein fitted in the same frame, and consequently the two rubbers together will be fully wound when only halfthe number of turns have been given. Consequently, if the two cogged wheels at the centre connecting the rubber to thepropeller shaft were the same size, the propeller would only make half the number of revolutions possible with a singleskein. The remedy is obvious ; a reduction of one to two must be given, that is to say, the pinion in the rubber spindlemust have twice the number of teeth given to the pinion on the screw shaft. This leads us to another possibility, thatof further utilising the principle of gearing by making a further reduction, say lour to one, at the same time addingmore strands to each of the skeins of rubber. The propeller shaft may have six or eight teeth, and the rubber spindle 24 or32 teeth ; by this means either very long flights with large diameter long pitch screws may be obtained, or a high thrustwith small screws. Geared /Voto Fig. 2. In Fig. 2, I show a compact geared rubber motor madepossible by Mr. Hando's ingenious suggestion. In this motor eight short powerful skeins of rubber are employed, gearingdown to the propeller on a ratio of, say, 6 to 1. The frame- work should be made from sheet aluminium of stout gauge, ofsufficient strength, and the pinion and gear-wheels of brass, the latter lightened as far as possible by cutting away to formspokes. Such a motor would possess the advantage of being self-contained like a piece of clockwork, and could, of course,be so placed on the model as to adjust the centres of pressure and gravity. GENERAL SYKES AT THE SUPERMARINE WORKS WITH a view to keeping in touch with the latest develop-ments of flying boats for civil aviation and firms building and using them, General Sykes, Controller-General of Civil Avia-tion, and Colonel Beatty paid an official visit to the Super- marine Works at Southampton on April 17. They were met at Southampton Station, and were con-veyed to the works, where, after a brief inspection, General Sykes requested to be taken out in one of the Supermarinecommercial four-seater flying boats to make a survey of the Southampton Water, the Isle of Wight, Spithead and theSolent. This was carried out by the firm's head pilot, Captain Hoare, who landed the General on the River Itchen amongstthe ordinary shipping that frequents Southampton at full water. This was followed by a series of demonstrations ofhow easily the Supermarine flying boat was manoeuvred, amongst ocean-going and river-going traffic in confinedwaters. Amongst other demonstrations, the flying boat, with the General on board, was stalled and let fall back into thewater from a height of about 15 ft., and was taxied over stretches of water at a speed varying from 40-60 knots, doingturns and being navigated, showing her handiness on the water at these speeds amongst the river traffic, also demon-strating the lengths of a run required for pull-up, the short- ness of which is very necessary, and is a particular featureof their boats. Practically the whole of the actual demonstrations werecarried out on the Itchen River, a branch of water running off the Southampton Water, which is crossed by floatingbridges and has a continual up and down stream run of traffic. The machine which the General went up in was one of thestandard flying boats, fitted with 160 h.p. Beardmore engine, which, with 3J hours' fuel and petrol, sea anchor, groundanchor and line, bilge pump, boat hook, semaphore flags, megaphone, engine spares, tools, etc., carries a useful loadof 480 lbs. It was fitted with dual control, a speciality of these machines, they being convertible in one hour from acommercial machine carrying three passengers to a dual- control school machine. This machine has been in daily usefor a period of six weeks, in training pilots of the Royal Norwegian Naval Air Service. After lunch on board the managing director's yacht, aninspection of the works was made, the General being shown two new types of machines which are under construction,which form part of the firm's new policy and which will probably be shown at the forthcoming Aero Show. 485 • #5
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