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Aviation History
1920
1920 - 1317.PDF
DECEMBER 30, 1920 \ - ••' I VI NOTE.—^4// communications should be addressed to the Model Editor. A stamp should be enclosed for a postal reply Weight-Lifting MonoplaneTHE drawings show the weight-lifting monoplane built ;and flown by the writer. Its best duration loaded was 35 sees.,unloaded 28 sees. The undesirability of too light a loading is manifest from these results. The loading in this instance•with the dead weight was 6 oz. per square foot, and the dead weight was 4 oz. (the rules of the competition for whichit was intended stipulating that the dead weight must equal a quarter of the total weight of the machine, the minimumweight of the latter to be 1 lb.). It flew much better with the •dead weight than without it, nor could it be coaxed into at have a tendency to throw the balls farther than the stop willpermit. A little trial and error with the length of travel of the sliding sleeve and the weight of the balls will soon reveal themost suitable arrangement. Such an adaptation of Watt's governor would be extremely useful on model hydroplanes,where a large quantity of elastic is required in order to over- come the extra resistance of the floats. It also eliminatesthe necessity for gearing down. With regard to compressed air, such an arrangement couldbe made to work behind the screw with stationary engines, or be attached to the engine itself with rotary ones. It could. T iH Sfior — — — _ J rudder mechon/rm A? ofterafe safety staAv cresrtor free on shaft' w~\ /7^.2. shaft foi-ruiief east equalling its loaded performance when unloaded. I donot think that a lighter loading than 3J oz. per square foot should ever be used ; a lighter loading makes the machine•extremely slow and susceptible to the slightest wind, apart from the fact that the elevation is difficult to adjust owingto the rush of power at the start. If the machine is adjusted for correct elevation when the screws are half unwound,.and the full number of turns then applied, the machine will be over-elevated, and if it is adjusted to fly correctly• -with full turns, it will appear to be under-elevated when the initial burst of power has subsided- More heavily-rioaded machines are not so difficult to adjust. Governor for Rubber and Compressed AirThe great objection to rubber and compressed air is that the thrust or power commences to drop directly the modelis released for flight. It has occurred to me that Watt's governor, as used on steam-engines and now adapted tomany other mechanisms, including the gramophone, would make an excellent reducer either for the rubber motor orfor compressed-air engines. The original governor design is shown in Fig. 1, and an adaptation for rubber motorsis sketched in Fig. 2 ; it will be noticed that when the power is high the ball balance weights fly outward and increase thediameter of what is virtually a flywheel ; and as the power decreases the balls revolve through a smaller- radius, andhence tend to stabilise the revolutions—to keep them con- stant. The total weight of such an apparatus need notbe more than 1 oz., but sufficient length of slide should be allowed so that the balls may fly to their correct radius in•consonance with the power applied. The point I wish to make clear is that if too short a sliding motion is allowed thereducing effect will be lost, because centrifugal force will moreover, be made to actually operate a reducing valve, byinterposing a spring between the stop and the sliding collar, so that the reducing valve remains closed whilst the machineis stationary. Many weird reducing valves have been advanced for use on compressed-air engines, but here, I think,lies the solution to the difficulty. The Need for ResearchI have many> times in these columns impressed the need for more research and more care in the tabulation of results,and perhaps the fact that model aeroplaning does not attain to the popularity accorded to fretwork (!) by the younger Iryis due to the easily satisfied and ephemeral desire to watch a model fly. This desire .does not last. There is too muchcultivation of the build-models-to-fly-them element by the clubs. How much more satisfying it is to know the whyand wherefore, to know just why that extra strand was required, or why that other pair of screws or wings is moreefficient. The hobbies of model locomotive and model yacht building are almost an exact science ; their protagonistshave carefully investigated every possible phase that lent itself to research. Only a small band indeed tackle modelaeroplaning from this standpoint. It is just as interesting to conduct whirling arm experimer ts, or find the lift drag ratioof a given wing section, as it is to watch a model flying over the tree-tops.Again, even with the flying of models, the same laissez-faire spirit exists. It is only in occasional cases that one seescarefully recorded the performances of each> model built, with results of alterations, etc., noted. Such records makeinteresting reading when in retrospective mood. It is hoped that the K.M.A.A. will not disregard this matter, which is of cardinal importance to the whole movement. ,r 1319 •-.*. \ •"'-••
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