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Aviation History
1920
1920 - 0383.PDF
APRIL I, 1920 MODEL AEROP o BVFJ.CAMM NOTB.—All communications should be addressed to the Model Editor. Wing Construction The subjoined drawings show a new way of constructingcambered wing framework. It is to cut the ribs to the correct camber, and then to let the spars in, as shown black. The usual metfao'd of bending the ribs to the camber is inefficient, because the bottom camber is thus equal to the top. This method, however, whilst it does not add to the weight, permits of a more efficient construction and also double surfacing. front Spar ]?ear 3pah Ffficieat Section I also show an efficient wing section for models, and spar sections which lend themselves to the construction of cambered surfaces more readily than do the ordinary rectilinear section. Easter Model Flying Will those model clubs holding an Easter meeting please acquaint me with the fact, as I should be glad to visit clubs in London and its environs as far as time permits. The Groves Compressed Air Plant Mr. H. H. Groves has forwarded his newly-designed com- pressed air plant for model aeroplanes recently shown at the British Industries Fair, and in all points I think the plant excellent. That flimsiness so typical of the several plants formerly on the market (with few exceptions) is markedly absent. It is designed on the double-acting principle, with a link motion connecting the crank to the pistons. The cylinders are rigidly made with separate heads, secured against pressure by means of buttress threads. The compression is such that one can scarcely run the engine over by the crankshaft in the reverse direction—yet friction is quite low. The well-known leather cup-washer principle has been embodied in the pistons. We recently inflated the container (substantially yet lightly built), and found that it maintained pressure for over three hours, so low has leakage been re- duced. The valve, too, is singularly airtight, and throughout every ounce of pressure is made full use of. The total weight of the plant is 14 ozs. barely without the H.P. Paris and Brussels Air Services ON the Handle ' Page Continental Air Services between September 2, 1919, and March 20, 1920, inclusive, 1,114 passengers and 58,123 lbs. of freight have been carried over a distance of 81,929 miles. .-..-' A Handley Page machine left Paris for London on the 18th inst., with five people and 1,250 lbs. of freight on board. Flying in the face of a strong wind at a height of about 1,000 ft., it reached the coast where it ran into fog with ar air-screw. I found that with an 18-inch screw an effectiveflight of 60 sees, should be easily obtained, with the glide which would undoubtedly follow. The writer is at presentmaking a tractor machine for the plant, and will announce results in due course. On a bench test a thrust of 5J ozs.was obtained—a truly remarkable result. Mr. Groves is to be congratulated on having satisfied nearly all of therequirements entailed by such a plant, and to have em- bodied them in a design which is an engineering job. Ishall refer to the plant in greater detail in due course. Building C.A. MotorsAccuracy in all portions must be aimed at. A y^^th part of an inch in some of the portions will make all thedifference to the engine's efficiency ; more especially is this so with the valves, which must be an air-tight fit. A smallDrummond lathe is quite suitable for turning the various parts. Balance, too, plays a part of some importance inthe efficient running of a C.A. motor. In connection with the latter it must be remembered that a piston, for instance,may only be a fraction of a dram heavier or lighter than the remainder, but under revolution a very considerable un-balanced force is set up, resulting in vibration and uneven torque. It is desirable that almost perfect reciprocationbe obtained, otherwise the motor may only give 30 per cent, or 40 per cent, efficiency. Some of the commercial motorsI have seen show an appalling lack of balance, albeit many of them are of sound design. There has been a general avoidance of rotary engines, owingto a reputed wastage of power, but provided that the pistons are made a free fit within the cylinder and a suitable meansis employed for packing them to ensure air-tightness, they are quite as efficient as the stationary ones I have seen. Inthe latter respect, the familiar cycle-pump principle has been utilised to attain this end, and has been found to work ex-tremely satisfactorily. The idea of its use is not new. I think the French first introduced it in some of their rotaries.By its use much circumferential friction may be eliminated between piston-surface and cylinder-walls, because theformer need not be made an air-tight fit, since the powerful blast of air let into the cylinder-head at high pressure ex-pands it, and so prevents leakage. Testing C.A. ContainersIn order that there shall be no leakage of pressure the con- tainer must be inflated to a pressure per square inch higherthan it will normally be called upon to withstand, and en- tirely immersed in paraffin. Many leaks are bound to existat first, and will reveal themselves by causing a series of bubbles to issue to the surface of the oil. These must bethoroughly stopped up, as the smallest leak will make a difference to the power developed by the motor. Do notuse spirits of salts, otherwise within a couple of days the container will be quite useless ; Fluxite or powdered resinis much better, as it leaves no deleterious acid residue. The most likely place for leaks to occur is along the seams, or ata place where the thin foil has been cracked or creased. A careful search must be made for them, because the minutestleak becomes enlarged after the container has been inflated two or three times. Thin sewing-machine oil diluted with paraffin should beused to lubricate such motors. When a plant has been com- pleted the thrust should be weighed on a spring balance,so that a model of suitable weight and area may be designed for it. . visibility of only 10 to 14 yards. The pilot, however, flewthe Channel, the journey occupying 1 hour 5 mins. On emerging from the fog after crossing the Channel, themachine ran into fine but very windy weather and safely landed at Cricklewood after a non-stop flight of 5 hours 10 mins.Three other single engine machines left Paris about the same time and were forced to return, being unable to cross theChannel; the Handley Page was the only machine which completed the journey on that day. 7 . ' 383
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