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Aviation History
1921
1921 - 0540.PDF
of resistance to bending, and inside which the oil channelleading to the piston-pin can easily be located. The engine fittings are arranged" on the principle that thecomparatively inaccessible end at the propeller should be left as free as possible when fhe engine is mounted on anaeroplane. On the other hand, the constructional length of the engine should be curtailed as much as possible, in 0/oprom of OsbhgSyjtvfn. „.•'•. .."-•". •• . ...... f Figs. 16 to 5. ••. ' * i - " order to avoid any detrimental influence on the(turning ability; of the aeroplane. For the same reason, the carburettors, which are joined in couples each supplying three cylinders,and the magneto driven by the camshaft are located in the space between the cylinder rows, while the spark-plugs, withthe pumps for fuel, oil, and water, are placed at the rear end • :• of the engine within reach of the pilot's seat.In lubricating the engine, the process of continually adding •' small quantities of fresh oil to the ever-circulating oil hasbeen replaced by simple rotary lubrication ; the piston pumps formerly used are now replaced by gear-wheel pumps, whichare far more easily driven and are of simpler construction. The former prejudice against simple rotary lubrication, basedon the more rapid wearing of the crankshaft bearings through carbon and metal dust impurities in the oil, has been proved , to be unjustified in experiments made with power-impelledvehicles, while in the case of aircraft engines, in particular, the frequent renewal of the entire oil supply must be takeninto account. As applied to gear-wheel pumps, its reliability was at first considered doubtful, as the gear-wheels must becaulked at the sides in the case, and the caulking cannot be : replaced later. Experience has shown, however, that thegear-wheel pump supplies sufficiently high oil pressure even after long usage, and that it never loses its tightness to suchan extent as to allow the oil to flow back into the crankcase out of the oil reservoir through the pump-case when the engineremains stationary for any length of time, and by so doing to involve difficulties at starting. A safety device, speciallyconstructed to remedy that defect, consisting of a piston kept open by the oil pressure and weighed down by a spring, cantherefore be dispensed with. AUGUST II, tgzi The triple gear-wheel pump located at the lowest part ofthe crankcase consists of three separate pumps (Fig. 25), one of which (I) drives the oil through a nozzle collector intothe distribution piping, which is installed on the outside of the crankcase, and is therefore easily accessible for cleaningpurposes (Fig. 1). This method of installing the distribution piping is now preferred to that of locating it in the crank-case and connecting it with the bearings by transverse boring, experience .having proved that cast aluminium has a strongtendency to become porous when the distribution pipe leads into it, and that the boring in question soon loses its tightness. From the principal bearings, the oil flows under pressure,through tubes bored in the crankshaft, to the crank-pin end, then through the tubular interior of the connecting-rod to thepiston-pin, which is hollow and'thus distributes the excess of oil on the inner surface of the cylinder swept by the piston.The regularity of the lubrication functions is checked by a manometer at the distribution piping, the pressure of whichshould never be lower than o • 5 atm. Two more oil pumps (I and II) draw off the oil used in theengine, to the front and rear ends of the crankcase, and force it back into the oil-tank. This prevents the oil from collectingat one end of the engine during the climb or in the course of a nose dive, and also from oiling the cylinder excessively.A method proposed by Benz and Co. for the construction of the oil tank is shown in Figs. 26 and 27. Its corrugatedouter wall forms a part of the fuselage covering, and is therefore effectively cooled by the wind caused by flight. The oilfirst enters at a by means of a partition wall, and reaches the jacket b of the tank, where it is strongly cooled. If the jacketis full, or coated with congealed oil through intense cold, the oil passes through the projecting rim c into the interior of thetank, from which it can flow, in turn, through the aperture d into the piping leading to the oil-pump. The tank must beprovided with a ventilating orifice of about 5 cm. in widt h .from O//Pump Venti/oHnaPip* O/J rank w/tn ftod/otor. Z6. Chon£S o*»rs*//ihch cock. Figs. 26 to 30. so located that the oil cannot run out either in climbing or insteep gliding flight. A horizontal sheet-iron collective piping is attached toeach of the oil vapour exhaust pipes (Fig. i) in order to carry off the oil vapour from the crankcase. From them, the vapouris carried downwards and into the open air by means of pipes 54°
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