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Aviation History
1914
1914 - 0097.PDF
AERO ENGINES AT THE design of engines of high power-weight ratio still continues to attract the attention of engineers, although the tendency to produce motors embodying some freak construction is not so much in evidence nowadays as formerly. At the Paris Show no fewer than 18 manufacturers exhibited 57 different engines, of which only one —the Austro-Daimler—was of other than French manufacture, and as is perhaps to be expected from the success which has been 100 h.p. 10-cyllnder Anzani engine. achieved in the past by air-cooled engines, the majority of makers have adopted this form of cooling. Without exception, this is true of all the engines of recent introduction, and because the disposition of the cylinders in star fashion renders the problem of weight reduction a comparatively simple matter, we find that this arrange ment is also employed, whilst all but the Anzani and the Edelweiss engines are of the rotary type. The absence of any British repre sentative is somewhat to be regretted, notwithstanding the proximity of the Aero Exhibition and the Military Aeroplane Engine Com petition, since there are several engines produced in this country which have performances to their credit that, to say the least, compare very favourably with those of the best engines manu factured abroad. The innovations made by established makers are principally in regard to the details of construction, and as such are less obvious than real. The reciprocating parts have been lightened, valve areas increased, the detail design has been simplified, made more compact, and improved by the natural process of evolution and as the result of experience, whilst a more extensive use has been made of the higher grades of materials now available, all of which should Teact beneficially by permitting higher powers, increased speeds and greater reliability to he attained. As regards the use of higher engine speeds, and gearing down the propeller (as is done on the Chenu, Renault, Panhard, and De Dion) within certain limits, there would not appear to be any insuperable objection to such a method, of obtaining a higher power-weight ratio, providing the engine has been designed for running continually at those speeds. The limit imposed is, however, reached when the loads upon the bearings at the moment of explosion are equal to the maximum inertia loading at the end of the exhaust stroke, which speed is attained when the engine revolutions are somewhere in the vicinity of 1,600 per minute, or, perhaps, slightly higher in modern work. This will also probably approximate to the most economical and reliable speed of the engine, providing that a sufficiently large charge of gas is drawn into the cylinder, since the bearings will, under these conditions, be subjected to the least maximum pressure. In this connection mention may be made of the absence of some form of oil cooler on any of these motors—a very desirable fitting on vertical, or any other tvpe of engine in which a large quantity of oil is carried in the crank-case, in order to keep up the viscosity of the oil on long distance nights and thus render failure through defective lubrication from taking place. Its utility would probably be limited on any PARIS SHOW, 1913. engine extravagant on oil, but not where the same lubricant is used over and over again. The limitations imposed on the bore of the cylinders where air- cooling is used is evident from the large number of cylinders now employed on high power engines of this type; which, whilst diminishing the falling off of power in the event of the failure of any one cylinder, as well as conducing to a greater uniformity of 200 h,p. 20-cylindcr Anzani engine. torque, and hence a better propeller efficiency, would appear to introduce increased complication and difficulty in locating defects should they arise. The problem of valve operation has been attacked in an exceed ingly novel manner on the two " monosnupape " Gnomes, whilst on the Esselbe and the S.H.K. motors a piston-sleeve combination has been adopted. The results of tests made with these engines under actual flying conditions are awaited with interest, as valve trouble is a most prolific cause of engine failure, especially in air-cooled engines. Anzani, This renowned firm of engine builders made an excellent display on their stand, as in addition to the large range of standard models, the three new engines—70, 125 and 200 h.p.—were exhibited. 120 h.p. Austro-Daimler engine.
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