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Aviation History
1910
1910 - 0305.PDF
APRIL 23, 1910. [/UGHT] THE COOLING OF AN AEROMOTOR. By H. S. ROWELL, A.R.C.Sc. (Lond)., Wh. Sch. THE efficient cooling of an aero motor has a very great influence on the reliability of running obtained. This statement may seem too obvious for publication, but few people seem to have a just appreciation of the effects of uneven or irregular cooling and the consequent distortions produced. It must be evident that with a cylinder of unsym- metrical form, uneven' cooling may lead to a non- circularity of cross-section or lack of axial straightness. Such distortions as these would clearly tend to interfere with the smooth working of the engine and might cause breakdown. How can we secure efficient and uniform cooling ? Fig. 1. The methods of cylinder cooling usually employed differ chiefly in the jacket medium used ; broadly speaking these are three :— (a) air, (b) water, (/) oil and other liquids. The third class is one which is not yet developed. Regarding the other two classes it might be well to mention that of about forty different types enumerated in Mr. Critchley's paper (" Proceedings of the Institution of Automobile Engineers," November, 1909) three-fourths are water- cooled and the remainder air-cooled. Of these air- cooled motors some are of the Gnome type in which the cylinders rotate bodily round the crank-shaft as a centre. Why, then, do we find air-cooling so unpopular, in spite of the undesirable weight which water cooling entails? Fig. 1 gives us an idea of the conditions prevailing round a cylinder cooled by the passing air.* It is seen that the leading side, A, is in contact with a continually changing mass of air, while the opposite side is in contact with a mass of dead air, so to speak, which is changing comparatively slowly, and which is, moreover, warmed by the air flowing past from the region of A. * The more elaborate systems of air cooling—involving the use of a fan and air channels—which have become so popular in America, are omitted here as being inconvenient of application to the aeromotor. What we must do then is to render the conditions round the cylinder more symmetrical. Fig. 2 shows diagrammatically an arrangement designed to give more even cooling; J and J1 are jets (moving with the engine) which direct streams of comparatively cool air on the rear parts of the cylinder. The resistance of these jets to motion should not be very great. Fig. 2. Of water cooling we need say little here. The rate of change of density of water with regard to temperature, at the temperature of a petrol motor jacket, is con siderable, and hence we have very vigorous convection of the cooling water. Thus, no great variation of temperature—from point to point of the cylinder—can last very long. The temperature being fairly uniform, the cylinder retains its original form, or nearly so. With regard to the use of oil and other liquids as cooling media, little can be said of a definite nature from the point of view of practical experience. The chief physical properties to be desired in a cooling medium are : low specific gravity, high diffusivity, and high convectivity. By diffusivity we mean the ratio of specific conductivity to the specific heat or thermal capacity per unit volume ; and by convectivity we mean the power of conveying heat by virtue of motion in the fluid. Convectivity is largely dependent on the variation 01 density produced in the liquid by changes of temperature. A little reflection will serve'to show that the higher the diffusivity and convectivity are, the more effective as a cooling agent will be each pound of liquid. Oils and such liquids would probably be more convenient than water for thermostatic arrangements, and thus we might be able to keep the cylinder at some definite desired temperature more easily with oil than with water. TOURING BY BIPLANE. MR. HENRY FARMAN has added yet another exploit to those which already stand to his credit by flying with a passenger from his new aerodrome at Beauce to Orleans. About 6.30 on Sunday evening Mr. Farman invited M. Robert Caudvilliere to take his seat in one of the new Farman machines which have been specially built for passenger carrying, and with all the necessaries for camping, the two set out on their excursion. Between Toury and Artenay the main road was followed, and then a beeline was made for Orleans, where a landing was effected in the Chevinny Camp, not far from the city. The machine was then anchored for the night, after its flight of 50 kiloms. On Monday Paulhan set out alone to continue the journey to Elois, but owing to the direction of the wind he altered his course and eventually landed at Arcis-sur-Aube, the distance flown being between 180 and 190 kiloms., a world's record for cross-country flying. On the following day Paulhan continued his journey, having Chalons as his objective, and he landed there after a flight of 1 hr. 10 mins., the 80 kiloms. being traversed without a hitch. Most of the time, as in his flight on the previous day, Paulhan kept at a height of 300 metres, although once or twice he soared to just about twice that altitude. Altogether in the three days the machine covered about 320 kiloms., or well over 200 miles, approxi mately the distance from London to Manchester. It was, therefore, excellent training, in view of Paulhan's early attempt to win the Daily Mail £10,000 prize. 303 C
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