358 SECTIONAL TRANSACTIONS.— G. 



The outstanding feature of the air movement observations, which were made under 

 ' motoring ' conditions, was the difficulty experienced in producing indiscriminate 

 movement as opposed to rotational movement. It was found that there was a strong 

 tendency for the air to swirl about a vertical axis and even when a predominating 

 indiscriminate motion was produced it was accompanied by varying degrees of swirl. 

 It was also found that with rotational movement the pressure was least and the linear 

 velocity greatest near the centre, which seems to indicate that the motion approximates 

 to that of a free vortex. The presence of inward radial flow near the surfaces of the 

 cylinder head and the piston was also demonstrated. 



Turbulence was found to have a marked influence on H.U.C.R. Thus, the H.U.C.R. 

 of an ordinary petrol varied from 5-7:lto 7-9:1 according to the type of vanes employed, 

 the former value being obtained with indiscriminate turbulence and the latter with a 

 purely rotational movement. It would appear that, in this connection, the initial 

 direction of the entering air is the determining factor rather than the initial speed. 



Swirhng motion was invariably accompanied by very harsh running, particularly 

 at the higher compression ratios, whereas with indiscriminate turbulence the running 

 of the engine was exceptionally smooth. 



A possible explanation of the diSerence in the results obtained with swirling and 

 indiscriminate turbulence is put forward and a suggestion is made that these experi- 

 ments might form the basis of a design for a new type of combustion chamber. 



Mr. C. F. Abell, O.B.E. — Some recent Progress in Air-cooled Aero-Engine 

 Development. 



The chief factors controlling the development of aircraft engines are : — ( 1 ) The 

 weight per horse-power ; (2) frontal area and head resistance ; (3) effect of high 

 altitude conditions on engine performance. 



These points are discussed and the progress of the air-cooled engine traced from 

 1919 when the aero engine was well advanced owing to the demands of the war, to the 

 present time. 



Several different types of air-cooled aircraft engines are considered and their 

 chief points noted, with illustrations, as follows : — (1) Radial type ; (2) in line type ; 

 (3) ' Vee ' type ; (4) hexagon type ; (5) ' H ' type. 



While manufacturers of air-cooled motors have been engaged on the work of 

 development in their own particular spheres, research organisations, both in this and 

 other countries, have carried out manj^ investigations into aerodynamic questions 

 affecting the drag of air-cooled engines. 



The special forms of cowling to which two such developments have led are 

 illustrated and explained. In both cases considerable reduction in drag is obtained 

 with consequent increase in efficiency. 



In connection with engine development, some interesting detail points of design 

 actually in production with modern air-cooled engines are reviewed and illustrated. 

 These include : — 



(1) The development of a split single-throw crankshaft to take the place of the 

 normal solid crankshaft. 



(2) The manufacturing problems in connection with crankcases, and the factors 

 which led to the abolition of castings in favour of drop forgings. 



(3) Developments in cylinder design from the sohd steel cyhnder with integral 

 combustion head, to a later cylinder employing a loose head, formed by a light alloy 

 forging. 



(4) Increase in engine performances at high altitudes and methods adopted to 

 secure these. 



The paper is illustrated with a number of slides, showing details of the components 

 discussed. 



Dr. S. J. Davies and Mr. E. Giffen. — The Present Position of the High- 

 speed Heavy-Oil Engine. 



The progress of the heavy-oil engine towards higher speeds of revolution in the last 

 five years has been such that it is to-day in direct competition with the petrol engine 

 for land transport, aircraft, motor boats and similar purposes. 



