180 SYMPOSIUM ON AERONAUTICS. 



volume-adiabatic cycle. Thus far. however, structural and opera- 

 tive difficulties in various details of the process have prevented the 

 wide use of this cycle. It is, however, just now the subject of 

 special investigation at the hands of engineers of insight and re- 

 source and it may well be that the near future w^ill open up to the 

 aeronautic engineer this cycle for practical use in engines for aero- 

 plane service. If engines operating on this cycle can be made a 

 success in the operative sense while at the same time keeping the 

 weights down to the limits reached with the type now employed, we 

 may anticipate a wide field of usefulness for this cycle. 



Under the head of auxiliaries the chief functions are ignition, 

 cooling and lubrication. To these we may perhaps add, as rapidly 

 approaching the status of common acceptance, some form of start- 

 ing motor or device with wireless outfit, especially for military pur- 

 poses. 



Under ignition the insistent requirement is reliability, commonly 

 assured, so far as auxiliary equipment is concerned, by magneto 

 installation in duplicate. 



Cooling is normally by w^ater, except in the rotating type of 

 engine, where air cooling prevails. The principal problems here 

 relate to methods of circulating and cooling the water, security of 

 joints and connections, minimizing loss of water by boiling and 

 assurance of adequate supply for long life in air without going to 

 needless excess weight in water carried. 



The principal problems presented by lubrication are reliability 

 and simplicity of means employed, usually some form of pressure 

 or positive supply system. 



Further references to problems presented by auxiliary equip- 

 ment are more conveniently made under the next following head. 



Under the general head of construction, time will only permit of 

 brief reference to the following topics : 



Materials. 

 Design. 

 Fabrication. 



The materials employed are chiefly cast and wrought steel, cast 

 iron for some few parts, aluminum and bronze. In order to reduce 

 weights to a minimum forged steel is used for the cylinders or 



