DURAND— MECHANICAL ASPECTS. 175 



The surface does not form a large fraction of the total weight 

 and saving here is not relatively as important as in the framework. 



The substitution of metal for wood in the framing has long 

 since attracted the serious attention of aeronautic engineers, and in 

 certain recent designs the problem has been worked out with ap- 

 parently a high degree of success. These results indicate the prob- 

 ability of an increasing use of steel for parts which have hitherto 

 usually been made of wood. The peculiar qualities of stififness and 

 resilience combined with readiness of shaping and forming have 

 combined to make wood broadly speaking the standard material for 

 the skeleton or framing of the wnngs and body. It seems, however, 

 a foregone conclusion that some parts now made of wood might 

 with advantage be made of the best modern alloys combining strength 

 with light weight. The extent to which this can be wisely done can 

 only be determined by trial, but it seems probable that perhaps im- 

 portant savings in weight may be made by a judicious substitution 

 of metal in certain elements of the structure. 



The outlook for the future calls for new and improved metal 

 alloys with certain of the physical characteristics of wood, as nearly 

 as may be realized, and with proper form and proportion securing 

 the development of the same strength with saving in weight. 



The use of steel wire and cable for ties is standard and prac- 

 tically universal. These elements form a relatively small part of 

 the total structural weight. It seems hard to imagine material 

 superior to the best modern alloy steel wire, but there seems no 

 reason for assuming that such material represents the last word in 

 the wire-makers' art and if we may anticipate new and improved 

 steel or bronze alloys, such material will provide the necessary 

 tension elements with some slight saving in weight. 



Fastenings have been made the subject of much study, experi- 

 mental and otherwise, and the field is still open for further im- 

 provement. Here again the total weight is relatively small, but 

 there may well be a chance to save something in weight and at the 

 same time add to the security and integrity of the design as a whole. 



Broadly speaking, there seems small ground for anticipating any 

 profound change in the near future in the schedule of materials 

 best available for the designer of aeroplane structures. Gradual 



