THE FORESTER. 205 



integral part of these tests, the efficiency of various kinds of hide and 

 casein glue was determined. , Later m the year, assistance was 

 requested in the design of a win^ beam, or the development of a 

 type suitable for very large macnines, with spans of 125 feet or 

 more. Special series of tests were made for this purpose, and a 

 type was developed which embodies sound mechanical principles 

 and is remarkablj light for its strength. 



Much specific information was needed by the- Army and Navy in 

 regard to the struts being used on various machines, and compre- 

 hensive tests were made by the laboratory upon various kinds and 

 sizes. These resulted in the development of two noniniurious 

 methods of testing struts, whereby the actual strength of each strut 

 could be determined without injuring it. Machines for the proper 

 carrying on of these tests were also developed, and specifications 

 for the inspection of struts by this means were prepared. This 

 method of test is unique, in that there are no other types of structural 

 members which can be tested to their maximum load without 

 injury. In addition, methods for the calculation of the strength of 

 tapered struts and for the determination of the taper which would 

 give the maximum efficiency were developed. 



An entirely different kind of investigation was undertaken by the 

 laboratory to develop a type of strut for extremely large flying 

 machines. A radical departure was made from all accep^d types 

 of airplane struts, and a type selected which years of experience in 

 the construction of buildings and bridges had proved to be very 

 efficient in long light columns. This type was then modified to 

 suit aircraft needs, and developed to a point where it was much 

 stronger for a given weight than any other type of strut which has 

 so far been developed. Wind-tunnel tests on models speciallj 

 constructed for the jDurpose showed that the air resistance of this 

 type is less than that of any other tyY)Q so far tested. 



Elevator and aileron spai*s, which are the main structural members 

 of airplane control surfaces, are subjected to a peculiar kind of 

 stress known as combined bending and torsion, and their design 

 has always been a matter of guesswork. In the case of small 

 machines this' method of design appeared to be quite satisfactory, 

 but in the design of radically new types of great size need was found 

 for accurate data on the design and also lor a better type of spar, 

 which would be both stiffer and stronger for. the same weight. 

 Tlirough a unique combination of hollow wood and veneer construc- 

 tion, it was possible for the laboratory to improve the spars to a 

 marked degree, both in strength and in stiffness. As a result of 

 this development, the laboratory was finally requested to design a 

 complete control surface, embodying this new type of spar. 



Numerous and varied other aircraft developments were carried 

 out, among them being the development of a flexible plywood for 

 control surfaces and of a special mechanism for the proper operation 

 of these surfaces. This pl}^wood and the control mechanism are in 

 process of being fitted to one of the fastest machines developed 

 during the war. 



One of the major lines of research was the determination of the 

 effect of various kiln-drying schedules upon the properties of air- 

 craft woods and substitutes for them. Exhaustive tests have 

 furnished conclusive evidence that under proper control of tempera- 

 ture and humidity Idln-dried material of these species is as strong 



