468 REPORTS ON THE. STATE OF SCIENCE. — 1919. 



From the examination of a large number of commercial tubes, Major 

 Wylie suggests that reasonable values would be 



, _ internal dia. _ Length 



Both the above formulse agree well with the results of the author's experi- 

 ments. 



Investigatiwis of Stresses in Aeroplane Wing Frametvorks. 

 By Professor L. N. G. Filon, F.R.S. 



A series of interesting experiments were carried out during 1918, in 

 the Engineering Laboratory at University College, under the auspices of 

 the Air Ministry. The experiments were carried out by Mr. Chakko and 

 Air-Cadet McGowan, under the general supervision of Major A. E. Low, 

 R.A.F., and Major L. N. G. FUon, R.A.F. An account of these experiments 

 has been given by Major A. R. Low in the Aeronautical Journal for Novem- 

 ber 1918. The object of the investigation was to test a theory, due to 

 Mr. Harris Booth and Mr. Harold Bolas, and further developed by Mr. 

 Arthur Berry, for calculating the stresses in the frameworks carrying 

 aeroplane wings. This theory, of which an account is being published 

 in the Transactions of the Royal Aeronautical Society, contains an extension 

 of Clapeyron's well-known theorem of Three Moments, so as to include 

 the effects of bending moment due to end-thrust. 



The fundamental assumption made in this theory is that the nodes of 

 the framework, originally collinear and horizontal, remain collinear and 

 horizontal when the load is applied, so that we can treat them, for mathe- 

 matical purposes, as fixed points. The second half of the assumption — 

 namely, that the nodes remain horizontal — is not essential, for we can, 

 without sensible error to the order of approximation considered, measure 

 deflections from the line of nodes. But the first assumption — namely, 

 that the nodes remain collinear — is of primary importance. It really 

 implies, unless a peculiar complex of values for the elastic constants of 

 each element of the framework is postulated, that these elements, although 

 capable of bending, cannot be materially stretched or compressed length- 

 ways, so that, considered as a node-system, the framework is practically 

 undeformable. Of course, if this were the case it would necessarily 

 involve the truth of the other assumption, that the nodes remain horizontal. 



The frameworks, considered generally, consist of two parallel hori- 

 zontal continuous wing spars, connected by jointed struts and cross-wires, 

 as shown in fig. 1, which is a photograph of the model actually used in 

 the investigations. Of the cross bracing wires, only one-half really come 

 efiectively into play, the other half being reserved for use in peculiar 

 conditions of flight, when for some reason the lifting surfaces of the wings 

 are reversed, or to take the kinetic reactions on landing. Owing to the 

 obliquity of these wires, discontinuities in the end thrust, as well as in 

 the shear, are introduced at each node, but it is assumed that the bend- 

 ing moment is continuous as we pass through a node, and also that the 

 central line of the beam is also continuous. The latter assumption is 



