2 Lander, Stresses in the Main Spars of Monoplanes. 



3°. Moments due to the axial or endlong loadings 

 acting through distances equal to the deflections of the 

 spar from its initial position. 



In actual flight the intensity of load is continually 

 changing, thus altering the loads on the bracing wires and 

 causing these latter to extend and contract slightly. On 

 this account the assumption that the points of support are 

 fixed is slightly inaccurate but owing to the slenderness 

 of the spar the errors introduced by slight changes in 

 alignment are small and their effect on the actual spar 

 may be estimated with fair accuracy when the design is 

 complete. 



The assumptions made then in obtaining the prelimi- 

 nary dimensions are that the points of support remain in 

 the same straight line. 



When designing a spar it is always necessary to take 

 into account the direct compression which is represented 

 in the above expression by 



and the moment due to the first of the three causes 

 enumerated. These moments may be obtained very 

 simply by the Claxton Fidler method of solving beams 

 continuous over several supports and which is as follows : 



B.M. diagram for Aeroplane having wires attaclied at 



neutral axis. 



If the bending moment diagrams be drawn upon a 

 horizontal base line for each span as though it were dis- 

 continuous, then the true base line from which moments 

 should be measured in order to determine those on the 

 continuous beam, passes over and under certain character- 

 istic points on each side of the support by equal amounts 





