Manchester Memoirs, Vol. lix. (191 5), No. % 



II. Graphical Determination of the Stresses in the 

 Main Spars of Monoplanes. 



By Cecil H. Lander, M.Sc, A.M. Inst.C.E., 



Lecturer in Civil Engineering in the University of Manchester. 

 {Read and received December ist, 191 4.) 



One of the most complex problems connected with 

 the design of beams continuous over several supports is 

 presented by the spars of aeroplanes, particularly those of 

 the Monoplane class. The stresses in the spar are made 

 up of direct compressions together with those due to 

 bending moments and the stress at any point may be 

 represented by the expression 



Pcosd My 

 f ~~ A ± I 



where .P=Pull in a bracing wire. 



6— Inclination of bracing wire to horizontal. 

 A = Sectional area of spar. 

 y = Distance of point under consideration from 



neutral axis. 

 I— Moment of inertia of spar. 



M = Total bending moment at the point under 

 consideration. 



The value of M at any point may be made up of 

 three terms due to three distinct causes. 



1°. The more or less uniform loading due directly to 

 the weight of the machine. 



2°. Moments due to the attachment of the bracing 

 wires not lying in the neutral axis of the spar. 



January 20th, 19/5. 



