172 SYMPOSIUM ON AERONAUTICS. 



At any given speed let the relation of total lifting capacity to area 

 be expressed by the ratio m. Then if W^ = total lifting capacity 

 we have 



lV==mA = mBx-. 



Denote the net lifting capacity by y. Then we shall have 



and 



For such a series of structures therefore the maximum net lift- 

 ing capacity will be given by a size determined by the value of .r in 

 equation (i) and the actual maximum net weight will be as in 

 equation (2). For larger sizes of structure the weight required 

 in the structure itself will increase more rapidly than the carrying 

 capacity depending on area, and hence the net lifting power will 

 decrease. It results furthermore that for such a family of structures 

 there will be some size for which, all at a given uniform speed, the 

 net carrying capacity will be zero, a size for which the total lifting 

 capacity at the stated speed will be only just able to carry the weight 

 of the structure itself. 



We may now ask two important questions. 



(i) What measures must be taken, in such a series of struc- 

 tures, to increase the m.aximum net carrying capacity? 



(2) To what extent do these conclusions apply to a series of 

 actual aeroplanes of continuously increasing wing surface? 



Regarding question (i) the form of the expression for Vm shows 

 that it varies directly with m^, directly with B^ and inversely with 

 C-. We must therefore seek to increase m and B and decrease C. 

 We cannot hope to affect the value of B, the relation of area to 

 linear dimension. We may, however, increase m by increasing the 

 speed and decrease C by improved design or by developing ma- 

 terials stronger for a given weight than those now employed. 



