The Estimation of Performance: An Account of a Practical Method by General Curves which has been Proved Accurate

Example 4 A COMMERCIAL aircraft is to be designed whose Absolute Ceiling must not be less than 12,500 ft. The machine is to be a biplane and both wings are to have the same span, which is 48 ft., the gap being 8 ft. However, the possibility of utilising existing stock, and thereby reducing design and manufacturing costs, make it desirable to use a gap of 5 ft. 4 in. What will be the effect of this change on pay load and maximum speed ? (We shall assume the wing structure in each case to be the same weight, which is a fair assumption since it means that with the small gap machine the saving of weight on strut length and cross section is approximately equal to the increased weight of spars necessary to deal with the higher end loads.)