NO. 3 LANGLE'S MEMOIE OH MECHANICAL PLIGHT L89 



difficult. The problem was that of constructing for a very little greater weighl 

 per square foot, wings containing approximately sixteen times the area of the 



model wings. 



It will be recalled from the previous description of model Aerodrome No. 

 5, that its four wings had a combined area of 68 square feet and weighed ap 

 proximately 2500 grammes, or 37 grammes per square foot. II was not ex- 

 pected that the large wings would be of so light a weight per square foot, 

 which would have meant only about 35,500 grammes (approximately 78 pounds) 

 weight for the 960 square feet originally planned. It was hoped, however, thai 

 the increase in weight per square foot for the large wings would be less than 

 the square root of the increased linear dimensions. In this case, the increase 

 in linear dimensions being approximately four, it was, therefore, hoped that 

 the larger wings would not have quite twice the weight per square foot of the 

 smaller ones; the computed weight permissible for the large wings was there- 

 fore placed at 120 pounds. 



To obtain the required area within the permissible limits of weight two 

 well-defined paths of procedure were open: First, it was possible to so modify 

 the structural form of the wing as to obtain the advantage of the increased 

 strength of trussed structures, that is, by superposing the wings. Or, second, 

 the " single-tier " type of wing, the efficiency of which had been fairly well de- 

 termined, could be retained, and strength gained without increase of weight by 

 improving the method of constructing the wooden framework and by extend- 

 ing the system of guy-wires. 



Some knowledge of the superposed type of supporting surfaces had already 

 been gained by the experiments at Allegheny and the tests of the rubber-driven 

 models, in which superposed wings had frequently been used; but it was felt 

 that this knowledge was altogether inadequate to aid in determining either 

 whether the superposed type of construction possessed in practice the advan- 

 tages which theory would indicate, or how and at what distance apart the sur- 

 faces should be superposed to obtain the best results. In order to obtain the 

 desired information, a series of tests on the whirling-table of complete wings 

 suitable for use on the models was made. These experiments were supplemented 

 by the practical tests with the models, which have already been described in 

 Chapter III, in order to give the wings a trial under the conditions of flight, 

 where they would be subjected to the action of the propellers and the uneven 

 character of the wind. 



In addition to determining what type of construction and what form of 

 surface would give the greatest " lift " with the smallest " drift," these whirl- 

 ing-table tests supplied data as to how much greater the actual resistance of 

 the wing with its necessary guy-posts and guy wires was than the theoretical 

 resistance, found by extrapolation from the results obtained in the tests of rigid 



