NO. 3 LANGLEY .MEMOIR ON MECHANICAL IMCIII 153 



II will be recalled that in " Experiments in Aerodynamics " Mr. Langley 

 made tests of tlie soaring speed, etc., of surfaces when superposed. In many 

 of liis experiments with rubber-driven models, lie also employed superposed sur- 

 faces. During the summer of 1898 several forms of superposed surfaces, of 

 a proper size for use on the steam-driven models Nos. 5 and (J, were con- 

 structed and were tested under as nearly as possible the same conditions as 

 would exist when used on the aerodrome, by mounting the surfaces on the whirl 

 ing-table and measuring their soaring speed, lift, drift, etc., to determine jusl 

 what arrangement of surfaces gave the greatest lifting effeci with the leasl 

 resistance. Two of the forms which were tested are shown in Plate 37, Figs. 

 1 and 2, and Plates 64 and (55. At the conclusion of these tests, it was decided to 

 construct a set of surfaces on the plan shown in Plates 64 and 65, and to have 

 them ready for use on either of the models Nos. 5 and 6. These surfaces were 

 taken to Chopawamsic Island in April, 1899, when all of the other aerodromic 

 material was first carried there. It was planned to make some tests with them 

 to determine whether or not it would be best to use superposed surfaces on the 

 large aerodrome or to follow the plan of " single-tier " ones, which had the 

 great advantage of having already proved their worth in the successful flights 

 of the models. On August 3, Aerodrome No. 5, equipped with these superposed 

 surfaces, was launched. It will be noted from Data Sheet No. 11 that the super- 

 ficial area of the superposed surfaces was considerably greater than thai provided 

 by the " single-tier " ones, and on the assumption of the same efficiency per unit of 

 surface in both cases, the aerodrome should, have soared al a less speed and re- 

 quired less power when using the superposed surfaces. The results obtained, 

 however, were just the reverse, the aerodrome being unable to sustain itself when 

 using the superposed surfaces, whereas with the " single-tier " ones it was evi- 

 dent that a slight excess weight might easily have been carried without preventing 

 the aerodrome from soaring properly. While it was fell that these tests were not 

 entirely conclusive as to the superior lifting power of the " single-tier " sur- 

 faces, yet as the engine builder was constantly promising, each time with in- 

 creased emphasis, that he would within less than a fortnight deliver the engine 

 for the large aerodrome, and that it would develop even more power than the 

 specifications called for, it was deemed best to cease the experiments with the 

 models and concentrate all effort on the completion of the large aerodrome 

 frame and the construction of a set of " single-tier " supporting surfaces for 

 it. It was recognized from the first that the " single-tier " supporting surfaces 

 lacked the rigidity which could be secured by the truss construction afforded by 

 the superposed plan, yet these models, which were the only machines in the 

 history of the world that had ever flown successfully, had been equipped with 

 " single-tier " surfaces; and the experience so dearly bought during the long 



