NO. 3 l..\.\i;i,KI MEMOIB (i\ MECHANICAL FLIGHT 81 



of the supporting surfaces given in this chapter arc, then, approximations made 

 from rules for " balancing," i. c, for obtaining equilibrium in actual flight, 

 rules which arc in fad tentative, since they arc founded on a priori consider- 

 ations with partial correction from 1 lie empirical knowledge gained by pre- 

 vious field trials. For these rules see Chapter VI. 



1893 



With reference to the supporting and guiding surfaces of Aerodromes Nos. 

 4, 5, and 6, Aerodrome No. 4, in its earliest condition mentioned in the preced- 

 ing chapter, was taken into the field, but never brought to trial in the air. It 

 is sufficient to say that in the Largest of the three sets of wings constructed, 

 each wing was 17x51 inches, and therefore contained about six square feet, so 

 that with the tail (which was at this time a supporting surface), whose area 

 was one-half that of the two wings, the total supporting surface was 18 square 

 feet, or since the flying weight was 9.1 pounds, the proportion of surface to 

 weight was somewhat less than 2 square feet to the pound. The wings were at 

 this time ribless, it being expected that the silk cover which was purposely left 

 loose would take its curve from the air filling it, which subsequent experience 

 lias shown would have led to certain disaster if the aerodrome had been launched. 

 It may be added that there was a vertical rudder of what is now seen to have 

 been a wholly inadequate size. These remarks may be applied with little modi- 

 fication to the attempted flight with No. 4 on May 25, except that the vertical 

 rudder had been made larger, but was still much too small. 



1894 



From the account of the field trials to be given in Chapter IX, it will be 

 seen that in numerous attempts at flight prior to October 6, 1894, the cause of 

 failure can in every instance he traced to imperfections more fundamental than 

 those of the sustaining- surfaces, either the launching device or some other 

 part failing to work satisfactorily. I therefore commence a description of the 

 sustaining surfaces with those of Nos. 4 a*nd 5 as used on that day. 



The construction of the wings of No. 4 and No. 5, which were nearly iden- 

 tical, is shown in Fig. A Plate 16. A rod of hickory, tapering from \ inch in di- 

 ameter at the larger end to ^ inch at the smaller, was steamed and bent, as 

 shown in the drawing, to form the main front rib of the wing. This was 

 firmly clamped to the midrod, and to the rib in turn were attached a number 

 of cross-ribs of hickory, slightly curved, the inner one of which was fastened 

 to the hull at its inner extremity, while the whole was covered with silk. The 

 length of each wing was 162 cm. (63.75 inches), and the width 54 cm. (21.25 

 inches). The tail was plane and equal in area to one of the wings, so that the 

 joint area of the wings and tail was 2.62 square metres (28.2 sq. ft.). 



