170 



SMITHSnNI A.V CONTRIBUTIONS TO KNOWLEDGE 



VOL. 2V 



guy-wires on the lower side of the frame, at the rear, were correspondingly 

 changed so thai the upper and lower systems should be similar, the wires which 

 started from Hie main tubes at the foot of the pyramid passing to the bearing 

 points, and from there to the rear end of the frame. 



In order to keep the main frame of the large aerodrome as short as pos- 

 sible, it had originally been planned to make the distance between the center of 

 pressure of the front wings and the center of pressure of the rear equal to five 

 metres. When lliese same proportions were followed in the quarter-size model, 

 il was found that it brought the rear wings so close to the propellers that their 

 lii'ling effect was certain to be interfered with by the blast of air created by the 

 slip of the propellers. It was therefore decided that all things considered it 

 would be best to increase this distance between the wings, even though this in- 

 volved an increase in weight, partly on account of the increased amount of 

 tubing, and still more on account of the ,i;uy-wires which it would be necessary 

 to add in order to make up for the weakness due to increased length. The large 

 aerodrome frame was accordingly lengthened 2.5 feet (76.2 cm.), and the guy- 

 wire system was changed to that clearly shown by the photographs of July 10, 

 1902, Plates 49, 50 and 51, the black cross-lines on the background being 50 

 centimetres apart. From an inspection of these photographs it will be seen that 

 two sets of guy-wires were carried from the upper and lower pyramids, re- 

 spectively, towards the rear of the frame, the first set being carried to the main 

 tubes at the foot of the "trestle " and the bearing points, and the second set to 

 these same main tubes at the second cross-tube. The sets of wires which started 

 from the feet of the pyramids were carried over the " trestle " on the upper 

 side and the bearing points on the lower side, and both joined to the main tubes 

 at the rear cross-tube. Additional cross-guy-wires for stiffening the frame side- 

 ways were added in each of the squares formed by the junction of the cross- 

 f lilies with the main tubes. A secondary system of truss ^ny-wires running 

 over short guy-posts attached to the tubes of the main frame also contributed 

 lo I he strength and rigidity of the whole. 



Although the pyramids had shown no signs of weakness, nevertheless, be- 

 cause of increased si rains due to the lene;thening of the main frame, -it was thought 

 advisable to make them stronger. Instead of the 15-mm. tubing, which had for- 

 merly been used, 25-mm. tubing of the same thickness was therefore substi- 

 tuted, and additional cross braces were added, as will be seen from the photo- 

 graphs, and from the scale drawings in Plates 52, 53 and 54, which show the 

 aerodrome as it was when completed. The numerals attached to these draw- 

 ings refer to the detail drawings shown in later plates. 



In order to secure the proper adjustment of the iiuy-wires, not only of the 

 frame but of many other parts, notably the wings, propellers and rudder, it 

 was necessarv to use a large number of turn-buckles. As almost every wire 



