NO. 3 LANGLEV MEMOIR ON MECHANICAL 1'UGHT 



165 



(lie ''main frame," must supporl the second principal part, the " transverse 

 frame," which formed a cross with the main frame, and at the ends of which 

 the propellers were mounted. While it was necessary that this transverse 

 frame should have considerable rigidity and strength in a vertical direction, 

 yet its main strength and stiffness was required in the horizontal plane for 

 withstanding the thrust of the propellers. It had been possible to construct, 

 the frames of the later steam-driven models stiff enough, and at the same 

 time light enough, by the use of properly proportioned steel tubing, but calcula 

 tion very soon showed that in order to secure sufficient rigidity for the frame of 

 the large aerodrome and at the same time keep the weight within the perm is 

 sible limit, it would be necessary to depend very largely on guy- wires and 1" 

 use tubing only for forming the struts against which the guy-wires should act. 

 But this obviously introduced a new series of problems. The extensive system 

 of guy-wires necessary would add materially to the head resistance of the aero- 

 drome, and this might conceivably be so great as to require more propulsive 

 power than would be required for a frame heavier but unincumbered by the 

 head resistance of the wires. It became necessary to consider these problems, 

 but no data were accessible from which the head resistance could be computed 

 with any confidence. The coefficient of resistance for a cylindrical body moving 

 through the air in a direction perpendicular to its Length may in general be taken 

 as one-half that of a flat body of the same cross-section; but it was thought 

 very certain that, owing to the fact that tightly stretched wires are in constant 

 vibration when the aerodrome is in the air, the resistance of the wires must 

 be considerably greater than would be calculated from treating them as cylin- 

 ders having a coefficient of 0.5. Unfortunately, no data on the resistance of vi- 

 brating wires were at hand. Before proceeding with the designs for the guy- 

 ing of the frame, therefore, the following brief series of tests was made in 

 November, 1898, on the whirling table, in order to learn approximately the resist 

 ance that the proposed system of guy-wires for the large aerodrome would 

 offer : 



MEASUREMENTS OF THE RESISTANCE OF GUY-WIRES. USING FRAME ATTACHED TO 



" BALANCE." 

 Resistance of Frame Without Wthes. 

 Frame consists of: 4 tubes, 1 cm. diameter, 14.5 cm. long; 2 tubes, 1 cm. diameter, 41 cm. long; 2 



tubes, 1 cm. diameter, 101 cm. long. 



Revolutions of v elocityof 



turn-table per frame. Feet 



minute. per minute. 



G.75 608 



9.75 877 



12.0 1080 



16.35 1475 



19.75 1775 



22.7 2045 

 2290 



