NO. 3 LANGLEY MEMOIB ON MECHANICAL FLIGHT 83 



The particulars of the launch will be found in Chapter IX. In the present 

 connection, it is sufficient to say that though launched with the requisite veloc- 

 ity and without accident, it fell into the water at a distance of about 15 metres 

 (49 feet) with the midrod nearly horizontal, the combined effect of engines and 

 initial impulse having in fact kept it in the air for less than two seconds. The 

 true cause of this failure not then being recognized, it was attributed to the 

 angle of the wings with the midrod having been too small. 



The launch of No. 5 followed almost immediately, but taking warning by 

 the supposed cause of failure of No. 4, its wings were set at a root angle of 20°, 

 and a hurried adjustment was made to secure greater rigidity, the tip being 

 partly secured against twisting by a light cross-piece, and guyed so that the 

 wing as a whole was not only at a greater angle, but stiffer than in the case of 

 No. 4. These changes it was hoped would cause the aerodrome to advance at 

 a considerable initial angle with the horizontal, and it did so, for instantly after 

 the launch, as the aerodrome escaped from its bonds into free air, the inclina- 

 tion of the midrod increased until it stood at about 60°, when the machine, 

 after struggling a moment to maintain itself, slid backward into the water 

 (with its engines working at full speed) after advancing about 12 metres (39 

 feet), and remaining in the air about 3 seconds. 



On the whole, the result of the first actual trial of an aerodrome in the field 

 was disconcerting, for unless the result was due to the wings being placed in 

 a position wholly unfavorable to support, there seemed to be no doubt that 

 either the engine power or the supporting surface was insufficient. Now this 

 engine power was by computation between three and four times what was nec- 

 essary to support the aerodrome in horizontal flight at an angle of 20°, and 

 after making every allowance for slip, there should have been still an excess of 

 power for the first flight of No. 4, whereas actual trial indicated that it was 

 insufficient. But on the other hand, the experiment with No. 5, which moment- 

 arily held its position in the air at an angle of 60°, seemed to indicate that the 

 engine power was abundant, and that the failure must be traced to some other 

 cause. 



As a result of these experiments it was concluded, " that it is an all-im- 

 portant thing that the angle of the front wing shall be correct, and that this 

 cannot be calculated unless it is known how much the tip will turn up under 

 pressure of the weight." I felt, then, that I had learned something from the 

 failures as to the need of greater rigidity of the wings, though how to obtain 

 this without adding to their weight was a trying problem. It was thus at an 

 early stage suspected that the evil to be guarded against in wing construction 

 was the distortion of the form of the wing under pressure, chiefly by torsion, 

 which is specially hard to provide against without a construction which is nee- 



