NO. 3 LANGLEY MEMOIR ON' MECHANICAL FLIGHT 99 



the weight of the aerodrome suddenly thrown on the wings, I inverted the aero- 

 drome and distributed a weight of dry sand equal to that of the whole machine 

 evenly over the supporting surfaces. It was found that under the weight of the 

 sand the extremity of the wings bent to an angle of 45° downwards (and con- 

 sequently must have bent to an angle of 45 upwards in the air), a condition of 

 affairs worse than anything that had been suspected, and seeming to demand 

 the entire reconstruction of the wings with a strength and consequent weight 

 for which there was no means of providing. 



There had been some injuries to the machines in the trials of the 5th and 

 6th, and these were repaired. A new float had been made for No. 4, and a new 

 set of larger wings for No. 5. Each of these wings had a length of 76 inches 

 and a breadth of 25 inches, making the total surface of the two 26.4 sq. ft., while 

 that of the tail was 13.2 sq. ft., or about 40 sq. ft. in all. 



October 22. When No. 5 was finally prepared for another trial, its condi- 

 tion was as follows : 



Flying weight 22 pounds 



Area of supporting surfaces (wings and tail) 40 sq. ft. 



Sq. ft. of surface per pound of weight 1.8 ' 



Engine power with 115 lbs. steam pressure 1.0 H. P. 5 



Power necessary to soar 0.35 H. P. 



Theoretical soaring speed (plane wings at 20°) .... 24 ft. per sec. 



Previous lift on pendulum 40 per cent of flying weight 



October 25. The aerodromes having been taken to Quantico on October 23, 

 and satisfactory experiments made with dummies in order to test the launching 

 apparatus, the house-boat was carried out into midstream and moored. 



Aerodrome No. 4 was launched in the face of a wind of about 1100 feet per 

 minute. The midrod was at a very small inclination with the horizontal, about 

 .'! . The angle (a) of the chord of the curved wing measured at the rod, where 

 it was rigidly held, was 15°. The adjustment was such as to bring the CG im- 

 mediately under the CP, without any allowance for the fact that the line of pro- 

 peller thrust was below the CP.'' The aerodrome under these conditions was 

 launched with the head high. It made a real, though brief, flight of about 130 

 feet in 4J seconds, when it swung abruptly round through 90°, and, losing head- 

 way, sank continuously, finally falling backward into the water. 



October 27. Aerodrome No. 4, having been repaired and guyed with wires 

 from the wings to vertical guy-posts beneath, was launched again, but one of the 



•On the data of " Aerodynamics," a plane having 1.8 sq. ft. of surface per pound, and advancing 

 at an angle of 20°, would soar at a speed of 24.1 ft. per second. 



5 It will be remembered that the purely theoretical conclusions just cited apply to the power 

 delivered in direct thrust, but that of the above actual H. P. an indefinite amount was lost in friction 

 and slip of propellers. 



" It may be observed that at this time the position of the CP was calculated on the assumption 

 that the pressure for flight surfaces was proportional to the areas, without also allowing for the 

 fact that the following surfaces, like the tail, were under the " lee " of the wind and so far less 

 efficient. It follows, then, that the value CP — CG was not really 0, as was assumed, but something 

 considerable. 



