14 THE FLIGHT OF BIRDS 



of a law. By experiment he had discovered an 

 indubitable principle, but subsequent experiments 

 have discovered an equally indubitable fact, which 

 at a certain point interferes with its operation. 

 The angle cannot be reduced below, approximately, 

 5° without bad results. At a less angle, with the 

 necessary increase of pace, the friction of the plane 

 against the air increases so rapidly that, so far from 

 there being any gain from the further reduction 

 of the inclination, there is an actual loss.* 



On this subject a writer in Flight has some very 

 interesting calculations, founded partly, it is true, 

 on theory, and requiring further verification by 

 experiment, but probably representing the facts 

 without any considerable deviation. f Indeed experi- 

 ment has already proved his main thesis, so that 

 it is only detail that requires further testing. He 

 imagines aeroplanes having the ideal camber or 

 curve for their planes, a large curve if they are to 

 travel slowly at a great angle of inclination, a slight 

 curve if they are to travel fast. They are to carry 

 a weight of 100 lb. Let us imagine them driven by 

 3 horse-power at the angles 30°, 25°, 20°, 15°, 10°, 5°. 

 The velocity will increase rapidly as the angle is 

 reduced. At 30° it will be 38 miles per hour. 

 With the successive reductions of the angle it will 

 increase to 47, 60, 78, 106, 134. The pace at 5° 

 and even at 10° is greater than most people would 

 wish to travel at, so the power applied might with 

 advantage be reduced. Two horse-power at 10° 



♦See The Aero Manual, p. 21 ; Flight, July 9, 1910; and 

 Langley's Aero-dynamics, p. 37. 



t Loc. cit. 



