130 RELATION OF WING SURFACE TO WEIGHT. 



The fact that a wing surface of 07 nini'- per gram enables the alba- 

 tross to sail, while the laughing gull requires 336 mm- for the same 

 parpose, and that the l)ustard gets along with 02. while the sparrow 

 needs 200 and the fly 1,800 mm-, can be explained only on the supposi- 

 tion that the resistance of the air against moving wings is not directly 

 proportional to their size, but that in enlarging the wrings the resisting 

 power of the air against them increases in a greater ratio than their 

 superficial dimensions. Knowing that the air requires an appreciable 

 time to yield to the pressure of the moving wing, and that the larger 

 the Aving surface the greater the quantity of air displaced and the 

 greater the resistance of this compressed air to the subsequent wing 

 strokes which must act upon it, it is evident that this conclusion is 

 correct. 



There can therefore be no doubt that increasing size of body is 

 accompanied by a relatiA'e decrease of wing surface, and from this 

 fact we are able to draw interesting conclusions as to the size of the 

 wings a man would need to be able to fly. If we show the relation of 

 the Aveight to the size of the Aving by the means of coordinates, con- 

 necting the points thus gained In^ a curA'e, and then extend this curve 

 as demanded by the relative Aveight of the heaviest aninuil, Ave secure 

 an approximate illustration of the Aving size Avhich such bodies Avould 

 require. Since the muscular poAver of a human being Avould by no 

 means suffice for flapj^ing flight, it could only be a question of sailing 

 flight in this case. I haA^e therefore draAAii a curve for sailing flyers 

 on the principle aboA'e indicated, from Avhich the foUoAA'ing is 

 deduced : 



70 kilograms, weight of body, would require o2 imii" of wing surface per gram. 

 80 kilograms, weight of body, would re(iuire 31 luiu^ of \Aiug surface per gram. 

 00 kilograms, weight of body, would re-iuire 30 uuu- of wing surface per gram. 

 100 kilograms, weight of body, would require 29.5 mm" of wing surface per gram. 



According to the foregoing, if the combined Aveiglit of the body and 

 the mechanical flying apparatus amounts to 90 kilograms, in order 

 to sail like an albatross a man Avoidd require 1)0,000 times 30, or 

 2.700,000 mm' of wing surface; that is to say, two Avings furnishing 

 together 2.7 square meters of surface. 



