FLYING-MACHINES. " 13 



We shall see presently that the force of the wind can be utilized 

 to a certain extent to make up these losses, but still some muscular 

 effort should be required. If our vulture or albatross would only 

 occasionally deign to flap a wing, all would be well. His obstinacy 

 is very perplexing. 



Leaving the birds to their own peculiar devices, let us now con- 

 sider what principles should guide us in constructing a flying - 

 machine. 



In the first place, by acting on the air, the machine should be able 

 to lift itself from the ground ; and, leaving out of account small mod- 

 els, this is a preliminary no one appears so far to have succeeded in. 

 Many pictures may be seen of flying-machines booming along through 

 the air with all sails set, passengers evidently happy, some serenely 

 smoking, others promenading the deck in the usual way, with perhaps 

 a couple behind the wheel-house ; but a representation of a machine 

 just on the point of starting out is not to be met with. 



In order to produce an upward pressure or reaction, the wings or 

 propeller acting on the air evidently should drive it downward. Sup- 

 pose now that our machine weighs 600 pounds, and that it has the 

 same propelling surface in proportion to its weight as the Australian 

 crane, we should then need about 246 square feet, and a pressure of 

 2*4 pounds acting upward on each square foot would lift it from the 

 ground. 



Referring again to the table giving the relation between wind ve- 

 locity and pressure, we notice that a pressure of 2*4 pounds would 

 be occasioned by a velocity of about twenty-two miles an hour. 



If, then, we should cause our propeller — be it a screw or wings, 

 or any other form — to drive downward a current of air at this rate, the 

 cross-section or area of the current being 246 square feet, the total 

 upward reaction would be great enough to raise the machine. 



Of course, for any other proportion of wing-surface to weight, our 

 table would give other results ; or if the air is already in motion, it 

 will tell us what increase of velocity should be given to produce the 

 desired pressure. 



The results given in the table can also be readily found in a purely 

 theoretical way, and they seem so important that it is a wonder 

 investigators have given them little or no attention. 



A machine possessing weight can fly only by doing something to 

 the air. It must put the air in motion, and it can be shown that the 

 amount of this motion will be a measure of the work done and reac- 

 tion obtained. 



If air is already in motion, we can not utilize its force, not wishing 

 to drift along, except by changing in some way its velocity. 



Granting all this, our table or formula will tell us, not only what 

 volume of air must be used to gain the desired reaction or motion, 

 but also the least power necessary. Knowing the weight of and ve- 



