FL YING-MA CHINES. 



15 



pose that, in addition to the propeller, we furnish it with an inclined 

 plane having the same area, or, perhaps after the manner of birds, 

 make the propeller act also as an inclined plane ; and let it be inclined 

 five degrees, with the wind blowing at the rate of twenty-three miles 

 an hour. Then the table shows us that the total lifting force due to 

 the wind would be 278 pounds, leaving 322 pounds to be supported 

 in some other way. The horizontal or drifting force would be 0'23 

 pounds on each square foot, or only 56 pounds altogether. To counter- 

 act this, let us make our propeller act as a kite-string by sending 

 backward the air at an increased velocity. Our other table tells us 

 how great this velocity should be, and makes the necessary power 

 amount to only about half a horse-power. To support the balance of 

 the weight, we should need also to send downward a current of air, 

 involving an additional expenditure of about seven horse-power. 



Combining the two, we get this extraordinary result, that while 

 nearly nineteen horse-power was necessary to lift our machine from 

 the ground, it could hold its own in a breeze of twenty-three miles 

 an hour with an expenditure of only seven and a half horse-power. 



No account has been taken of the wind blowing against dead sur- 

 faces, such as the body of the bird or machine. This, of course, 

 would depend upon the shape. A bird's body is long and narrow, 

 cleaving the air without great resistance, and a flying-machine should 

 be fashioned similarly. 



Other losses have not been considered, but still the broad result 

 holds that it is possible in this way to utilize part of the energy stored 

 up in the wind. The accuracy of the results will depend upon that 

 of Mr. Skye's table ; but if future experiment should verify it, we can 

 understand why it is that the albatross, and wild-duck, and heavy 

 birds generally, while rising with great difiiculty, when once up keep 

 on the wing with so much apparent ease. 



However, there is still the necessity for a kite-string of some sort. 

 There is a force tending to carry the bird along with the wind which 

 must be overcome somehow, and I still fail to understand how the 

 albatross can sail in the air indefinitely without some muscular effort. 



From Mr. Skye's table, in connection with the other, we get this 

 important practical result — that in a flying-machine, properly con- 

 structed, the greatest power required will be that necessary to lift it 

 from the ground ; and that once off, up to a certain limit, the stiffer 

 the breeze the better. 



The efiiciency of a propeller of any sort will depend not only upon 

 its area, but also upon its ability to send the air away in parallel 

 streams. If we wish to go forward, the air must be driven aft, and a 

 forced current in any other direction will at best give us back but a 

 fraction of its energy. Ordinary screw-propellers have not proved 

 very effective, for the reason, probably, that revolving at great speed, 

 they send off a large amount of air tangentially. 



