Record. xxix 



pitching and gyration. After discussing these phases the speaker 

 passed to the future of the aeroplane. 



That mechanical flight is possible is evident, but it is equally evi- 

 dent that the aeroplane even yet is at the mercy of the wind and one 

 of the most important advances of the future is some method of real- 

 izing certain stability of flight so that inequalities in air conditions 

 and variations in skill on the part of the aviator shall have but negli- 

 gible effect. It is desirable that the stability may be rendered auto- 

 matic while at the same time the machine is not deprived of all sen- 

 sitiveness but remains easy to manoeuver. Stabilization must be at- 

 tained by mechanical methods which call into play the stabilizing 

 devices at will by a mechanism of transmission. Theoretically either 

 pendular or gyroscopic masses may be used and brought into effective 

 play by the transmitting device. 



It has already been pointed out that the speed required for susten- 

 tion depends on the angle of attack and increases as this angle de- 

 creases, while the power required to drive the sustaining plane 

 against the air resistance decreases with this angle. Theoretically 

 then at least, a given motor might drive an aeroplane at any desired 

 speed however high by flying it "close to the wind." Practically this 

 is not the case because of the passive resistances developed by mov- 

 ing the accessory parts of the machine through the air at high veloc- 

 ity. The resistance to flight offered by the sustaining planes is for 

 high velocities only a small fraction of the total resistance, and it 

 is very difficult to get even an approximate idea of the value of the 

 passive resistances. They are very considerable even for trains and 

 automobiles and for the greatest velocities actually attained by these 

 they absorb nearly all the driving energy. The problem of velocity 

 is then much the same for high speed machines whether they are 

 designed to move on the ground or through the air. Their principal 

 parts are the motor and its accessories, including the full reservoirs, 

 and the problem is essentially one of building a motor which will 

 develop sufficient power to drive itself, including the full tanks and 

 the rigid frame which carries it, against its own resistance. 



The power of a motor is roughly proportional to its weight and a 

 motor of 100 horse power is capable of moving at 100 kilometers per 

 hour. A motor of 800 horse power, homothetic to the first and mak- 

 ing the same number of strokes per second will have a volume eight 

 times as great and hence a surface four times as great. The power 

 required to move this at the same velocity as before is then quadru- 

 pled, but since the power is now eight times as great as formerly 

 the velocity may be increased. How much? The passive resistances 

 are proportional to the square of the velocity and hence the power 

 required to overcome them is proportional to the cube of the velocity 

 and also to the resisting surface. But this resisting surface has been 

 quadrupled and hence the new velocity is only the cube root of two 

 times the old and cannot exceed 126 kilometers per hour. To raise 

 it to 200 kilometers per hour would require — on the same theory — 

 a 50,000 horse power motor. Very little is to be gained by increasing 



