ON A COMPRESSED-AIR FLYING -MACHINE. 53 



writer that the work done by the 145 cubic inches of air at 230Ibs. 

 initial pressure above the atmosphere in 40 double vibrations of 

 the engine, on the assumption that it expands approximately, 

 adiabatically into the cylinder and at the end of each stroke 

 escapes into the air, is 2,500 foot-pounds. If the adiabatic relation 

 was fully realized the pressure in the receiver after the forty-third 

 double vibration would be 3 2 lbs. above the atmosphere. As the 

 final pressure by the diagram is really 501bs. at the end of the 

 forty-third double vibration a correction has been applied to the 

 above calculation. 



Mr. Pollock has also no doubt that the calculation of 300 foot- 

 pounds for the work required to flap the wings is quite unreliable 

 as it takes no account of the disturbances set up in the air, and 

 he feels confident that very nearly 2,500 foot-pounds is spent in 

 driving the machine. On the other hand the writer thinks that 

 if the wings flapped up and down in the same place at every stroke 

 the eddies created would be a waste of a further portion of the 

 300 foot-pounds ; and if the 2,500 foot-pounds was really a applied 

 to the air through the piston and rod, 5*7 double vibrations per 

 second would be the result instead of 2 as there are actually. We 

 now begin to grasp the idea of how imperfect the motor is still, 

 and what a trifle of thrust makes the machine fly. 



On the supposition that 7*32 ounces is the force resisting the 

 motion of each wing, a similar wing was held rigidly by the butt 

 and a weight of 7 '5 ounces put on the membrane 24 inches from 

 the fixed point and If inches abaft the wing arm ; the deflection 

 produced due to torsional stress was 3^ degrees ; and even by 

 moving the weight from If inches to 3^ inches, that is half way 

 across the wing, it was only twisted 8^ degrees. So that only \ 

 of the 300 foot-pounds is actually used in pushing the machine 

 forward, the rest being lost work. This suggests a wide field for 

 experimenting with slow-burning rocket compounds and well 

 proportioned direct-acting jets. 



- The valve gear is thought to be a truly original invention, but 

 surprise will not be felt if it comes into general use to see others 

 claim and prove too, that it is quite common and has been known 

 for years. The problem to be solved in its construction was to 

 make the valve reciprocate when the piston was in two positions, 

 at all other parts of the stroke the valve was to be stationary ; 

 the force that moved the valve was to be uniform and independent 

 of the pressure in the cylinder, as from the nature of the case the 

 cylinder pressure was decreasing. A slight variation makes this 

 gear suitable for using the air expansively ; the model shows it 

 in its first form, from which it will be seen that three additional 

 moving pieces are required for cutting off at half stroke, and two 

 more enable us to do so instantaneously at any earlier point. 



