TRANSACTIONS 0& SECTION G. 481 



The copper series have shown that alloying commercial aluminium alone with 

 copper to the extent of 2 - 6 per cent, is not to be recommended. The copper 

 manganese specimens have not seriously deteriorated in ten years. An alloy 

 known as a ' duralumin ' has been tested, and a report is made thereon. Its 

 specific resistance is 5"35xl0- 6 ohms at 15° C. as against 2-76X10- 6 for pure 

 commercial aluminium. 



MONDAY, SEPTEMBER 4. 

 Joint Discussion with Section A on Aeronautics. 



The Principles of Flight. By Algernon E. Berriman. 



One of the greatest services that can be rendered to the science of aeronautics 

 at the present time is to attract towards it the serious interest of minds that have 

 matured in other departments of the world's work. With this object in view an 

 attempt will be made to give a resume of the more interesting problems as they 

 are understood by the majority of students, in the hope that those taking part 

 in the discussion may thereby be enabled to direct their remarks along such lines 

 as shall -add most to the sum total of our little knowledge in the short space of 

 time available. 



The present predominance of the military aspect in the perspective view of 

 the immediate future of aeronautics serves also to draw a dividing line between 

 different forms of aircraft, such as to group all systems essentially possessed of 

 the ability to ascend vertically and hover stationary in the air on one side, and 

 all those that can neither stand still in the air nor get up from anywhere, on the 

 other. 



Balloons and Kites. — Thus, the captive balloon and the man-lifting kite both 

 perform useful work, although neither navigates the air at large. The free 

 moving aeroplane, on the other hand, is frequently criticised because it does not 

 at present possess the potential qualities of the as yet unsuccessful helicopter. 



The Helicopter. — It seems necessary to pay some attention to the problem of 

 the helicopter, therefore, in order to see how far an elementary investigation of 

 its principles supports the likelihood of realising the possibilities frequently 

 assumed in its favour. It has been suggested that some insects fly on the heli- 

 copter principle. 



It may be demonstrated that the very small helicopter is a remarkably success- 

 ful toy, although the large helicopter is as yet an unsuccessful machine. A 

 mathematical ratio (see the ' two-thirds power law ' in summary of formulae) indi- 

 cates that the application of increased power to a given screw is an inefficient 

 ancthod of increasing the lift. It is suggested that the ratio of essential 

 deadweight to effective lifting area may also increase so disproportionately in 

 large machines as to prevent the practical success of the helicopter class. Inas- 

 much as the largest screw for a given load is the most efficient, it is argued that 

 .the aeroplane is the helicopter of maximum efficiency; inasmuch as it represents 

 a blade element flying on the straight line periphery of a circle of infinite diameter. 



Dirigibles. — Under the assumed division, dirigibles and aeroplanes have to be 

 ■compared as alternative machines for fulfilling the same purpose. Both navigate 

 the air, but the dirigible, in addition, can ascend vertically and hover stationary 

 above any given spot. Windy weather adversely affects both types of machines. 

 In the aeroplane the gust is inimical to stability; in the dirigible a high wind 

 'exerts an enormous drifting force. Comparatively large sizes are necessary in 

 dirigibles if they are to have a wide range of action. The more important dis- 

 advantages of dirigibles result from the permeability of the fabric to hydrogen, 

 the costliness and inconvenience of using this gas, and the disturbing influences 

 of sunshine and shadow on buoyancy. 



Aeroplanes. — The aeroplane is the more interesting machine of the two in 

 the eyes of the majority of students, owing to the popularity of flight as a sport. 

 A broad treatment of the problems relating to this section divides them under 



1911. T T 



