TRANSACTIONS OP SECTION G. 265 



made in the design of gears; the introduction of double reduction gears; main- 

 tenance of efficiency and economy under long continued service as the result 

 of actual experience; and the application of geared turbines for land purposes 

 were all dealt with by the author. 



In tlie afternoon a Sectional Visit was paid to Christchurch R.E. Training 

 Uamp, when a demonstration of bridge-construction was given. 



THURSDAY, SEPTEMBER 11. 

 The following Papers were read : — 



1. Airships. By Wing-Commander T. E. Cave-Browne-Cave, C.B.E.^ 



The paper is intended to set out the present difficulties in development 

 and the lines along which future research is required. 



The principal diiiicuxty experienced with tJie use of airships in ti-opical 

 climates is the deterioration of the strength and gastightness of the fabric 

 under the action of light. The gastightness of the bags of a rigid ship is 

 obtained by goldbeater's skin, the supply of which is very limited, and a 

 sut>stitute of equal gastightness and low weight is badly wanted. 



AA\ important function of the outer cover of a rigid ship is to reflect as 

 much as possible of the light and heat which falls upon it. This is necessary 

 in order to reduce the superheating of the gas to a temperature above that 

 of the surrounding air, thereby causing a false lift, which decreases as soon 

 as the intensity of radiant fieat is reduced. 



The reinforcement of non-rigid envelopes is discussed. It is suggested that 

 fabric, which is usually of equal strength in both warp and weft directions, 

 shou.d be reinforced by circumterentiai bands of string tape, wh.ch will supply 

 the excess of tiie circumferential tension over the longitudinal tension. 



Attention is drawn to the relative unimportance of permeability to hydro- 

 gen as compared with ability to resist the passage of air into the gas space, 

 as air wh.ch has leaked in can only be eliminated by the discharge of large 

 quantities of gas. 



The importance of being able to take weight into the ship during flight to 

 compensate for superheating or for petrol consumed is discussed. 



ii,xperiments nave been made in using hydrogen as supplementary fuel. 

 It is found that tne use of hydrogen alone causes excessive detonation, but by 

 suitably proportioning the mixtures of hydrogen and petrol, satisfactory 

 running can be oDtained, and very considerable economy of fuel achieved. 



Attention is drawn to the much greater relative importance of fuel economy 

 than engine weignt, which obtains in an airship by reason of the much greater 

 duration of flight. The need of accessibility and ease of repair during flight 

 are discussed, and also various minor aspects in which the ideal airship 

 engine differs from that of the aeroplane. 



The desirability of having a propeller of variable pitch and one capable 

 of sufficient variation to produce reverse thrust is discussed. 



Attention is urawn to the necessity of obtaining some method of deter- 

 mining the height of an airship by means other than barometric pressure, so 

 that the reading of the barometer at a point on the ground below the airship 

 can be taken for meteorological purposes. 



Attention is drawn to the improved ratio of weight carried to fuel expended, 

 which results from increased size. It is shown that the limitation to the 

 size of a rigid airship is set by the diameter of cross-section, which is pos- 

 sible in view of the lateral pressure of the gasbags when unequally inflated 

 In the case of a non-rigid ship without effective tran.<;verse bulkheads, the 



1 See Engineering, Sept. 12, 1919, p. 356. 



