266 TRANSACTIONS OF SECTION G. 



limitation to size is probably set by the accumulation of pressure at the upper 

 end of a long ship when at a considerable angle of pitch. 



It IS shown that a non-rigid ship of 500,000 cubic feet capacity and a 

 rigid ship of 2,000,000 cubic feet capacity are each capable of carrying a 

 useful weight equal to about 50 per cent, of their displacement. The relatively 

 high ratio in the case of non-rigid ships renders it most desirable that ships 

 of this type shoidd be developed and considered where the loads to be 

 carried and the distances to be covered are not so great as to render the more 

 expensive rigid construction necessary. 



Particulars are given of the recent success, obtained in mooring out a 

 rigid airship to a mast. She remained for three weeks in charge of watches, 

 each consisting of one N.C.O. and five men, and experienced gusts up to 

 43 m.p.h., very heavy rain, bright sunshine, and several thunderstorms, 

 including one of exceptional violence. This development is one of the greatest 

 importance, as it materially reduces the difficulties of landing and handling 

 an airship. 



2. The Scientific Progress of Aviation during Ihe War. 

 By L. Bairstow, F.R.S.^ 



At the beginning of the war aeroplanes had a maximuni speed of 85 to 

 90 m.p.h., and were capable of climbing to a height of 10,000 ft. At the end 

 the greatest speed was over 130 m.p.h., and the greatest height reached over 

 25,000 ft. in the fighting scouts. The weight-carrying aeroplanes used for bomb- 

 ing were of similar speed to those of the earlier period of the war, but the 

 weight has increased from 2,000 lb. to nearly 30,000 lb., with a possible non- 

 stop journey of 2,500 miles. It is not economical in fuel to fly fast, and there 

 seems to be no possibility of producing the highest speed and the greatest load- 

 carrying capacity in a single craft. The increase in performance has been made 

 chiefly by increased horse-power, the aerodynamics having been well found 

 from the beginning and subject to little change. 



When dealing with control and stability as distinct from performance aero- 

 dynamic progress has been continuous and is still far from completeness. The 

 aim in the fighting scouts has been to give the pilot power to manoeuvre with 

 least effort, whilst in the bombing aeroplanes inherent stability has been sought 

 in order to render manual control unnecessary for the greater part of the period 

 of flight. 



Many experiments have been made, both on the model and full scales, but 

 most of the detailed design in an aeronautical drawing office is based on model 

 tests which in many directions are well ahead of application. The theory of 

 the relation between tests on models and on the full scale is of considerable 

 importance and has its special difficulties. It is not possible, as in the case 

 of ship models, to make full use of a law of corresponding speeds, since the 

 requirements indicated involve forces on the model equal to those on the full 

 scale without using velocities in excess of 500 square feet. Apart from changes 

 at the velocity of sound, which affect airscrews to a very great extent, there 

 are critical velocities of fluid motion determined by viscosity. The existence 

 of such a change between model and full scale would render model tests of 

 little utility, for the connection between the flow above and below the critical 

 velocity is frequently very slight. The criterion for change is departure from 

 the law that resistance varies as the square of the speed, and experiments have 

 been made in the last few years which cover all the important parts of an 

 aeroplane. For wings the pressure at points on a section has been measured, 

 both in flight and on a model, and the agreement is close. Model testing is 

 now firmly established and gives confidence in attacking the complex .problems 

 of stability and control on which the safety of aeroplane transport depends. 



The truth of the last observation is shown by a comparison of calculations 

 made some years ago on the nature of disturbed motion following Bryan's 

 mathematical theory and observations taken during flight in the last two years. 

 All the salient features are indicated by the theory which has been extended 



2 See Engineering, Oct. 10, 1919, p. 493. 



