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Knowledgfe 6t Scientific News 



A MONTHLY JOURNAL OF SCIENCE. 



Conducted by MAJOR B. BADEN-POWELL, F.R.A.S., and E. S. GREW, M.A. 



Vol. IV. No. 2. 



[new series.] FEBRUARY, 1907. 



[Entered at "i 

 Stationers' Hall. J 



SIXPENCE NET. 



CONTENTS.- See page V. 



Pra.cticacl AerodyrvaLmics 

 And the Theory of Aeroplanes. 



Bv Major B. Baden-Pow ell. 



Introduction. 



Just now the subject of aerial navig-ation has been 

 prominently brought before the public. .'\ wide interest 

 has been aroused, and people generally are beginning to 

 see what a vast future there is open to a machine able 

 to traverse, surely and safely, the realms of blue. 

 .Although I am one of those who always prefer fact to 

 theory, and though most of the important inventions 

 which have aided human progress have not sprung from 

 the mathematician's brain, I quite realise that a certain 

 amount of study of the principles underlying any such 

 subject is most necessary to one who would add any 

 important work towards the conquest of the atmo- 

 sphere. 



The air, then, and the effects of its pressure on bodies 

 moving through it, demands our earnest attention. 



.Air may seem a light, subtle fluid. If we pass our 

 hand through it we notice very little resistance to the 

 motion, and we mav wonder how it is possible to 

 utilise this verv vielding medium to support the heavy 

 weight of a human body or metal machinery against 

 the force of gravity. From a mechanical point of 

 view it is just the same whether a body be pushed 

 against the air, or the air blows against a stationary 

 body. Yet we all know what air, when in motion at a 

 great speed, may effect. We know that if the wind be 

 Jilowing with the force of a gale — perhaps 60 or 80 

 miles an hour — it is capable of exerting a ver\' great 

 pressure, especially on suitably disprscd surfaces. We 

 know well enough that when out on a windy day, an 

 umbrella held even with its convex side to the wind, is 

 sometimes most diflieult to hold, and that directly it is 

 turned so as to present a concave surface it is immedi- 

 ately blown inside out, or if made strong enough to 

 resist this action, would pull with such force as to be 

 almost impossible to hold. This enables one to realise 

 what mav he effected bv making an ajiparatus to travel 

 very rapidiv through the air. 



It seems probable th:it an ordinary umbrella (suitably 

 strengthened) held so as to let a very strong wind strike 

 underneath it, would pull so hard as to be almost 

 capable of lifting a man off his legs, momentarily, at 

 least. This fact hardly seems extraordinary, yet if we 

 imagine a flying apparatus only ns big as an umbrella 

 progressing at 40 or 50 miles an hour through the air, 

 it would surprise most of us to think that it was capable 

 of raising a man. 



This enables one to realise that if only we can get 

 the pmi'cr, propcrlv applied, n vcrv small ajiparatus 

 may be sufficient for our ]nirposc — and, if a very large 



aeroplane be used, what great lifting power is to be 

 derived from it. 



This subject, though likely, as already intimated, to 

 become one of very great importance, yet is one that 

 has received but comparatively little attention among 

 scientific experimentalists. 



Langley, in the introduction to his book, " Experi- 

 ments in Aerodynamics," published in i8gi, says : " In 

 this untrodden field of research '. . . I think it safe 

 to say that we are still, at the time this is written, in a 

 relatively less advanced condition than the study of 

 steam was before the time of Xewcomen." 



Xo complete treatise on the subject exists. .All the 

 information that is available has to be extracted from 

 works dealing with aeronautics (mostly historical), 

 hydrostatics, and pneumatics, and from the various 

 technical papers which have been compiled on certain 

 definite branches and on results of particular series of 

 experiments. The following is a general review of the 

 whole subject gathered from these sources. It does 

 not pretend to be complete or exhaustive, but it is 

 hoped that it may be of assistance to those anxious to 

 get an idea of the science, and who are unable to wade 

 through the various sources of information enumerated. 



I propose treating of the subject in the following 

 order. It will be necessary first to brieflv refer to the 

 theory of the balloon, and ascent by reaction of a fluid, 

 and then to get on to the main subject of aeroplanes 

 and apparatus working on kindred principles. 



This latter subject must again be subdivided into air 

 pressures acting perpendicularly on a plane surface, 

 air pressures on inclined plane surfaces, the effect on 

 the back of such planes, and pressures on curved sur- 

 faces moving through the air. 



Finally, to consider the combined effects on various 

 shaped bodies in practice, the flight of birds, and the 

 theoretical action of aerial screw propellers. 



In considering the different methods possible for the 

 attainment of artificial flight — which is practicallv 

 synonymous with means of overcoming the force of 

 gravity — there are three principles to be taken into 

 account : — 



(i) Displacement. — By displacing a bulk of air bv a 

 body of less total weight than that air. Under this 

 head would be included hot-air balloons, gas balloons, 

 and the theoretical, if impracticable, vacuum balloon. 



(2) Dcnvmcard Reaction. — By the reaction of a fluid 

 driven forcibly downwards. Such is the principle of 

 the rocket. 



(3) Sub-Pressure. — Deriving support from the pressure 

 of the air on the under surface of a body driven through 

 it. This would include not only what is understood bv 

 the term ".Aeroplane," but also revolving aeroplanes 

 or lifting screws, and wings and paddles striking the 

 air downwards. I'nder this heading, too, must come 

 the wind-borne soaring birds and thistledown. 



.As regards the first of these methods wo need but 

 briefly go into it, since the subject of ballooning is 

 rather beyond our present scope. 



