96 



NATURE 



[March 25, 1920 



merely a record of war developments, still less 

 an apologia for the aerodynamics laboratories. It 

 is, both in intention and in effect, a handbook for 

 the student, for the designer, and for the research 

 worker, which assumes no previous knowledge in 

 the reader, beyond the elements of hydrostatic 

 theory, and illustrates the applications of aero- 

 dynamics in all its essential branches. Mr, Bair- 

 stow's qualifications for authorship are too well 

 known to need description here. A leader in aero- 

 dynamic research at the National Physical Labora- 

 tory since the formation of the Advisory Com- 

 mittee for Aeronautics in 1909, his duties as expert 

 adviser to the Air Board and Ministry during the 

 war brought him into intimate contact with every 

 side of aeronautical activity. Of great import- 

 ance, in our opinion, is the fact that he has had 

 first-hand acquaintance with research on both the 

 model and the full-scale aeroplane, and so is 

 entitled — whether we agree with his conclusions 

 or not — to pronounce with authority upon the 

 vexed questions which relate to "scale effect." 

 But copious knowledge has not always, in the 

 past, given us satisfactory text-books, and it is a 

 real pleasure to find how well balanced is the 

 structural scheme which Mr. Bairstow has devised. 

 After touching lightly, but adequately, upon the 

 early history of his subject, and having illustrated 

 its present state of development by brief descrip- 

 tions of typical modern aircraft and engines, he 

 passes at once to a discussion of the principles of 

 flight, and in his second chapter, within some fifty 

 pages, the reader learns, by actual examples fully 

 explained, how to make practically all the funda- 

 mental calculations required in estimating the per- 

 formance and characteristics of aircraft. 



Ip our opinion, this is one of the best features 

 of the book. Aerodynamics is an empirical science, 

 and design proceeds by the manipulation of ex- 

 perimental curves which, with rare exceptions, 

 . cannot be represented by mathematical functions ; 

 present-day developments consist almost entirely 

 in refinement of the experimental data and of 

 the methods of their manipulation, and thus have 

 a tendency to obscure, for the general reader, 

 the basic principles involved. By discarding all 

 refinements, whilst extending his specimen calcu- 

 latit>ns to cover a wide range of problems, Mr. 

 Bairstow emphasises the fundamental principle 

 that all design is conditioned by the experimentally 

 determined properties of the wing section, and 

 thus prepares his reader for an intelligent 

 appr€cia,tion of the more detailed considerations 

 whiqh fpUow. 



Chap, iii., which deals with experimental 

 roethpds of m,easurement, as they have been 

 developed in the aerodynamics laboratories, is 

 NO. 2630, VOL. 105] 



characterised by the same breadth of view and 

 neglect of unnecessary refinement. In it the 

 reader, now initiated into the problems which the 

 science of aerodynamics has to solve, learns how 

 these problems are attacked on the experimental 

 side, and what order of accuracy may reasonably 

 be expected in their solution. The account given 

 on p. 115 of the theory of model experiments on 

 non-rigid airship envelopes might seem ,to suggest 

 that the model scale should be chosen so as to 

 give (in theory) equality of fabric tensions, 

 whereas actually, of course, it is easy to obtain 

 proportionality in a model of any scale, and 

 increase in scale has the advantage that it reduces 

 the error introduced by the weight of the fabric. 

 Again, we could have wished that some descrip- 

 tion had been included of the " cascade " experi- 

 ment on aerofoils, which seems so promising a 

 line of development for propeller theory ; but from 

 a footnote on p. 290 we gather that the technique 

 of this experiment had not been fully worked out 

 at the time of writing. 



Considerations of space prevent us from dealing 

 as we could have wished with chap, vii., an admir- 

 able resume of the investigations which have been 

 made — without very much result, . so far, as 

 regards their practical application — into the 

 theory of fluid motion, and with chap, viii.j in 

 which the author states his present position on 

 the question of "scale effect." Not long ago this 

 was a question which divided aeronautical experts 

 into two fiercely warring bands : but the heat 

 of that battle has since died down, and we 

 imagine that few will take exception to Mr. 

 Bairstow's summing up of the position. Scale 

 effect, or at any rate its possibility, is indicated 

 by theory ; it is proved beyond question to exist 

 in many of the problems which can be investigated 

 in wind-channels ; and it may very well be present 

 to a troublesome degree in many of the problems 

 which concern the complete aircraft : but the 

 order of accuracy hitherto attainable in full-scale 

 work is too far below the ordinary standard of 

 wind-channel work to justify us in attributing to 

 scale effect every discrepancy which has been dis- 

 covered in the comparison of model and full-scale 

 data. 



The remainder of the book, which analyses and 

 applies the design data from the aerodynamics 

 laboratories, scarcely affords suitable material for 

 criticism on a first reading; ultimately these 

 chapters must be judged by the service 

 which they render, in daily use, to the 

 design office and the laboratory. We shall con- 

 tent ourselves by mentioning one particular in 

 which, as we believe, the book could be improved 

 in a second edition. We do not think it is merely 



