REVIEWS 337 



ENGINEEBIITG 



The Mechanical Principles of the Aeroplane. By S. Brodetsky, M.A.,. 

 Ph.D. [Pp. vii + 272, with 119 illustrations.] (London: J. & A. 

 Churchill, 1921. Price 21s. net.) 



Dr. Brodetsky takes his place between Greenhill, Bothezat, Bader, and 

 Joukowsky on the one hand, and Bairstow and Thomson on the other. 



The former attempt to place Aerodynamics on a basis of mathematical 

 physics, the latter are content to build on a foundation of results obtained 

 experimentally in the wind tunnel and the field. 



Dr. Brodetsky follows both methods, but it must be admitted that there 

 seems little hope of bridging the gap between them until the mechanism of 

 turbulent flow is better understood than at present. 



This is a field of effort which should attract the best intellect to be found 

 among students of Aerodynamics. 



The introduction is an ambitious attempt to classify the problems of 

 flight in eight pages. 



Chapter I, on dimensions, should be digested with thoroughness, and 

 should lead to an irresistible preference for a consistent system of units, and 

 thence to the sole employment of the C.G.S. system, and of the practical 

 units derived from it. 



Chapter II is restricted to dynamics of a particle in a resisting medium, 

 and is useful as an introduction to bomb-dropping rather than to aeroplane 

 theory. More than due weight is given to Lanchester's contributions to the 

 theory and nomenclature of stability. Bryan's long pitch and tumbler 

 flight or plain pitching, stalling, and looping are preferable to phugoid, and 

 to such a phrase as " catastrophic instability." 



Chapters III and IV develop the rigid dynamics of the aeroplane along the 

 lines of Bryan's classical work, and, later on. Chapters VII and VIII go further 

 into the numerical determination of rotary and linear derivatives, and their 

 application to actual problems of stability, and of free and forced oscillations. 



Much of the treatment is fresh and worth the consideration of those 

 whose professional business it is to carry out such calculations as well as of 

 the ambitious student. 



Chapters V and VI recapitulate the well-worn methods of conformal 

 representation applied to the flow of an ideal fluid without and with free 

 stream lines. It cannot be said that this abstract theory has much relation 

 to the flow of viscous fluids as we observe them, yet the student simply 

 cannot afford to neglect the acquirement of at least some familiarity with 

 the method and its results, if only to clear his mind of any lingering false 

 analogy with the principles of rigid dynamics. In particular, Bernoulli's 

 theorem can be applied where we have established experimentally the general 

 lines of flow. 



The discussion of airscrew theory in six pages at the end of Chapter VII 

 will give some idea of the severe condensation from which the exposition 

 suffers or benefits according to the point of view. 



The author has not adopted the noinenclature of the Royal Aeronautical 

 Society, which imposes on the reader the burden of interpreting yet another 

 system of symbols. 



Yet these criticisms are rather of detail, for this must take its place as 

 one of the most serious and valuable text-books yet published towards estab- 

 lishing a rational theory of the aeroplane. A. R. L. 



The Dynamics of the Airplane. By Kenneth P. Williams, Ph.D. (Mathe- 

 matical Monographs, No. 21.) [Pp. viii + 138, with 50 diagrams.] 

 (New York: John Wiley & vSons ; London: Chapman & Hall, 1921. 

 Price 13s. bd. net.) 



The application of dynamical principles to the motion of the aeroplane is 



