i6 



NATURE 



[September 30, 19 15 



the 25 h.p. Anzani, with which Bleriot first flew 

 the Channel, to some of the more modern engines 

 of 200 h.p. The growth of the art of flying is 

 strikingly illustrated by the fact that whilst 25 

 h.p. was a useful size of engine in 1909, no 

 present-day aeroplane, other than those for school 

 purposes, has a horse-power less than 80, whilst 

 many considerably exceed this. The celebrated 

 Gnome engine, by means of which Farman and 

 Paulhan achieved their early successes, is de- 

 scribed very fully. The power was then a 

 nominal 50 h.p., but really only 42 h.p., but Fig. 2 

 shows a much larger model weighing only 540 lb. , 

 whilst developing 180 h.p. The complication of 

 cylinders which is essential for light engines is 

 most clearlv shown in this illustration. 



Fk;. 2. — Eighteen-cylindered 200 h.p. Gnome rotary engine. From " Aero Engines," by G. A. Burls, 



As engines get more and more powerful, the 

 advantages of the rotary air-cooled type over the 

 more trustworthy but somewhat heavier water- 

 cooled engines become less and less, and may ulti- 

 mately lead to extinction of the former type. The 

 very high proportion of their existence which aero- 

 engines spend in the repair-shop is clear evidence 

 that finality of design is not yet even closely ap- 

 proached, but there is reason to hope that the 

 introduction of large water-cooled engines will 

 considerably reduce the time of repair without the 

 disadvantage of greater weight. 



The earlier part of the book contains theoretical 



matter relating to the working of hot-air engines 



and follows standard lines in most respects. After 



contrasting the weights of internal combustion 



NO. 2396, VOL. 96] 



engines, the air-cooled engine of about 3 lb. per 

 b.h.p. with the workshop engine weighing 200 lb. 

 per b.h.p., the author proceeds to a discussion of 

 the working cycle. By some extraordinary calcu- 

 lation he concludes that an engine using the Car- 

 not cycle would weigh 17 tons per b.h.p. ; one 

 feels that this is overdone, and that part of the 

 trouble at least is not legitimately laid on the 

 Carnot cycle, but should be borne partly by the 

 designer and partly by the calculator. 



Excursions into aerodynamics have already been 

 stated to be few; they are also mostly unfortun- 

 ate. It is stated that a reduction of gross weight 

 of an aeroplane improves the gliding angle, where- 

 as the two are independent, the effect of reducing 

 the weight being to reduce the flying speed at 

 the same gliding angle. A little 

 later occurs a meaningless state- 

 ment that "the power, caeteris 

 paribus, varies as the cube of 

 the air speed, etc." What the 

 Latin expression covers it is not 

 easy to see ; for any given aero- 

 plane the horse-power at first 

 decreases as the speed increases, 

 becomes steady, and then 

 gradually increases. No power 

 of the speed at all can be stated 

 in such general terms. On the 

 same page there occurs a con- 

 spicuous error in applying the 

 principles of relative motion to 

 flight In a gale. 



These are, however, minor de- 

 fects which can be put right in 

 later editions, and the informa- 

 tion on engines gives the book 

 a right to the bookshelves of all 

 serious students of aviation. 



(3) This work is a summary 

 of the dynamics of the aero- 

 plane, and has apparently aimed 

 at the suppression of detail in 

 order to make the important 

 features clear. The early part 

 of the book is based on the re- 

 sults of tests at the various 

 aerodynamical laboratories, on 

 the lift and resistance of wing 

 forms, and the resistances of 

 wheels, etc. In dealing with the 

 photographs are reproduced 

 stream- 



wires, struts, 

 problem of flow, 



which indicate the difference between 

 line " bodies and forms having high resistance. 

 The " stream-line " body is shown as allowing the 

 fluid to move In towards the tail, whilst in the 

 blunter forms the tail region is occupied by eddies. 

 This Is one of the more clearly exhibited forms of 

 the effects of viscosity, but in later photographs, 

 showing the velocity of the fluid at any point, the 

 very great difference between the flow round 

 " stream-line " bodies and those of mathematical 

 calculation is almost equally striking. 



After discussing the effects of changes of sec- 

 tions of the wings on their efficiency, a few aero- 

 planes are described, with particulars as to 



