230 



NATURE 



[August 25, 1910 



given showing the numerical data (dimensions, weight, 

 horse-power, speed, and so forth), both in regard to 

 motors and aeroplanes. The reader can see at a 

 glance what the present position is with regard to 

 details of construction. 



The book is a compilation of useful informa- 

 tion, and not a mere exposition of the author's fads; 

 in fact, it is conspicuously free from dogmatic expres- 

 sions of opinion. Indeed, the author carefully states 

 that " it is not intended that an aeroplane could be 

 desig;ned upon the data contained herein." He has, 

 however, directed attention clearly to the great im- 

 provements still required in those details of construc- 

 tion with which he is most conversant. For example, 

 he says ; — 



"The study of aerial propellers is only in its in- 

 fancy, and an enormous amount of experimental work 

 remains to be done. The efficiency of present-day 

 desig;ns is abnormally low, and in many cases not 

 more than 50 per cent." 



Again, in the chapter on "future developments," 

 we are told :■ — 



"The depreciation of the igoq flying machine is 

 enormous, the life of the engine is seldom more than 

 200 miles; in some cases it is a very few miles indeed, 

 and breakdowns or seizures are a constant evil." 



The author believes in an internal-combustion tur- 

 bine. This might obviate the rotatory inertia of the 

 present Gnome motor, which must affect the steering 

 by its gyroscopic action. " Strength of materials " 

 also receives discussion, and derives additional interest 

 from the fact that it is a moot point whether defect 

 in this respect or instability was the cause of certain 

 recent fatalities. Mr. Brewer believes that the flying 

 machine of the future will, like a ship, have living 

 accommodation for passengers and crew ; and had he 

 permitted himself to go a little outside his own 

 speciality he would have seen that a necessary condi- 

 tion for progress is the abolition of "ailerons," 

 " gauchissement," or "warping." But the author 

 very wisely fights shy of stability considerations, 

 though he has, on the other hand, an instructive 

 chapter on the art of flying, in which he says : — 

 " Mr. Rolls has described the initial sensations as 

 those received in driving a motor-car which is skidding 

 in all directions at once." 



The details of Henson's model of 1843 show that 

 the conception of an aeroplane is by no means new, 

 but that the want of a sufficiently light and powerful 

 motor is the obstacle which has hitherto prevented 

 its realisation. 



-As the author carefully disclaims any attempt to 

 deal with mathematical considerations, one cannot, 

 of course, take very serious exception if the few refer- 

 ences which he gives are occasionally inaccurate or 

 obscurely stated. It will be sufficient to take 

 a few examples. On p. 12 he says, when 

 speaking of the components of pressure he refers to 

 the lift, as one of them, "and that, acting in a 

 horizontal direction to overcome the skin friction of 

 the machine, this is called the drift," forgetting that 

 in an inclined plane drift exists independently of skin 

 fricrion. On p. 15 he states Joessel and .Aranzini's 

 NO- 2130, VOL. 84] 



formula for the centre of pressure, and proceeds to 

 e.xplain that the coordinate of this point has a maxi- 

 mum value — a conclusion at variance with the formula 

 in question. In the next sentence he speaks of " con- 

 ditions of stability " where equilibrium is meant. On 

 p. 87 he reminds us of the Irishman who said, "There 

 were five of us ; there was myself, that's one, there 

 were the two Flynns, that's two, there was Mike 

 Murphy, that's three," and so on. For of the " five 

 variables" in propeller design, the first is "the speed 

 of the machine and the power available." (This is, 

 however, a trivial objection.) On p. 20 he says that 

 the sum of the sine of a certain angle and the tangent 

 of another angle may be written down as twice the 

 sine or tangent of either angle ; but there is no 

 evidence that the angles are meant to be equal or 

 nearly so. And the statement of von Loessl's law 

 of resistance (p. 236) gives P = P„sina, whereas on 

 p. 15 we have P = 2P„sino with a small. 



Criticisms of a similar character apply with greater 

 force to M. Petit's book (2), for which we have to 

 thank Messrs. Hubbard and Ledeboer, editors of the 

 Aeronautical Journal, for an English translation. 



It would have been better if M. Petit had confined 

 his attention to the theme described by the title " How 

 to Build an .Aeroplane," and had not trenched on 

 dangerous ground of a theoretical character. To 

 begin withj the author bases his discussion of thrust 

 on a moving plane on VVegner von Dallwitz's for- 

 mula. .According to this the thrust varies as the 

 tangent-squared of the angle of attack. When this 

 angle is small the thrust would thus become a quan- 

 tity of the second order of small quantities, and the 

 law would approximate to the "sine-squared" law 

 originally proposed by Newton. That this result is 

 not in accordance with experiment has been sufficiently 

 shown by Langley and others. If in order to cut 

 matters short it is necessary to confine the discussion 

 to one theory of air resistance, the choice is therefore 

 a bad one. English readers will do well to remember 

 that tg stands for tangent, otherwise the printing of 

 this in italics, while sin and cos are in Roman type, 

 may mislead them. 



On pp. 22-36, in discussing lateral stability, the 

 author falls into a very common error in regard to 

 the effects of varying the height of the centre of 

 gravity, and when his treatment of the subject con- 

 tains such statements as that " this application of the 

 centre of gravity is shown in elementary physics by 

 the pendulum," misunderstandings are likely to arise. 

 In reality equilibrium and stability are but little 

 affected by raising or lowering the main planes rela- 

 tively to the centre of gravity, or, what is the same 

 thing, lowering or raising the centre of gravity rela- 

 tively to the main planes. If the resultant pressure 

 always acts along a perpendicular to the main planes 

 through their centre of pressure, and if this perpen- 

 dicular passes through the centre of gravity, it will 

 continue to do so when the aeroplane receives an 

 angular displacement, and there will be no moment s 

 tending to right the machine. In this respect an j 

 aeroplane differs from a pendulum and a balloon. 

 The matter is a little difficult to make clear, and will 



