io6 



NATURE 



[September 26, 19 12 



iny point in this chapter is the author's suggestion 

 that nig-ht travelhng is an adaptation to the neces- 

 sity that most birds have of devoting the daytime 

 to the seach for food. 



The book is lucidly and carefully written and 

 the author occasionally slackens his rein and re- 

 veals his power as a stylist, the description of a 

 "bird-night" at Eddystone being perhaps the finest 

 example. There are several good photographs of 

 various stations, notably those of Fair Isle by Mr. 

 \\'. Norrie, but the chief illustrations are maps 

 and weather-chart.s — all conspicuous for clearness 

 and simplicity. We have already referred to the 

 admirable first frontispiece. The book is dedicated 

 to the Duchess of Bedford, herself an ardent 

 ornithologist, who has given the author valued 

 assistance. 



THE QUESTION OF THE BIPLANE 

 VERSUS THE MONOPLANE. 



THE recent order of the War Office suspending 

 the use of monoplane flying machines for 

 military purposes has led to the renewal, in the 

 daily Press, of a discussion of the old riddle, 

 " \Miich is the better, the monoplane or the 

 biplane?" When Bleriot crossed the Channel, 

 the daily papers rang with the praises of the mono- 

 plane ; now everyone favours the biplane, and 

 there is a danger lest the monoplane may be con- 

 demned for faults not necessarily attributable to 

 the mere fact that it is a monoplane. 



The military authorities have wisely called in 

 the assistance of the National Physical Laboratory 

 in seeking an explanation of why so many of the 

 recent accidents have occurred with monoplane 

 machines. Even if the work placed in the hands 

 of the Teddington department does not extend 

 beyond overhauling and testing the machines used 

 in the Army, the physicists ought to have sufficient 

 scope for arriving at many important conclusions 

 regarding essential features of aeroplane con- 

 struction. For the purposes of an inquiry of the 

 type proposed, it appears desirable that the same 

 tests should be applied to biplanes as to mono- 

 planes ; but the value of the work will be ereatly 

 enhanced if the investigation is conducted on 

 general lines, and not confined to the mere testing 

 of the Army machines. It is easy enough to say 

 that when a stay has broken it should be replaced 

 by a stronger one, and to draw up a report, which 

 would suffice to enable any defects in existing 

 machines to be patched up, but it is essential for 

 real progress that the Laboratory authorities 

 should have a free hand to assist in the evolution 

 of a more perfect type of flying machine than either 

 the existing monoplane or biplane. 



It must not be forgotten that the terms mono- 

 plane and biplane usually imply something more 

 than the mere difference between a "single- 

 decker" and "double-decker" (to quote the 

 German equivalents). The former usuallv has the 

 propeller in front, the latter behind. Thus an 

 inquiry necessarily turns on at least two noints. 

 namely, the relative advantages of the single- and 

 doulilc-derker, and whether the propeller i"s better 

 NO. 2239, VOL. go] 



placed in front or behind. Further subjects sug- 

 gested are the gyrostatic effect of the propellers, 

 the relative merits of rotary and oscillating 

 engines, and so forth. 



In regard to the first point, it must be remem- 

 bered that even Liilenthal experimented success- 

 fully with the double-decked type ; that Chanute, 

 after trying not only " single- " and " double- 

 decked " gliders, but also "multiple-winged 

 machines," finally decided on the glider with two 

 superposed surfaces as the best on which to experi- 

 ment ; that his experiments were continued by the 

 Wrights, and led to their first realisation of arti- 

 ficial flight. One advantage of the two-surfaced 

 arrangement is that, with an equivalent area, the 

 wings can be made of lesser span, and thus the 

 bending moments they have to sustain are propor- 

 tionately reduced ; moreover, these bending 

 moments are much better sustained by the frame- 

 work, which naturally takes the form of a latticed 

 girder. Of course, from this point of view a 

 triplane would even be better than a biplane, but 

 the gain would be less important. 



There would be no difficulty in constructing a 

 "two-decker" with a propeller in front, and, from 

 the point of view of the physicist, the position of 

 the propeller depends largely on whether it is 

 better for the propeller to receive the wash from 

 the planes or for the planes to receive the wash 

 from the propeller. One advantage of the latter 

 plan has not, perhaps, received the attention that 

 it deserves. It must not be forgotten that the 

 action of the propeller sets up a rotation in the 

 "wash" behind it, and, as Sir G. Greenhill 

 has pointed out, so far from being negli- 

 gible, the amount of this rotation is directly related 

 to the horse-power and rate of revolution of the 

 engine. In fact, the propeller exerts on the air :» 

 constant torque, which tends to produce angular 

 momentum, and is equal in amount to the torque 

 of the engine. If, then, the main planes are 

 placed in the wash of the propeller, the rotating 

 air on striking them will produce a difference of 

 pressure on the two sides tending to counteract 

 the corresponding torque on the aeroplane, and 

 the machine will not heel over sideways to the 

 same extent that it would if a single propeller 

 were placed behind. For the purposes of the War 

 Office, the propeller in front is disad\'antageous, 

 as it interferes with scouting or shooting from an 

 aeroplane. On the other hand, we have the 

 recommendation of a well-known engineer that the 

 engine should be in front of the aviator, so that 

 the latter shall not be crushed underneath the 

 former in case of an accident. 



.•\part from these essential differences between 

 monoplane and biplane, great importance attaches 

 to an investigation into the gyrostatic couples 

 caused by both rotary engines and propellers. At 

 present, apart from setting up strains in the 

 framework, which require the latter to be ade- 

 quately staved, these cause a mixing-up of 

 the longitudinal and lateral motions of the machine 

 which must necessarily greatly increase the danger 

 of accidents when the machine is being navigated 

 in gusts of wind. It is important that more 



