March 3, 19 10] 



NATURE 



13 



The failure of practical aviators to obtain auto- 

 matic stability may be due in no small measure to 

 the number of conditions that have to be satisfied. 

 A vertical fin in front might satisfy one condition 

 •of stability, and introduce instability through another 

 •condition, while a similar fin at the back might 

 satisfy the second condition and introduce instability 

 through the first. In either case the impression 

 produced would be that the device secured automatic 

 stabilit},-, but that such stability was a hindrance 

 rather than a help, the correct interpretation being 

 that the conditions of stabilit}.- had not been sufficiently 

 investigated. By abolishing the fins the aviator 

 would obtain a machine with defective stability, i.e. 

 with one or more roots of the biquadratic vanishing, 

 and would find it easier to maintain his balance by 

 artificial control than in the previous unstable arrange- 

 ment. 



Of arrangements with two fins, the cases have been 

 considered where both fins are at the level of the 

 centre of gravity, where one is above, and where both 

 are above. The conditions of stability assume various 

 forms, but there is one arrangement which appears 

 to possess an exceptionally wide range of stability, 

 and I have made provisional application for a patent 

 in this connection. 



A machine such as the Voisin t)pe, with two planes 

 of considerable span at different angles of attack, is 

 more stable than one with a single sustaining system, 

 and the difference is equivalent to a variation in the 

 arrangement of the fins which is easily calculated. 



The asymmetric oscillations of an aerodrome do 

 not separate into two kinds, of long and short period, 

 like the symmetric ones. As a general rule the bi- 

 quadratic has one root determined approximately by 

 the first two terms representing a quick subsidence, 

 one root determined by the last two representing a 

 iilow subsidence, and a pair of roots determined by 

 the middle terms representing a damped oscillation. 



The inclination of the flight-path to the horizon has 

 a considerable influence on the asymmetric stability. 

 In several instances we found that instaHilit}- occurs 

 when an aerodrome is descending at an angle to the 

 horizon the tangent of which is double that of the 

 angle of attack of the main planes. Other arrange- 

 ments become unstable when rising at more than a 

 certain angle ; in the best arrangement referred to 

 above the stability is practically independent of the 

 inclination. As the symmetric and asymmetric oscil- 

 lations of an aeroplane are independent, it is important 

 that it should preser\'e its asymmetric stability even 

 when it is not in longitudinal equilibrium. The de- 

 pendence of stability on inclination aff'ords a very 

 simple and likely explanation of certain " vagaries " 

 described on pp. 342, 343 of Lanchester's "Aero- 

 donetics " ; account would, however, have to be taken 

 of accelerations of the centre of mass in an exact 

 comparison of theor}- with observation. 



Bent-up or V-shaped wings lead to much more 

 difficult analysis, and it appears that their effect is not 

 exactly equivalent to any combination of vertical fins 

 except in certain cases. \ pair of " stabilisers " or 

 small planes, which may be fixed at the extremities 

 of the main aeroplanes at an angle of, say 45°, is 

 equivalent to a single raised vertical fin if the planes 

 of the stabilisers are parallel to the line of flight. 



Mr. Harper has worked out the asymmetric stability 

 of the Antoinette type with a single pair of bent-up 

 supporting surfaces. The conditions of stabilit],' are 

 satisfiable by furnishing the machine with a tail of 

 suitable length, or by raising the dihedral angle of 

 the V-shaped wings above the centre of gTa\-it\\ 



I should like to direct attention to the importance 

 of eliminating the personal element in experimental 

 NO. 2105, VOL. 83] 



tests of aeroplane stability, by the use of models. 

 The possibility of long-distance flights by skilled 

 aviators having been demonstrated, there is not so 

 much point in repeating these verifications as in 

 extending our knowledge in other directions, and find- 

 ing how far the element of skill can be dispensed with 

 by effecting improvements in aeroplane design. 



The stability of dirigibles opens up another field of 

 study, on which we hope to do something during the 

 coming year. 



Owing to the attention now given to aeroplane con- 

 struction, it appeared desirable to give, in the present 

 article, an advance account of investigations which 

 may not be ready for publication in extenso for some 

 time to come. G. H. Bryan. 



Added January 27, 19 10. — The .Aeronautical Journal 

 for January, now to hand, includes a short abstract, 

 illustrated by badly executed diagrams, and contain- 

 ing numerous uncorrected printers' errors, in which 

 the symmetric stability of a single-surfaced aerodrome 

 without tail is made to depend on a cubic instead of a 

 biquadratic equation. This result is obtained by the 

 ver\- doubtful method of "assuming V to be constant 

 for a short period," that is, neglecting fluctuations 

 in horizontal velocity. Owing to this assumption the 

 conclusions reached may perhaps represent the condi- 

 tions that the machine may be stable with reference 

 to the shorter oscillations, but not with respect to 

 the longer ones, and the inference that a machine can 

 be much more stable at moderate velocities than is 

 generally supposed must not be regarded as conclu- 

 sive. 



THE WORK OF THE WO BURN FRUIT F.4i?3/.» 



AMONG the profusion of ag^cultural and horticul- 

 tural reports, many of which can at best be said 

 only to possess a ven,- ephemeral interest, it is pleasant 

 to come across something of permanent and abiding 

 value, work carefully executed and followed to its 

 logical conclusion. 



Such must be the feeling of every discerning reader 

 as he studies the report by the Duke of Bedford and 

 Mr. Spencer Pickering on the chemical relationships 

 of the copper fungicides. The problem is one of ven.' 

 great economic importance. Modem conditions of 

 fruit-growing tend to foster and distribute from 

 countr}' ta countr\^ the fungi parasitic on fruit trees. 

 On the other hand, the grower is more and more 

 anxious to keep them down ; not only do they 

 adversely affect his ^ield, but they often spoil the 

 looks of his fruit, a very serious matter in modern 

 markets. 



The most popular fungicides are the copper com- 

 pounds, more particularly Bordeaux mixture, a basic 

 salt prepared by adding lime to a solution of copper 

 sulphate. This mixture has been used by fruit and 

 potato growers for a number of years with great 

 success, and has formed the subject of a vast number 

 of papers. Unfortunately few of them are of much 

 value, since it only rarely happens that a man is 

 found to combine an interest in horticultural problems 

 with exact habits of thought. Until recently nothing 

 was known of the composition of Bordeaux mixture, 

 not even the proportions in which the constituents 

 should be mixed to give the best results. Certain 

 American investigators recommended 4 lb. of copper 

 sulphate in fift\' gallons of water, and some of the 

 English writers, borrou-ing not too intelligently in 

 this as in other matters, recommended the same 

 strength, oblivious of the fact that the American 

 gallon is little more than four-fifths of the English 



1 Eleventh Report of the Wobarn Experimental Fruit Farm, by the Duke 

 of Bedford, K.G., F.R.S., and Spencer U. Pickering, F.R.S. (Tke Amal- 

 gamated Press, Ltd., (910.) 



