P April 14, 1910] 



NATURE 



205 



side of a plane has nothing whatever to do with lifting 

 power. For instance, there is the familiar experiment with 

 paper sometimes brought forward to show that the air 

 passing over the back of the plane lifts it. As Phillips 

 believed, it creates a vacuum on the upper rear extremity, 

 and the paper naturally is pressed upwards ; but let me 

 explain the fallacy of the argument which seeks to show 

 that the upper side of the plane therefore gives lifting 

 power. If that piece of paper were free in the air, it 

 would not matter how hard one blew on its upper surface it 

 would not lift. It is only when it is held, in fact ; and 



Fig. I. — Course of Airship against Side Wind. A, starting-poinu B, destination. The shaded portion is a moving 

 body of air, i.e. the wind. The diagonal line, C, is the path of the airship with regard to the air. The dotted 

 horizontal line is its path with respect to the earth. 



the lifting power is derived entirely from the expenditure 

 of energy. The harder one blows the more it lifts. The 

 power to rise is derived entirely from the energy with 

 which one blows, or, in the alternative of a plane being 

 driven through the air, entirely from the energy of the 

 motor. There is no lift at all without the expenditure of 

 power by the engine. 



Scarcely any of these theories of the action of the air 

 on the back of the plane have been mathematically formu- 

 lated. Indeed, we are only on the threshold of the science. 



No analogy of the behaviour of other fluids is of much 

 use when we come to deal with the air. The air is not 



Fig. 2.— In this case the wind is stronger, i.e. a longer body of air 

 passes in the same time. The airship therefore has farther to 

 travel with regard to its passage through the air and takes longer 

 in order to arrive at B. Apparently, while the airship keeps to 

 a much greater angle, it moves along the dotted line A. B. 



X perfect fluid. It is a very turbulent fluid. There are 

 vortices and reverse movements at the back of the plane. 

 Practically nothing is known of the mathematics of the 

 subject. The leading mathematicians are silent, and I 

 have observed that the only theorists putting forward their 

 conclusions as if they were capable of scientific proof are 

 minor men of science. It is very necessary at present to 

 keep an open mind. Sir George Greenhill and Mr. Horace 

 Darwin, who have been appointed to the Aeronautical 

 Advisory Committee, have not yet issued any statement as 

 ta their researches — not that they are unwilling, but prob- 



NO. 21 II, VOL. 83] 



ably because they are unable at present to speak with any 

 certainty. 



It seems a long way from cricket to flying, but a re- 

 mark by Mr. P. F. Warner in an article on modern bowl- 

 ing the other day suggests an important consideration for 

 aviators. The great cricketer was discussing " swerving " 

 balls, and he said, " The heavier the air the greater the 

 cushion, and in the thick, smoke-laden atmosphere of 

 Sheffield or Bradford Hirst will swerve infinitely more than 

 in the clearer and brighter climate of Sydney, Adelaide 

 or Johannesburg." It is scarcely necessary that we should 



point out the applica- 

 tion to flight. An aero- 

 planist who found it 

 easy to sustain flight at 

 twenty miles an hour 

 when near the ground 

 might, on attaining an 

 altitude of 4000 feet, 

 find it necessary to in- 

 crease his speed to forty 

 miles an hour, or, 

 rather, he could never 

 get so high unless his 

 engines were capable of 

 giving the increased 

 speed. 

 An attempt to secure some measure of stability is to 

 place the planes at a dihedral angle, as in the Antoinette 

 monoplane, in which the wings extend from the body in 

 the form of a shallow V. This method was also formerly 

 used by Bl^riot, but the tendency nowadays is to have 

 horizontal and even slightly concave surfaces for the sake 

 of the economy of surface involved. Now if Bleriot re- 

 verted to the dihedral plane, he would have to make his 

 machine two or three feet longer on each side. The 

 dihedral plane is also wasteful of power. Instead, as we 

 have seen, he relies entirely on the wing-warping arrange- 

 ment for stability. 



Cocking tried an inverted parachute in order to secure 

 a steady fall instead of the swinging movement which all 

 parachutists have to endure. It is true Cocking's 

 apparatus gave way under the strain, but in any case it 

 is quite certain that he did not give large enough diameter 

 to his parachute, made on that principle, to sustain him. 



This brings us to the discussion of a rather contentious 

 point — that of the suspended centre of gravity. We have 

 seen how early gliders depended below the sustaining 

 planes. Now, in the Antoinette the weight is carried on 



Fig. 3. — A Paper Experiment. The effect of blowing on the forward edge 

 of a curved plane. Dotted lines show how paper rises. 



the same level as the sustaining surface. Well, in the 

 Bleriot cross-Channel machine the centre of weight is 

 slightly below the sustaining surface. In the Santos- 

 Dumont it is considerably below. In the newest Bleriot 

 it is also well below, and in the Chauvi^re monoplane it 

 is as much as 3 feet below. Now from what has been 

 already said it will be seen that this secures stability only 

 in the very smallest degree, and that the weight would 

 have to be 30 or 40 feet below in order to secure the 

 desired effect ; and then you could never get the driving 

 power necessary ; but it is probable that M. Bleriot, M. 

 Santos-Dumont, and M. Chauviere, in constructing their 

 machines in this way, have an eye, not to improve stability, 

 but to other advantages. By this method they can obtain 

 various constructional advantages, above all, a continuous 

 leading edge by which they greatly economise lifting power. 

 In short, they manage with a smaller machine. They 

 make no effort, be it noted, to rely any less upon their 

 wing-warping arrangements. 



An aeroplane must travel at a certain speed to support 

 itself at all. To enable it to rise to a higher altitude the 

 power must be increased. There is, of course, a margin 



