Artificial and Natural Flight — Context and Discussion

Air Currents and the Flight of Birds, 11

Principally Relating to Screws, 31

Experiments with Apparatus Attached to a Rotating Arm--Crystal Palace Experiments, 62

Hints as to the Building of Flying Machines--Steering by Means of a Gyroscope, 77

The Shape and Efficiency of Aeroplanes--The Action of Aeroplanes and the Power Required Expressed in the Simplest Terms--Some Recent Machines, 99

Recapitulation of Early Experiments--Efficiency of Screw Propellers, Steering, Stability, &c.--The Comparative Value of Different Motors--Engines--Experiments with Small Machines Attached to a Rotating Arm, 130

INDEX OF ILLUSTRATIONS.

1. Diagram showing the reduction of the projected horizontal area, 2 2. Professor Langley’s experiments, 5 3. Eagles balancing themselves on an ascending current of air, 14 4. Air currents observed in Mid-Atlantic, 16 5. Glassy streaks in the Bay of Antibes, 17 6. Air currents observed in the Mediterranean, 18 7. The circulation of air produced by a difference in temperature, 27 8. Kite flying, 29 9. Group of screws and other objects used in my experiments, 32 10. Some of the principal screws experimented with, 32 11. The three best screws, 33 12. Apparatus for testing the thrust of screws, 34 13. Apparatus for testing the direction of air currents, 35 14. The ends of screw blades, 36 15. The manner of building up the large screws, 39 16. A fabric-covered screw, 40 17. The hub and one of the blades of the screw on the Farman machine, 42 18. Section of screw blades having radial edges, 43 19. Form of the blade of a screw made of sheet metal, 44 20. New form of hub, 45 21. Small apparatus for testing fabrics for aeroplanes, 50 22. Apparatus for testing the lifting effect of aeroplanes and condensers, 51 23. Apparatus for testing aeroplanes, condensers, &c., 52 24. Cross-sections of bars of wood, 53 25. Sections of bars of wood, 54 26. A flat aeroplane placed at different angles, 55 27. Group of aeroplanes used in experimental research, 56 28. An 8-inch aeroplane which did very well, 57 29. Resistance due to placing objects in close proximity to each other, 58 30. Cross-section of condenser tube made in the form of Philipps’ sustainers, 60 31. The grouping of condenser tubes made in the form of Philipps’ sustainers, 61 32. Machine with a rotating arm, 63 33. A screw and fabric-covered aeroplane in position for testing, 64 34. The rotating arm of the machine with a screw and aeroplane attached, 65 35. The little steam engine used by me in my rotating arm experiments, 66 36. The machine attached to the end of the rotating shaft, 68 37. Marking off the dynamometer, 69 37_a_. Right- and left-hand four-blade screws, 70 38. Apparatus for indicating the force and velocity of the wind direct, 71 39. Apparatus for testing the lifting effect of aeroplanes, 73 40. Front elevation of proposed aeroplane machine, 77 41. Side elevation of proposed aeroplane machine, 78 42. Plan of proposed aeroplane machine, 79 43. Plan of a hélicoptère machine, 82 44. Showing the position of the blades of a hélicoptère as they pass around a circle, 83 45. System of splicing and building up wooden members, 86 46. Cross-section of struts, 86 47. Truss suitable for use with flying machines, 87 48. The paradox aeroplane, 88 49. The Antoinette motor, 89 50. Section showing the Antoinette motor as used in the Farman and De la Grange machines, 90 51. Pneumatic buffer, 91 52. Gyroscope, 94 53. Adjusting the lifting effect, 95 54. Showing that the machine could be tilted in either direction by changing the position of the rudder, 96 55. Adjusting the lifting effect, 97 56. Adjustment of the rudders, 98 57. Diagram showing the evolution of a wide aeroplane, 102 58. In a recently published mathematical treatise on aerodynamics an illustration is shown, representing the path that the air takes on encountering a rapidly moving curved aeroplane, 104 59. An illustration from another scientific publication also on the dynamics of flight, 104 60. Another illustration from the same work, 105 61. The shape and the practical angle of an aeroplane, 105 62. An aeroplane of great thickness, 106 63. Section of a screw blade having a rib on the back, 106 64. Shows a flat aeroplane placed at an angle of 45°, 107 65. The aeroplane here shown is a mathematical paradox, 107 66. This shows fig. 65 with a section removed, 107 67. Diagram showing real path of a bird, 108 68. The De la Grange machine on the ground, 111 69. The De la Grange machine in full flight, 111 70. Farman’s machine in flight, 112 71. Bleriot’s machine, 113 72. Santos Dumont’s flying machine, 113 72_a_. Angles and degrees compared, 115 72_b_. Diagram showing direction of the air with a thick curved aeroplane, 118 72_c_. Aeroplanes experimented with by Mr. Horatio Philipps, 118 73. The enormous balloon “Ville de Paris,” 123 74. Photograph of a model of my machine, 130 75. The fabric-covered aeroplane experimented with, 131 76. The forward rudder of my large machine showing the fabric attached to the lower side, 131 77. View of the track used in my experiments, 134 78. The machine on the track tied up to the dynamometer, 135 79. Two dynagraphs, 136 80. The outrigger wheel that gave out and caused an accident with the machine, 137 81. Shows the broken planks and the wreck that they caused, 138 82. The condition of the machine after the accident, 139 83. This shows the screws damaged by the broken planks, 140 84. This shows a form of outrigger wheels which were ultimately used, 141 85. One pair of my compound engines, 142 86. Diagram showing the path that the air has to take in passing between superposed aeroplanes in close proximity to each other, 144 87. Position of narrow aeroplanes arranged so that the air has free passage between them, 145 88. The very narrow aeroplanes or sustainers employed by Mr. Philipps, 146 89. One of the large screws being hoisted into position, 149 90. Steam boiler employed in my experiments, 157 91. The burner employed in my steam experiments, 157 92. Count Zeppelin’s aluminium-covered airship coming out of its shed on Lake Constance, 161 93. Count Zeppelin’s airship in full flight, 161 94. The new British war balloon “Dirigible” No. 2, 162 95. The Wright aeroplane in full flight, 162

ARTIFICIAL AND NATURAL FLIGHT.

It has been my aim in preparing this little work for publication to give a description of my own experimental work, and explain the machinery and methods that have enabled me to arrive at certain conclusions regarding the problem of flight. The results of my experiments did not agree with the accepted mathematical formulæ of that time. I do not wish this little work to be considered as a mathematical text-book; I leave that part of the problem to others, confining myself altogether to data obtained by my own actual experiments and observations. During the last few years, a considerable number of text-books have been published. These have for the most part been prepared by professional mathematicians, who have led themselves to believe that all problems connected with mundane life are susceptible of solution by the use of mathematical formulæ, providing, of course, that the number of characters employed are numerous enough. When the Arabic alphabet used in the English language is not sufficient, they exhaust the Greek also, and it even appears that both of these have to be supplemented sometimes by the use of Chinese characters. As this latter supply is unlimited, it is evidently a move in the right direction. Quite true, many of the factors in the problems with which they have to deal are completely unknown and unknowable; still they do not hesitate to work out a complete solution without the aid of any experimental data at all. If the result of their calculations should not agree with facts, “bad luck to the facts.” Up to twenty years ago, Newton’s erroneous law as relates to atmospheric resistance was implicitly relied upon, and it was not the mathematician who detected its error, in fact, we have plenty of mathematicians to-day who can prove by formulæ that Newton’s law is absolutely correct and unassailable. It was an experimenter that detected the fault in Newton’s law. In one of the little mathematical treatises that I have before me, I find drawings of aeroplanes set at a high and impracticable angle with dotted lines showing the manner in which the writer thinks the air is deflected on coming in contact with them. The dotted lines show that the air which strikes the lower or front side of the aeroplane, instead of following the surface and being discharged at the lower or trailing edge, takes a totally different and opposite path, moving forward and over the top or forward edge, producing a large eddy of confused currents at the rear and top side of the aeroplane. It is very evident that the air never takes the erratic path shown in these drawings; moreover, the angle of the aeroplane is much greater than one would ever think of employing on an actual flying machine. Fully two pages of closely written mathematical formulæ follow, all based on this mistaken hypothesis. It is only too evident that mathematics of this kind can be of little use to the serious experimenter. The mathematical equation relating to the lift and drift of a well-made aeroplane is extremely simple; at any practicable angle from 1 in 20 to 1 in 5, the lifting effect will be just as much greater than the drift, as the width of the plane is greater than the elevation of the front edge above the horizontal--that is, if we set an aeroplane at an angle of 1 in 10, and employ 1 lb. pressure for pushing this aeroplane forward, the aeroplane will lift 10 lbs. If we change the angle to 1 in 16, the lift will be 16 times as great as the drift. It is quite true that as the front edge of the aeroplane is raised, its projected horizontal area is reduced--that is, if we consider the width of the aeroplane as a radius, the elevation of the front edge will reduce its projected horizontal area just in the proportion that the versed sine is increased. For instance, suppose the sine of the angle to be one-sixth of the radius, giving, of course, to the aeroplane an inclination of 1 in 6, which is the sharpest practical angle, this only reduces the projected area about 2 per cent., while the lower and more practical angles are reduced considerably less than 1 per cent. It will, therefore, be seen that this factor is so small that it may not be considered at all in practical flight.

Some of the mathematicians have demonstrated by formulæ, unsupported by facts, that there is a considerable amount of skin friction to be considered, but as no two agree on this or any other subject, some not agreeing to-day with what they wrote a year ago, I think we might put down all of their results, add them together, and then divide by the number of mathematicians, and thus find the average coefficient of error. When we subject this question to experimental test, we find that nearly all of the mathematicians are radically wrong, Professor Langley, of course, excepted. I made an aeroplane of hard rolled brass, 20 gauge; it was 1 foot wide and dead smooth on both sides; I gave it a curvature of about 1/16 inch and filed the edges, thin and sharp. I mounted this with a great deal of care in a perfectly horizontal blast of air of 40 miles an hour. When this aeroplane was placed at any angle between 1 in 8 and 1 in 20, the lifting effect was always just in proportion to its angle. The distance that the front edge was raised above the horizontal, as compared with the width of the aeroplane, was always identical with the drift as compared with the lift. On account of the jarring effect caused by the rotation of the screws that produced the air blast, we might consider that all of the articulated joints about the weighing device were absolutely frictionless, as the jar would cause them to settle into the proper position quite irrespective of friction. I was, therefore, able to observe very carefully, the lift and the drift. As an example of how these experiments were conducted, I would say that the engine employed was provided with a very sensitive and accurate governor; the power transmission was also quite reliable. Before making these tests, the apparatus was tested as regards the drift, without any aeroplane in position, and with weights applied that would just balance any effect that the wind might have on everything except the aeroplane. The aeroplane was then put in position and the other system of weights applied until it exactly balanced, all the levers being rapped in order to eliminate the friction in their joints. The engine was then started and weights applied just sufficient to counterbalance the lifting effect of the aeroplane, and other weights applied to exactly balance the drift or the tendency to travel with the wind. In this way, I was able to ascertain, with a great degree of accuracy, the relative difference between the lift and drift. If there had been any skin friction, even to the extent of 2 per cent., it would have been detected. This brass aeroplane was tested at various angles, and always gave the same results, but of course I could not use thick brass aeroplanes on a flying machine; it was necessary for me to seek something much lighter. I therefore conducted experiments with other materials, the results of which are given. However, with a well-made wooden aeroplane 1 foot wide and with a thickness in the centre of 7/16 inch, I obtained results almost identical with those of the very much thinner brass aeroplane, but it must not be supposed that in practice an aeroplane is completely without friction. If it is very rough, irregular in shape, and has any projections whatsoever on either the top or bottom side, there will be a good deal of friction, although it may not, strictly speaking, be skin friction; still, it will absorb the power, and the coefficient of this friction may be anything from ·05 to ·40. These experiments with the brass aeroplane demonstrated that the lifting effect was in direct proportion to the angle, and that skin friction, if it exists at all, was extremely small, but this does not agree with a certain kind of reasoning which can be made very plausible and is consequently generally accepted.