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Aviation History
1909
1909 - 0028.PDF
JANUARY 9, 1909. quence, it follows from the equation that its factor of stability was about three times that of the full scale machine, so that the experi- ment cannot be considered conclusive. The evidence of the flight of the actual machine in the hands of Delagrange also is insufficient, for the horizontal distance that the machine would glide from a height of 8 metres altitude would be approximately 55 metres, and this is little more than one quarter of a phase length. For this test to be considered satisfactory, the machine should be allowed some four or five free oscillations, and the phase length being about 600 ft., this involves a flight path of about 3,000 ft. length, or a fall of about 500 ft., that is, 150 metres. There is thus no proof at present forthcoming as to the stability or otherwise of the flight path of the Voisin machine, but it is at least the intention of the makers that it should be longitudinally stable, and, from con- versations that the author has had with MM. Voisin, and with their engineer, M. 'Colliex, they appear to be alive to niany of the points that conduce to such stability. (B) Lateral Stability.—In the Wright machine the lateral stability is under the direct control of the aeronaut, the " two wings " of the aerofoil being given a twist by straining the structure by means of wires arranged diagonally in the rear panels of the two end bays on either hand. This causes the wings to meet the air at different angles of incidence, and so any desired turning moment about the axis of flight (within certain limits) is at command. This mechanism is employed to neutralise the influeuce of wind gusts, and to correct the position of the machine should it acquire an undesirable list. It is also utilised to prevent the machine canting too much when turning, and to facilitate its employment in this respect, the rudder aft and the twisting of the wings are operated by one lever, the motion to the right and left being utilised to put tension on the diagonal wires one way or the other, and the move- ment forward and backward works the rudder. It is desirable to correct a false impression that is current on the action of the wing-twist. It has been supposed by some that it is used to give the cant required by the machine when turning, but such is not the case. If the rudder is used, the machine almost imme- diately gets a cant owing to the greater pressure on the wing that in turning is moving faster through the air, and this cant becomes, if unchecked, far too severe. The twist is then used to check the •cant, the wing on the outer circle (that is, farthest from the centre of curvature), being "feathered," the inner one having its angle of .incidence increased.* In the Voisin machine no hand-adjustment is provided to enable the aeronaut to control the lateral stability, hence in this case it is definitely automatic. The Voisin machine is steered by means of a •vertical rudder arranged between the fixed tail members, and there is apparently no special mechanism to prevent the over canting ; consequently Farman, in his flights, commonly turns in a leisurely manner, employing a circle of considerable radius, whereas Wright may often be seen to perform sensational evolutions, turning with his wings canted to nearly 30 degs. on a radius of perhaps not more than 60 or 70 yards. Farman has recently had fitted to his machine some adjustable flaps, to give, in effect, the wing-twist employed by Wright. Presumably this is to facilitate turning, for the flight of the machine does not suggest that they are otherwise wanted. Under other circumstances the lateral stability leaves little to be desired. Summarising the comparison, from the aerodonetic standpoint, the author is inclined to think that the Voisin machine has the advantage, as containing more of the features that will be embodied in the flying machine of the future. Mr. Wright's contention that it only requires a big enough puff of wind to upset a machine that depends upon its own inherent stability is certainly true, but probably the same is equally true of the hand-controlled machine. There is a limit to the extent of the control that can be exercised, and with hand control we have, too, the possible failure of the human machine. The fact is that the secret of stability is contained in the one word velocity, and until it is possible to aLtain higher speeds of flight, we cannot hope to see the flying machine in everyday use. There is one other point of comparison, that if space permitted the author wyuld like to make. As il is a few words must suffice. The constructional methods employed by Wright and Voisin present a striking contrast. The Wright machine is astonishing in its simplicity—not to say apparent crudity of detail—it is almost a matter of surprise that it holds together. The Voisin machine has at least some pretensions to be considered an engineering job. Mr. Wright defends his methods by asking what would be safd by an engineer to the rigging of a sailing vessel if shown it for the first time, and to some extent the analogy is a good reply to the objection; still the author feels (perhaps wrongly) that there is a considerable amount of the Wright " mechanical detail " that might * A certain patentee sent the author a specification of his invention in which arudder was carefully arrangeH to act spirally, to give a cant in the direction of the banking, that is, the direction in which the turning moment is alreadyexcessive. He might be well advised to take out another patent for the same device, arranged to act in exactly the opposite way. be revised with advantage, at least before the machine is placed in the hands of the private user. However, " the proof of the pudding is in the eating," and in spite of the rudimentary character and aggressive simplicity of the constructional detail of the Wright machine, it appears not to come to pieces, but continues to fly day after day without showing any signs of weakness or disintegration. On the question of the motor and transmission mechanism we tread on difficult ground, for the Voisin system of metal propeller keyed direct to the crank-shaft is so immeasurably superior, from the purely mechanical standpoint, to the chain-drive and wooden propellers of Wright that comparison is unnecessary. Since, how- ever, the simple and direct arrangement adopted by M M. Voisin is paid for at the price of about a 15 per cent, tax on the transmitted horse-power, the question is evidently one of the balance of advan- tages and disadvantages that are of entirely different kinds. The author has reasons for supposing that if in the machine of the future the geared propeller survives (for it is essentially the use of gearing in the Wright machine that permits the better proportions of propeller to be usedl it will be in the form of a propeller or propellers centrally situated, thus resembling the Voisin arrangement, rather than in the distribution of propellers such as at present employed by the Brothers Wright. The simplicity of the direct-drive may, however, alone be sufficient to outweigh any economic advantages that gearing may possess. I personally consider the Wright disposition of propellers to be a source of danger. If a torque is applied to an aerodrome about a vertical axis, rotation about this axis at once begins, and the outer wing travelling through the air faster than the inner experiences a greater lifting reaction, and if the torque is sufficient, the machine is very soon (in nautical phraseology) on its "beam-ends." It is evident that if one of the propellers fail from the fracture of a chain or other cause, unless the motor be instantly stopped, the whole power of the motor, and therefore the whole thrust, will be trans- mitted through the other propeller, causing a torque about a vertical axis that must be overwhelming. If the motor is promptly stopped then much will depend whether the propeller that has failed is scotched or free. If it has jambed then it will probably balance by its drag the other propeller, which is either stopped also or is driving the motor against its internal friction ; if, on the contrary, it is free, then the drag of the other propeller will be unbalanced, and there is a serious torque in the opposite sense to that which would have existed if the motor had still been running. Whether Mr. Wright can, in the latter case, by wing-twisting and other contortions, save himself from destruction I do not know. It is said (vide Press a short time ago) that a chain actually broke in flight and the machine safely landed ; the altitude when the accident occurred was stated to be only 4 or 5 metres, so that Mr. Wright did not have a fair chance of exhibiting his resources. It is to be hsd that he will not htve such a mishap at a higher altitude. Photo by J. Theodoresco, Paris. '• .Goupy Triplane, fiited with Anzani motor. NEW COMPANIES REGISTERED. Aeroplanes, Ltd.—Capital ^100, in £1 shares. Formed to manufacture, let on hire, and otherwise deal in aeroplanes, flying machines, balloons, &c, whether propelled by petrol, steam, gas, or other motive power. BOOKS RECEIVED.—Artificial and Natural Flight. By Sir Hiram Maxim. London : Whittaker and Co. Price 5.5-. net. Aeronautical Patents—Applied for in 1909. Published January "jth, 1909. 7i37°> J- SAWAKD. Airship.
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