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Aviation History
1912
1912 - 0328.PDF
[/JJGHT] wings in place of below. It is also possible to calculate what radius of the vertical turn is necessary to produce this and to calculate the amount of pressure for any radius of turn and speed. Any failure from this course would, however, take place at the beginning of a volplane1 and not at the end as has certainly been the case with several failures. A point of great importance in his letter is the question of what is meant by the " factor of safety of five" allowed for the main truss wires. If it means that their breaking strength (as per testing machinej is only five times the static load due to the weight of the machine, &c, I think most engineers would certainly think it very low and would expect accidents. I may point out also that single ribbon and wire such as used for the trusses of aeroplanes, have been found too unreliable for use in racing sailing boats and have been abandoned in favour of wire rope. It does not necessarily follow that they are unsuitable for aeroplanes but the point is worth considering. APRIL 13, 1912. Arguing solely from theoretical considerations I would suggest :— 1. Providing the wings with substantial fore stays independent of the main truss wires. 2. Ascertaining by experiment the shortest practicable radius of turn at the beginning and end of a volplane, and providing truss wires to take the centrifugal force caused by such turns with the usual factors of safety. The pressures on the wings are easily calculable, as accurately as such other stresses in structures (vide " Monoplanes and Biplanes," published by Munn and Co., and Engineering, for January 12th, 1912). It also seems to me that it would restore public confidence greatly if persons who allow a good factor of safety would publish their calculations. "Monoplanes and Biplanes" is a book written by Grover Cleveland Loening, published by Munn and Co., New York, and Sampson, Low, Marston and Co., Ltd., London. ® ® ® ® AERONAUTICAL SOCIETY OF GREAT BRITAIN. ABBREVIATED FORECAST OF MR. T. W. K. CLARKE'S PAPER ON "AUTOMATIC STABILITY" (WITH SPECIAL REFERENCE TO THE CLARKE-JOHNSON GYROSCOPIC CONTROL) WHICH WILL BE READ AND DISCUSSED AT THE ROYAL SOCIETY OF ARTS, MONDAY, APRIL 15th, at 8.30 p.m. PROF. JOHN PERRY, F.R.S., IN THE CHAIR. 1. There are three systems of stabilising aeroplanes :— a. Natural. I. Personal, c. Automatic. 2. Natural stability is inherent in the form of the machine. A well-known example of this principle is the dihedral angle. The characteristic of this system is that the machine tends to maintain a constant attitude to the relative wind, consequently if the wind veers excessively the machine becomes unsteady in trying to maintain its balance. 3. Personal control, by the operation of balancing planes, wing warping, &c, is the system commonly in use to-day. Its limita tions are those incidental to the human factor in air-controlling systems, which it is the purpose of natural and automatic stability to as far as possible remove. 4. Automatic control utilises the same balancing organs as are ordinarily controlled by human agency, but brings them auto matically into action by mechanical means. 5. It is with the last mentioned system that this paper deals in particular. 6. A point that is immediately obvious from a study of the principle of automatic control is that the instrument applied to this purpose must have an inherent " sense of direction." 7. This narrows the investigation to three devices (i) the pendulum weight, which possesses the inherent directive effort of gravity; (ii) the compass, which is directed by the earth's magnetism ; (iii) the gyroscope, which is directed by its rotational momentum. 8. The objection to the pendulum weight is its natural oscillation, which is likely to make the machine unsteady while recovering from a disturbance, and also to make the control unreliable when it is sensitively set. 9. The objection to the compass is its weakness as a force for operating practical mechanisms. 10. With the properties of the gyroscope it is the purpose of this paper to deal. 11. It is self-evident that direct control of the balancing organs by the stabilising instrument involves a very heavy apparatus and tends to reduce sensitiveness, consequently the principle of the relay must be accepted as fundamental, whatever the nature of the instrument. 12. Assured of adequate sensitiveness, it is natural to conclude that the most satisfactory way of bringing the instrument into operation is to make it subject to the tilting of the machine. 13. This principle has the great advantage of ensuring that the conditions to be corrected are those actually disturbing the machine, whereas if the instrument is controlled by a small supplementary wind vane the conditions that it attempts to correct may not quite ® ® Belgium Proposes an International Contest. THE Belgian Aero Club has suggested the holding, in about two months' time, of an International competition, in which Germany, Belgium, France, and Great Britain should be represented by teams consisting of a monoplane and a biplane. It is proposed that the contest should be over an out-and-home course of 500 kiloms., starting from the neighbourhood of Brussels, and the prizes to be 50,000 francs, 30,000 francs, and 20,000 francs respectively for the teams placed first, second, and third. The winning team would be the one whose aggregate time was the best. be the same as those actually disturbing the machine, and a lack of harmony in its operation is the result. 14. The following is a description of an apparatus embodying the chief points enumerated above. It is a gyroscopic control and is brought into operation by the tilting of the machine. It regulates a relay mechanism, whereby the balancing organs are actually mani pulated. It is light, compact, and can be sensitively adjusted without becoming unreliable. 15. The gyroscope is four inches in diameter and consists of the external rotor of a small electric motor that is driven by a io-volt battery. 16. Its axis of rotation is horizontally across the line of flight and its supporting frame is pivoted on a vertical axis. 17. All students are familiar with the fact that tilting the spinning axis of a gyroscope in one plane causes ia reactionary "kick" precession in a plane at right angles thereto. 18. If, therefore, the aeroplane tilts laterally, the gyroscope will swing round on its vertical pivots in consequence. 19. Such action on the part of this gyroscope operates a switch that energises a magnetic clutch normally running free on a rotating shaft that is driven by the engine of the aeroplane. 20. There are two such clutches, either of which comes into operation according to the direction in which the gyroscope swings, which direction is determined by the direction of tilt on the part of the aeroplane. 21. When one of the clutches is engaged it throws the mechanism into gear by means of which the engine power is utilised for opera ting the balancing planes and thus restoring equilibrium. 22. There is an important time factor in the sensitiveness of gyroscopic control inasmuch as the precessional movement towards the switch contacts is proportional to the speed of tilt, that is to say a sudden disturbance of the machine's equilibrium produces a corres pondingly sudden switching on of the controlling apparatus. 23. The gyroscope as a whole is mounted on a hinged board that is normally in the same plane as the wings of the machine, but is so interconnected with the steering gear as to cause the board to be tilted while steering. This enables the machine to be banked for turning, whereas otherwise the automatic control would maintain an even keel during this evolution and thus tend to induce skidding. 24. Electric current is fed to the gyroscope by contacts in the bottom pivot bearing. 25. The controlling mechanism for operating the balancers is so arranged that they can be hand-controlled independently. The influence of such hand control is additional to that caused by the gyroscope, that is to say, if both happen to operate together then the result produced is correspondently magnified. ® ® Pekio to Paris by Aeroplane. THE Matin, which surprised the world with the audacity of its proposal to organise a motor car race from Pekin to Paris in 1907, and which, as will be remembered, was successfully carried through, has now definitely announced that it will organise a flying race between the same two capitals. No details have been published yet, but our contemporary announces that the prize will be com mensurate with the time, trouble and expense involved in flying over such a course of 7,500 miles. Mr. Hamel has expressed his intention of taking part in the race. 328
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