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Aviation History
1914
1914 - 0656.PDF
ffiiCHT) JUNE 19, 1914. could also be lowered. It may be objected that these same forces will be at work during the time that the machine is being brought back to an even keel, but if the directions in which they are effective are examined, it will be found that they will normally assist, rather than retard, the restoring forces. In regard to the constructional difficulties which might arise, it will be seen that some form of gearing would be absolutely essential, but in view of the high efficiency attained with modern gears, and the better efficiency of the propeller at lower speeds of revolution, this is not likely to altogether prohibit its adoption, as it has, in fact, been already successfully employed on many engines. Fig. 4 shows the completed arrangement of such a design on a machine fitted with two propellers, but it will be readily apparent that by the embodiment of either a bevel or a worm drive, preferably, as an integral part of the engine, it would be possible to drive a single screw placed either in front or at the rear of the main supporting surfaces. 9) ® THE ACTION OF THE CONTROL ORGANS OF AN AEROPLANE IN CRITICAL ATTITUDES. Fig. 2, as indicated by the arrows, the full arrows showing the direction of the applied forces and the unshaded arrow the resultant tendency due to precession. When a right-hand turn is made, as in Fig. 3, the engine is rotated about its vertical axis, the cylinders passing through the leading upper quadrant are decelerated— hence there is a torque tending to bank the machine over towards the right. These actions, as well as others that result from a disturbance in a lateral direction, and which will readily suggest themselves to the reader, are similar to those which a pilot endeavours to produce with the assistance of his controls; consequently, such an arrangement of engine would conduce to some degree of lateral stability ; while, in addition, the mounting of the motor would be considerably facilitated, a better and more rigid framework of the body would be made possi ble, and the construction of the body would readily lend itself to a streamline formation of lower air resistance than is customary. The centre of gravity of the machine sa (V. Tin following is an abbreviated translation of a lecture by M. Louis Hrtguet to SocUte Fran<;aise dc Navigation A&rienne :— The two main problems which confront the aeroplane con structors are : •Firstly, to design machines capable of carrying their load with a small expenditure of power, while at the same time having motors capable of developing two or three times, or even four or five times as much power as is required for ordinary flight. These qualities are obtained by reducing the passive head resistance to a minimum, by refining the lines of the machine generally, and by giving the wings the best possible section. Secondly, to bring out machines possessing a good stability in the air, and having control organs which are effective in all conceivable positions of the machine. In this lecture I propose to deal with the study of the forces to which aeroplanes are subject, and the way of modifying the points of application of these forces by means of rudders, elevators and ailerons, in order to right a machine which has been Thrown out of "Is normal attitude of flight. The frequent accidents tend to give one the impression that the equilibrium of an aeroplane is very precarious, and that once the machine gets past certain attitudes the pilot is unable to control it and thus prevent a fatal accident. Is it true that these critical attitudes are so dangerous ? Evidently not, for aviators like Pegoud, Chevillard, Garros, &c. have proved by actual experience that a machine can occupy all conceivable positions and yet be righted with ease. The critical conditions are : 1. Too low speeds. 2. Too high speeds. 3. Sideslips and dives. I. Too Low Speeds.—When an aeroplane loses its speed the reaction of the air on its planes is insufficient to support it in spite of the increased angle of incidence. For angles of incidence of from 15 degrees the lifting forces do not increase with the angle of incidence, and for angles from 20 degrees they decrease. Generally when an aeroplane lo-es speed it turns over either to the right or to the left. This is what is called a sideslip. If the pilot tries to right his machine by warping he will only increase the sideslip, and if his motor is failing he can only right the machine by diving it until it has regained it flying speed. If the motor possesses great reserve power it is possible to right the machine before the sideslip has become very pronounced. Whilst this sideslip is, of course, dangerous when the machine is close to the ground, there is little or no danger when it is flying at an altitude sufficiently high to allow of regaining its speed by a dive. Besides, a machine with a proper empennage will not lose its speed unless the pilot wishes it to do so, and it does not seem necessary to fit an automatic control ® ® A Prize for a Safety Belt. IT will be seen from the Official Notices of the Royal Aero Club on page 648 that the Committee, acting on a suggestion of the Accidents Investigation Committee, is offering a prize of ,£50 for the most suitable form of Safety belt. The conditions under which the prize will be awarded are now being considered by the Accidents Investigation Committee. It will also be noticed that the Committee in their report on the fatal accident to Philippe Marty make a reference to the use of safety belts. organ for the purpose of helping the pilot. It is, however, alway advisable to fit speed indicators which will keep the pilot informed as to the behaviour of his machine. 2. Too High Speeds.—It is generally admitted that the conditions of too high speeds present a certain danger. It has been said that aeroplanes flying at very small angles of incidence may, by a sudden longitudinal swerve or dive, receive a sudden pressure on top of their wings, and thus losing all sustentation, they fall. The point to be studied with regard to high speeds is : How do the points of application of the forces to which an aeroplane is sub ject vary for possible variations in the angle of incidence during these high speeds ? Experiments with scale models in the labora tories are very instructive, and it has been possible to verify that certain machines with too deeply cambered wings, or with insufficient empennage or badly adjusted, may become unstable when flying with very small angles of incidence. It should be remembered that for a cambered plane the centre of application of the resultant of the forces acting on it travels backwards, progressively as the angle of incidence decreases, and that for very small angles of incidence the travel of these centres is considerable. At the Eiffel laboratory a series of experiments have been com menced with scale models of aeroplanes flying with the most critical angles of incidence by placing them in the air current, and the interesting results obtained lead to the conclusion that it is easy to design machines which the pilot can always right by means of the control organs. 3. Sideslips and Dives. —A fall started either by side-slipping or stalling always terminates, if the machine has a.suitable empennage, in a vertical nose dive. The study of forces, acting on scale models, shows that even from this attitude the machine may be righted by suitably operating the control organs. The most important thing to observe is that the pilot is not thrown out of his seat, and that, thanks to an efficient safety belt he is able to operate his controls, whatever the attitude of his machine. Suppose that a machine through some cause or other is making a nose dive, and that the pilot is strapped in his seat. He finds that he is unable to right the machine by operating his elevator— such a contingency occurs often, and many pilots have experienced it. The thing to do in a case like that is to push the rudder over as far as it will go, for instance, to the right, in order to make the machine turn to the right with relation to its vertical path of flight, and at the same time warp the wings so as to make the machine revolve around its longitudinal axis after the fashion of the hands of a clock. The aeroplane will then right itself by describing a spiral similar to those favoured by certain pilots in their exhibition flying. ® ® The British Gordon-Bennett Trials. BOTH the War Office and the Admiralty are lending splendid assistance to the Royal Aero Club in connection with the organisa tion of the British Eliminating Trials for the Gordon-Bennett Cup which will be held at the Central Flying School, Upavon, during the last week in August. Shed accommodation for each competitor will be available on August 20th, and the speed tests will commence about three days later. The officers' mess at the C.F.S. has been placed at the disposal of the Royal Aero Club for the use of the officials and competitors. 656
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