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Aviation History
1911
1911 - 0979.PDF
NOVEMBER II, 191 I. observed to have been rotated in the opposite direction. For instance, a wing depression of the left wing may occur and steer the bird to the left at a time when the right side of the tail is depressed. As soon as my acquaintance with the facts led me to doubt whether rotations of the tail produce steering movements, I made a point of looking to see whether, in normal turns, the depressing of the side of the tail was coincident with or preceded the wing depression. To my surprise I found that the rotation of the tail, if it occurred at all, preceded the wing depression. In view of the facts described relating to tailless cheels, there can be little doubt that the function of the tail is to act as a break for turns round the dorso-ventral axis, and that it does so more efficiently if the side of the tail is depressed on the side ol the turn. Supposing the bird is about to steer to the right, this steering tends to be checked by the tail if this organ has so rotated round its longitudinal axis that the right half of the tail is depressed below the horizontal plane. Obviously if movements of the tail produced steering, then tailless cheels should turn less readily than complete cheels. But, as we have seen, the contrary is the case. Hence the dorso-ventral axis instability of tailless cheels gives strong support to the view that the function of the tail is to act as a break in the manner described. The numerous apparently purposeless rotations of the tail when cheels are manoeuvring in complicated air currents must on this view be regarded as "anticipatory movements." They are preparations for turns that it may or may not make as it is influenced by changing air currents or the necessity of avoiding other birds. Flying foxes when poising before perching may frequently be seen to advance the hind legs. No doubt this movement is pre paratory to grasping the bough with their feet. But as it results in bringing the posterior part of the wing surface to a position at right angles to the direction in which the animal has been gliding, it is possible that to some small extent the action has a braking effect similar to that produced by the depressed and expanded tail of birds when perching. It remains to consider the possibility that the tail has an action [/XlCHTl similar to the horizontal rudder ot aeroplanes in steering the bird up and down. I have already stated that the tailless cheel, in an irreglar wind, may show double dips more often than complete cheels. This statement is illustrated by the following observation :— December 13th, 1910. At 11.20.—Wind rather strong and moving branches. A tailless cheel seen overhead about 10 metres above the tree-tops. It showed slight instability round the dorso- ventral axis. This consisted in occasional sudden turns (round this axis) through about 10'. Each time it turned back to its original position with equal suddenness and after an appreciable pause. There was no attempt to check rotation round the dorso- ventral axis by double dips. It made double dips more often than did complete cheels that were gliding near. Its double dips seemed larger and more sudden than usual. Though double dips were not used to check rotation round the dorso-ventral axis, it is possible, on the one hand, that such rotation! caused loss of speed ahead, and hence there was the necessity for an occasional double dip to increase speed. On the other hand, it is possible that the surface of the expanded tail of the complete cheel acts, so to speak, passively in checking rotation round the transverse axis. Possibly, lacking this break, the tailless cheel is apt to be rotated upwards round the transverse axis, and hence occasionally finds it necessary to make a downward rotation round this axis by means of a double dip. But, on the other hand, there is no doubt that the tail does not actively produce rotation round the transverse axis after the manner of the horizontal rudder of an aeroplane. If it did so, the tail should be depressed when the bird is gliding downwards. But, as we have seen, when the bird is gliding downwards tiie tail is furled and raised. It then acts by raising the position of the centre of gravity relatively to the centre of resistance of the wing-tips, thus tending to cause rotation down wards round the transverse axis. Conversely, when the bird is perching, it rotates upwards round its transverse axis. If the tail acted as the horizontal rudder of an aeroplane, it should then be elevated; but, as we have seen, the expanded tail of the perching bird is depressed. • m 'Io be continued.) ® • • • THE MILITARY AEROPLANE. IN the October issue of the Army Review, Major Sir A. Bannerman, Bart., R.E., commanding the Air Battalion, has an interesting article, in which he sets forth a few of the things which should be borne in mind by the designer of an aeroplane for military work. He summarises the broad outlines of the requirements to be met by air-craft for use in the British Army as follows :—" Airships must be small and speedy. Aeroplanes must be readily dismountable, not too large, have speed enough to allow of flying in moderate winds, be able to land on rough ground, and start from it, and need but little run for starting. The settlement of details, such as loads to be carried, speed of ascent, duration of flight, &c, falls within the province of practical military flyers, who hold very various opinions." With regard to the use of aeroplanes, the author points out that, although damage to important points may occasionally be done by dropping explosives from aeroplanes, it is impossible to take the prospect seriously ; air-craft may be so useful in other ways that a commander can really be justified in risking their loss by using them for offensive purposes. Tcere remain the two functions of despatch carrying and reconnaisance, and, as for the latter a passenger must be carried, it should be possible to design one type to suit both cases. A wireless telegraphy installation will probably form part of the equipment in the future. Standardization of parts is essential to war material, therefore there should be as few varieties of aeroplanes as possible. With regard to arrangements for aeroplanes in actual service, Major Bannerman suggests that it appears advisable to group aeroplanes in pairs so that at least one should always be available. Two pairs could be combined to form a section, and two or more sections made into a company, but it is important that each section should contain machines of only one type, as by that means the expert supervision Is simplified and personnel reduced. One of the most difficult problems is the repair and maintenance of aeroplanes in the field. Some form of mobile workshop must be maintained close to the front, otherwise it may be necessary to abandon machines that have only slight defects. With regard to the airship, it has been proved that large vessels are unsuitable for use in this country owing to the numerous trees, woods, tosvns and villages, combined with a strength and gustiness of winds. The exact size most suitable for the British Army can only be found by experiments, but it seems that the gas capacity should be between 80,000 and 100,000 cub. ft. One of the chief difficulties in dealing with airships is the establishment required to maintain them. Sixty men are needed to handle a vessel of moderate size, while the gas to keep it properly inflated means much heavy transport. In concluding the article Major Bannerman points out that the kite is by no means superseded in military operations. He also draws attention to the fact that officers for aerial work are much rarer than is supposed, and as the work is peculiarly trying, few individuals long retain a taste for it. The remedy must be to induce larger numbers to take up the duties and consequently to replace the elder hands by fresh recruits. Far more candidates are available than are required ; it remains only to give them a chance for showing what they can do. We are reminded that Great Britain's frontier is the enemy's coast, and the moment he puts to sea we are invaded. That being so, it follows that large aerial stations in the interior of England, or even near the coast, cannot be so effective as those in the frontier fortresses of Continental Powers. They may be suitable for passive defence, but their distance from the enemy will make it very un economical, if not impossible, to use them as points of departure for air-craft intended to operate overseas. It is therefore obvious that, although we have much to learn about aerial work from our neighbours, it will not be safe for us blindly to follow their lead. The main lines of a British defensive policy must be decided by the needs of the Navy, and, unfortunately, little is as yet known about the use of air-craft in connection with Naval forces. Develop ments are likely to take place during the next two or three years, and by the end of that period we should know definitely what are the offensive and defensive powers of dirigible balloons and aeroplanes, respectively ; then it will be possible to come to some decision as to the class of air-craft to be employed, and the size and position of the stations to be formed. ® ® ® ® Death of J. T. Montgomery. WE regret having to record the death of Prof. John f. Mont gomery, of California, which took place while he was experimenting with his gliders at Santa Clara. One of the earliest practical workers, and also one of the closest students of the science, Mr. Montgomery was, perhaps, best known to the public through the experiments made with his Langley type gliders by Maloney, who launched himself into the air on these machines after ascending with them attached to a balloon. 98I
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