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Aviation History
1918
1918 - 0018.PDF
JANUARY %, 1918. politician—in the affirmative, and the second in the negative ? A further point. When " propeller pots" are a feature of body design the distance between the rear of the airscrew and the front of the first cylinder can be reduced ; a lighter crankshaft and crankcase resulting. When, however, a flat radiator forms the nose of the fuselage it is necessary—in the interests of airscrew efficiency—to keep this dimension as large as practicable, which, of course,~entails added weight. It might be argued that if this design is so usual amongst German-designed single-engined machines, why is it not so often employed for the engine nacelles of their twin-engined bombers ? The probable explanation is that some of their large bombers are twin pushers, in which case the use of a flat radiator in the nose does not detract from the airscrews' efficiency. Also the conditions governing the design of a fuselage and an engine nacelle are not the same. A fuselage carries the crew, fuel, oil, tail unit, &c, and has, in consequence, to be of fairly generous proportions at the largest point, but as this can be conveniently situated a little to the rear of the engine easy " lines " will suffice to merge this with a reasonable size of " pot " on the nose. On the contrary, the engine nacelles of multi-engined bombers generally have only to cover in the engine, so their cross sectional area and length are reduced to the extreme, and the prospect of saving any resistance by making the section round or oval with a " pro- peller pot " in front is extremely remote. The success the German designers have achieved with semi-monocoque bodies is of as much interest and warrants as much attention as the subject just dealt with—viz., the actual shape of the nose con- sidered in conjunction with the type of engine employed. The true monocoque body was intro- duced with success on special racing machines about five years ago, but the high manufacturing costs prevented it coming into general use, although its good aerodynamical qualities were fully realised. Another advantage this system of body construction has over the more common wire braced body is that it is less vulnerable to the effects of bullets, owing to there being no vital parts—such as wires and struts —liable to damage. Also there is no risk of a strip of the fabric covering the body being ripped up by a bullet and wrapping itself round the control cables. Some of these objections were overcome by sub- stituting the wire bracing by sheets of plywood screwed to the struts and longerons, thereby com- bining a strong bracing with an unrippable covering. This type of body construction has been very popular with German designers for some years past, and was only modified when higher speeds demanded a body of less resistance than that offered by one of rect- angular section, so whilst retaining the old system of construction, but replacing the flat sides with curved ones resulted in the formation of the low resistance, oval section, semi-monocoque body employed on Albatros scouts and two-seaters, during the past year. Whilst on the subject of bodies it will be well to consider the requirements in this direction of a new type of machine which has come into promin- ence lately—i.e., the Flying Tank. The duties of this machine are to co-operate with the attacking infantry by harassing with machine gun fire all enemy troops in the neighbourhood. As this entails flying at a low altitude armouring is essential to protect the vital parts, such as the engine tanks, crew, &c, from the heavy and concentrated fire of the enemy with rifles and machine guns. During 1914 a French firm produced a very interesting armoured monocoque body, in which the fore part was of sheet steel as far as the rear of the gunner's cockpit, thus protecting the vital parts already men- tioned. From this point to the tail the pure mono- coque type of construction was employed. Although this body fulfilled all requirements of strength, low resistance, lessened risk of fire and protection of the vital parts, it was not adopted owing to the reduction of climbing speed due to the extra weight. This objection does not apply to a Flying Tank, because excessive rate of climb is not required. The employment of a circular section body for this type of machine where low resistance is not of primary importance may appear to be unnecessary, but as it is quite probable that a round section body would deflect bullets which could easily penetrate a flat sided one, it will be seen that its employment with this type of machine is of as much value as in the case of ordinary scouts and two-seaters. Controlling Surfaces. There are points in the design of controlling sur- faces which it will be of interest to deal with, and one of these is the rapidly growing practice of balancing —or, more correctly, partially balancing—not only the rudder, but also the ailerons and elevators on small, as well as on large, machines. There can be little doubt that this practice has come to stay, in fact the wonder is that it has been so long coming, for by its adoption the stress on the pilot and controls is greatly reduced. A small point, but one of certain importance, is the placing of all control cables inside the body, where the risk of damage by flying splinters- of shell is considerably reduced. Also by not being exposed to the elements there is less risk of rust and consequent deterioration. Admittedly these cables are kept greased, but is it not possible for some of this to be accidentally rubbed off and the machine make a long flight in the rain before this can be replaced ? Once damp has penetrated to the core of a cable grease will not fetch it out. Except for the protection from shell splinters, the same arguments apply to running the aileron controls through the wings, and in both cases there is a small, but not negligible, saving of resistance. Conclusion. There are many more interesting points to consider, but as space is limited it will be-necessary to deal with the most important very briefly. Undercarriages have undergone many extensive changes in the past, and the number of types produced during the last ten years must be legion. Although some were very ingenious, those of low resistance, simplicity and lightness have been most popular. The type which satisfies these requirements best is that composed of two Vees of wood or steel tube with the axle slung from the apex by rubber cord, and its use has been almost universal during the last year or two on all except large machines. It is difficult to see how the low resistance, simplicity and lightness of this type can be improved upon, so one is forced to the con- clusion that any further improvement lies in the direction of an undercarriage capable of being drawn into the fuselage when the machine is flying. It is doubtful whether the scout type of machine would be improved by employing this feature, as the weight of the necessary mechanism would probably nullify any advantage, so the reduction of undercarriage 16
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