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Aviation History
1940
1940 - 0412.PDF
'32 FEBRUARY 8, 1940 UN DERCARRIAGES (CO NT! NU ED ) dashboard and even interlocking mechanisms between the undercarriage and its door. At the mention of the word undercarriages one is apt to think only of wheels. But there are at least three other types. Skis are used in countries such as Canada and in parts of U.S.A. where snowfalls may be so heavy that aerodromes cannot be kept clear. And floats of seaplanes are another form of alighting gear 01. which much ingenuity of design has been expended. The provision of stability on the water by avoidance of '' porpoising'' makes design difficult, as this consideration hab to be added to those of low hydrodynamic and aerodynamic drag. In this country the single float has never been adopted, but this type, • with wingtip floats for stability, has been seen on several American designs. The Curtiss scout observation has the long float attached as a cantilever on a single pedestal. The German Ha 140, made by Blohm and Voss, is an example of a very large floatplane, and it also has the single pedestal floats giving a very clean appearance. Dowty internally-sprung wheels allow this very clean single-leg undercarriage to be used on the Gloster Gladiator. (Right). The Martin-Baker fighter is an example of a well-faired " trousered " type of landing gear. such a vast subject that its complexity and many-sidedness has led to the establishment of a firm specialising in this work. Aircraft Components, Ltd. With this firm the name of Dowty has become inseparably linked as the designer of components or of whole undercarriage units which the firm supplies to many of'the aircraft factories. The Dowty "nutcracker" undercarriage is a neat design with two hydraulic jacks on the retracting strut. As pressure is applied to these they lengthen, and, breaking the strut at its central pin-joint, rotate the undercarriage and so pull it up into the wing. Latest of the components to be developed under Dowty design is a shock-absorbing strut of unorthodox appear- ance referred to as "Levered Suspension." And the new "Live-Line"' engine-driven pump maintaining full pres- sure in hydraulic lines even at zero delivery has been added to the firm's range. To reduce friction between the telescopic tubes of shock-absorber struts and so reduce sticking and wear, a Lockheed design of roller bearing has been evolved. A tubular sleeve between the two telescoping tubes carries, circumferentially set into slots cut in the sleeve, a series of coiled spiral spring rollers., These act as the balls of a ball-bearing and the sleeve is the cage. Unlike the solid ball, the spring is stressed in bending by compression across its diameter and so must be made of a deep-section flat strip to resist the load. Under load the spring roller is compressed to an oval shape and so increases its bear- ing area and reduces the load concentration. Hardening of the bearing surfaces is not necessary. All Lockheed designs are produced by the Automotive Products Company, Ltd., and this company, too, produces complete undercarriage installations ready for attachment to air frames. A notable undercarriage with Lockheed hydraulic equipment is that on the Armstrong Whitworth Ensign. The combination of high-wing monoplane and retractable undercarriage has caused it to be the largest such unit in the world. With wheels of over 6ft. diameter there are two hydraulic jacks per wheel, and these are each 7ft. long when extended and can exert a maximum thrust of six tons. The accessories belonging to hydraulic undercarriage systems are too numerous to more than mention. There are engine or electrically driven pumps, hand pumps for emergency operation, selector valves, emergency selector valves, flow control valves, position indicators for the The third iorm oi alighting gear is the planing bottom of the flying boat. Flying boat hull design has undergone progressive changes—and they are still occurring. The shape and location of the steps on the planing bottom is not susceptible to treatment by formula—model tank tests and subsequent full-scale behaviour are what the designer goes upon, and he must make his changes cautiously. So we see in flying boat design a state of gradual but con- tinuous change. The vertical step is giving way to a shape less abrupt, and hull shape, with the rear step nearer the tail and pointed in plan form, is now combining less aero- dynamic resistance with good hydrodynamic properties. The Future Just as there is nothing new under the sun, so is the last word never said on any subject. Developments in landing gears will occur in the future, but they may not be spectacular. Simplification below three points of support is manifestly impossible, and improvements in materials will not cause spectacular changes. But the nosewheel design is here to stay und is going to be helpful in landing aircraft in conditions of bad visibility, or at night when it may be hard to fell just where the ground is. In such conditions a nosewheel aeroplane can be practically glided on to the ground without harm instead of having to be stalled just a foot or two above it. And increased shock- absorption characteristics will, of course, help very much. Air transport strives always towards ioo per cent, adher- ence to schedules, and instrument-landing will become a regular feature of airline operations to this end. It is going to aid instrument-landing if the pilot is helped by a long-travel undercarriage which will take without com- plaint, if called upon to do so, a somewhat more vigorous contact than usual with the earth. Such a development would have its applications in military as well as civil work.
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