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Aviation History
1943
1943 - 2269.PDF
SEPTEMBER I6TH, 1943 FLIGHT 317 GERMAN AIRCRAFT STRUCTURES •f another screw jack driven from the same motor, which transmits power by means of a second shaft running down the side of the fuselage and driven by a bevel gear on the trans- verse shaft. The tail wheel is centred by elastic cords but there is not anti-shimmy damping. ]u88:—The Ju88 undercarriage is the most unusual type of all those in use. Each of the two main undercarriage units comprises a semi-cantilever type shock absorber strut with wheel and tyre. The units are designed to retract rear- wards into the engine nacelles and during retraction are rotated through 90 deg., so that the wheels lie flat against the underside of the wing when fully retracted. In each strut the shock-absorbing mechanism consists of two columns of steel "ring springs," operating in series. One of the columns operates also as a recoil buffer. The scheme is illustrated in Fig. 15. When the strut is compressed the outer ring of each part is ex- panded elast^cally and the inner ring contracted. Thus energy is mainly stored in straining the springs and is partly dissipated n friction between the conical surfaces. The tail wheel unit is self-centring and retractable and can be locked in the central position and incorporates a similar type of shock absorber. An interesting feature of these shock absorbers is the employment of steel compres- sion springs of the " solid " ring type, as the energy-absorb- Fig. 14. Fw 190 tail wheelmechanism. retraction ing medium in both the main and tail wheel struts. In springs of this type the material will be stressed uniformly and therefore economic- ally, and a large proportion of the energy absorbed by the springs may be dissipated in friction be- tween the sliding conical surfaces of the rings. This type of shock absorber requires little maintenance work in service and is less suscep- tible to damage than an oleo-pneu- matic shock absorber. The "ring spring" type is, however, rather heavier than an oleo-pneumatic strut of the same energy-absorbing capacity. In the latest marks of Ju 88 this type of leg, however, has been abandoned in favour of an oleo leg. Me 210:—The Me 210 uses oleo- pneumatic shock absorbers on the main wheels. The legs are arranged as in the Ju 88 to rotate through 90 deg. as they are retracted rear- wards into the engine nacelles so that the wheels lie flat in the wings when fully fetracted. The tail wheel has a "ring spring" shock absorber with additional hydraulic damping. . Weight Summary Do 217-1. Wings with c/s fuselageFuselage .. .. .. • . - Tail unitMain undercarriage Tail wheel unitControls Engine mounting, cowling andnacelles TOTAL STRUCTURE .. 2x Engine and accessories 2x Airscrew and spinner TOTAL POWER PLANT (exclud- ing mounting and cowlings) Fuel and oil tanks .. Bare weight Armour Fixed equipment Removable equipment TOTAL EQUIPMENT . . Crew and parachutesFuel (655 gal.) .. Oil (88 gal.) Bomb load (approximate) ALL UP WEIGHT Weight (lb.). 4,600 2,815 6ro 1,830 135600 900 11,400 5.365 785 6,150 19,190 400 900 610 1,910 800 4,700 800 6,400 33.8oo Weight per cent. all up wt. 13.6 8.3 *1.8 5-40.4 1.8 2.7 34-° 159 2-3 ' 18.2 4.6 56.7 1.2 2-1 1.8 5-7 2.4 13-9 2.4 18.9 Miscellaneous Design Features Castings and Welded Components:—It will have been apparent in reading the above paragraphs on undercarriages and engine mountings that the Germans are using castings and welded components for many important structural parts. Undercarriage and tail wheel castings in the Fw 190 and Do 217 have al- ready been mentioned, as have the welded tubular supporting struts in the liquid - cooled engine mount- ings and the welded tubular engine mount- ings for radial engines. A selection of typical castings is shown in Figs. 16 and 17. Fig I6A illustrates the steel bottom connecting piece between the axle (also seen in the photo- graph) and the shock absorber strut of a Ju88. Fig I6B shows the cast-steel fitting, one of which is attached to each end of the front centre section I-beam in the Me 109. Each of these fittings carries the hinged lug which forms the front point of attachment for the wing unit, the pin joint of the undercar- riage strut, the down locks for the under- carriage, the engine bearer supporting strut Fig. 15. Junkers Ju 88 under- and a second strut carriage leg. which braces each of 6EASNG
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