GB580158A - Improved tricycle undercarriage for aircraft - Google Patents

Abstract

580,158. Aircraft undercarriages. LACHMANN, G. V., and SUPPANCIC, G. O. June 13, 1944, No. 11311. [Class 4] [Also in Group XXIX] In a tricycle undercarriage having a castoring or steerable front wheel located in front of, and a pair of main wheels aft of, the centre of gravity of the aircraft, means are provided for increasing the ground angle for take-off, whereby the front wheel strut is lengthened whilst the trailing distance of the front wheel remains substantially unaltered. The length of the main undercarriage struts may be shortened simultaneously with the elongation of the front wheel strut so as to avoid raising the centre of gravity of the aircraft. In one form, Fig. 1, the nose wheel 20 is carried by a fork 21 rotatably mounted on an oleo-pneumatic shockabsorber strut 22 which is slidable within a cylinder 24 pivoted at 26 to the aircraft and at' 25 to retracting mechanism 23. The outer cylinder of strut 22 is formed with annular pistons 15, 16, Fig. 10, and is extended from, or retracted into the cylinder 24 by admitting fluid under pressure into the space above piston 15 and discharging fluid from the space below piston 16, and vice versa. Fluid is admitted or discharged through pipes 12 and 10, passages in a spindle 193 forming the pivot 26, and rotatable glands 141, 142 attached by arms 131, 132 to the cylinder 24. Hydraulically-releasable mechanical locks are provided to hold the strut in extreme positions. To maintain the trailing distance constant during extension of the strut, the cylinder 24, strut 22 and wheel 20 are swung rearwardly through an angle approximately equal to the increase in ground angle. For this purpose the pivot 26 is slidable in a slot in the aircraft and is moved forward by operating a jack 32 to break a toggle linkage 27, 28. Alternatively, the cylinder 24 may be rotated about pivot 26 by a partial retraction of the undercarriage. The control of the mechanism for effecting retraction of the undercarriage or operation of jack 32 is co-ordinated with the means for extending the strut so that the latter is rotated through the correct angle, as it elongates. The fluid pressure mechanism is so arranged that on retraction of wheel 20 after take-off, the strut 22 is withdrawn into cylinder 24 and jack 32 operates to return the pivot 26 to the rear position. Lowering of the undercarriage for landing, however, has no effect on strut 22. In a modified form, Figs. 3 and 5, the wheel is mounted for castoring about the axis of a tubular member 40 which is pivoted at 41 to the aircraft and has a bracket 42 for attachment of retracting mechanism. The wheel is mounted in a fork 50 carried by shock-absorber struts 48, 49 slidable within cylinders 46, 47 rotatably mounted, on the member 40. The plane containing the axes of cylinders 46, 47 is forwardly inclined to the axis of member 40 so that, on extension or retraction of the struts 48, 49 the trailing distance of the wheel is maintained constant within small limits. To obtain a truly constant trailing distance, the wheel should be moved in a forwardly-curved path, and in a further form, Figs. 6 and 8, the wheel is carried by a fork 64 pivoted to a yoke 63 carried by a shockabsorber strut 62 which is slidable within a cylinder 60 pivoted to the aircraft at 61. The fork 64 is extended upwardly to form curved, slotted guide rails 65 which engage the trunnion rollers 67 of a ring 66 rotatable on the cylinder 60. On extension of the strut 62, the rails 65 will cause the wheel to move in a forwardlycurved path. The shock-absorber struts carrying the main rear wheels may be telescopically housed within guide cylinders similar to those described for the front wheel strut so that the length of the rear wheel struts may be shortened, simultaneously with the extension of the front wheel strut, by a smaller amount. The energy freed by the consequent lowering of the centre of gravity of the aircraft is stated to assist the action of the operating mechanism. The fluid pressure system for controlling operation of the front and rear wheel struts is illustrated diagrammatically in Figs. 11-14 (not shown) (see Group XXIX), the arrangement being such that, in the landing position, the front strut is shortened and the rear struts extended ; in the take-off position, the front strut is extended and the rear struts shortened, and, after take-off, all the struts are shortened to facilitate retraction. The use of the elevators for take-off is stated to be considerably reduced or entirely eliminated. The tensioning tabs on the elevators may be set so that the aircraft will assume the attitude for best climb after becoming airborne. Specifications 289,109, [Class 4], and 505,263 are referred to.