Fig. 89.—Bleriot undercarriage.
Recent Developments.
During the last three years the vital necessity of speed and climb, and more speed and climb, has resulted in the gradual elimination of skids, struts, and wires, until to-day the chassis for machines of average dimensions is almost invariably the V type ([Fig. 90]). The wheels are placed about a foot in front of the C.G., as, owing to the absence of any forward skid, no other provision exists to counteract the tendency to pitch over. In the actual construction of the Vee undercarriage, some diversity of practice exists with regard to the material chosen. In some cases the struts forming the Vees are constructed of a streamline section steel tubing, in others round tubing, the streamline section being obtained by a wooden fairing bound on, while a number of constructors use wood for the struts.
Fig. 90.—Vee type undercarriage.
CHAPTER XI.
UNDERCARRIAGE DETAILS.
The details of construction associated with the undercarriage are those concerned with the forming of the struts and main members, and the suspension of the axle. As noted in the previous chapter the Vee undercarriage is greatly in favour at present, but the fact that with this type no forward support exists to prevent pitching over when obstructions are met in rolling, will almost certainly result in some arrangement of wheels and skids for the touring machines of the post-war period. Machines are now designed for air performance pure and simple, so that an undercarriage of the simple Vee type is all that is permissible; but in the post-war machine general utility will be the desideratum sought for by designers. At one time the majority of the undercarriage arrangements incorporated one or more skids. The material most suited for this purpose is hickory, although some designers prefer ash, steamed to the desired curve, and generally channelled out between the points of intersection of the struts, fittings, etc., in a similar manner to longerons and wing spars.
Where the bend is sharp, and therefore difficult to obtain by steaming, it is usual to form the skid from a number of strips, or laminations, glued together. Quite a good method of stream-lining the curved toe of the skid is shown by [Fig. 91], consisting of a spruce block attached to the skid by screws, and it has additional value in ensuring permanency of curve. Where the design is such that the rear end of the skid performs the functions of a tail skid it is saw-kerfed, as in [Fig. 92], the laminations so formed being stepped back, and the bottom layer shod with a plate, or claw fitting, acting as a brake, and also preventing wear produced by contact with the ground. At one time this constituted popular practice, but it is a matter of some difficulty to prevent the saw-cuts from developing into fractures. As a matter of fact, on one type of machine replacements were so frequent that eventually the skid end was left solid.
Fig. 91.—Streamlining curved toe of skid.