FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1912
1912 - 0218.PDF
while on the ground. There must be the least possible resistance while rolling in order that the machine may accelerate to the required speed as quickly as possible. (#) It must be arranged to give a high degree of stability in a fore and aft direction, as well as laterally, while travelling at high speed over uneven ground. (e) It must be efficiently sprung to eliminate rolling shocks. (d) The machine must be capable of being steered on the ground without the aid of the propeller blast. (e) Some efficient form of brake must be provided. /) It must be designed with a view to easy repairs. [Most of the above conditions apply to rolling and taking oft from the ground ; the following are connected with alighting] :— (g) It must be provided with a suitable device for absorbing the shocks of landing. (h) It must be capable of withstanding the considerable side strains attendant upon landing in a broadside wind. (*) It must be provided with some form of leading skid or wheel, which is normally clear of the ground, but which is sufficient in all cases to prevent the machine turning over. While considering these features there are other important points that must not be overlooked. While an aeroplane is actually flying, C\G while other types of machine may present difficulties in a different direction. . „ However, the generally accepted arrangement for practically any type of machine is to place the main wheels approximately under the centre of gravity and a rear support, which generally takes the form of a skid, is provided in front of the main wheels. When resting on the ground most of the weight is taken by the main wheels, and a comparatively small loading given to the rear skid. The height of the undercarriage is determined by the propeller, which must be allowed suitable clearance from the ground under all conditions. It is advisable, therefore, to place the propeller as high as possible in order to keep the centre of gravity in the vertical line low down, but there are other principles of design which govern the position of the propeller within certain limits. In order to leave the ground, or to alight, at a speed below that normally attained when Hying, it is necessary to increase the angle of incidence, and this must be allowed for by so arranging the rear skid that the machine lies at an angle of about 18°; the front skid or wheel will then be well clear of the ground, and will only come into action when the machine pitches forward. The weight supported by the rear skid depends upon whether a lifting or non-lifting tail plane is used, but in any case, the skid must be so loaded as to leave the ground in a short distance, as otherwise it will prevent rapid acceleration when starting. Also, a heavy load on the rear skid means that the main wheels are some dis tance in front of the centre of gravity, and this tends to tilt the machine back when landing, thus causing it to rise again owing to its suddenly increased angle, and Fig. 2.— Farman Biplane. the undercarriage is merely an encumbrance I in the form of weight and head resistance, and although it is obviously desirable to cut weight to a minimum wherever possible, this is not the place where a great reduction should be made, as it is practically impossible to estimate correctly the strains to which the various members are subjected, and therefore a liberal factor of safety must ha allowed. Improvement lies more in the direction of simplifying the design, thus reducing head resistance and weight, at the same time fulfilling the conditions of the ideal undercarriage as far as possible. It is no easy matter to decide what constitutes unsuitable ground for landing. If it was desired that a machine should alight safely in a cornfield, on the side of a steep hill, or amongst ditches and marsh ground, the undercarriage would assume impossible dimen sions as regards weight and size. It is reasonable, however, to assume that the ground will be of uneven surface, such as ploughed land, sand, or long grass on a medium incline. The landing gear is seldom subjected to abnormal strains in landing, provided, of course, that the pilot is fairly experienced, but in rolling over bad ground after landing or before getting off, it may have to withstand far greater shocks, especially when rolling with a following wind, in which case the normal flying speed of the machine will l>e exceeded. The design of an undercarriage is, to a large extent, governed by the type of machine to which it is fitted. The popular type of single tractor machine offers certain difficulties to the fitting of a reliable gear, chiefly owing to the position of the tractor, which prevents a substantial skid arrangement being provided in front, in this manner the machine \ may rebound several times before coming to rest. With a directional tail, or one giving slight lift, the construction of the framework between this member and the main planes can be very light, as the bending moment is small; but, if it has to withstand the shocks transmitted by a heavily loaded skid, weight must be added to give it sufficient strength. It is therefore apparent that the main rolling twheels should be nearly under the centre of gravity. I Types of Undercarriage. The Wright aeroplane is chiefly interesting from the fact that it was the first practical machine in which a rigid framework was provided beneath the planes in place of the flexibly mounted undercarriages adopted by the French constructors at about the same period, the outcome of these two systems being the combination of skids and wheels in later types of machines. The chief advantage of this system is, that it provides a rigid structure to which the main lifting-wires may be fixed, these wires also being effective in taking any side-strains imposed on the under carriage itself. Farman Biplane.—Farman was the first to combine wheels with skids, and this type of undercarriage has found favour with a large number of constructors. Ash is chiefly used, and the machine is supported from the skids by four or more struts, which are wired-up rigidly to the main planes. The skids are 9 feet apart, and each carries a pair of rolling-wheels, which are attached by rubber bands. A short radius-rod allows the wheels a certain amount of lateral 2l8
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
