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Aviation History
1920
1920 - 0075.PDF
JANUARY 15, 1920 with their weights—complete with wheel and shield—and their safe load, carrying a factor of safety approximately 5 :— Tyre. 600 x 75 mm. 700 x 75 mm. 700 x 100 mm. 750 X 125 mm. 800 X 150 mm. 900 x 200 mm. X 220 mm. X 250 mm. x 300 mm. 1,100 1,250 1,500 1,750 x 300 mm. Weight,lbs. ozs. 12 3 14 14 6 8 2 o o o o o 21 23 28 55 81 114M5 194 Safe load, lbs. 1,000 1,100 1,600 1,800 2,200 4,000 5,000 6,000 8,000 9,000 Fig. 12 : Wheels in testing-machine under 5 tons dead load The loads given for all wheels up to and including900 x 200 mm. are the results of actual testing. Beyond this size the loads are calculated. The permissible normal loads on wheels are often deter-mined by ground conditions. The formula W = tread " X dia. " x 12 is generally employed to check for bearingpressure. In the event of abnormally soft ground special square treads are used. The wheels are tested in a special machine, and the deflectionsdue to given loads are noted (Figs. 12 and 13). In Fig. 5, giving deflection against load for a 1,100 x 220 mm. wheel,was also given the deflection of the wheel ; this is obviously so small that it can be safely neglected, and has been omittedin the other cases (Fig. 14). On unloading the load deflection curve falls below thatobtained on loading ; the area between the curves is a measure of the work dissipated. This, in the case of "-static "loading,is of the order of 8 per cent, of the total work. Fig. 15 gives the area of contact for the same four wheelsunder varying load. Fig. 13: Wheel being tested for deflection
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