Model tests of buoyant screw rotor configurations

SUMMARIES The Problems of Pneumatic Tracks by D. I. GORIN and P. S. VLASOV. The drawbacks of conventional metal tracks are reviewed and the possibilities of using commercially available new materials for the construction of high-performance tracks are discussed. The performance of three comparable tractors equipped with pneumatic wheels, metal tracks and pneumatic running gear are compared and the general conclusion is drawn that pneumatic tracks combine all the good features of wheeled and tracked running gear without many of their major disadvantages. Model Tests of Buoyant Screw Rotor Configurations by H. DUGOFF and I. R. EHRLICH. Scale model tests of a systematic series of buoyant screw rotor configuration in dry sand and soft wet mud are described. The effects of speed, slip, load and load distribution on rotor performance are discussed. Relative effectiveness of various rotor configurations is assessed on the basis of maximum attainable drawbar-pull. Experimental values of torque required for no-load operation in sand are compared with existing theory. An unsuccessful effort to investigate scale effects by testing models of two different scales using the same apparatus is described, and basic difficulties intrinsically associated with this approach are discussed. A Technique for Estimating the Performance of Tracked Vehicles in Muskeg by B. G. SCHRE1NER. The Waterways Experiment Station has participated in five field trafficability test programs in muskeg to date. From these programs results of tests with 23 tracked vehicles were analyzed to determine the muskeg strength necessary to support traffic for 40-50 passes. A correlation was found to exist between 40-50 pass go-no-go vehicle performance and cone index measured with the cone penetrometer. For tracked vehicles the experimental vehicle cone index (VCI) the minimum cone index required for 40-50 vehicle passes was determined. The experimental VCI's for the 23 vehicles were used to develop the following single expression for predicting VCI: VCI 14+l.5(W/P) where W is vehicle weight (lb) and P is the ground contact perimeter of both tracks (in.). Theory for a Powered Wheel in Soil by J. L. MCRAE. This paper presents the results of the development of semi-empirical formulas for the towed force and for the maximum drawbar-pull of pneumatic tyred wheels in soft soils. It assumes that the depth of sinkage of the wheel is known, and utilizes an "effective shear strength" for the soil based upon an empirical correlation with the WES cone index. Symmetrical Three-Dimensional Soil Failure by D. R. P. HETTIARATCH1and A. R. REECE. A general equation for the evaluation of forces on plane interfaces involving three-dimensional soil failure has been derived. Since a rigorous solution to this problem is not feasible at the present stage, this analysis has been made on the basis that a three-dimensional failure situation is composed of two planar components, each of which can be analysed by methods developed recently. Experimental evidence shows that this analysis is capable of predicting the general shape of the draught curves of rigid times of quite large aspect ratios and forward inclination, but due to the simplifying assumptions made the values obtained are generally too high. Due regard has been paid to checking analytically the failure geometry in three dimensions and is shown to be in reasonable agreement with observation. The theory has the advantage of giving a simple and convenient method of obtaining the soil reaction forces and the failure geometry for most three-dimensional soil failure problems of plane interfaces.

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