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8. Vietnam—military engineering in Vietnam
ABSTRACTS
69
8.
Coradi, P. A. Vietnam---military engineering in Vietnam. Civil Engineering, ASCE, November, 1965, pp. 47-50. The Bureau of Yards and Docks U.S. Navy has responsibility for military engineering and construction in Southern Asia. The chief of the Bureau tells about building airfields and other facilities under harassment by the Viet Cong. Aluminium strips surface an airfield; cable arresters stop planes in a short land version of carrier landing. [Author's Summary.]
9.
D~gcr, W. The effect of tractive force on motor-vehicle stability. A.T.Z., July, 1965, VOl. 67, No. 7, pp. 205-213 (in German). Theoretical vehicle-stability studies published in the past did not take into account the effect of a circumferential force on the cornering force and aligning torque of the automobile tyre, but relied on graphs showing cornering force and aligning torque only as a function of wheel load and slip angle. The purpose of the present study is to include the effect of tractive force in the theoretical investigation of vehicle stability. By a method of analytical approximation, a tyre characteristic diagram is established which shows the characteristic effect of circumferential force. Stability functions are then evolved which describe in a general way, both for front-wheel drive and rear-wheel drive, the effect of the tractive force on vehicle stability by the reduction of the cornering force and tyre aligning torque. A sample calculation for a private car shows that both for front-wheel-drive and rear-wheel-drive vehicles, the adequate condition of stability is always satisfied. Therefore, stability studies can be confined to a consideration of the necessary stability condition. This consideration shows that only in the case of the rear-wheel-drive vehicle is there a decisive influence of the traction force in conjunction with the magnitude of the friction coefficient between tyre and road on vehicle stability; the range of stability of the vehicle is considerably restricted, especially on roads with a low friction coefficient (<0"6). For the front-wheel-drive vehicle, on the other hand, no significant effect is found; stability is retained over the whole operating range. Elasticity in the steering mechanism and weight distribution exert a great influence on the stability limit; the stable region is extended with increasing elasticity of the steering mechanism and increasing front-wheel load. Increased rear-axle load reduces the region of stability. It is shown, however, that the stabilising effect of steering elasticity must be viewed in connection with the magnitude of the tyre aligning torque; the greater this is the greater the effect of steering-mechanism elasticity. The tyre aligning torque should therefore not he ignored in stability studies. Another point investigated is the deviation of the vehicle from its path as a result of disturbances. Both for rear-wheeldrive and front-wheel-drive vehicles and over the whole operating range, these deviations die down periodically, except in the special case of a rear-wheel-drive vehicle going into a power-slide. [M.I.R.A.]
10.
Dodge, R. N. The dynamic stiffness of a pneumatic tyre model. S.A.E. Paper, Mid-Year Meeting, May 17-21, 1965, p. 8. Expressions are determined for the load/reflection characteristics of a rotating cylindrical shell loaded by an external stationary point load, such shell serving as a model to represent the dynamic response of an actual pneumatic tyre. The shell is explained to have characteristics such as are present where a relatively inextensible outer band of known elastic properties is supported by an elastic foundation which, in turn, is caused to rotate about a central hub; shell width is considered small in relation to shell diameter. Calculated and measured load/reflection curves are compared. The analysis of a rotating cylindrical shell supported by an elastic foundation is presented, simplifying assumptions being explained and final equations for load/deflection relationships derived. A model designed to permit simple experiments for verifying these equations was constructed. It consisted of a cylindrical shell made of a thin tubber belt reinforced with twisted steel cords wrapped in the circumferential direction. The elastic foundation consisted of a sponge-tubber insert bonded to the belt with silicone rubber and was attached to a control hub of plexi-glass and aluminium. For the experiments made, the test-rig used consisted of a variable*speed motor for controlling the angular velocity, a pivoted arm for applying the load, a ball-bearing roller to serve as loading point, and a load cell for measuring magnitude of applied load. A mechanical dial gauge recorded deflection. Slight errors in the deflection data obtained and their sources are explained. Typical load/deflection data taken from the model and load/deflection curves predicted from the equations are compared in graphs. In general, agreement is reasonably
69
8.
Coradi, P. A. Vietnam---military engineering in Vietnam. Civil Engineering, ASCE, November, 1965, pp. 47-50. The Bureau of Yards and Docks U.S. Navy has responsibility for military engineering and construction in Southern Asia. The chief of the Bureau tells about building airfields and other facilities under harassment by the Viet Cong. Aluminium strips surface an airfield; cable arresters stop planes in a short land version of carrier landing. [Author's Summary.]
9.
D~gcr, W. The effect of tractive force on motor-vehicle stability. A.T.Z., July, 1965, VOl. 67, No. 7, pp. 205-213 (in German). Theoretical vehicle-stability studies published in the past did not take into account the effect of a circumferential force on the cornering force and aligning torque of the automobile tyre, but relied on graphs showing cornering force and aligning torque only as a function of wheel load and slip angle. The purpose of the present study is to include the effect of tractive force in the theoretical investigation of vehicle stability. By a method of analytical approximation, a tyre characteristic diagram is established which shows the characteristic effect of circumferential force. Stability functions are then evolved which describe in a general way, both for front-wheel drive and rear-wheel drive, the effect of the tractive force on vehicle stability by the reduction of the cornering force and tyre aligning torque. A sample calculation for a private car shows that both for front-wheel-drive and rear-wheel-drive vehicles, the adequate condition of stability is always satisfied. Therefore, stability studies can be confined to a consideration of the necessary stability condition. This consideration shows that only in the case of the rear-wheel-drive vehicle is there a decisive influence of the traction force in conjunction with the magnitude of the friction coefficient between tyre and road on vehicle stability; the range of stability of the vehicle is considerably restricted, especially on roads with a low friction coefficient (<0"6). For the front-wheel-drive vehicle, on the other hand, no significant effect is found; stability is retained over the whole operating range. Elasticity in the steering mechanism and weight distribution exert a great influence on the stability limit; the stable region is extended with increasing elasticity of the steering mechanism and increasing front-wheel load. Increased rear-axle load reduces the region of stability. It is shown, however, that the stabilising effect of steering elasticity must be viewed in connection with the magnitude of the tyre aligning torque; the greater this is the greater the effect of steering-mechanism elasticity. The tyre aligning torque should therefore not he ignored in stability studies. Another point investigated is the deviation of the vehicle from its path as a result of disturbances. Both for rear-wheeldrive and front-wheel-drive vehicles and over the whole operating range, these deviations die down periodically, except in the special case of a rear-wheel-drive vehicle going into a power-slide. [M.I.R.A.]
10.
Dodge, R. N. The dynamic stiffness of a pneumatic tyre model. S.A.E. Paper, Mid-Year Meeting, May 17-21, 1965, p. 8. Expressions are determined for the load/reflection characteristics of a rotating cylindrical shell loaded by an external stationary point load, such shell serving as a model to represent the dynamic response of an actual pneumatic tyre. The shell is explained to have characteristics such as are present where a relatively inextensible outer band of known elastic properties is supported by an elastic foundation which, in turn, is caused to rotate about a central hub; shell width is considered small in relation to shell diameter. Calculated and measured load/reflection curves are compared. The analysis of a rotating cylindrical shell supported by an elastic foundation is presented, simplifying assumptions being explained and final equations for load/deflection relationships derived. A model designed to permit simple experiments for verifying these equations was constructed. It consisted of a cylindrical shell made of a thin tubber belt reinforced with twisted steel cords wrapped in the circumferential direction. The elastic foundation consisted of a sponge-tubber insert bonded to the belt with silicone rubber and was attached to a control hub of plexi-glass and aluminium. For the experiments made, the test-rig used consisted of a variable*speed motor for controlling the angular velocity, a pivoted arm for applying the load, a ball-bearing roller to serve as loading point, and a load cell for measuring magnitude of applied load. A mechanical dial gauge recorded deflection. Slight errors in the deflection data obtained and their sources are explained. Typical load/deflection data taken from the model and load/deflection curves predicted from the equations are compared in graphs. In general, agreement is reasonably