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Slip ratio is a means of calculating and expressing the slipping behavior of the wheel of an automobile.It is of fundamental importance in the field of vehicle dynamics, as it allows to understand the relationship between the deformation of the tire and the longitudinal forces (i.e. the forces responsible for forward acceleration and braking) acting upon it.
There are a number of correlations for slip ratio. For homogeneous flow, S = 1 (i.e. there is no slip). The Chisholm correlation [2] [3] is: = The Chisholm correlation is based on application of the simple annular flow model and equates the frictional pressure drops in the liquid and the gas phase.
In (automotive) vehicle dynamics, slip is the relative motion between a tire and the road surface it is moving on. This slip can be generated either by the tire's rotational speed being greater or less than the free-rolling speed (usually described as percent slip), or by the tire's plane of rotation being at an angle to its direction of motion (referred to as slip angle).
The ratios between the slip angles of the front and rear axles (a function of the slip angles of the front and rear tires respectively) will determine the vehicle's behavior in a given turn. If the ratio of front to rear slip angles is greater than 1:1, the vehicle will tend to understeer, while a ratio of less than 1:1 will produce oversteer. [2]
The exact ratio of sidewall compliance to tread compliance is a factor in tire construction and inflation pressure. [ 3 ] Because the tire deformation tends to reach a maximum behind the center of the contact patch, by a distance known as pneumatic trail , it tends to generate a torque about a vertical axis known as self aligning torque .
These coefficients are then used to generate equations showing how much force is generated for a given vertical load on the tire, camber angle and slip angle. [5] The Pacejka tire models are widely used in professional vehicle dynamics simulations, and racing car games, as they are reasonably accurate, easy to program, and solve quickly.
Mathematically, the Slip factor denoted by 'σ' is defined as the ratio of the actual & ideal values of the whirl velocity components at the exit of the impeller. The ideal values can be calculated using an analytical approach while the actual values should be observed experimentally. = ′
Flying in a slip is aerodynamically inefficient, since the lift-to-drag ratio is reduced. More drag is at play consuming energy but not producing lift. Inexperienced or inattentive pilots will often enter slips unintentionally during turns by failing to coordinate the aircraft with the rudder.