Rg = W sin g (1.3)
Where
g = Grade angle
W = Vehicle weight
Aerodynamic Force
Figure 1.4 Forces on an Aerofoil in Free Stream Flow [28]
Aerodynamic force is combination of two main forces, lift and drag as shown in Figure 1.4. Lift force is force acting on vehicle produced by different fluid speed flow over vehicles, and it is perpendicular to the flow direction. As Bernoulli’s principle states that for an inviscid fluid, with the increase in speed of fluid, the flow will result in decrease in pressure or fluid’s potential energy [9]. As vehicles running on road, the airflow at the different flow speed of up and down face of the vehicle generates the lift or upward force, which matters the vehicles stability and load. There is another popular explanation of lift, the Newton camp. Nevertheless, both of them are considered to be correct. According to the Newton’s third law of motion, a turning action of the flow will result in a re-action (aerodynamic force) on the object [10]. The lift force could be calculated by:
L = ½ ρv2ACL (1.4)
Where:
L = lift force
Ρ = fluid density
V = fluid speed
A = Plan form area
CL = Lift Coefficient at Desired Angle of Attack, Mach Number, and Reynolds Number
Aerodynamic drag is the force acting on any moving object in a free stream flow, which is due to the pressure distribution over body surface (Dpr) and surface frictions (Df) [7]. Since the surface friction is due to viscosity, the friction drag is separated from pressure drag as shown in Figure 1.5.
Figure 1.5 Aerodynamic Drag Distributions [7]
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