If we consider that aerodynamics, from a modern point of view, is a branch of physics that
study physical laws and their applications, regarding the displacement of a body into a fluid,
such concept could be applied to any body moving in a fluid at rest or any fluid
moving around a body at rest. The general concept outlined above is applicable to
planes; cars; boats; big ships; missiles; wind energy generators; small flying objects,
like UAVs; etc.
The forces and moments the vehicle receives from the surrounding air depend more on the shape of the body than on the characteristics of the chassis. A detailed study of motor vehicle aerodynamics is thus beyond the scope of a book dealing with the automotive chassis. However, aerodynamic forces and moments have a large inﬂuence on the longitudinal performance of the vehicle, its handling and even its comfort, so it is not possible to neglect them altogether.
The deﬁnition of comfort in a motor vehicle is at once complex and subjective, changing not only with time (cars considered comfortable just twenty years ago are nowadays considered unsatisfactory) but also from user to user. The same user may change his appraisal depending on circumstances and his psychophysical state. But comfort remains an increasingly important parameter in customer choice and strongly competitive factor among manufacturers.
Vehicles require thrust forces, generated at the tires, to initiate and maintain motion. These forces
are usually referred to as tractive forces or the tractive force requirement. If the required tractive
force (F) is broken into components the major components of the resisting forces to motion are
comprised of acceleration forces (Faccel = ma & I forces), Gradeability requirements (Fgrade),
Aerodynamic loads (Faero) and chassis losses (Froll resist ).
As already stated, a road vehicle on pneumatic tires cannot maintain a given trajectory under the eﬀect of external perturbations unless managed by some control device, which is usually a human driver. Its stability solely involves such state variables as the sideslip angle β and the yaw velocity r. In the case of two-wheeled vehicles the capsize motion is intrinsically unstable forcing the driver not only to control the trajectory but stabilize the vehicle. A possible scheme of the vehicle-driver system is shown in Fig. 27.1.
Two-axle vehicles without trailer
Low speed or kinematic steering is, as already stated, deﬁned as the motion of a wheeled vehicle determined by pure rolling1 of the wheels. The velocities of the centres of all the wheels lie in their midplane, that is the sideslip angles αi are vanishingly small. In these conditions, the wheels cannot exert any cornering force to balance the centrifugal force due to the curvature of the path. Kinematic steering is possible only if the velocity is vanishingly small.
A vehicle on elastic suspensions may be modelled as a system made by a certain number of rigid bodies connected with each other by mechanisms of various kinds and by a set of massless springs and dampers simulating the suspensions. A vehicle with four wheels can be modelled as a system with 10 degrees of freedom, six for the body and one for each wheel. This holds for any type of suspension, if the motion of the wheels due to the compliance of the system constraining the motion of the suspensions (longitudinal and transversal compliance of the suspensions) is neglected....
Buying a car from a traditional lot and getting a bank loan aren’t always
the only options. There are a number of programs, such as Vehicles
for Change in Baltimore, MD, and Working Wheels in Seattle, WA,
both highlighted in the documentary; and Ways to Work, with offices
across the country, that help low-income workers achieve the goal of