Yaw (rotation)

The yaw rate or yaw velocity of a car, aircraft, projectile or other rigid body is the angular velocity of this rotation, or rate of change of the heading angle when the aircraft is horizontal.

It is the primary measure of how drivers sense a car's turning visually.

The yaw rate is directly related to the lateral acceleration of the vehicle turning at constant speed around a constant radius, by the relationship The sign convention can be established by rigorous attention to coordinate systems.

Studying the stability of a road vehicle requires a reasonable approximation to the equations of motion.

The diagram illustrates a four-wheel vehicle, in which the front axle is located a metres ahead of the centre of gravity and the rear axle is b metres towards the rear from the center of gravity.

The tyre treads at the region of contact point in the direction of travel, but the hubs are aligned with the vehicle body, with the steering held central.

The tyres distort as they rotate to accommodate this mis-alignment, and generate side forces as a consequence.

will be called the 'stiffness', as its function is to return the system to zero deflection, in the same manner as a spring.

The form of the solution depends only on the signs of the damping and stiffness terms.

Corrections for relative effect of front and rear tyres and steering forces are available in the main article.

The first aircraft to demonstrate active control about all three axes was the Wright brothers' 1902 glider.