This paper has developed a yaw dynamic model for a
tractor with a hitched implement. It was shown that a lin-
ear tire model could be used in modeling the hitch forces
created by the implement and was validated using experi-
mental data from a hitch dynamometer. Analysis of the
experimental data showed that the lateral hitch force vs.
slip angle of the implement is relatively linear and can be
represented by the linear tire model. The ‘‘3-wheeled” Bicy-
cle Model developed in this paper was shown to capture the
steady state yaw rate by accounting for changing hitched
implement conditions using a hitch cornering stiffness term.
Steady state experiments were used to determine the hitch
cornering stiffness term which ranged from 0 N/deg to
3385 N/deg for increasing implement size and depth. Front
and hitch relaxation lengths were added to the ‘‘3-wheeled”
Bicycle Model (FHRL Model) in order to capture the
dynamic data. Dynamic steering experiments were used
to produce empirical system identification models for the
implements at each respective depth to identify the front
tire and hitch relaxation lengths of the FHRL Model.
Finally, a variation in the steady state yaw rate of 9–21%
due to the effect of the front axle traction forces in a
four-wheel drive tractor was shown.
This paper has presented a baseline study of the yaw
dynamic of a tractor with a hitch-mounted implement
and the effect of front wheel drive forces on the yaw
dynamics was shown. However, sensitivity of the dynam-
ics and model coefficients to other parameters and terrain
conditions was not studied in depth. Varying ground con-
ditions such as ground moisture, type and compaction
may in fact affect the amount of lateral force an imple-
ment generates. Therefore, additional research is needed
to study and quantify these effects on the tractor dynam-
ics and/or parameters and to determine how to extrapo-
late the results of this paper to other departments, soils,
implements, etc. Also, the four-wheel drive model should
be studied further to determine if the analytical model can
capture the effect of the front wheel drive forces on the
vehicle turning shown in this paper. Finally, the work in
this paper could be extended to model the dynamics of
towed implements, articulated tractors, skid steer, and
even rear steer tractors.