The design of a combine harvester system for controlling feedrate, sieve airflow, and cylinder speed is presented. Field tests show that feedrate control can lead to increased harvesting (productivity) rates. This feature, in combination with cylinder speed control, also reduces the risk of plugging under normal conditions. Airflow control on the sieves should contribute to increased separation efficiency and reduced loose grain loss. Cylinder speed control through an engine throttle boost compensates for sudden surges in feedrate, resulting in reduced cylinder and separation losses. This indicates that the throttle boost and simultaneous reduction in ground speed, as a result of a momentum interchange, is very effective in maintaining cylinder speed for sudden increases in feedrate. >