An investigation was undertaken in the laboratory to determine the impact cutting energy while cutting single stems of forage sorghum by the knife of a #ail harvesting machine. The minimum cutting speed required for complete cutting is fairly insensitive to the knife rake angle. The minimum cutting speed increased from 12)9 to 18)0 m/s for a knife rake angle range of 20}603 as the knife bevel angle was increased from 30 to 703. Such low cutting speeds would not be capable of conveying the chopped forage successfully into the accompanying forage wagon. When the cutting speed was increased from 20}60 m/s, the cutting energy per unit cross-sectional area (speci"c cutting energy) for direct impact decreased by a factor of about three for bevel angles from 30 to 703. When cutting was performed against a shear bar, the speci"c cutting energy drastically reduced to between one-"fth and one-"fteenth of that required for direct impact. Forward speed of the machine did not have any signi"cant e!ect on speci"c cutting energy. The speci"c cutting energy is not greatly sensitive to knife rake angle, but the minimum energy requirement was observed at 403 rake angle for the experimental ranges of cutting speed and bevel angle.
The plant inclination angle in#uenced the speci"c cutting energy requirement and minimum energy was required at a plant inclination angle of about 203 to the vertical in the direction of machine movement.
The contribution of the cutting energy to the total energy consumption (which includes cutting energy and windage energy) was found to be less than 10%. The total speci"c energy requirement increased by 3}4 times as the cutting speed was increased from 20 to 60 m/s and it reduced by 25}30% when the knife rake angle was increased from 20 to 603. The knife bevel angle did not appear to have any signi"cant e!ect on total speci"c energy requirement.