IntroductionThe speed of the cutting blades is one of the main factors that allow cutting without a counter edge and this depends on the diameter of the trajectory, the inertia, the stem's resistance to fl exion and on the maximum cutting force of the apparatus. The energy and the cutting power of mowers and shredders also depend on the knives speed, on the feed speed, on the crop properties, on the knives' cutting width and on the number of blades cutting simultaneously (Fernández and Martínez, 1988;Moore Almeida and Benez, 1997 The power demand for the demolition of pineapple (Ananas comosus) fi elds at the end of their productive cycle with a fl ail mower has been determined using strain gage measures, the trials were conducted at three different angular velocities of the cutting apparatus and three translation velocities, using two different sets of knives. The results of the investigation show the infl uence of the knife type and cinematic regime of the cutting apparatus in the energy demand; furthermore they allow the validation of fl ail mower power demand models.