Use Of Collective

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The collective is more effective in controlling the rolling motion than lateral cyclic, because it reduces the main rotor thrust (lift). A smooth, moderate collective reduction, at a rate less than approximately full up to full down in two seconds, is adequate to stop the rolling motion. Take care, however, not to dump collective at too high a rate, as this may cause a main rotor blade to strike the fuselage. Additionally, if the helicopter is on a slope and the roll starts to the upslope side, reducing collective too fast may create a high roll rate in the opposite direction. When the upslope skid/wheel hits the ground, the dynamics of the motion can cause the helicopter to bounce off the upslope skid/wheel, and the inertia can cause the helicopter to roll about the downslope ground contact point and over on its side. [Figure 11-8]

Figure 11-8. Downslope rolling motion.

The collective should not be pulled suddenly to get airborne, as a large and abrupt rolling moment in the opposite direction could occur. Excessive application of collective can result in the upslope skid rising sufficiently to exceed lateral cyclic control limits. This movement may be uncontrollable. If the helicopter develops a roll rate with one skid/wheel on the ground, the helicopter can roll over on its side.