HELICOPTER DYNAMIC ROLLOVER

HELICOPTER DYNAMIC ROLLOVER

INTRODUCTION:

Dynamic rollover is defined as "the occurrence of a rolling motion, while any part of the landing gear is acting as a pivot, which causes the aircraft to exceed a critical angle and roll over".

Dynamic rollover can occur during or prior to the hover when any part of the heli-copter acts as a pivot and the helicopter exceeds a critical angle of roll. This angle is dependant upon control limits and, in most helicopters, is in the order of 15 degrees.

The problem is caused by main rotor thrust and other physical factors. Untrimmed lateral main rotor thrust causes roll rates that make the aircraft exceed its critical rollover angle.

Main rotor thrust is laterally trimmed when it is acting more or less vertically. When hovering, a helicopter is laterally trimmed when ground movement is zero. If the heli-copter has a pivot point in contact with the ground and main rotor thrust is not laterally trimmed, the sideward component of that thrust will roll the helicopter around that pivot. The same reaction can occur during sling load operations if the helicopter is allowed to drift sideways and the strop becomes taut. The roll rate depends upon displacement of the cyclic control and the amount and rate of collective input. If the roll rate is high, the aircraft can rapidly reach its critical rollover angle.


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