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To view this page ensure that Adobe Flash Player version 9.0.124 or greater is installed. With an understanding of when dynamic rollover occurs, the excessive angular momentum. next step is to study why it occurs. The basic cause of dynamic rollover is excessive angular momentum. Isaac Newton said that an unbalanced force equals the time rate of change of momentum . . . F = ma. That is true for objects moving in straight lines. However, for rotational motion, Newton’s law changes slightly — an unbalanced moment equals the time rate of change of angular momentum. There are several contributing factors that can make condi-tions worse. Any shift of the center of gravity toward the roll point makes the helicopter more likely to statically roll over. This CG shift could be caused by a cargo shift or by personnel changing positions in the aircraft. For American-made heli-copters, the thrust of the tail rotor is directed toward the right. For rollovers to the right, the tail rotor thrust would be an Angular momentum is defined as the moment of inertia (I) multiplied by the angular velocity ( ). Newton’s law really does make sense in relation to helicopters. In a hover, there is no roll rate or angular velocity. However, when the cyclic is displaced, the rotor system is tilted. The thrust of the rotor system then creates a moment about the center of gravity, and the helicopter develops a roll. aggravating condition. Winds can also make conditions worse. If the winds are strong enough, the side force on the fuselage may be sufficient to roll the helicopter. Winds from the left will increase the tail rotor angle of attack, increasing the tail rotor thrust. Finally, winds in the direction of the rollover will cause “blowback” of the main rotor, tilting it in the direction of roll. Remember, the moment of inertia is a body’s resistance to Tips to Prevent Rollover rotation and is defined for rolls about the center of gravity as the sum of all the bits of mass of the body (m) multiplied by The conditions for occurrence are present for nearly every 直升机网 www.helicopter.cn 直升机翻译 www.aviation.cn 本文链接地址：FLIGHT SAFETY FOUNDATION HELICOPTER SAFETY Preventing Dynamic Rollover(3) |
