One of the tail rotor blades of a helicopter has an unbalanced mass of \(m=0.5 \mathrm{~kg}\) at a distance of \(e=0.15 \mathrm{~m}\) from the axis of rotation, as shown in Fig. 3.63. The tail section has a length of \(4 \mathrm{~m}\), a mass of \(240 \mathrm{~kg}\), a flexural stiffness ( \(E I\) ) of \(2.5 \mathrm{MN}-\mathrm{m}^{2}\), and a damping ratio of 0.15. The mass of the tail rotor blades, including their drive system, is \(20 \mathrm{~kg}\). Determine the forced response of the tail section when the blades rotate at \(1500 \mathrm{rpm}\).

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A Tail section, El FIGURE 3.63 Unbalance in tail rotor blade of helicopter. B Tail rotor blades m