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Solution Procedures 41<br />

Table 5-4. Trim solution.<br />

trim variable perturbation<br />

aircraft orientation θ (pitch), φ (roll) 100AΔ<br />

aircraft velocity Vh (horizontal velocity) V Δ<br />

aircraft velocity Vz (vertical velocity) V Δ<br />

aircraft velocity β (sideslip) 100AΔ<br />

aircraft angular rate ˙ θ (pullup), ˙ ψ (turn) ΩΔ<br />

aircraft control angle 100AΔ<br />

5-1.7 Rotor-Flap Equations<br />

Evaluating the rotor hub forces may require solution of the flap equations E(v) =0. For tippath<br />

plane command, the thrust and flapping are known, so v =(θ0.75 θc θs) T . For no-feathering plane<br />

command, the thrust and cyclic pitch are known, so v =(θ0.75 βc βs) T . A Newton–Raphson solution<br />

method is used: from E(vn+1) ∼ = E(vn)+(dE/dv)(vn+1 − vn) =0, the iterative solution is<br />

vn+1 = vn − CE(vn)<br />

where C = f(dE/dv) −1 , including the relaxation factor f. The derivative matrix for axial flow can be<br />

used. Alternatively, the derivative matrix dE/dv can be obtained by numerical perturbation. Convergence<br />

of the Newton–Raphson iteration is tested in terms of |E|

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