Rotorspeed/torque partial trim
When the lateral and directional trim have converged, the tail rotor downwash is calculated (I), followed by the tail rotor collective (J), including the effect of the S3 pitch/flap coupling (K), and tail rotor torque (L). The total engine torque required can now be calculated, from which the rotorspeed can be updated using the droop law (M in Fig. 4.5). The rotorspeed calculation is the final stage in the iterative cycle and the whole sequential process described above must be repeated until convergence is achieved.
The remaining calculations in Fig. 4.5 determine the main rotor control angles, first in the hub/wind axes system (N, O) (see the Appendix Section 3A.4), followed by a transformation into hub axes, to give the swash plate control outputs (P). We shall return to discuss the controls to trim below in Section 4.2.6.
Table 4.1 Trim forces and moments – Lynx at 80 knots in climbing turn (yfe = —0.15 rad, Qae = 0.4 rad/s)