Balance of forces and moments

Trim is concerned with balancing the forces and moments acting on the aircraft. A typical trim is given by Table 4.1, where the various contributions to the forces and moments are given for a Lynx in a climbing turn (case уfe = —0.15 rad, Q, ae = 0.4 rad/s in Fig. 4.6(b)).

For our approximate model, many of the second-order effects have been neglected as can be seen in Table 4.1. (e. g., the X force from the empennage and X and Z force from the tail rotor, the fuselage rolling moment and tail rotor pitching moment). The inertial force components along the body axes are seen to be large, arising from the centrifugal force due to the angular motion of the aircraft. For the case shown, the trim tolerances were set at values that left the residual forces and moments as shown in the ‘Totals’ row. With zero initial value for pitch attitude and roll attitude set by eqn 4.34, convergence can usually be achieved to these levels of force within a few iterations.

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