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In straight flight, as speed is reduced, whilst trimming to keep the stick force zero:
  • A
    the elevator and trim tab do not move.
  • B
    the elevator is deflected further upwards and the trim tab further downwards.
  • C
    the elevator is deflected further downwards and the trim tab further upwards.
  • D
    both elevator and trim tab are deflected further upwards.

Refer to figure.
There is an increment of force dependent on the trim tab setting which varies with the dynamic pressure or the square of equivalent airspeed. Figure 1 indicates the variation of stick force with airspeed and illustrates the effect of tab setting on stick force.

To trim the airplane at point (1) a certain amount of up elevator is required, and zero stick force is obtained with the use of the trim tab. To trim the airplane for higher speeds corresponding to points (2) and (3), less and less aircraft nose-up tab is required.

Note that when the airplane is properly trimmed, a push force is required to increase airspeed and a pull force is required to decrease airspeed. In this manner, the airplane would have positive stick force stability with a stable “feel” for airspeed.

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