Fig. 15. Classical form of the frequency—response curve of an aircraft, illustrating the effect of making a sinusoidal control input to the elevator. The graph plots how the ratio of the output (in this case, pitch attitude ) to input (in this case, elevator angle) varies with the frequency of the control input. The gain is plotted in decibels and the control input frequency is plotted on a logarithmic scale. The graph indicates that the gain peaks (due to resonance effects) when the control input frequency coincides with the natural frequencies of the natural modes of motion. The gain drops off sharply at control input frequencies higher than the natural frequency of the short period mode, which therefore limits the bandwidth of the aircraft's frequency response. In insects, control inputs made at the level of a single wingbeat will not be effective if the wingbeat frequency is much greater than the natural frequency of the short period mode.