Resume of the four reference points

Figure 2.13 illustrates in composite form the interactional nature of the flight dynam­ics process as reflected by the four reference points. The figure, drawing from the parlance of ADS-33, tells us that to achieve Level 1 handling qualities in a UCE of 1, a rate response type is adequate; to achieve the same in UCEs of 2 and 3 require AC (attitude command) or TRC (translational rate command) response types respec­tively. This classification represents a fundamental development in helicopter handling qualities that lifts the veil off a very complex and confused matter. The figure also shows that if the UCE can be upgraded from a 3 to a 2, then reduced augmentation will be required. A major trade-off between the quality of the visual cues and the quality of the control augmentation emerges. This will be a focus of attention in later chapters. Figure 2.13 also reflects the requirement that the optimum vehicle dynamic characteristics may need to change for different MTEs and at the edges of the OFE; terminology borrowed from fixed-wing parlance serves to describe these features – task-tailored or mission-oriented flying qualities and carefree handling. Above all else, the quality requirements for flying are driven by the performance and piloting workload

demands in the MTEs, which are themselves regularly changing user-defined require­ments. The whole subject is thus evolving from the four reference points – the mission, the environment, the vehicle and the pilot; they support the flight dynamics discipline and provide an application framework for understanding and interpreting the mod­elling and criteria of task-oriented flying qualities. Continuing on the Tour, we address the first of three key technical areas with stronger analytical content – theoretical modelling.