Rotorcraft Handling Qualities Engineering: Managing the Tension between Safety and Performance 32nd Alexander A. Nikolsky Honorary Lecture

Abstract

In this Nikolsky paper, I look back nearly 70 years and highlight particular events that reflect the continual growth of the handling qualities discipline. This growth has brought us to a point where designers have, within their grasp, the performance standards, the criteria and test techniques, the understanding of rotorcraft aeromechanics and control, and the design tools, to ensure that handling deficiencies never again have to define the boundary of the operational flight envelope. This point is considered very important in the evolution of the discipline and the associated flight control technologies. The pilot is a vital component in the rotorcraft system; a nearly perfectly functioning component normally, but one that can be stressed, fatigued, or overloaded, particularly when dealing with the consequences of handing qualities deficiencies, and when managing high tension between flight performance and safety. It is argued that this tension is more manageable when an aircraft has good handling qualities, throughout all missions, including flight in degraded environments and hazardous operations. This paper tells the story of how our industry has arrived at this point, how the standards and the enabling technologies have developed, spurred by user needs, and enabled by research. The paper also looks forward, highlighting how we need to strive for super-Level 1 handling qualities, a state where pilot errors, in any shape or form attributable to deficient flight characteristics, are things of the past.

A handling qualities analysis tool for rotorcraft conceptual designs

“…Rotorcraft, in particular high performance designs, cannot rely on such methods, since most bare-airframe designs are typically unstable and require a stabilizing control system to make them adequately flyable. In the context of rotorcraft, Padfield (4) notes that 25–50% of flight testing time in an aircraft development program might be spent on fixing HQ problems. Furthermore, Padfield suggests that HQ were not given their proper place in the early design trade-space, and were often left until flight test to discover and “put right”.…”

“…Reference 5 emphasizes ‘flying qualities’ as the vehicle stability, control and manoeuvring characteristics and ‘handling qualities’ as the combination of flying qualities and the broader aspects of the mission task, visual cues and atmospheric environment. However, as Ref. 4 notes, there appears to be no universal acceptance on the distinction.…”

“…In a future context, this process might be represented by a variety of other analyses encompassed in a MDAO environment. Stage (1) is the source of input for SIMPLI-FLYD that encompasses stages (2) through (4) where simplified linear flight dynamics models are calculated, integrated with control laws, and then analysed and optimized by CONDUIT. The output of stages (2) through (4) are set(s) of stability, control and HQ parameters (stage 5), and an X-Plane compatible real-time simulation model for use in an X-Plane simulation station (stage 6).…”

“…Stage (1) is the source of input for SIMPLI-FLYD that encompasses stages (2) through (4) where simplified linear flight dynamics models are calculated, integrated with control laws, and then analysed and optimized by CONDUIT. The output of stages (2) through (4) are set(s) of stability, control and HQ parameters (stage 5), and an X-Plane compatible real-time simulation model for use in an X-Plane simulation station (stage 6). Reference 7 reports a full description of SIMPLI-FLYD and its sub-functions; some of the key aspects are highlighted in the following section:

Figure 1.SIMPLI-FLYD architecture for including stability and control analysis into conceptual design.

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“…For the control derivatives, a simplification was imposed for the CONDUIT point analysis flight dynamic models such that any vehicle always has a fixed set of four ‘controls’ for the primary roll, pitch, thrust and yaw response axes. The effects of multiple or redundant control effectors such as combinations of rotor controls and wing or aerodynamic surface controls are combined via an NDARC-defined ‘mixing matrix’ in advance of analysis at stages (3) and (4) (the separate control derivatives are retained for use in the real-time model). The actuator characteristics are configurable for each analysis point model to allow representation of different actuator classes (i.e.…”