Missing Topics

It seems to be a common feature of book writing that the end product turns out quite different than originally intended and Helicopter Flight Dynamics is no exception. It was planned to be much shorter and to cover a wider range of subjects! In hindsight, the initial plan was perhaps too ambitious, although the extent of the final product, cut back considerably in scope, has surprised even the author. There are three ‘major’ topic areas, originally intended as separate chapters, that have virtually disappeared – ‘Stability and control augmentation (including active control)’, ‘Design for flying qualities’ and ‘Simulation validation (including system identification tools)’. All three are referred to as required, usually briefly, throughout the book, but there have been such advances in recent years that to give these topics appropriate coverage would have extended the book considerably. They remain topics for future treatment, particularly the progress with digital flight control and the use of simulators in design, development and certification. In the context of both these topics, we appear to be in an era of rapid development, suggesting that a better time to document the state of the art may well be in a few years from now. The absence of a chapter or section on simulation model vali­dation techniques may appear to be particularly surprising, but is compensated for by the availability of the AGARD (Advisory Report on Rotorcraft System Identification), which gives a fairly detailed coverage of the state of the art in this subject up to the early 1990s (Ref. 1.7). Since the publication of the first edition, significant strides have been made in the development of simulation models for use in design and also training simulators. Reference 1.8 reviews some of these developments but we are somewhat in mid-stream with this new push to increase fidelity and the author has resisted the temptation to bring this topic into the second edition.

The book says very little about the internal hardware of flight dynamics – the pilot’s controls and the mechanical components of the control system including the hydraulic actuators. The pilot’s displays and instruments and their importance for flight in poor visibility are briefly treated in Chapter 7 and the associated perceptual issues are treated in some depth in Chapter 8, but the author is conscious of the many missing elements here. In Chapter 3, the emphasis has been on modelling the main rotor, and many other elements, such as the engine and transmission systems, are given limited coverage.

It is hoped that the book will be judged more on what it contains than on what it doesn’t.