Showing papers by "Don Harris published in 2000"

Engine system loads development for the fastrac 60k flight engine

Abstract: Early implementation of structural dynamics finite element analyses for calculation of design loads is considered common design practice for high volume manufacturing industries such as automotive and aeronautical industries. However, with the rarity of rocket engine development programs starts, these tools are relatively new to the design of rocket engines. In the new Fastrac engine program, the focus has been to reduce the cost to weight ratio; current structural dynamics analysis practices were tailored in order to meet both production and structural design goals. Perturbation of rocket engine design parameters resulted in a number of Fastrac load cycles necessary to characterize the impact due to mass and stiffness changes. Evolution of loads and load extraction methodologies, parametric considerations and a discussion of load path sensitivities are discussed.

The Cranfield aircraft handling qualities rating scale : a multidimensional approach to the assessment of aircraft handling qualities

Abstract: The Cooper-Harper scale is currently the only well-established scale for assessing aircraft handling qualities. However, as a result of having a unidimensional format the Cooper-Harper scale lacks diagnostic power and has also been criticised for exhibiting poor reliability. The Cranfield Aircraft Handling Qualities, Rating Scale (CAHQRS) is a new, multidimensional rating scale using concepts from two established scales, the NASA-TLX workload scale and the Cooper-Harper scale. This paper provides an overview of the development of the CAHQRS and the results from a series of validation trials in an engineering flight simulator. An in-flight refuelling task and an approach and landing task using a range of control laws were used in these evaluations. The results showed that the CAHQRS had high positive correlations with the Cooper-Harper scale. However, the CAHQRS also demonstrated greater validity, diagnostic power and higher test/re-test reliability than the previous scale.

Measurement of Pilot Opinion When Assessing Aircraft Handling Qualities

Abstract: The assessment of aircraft handling qualities poses an interesting measurement problem. Such assessments ha~e always been an important part in an aircraft's design and development process. Since the end of World War n, the US Department of Defense has required military aircraft to exhibit 'acceptable' handling qualities. Initially these qualities were defined simply in terms of stability and control. However, the more recent version of these specifications9 also incorporates pilot opinion in addition to the classical engineering parameters. Civil airworthiness requirements also require aircraft to demonstrate satisfactory handling qualities as part of the certification process. With the advent of fly-by-wire (FBW) flight control systems, the control engineer is no longer restricted to producing an aircraft that handles 'conventionally'. The control col. umn may now command flight path angle directly, rather than using the first-order surrogate of aircraft pitch rate. Alternatively the column may now make an acceleration (or 'g') demand. These options for flight path control, which were not available thirty years ago, have made the assessment of aircraft handling qualities even more important than in the past. There are now many more options from which to choose, and considerably more precise ways to refine an aircraft's behaviour. Despite the importance of providing an aircraft with acceptable handling qualities, it still remains difficult to define precisely what is meant by this term and it is even more difficult to operationalise through measurement. Harper and Cooper5 defined handling qualities as 'those qualities or characteristics of an aircraft that govern the ease and precision with which a pilot is able to perform the tasks required in support of the aircraft's role'. Gibson3 suggested that this definition be expanded to include the ease with which the pilot can compensate for any disturbing effects of the environment. However, both definitions implicitly incorporate pilot opinion. This is essential as the simple physical measurement of an aircraft's open-loop response to a disturbance input can give an extremely misleading impression about how easy it is to control. An aircraft may exhibit excellent open-loop stability, but when the pilot is trying to fly a high-gain, closedloop task such as air-to-air refuelling, it may be almost uncontrollable. An engineer makes judgements about the aircraft's handling qualities from data derived from only a part of the total pilot/vehicle system. The pilot alone can observe the complete dynamic behaviour of the aircraft. As a result, handling qualities cannot be defined simply by engineering descriptions of an aircraft's response to a pilot's input. Any assessment of handling qualities must include the pilot's perceptions of the aircraft's behaviour.