DEVELOPMENT AND OPERATIONAL ENVIRONMENT .1 Design environment .1 Design environment

The current end users associated with aircraft modification development projects fall within the following:

• Design organisation – The organisation which undertakes the modification design activity including development of methodologies to evaluate the design options and solutions (CASA, 2014). This organisation may be the Applicant as described earlier.

• Modification installation organisation – The organisation undertaking the physical installation of the modification.

• Supplier organisation – The organisation providing components and subsystems.

• Client – This may be the operator or owner of the aircraft.

• NAA - The Regulator which is responsible for provision of certification review, advice and approval.

3.6.2 Support environment

The support environment associated with aircraft modification projects fall into the following categories:

• Design Organisation - The organisation providing ongoing engineering support to the modification (CASA, 2014).

• Approved Maintenance Organisation – The organisation undertaking

routine aircraft maintenance including systems and subsystems impacted by the modification. This organisation may also support in-service changes or updates to the modification.

• NAA - provision of Airworthiness Directives (AD) and Airworthiness Bulletins (AWBs) as required.

3.6.3 Operational environment 3.6.3.1 Commuter aircraft charter

Typical charter operations conducted by a commuter category aircraft are based on the business of renting an entire aircraft as opposed to purchasing individual aircraft seats (BITRE, 2017). These charter operations involve operations which are flown to the passengers’ itinerary, in day or night, and in Visual Flight Rules (VFR) or Instrument Flight Rules (IFR) conditions.

A typical charter operation involves passengers arriving at the airport 30 minutes prior to scheduled departure, especially if the charter itinerary is time critical. The aircraft is usually fuelled prior to the passenger’s arrival. Passenger and baggage weights are processed and are loaded according to the aircraft weight and balance system. This step takes less than 10 minutes as aircraft weight limitations sometimes impose a single baggage item for each passenger (Altitude Aviation, 2015). Given aircraft weight restrictions, it is sometimes necessary that refuelling is required at some intermediate airport enroute to the final destination. This refuelling stop may about 30 minutes depending on operational factors. Typically, intermediate stops would be made into regional airports with AVGAS self-service bowsers or fuel tankers. Note that other factors may also require enroute refuelling such as stronger than planned headwinds or other operational constraints. In this case flight planning would consider availability of fuel at these intermediate stops.

Typically charter operations have the advantage that the itinerary can be developed in accordance with passenger needs as outlined by the National Air Transportation Association (2012). In addition, the itinerary can take flights to airports which are not normally serviced by Regular Public Transport (RPT). It also follows that these charter aircraft can be operated from airports with shorter unsealed airstrips, which provides significant flexibility over larger RPT aircraft, where sealed runways are generally required.

3.6.3.2 Skydiving aircraft operational scenario

The Cessna 182 has been used by the skydiving community since the early days of skydiving. This aircraft can carry a pilot, three (3) to four (4) skydivers to an altitude of 14,000 feet, which usually takes about half an hour with a full payload to climb to the jump altitude (Glesk, 2018, pers. comm., 8 October).

Correspondence with Glesk (2018, pers. comm., 8 October), highlighted that a typical skydiving mission would comprise a payload of skydivers and pilot plus minimum fuel required with fixed reserves. These flights would attempt to achieve a duty cycle of one (1) to two (2) loads per hour, depending on a range of operational factors and skydiver demand. Refuelling would occur between these flights depending on the skydiver loadings.

Chapter 4. Formulation

Without doubt, weight and weight distribution, or balance, are of more importance in airplane design than in any other branch of engineering.

T.P. Wright (1999)

4.1 OVERVIEW

4.1.1 Conceptual design methodologies

Design methodologies as defined by Pahl et al. (2007) “is a course of action for the design of technical systems that derives its knowledge from design science, cognitive psychology and practical experiences gained from different domains”. These design methodologies make it easier to reapply and establish solutions from earlier projects, and to use technical databases or common structures to apply to design modification projects. Indeed, the establishment of common structures or design catalogues is a pre-requisite for computer applications and support of the design process using simplified mathematical relationships representing performance attributes of the system. As stated by Pahl et al. (2007) systematic design methodologies make the task easier to divide between the designer and the computer, thus providing efficiencies to the modification project.

Conceptual design as described by Blanchard and Fabrycki (1998) is a process that evolves from a need, to the definition of the requirements in functional terms through establishment of the design metrics, and preparation of a system development specification. This introduction of a design methodology within conceptual design therefore provides a framework that defines a course of action within the early design lifecycle phases of a project. The accomplishment of a feasibility analysis or a trade study is a major step within conceptual design that involves three main steps. These steps being:

1. identification of possible design approaches,

2. evaluation of these approaches based on performance, effectiveness, maintenance, logistic support, and cost economics, and

3. a recommendation of the preferred course of action.

In addition, considerations are given to the application of different technologies as part of the design approach. The system requirements analysis steps within this process involve definition of operational requirements, support concepts, the provision of TPMs, functional analysis allocation, synthesis and evaluation. Blanchard and Fabrycki (1998) describe TPMs as the metrics or quantitative factors associated with the system under development.

The most important engineering design document produced during the conceptual design phase is the system specification as described by Blanchard and Fabrycki (1998). This document defines the system functional baseline, including results from the needs analysis, trade-off analysis, operational requirements and maintenance concept, top-level functional analysis, and identifies the TPMs and Design Dependant Parameters (DDPs). This specification may lead into one of more subordinate specifications covering subsystems, support equipment, materials, processes software and other components of the system.

Ullman (2010) describes this conceptual design phase as being primarily concerned with the generation and evaluation of concepts. Generation of concepts is described by Ullman (2010) where customer requirements are utilised to develop a functional model of the system. This functional modelling approach is essential for developing and generating concepts that will eventually lead to a system that is fit for purpose. The evaluation of concepts is a step that compares the concepts generated by the requirements, which is then used to make decisions about selection of the best alternatives. The latter steps of this phase, as shown by Figure 21, involve documenting of the candidate solution, refinement of the project plan, and formal approval of the concepts.

Figure 21. Conceptual design steps of mechanical systems design

Ullman (2010)

4.1.2 Conceptual design methodology requirements

Systematic design provides a way to rationalise the design and its associated through life support processes. Structuring the problem and task makes it easier to recognise established solutions from previous projects as stated by Pahl et al. (2007).

This stepwise development of established solutions makes it possible to generate, select and evaluate them at an early stage of the design activity and with a reduced level of effort. Furthermore, these systemic processes also make it easier to divide the task between designers and computers, as described earlier. Pahl et al. (2007) states that in order that a design methodology meet these needs it must possess various attributes. These attributes which form the basis of requirements for this conceptual design methodology are quoted as follows:

1. “Allow a problem-directed approach, in that it must be applicable to every type of design activity, no matter the specialist field it involves.

2. Foster inventiveness and understanding in searching for an optimum solution.

3. Be compatible with the concepts, methods and findings of other disciplines.

4. Not rely on finding solutions by chance.

5. Facilitate the application of known solutions to related tasks.

6. Be compatible with electronic data processing.

7. Be easily taught and learned.

8. Reflect the findings of cognitive psychology and modern management science, that is reduce the workload, reduce design time, prevent human error, and help maintain an active interest.

9. Ease the planning and management of teamwork in an integrated and inter-disciplinary product development process.

10. Provide guidance for leaders of product development teams”.

4.1.3 Formulation approach

The formulation of the conceptual design methodology in this Chapter involves breaking down the process elements from the highest levels, developing new approaches, and adapting existing tools and techniques to provide a multi-step universal framework to apply to aircraft modification programs. This approach embraces systems engineering, product development, and traditional aircraft design methods within a broader framework which formulates the problem in terms of synthesis, evaluation and analysis. It then decomposes these three elements into a unique matrix-based framework by adapting existing tools and techniques or developing new approaches to cater for design modification space. It has adopted a matrix-based method, as it provides a structured and rigorous framework from which to (1) manage requirements, (2) generate and evaluate concepts, (3) validate concept selection decisions, (4) evaluate design change/modification options, (5) evaluate change propagation impacts, (6) manage engineering and certification resources and risks, and (7) analyse performance. Furthermore, it is recognised that the engineering and certification related activities can be managed more effectively and efficiently if structured in a matrix-based framework. Indeed, the aviation industry presents

certification information in a tabular format which is sometimes referred to as a compliance summary matrix document. This methodology therefore extends this approach and incorporates and refines the format to encompass the impact of the change propagation resulting from the modification, in addition to providing a structure to manage related resources and costs. Although not presented in this thesis, the design outputs of the conceptual design methodology are structured in such a way that they provide information and data inputs to the necessary design documentation.

This approach provides a standardised systems engineering, airworthiness regulation and project management documentation suite. This design information is used throughout the various phases of the design lifecycle, to support further analysis and development effort in refining the modification design.

This chapter therefore details the research theory, techniques, tools and approaches used in formulating this conceptual design methodology.

4.2 CONCEPTUAL DESIGN