Unmanned Aircraft Design. Mohammad Sadraey H.

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СКАЧАТЬ is at this early stage in the life cycle that major decisions are made relative to adapting a specific design approach and technology application, which has a great impact on the life-cycle cost of a product. In this phase, the designer addresses the fundamental question of whether to proceed with the selected concept. It is evident that there is no benefit or future in spending any more time and resource attempting to achieve an unrealistic objective. Some revolutionary concepts initially seem attractable, but when it comes to the reality, it is found to be too imaginary. Feasibility study distinguishes between a creative design concept and an imaginary idea. Feasibility evaluation determines the degree to which each concept alternative satisfies design criteria.

      In this phase, the designer addresses the fundamental question of whether to proceed with the selected concept. Feasibility study distinguishes between a creative design concept and an imaginary idea. Feasibility evaluation determines the degree to which each concept alternative satisfies design criteria.

      In the feasibility analysis, the answers to the following two questions are sought: (1) Are the goals achievable?; or are the objectives realistic?; or are the design requirements meetable? and (2) Is the current design concept feasible? If the answer to the first question is no, the design goal and objectives, and design requirements must be changed. Hence, no matter where is the source of design requirements; either direct customer order or market analysis; they must be changed.

1.7 DESIGN GROUPS

      An aircraft chief designer should be capable of covering and handling a broad spectrum of activities. Thus, an aircraft chief designer should have years of experiences, be knowledgeable of management techniques, and preferably have full expertise and background in the area of “flight dynamics.” The chief designer has a great responsibility in planning, coordination, and conducting formal design reviews. He/she must also monitor and review aircraft system test and evaluation activities, as well as coordinating all formal design changes and modifications for improvement. The organization must be such that facilitate the flow of information and technical data among various design departments. The design organization must allow the chief designer to initiate and establish the necessary ongoing liaison activities throughout the design cycle.

      A primary building block is organizational patterns is the functional approach, which involves the grouping of functional specialties or disciplines into separately identifiable entities. The intent is to perform similar work within one organizational group. Thus, the same organizational group will accomplish the same type of work for all ongoing projects on a concurrent basis. The ultimate objective is to establish a team approach, with the appropriate communications, enabling the application of concurrent engineering methods throughout.

      Figure 1.2: UAV main design groups.

      There are two main approaches to handle the design activities and establishing design groups: (1) design groups based on aircraft components, and (2) design groups based on expertise (Figure 1.2). If the approach of groups based on aircraft components is selected, the chief designer must establish the following teams: (1) wing design team, (2) tail design team, (3) fuselage design team, (4) propulsion system design team, (5) landing gear design team, (6) autopilot design team, (7) ground station design team, and (8) launch and recovery design team. The ninth team is established for documentation, and drafting. There are various advantages and disadvantages for each of the two planning approaches in terms of ease of management, speed of communication, efficiency, and similarity of tasks. However, if the project is large, such as the design of a large transport aircraft, both groupings could be applied simultaneously.

1.8 DESIGN PROCESS

      UAV Design is an iterative process which involves synthesis, analysis, and evaluation. Figure 1.3 demonstrates the design process block diagram. Design (i.e., synthesis) is the creative process of putting known things together into new and more useful combinations. Analysis refers to the process of predicting the performance or behavior of a design candidate. Evaluation is the process of performance calculation and comparing the predicted performance of each feasible design candidate to determine the deficiencies. A design process requires both integration and iteration. There is an interrelationship between synthesis, analysis, and evaluation. Two main groups of design activities are: (1) problem solving through mathematical calculations, and (2) choosing a preferred one among alternatives.

      Figure 1.3: The UAV life-cycle.

      In general, design considerations are the full range of attributes and characteristics that could be exhibited by an engineered system, product, or structure. These interest both the producer and the customer. Design-dependent parameters are attributes and/or characteristics inherent in the design to be predicted or estimated (e.g., weight, design life, reliability, producibility, maintainability, and disposability). These are a subset of the design considerations for which the producer is primarily responsible. On the other hand, design-independent parameters are factors external to the design that must be estimated and forecasted for use in design evaluation (e.g., fuel cost per gallon, interest rates, labor rates, and material cost per pound). These depend upon the production and operating environment of the UAV.

      A goal statement is a brief, general, and ideal response to the need statement. The objectives are quantifiable expectations of performance which identify those performance characteristics of a design that are of most interest to the customer. Restrictions of function of form are called constraints; they limit our freedom to design.

1.9 SYSTEMS ENGINEERING APPROACH

      Complex UAV systems, due to the high cost and the risks associated with their development become a prime candidate for the adoption of systems engineering methodologies. The UAV conceptual design process has been documented in many texts, and the interdisciplinary nature of the system is immediately apparent. A successful configuration designer needs not only a good understanding of design, but also systems engineering approach. A competitive configuration design manager must have a clear idea of the concepts, methodologies, models, and tools needed to understand and apply systems engineering to UAV systems.

      The design of a UAV begins with the requirements definition and extends through functional analysis and allocation, design synthesis and evaluation, and finally validation. An optimized UAV, with a minimum of undesirable side effects, requires the application of an integrated life-cycle oriented “system” approach. The design of the configuration for the UAV begins with the requirements definition and extends through functional analysis and allocation, design synthesis and evaluation, and finally validation. Operations and support needs must be accounted for in this process. An optimized UAV, with a minimum of undesirable side effects, requires the application of an integrated life-cycle oriented “system” approach.

      The design of the UAV subsystems plays a crucial role in the configuration design and their operation. These subsystems turn an aerodynamically shaped structure into a living, breathing, unmanned flying machine. These subsystems include the: flight control subsystem, power transmission subsystem, fuel subsystem, structures, propulsion, aerodynamics, and landing gear. In the early stages of a conceptual or a preliminary design these subsystems must initially be defined, and their impact must be incorporated into the design layout, weight analysis, performance calculations, and cost benefits analysis.

      A UAV is a system composed of a set of interrelated components working together toward some common objective or purpose. Primary objectives include safe flight achieved СКАЧАТЬ