Unmanned Aircraft Design. Mohammad Sadraey H.
In the detail design phase, the technical parameters of all components (e.g., wing, fuselage, tail, landing gear (LG), and engine) including geometry are calculated and finalized.
1.10 CONCEPTUAL DESIGN
Throughout the conceptual system design phase (commencing with the need analysis), one of the major objectives is to develop and define the specific design-to requirements for the system as an entry. The results from these activities are combined, integrated, and included in a system specification. This specification constitutes the top “technical-requirements” document that provides overall guidance for system design from the beginning. Conceptual design is the first and most important phase of the UAV system design and development process. It is an early and high-level life cycle activity with potential to establish, commit, and otherwise predetermine the function, form, cost, and development schedule of the desired UAV system. The identification of a problem and associated definition of need provides a valid and appropriate starting point for design at the conceptual level.
Selection of a path forward for the design and development of a preferred system configuration, which will ultimately be responsive to the identified customer requirement, is a major responsibility of conceptual design. Establishing this early foundation, as well as requiring the initial planning and evaluation of a spectrum of technologies, is a critical first step in the implementation of the systems engineering process. Systems engineering, from an organizational perspective, should take the lead in the definition of system requirements from the beginning and address them from a total integrated life-cycle perspective.
As the name implies, the UAV conceptual design phase is the UAV design at the concept level. At this stage, the general design requirements are entered in a process to generate a satisfactory configuration. The primary tool in this stage of design is the “selection.” Although there are variety of evaluation and analysis, but there are no much calculation. The past design experience plays a crucial role in the success of this phase. Hence, the members of conceptual design phase team must be the most experienced engineers of the corporation. Figure 1.5 illustrates the major activities which are practiced in the UAV conceptual design phase. The fundamental output of this phase is an approximate three-view of the UAV that represents the UAV configuration.
Figure 1.5: UAV conceptual design.
A UAV comprised of several major components. It mainly includes wing, horizontal tail, vertical tail, fuselage, propulsion system, landing gear, control surfaces, and autopilot. In order to make a decision about the configuration of each UAV component, the designer must be fully aware of the function of each component. Each UAV component has inter-relationships with other components and interferes with the functions of other components. The above six components are assumed to be the fundamental components of an air vehicle. However, there are other components in a UAV that are not assumed here as a major one. The roles of those components are described in the later sections whenever they are mentioned. Table 1.4 illustrates a summary of UAV major components and their functions. This table also shows the secondary roles and the major areas of influence of each UAV component. The table also specifies the design requirements that are affected by each component.
Table 1.5 illustrates a summary of configuration alternatives for UAV major components. In this table, various alternatives for wing, horizontal tail, vertical tail, fuselage, engine, landing gear, control surfaces, and automatic control system or autopilot are counted. An autopilot tends to function in three areas of guidance, navigation and control. More details are given in the detail design phase section. For each component, the UAV designer must select one alternative which satisfies the design requirements at an optimal condition. The selection process is based on a trade-off analysis with comparing all pros and cons in conjunction with other components.
Table 1.4: UAV major components and their functions
Table 1.5: UAV major components with design alternatives
| No | Component | Configuration Alternatives |
| 1 | Fuselage | - Geometry: lofting, cross section - Internal arrangement - What to accommodate (e.g., fuel, engine, and landing gear)? |
| 2 | Wing | - Type: swept, tapered, dihedral; - Location: low-wing, mid-wing, high wing, parasol - High lift device: flap, slot, slat - Attachment: cantilever, strut-braced |
| 3 | Horizontal tail | - Type: conventional, T-tail, H-tail, V-tail, inverted V - Installation: fixed, moving, adjustable - Location: aft tail, canard, three surfaces |
| 4 | Vertical tail | Single, twin, three VT, V-tail |
| 5 | Engine | - Type: turbofan, turbojet, turboprop, piston-prop, rocket - Location: (e.g., under fuselage, under wing, beside fuselage) - Number of engines |
| 6 | Landing gear | - Type: fixed, retractable, partially retractable - Location: (e.g., nose, tail, multi) |
| 7 | Control surfaces | Separate vs. all moving tail, reversible vs. irreversible, conventional vs. non-conventional (e.g., elevon, ruddervator) |
| 8 | Autopilot | - UAV: Linear model, nonlinear model - Control subsystem: PID, gain scheduling, optimal, QFT, robust, adaptive, intelligent - Guidance subsystem: Proportional Navigation Guidance, Line Of Sight, Command Guidance, three point, Lead - Navigation subsystem: Inertial navigation (Strap down, stable platform), GPS |
| 9 | Launch and recovery | HTOL, ground launcher, net recovery, belly landing |
In order to facilitate the conceptual design process, Table 1.6 shows the relationship between UAV major components and the design requirements. The third column in Table 1.6 clarifies the UAV component which affected most; or major design parameter by a design requirement. Every design requirement will normally affects more than one component, but we only consider the component that is influenced most. For example, the payload requirement, range and endurance will affect maximum take-off weight, maximum take-off weight, engine selection, fuselage design, and flight cost. The influence of payload weight is different than payload volume. Thus, for optimization purpose, the designer must know exactly payload weight and its volume. On the other hand, if the payload can be divided into smaller pieces, the design constraints by the payload are easier to handle. Furthermore, the other performance parameters (e.g., maximum speed, stall speed, rate of climb, take-off run, ceiling) will affect the wing area and engine power (or thrust).
Table 1.6: Relationship between UAV major components and design requirements
| No | Design Requirements |
UAV Component |