with the next stage. There is a series of formal design reviews conducted at specific times in the overall system development process. An essential technical activity within the design process is that of evaluation. Evaluation must be inherent within the systems engineering process and must be invoked regularly as the system design activity progresses. When conducted with full recognition of design criteria, evaluation is the assurance of continuous design improvement. The evaluation process includes both the informal day-to-day project coordination and data review, and the formal design review.
The purpose of conducting any type of review is to assess if (and how well) the design configuration, as envisioned at the time, is in compliance with the initially specified quantitative and qualitative requirements. A design review provides a formalized check of the proposed system design with respect to specification requirements. In principle, the specific types, titles, and scheduling of these formal reviews vary from one design project to the next. The following four main formal design reviews are recommended for a design project.
1. Conceptual Design Review (CDR)
2. Preliminary Design Review (PDR)
3. Evaluation and Test Review (ETR)
4. Critical (Final) Design Review (FDR)
Figure 1.6 shows the position of each design review in the overall design process. Design reviews are usually scheduled before each major design phase. The CDR is usually scheduled toward the end of the conceptual design phase and prior to entering the preliminary design phase of the program. The purpose of conceptual design review (CDR) is to formally and logically cover the proposed design from the system standpoint. The preliminary design review is usually scheduled toward the end of the preliminary design phase and prior to entering the detail design phase. The critical design review (FDR) is usually scheduled after the completion of the detail design phase and prior to entering the production phase.
The evaluation and test review is usually scheduled somewhere in the middle of the detail design phase and prior to production phase. The ETR accomplishes two major tasks: (1) finding and fixing any design problems and the subsystem/component level, and then (2) verifying and documenting the system capabilities for government certification or customer acceptance. The ETR can range from the test of a single new system for an existing system to the complete development and certification of a new system.
1.14 QUESTIONS
1. What are the five terms which are currently used for unmanned aircraft?
2. What are the primary design requirements for a UAV?
3. Describe features of a Tier II UAV in the Air Forces.
4. Describe the features of a micro UAV.
5. What is the main objective for the feasibility study?
6. What is the size range for mini UAVs?
7. What do MALE and HALE stand for?
8. What is the operating altitudes for HALE UAVs?
9. What is the endurance range for MALE UAVs?
10. What are the wingspan and MTOW of Global Hawk?
11. What are the cruise speed and endurance for Predator (RQ-1A)?
12. What was the major setback during Phase II flight testing of the Global Hawk on March 29, 1999? What was the reason behind that?
13. Describe the fundamentals of systems engineering approach in UAV design.
14. What are the main four formal design reviews?
15. What are the UAV main design groups?
16. Describe conceptual design phase.
17. Describe main outputs of the preliminary design.
18. Describe process of detail design.
19. Describe trade-off analysis process.
20. From systems engineering approach, what are the main design phases?
CHAPTER 2
Design Disciplines
2.1 INTRODUCTION
There are several design disciplines which work in parallel within a UAV design project. Some examples are: (1) aerodynamic design, (2) structural design, (3) propulsion system design, (4) power transmission system design, (5) mechanical system design, and (6) control surfaces design, (7) ground station, and (8) launch and recovery system. This chapter briefly covers the first six topics disciplines; the other two are presented in Chapters 8 and 9, respectively. Due to the limited volume of the book, only the basic fundamentals are presented. The interested reader should refer to Sadraey [37] for more details. Table 2.1 shows the UAV major components and their primary functions.
Table 2.1: UAV vehicle major components and their functions
In a UAV design process, some UAV parameters must be minimized (e.g., weight), while some other variables must be maximized within constraints (e.g., range, endurance, maximum speed, and ceiling), and also others must be evaluated to ensure that they are acceptable. The optimization process must be accomplished through a systems engineering approach. In some cases, the design of the UAV may impose slight to considerable changes to the UAV mission during the conceptual design process. The strong relationship between the analysis and the influencing parameters allow definite, traceable relationships to be constructed. In the case of a UAV design, the major parameters are derived almost completely from operational and performance requirements.
It is clear that some steps may be moved along with regard to the UAV mission, design team members, past design experiences, design facility, and manufacturing technologies. As it is observed, the design process is truly an iterative process and there are several modification steps to satisfy all design requirements. An important feature of the design process is the lessons learned in the past. The lesson will be utilized in improving the next generation, for instance, the major setback during Phase II flight testing of Global Hawk (Figure 1.1) was the destruction of air vehicle 2 on March 29, 1999, during the program’s 18th sortie. The loss of air vehicle 2 and its payload was estimated at $45 million. Of more importance, however, was the fact that the program lost its only integrated sensor suite. The crash was due to a lack of proper frequency coordination between the Nellis Air Force Base and EAFB flight test ranges. Essentially, Nellis officials who were testing systems in preparation for Global Hawk’s first planned D&E exercise were unaware that Global Hawk was flying over China Lake Naval Air Weapons Station, which is within EAFB’s area of responsibility. Thus, many changes have been applied in the design of Northrop Grumman RQ-4B Global Hawk as compared with RQ-4A. For instance, the Northrop Grumman RQ-4B Global Hawk has a 50% payload increase, larger wingspan (130.9 ft) and longer fuselage (47.6 ft), and new generator to provide 150% more electrical output.
The integration of system engineering principles with
