Weeding Out a Solution!

Problem statement

A UAS is to be designed for precision crop-dusting. In the middle of the design process, the system is found to be overweight.

• Two subsystems – 1) Guidance, Navigation & Control [flying correctly] and 2) Payload delivery [spraying correctly] have attempted to save costs by purchasing off-the-shelf hardware, rather than a custom design, resulting in both going over their originally allotted weight budgets. Each team has suggested that the OTHER team reduce weight to compensate.
• The UAS will not be able to carry sufficient weight to spread the specified (Marketing has already talked this up to customers) amount of fertilizer over the specified area without cutting into the fuel margin. The safety engineers are uncomfortable with the idea of changing the fuel margin at all.

Write a response describing how you, as the Systems Engineer, would go about resolving this issue. Use your imagination, and try to capture what you would really do. Take into account and express in your writing the things you’ve learned so far in this module: What are your considerations? What are your priorities? What do you think about the future prospects for the “next generation, enhanced” version of the system as a result of your approach?

Problem analysis

A struggle between two development teams might indicate a loosely structured lifecycle process model.  The System Engineer (SE) did not perform a proper System Work Breakdown Structure, thus the in-house consumer (marketing department) requirements were not clear for the baseline development teams.  Moreover, the SE did not properly utilize a phase gate concept and allowed the product lifecycle to carryforward lapses of previous phases.

To overcome such a design problem, accompanied with a power struggle, the SE should construct a formal design process with a clear System Work Breakdown Structure communicate it to the development teams; these models are suitable for developing Unmanned Aerospace Systems (UAS).  This will provide teams with clear specific tasks and the ability to appropriately develop and document the design process, proper communication across the board, enable the whole process to handle change management and allow traceability of change effects on other process elements (Loewen, 2013). To ascertain the establishment of the aforementioned qualities the development process, the relevant phase gates are Alternative Systems Review (ASR), System Requirements Review (SRR), and System Functional Review (SFR) (“Systems Engineering,” 2001).

To reach a decision on weight reduction of both or either systems, a Trade Study should examine the engineering trade-offs in their choice of Commercial Off-The-Shelf (COTS) products, figure 1 illustrates all the steps in a Trade Study.  At the product synthesis phase, the pertinent aspects to the problem at hand are (“Systems Engineering,” 2001):

•  Identifying the conflicts between desired characteristics and suggested alternatives, a database survey of alternatives should produce more choices.  Here the COTS weights do not fulfill design requirements.  A survey of different market alternatives will allow for a better realization of weight constraints of various COTS.
•  A methodological basis for comparing alternatives based on a rational development of their trade-off relationships.  Basis of alternatives comparison must rely on a matrix of predefined criteria, like functionality, material, customizability, weight, and cost.
• Identification of all potential combinations for a problem solution.  For instance, by consulting the COTS producers on how to customize their product to reduce weight, if they can provide alternative casing or different construction material.  The navigation capability of the system cannot be compromised, since it also affects the payload distribution capability of the system.  The process is both recursive and modular, thus it can adapt any future modification to the design or serve as basis for future designs.

References

Loewen, H. (2013). Requirements-based UAV Design Process Explained. A UAV Manufacturer’s Guide. Retrieved from http://www.micropilot.com/pdf/requirementsbaseduav.pdf

Systems Engineering Fundamentals. (2001). Department of Defense Systems Management College. Retrieved from http://ocw.mit.edu/courses/aeronautics-and-astronautics/16-885j-aircraft-systems-engineering-fall-2005/readings/sefguide_01_01.pdf

Figures

Figure 1.  Adapted from Systems Engineering Fundamentals.  It shows the process of trade-off analysis steps (“Systems Engineering,” 2001, p. 113).