UAS Weight Risk Analysis from a Systems Engineering Perspective

UAS Weight Risk Analysis from a Systems Engineering Perspective

For this assignment, it is imperative that the Systems Engineer think about risk in terms of probability and severity, and evaluate the program on the variables of cost, schedule and performance (Piette, 2013). Analyzing the priority, which is to deliver a UAS that can safely and effectively execute the mission of precision crop-dusting, is critical for success.

Problem Summation

            In the UAS design process, it is found that the system is heavy and a weight savings effort needs to be executed. Determination of the specific weight excess from each subsystem will be required for additional analysis, as well as the timeline of margin consumption (if available). For the Systems Engineer to make a sound decision, each subsystem will have to be quantified in terms of risk, and subsequently prioritized.

Risk Analysis

            Risk areas. For this assignment, the major risk areas are determined as follows:

(1)   Guidance, Navigation, and Control subsystem (GNCS) – over weight allocation due to purchasing of commercial off-the-shelf (OTS) hardware

(2)   Payload subsystem – over weight allocation due to OTS acquisition

(3)   Flight safety – due to increased weight, the system will not be able to carry enough fuel to execute mission

Considerations for determining program risk. As mentioned previously, evaluating risk in terms of probability and severity is important in determining subsystem priorities. Using the variables of cost, schedule, and performance are key factors that will contribute to the overall prioritization of adjuncts and subsystem “needs”. It would be beneficial to highlight the system requirements as an initial plan of action; these include: (1) ensuring safe flight execution, and (2) meeting end-user requirements (i.e. fertilizer distribution). Despite the initial priority to deliver a UAS that can safely execute a flight profile, each area would need to be evaluated for overall risk. It should be noted that both mission and flight safety are arguably equally important, and as a result the considerations should be given to optimizing the UAS structural frame and other subsystems (i.e. power subsystem as more weight would require more energy for propulsion) to accommodate for a larger vehicle. If there are no specific size or weight limitations for the vehicle, and there is no way to make the GNCS or payloads smaller, it may be possible to increase the overall size of the UAS.

            Cost for rework/redesign. An important question to ask each subsystem is: “what is the projected cost to design your own box to meet your specifications?” The second question would be: “will each subsystem box (i.e. payload and GNCS box) incur weight savings by switching to a custom design?” If there is value to rework each system to yield weight savings, then the extra costs for redesign may be justified. Additional costs may be incurred as a result of increasing the system size to accommodate for larger flight boxes, where stress and electrical systems testing may also need to be conducted.

            Time/schedule impacts. An additional variable in the process is adjusting the delivery schedule. Therefore, another question to be asked would be: “how much time will you need for box redesign and testing?” Testing through flight verification or modelling may be costly and time consuming, however this would be recommended in order to increase system confidence and reliability metrics (Piette, 2013).

Risk burn-down plan. The following three options have been generated based on the initial analysis, with the risk information noted in Figure 1.

Figure 1. Identified risks for the UAS weight issue.

            Figure 1 describes at the basic level some of the concerns with each plan of action, with emphasis to be placed on the primary risk which is reducing GNCS weight. Through an initial assessment, it is determined that potentially redesigning the GNCS box by reducing weight can pose the greatest risk in terms of redesign costs due to system complexity, schedule impacts due to testing, and the importance of the box to flight safety. Since this UAS is intended to be used in a terrestrial environment, where interaction/proximity with bystanders and workers yields the potential for injury or death in the event of a flight malfunction, the risk level is significant. As more variables arise, with time and cost impacts becoming more apparent, the risk matrix and priorities may change.

            Since the team has forecasted the payload capacity to the customer, in order to maintain the high levels of customer confidence it would be beneficial to maintain payload integrity. More specifically, in terms of the payload box, rework as required to achieve high levels of performance that mirror what was projected to the customer. Holding true to the baseline may be in the best interest of the company to secure future work, similar to what has been seen in similar aviation programs (Novacek, 2017).

            Independent validation and verification (IV&V). Working concurrently with the cooperation with an outside source to provide analysis and recommendations may be helpful in time sensitive schedules (ENSCO, 2017). In this case, it may be beneficial for the program to utilize an outside source to generate the models/simulations and conduct flight analysis and testing, especially when working parallel-path risk mitigations (Sinde & Ho, 2008). However, additional funds for this effort would need to be incorporated into the estimate at completion.

            Use of modelling and simulation. Using different mathematical models for different configurations the UAS can have may be an effective method for quickly and accurately determining the optimum configuration for flight (ENSCO, 2017). This tool can be used to determine the ideal individual weights for components, center of gravity, flight path, and resultant impacts to flight performance. In the event that the GNCS box, payload, or both, are required for redesign that it will be pertinent that the program utilize modelling and simulation software to accurately identify the potential areas for each box in the redesign process.

            Using commercial off-the-shelf (OTS) products. Using OTS products can greatly reduce technical risk, by using flight proven products that are already built and tested. Disadvantages of this could be increased cost and inability to tailor software and/or hardware to individual user specifications, however advantages such as product convenience (i.e. quick acquisition time) and completed flight testing builds confidence in system quality/reliability (Carter, 2015). Commercial off the shelf (COTS) solutions are “software solutions aimed at addressing specific needs, but they are targeted towards a mass-market audience vs. a specific company or industry” and “are typically affordable because their development costs are distributed across the broader audience” (Carter, 2015, p.2). Therefore, it may be more beneficial to utilize a custom design for future iterations, or in this case have both the payloads and GNCS team redesign their boxes to meet weight and end-user requirements.

Future Prospects/Conclusions

            In the effort to identify, quantify and prioritize risks, and execute sound judgement based on technical and programmatic risk, it is the recommendation to evaluate the possibility of increasing system size to accommodate for both payloads and GNCS capabilities. For future programs, it may be beneficial for engineers to execute a redesign and formulate the best possible way to establish a weight margin scheme. Having clearly delineated margins for each subsystem will allow program managers to monitor box growth as the custom design evolves, and manage risk at the subsystem level.

References

Carter, P. (2015, September 28). The pros and cons of custom software vs. off-the-shelf solutions. Retrieved from http://pcdgroup.com/the-pros-and-cons-of-custom-software-vs-off-the-shelf-solutions/

ENSCO. (2017). Systems engineering and integration. Retrieved from http://ensco.com/aerospace/systems-engineering-integration

Novacek, P. F. (2017). Exploration of a Confidence-Based Assessment Tool within an Aviation Training Program. Journal of Aviation/Aerospace Education & Research, 26(1), 65-88. doi:10.15394/jaaer.2017.1717

Piette, D. (2013, October 24). Advantages of the system engineering approach. Retrieved from http://archive.eetindia.co.in/www.eetindia.co.in/ART_8800691030_1800007_TA_41d623e6_2.HTM

Sinde, A., & Ho, C. (2008, March). Independent verification and validation. 2008 International Conference on Railway Engineering - Challenges for Railway Transportation in Information Age, Hong Kong, 2008, pp. 1-5.