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.
