Heavy UAV

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

 

 

In a requirements based design process such as in the scenario described above it is vital to break down high level requirements, such as those promoted by the marketing department and management, into more design-specific lower level instructions and be able to communicate them clearly to subsystem design teams (Loewen, 2013). The design must meet prescribed requirements without sacrificing performance or safety, which in turn set lower level design parameters not met by the two subsystem teams. Weight is an important factor in aviation; it affects all aspects of aircraft design from propulsion, aerodynamics, structure, capacity and load, performance, and endurance, to name a few. The weight of all aircraft components, to include fuel and payload, goes into consideration when calculating center of gravity and ensuring the designed aircraft limits are not exceeded.

 

As the Systems Engineer (SE) in this scenario it is important to plainly communicate the requirements of the project to the entire group, that requirements based design does not tolerate slip ups (Loewen, 2013). While the use of commercial off-the-shelf (COTS) equipment saved some cost it did not succeed in meeting design limitations. Clearly, both teams in question will need to get back to the drawing board. Subsequent research and development (R&D) can move a step further by searching for even lighter alternatives to other components of the UAV. For example, materials used for airframe have evolved from the use of wood and canvas to aluminum to titanium to composite materials (Unmanned Aircraft Systems Roadmap, 2005). In essence, using lighter and stronger materials for aircraft structures as weight-saving alternatives is preferred in aircraft design. The teams can also search for innovative weight-cutting alternatives for other components of the UAV. However, the priority is to meet initial requirements first and get the final product out the door, while saving product enhancements for later versions. For example, using the fuselage or wing as the antenna can cut almost the entire weight of a traditional antenna system. Reducing weight even further will net improvements in payload capacity, performance, and operational costs which can make for desirable “nextgen” versions.

Reference

 

Loewen, H. (2013). Requirements-‐based UAVDesign Process Explained. MicroPilot, 1-17.

Unmanned Aircraft Systems Roadmap. (2005). Washington, DC: Office of the Secretary of Defense.