Inside Unmanned Systems

JUN-JUL 2016

Inside Unmanned Systems provides actionable business intelligence to decision-makers and influencers operating within the global UAS community. Features include analysis of key technologies, policy/regulatory developments and new product design.

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63 unmanned systems inside June/July 2016 ENGINEERING. PRACTICE. POLICY. bitantly expensive. Because of this an alternate approach, sometimes referred to hardware re- dundancy, is used. As the name implies, in this approach a single GNC system is designed such that it is the amalgam of several functionally identical, parallel, but independent GNC sys- tems. Therefore, a failure of components in one of the parallel systems does not necessarily lead to loss of the entire GNC system's functionality. Examples of this approach to designing naviga- tion and control systems can be found in any modern commercial airliner such as the Boe- ing 777 or Airbus 330. To a lesser extent it can also be found on the systems driving the "glass cockpits" of modern general aviation aircraft. This tried-and-true approach to designing a reliable GNC system is not tenable in small UAS applications. The severe size, weight and power (SWAP) constraints limit the level of hardware redundancy that can be used. Most small UAS have barely enough power or volume to carry extra or redundant sensors. Unless sensors and components can be miniaturized further with- out increasing their associated cost, hardware Figure 1: The Ultra Stick 120 aircraft. redundancy in the traditional sense is not a tenable approach for increasing the reliability of small UAS GNC systems. An alternate approach will rely on a mix of some physical redundancy coupled with what we in this article refer to as analytical redundancy. In simple terms, it is an approach to enhancing reli- ability whereby intelligent hardware design com- bined with sophisticated and flexible algorithms are used in lieu of simple hardware redundancy. While it may not always be possible to achieve the same level of reliability, in some instances it can provide a comparable level of reliability as hard- ware redundancy approaches. Of course, there is a trade off when using analytical redundancy to achieve reliability. The complexity of the resulting KEY INSIGHTS The article describes the use of analytical redundancy to improve the reliability of low cost unmanned aerial vehicles (UAVs). Fault monitor- ing systems are presented and tested for the actuation mechanism and navigation system. The reconfi guration of a UAS in the presence of system failures is successfully demonstrated using real fl ight tests.

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