A need exists to safely integrate Unmanned Aircraft Systems (UAS) into the United States' National Airspace System. Replacing manned aircraft's see-and-avoid capability in the absence of an onboard pilot is one of the key challenges associated with safe integration. Sense-and-avoid (SAA) systems will have to achieve yet-to-be-determined required separation distances for a wide range of encounters. They will also need to account for the maneuver performance of the UAS they are paired with. The work described in this paper is aimed at developing an understanding of the trade space between UAS maneuver performance and SAA system performance requirements, focusing on a descent avoidance maneuver. An assessment of current manned and unmanned aircraft performance was used to establish potential UAS performance test matrix bounds. Then, near-term UAS integration work was used to narrow down the scope. A simulator was developed with sufficient fidelity to assess SAA system performance requirements. The simulator generates closest-point-of-approach (CPA) data from the wide range of UAS performance models maneuvering against a single intruder with various encounter geometries. Initial attempts to model the results made it clear that developing maneuver performance groups is required. Discussion of the performance groups developed and how to know in which group an aircraft belongs for a given flight condition and encounter is included. The groups are airplane, flight condition, and encounter specific, rather than airplane-only specific. Results and methodology for developing UAS maneuver performance requirements are presented for a descent avoidance maneuver. Results for the descent maneuver indicate that a minimum specific excess power magnitude can assure a minimum CPA for a given time-togo prediction. However, smaller amounts of specific excess power may achieve or exceed the same CPA if the UAS has sufficient speed to trade for altitude. The results of this study will support UAS maneuver performance requirements development for integrating UAS in the NAS. The methods described are being used to help RTCA Special Committee 228 develop requirements. NomenclatureA. Variable Definitions = Aspect ratio of the wing, wing span divided by chord = Oswald's Efficiency Factor = Closest Point of Approach (ft) = Coefficient of lift = Lift coefficient at stall, i.e., maximum lift coefficient = Drag (lbs) = Load factor limit (g) = Estimated or actual time-to-go to closest point of approach (seconds) = Initial percent of maximum coefficient of lift B. Subscripts = Commanded value = Initial = Intruder = Minimum I.
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In support of NASA's Unmanned Aircraft Systems Integration in the National Airspace System project and RTCA Special Committee 228, an analysis has been performed to provide insight in to the trade space between unmanned aircraft speed and turn capability and detect and avoid sensor range requirements. The work was done as an initial part of the effort to understand low size, weight, and power sensor requirements for aircraft that have a limited speed envelope or can limit the envelope for portions of their mission and may be able to turn at higher than "standard rate." Range and timeline reductions coming from limiting speed range and from increasing available turn rate in some speed ranges are shown.
Demands for access of Unmanned Aircraft Systems (UAS) to the United States NationalAirspace System continue to increase. Per Title 14 of the Code of Federal Regulations part 91, §91.113, "vigilance shall be maintained by each person operating an aircraft so as to see and avoid other aircraft. When a rule of this section gives another aircraft the right-of-way, the pilot shall give way to that aircraft and may not pass over, under, or ahead of it unless well clear." In lieu of an onboard pilot's practical judgement and ability to see and avoid other aircraft, UAS must possess the capability of remaining equivalently separated based upon a quantified definition of "well clear." This separation will be quantified using the Detect and Avoid (DAA) Well Clear definition. Before DAA systems can be developed for this purpose, the requirements for the DAA systems must be determined. To fill this gap, RTCA, Inc., Special Committee 228 is currently working to develop Minimum Operational Performance Standards for UAS that will include DAA system requirements. For a manned aircraft to remain well clear of another aircraft, the pilot uses both visually estimated distance from the traffic aircraft as well as his judgement of how quickly and responsively his aircraft can maneuver to plan when to initiate an avoidance maneuver. Likewise, aircraft maneuver performance and its impact on avoidance maneuver timing will be important factors in the quantified DAA system requirements. To support RTCA in developing these requirements, NASA has tasked Adaptive Aerospace Group, Inc., with conducting a series of trade studies to evaluate the impact of aircraft maneuver capability across an array of commanded avoidance maneuvers and encounter geometries on DAA across a wide range of UAS aircraft performance capabilities. This paper discusses efforts to determine maneuver performance requirements and associated time and range requirements needed for level-turn maneuvers to avoid violating the specified DAA Well Clear volume. Insight to this process, proposed requirements, and associated implications are presented in this paper. NAS= United States National Airspace System r = Range (t) ̇ = Range rate (ft/sec) = Initial Range (ft) SC-228 = RTCA, Inc., Special Committee 228 TCAS = Traffic alert and Collision Avoidance System UAS = Unmanned Aircraft System = Velocity Never to Exceed (knots) = Intruder Velocity (knots) ℎ = Time to vertical displacement (sec) * = Superscript represents fixed values of well-clear parameters = Azimuth (deg) ̇ = Roll rate (deg/sec) ̇ = Turn rate (deg/sec) = Ownship tau (sec) = Modified tau (sec) = Time to co-altitude (sec)I. Introduction RTCA, Inc., Special Committee 228 (SC-228) is currently working to develop Minimum Operational Performance Standards (MOPS) for Unmanned Aircraft Systems (UAS) that will include Detect and Avoid (DAA) system requirements. NASA is supporting RTCA in this effort and has tasked Adaptive Aerospace Group, Inc., with conducting a series of trade studies that are needed to define the DAA sys...
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