Charles E. Hall

A Real-Time Linux system for autonomous navigation and flight attitude control of an uninhabited aerial vehicle

A Commercial-Off-The-Shelf PC-104 system using the Real Time Linux operating system is used for flight attitude control and navigation for autonomous flight testing of the Stingray UAV. The fast, time critical tasks of attitude control of the aircraft are placed in real time tasks in kernel space. The slower navigation routines, based on GPS data, is a user space task that provides attitude commands to the real time tasks. Data from the GPS, and attitude controllers are stored on board the aircraft for post-flight analysis. For these flight tests, the take-off and landing of the Stingray UAV will be by an external pilot.

Development of Stable Automated Cruise Flap for an Aircraft with Adaptive Wing

Cruise flaps are devices designed to minimize drag, and previous research has explored using a wing-based pressure differential to automate them. Different presentations of the pressure-differential data tend to lead to the development of different types of controllers for automated cruise flaps. A presentation used by previous researchers led to an unstable drag-minimizing controller, whereas a presentation used in this research leads to a stable controller that implements multiple functions. Techniques previously used for high Reynolds number natural-laminar-flow airfoils are modified for use with the low Reynolds number SD7037 planned for future flight testing. The results of rigid-aircraft simulations are presented, showing the effectiveness of the multifunction controller, which is able to simultaneously reduce drag and alleviate the effects of vertical gusts.

Flight Test of Stable Automated Cruise Flap for an Adaptive Wing Aircraft

0p-optimization function was effective in producing pressure differentials that would have reduced drag. The effectivenessoftheC 0 p-maintenancefunctioncouldnotbedeterminedbecauseoflargesample-to-samplevariations in measured C 0 p values. It remains unknown whether this high-frequency content actually represented rapidly varying pressures on the airfoil surface or if it was the result of noise in the measurement system.

System-Level Airworthiness Tool

One of the pillars of aviation safety is assuring sound engineering practices through airworthiness certification. As unmanned aircraft systems grow in popularity, the need for airworthiness standards and verification methods tailored for unmanned aircraft systems becomes critical.While airworthiness practices for large unmanned aircraft systemsmay be similar to manned aircraft, it is clear that small unmanned aircraft systems require a paradigm shift from the airworthiness practices of manned aircraft. Although small in comparison with manned aircraft these aircraft are not merely remote-controlled toys. Small unmanned aircraft systems may be complex aircraft flying in the national airspace system over populated areas for extended durations and beyond line of sight of the operators. A comprehensive systems engineering framework for certifying small unmanned aircraft systems at the system level is needed. This work presents a point-based tool that evaluates small unmanned aircraft systems by rewarding good engineering practices in design, analysis, and testing. The requirements scale with vehicle size and operational area, while allowing flexibility for new technologies and unique configurations.

Passively Varying Pitch Propeller for Small UAS

A novel design for a passively-varying pitch propeller to improve small UAS performance is examined. The proposed system uses propeller blades free to pivot on a radial axis and blade cross sections tailored fo r positive pitching moment to achieve stable and efficient operation over a large advance ratio range. Computational analysis of the passively-varying propeller system indicates that large improvements can be gained, especially at high advance ratios, while sacrificing very lit tle low speed performance. A properly designed propeller will enable a much expanded flight envelope and, with proper limits to rotation angle, good takeoff/ climb performance and automatic feathering in the engine off case. Experimental analysis to corroborate computational findings is currently underway.

A real-time Linux based system for flight testing of remotely piloted vehicles

The Linux in flight testing system is a versatile, general purpose avionics computer for flight testing remotely piloted vehicles. The tools provided with the Linux system allow an ease of use. The RTLinux subkernel has shown the hard real time capabilities of a Linux based system.

Analysis of Different Stabilizing Control Systems for Aircraft with Automated Cruise Flaps

Cruise flaps are a promising method of increasing aircraft performance by reducing drag, but their use is restricted to applications where increased pilot workload is not a significant detriment. Recent research has focused on automating the cruise flap to achieve low drag without the increased pilot workload. In this paper, a flap controller developed in an earlier research effort is revisited and is compared with a new controller developed in this effort. The earlier controller uses the current lift coefficient to adjust the flap angle towards the optimum value for minimum profile drag. As shown using static-stability analysis in earlier research, such a controller is unstable unless it is accompanied by an elevator controller that maintains the lift coefficient. The current work revisits this controller and confirms the earlier results using dynamic-stability analysis. A new controller is developed in which the flap angle is adjusted to achieve a desired lift coefficient, leaving the elevator controller to achieve a desired angle of attack as needed to minimize profile drag or any other objective. The new controller has the advantage that it can be implemented to automate multiple flaps along the span of a wing. Dynamic analysis of the aircraft with the new controller is explored in this paper.

Correlation of Population Density to Designated Urban Areas

T HIS work relates the correlation of United States (U.S.) census population data with the designated urban areas shown on the Federal Aviation Administration (FAA) sectional charts used by visual flight rules (VFR) pilots. This will be useful for mission planning purposes for UnmannedAerial Systems (UAS). Geographic Information Systems (GIS) softwarewas used to import the raw census data andmarked urban areas from the sectional maps. This data was examined to determine the average population inside the marked urban areas and to determine how the population density reduces outside the urban areas. North Carolina State Flight Research has been developing the SystemLevelAirworthiness Tool (SLAT) [1,2], a comprehensive framework for evaluating the airworthiness of small UASwith maximum takeoff weights less than 350 lb. SLAT scales its requirements based on the size of the unmanned aircraft, aswell as the population density of themission area. The population density research presented in this technical notewas done as a part of the development of SLAT. It is expected that the results will be applicable to others in the aerospace community. To simplify analysis, SLAT divides population density into four categories: unpopulated (UP), sparsely populated (SP), densely populated (DP), andOpenAirAssembly (OAA).OAA is defined by the FAAas “an organized open-air assembly ofmore than 1,000 persons” [3], such as an occupied football stadium or outdoor concert. SP is defined by the U.S. Census Bureau as 500 people per square mile [4]. Determining the boundary between SP and DP was the goal of this work. One resource that attempts to designate a border between the two regions is the FAA sectional charts. These charts are used by pilots to aid navigation under VFRs. The sectional charts show airports, controlled airspace, antenna towers, and notable landmarks, as well as the locations and relevant information of navigation beacons. The sectional charts also include yellow regions denoting observable urban development; an example is shown in Fig. 1. Inquiries into how the FAA defines these boundaries revealed that they are defined primarily by visual inspection of satellite photos. Areas that appear to be urban, i.e. shopping centers, housing developments, and so on are included in the urban areas on the sectional charts. Although these boundaries are based on satellite photos, rather than some population density metric, it is logical that the population density would be highest in regions of observable urban development. This research focused on quantifying the correlation between actual population density and these regions of observable urban development as marked on the FAA sectional charts. One of the primary goals for SLAT is to aid in the integration of UAS into the National Airspace System (NAS) and, as such, the scope of this research is constrained to the U.S. To simplify the correlation it was decided to limit the scope to the continental U.S.

Testing of the Passively Varying Propeller Concept

A novel design for a passively varying pitch propeller has been tested in the NCSU subsonic wind tunnel. The system uses propeller blades designed to freely pivot on a radial axis and blade cross sections tailored for positive zero-lift pitching moment to achieve stable and efficient operation. Previous computational analysis and simulation indicated that by allowing the blades to rotate in this manner the envelope of efficient operation could be greatly expanded. Wind tunnel test articles corroborated the computational results and demonstrated that the propeller maintained near peak efficiency by passively adjusting blade pitch rotation angles by over 15 degrees to match changing inflow conditions. Following wind tunnel tests the passively varying pitch propeller was successfully demonstrated in-flight on the NCSU aerial vehicle Converse.

Incorporating Airworthiness into the Academic Curriculum

Airworthiness considerations are critically important in the design, development, and certification of civil and military aircraft. A solid understanding of airworthiness certification criteria, standards, verification methods, and artifacts are key pieces of knowledge for aerospace engineers who are actively engaged in aircraft design and development. Nevertheless, it is unclear how airworthiness considerations in aircraft design are incorporated into the academic curricula of many engineering schools. Young engineers who enter a career in aircraft design may lack critical information with regard to certification requirements that impact the aircraft design process. Incorporating airworthiness into the academic curriculum will produce engineers who understand how airworthiness considerations impact aircraft design and who are equipped to resolve airworthiness-related challenges.