Powered Testing Success Stories:
The Development of the Skytote UAV

The development of new and complex unmanned air vehicles (UAVs) that employ novel aerodynamic and configurational features can introduce significant program risk. The need for UAVs that can quickly move from target to target yet loiter as a fixed and stable platform, all the while operating with no launch and retrieval infrastructure has led to the postulation of a number of innovative configurations.
AeroVironment of Simi Valley, California, working under contract with the Air Force Research Laboratory (AFRL), has recently developed a UAV configuration designed to provide these sorts of operational capabilities. The Skytote is a novel vehicle using dual counter rotating propellers designed to enable operation in a helicopter mode, while also being able to transition to wing born flight for efficient point-to-point operation. This complex vehicle uses an intricate drive system to allow helicopter operations with cyclic and collective control, as well as blade pitch control, combined with normal aircraft control surfaces in conventional flight operations. Obviously, the design, development and testing of such a vehicle entails the assessment of a range of configurational issues. AFRL recognized the need to undertake a more detailed developmental evaluation of the flight operations of this UAV, consequently Bihrle Applied Research was tasked with an extensive series of static and dynamic tests to quantify the aerodynamic characteristics of this novel configuration.
	These tests had several goals; to assist AeroVironment in the development phase of the configuration by providing pertinent aerodynamic analysis of the test data, as well as to develop the database necessary to describe the flight operations in a comprehensive nonlinear 6 degree-of-freedom simulation of the vehicle and power train. The wind tunnel model was developed and built by the Bihrle model shop. The test was conducted using the test rig designed and installed by Bihrle. This highly flexible test rig allowed the continuous static and dynamic testing of the scaled test article (view with hatch removed, showing internal drive system and propellers). The model itself was capable of power on and power off testing, with precise control of the individually powered counter rotating propellers. The propellers were also outfitted to allow the variation of the individual blade angles as a test variable. The vehicle's conventional controls were also individually controllable to enable the acquisition of control effects in the aircraft as well as the helicopter mode.
With the model so configured, the characteristics of the basic airplane and its controls were defined and the power effects were acquired and reduced using a more physically representative methodology developed by Bihrle under an AFRL Small Business Innovation Research (SBIR) program. The test data was acquired over an extensive range of angle of attack and sideslips to cover the requisite conditions experienced by the Skytote in its vertical takeoff/hover/conventional flight operational envelope. One of the most unique aspects of this test was the acquisition of the effect of body axis rates in both unpowered as well as powered conditions. The definition of the variation of damping behavior in the presence of power represents a unique capability developed by Bihrle, and the results gained provided an important component of the definition of the vehicle's flight characteristics.
Using the SBIR developed power effect mechanization methodology, the basic airplane data and power effects were assembled into a comprehensive non-linear six degree of freedom simulation using Bihrle's D-Six simulation environment. This flight model host enabled the assessment of the vehicle's unusual flight characteristics with D-Six's numerous analytical tools, while providing the Air Force and AeroVironment the ability to investigate the requirements of manned flight using a variety of controller interfaces and visualizations. In this respect, D-Six's flexible Input/Output interface allowed the rapid interfacing of a hobby Radio Control trainer control box for pilot familiarization for the first unaugmented piloted flights using a similar interface. Pilot response to the correlation of the simulation predicted flight behavior with the actual flight responses was enthusiastic. The availability of the high fidelity simulation was key in the further development, assessment and validation of vehicle flight control and autopilot systems for subsequent more complex flight test functions. Utilization of the simulation for numerous flight test associated activities continues as the Skytote flight test program advances.
	As UAV developers strive to develop more complex and specialized vehicle applications, the need to provide the most comprehensive aerodynamic representation of these aircraft increases. As demonstrated in the Skytote program, the application of novel test and simulation technologies can significantly reduce the risk and cost associated with UAV development, ultimately leading to faster, safer, and more successful configuration deployments. View Movie

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