Finally it is important to briefly describe some

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Finally, it is important to briefly describe some current flight control features of the RASCAL helicopter, since it, along with flight displays, affects the handling qualities and the tracking performance, which are discussed later in the paper. The basic UH-60 helicopter is equipped with a rate damping stability augmentation system in pitch, roll, and yaw, with turn coordination capability implemented via limited authority electrohydraulic series actuators. Additionally, parallel electromechanical actuators pro- vided both trim centering and outer loop stabilization. Below 60 knots, the outer loop stabilization included atti- tude and heading hold features; above 60 knots, it con- sisted of turn coordination and airspeed stabilization. A trim release switch and a trim beep switch were available for the pilot to change the reference condition or to relieve control forces. Flight Test Instrumentation and Data Acquisition and Reduction Extensive flight data were gathered during the tests, including those from an inertial navigational unit (INU), airdata, cockpit controls and servo actuator displacements, LDGPS, laser tracker, and a newly developed laser-based rotor state measurement system on board the aircraft. The rotor state measurement system (ref. 14) consists of three laser distance transducers mounted on each hub arm of the main rotor, and four linear accelerometers mounted near the root of each blade. Measured data from this system were collected at a rate of 263 Hz, which corresponded to one sample for approximately every 5.88 deg increment in the azimuth angle of the RASCAL main rotor system. This system thus provided a robust measurement and accurate estimation of the space orientation of the rotor tip-path-plane, among other blade motion variables. The tip-path-plane measurements, along with the aircraft atti- tude and flightpath, permitted an accurate estimation of tip-path-plane angle of attack, which is an important parameter for understanding and correlation of the BVI acoustic data obtained from the wind tunnel with those from flight. This will be further elaborated in the paper later. Accoustic and Weather Measurement Systems For the requirements of this experiment, an array of four microphones was used. This array consisted of two micro- phones located on the flight track centerline and one each at the starboard and port sidelines located at 500 ft from the center mics. The array was linear and perpendicular to the flight track centerline (see fig. 7). Except for the #3 center mic, which was on a 1.2 meter tripod, each of the remaining three mics (#1, #2, and #4) was placed on a 42in. × 42 in. × 1/2 in. PVC ground board. This was done so that in addition to obtaining acoustic data for the spe- cial flight procedures associated with this test, the data could be added to the extensive database associated with reference 6. Additionally, these data would permit researchers to be able to compare EPNL noise footprints as determined from a 3 microphone array to EPNL con- tours generated from different combinations of micro- phones used to collect the reference 6 data. The spacing
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