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Aircraft with supersonic, short takeoff and vertical landing capability have been proposed to replace some of the current high-performance aircraft. Several of these configurations use a ventral nozzle in the lower fuselage, aft of the center of gravity, for lift or pitch control. Internal vanes canted at 20° were added to a swivel-type ventral nozzle and tested at tailpipe-to-ambient pressure ratios up to 5.0 on the Powered Lift Facility at NASA Lewis Research Center. The addition of sets of four or seven vanes decreased the discharge coefficient of the nozzle by at least 6 percent and did not affect the thrust coefficient. Side force produced by the nozzle with vanes was 14 percent or more of the vertical force. In addition, this side force caused only a small loss in vertical force in comparison to the nozzle without vanes. The net thrust force was 8° from the vertical for four vanes and 10.5° for seven.

Flow in a generic ventral nozzle system was studied experimentally and analytically with the PARC3D computational fluid dynamics program (a full Navier-Stokes equations solver) in order to evaluate the program's ability to predict system performance and internal flow patterns. A generic model of a tailpipe with a rectangular ventral nozzle, about one-third of full size, was tested with unheated air at steady-state pressure ratios up to 4.0. The end of the tailpipe was closed to simulate a blocked exhaust nozzle. Measurements showed about 5½-percent flow-turning loss and reasonable nozzle performance coefficients. The flow turned more than the designed 90°, causing an aftward axial component in the total thrust. Flow behavior into and through the ventral duct is discussed and illustrated with paint streak flow visualization photographs. PARC3D graphic images are shown for comparison with the experiment photographs.

A variable inlet guide vane (VIGV) convertible engine that could be used to power future high-speed V/STOL and rotorcraft was tested on an outdoor stand. The engine ran stably and smoothly in the turbofan, turboshaft, and dual (combined fan and shaft) power modes. In the turbofan mode with the VIGV open, fuel consumption was comparable to that of a conventional turbofan engine. In the turboshaft mode with the VIGV closed, fuel consumption was higher than that of present turboshaft engines because power was wasted in churning fan-tip airflow. In dynamic performance tests with a specially built digital engine control and using a waterbrake dynamometer for shaft load, the engine responded effectively to large steps in thrust command and shaft torque.