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The effectiveness of an aerodynamic boattail on a tractor/trailer road vehicle was measured in the NASA Ames Research Center 80- by 120- Foot Wind Tunnel. Results are examined for the tractor/trailer with and without the drag reduction device. Pressure measurements and flow visualization show that the aerodynamic boattail traps a vortex or eddy in the corner formed between the device and the rear corner of the trailer. This recirculating flow turns the flow inward as it separates from the edges of the base of the trailer. This modified flow behavior increases the pressure acting over the base area of the truck, thereby reducing the net aerodynamic drag of the vehicle. Drag measurements and pressure distributions in the region of the boattail device are presented for selected configurations. The optimum configuration reduces the overall drag of the tractor/trailer combination by about 10 % at a zero yaw angle.

Using a generalized simulation model developed for piloted evaluations of short take-off/vertical landing aircraft, an initial fixed-base simulation of a mixed-flow, remote-lift configuration has been completed. Objectives of the simulation were to evaluate the integration of the aircraft's flight and propulsion controls to achieve good flying qualities throughout the low-speed flight envelope; to determine control power used during transition, hover, and vertical landing; and to evaluate the transition flight envelope considering the influence of thrust deflection of the remote-lift component. Pilots’ evaluations indicated that Level 1 flying qualities could be achieved for deceleration to hover in instrument conditions, for airfield landings, and for recovery to a small ship when attitude and velocity stabilization and command augmentation control modes were provided.

Propulsion induced effects encountered by moderate- to high-disk loading STOVL or VSTOL aircraft out-of-ground effect during hover and transition between hover and wing-borne flight are discussed. Descriptions of the fluid flow phenomena are presented along with an indication of the trends obtained from experimental investigations. In particular, three problem areas are reviewed: 1) the performance losses sustained by a VSTOL aircraft hovering out-of-ground effect, 2) the induced aerodynamic effects encountered as a VSTOL aircraft flies on the combination of powered and aerodynamic lifts between hover and cruise out-of-ground effect, and 3) the aerodynamic characteristics caused by deflected thrust during maneuvering flight over a wide ranges of both angle of attack and Mach number.

Takeoff predictions for powered lift short takeoff (STO) aircraft have been added to NASA AMES Research Center's aircraft synthesis (ACSYNT) code. The new computer code predicts the aircraft engine and nozzle settings required to achieve the minimum takeoff roll. As a test case, it predicted takeoff ground rolls and nozzle settings for the YAV-8B Harrier that were close to the actual values. Analysis of takeoff performance for an ejector-augmentor design and a vectoring-nozzle design indicated that ground roll can be decreased, for either configuration, by horizontally moving the rear thrust vector closer to the center of gravity, by increasing the vertical position of the ram drag-vector, or by moving the rear thrust vector farther below the center of gravity.

Piloted, moving-base simulations have been performed in the evaluation of several VTOL control system concepts during landings on a destroyer in adverse weather conditions. All the systems incorporated attitude control augmentation; most systems incorporated various types of translational control augmentation implemented either through aircraft attitude or, more directly, through the propulsion system (thrust magnitude and deflection). Only one of the control systems failed to provide satisfactory handling qualities in calm seas. Acceptable handling qualities in sea state 6 seem to require a system with control augmentation in all translational degrees of freedom.

Ames Research Center is developing the technology for turbine-powered jet engine simulators so that airframe/propulsion system interactions on V/STOL fighter aircraft and other highly integrated configurations can be studied. This paper describes the status of the compact multimission aircraft propulsion simulator (CMAPS) technology. Three CMAPS units have accumulated a total of 340 hr during approximately 1-1/2 yr of static and wind-tunnel testing. A wind-tunnel test of a twin-engine CMAPS-equipped close-coupled canard-wing V/STOL model configuration with nonaxisymmetric nozzles was recently completed. During this test approximately 140 total hours were logged on two CMAPS units, indicating that the rotating machinery is reliable and that the CMAPS and associated control system provide a usable test tool. However, additional development is required to correct a drive manifold O-ring problem that limits the engine-pressure-ratio (EPR) to approximately 3.5.

Over the years, a wide variety of aircraft configurations have been flown with varying degrees of success. A brief survey of the handling qualities of canard, tandem wing, and flying wing designs indicates that longitudinal stability and control, lateral/directional stability and control, and stall behavior of these concepts were important factors in achieving pilot acceptance.

Low-speed wind-tunnel tests were performed on a generic forward-swept-wing aircraft model in the 7- by 10-Foot Wind Tunnel (No. 2) at Ames Research Center. The effects of various configurational changes and control-surface deflections on the performance of the model were measured. Six-component force measurements were augmented by flow-visualization photographs, using both surface oil-flow and tufts. It was found that the tendency toward premature root separation on the forward-swept wing could be reduced by use of either canards or leading-edge wing strakes and that differential canard deflections can be used to produce direct side-force control.