Lift-generated vortex wakes of subsonic transport aircraft

The use of CADD has effected many changes in traditional work methods of the various interfacing disciplines at MCAIR. We have streamlined our tasks by utilizing the cost/time saving techniques presently afforded by this system, and plan to continue additional development efforts which will further improve it. As we discover more and more practical applications for CADD, new or modified software routines will be formulated to make the system as responsive and reliable as possible. Since the potential for substantial dollar savings exists, particularly in the area of manufacturing, we are consciously attempting to align our techniques to make engineering data as usable as possible by manufacturing personnel in its existing form, thus eliminating as many intermediate manual processes as possible. Our final objectives, however, cannot now be defined. CADD's utility will increase as we continue to conceive new ideas for its application. Its ultimate benefits can only be determined by the limits of our creative imagination.

Rapid Scanning, Three-Dimensional Hot-Wire AnemometerSurveys of Wing-Tip Vortices

Description of velocity measurements made in the wake of wings in the Ames 7 x 10 ft wind tunnel. Distributions of velocity components were measured with a three-wire anemometer up to 12 chord lengths downstream of a CV-990 aircraft model and a rectangular wing. Results show that increasing the drag increases the vortex core radius, reduces the maximum tangential velocities, and increases the magnitude of axial velocity defects. For the rectangular wing, axial velocity changes from a defect (wake flow) for angles of attack less than 9 deg to an excess (jet flow) for angles of attack greater than 9 deg. Wind-tunnel measurements of the near flowfield are compared with flight measurements of the far flowfield.

Wind-Tunnel Studies of Wing Wake Turbulence

A state-of-the-art computational facility for aircraft flight control design, evaluation, and integration called CONDUIT (Control Designer's Unified Interface) has been developed. This paper describes the CONDUIT tool and case study applications to complex rotary- and fixed-wing fly-by-wire flight control problems. Control system analysis and design optimization methods are presented, including definition of design specifications and system models within CONDUIT, and the multi-objective function optimization (CONSOL-OPTCAD) used to tune the selected design parameters. Design examples are based on flight test programs for which extensive data are available for validation. CONDUIT is used to analyze baseline control laws against pertinent military handling qualities and control system specifications. In both case studies, CONDUIT successfully exploits trade-offs between forward loop and feedback dynamics to significantly improve the expected handling, qualities and minimize the required actuator authority. The CONDUIT system provides a new environment for integrated control system analysis and design, and has potential for significantly reducing the time and cost of control system flight test optimization.

CONDUIT: A New Multidisciplinary Integration Environment for Flight Control Development

CONDUIT, a computational facility for aircraft flight control design and evaluation, has been developed and demonstrated. CONDUIT offers a graphical environment for integrating simulation models and control law architectures with design specifications and constraints. This tool provides comprehensive analysis support and design guidance to a knowledgeable control system designer. Combining the easy-to-use graphical interface, the preprogrammed libraries of specifications, and the multiobjective function optimization engine (CONSOL-OPTCAD) in a single environment, CONDUIT offers the potential for significant reduction in time and cost of design, analysis, and flight-test optimization of modern flight control systems. A case study application to a complex rotary-wing flight control problem was presented. The baseline RASCAL UH-60 control system, as provided by the flight control contractor, was evaluated versus the ADS-33D handling-quality specifications. The selectable system gains were optimized to meet all system performance and handling-quality specifications. CONDUIT successfully exploited the tradeoff between forward loop and feedback dynamics to significantly improve the expected handling qualities and stability robustness, while reducing crossover frequency and minimizing actuator activity. The tradeoff studies showed the effect of increasing design margin (overdesign) on closed loop performance and actuator activity. Design margins exceeding 7.5% led to rapidly increasing actuator energy and saturation, resulting in shortened fatigue life of rotor control.

A multidisciplinary flight control development environment and its application to a helicopter

An experimental study was carried out on a rectangular wing in the NASA-Ames 7- by 10-Foot Wind Tunnel. Flow visualization studies were made using a tuft grid and smoke. Preliminary studies showed that the introduction of a bluff body into the trailing vortex downstream of the wing resulted in modification of the vortex. Further studies showed that a small vertical panel, termed a vortex dissipater, mounted on the wing upper surface near the wing tip also caused modification of the vortex. Both the smoke and tuft grid visualization studies indicated that the dissipater caused a significant reduction in the maximum tangential velocities in the trailing vortex. Additional studies using a hot wire anemometer showed significant reductions in the magnitude of the tangential velocities, increases in the cross-sectional dimensions of the core of the dissipated vortex and changes in the turbulence structure. Limited flight tests with a dissipater fitted to a Convair 990 wing tip and using a Lear jet aircraft as a probe indicated that the rolling acceleration and the degree of roll control required was less in the modified vortex than in the unmodified vortex.

An experimental investigation of trailing vortices behind a wing with a vortex dissipator

Salient design features of a new NASA/Army research rotorcraft - the Rotorcraft-Aircrew Systems Concepts Airborne Laboratory (RASCAL) - are described. Using a UH-60A Black Hawk helicopter as a baseline vehicle, the RASCAL will be a flying laboratory capable of supporting the research requirements of major NASA and Army guidance, control, and display research programs. The paper describes the research facility requirements of these programs together with other critical constraints on the design of the research system, including safety-of-flight. Research program schedules demand a phased development approach, wherein specific research capability milestones are met and flight research projects are flown throughout the complete development cycle of the RASCAL. This development approach is summarized, and selected features of the research system are described. The research system includes a full-authority, programmable, fault-tolerant/fail-safe, fly-by-wire flight control system and a real-time obstacle detection and avoidance system which will generate low-altitude guidance commands to the pilot on a wide field-of-view, color helmet-mounted display.

Preliminary design features of the RASCAL - A NASA/Army rotorcraft in-flight simulator

Salient design features of a new NASA/Army research rotorcraft - the Rotorcraft Aircrew Systems Concepts Airborne Laboratory (RASCAL) - are described. Using a UH-60A Black Hawk helicopter as a baseline vehicle, the RASCAL will be a flying laboratory capable of supporting the research requirements of major NASA and Army guidance, control, and display research programs. The paper describes the research facility requirements of these programs together with other critical constraints on the design of the research system, including safety-of-flight. Research program schedules demand a phased development approach, wherein specific research capability milestones are met and flight research projects are flown throughout the complete development cycle of the RASCAL. This development approach is summarized, and selected features of the research system are described. The research system includes a full-authority, programmable, fault-tolerant/fail-safe, fly-by-wire flight control system and a real-time obstacle detection and avoidance system which will generate low-latitude guidance commands to the pilot on a wide field-of-view, color helmet-mounted display.

/pdf/preliminary-design-features-of-the-rascal-a-nasa-army-1tnot2mojw.pdf

The Airspace Systems Program (ASP) has identified a set of goals based on projections of annual passenger demands. The topics of discussion include: 1) Virtual Airspace Modeling and Simulation Project (VAMS) Project Description; 2) VAMS Project Management; 3) VAMS Project Schedule; and 4) Technical Interchange Meeting (TIM). This paper is in viewgraph form.

Robert A. Jacobsen

Papers

An experimental investigation of trailing vortices behind a wing with a vortex dissipator

Preliminary design features of the RASCAL - A NASA/Army rotorcraft in-flight simulator

Preliminary design features of the RASCAL - A NASA/Army rotorcraft in-flight simulator

Airspace Systems Program: Virtual Airspace Modeling and Simulation Project