Download Free Design And Flight Test Of A Cable Angle Feedback Control System For Improving Helicopter Slung Load Operations At Low Speed Book in PDF and EPUB Free Download. You can read online Design And Flight Test Of A Cable Angle Feedback Control System For Improving Helicopter Slung Load Operations At Low Speed and write the review.

The ability of a helicopter to carry externally slung loads makes it very versatile for many civil and military operations. However, the piloted handling qualities of the helicopter are degraded by the presence of the slung load. This dissertation investigates the dynamics, handling qualities requirements, and control aspects of the helicopter/slung load system that contribute to the performance of piloted slung load operations. A control system is developed that integrates measurements of both slung load motions and conventional fuselage feedback to improve the handling qualities for hover/low speed operations. Despite the fact that this technology was developed 40 years ago, it has not been tested in a manned helicopter since the 1970s, due to problems with handling qualities and pilot perception. This dissertation leverages advances in fly-by-wire, complex control design procedures (direct multi-objective optimization), and recently developed work that relates handling qualities to dynamic response (specifications) to successfully flight test cable angle feedback technology in a manned helicopter. The key contributions of this work are developing an understanding of the handling qualities trade-offs for cable angle/rate control system design, implementing an approach to solve the problem with a novel task-tailored control system, and performing extensive piloted flight tests of the control system on a fly-by-wire Black Hawk. The flight tests demonstrated that average precision load set-down time was reduced by 50% for a light load, 30% for a heavy load, and the average handling qualities rating for the external load placement task was improved from Level 2 to Level 1 on the Cooper-Harper rating scale, a significant improvement.
A control design method to address low-speed stability and handling qualities issues of helicopter slung load operations is presented. A simple model was developed using first principle physics with application of basic control techniques to understand the couple dynamics. Subsequently, a non-linear slung load model was developed and integrated with the GenHel-PSU simulation of the UH-60A. Linear model frequency responses were verified against AFDD OVERCAST models and flight data. A control architecture based on dynamic inversion was developed, combining fuselage and load state feedback. Slung load states were incorporated in feedback linearization and lagged cable angle feedback was introduced. A controller that uses only lagged cable angle feedback (and no load states in feedback linearization) was also investigated. Sensitivity to load parameter variations and optimization methodologies were considered in aiding the design process. The controller and its variations demonstrated key trade-offs between load swing damping and piloted response. The controller was robust and maintained closed-loop stability for a wide range of load mass and cable length values.
Helicopters performing external load missions are subject to instabilities that arise in high speed flight that limit their operational flight envelope. This thesis addresses the problem of active stabilization of slung loads in high speed flight. To demonstrate the method, simulations of a utility helicopter with a dynamic inversion controller (as its automatic flight control system) and a CONEX cargo container were used. An airspeed scheduled controller utilizing cable angle feedback to the primary dynamic inversion controller was designed for the nonlinear coupled system by the classic root locus technique. Nonlinear simulations of straight and level flight at different airspeeds were used to validate the controller performance in stabilizing the load pendulum motions. Controller performance was also evaluated in a complex maneuver and in more demanding scenarios by adding different levels of atmospheric turbulence to the previous cases. The results show that the use of cable angle feedback provides or improves system stability when turbulence is not included in the simulation. When light/moderate turbulence is present sustained limit cycle oscillations are avoided by the use of the controller. For severe turbulence levels, the controller did not provide any significant improvement.
Helicopters must carry out a variety of missions, ranging from military to civilian uses. Missions mayinvolve delivery of a payload from one location to another. Some loads are externally attached to thehelicopter by cables. In this configuration, the loads are referred to as slung loads. Due to the couplingbetween the slung load aerodynamics and inertial forces, loads dynamics can become unstable whenairspeed increases. Slung load instabilities limit the flight operations of a rotorcraft. Because limitingflight speeds reduce the operational efficiency of the rotorcraft, methods for stabilizing external loadsin forward flight are the subject for research. In recent years, the dynamics and control of slung loadswere studied using analysis, dynamic wind tunnel tests, and flight tests.The research presented in this thesis investigated a control design methodology and its feasibilityto stabilize an external load across the flight envelope, including high speed flight. The capability of anactive cargo hook (ACH) to provide external load stabilization in high speed flight is studied. The ACHis an electromechanical device that can slide longitudinally and laterally along the base of the fuselage.Previous work used the ACH to directly control the loads roll and pitch but only during hover and lowspeed flight. Previous studies results proved promising.The test load and helicopter simulated in this thesis is a CONEX cargo container and a UH-60 BlackHawk helicopter, respectively. During high speed flight, the load can become unstable, exhibiting sustainedperiodic motion, or limit cycle oscillations, which can degrade helicopter handling qualities. Previousstudies observed the load dynamics in a wind tunnel. The findings showed the excessive swingingand rotation in the slung load are due to its nonlinear dynamics.The control methodology first examined designed a full-state feedback (FSF) linear-quadratic regulator(LQR) controller. In this controller, the load states and cargo hook longitudinal and lateral positionsare used as inputs to the controller with the commanded cargo hook longitudinal and lateral positionsas outputs. Results showed high damping in the loads attitude response with little saturation in theACH stroke and stroke rate. The full-state LQR controller demonstrated success in stabilizing the slungload.The FSF controller, however, requires sensors to measure the loads states real-time. A more practicalapproach is using a reduced order model (ROM) using relative cable angle feedback (RCAF). With RCAF,the relative cable angles can be measured real-time, requiring less sensors and measurements. Thereduced order model is used to design an LQR controller for the ACH. The inputs for the controllerare the relative cable angles, relative cable angular rates, and ACH positions. The results demonstratedbetter performance than the FSF LQR controller, stabilizing the load approximately 20 percent quicker.The loads damping of the RCAF controller is higher than the FSFs and the ACH does not saturate instroke or stroke rate. The settling time of the load was also improved significantly. Furthermore, thecontrollers robustness was tested through applying a Dryden Turbulence model in the simulations. TheRCAF was able to appropriately stabilize the load through low, mild, and severe turbulence levels.
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.