Download or read book A Survey of Research in Helicopter Higher Harmonic Control with Plans for Nearterm Naval Postgraduate School Test written by Jeffrey H. Carlsen and published by . This book was released on 1995 with total page 66 pages. Available in PDF, EPUB and Kindle. Book excerpt: A survey of research in the area of helicopter vibration reduction through the use of higher harmonic bade pitch control is presented. Higher Harmonic Control (HHC) is an active vibration suppression system for helicopters. Vibration is reduced through feathering of helicopter rotor blades at (b-1)omega, bomega, and (b+1)omega harmonic relationships to reduce airframe vibrations at the blade passage frequency bomega where b is the number of blades and omega is the main rotor rotational speed. Research has been in the areas of blade stresses, vibrations, control systems HHC algorithms, and methods of actuation. HHC has also been reported to affect helicopter performance and main rotor noise. Also presented are preliminary plans for performance testing testing of a Higher Harmonic Control system by the Naval Postgraduate School on the U.S. Naval Academy whirl tower at Annapolis.

Download or read book A Survey of Research in Helicopter Higher Harmonic Control with Plans for Nearterm Naval Postgraduate School Tests written by and published by . This book was released on 1995 with total page 71 pages. Available in PDF, EPUB and Kindle. Book excerpt: A survey of research in the area of helicopter vibration reduction through the use of higher harmonic bade pitch control is presented. Higher Harmonic Control (HHC) is an active vibration suppression system for helicopters. Vibration is reduced through feathering of helicopter rotor blades at (b-1)omega, bomega, and (b+1)omega harmonic relationships to reduce airframe vibrations at the blade passage frequency bomega where b is the number of blades and omega is the main rotor rotational speed. Research has been in the areas of blade stresses, vibrations, control systems HHC algorithms, and methods of actuation. HHC has also been reported to affect helicopter performance and main rotor noise. Also presented are preliminary plans for performance testing testing of a Higher Harmonic Control system by the Naval Postgraduate School on the U.S. Naval Academy whirl tower at Annapolis.

Download or read book Compilation of Theses Abstracts October 1994 September 1995 written by United States. Naval Postgraduate School, Monterey, CA. and published by . This book was released on 1995 with total page 564 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Baseline Vibration Measurements of Remotely Piloted Helicopters for Higher Harmonic Control Research written by Kevin M. Ransford and published by . This book was released on 1991 with total page 64 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Government Reports Announcements Index written by and published by . This book was released on 1995-12 with total page 1578 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Application of Chaos Methods to Helicopter Vibration Reduction Using Higher Harmonic Control written by Martinus M. Sarigul-Klijn and published by . This book was released on 1990 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Chaos is a discipline used in understanding complex nonlinear dynamics. The geometric and topological methods of Chaos theory are applied, for the first time, to the study of flight test data. Data analyzed is from the McDonnell Douglas OH-6A Higher Harmonic Control (HHC) test aircraft. HHC is an active control system used to suppress helicopter vibrations. Some of the first practical applications of Chaos methods are demonstrated with the HHC data. Although helicopter vibrations are mostly periodic, evidence of chaos was found. The presenc3e of a strange attractor was shown by computing a positive Lyapunov exponent and computing a non-integer fractal correlation dimension. Also, a broad band Fourier spectrum and a well defined attractor in pseudo phase space are observed. A limit exists to HHC vibration reduction due to the presence of chaos. A new technique based on a relationship between the Chaos methods (the Poincare section and Van der Pol plane) and the vibration amplitude and phase was discovered. This newly introduced technique results in the following: 1) it gives the limits of HHC vibration reduction, 2) it allows rapid determination of best phase for a HHC controller, 3) it determines the minimum HHC controller requirement for any helicopter from a few minutes duration of flight test data (for the OH-6A, a scheduled gain controller for HHC appears to be adequate for steady level flight), 4) it shows that the HHC controller transfer matrix is linear and repeatable when the vibrations are defined in the?Rotor Time Domain? and that the matrix is nonlinear and nonrepeatable when the vibrations are defined in the?Clock Time Domain.? This technique will reduce future HHC flight test requirements. Further, the technique does not require the helicopter to be equipped with HHC. These methods may be applicable to other vibration control and flight testing problems.

Download or read book Application of Chaos Methods to Helicopter Vibration Reduction Using Higher Harmonic Control written by Martinus M. Sarigul-Klijn and published by . This book was released on 1990 with total page 194 pages. Available in PDF, EPUB and Kindle. Book excerpt: Chaos is a discipline used in understanding complex nonlinear dynamics. The geometric and topological methods of Chaos theory are applied, for the first time, to the study of flight test data. Data analyzed is from the McDonnell Douglas OH-6A Higher Harmonic Control (HHC) test aircraft. HHC is an active control system used to suppress helicopter vibrations. Some of the first practical applications of Chaos methods are demonstrated with the HHC data. Although helicopter vibrations are mostly periodic, evidence of chaos was found. The presenc3e of a strange attractor was shown by computing a positive Lyapunov exponent and computing a non-integer fractal correlation dimension. Also, a broad band Fourier spectrum and a well defined attractor in pseudo phase space are observed. A limit exists to HHC vibration reduction due to the presence of chaos. A new technique based on a relationship between the Chaos methods (the Poincare section and Van der Pol plane) and the vibration amplitude and phase was discovered. This newly introduced technique results in the following: 1) it gives the limits of HHC vibration reduction, 2) it allows rapid determination of best phase for a HHC controller, 3) it determines the minimum HHC controller requirement for any helicopter from a few minutes duration of flight test data (for the OH-6A, a scheduled gain controller for HHC appears to be adequate for steady level flight), 4) it shows that the HHC controller transfer matrix is linear and repeatable when the vibrations are defined in the?Rotor Time Domain? and that the matrix is nonlinear and nonrepeatable when the vibrations are defined in the?Clock Time Domain.? This technique will reduce future HHC flight test requirements. Further, the technique does not require the helicopter to be equipped with HHC. These methods may be applicable to other vibration control and flight testing problems.

Download or read book Experimental and Analytical Investigation of the Vibration Characteristics of a Remotely Piloted Helicopter written by William T. Trainer and published by . This book was released on 1992 with total page 138 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Establishment of a Remotely Piloted Helicopter Test Flight Program for Higher Harmonic Control Research written by James Georg Scott and published by . This book was released on 1990 with total page 65 pages. Available in PDF, EPUB and Kindle. Book excerpt: An analytical research study was begun on a helicopter vibration reduction concept known as higher harmonic control (HHC). To supplement this research, a helicopter flight test program was established to generate flight test data in support of the NPS HHC research efforts. To accomplish this task, a remotely piloted helicopter was chosen as the test vehicle. The research efforts for HHC studies, the selection and acquisition of an RPH capable of completing the intended research mission, and the preliminary analysis of the RPH's flight control system for modification to an HHC configuration. A brief overview of helicopter vibrations and HHC fundamentals, along with an in-depth description of the selected RPH, is presented. Preliminary analysis of the RPH's flight control system includes the determination of associated freeplay and torsional constant values for the flight control components and the calculation of the necessary actuator torque requirements for HHC actuation. This research effort is the first stage of a long tern program designed to provide NPS with an in house asset capable of generating HHC flight test data in support of analytical research.

Download or read book A Flight Study with a Large Helicopter Showing Trends of Lateral and Longitudinal Control Response with Size written by Robert J. Tapscott and published by . This book was released on 1966 with total page 18 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Preliminary Vibration Survey of a Suspended Full scale OH 6A Helicopter from 0 to 45 HZ written by John H. Harris and published by . This book was released on 1996 with total page 64 pages. Available in PDF, EPUB and Kindle. Book excerpt: Efforts to establish a helicopter research program in structural dynamics at NPS were greatly enhanced when the U. S. Army donated two OH-6A light observation helicopters. One of the helicopters is reserved for ground vibration testing and dynamics research. Vibration measurements are extremely important in predicting and understanding an aircraft's dynamic behavior and durability. A comparison of a helicopters natural frequencies and those frequencies transmitted to the airframe through the rotor system can alert the designer/evaluator to possible dynamic problems. This thesis establishes a baseline vibration test program on the OH-6A helicopter for future testing and comparison to analytic models. The goal of the research is to establish natural frequencies (eigenvalues) principal mode shapes (eigenvectors), and damping characteristics of the OH-6A and to compare these values to test and analytical data obtained from the McDonnell Douglas Helicopter Company.

Download or read book Higher Harmonic Control Analysis for Vibration Reduction of Helicopter Rotor Systems written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-07-17 with total page 138 pages. Available in PDF, EPUB and Kindle. Book excerpt: An advanced higher harmonic control (HHC) analysis has been developed and applied to investigate its effect on vibration reduction levels, blade and control system fatigue loads, rotor performance, and power requirements of servo-actuators. The analysis is based on a finite element method in space and time. A nonlinear time domain unsteady aerodynamic model, based on the indicial response formulation, is used to calculate the airloads. The rotor induced inflow is computed using a free wake model. The vehicle trim controls and blade steady responses are solved as one coupled solution using a modified Newton method. A linear frequency-domain quasi-steady transfer matrix is used to relate the harmonics of the vibratory hub loads to the harmonics of the HHC inputs. Optimal HHC is calculated from the minimization of the vibratory hub loads expressed in term of a quadratic performance index. Predicted vibratory hub shears are correlated with wind tunnel data. The fixed-gain HHC controller suppresses completely the vibratory hub shears for most of steady or quasi-steady flight conditions. HHC actuator amplitudes and power increase significantly at high forward speeds (above 100 knots). Due to the applied HHC, the blade torsional stresses and control loads are increased substantially. For flight conditions where the blades are stalled considerably, the HHC input-output model is quite nonlinear. For such cases, the adaptive-gain controller is effective in suppressing vibratory hub loads, even though HHC may actually increase stall areas on the rotor disk. The fixed-gain controller performs poorly for such flight conditions. Comparison study of different rotor systems indicates that a soft-inplane hingeless rotor requires less actuator power at high speeds (above 130 knots) than an articulated rotor, and a stiff-inplane hingeless rotor generally requires more actuator power than an articulated or a soft-inplane hingeless rotor. Parametric studies for a hingeless rotor operati...

Download or read book Flight Tests of an Open Loop Higher Harmonic Control System on an S 76A Helicopter written by David M. Walsh (M.S. Eng.) and published by . This book was released on 1986 with total page 98 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book A Feasibility Study of Helicopter Vibration Reduction by Self optimising Higher Harmonic Blade Pitch Control written by John Shaw and published by . This book was released on 1967 with total page 2 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book A Feasibility Study of Helicopter Vibration Reduction by Self optimizing Higher Harmonic Blade Pitch Control written by John Shaw (Jr) and published by . This book was released on 1967 with total page 192 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book An Investigation of Helicopter Higher Harmonic Control Using a Dynamic System Coupler Simulation written by Kip Peter Nygren and published by . This book was released on 1987 with total page 346 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Helicopter Controllability written by Dean Carico and published by . This book was released on 1989 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The concept of helicopter controllability is explained. A background study reviews helicopter development in the U.S. General helicopter configurations, linearized equations of motion, stability, and piloting requirements are discussed. Helicopter flight controls, handling qualities and associated specifications are reviewed. Analytical, simulation, and flight test methods for evaluating helicopter automatic flight control systems are discussed. A generic simulation is also conducted. This thesis is intended to be used as a resource document for a helicopter stability and control course at the Naval Postgraduate School. Helicopter controllability, Helicopter automatic flight control systems, Helicopter flying qualities, Flying qualities specifications. (eg).