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Book Higher Harmonic Blade Pitch Control for Helicopter Vibration Reduction a Feasibility Study

Download or read book Higher Harmonic Blade Pitch Control for Helicopter Vibration Reduction a Feasibility Study written by John Shaw (Jr) and published by . This book was released on 1968 with total page 87 pages. Available in PDF, EPUB and Kindle. Book excerpt: The concept of eliminating most helicopter vibration by changing certain rotor harmonic airloads and blade motions with harmonic pitch control is discussed in detail. A simple method of obtaining the required pitch harmonics by periodic tilting of the swashplate is presented. Attention is given to the origin and characteristics of four problems expected in applying the pitch control concept: shed wake reduction of harmonic pitch effectiveness, high blade bending moments, high blade bending moments, high loads in the pitch control linkages, and the need for adjustment of the pitch control as flight condition changes. Numerical results are given to show the effect of third harmonic pitch on the cockpit vibration caused by a three-bladed articulated rotor at moderate forward speed. Several examples are given to illustrate the strong influence of shed wake on the effectiveness of harmonic pitch variations. Finally, the smooth single-minimum character of vibration dependence on pitch harmonic magnitude and phase suggests that inflight adjustment by steepest-descent type search is feasible. (Author).

Book Higher Harmonic Blade Pitch Control

Download or read book Higher Harmonic Blade Pitch Control written by John Shaw and published by . This book was released on 1980 with total page 1010 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book On the Use of Active Higher Harmonic Blade Pitch Control for Helicopter Vibration Reduction

Download or read book On the Use of Active Higher Harmonic Blade Pitch Control for Helicopter Vibration Reduction written by Charles E. Hammond and published by . This book was released on 1980 with total page 17 pages. Available in PDF, EPUB and Kindle. Book excerpt: Vibration levels have been a problem in helicopters since their inception. The reason for this lies in the method whereby the helicopter generates its lift, namely, the rotor system. As the rotor blades rotate they encounter a continuously changing aerodynamic environment which results in a continuously changing environment which results in a continuously changing aerodynamic loading on the blades. This changing environment is repeated on each revolution of the rotor. Hence, the rotor develops aerodynamic loads which are oscillatory in nature. These oscillatory loads are transferred directly to the helicopter airframe through the mechanical connection of the rotor to the airframe, i.e., the rotor-shaft/transmission attachment. Oscillatory loads are also transmitted to the airframe by impingement of the rotor wake on the upper portion of the airframe, but the mechanically transferred loads are in most cases much more significant than the aerodynamically transferred loads. (Author).

Book A Survey of Research in Helicopter Higher Harmonic Control with Plans for Nearterm Naval Postgraduate School Tests

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.

Book A Survey of Research in Helicopter Higher Harmonic Control with Plans for Nearterm Naval Postgraduate School Test

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.

Book Application of Higher Harmonic Blade Feathering for Helicopter Vibration Reduction

Download or read book Application of Higher Harmonic Blade Feathering for Helicopter Vibration Reduction written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-08-22 with total page 38 pages. Available in PDF, EPUB and Kindle. Book excerpt: Higher harmonic blade feathering for helicopter vibration reduction is considered. Recent wind tunnel tests confirmed the effectiveness of higher harmonic control in reducing articulated rotor vibratory hub loads. Several predictive analyses developed in support of the NASA program were shown to be capable of calculating single harmonic control inputs required to minimize a single 4P hub response. In addition, a multiple-input, multiple-output harmonic control predictive analysis was developed. All techniques developed thus far obtain a solution by extracting empirical transfer functions from sampled data. Algorithm data sampling and processing requirements are minimal to encourage adaptive control system application of such techniques in a flight environment. Powers, R. W. Unspecified Center NASA-CR-158985 NAS1-14552...

Book Higher Harmonic Control Analysis for Vibration Reduction of Helicopter Rotor Systems

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...

Book Higher Harmonic Blade Pitch Control

Download or read book Higher Harmonic Blade Pitch Control written by John Shaw and published by . This book was released on 1980 with total page 1010 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book Vibration Reduction of Helicopter Blade Using Variable Dampers

Download or read book Vibration Reduction of Helicopter Blade Using Variable Dampers written by National Aeronautics and Space Adm Nasa and published by Independently Published. This book was released on 2018-09-21 with total page 70 pages. Available in PDF, EPUB and Kindle. Book excerpt: In the report, the investigation of controlling helicopter-blade lead-lag vibration is described. Current practice of adding passive damping may be improved to handle large dynamic range of the blade with several peaks of vibration resonance. To minimize extra-large damping forces that may damage the control system of blade, passive dampers should have relatively small damping coefficients, which in turn limit the effectiveness. By providing variable damping, a much larger damping coefficient to suppress the vibration can be realized. If the damping force reaches the maximum allowed threshold, the damper will be automatically switched into the mode with smaller damping coefficient to maintain near-constant damping force. Furthermore, the proposed control system will also have a fail-safe feature to guarantee the basic performation of a typical passive damper. The proposed control strategy to avoid resonant regions in the frequency domain is to generate variable damping force in combination with the supporting stiffness to manipulate the restoring force and conservative energy of the controlled blade system. Two control algorithms are developed and verified by a prototype variable damper, a digital controller and corresponding algorithms. Primary experiments show good potentials for the proposed variable damper: about 66% and 82% reductions in displacement at 1/3 length and the root of the blade respectively.Lee, George C. and Liang, Zach and Gan, Quan and Niu, TiechengAmes Research CenterHELICOPTERS; ROTORS; VIBRATION DAMPING; ALGORITHMS; RESONANCE; FAIL-SAFE SYSTEMS; VIBRATION

Book Active Control of Noise and Vibration

Download or read book Active Control of Noise and Vibration written by Colin Hansen and published by CRC Press. This book was released on 2012-11-02 with total page 1564 pages. Available in PDF, EPUB and Kindle. Book excerpt: Integrating active control of both sound and vibration, this comprehensive two-volume set combines coverage of fundamental principles with the most recent theoretical and practical developments. The authors explain how to design and implement successful active control systems in practice and detail the pitfalls one must avoid to ensure a reliable and stable system. Extensively revised, updated, and expanded throughout, the second edition reflects the advances that have been made in algorithms, DSP hardware, and applications since the publication of the first edition.

Book Adaptive control of helicopter vibrations via theimpulse response method

Download or read book Adaptive control of helicopter vibrations via theimpulse response method written by Carl Richard Knospe and published by . This book was released on 1989 with total page 154 pages. Available in PDF, EPUB and Kindle. Book excerpt: