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

Download or read book A Variable Hydraulic Damper for Vibration Reduction in Helicopter Blades written by Quan Gan and published by . This book was released on 2003 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Optimal Placement of Tuning Masses for Vibration Reduction in Helicopter Rotor Blades written by and published by . This book was released on 1988 with total page 20 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Optimizing Tuning Masses for Helicopter Rotor Blade Vibration Reduction Including Computed Airloads and Comparison with Test Data written by and published by . This book was released on 1992 with total page 14 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Vibration Handbooks for Helicopters written by Robert A. Wagner and published by . This book was released on 1954 with total page 94 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Smart Helicopter Rotors written by Ranjan Ganguli and published by Springer. This book was released on 2015-12-16 with total page 264 pages. Available in PDF, EPUB and Kindle. Book excerpt: Exploiting the properties of piezoelectric materials to minimize vibration in rotor-blade actuators, this book demonstrates the potential of smart helicopter rotors to achieve the smoothness of ride associated with jet-engined, fixed-wing aircraft. Vibration control is effected using the concepts of trailing-edge flaps and active-twist. The authors’ optimization-based approach shows the advantage of multiple trailing-edge flaps and algorithms for full-authority control of dual trailing-edge-flap actuators are presented. Hysteresis nonlinearity in piezoelectric stack actuators is highlighted and compensated by use of another algorithm. The idea of response surfaces provides for optimal placement of trailing-edge flaps. The concept of active twist involves the employment of piezoelectrically induced shear actuation in rotating beams. Shear is then demonstrated for a thin-walled aerofoil-section rotor blade under feedback-control vibration minimization. Active twist is shown to be significant in reducing vibration caused by dynamic stall. The exposition of ideas, materials and algorithms in this monograph is supported by extensive reporting of results from numerical simulations of smart helicopter rotors. This monograph will be a valuable source of reference for researchers and engineers with backgrounds in aerospace, mechanical and electrical engineering interested in smart materials and vibration control. Advances in Industrial Control aims to report and encourage the transfer of technology in control engineering. The rapid development of control technology has an impact on all areas of the control discipline. The series offers an opportunity for researchers to present an extended exposition of new work in all aspects of industrial control.

Download or read book Vibration Reduction in Helicopters Using Lag Dampers written by and published by . This book was released on 2005 with total page 193 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book The Shock and Vibration Digest written by and published by . This book was released on 1988 with total page 492 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Fluidic Flexible Matrix Composite Vibration Treatments for Helicopter Airframes and Rotor Blades written by Matthew Joseph Krott and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Vibrations caused by periodic and unsteady loading in rotorcraft must be minimized to maintain acceptable fatigue life in structural parts and ride quality for passengers and crew. Rotorcraft vibrations are typically addressed through some combination of passive and active solutions that focus on reducing steady-state vibrations at the n/rev frequency, where n is the number of rotor blades. Currently existing passive treatments are often heavy, bulky variations of the classical tuned vibration absorber. Active treatments either attempt to isolate the cabin from hub vibratory loads or reduce cabin vibrations using a set of actuators, but they are more difficult to implement because they require a power supply and controller. This research covers the modeling, design, and experimental verification of fluidic flexible matrix composite (F2MC) vibration treatments for two main rotorcraft applications: airframe vibration control and rotor blade damping. The main advantages to using F2MC tubes over conventional hydraulic devices with pistons are their high strain-induced pumping capability and high force output per unit pressure.A laboratory-scale rotorcraft tailboom was used as a testbed for demonstrating new F2MC vibration absorber concepts. The tailboom is modeled using Euler-Bernoulli beam finite elements and coupled to a model of the F2MC tubes and fluidic circuit. Based on the combined structural and fluid system model, an F2MC damped vibration absorber was designed and built using four F2MC tubes placed near the corners of the rectangular tailboom. Experimental results showed reduction of both lateral and torsional vibrations in a 26.7 Hz coupled tailboom vibration mode by up to 80%. Three fluidic circuits were tested for performance and model verification. This single-mode F2MC vibration absorber was then modified so that two tailboom vibration modes can be treated by the same device. A lateral absorber frequency was tuned by selecting lengths of short branch segments connecting the left and right F2MC tube pairs. Then, a vertical absorber frequency was tuned by selecting the appropriate length of tubing to connect the top and bottom F2MC tube pairs. The tuned multi-mode vibration absorber reduced vibration by 63% in the vertical mode and 65% in the lateral mode, whereas a comparable absorber designed to only treat the vertical mode reduced vibration by 68% in the vertical mode but only 42% in the lateral mode. The weight penalty from modifying the circuit to treat both modes was only 2% of the original absorber weight.New F2MC devices are proposed to augment the damping of both articulated and hingeless rotor blades. The proposed device for articulated blades dissipates energy by using an F2MC tube to pump fluid through an orifice. In contrast, the proposed device for hingeless blades uses an F2MC tube as part of a damped vibration absorber with a tuned inertia track. Models are derived for both conceptsto assess the feasibility of these dampers for representative articulated, stiff-inplane, and soft-inplane rotor blades. Parametric studies are conducted to understand how fluidic circuit design variables impact damper performance. For the articulated blade damper, increasing orifice resistance increases the damping ratio of the blade-damper system at the cost of increased F2MC tube oscillatory pressures. Increasing the accumulator capacitance reduces the F2MC damper stiffness and also increases the achievable damping, although the benefits diminish as the accumulator becomes larger. A stiff-inplane hingeless blade is modeled with beam finite elements, and F2MC damped absorbers are tuned for the first chordwise bending blade mode.Eigenvalue analysis predicts an increase in the first chordwise blade mode damping ratio from a baseline of 0.02 to a range of 0.059-0.066 with the F2MC damped absorber. Using a large accumulator in the absorber fluidic circuit improves the absorber effectiveness and reduces the inertance required for tuning the fluidic circuit to a specific frequency. Benchtop tests were conducted on a 9.7-foot diameter rotor integrated with a prototype articulated blade F2MC damper. Springs were attached to the blade to simulate centrifugal stiffness, and both frequency-domain and time-domain data were collected to assess damper performance. Model predictions of blade displacement and F2MC tube pressure were verified by experiments. Blade damping ratios in frequency-domain benchtop tests increase from a range of 0.054-0.064 with the orifice fully closed to a range of 0.300-0.335 with the orifice tuned to maximize damping. In time-domain benchtop tests, measured damping ratios increase from 0.062-0.090 with the orifice fully closed to a range of 0.298-0.404 with the orifice tuned. The benchtop tests and model verification are a key first step in developing functional F2MC damper technology for rotor blade applications.

Download or read book Vibration Reduction in Helicopter Rotors Using an Actively Controlled Partial Span Trailing Edge Flap Located on the Blade written by Thomas Alexander Millott and published by . This book was released on 1993 with total page 428 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Individual Blade Control for Vibration Reduction of a Helicopter with Dissimilar Blades written by Beatrice Roget and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book written by and published by . This book was released on 1937 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: O trabalho constitui repositorio de elementos basicos para o planejamento hidrico, calcado em dados reais e fidedignos, sem o qual nao se podem elaborar projetos de utilizacao racional de recursos de agua da bacia do Sao Francisco. Reune estudos hidrologicos de analise dos dados fluviometricos dos principais postos no rio Sao Francisco, a jusante de Tres Marias. Os dados origianis de campo, resultados de 39 anos de observacoes hidrologicas ao longo do grande rio, foram submetidos a uma analise de consistencia, levada a efeito por meio de correlacoes de cotas medias, diarias e mensais, entre cada posto e o posto mais proximo.

Download or read book Helicopter Vibration Suppression Using Simple Pendulum Absorbers on the Rotor Blade written by G. Alvin Pierce and published by . This book was released on 1982 with total page 148 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Vibration Reduction in Helicopter Rotors Using an Actively Controlled Partial Span Trailing Edge Flap Located on the Blade written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-08-04 with total page 428 pages. Available in PDF, EPUB and Kindle. Book excerpt: This report describes an analytical study of vibration reduction in a four-bladed helicopter rotor using an actively controlled, partial span, trailing edge flap located on the blade. The vibration reduction produced by the actively controlled flap (ACF) is compared with that obtained using individual blade control (IBC), in which the entire blade is oscillated in pitch. For both cases a deterministic feedback controller is implemented to reduce the 4/rev hub loads. For all cases considered, the ACF produced vibration reduction comparable with that obtained using IBC, but consumed only 10-30% of the power required to implement IBC. A careful parametric study is conducted to determine the influence of blade torsional stiffness, spanwise location of the control flap, and hinge moment correction on the vibration reduction characteristics of the ACF. The results clearly demonstrate the feasibility of this new approach to vibration reduction. It should be emphasized than the ACF, used together with a conventional swashplate, is completely decoupled from the primary flight control system and thus it has no influence on the airworthiness of the helicopter. This attribute is potentially a significant advantage when compared to IBC. Millott, T. A. and Friedmann, P. P. Unspecified Center NASA-CR-4611, A-94096, NAS 1.26:4611 NAG2-477; NGT-50444...

Download or read book An Analysis of the Flapwise Bending Frequencies and Mode Shapes of Rotor Blades Having Two Flapping Hinges to Reduce Vibration Levels written by George W. Brooks and published by . This book was released on 1960 with total page 34 pages. Available in PDF, EPUB and Kindle. Book excerpt:

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...

Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1995 with total page 704 pages. Available in PDF, EPUB and Kindle. Book excerpt: