helicopter ground resonance

Helicopter Ground Resonance. Ground resonance can occur in model helicopters, full size helicopters and everything in between. An airplane started to taxi in front of the helicopter. Ground Resonance Ground resonance is one of the most dangerous situations a helicopter pilot can face. These results are displayed graphically and reveal the dependence of the unstable range on rotor and fuselage damping. Helicopter ground resonance is a highly non-linear dynamic problem involving complex interactions between the various parts of a helicopter and constituting a major design consideration. The lifting procedure involves a periodic switching linear-time-invariant piecewise . Ground resonance is an imbalance in the rotation of a helicopter rotor when the blades become bunched up on one side of their rotational plane and cause an oscillation in phase with the frequency of the rocking of the helicopter on its landing gear. . With the collective full down, I rolled the throttle to idle to try and get rid of ground resonance. Simon Newman has brought this third edition completely up to date with a full new set of illustrations and imagery. Helicopter ground resonance is a self exited dynamic instability, which may occur when helicopter is in contact with the ground. The air and ground resonance instabilities of hingeless rotor helicopters are examined on a relatively broad parametric basis including the effects of blade tuning, virtual hinge locations, and blade hysteresis damping, as well as size and ... 1] and [Ref. Written at a basic level, this text starts from first principles and moves fluidly onward from simple to more complex systems. AMI Ground Resonance 10272016.mp4 Page 3 of 4 "Ground resonance has not been "solved", and is still a big concern for anyone who flies a helicopter with a fully-articulated rotor system. New material is included on blade tip design, flow characteristics surrounding the rotor in forward flight, tail rotors, brown-out, blade When ground resonance occurs, a helicopter becomes unbalanced when its skids or wheels touch the ground, according to a 2012 Federal Aviation Administration handbook for helicopter instructor pilots. In this paper the phenomenon is studied on a spatial helicopter model of six degrees of body freedom. The ground resonance event separated the transmission/rotor system, the engine from the fuselage, and one main rotor blade impacted the cabin. 0000065875 00000 n My engine RPM was too low, as was my collective, to pick the helicopter up off the ground to restore the rotor blades to their correct phase in time. A model of helicopter with a minimum number of degrees of . It's not nearly as obvious as the video linked, but at about 40s you . Found inside – Page 59Ground resonance can be recognized as a rocking movement around the roll axis of the helicopter . This movement progresses very rapidly to the point of destruction in a few seconds , if immediate corrective action is not taken . It's caused by resonance between an oscillation in the main rotor and an oscillation of the helicopter on it's landing gear, typically in a poorly maintained helicopter. A similar problem may occur immediately after landing. The cyclic lag modes (lc and (is produce a wobble . Traditionally, ground resonance is mitigated by using passive lead-lag dampers that provide sufficient in-plane damping. 0000068953 00000 n This dynamic instability results from lag motions of the rotor blades coupling with airframe degrees of freedom, while the helicopter is in ground contact. Found inside – Page 12Ground Resonance Unbalanced Rotors Can Give You a Fit “ Helicopters are different from airplanes , " as a network newscaster He had noticed a low oleo strut on the rental helicopter he was about once explained . When in contact with the ground (at touchdown), a helicopter with an articulated rotorhead (more precisely, a rotorhead with drag hinges) can get into resonance mode, which has the potential to destroy the aircraft. Ground resonance is primarily a problem in a fully-articulated rotor system. . The pilot, in part, stated:\"To avoid my downwash disturbing the airplane, or his prop wash from disturbing me, I set the helicopter back onto the ground as a courtesy. The rotor includes a freely tiltable rotor head mounted on a non-rotatable universal joint having an outer gimbal ring and an inner ring carried by a pylon. Maybe it's just a plastic Ozzy thing. When ground resonance occurs, a helicopter becomes unbalanced when its skids or wheels touch the ground, according to a 2012 Federal Aviation Administration handbook for helicopter instructor pilots. Technical issue on maintenance flight and happened just North of the airport. B3 incident not ground resonance at all. 0000044017 00000 n the lag motion) and the helicopter fuselage motion. 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INTRODUCTION Ground resonance (GR) is an instability that can occur during landing or take-off conditions when a helicopter is in contact with the ground. If one is landing the helicopter, this is a frustrating condition because it stops the pilot from accomplishing his initial goal of alighting on the surface of the earth. A damping mechanism is disclosed for damping the oscillations of the rotor hub which are coupled with periodic motions of the fuselage when on the ground, known as ground resonance, and a waddle when in the air. Flying a helicopter (full size or model) from a hard landing surface will aggravate the resonance because the harder surface tends to impart more energy to the helicopter. Ground resonance occurs when the low frequency lag mode of the rotor (in the non-rotating frame) coalesces with a fuselage or body frequency. Show Printable Version; 9th May 2021, 07:04 PM #11. 0000067129 00000 n Recent works have studied ground resonance in helicopters under the aging or damage effects. 0000042588 00000 n 0000068974 00000 n Ground resonance is a divergent oscillation of the helicopter usually in lateral motion, rolling left and right. (graphics to be added) videos of ground resonance. The influence of stiffness dissimilarities between blades on the stability of the ground resonance phenomenon is determined through . Contents: Coriolis coupled bending vibrations of hingeless helicopter rotor blades; Scale effects in the bending vibrations of helicopter rotor blades; The influence of pitch and twist on blade vibrations; The dynamics of blade pitch ... A new design undergoing testing may encounter severe vibration while it is on the ground, preparing for takeoff. What exactly is the spin-up leve. Airport manager Randy Sharkey said the shaking apparently was caused by ground resonance, a phenomenon that occurs when a helicopter's rotors get out of synch while it is on the ground. 2]. Helicopter ground resonance is a self exited dynamic instability, which may occur when helicopter is in contact with the ground. Model helicopters are plagued by ground resonance because they usually lack lead-lag dampeners in the rotor system and almost exclusively have rigid landing gear structures. This is ground resonance. 0000067762 00000 n When a rolling motion (left to right tilting) is imparted to the helicopter and thus the rotor mast, the rotor disk is accelerated laterally to the left or right. The effective massex an rriy)d s an (md the effective stiffness (Kx and Ky) of the helicopter are determind so as to Proceedings of the N. E. Zhukovskii Central Aerohydrodynamic Institute [in Russian] (1970). In order to accurately predict the dynamic instability of helicopter ground resonance, a modeling and simulation method of helicopter ground resonance considering nonlinear dynamic characteristics of components (rotor lead-lag damper, landing gear wheel and absorber) is presented. In the case of vibration testing, the stimulus is the shaker vibrating the product. This resonance can then destroy the aircraft in a short amount of time. It is found that in general there exist six regions of . 0000043410 00000 n A. In the case of a take-off resonance event, this is the natural tendency. Helicopter ground resonance. Solution of real and imaginary equations of ground resonance, for articulated rotor (lag frequency ν ζ 2 = 0.22+ (0.265Ω) 2 ) on symmetric support; frequency (in fixed system) as a function of rotor So the angle between each blade is 120°. Ground resonance is mitigated in full size helicopters by employing the use of damping vibration isolators to attach the landing gear to the airframe. It basically is an out-of-balance condition in the rotor system of a helicopter on the ground that rapidly increases in frequency until the The American Helicopter Society listed the characterization of air and ground resonance as one of the top twenty advances in vertical flight history [7]. Day visual flight rules (VFR) conditions prevailed for the flight, which operated on a company VFR flight plan. 0000065854 00000 n Thread Tools. This is a destructive harmonic vibration caused by a dynamic reaction of the rotor blades to the lateral motion of the helicotper. Ground resonance can destroy a helicopter. Ground resonance is a divergent oscillation of the helicopter usually in lateral motion, rolling left and right. C. Ground Resonance D. Retreating Blade Stall E. Low Rotor RPM F. Low G/Mast bumping G. LTE. Modern helicopters avoid ground resonance by using dampers on the blades and on the landing gear. over the nose and tail of the helicopter), they will develop a slight lead or lag orientation to thier normal state. 1. Miscellaneous Flight Requirements Interestingly, the way to deal with ground resonance is just to take off. Ground resonance is an aero-mechanical instability in helicopters that use soft in-plane rotors. He found the primary modes likely to be excited in the normal operation of the rotorcraft were the hinged It is most likely if the helicopter has a fully articulated rotor . Now what is ground resonance? L. N. Grodko, Ground Resonance of Helicopter on Its Run. The equations of motion developed by R. P. Coleman have been evaluated for a particular helicopter configuration and a large number of different combinations of rotor and fuselage damping. H�\U P�G�^w�3����� �r��(Q2�\���F���Q��x���5�f0Ѩq7�Fw��׈V4Y�k�5%N��n%;_�S��_w���A |�#�DǍ6v5�P�1����U�/��O�]f��~q�]̇�\�%�����`��/����kjl��`�s�����zew����#��n���ͩK�?��& 0��t�S���4��������wy�b�4gɔ~�F.~�|2\�3˘7�V5��fLq]��b.ݙ��J�� �:�*t�U���w�3T7Sa��+����> k�Bq�bq ���2P��8�O�s�(lH�6�QRa!Ѐ�0�qH�ej��8��?��[���ez{y#۱��i��Nv��W�zX����ڄ�����h�nX���E8���3�\��|��`�R�Rz*�c'�R:[�1׸�j'�y�V�P�n�7�gE��+��e�x�EO�l�+��. It basically is an out-of-balance condition in the rotor system of a helicopter on the ground that rapidly increases in frequency until the helicopter shakes itself apart. In these systems, ground contact can jolt the aircraft and produce a shock wave that can resonate in the aircraft. The correct answer is "Close the throttle and slowly raise the spin-up lever." Am I just reading this really really wrong? google_ad_client = "pub-7150318280681240"; google_ad_slot = "7456372054"; KAMOV Company has developed software to simulate a coaxial rotor aeroelasticity [1,2,3,8,9,10]. The pilot indicated that he picked the helicopter up into a two-foot skid height hover. Robert Coleman, the forefather in the field of helicopter mechanical instability was the first to address the problem of ground resonance [Ref. However, these dampers because of their passive nature cannot adapt to all operating conditions. 0000001520 00000 n Answer (1 of 4): Indeed theory wise ground resonance should only be limited to fully articulated rotor system. The effect is similar to the behavior of a washing machine when the clothes are concentrated in one place during the spin cycle. : anisotropic rotor). On the knowledge exam, there's a question: If the pilot experiences ground resonance during rotor spin-up, what action should the pilot take? A way to picture this is drop a quarter on a table and watch it waller around before it stops. and ground resonance. Classic theory of helicopter ground resonance studies the phenomenon on a planar model obtained by reducing the dynamic parameters of the full helicopter into the plane of rotation. Ground resonance is an instability phenomenon in the helicopter-ground system that can cause serious damage to the helicopter in a very short time. (iii) The helicopter in-ground effect at a height consistent with normal takeoff procedures; and (2) The hovering ceiling determined under paragraph (a)(1) . The pilot said that he had experienced at least two incipient ground resonance events with this helicopter during the previous 18 months. Through practical examples and illustrated case studies, supported by all the relevant theory, this primer text provides an accessible introduction which guides the reader through the theory, design, construction and operation of ... Imagine if you cou. Please let us know if this was helpful information or if you have suggestions, comments or other questions you would like answered. Passive suppression of helicopter ground resonance using nonlinear energy sinks attached on the helicopter blades Journal of Sound and Vibration, Vol. 0000042387 00000 n As an addition to slope landing studies in the past and investigations of non-linear landing gear effects, this work focuses on a . The instability is introduced by unfavorable coupling of hub motion in-plane with low frequency lag mode and identified by negative modal damping on the corresponding de-gree of freedoms. Simon Newman has brought this third edition completely up to date with a full new set of illustrations and imagery. a book basic helicopter aerodynamics an account of first principles in the fluid mechanics and flight dynamics of the . google_ad_height = 90; . Helicopter Operations including hot weather operations, running takeoffs, slope operations, confined area operations, pinnacle operations, quick stops, settling with power, tail rotor failure, autorotation, and ground resonance For example, the landing gear may have shock absorbed struts. The passive device consists of a set of essential cubic nonlinear absorbers named Nonlinear Energy Sinks (NES) each of them positioned on a blade. Elastic deformation and out of phase lagging motion of the rotor blades during rotor rotation lead to the oscillation of the rotor centre of gravity around the rotor rotation axis. This paper discusses the semi-active control of helicopter ground resonance using magnetorheological (MR) damper. It is divergent because when ground resonance occurs, the energy of the spinning rotor and the condition of imbalance aggravates the . View Profile View Forum Posts TopicToaster Silver Subscriber. google_ad_width = 728; A destructive instability known as ground resonance can occur when a helicopter is on the ground. The Rotorcraft Flying Handbook is designed as a technical manual for applicants who are preparing for their private, commercial, or flight instructor pilot certificates with a helicopter or gyroplane class rating. The safety report, he said, seemed to show some indication of "ground resonance," a phenomenon caused in part by an imbalance within the rotor system that can cause helicopters to shudder . This thesis develops a technique for formulating the full nonlinear equations of motion for a coupled rotor-fuselage system utilizing the symbolic processing software MAPLE(registered). Jump to page: Results 11 to 20 of 29 Thread: Helicopter ground resonance. The helicopter sustained substantial damage. The helicopter will now join the Perseverance rover . Note: There is no collision between the helicopter and the passing general aviation aircraft.On June 2, 2012, about 1135 mountain daylight time, a Schweizer 269C helicopter, N2196F, entered ground resonance when it set down on the ramp at the Rocky Mountain Metropolitan Airport (BJC), near Denver, Colorado. Ground resonance is most likely to develop when (A) there is a sudden change in blade velocity in the plane of rotation. 0000001667 00000 n As a result of this and a similar accident, the helicopter manufacturer has committed to revising the overhaul manual to include testing procedures and criteria for overhauled landing gear dampers. coupling of the blades motion in the rotational plane (i.e. Prediciting ground resonance is difficult but possible. 0000066517 00000 n dynamic characteristics of components (rotor lead-lag damper, landing gear wheel and. Found inside – Page 196Blade lags back Blade lags forward Center of mass Progressing Regressing 22 Figure 4.18 Ground resonance is a potentially catastrophic aeromechanical instability of the rotor resulting from an out - of - pattern in - plane lead - lag ... The numerical integral method is used to calculate the transient . Zherebtsov, Dynamic Stability of the Main Rotor of a Helicopter, Taking into Account the Elexibility of Its Blade. Found inside – Page 3-12For example, on the Bell 206, you should accelerate the rotors through 50-60% RRPM because the old one-piece tail rotor drive shaft (when fitted) will start to whip: GROUND RESONANCE On the ground, vibrations will collect through the ... Just as well the internet is a recent thing and older skeletons remain in the closet? Ground resonance is a vibration phenomenon that occurs at certain rotor speeds when the helicopter is on the ground. L Sanches, G Michon, A Berlioz, D Alazard. helicopter rotor systems. This paper investigates the passive control of a rotor instability named helicopter Ground Resonance (GR). For the modelers, the only remedies are to tighten the blade grips a bit, effectively creating more of a lead-lag dampening force, to encompass the helicopter skids with rubber tubing or foam padding, or to fly from a surface with more forgiving characteristics such as soft dirt. What is "Settling with Power"? Helicopter ground resonance phenomenon with blade stiffness dissimilarities: experimental and theoretical developments.

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