Rotor System

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  ROTOR SYSTEM CONTENTS 1INTRODUCTION 1 2TYPES OF ROTOR 12.1Articulated Rotor12.2Gimbled Rotor22.3Teetering Rotor22.4Hingeless Rotor22.!earingless Rotor3 3ROTOR CONTROL 3 4BLADE RETENTION 34.1Articulated Rotor34.2Hingeless Rotor44.3!earingless Rotor4.3.1 !earingless Main Rotor4.3.2!earingless Tail Rotor 5ROTOR COMPONENTS .1Rolling Element !earings .2Elastomeric !earings .2.1#onical !earing .2.2Radial !earing$.2.3Snubber !earing$.2.4S%&erical !earing$.2.T&rust !earing$.3'ead('ag )am%er$.4Te*lon 'ined !earing+ #O,TE,TS -A,(21 /AGE 1  ROTOR SYSTEM 6ROTOR CONTROL SYSTEM 0 .1Main Rotor %%er #ontrol Sstem0 .2Main Rotor #ontrol Mec&anism0 .3Tail Rotor #ontrol Mec&anism 1 .4Materials11 7DESIGN AND CONSTRUCTION OF ROTOR BLADES 11$.1Articulated !lades12$.2Hingeless !lades12$.3!lades *or !earingless Rotor12$.4Structures o* Rotor !lades13$.4.1Metal Rotor !lades13$.4.2#om%osite Main Rotor !lades13$.4.3#om%osite Tail Rotor !lade14 8BLADE FOLDING 14+.1 Manual !lade olding1+.2Automatic !lade olding1 9FIGURE 1 TO 36 1$ TO 1 #O,TE,TS -A,(21  PAGE 2  ROTOR SYSTEM DESIGN Dr. K. M! #!$% U&#'D('#$) G(!(r* M!+(r ,D(-+!/R0$r) !+ R(-(r%  D(-+! C(!$r(!&#-$! A(r0!#$- L$(&B!+*0r(  5617 INTRODUCTION  A conventional rotorcraft is provided with main and tail rotors. The main rotor produces thrust, the vertical components of which lifts the helicopter and the horizontal component causes lateral movement of the helicopter. The tail rotor thrust is required to counter the reaction torque of the main rotor. By chanin the tail rotor thrust, the helicopter can !e yawed a!out the main rotor a is. The other three types of rotors are contra#rotatin, tandem and side !y side. $n contra#rotatin system, two identical rotors rotatin in opposite directions are placed one a!ove the other alon the same a is. $n tandem arranement, two main rotors are placed one !ehind the other. $n side !y side arranement, the two rotors are positioned alon the lateral a is. These three confiurations do not need tail rotors. A rotor system consists of rotor hu!, rotor !lades and upper control system. These systems are e plained in the su!sequent chapters. 2 TYPES OF ROTOR   %otor system can !e descri!ed as articulated, im!led, teeterin, hineless and !earinless. The !lades of an articulated rotor system are attached to the hu! with mechanical hines, allowin the  !lade to flap up and down and swin !ac& and forth 'lead and la( in the plane of the rotor disc. The  !lades of the hineless rotor are attached to the hu! without mechanical hines for flap or lead#la motion. Bearinless rotor employs a fle i!le structural attachment of the !lade. $n a teeterin rotor, the two opposite !lades are connected toether riidly and hined at the rotor centre. $n a im!led rotor, each  !lade is attached to a yo&e which is im!le mounted to the rotor mast. 2.1 Articulated Rotor  )ertical motion of the pitch lin& in response to swash plate tilt produces pitchin rotation at the pitch  !earin correspondin to cyclic pitch of the rotor. The la hine allows the !lade to move in the disc  plane. *ue to this hine, the steady la !endin moment at the !lade root is reduced. $ndividual !lade la dampers are required to provide enery dissipation to control the mechanical insta!ility associated with coupled rotor#airframe system. The riid !ody la natural frequency of this rotor !lade is usually +.2 to +. times the rotor speed.  ROTOR SYSTEMCHAPTER 1JAN 1 PA!E 1   ROTOR SYSTEM  Blade flappin freedom is provided !y the horizontal flappin hine located close to the rotor hu! to minimise the flap !endin of the rotor hu!. The natural frequency of articulated !lade is near resonance with rotor shaft speed. Aerodynamic dampin of the flappin !lade provides an accepta!le desin. The rotor should !e desined such that as the !lade flaps up, the pitch anle of the !lade remain the same or reduce. The &inematic couplin ratio !etween pitch anle and flap anle is defined as delta - .  eative delta - is required to improve sta!ility of the rotor. General arranement of an articulated rotor is flap hine first and ne t la hine and featherin !earins. Articulated rotors are used in Alouette#$$$, /#01, i#3, 4amov#25. 6iure#7 shows the arranement of this rotor. 2.2 !i #led Rotor  The !lade root moments are reacted at the yo&e, leavin the hu! undistur!ed. 8o&e should !e stiff to achieve !lade cantilever mode frequency reater than the rotor speed. General arranement is iven in fiure#2. 2.$ Teeteri%& Rotor  The teeterin hine allows only seesaw flap motion of the !lades. 6or rotor tilt, the !lades are forced  !y the trunion out of their ideal position !y special mechanisms connected to swash plate. E amples for teeterin rotor are Bell#2+1,272 9 222. General arranement of this rotor is shown in fiure#-. 2.' Hi%&ele(( Rotor  $n this type of rotor, no mechanical means are provided to allow chordwise or flapwise displacement of the !lades. The !lades are cantilevered from the rotor hu! which is attached riidly to rotor shaft. The  pitch anle of the !lade is chaned !y rotation of the !lade a!out the featherin a is. :yclic pitch input  provides control moment as result of !oth tiltin of the resultant lift vector and a moment actin at the hu!. The natural frequency of the first flapwise !endin mode fi es the offset of the equivalent flap hine. This is enerally 7.7 to 7.75. This provides an equivalent flap hine location of +.72%. The first lead#la  !endin natural frequency is ad;usted to around +.0 of rotor speed to eliminate round resonance. This  provides an equivalent lead#la hine location of +.75%. Precone of the !lades permit cancellation of steady lift moment due to centrifual force actin throuh the vertical displacement of the !lade a!ove disc plane. E amples of hineless rotor are found in B<#7+5, B4#770, =yn , /A#-15 *auphin, Bell # 72 and A=>. CHAPTER 2JAN 1 PA!E 2
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