The Art of the Helicopter John Watkinson - Karatunov.net

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path axis and the flybar axis diverge, which must result in cyclic feathering. This will counter the disturbance and restore the attitude of the disc. The resultant helicopter is very stable because the action of the flybar resists disturbances to the disc attitude. The action of the flybar when the cyclic control is applied is also beneficial. The mixing levers also allow the flybar to oppose the cyclic input from the swashplate. If the swashplate is tilted to initiate a roll, the blades will cyclically be feathered through the mixing levers and the roll will commence. However, the flybar is measuring the roll rate, and the flybar axis will diverge from the shaft axis. In fact the flybar axis lags behind the shaft axis. This divergence applies an opposite feathering action to the swashplate. For a given application of cyclic control, the blade cyclic feathering will be nulled for a given angle of divergence between the flybar axis and the mast axis. As this divergence is proportional to the roll rate of the helicopter, it follows that the roll rate actually achieved is proportional to the swashplate tilt. Thus the rotor system is turned into a rate control whose following rate is determined by the inertia of the flybar and the viscosity of the dampers. As the flybar axis can only roll slowly, the following rate of the rotor to the cyclic controls is reduced, giving the effect of a heavier rotor but without the actual mass. The response of the rotor can be adjusted by changing the degree of damping. If the dampers are made more viscous, the following rate increases because the flybar is more powerfully tied to the shaft axis. The action of the flybar can be analysed by treating it as a servo. Figure 7.44 shows that the swashplate supplies the desired roll rate, and the flybar measures the actual Fig. 7.44 The Bell flybar acts like a servo, adjusting cyclic pitch to obtain the desired roll rate. If the flybar is tilted with respect to the mast, the dampers will gradually bring it back into alignment. The rate of response to the controls is proportional to the degree of damping. Control 307
308 The Art of the Helicopter roll rate. The mixing levers subtract the actual roll rate from the desired roll rate to produce the roll rate error. This applies cyclic feathering in the sense that reduces the error. Thus the error is kept small such that the actual roll rate is equal to the desired roll rate. 7.25 The Hiller system The second major flybar development was due to Stanley Hiller and this was used in many of the early Hiller machines. The main difference between the Young and the Hiller systems is that in the Hiller the flybar has aerodynamic properties as well as gyroscopic properties and so is properly called a control rotor. Figure 7.45 shows that the control rotor is mounted transversely on a bearing as before, but there are two major contrasts with the Young system. First, the Hiller control rotor has full authority over the cyclic pitch of the main rotor, such that the control rotor axis completely determines the control axis of the main rotor. Second, the Hiller control rotor has small blades or paddles and it has feathering bearings. Pitch control arms on the control rotor lead to the swashplate so that cyclic pitch control of the control rotor is obtained. The pilot’s cyclic control actually flies the control rotor, whose attitude will then be followed by the main rotor. The following rate of the control rotor can be made as slow as required by changing its Lock number, i.e. the relationship between the mass of the paddles and their lifting area. Thus as before, relatively light blades can be made to respond relatively slowly. The control rotor will not respond rapidly to gusts and so the attitude of the machine is stabilized as it is in the Young system. The Hiller system has the advantage that the pilot only has to produce enough force to feather the control rotor. The control forces to feather the main rotor are created by lift on the paddles. Thus not only does the Hiller system provide following rate control Fig. 7.45 In the Hiller system, the flybar is gyroscopic as in the Bell system, but damping is aerodynamic. The flybar also provides power assistance through the application of cyclic pitch to the paddles.
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The Art of the Helicopter
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The Art of the Helicopter John Watk
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Contents Preface xi Acknowledgement
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4.12 Feathering 134 4.13 Pitch cont
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8.5 Power management 326 8.6 Flying
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xii Preface reader to make sense of
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1 Introduction to rotorcraft 1.1 Ap
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Introduction to rotorcraft 3 Fig. 1
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Introduction to rotorcraft 9 for th
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Introduction to rotorcraft 11 Fig.
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(a) (b) (c) (d) Introduction to rot
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Fig. 1.18 The contra-rotating coaxi
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Fig. 1.20 The structure of a light
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Introduction to rotorcraft 19 wings
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Introduction to rotorcraft 21 a rot
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Technical background 23 Fig. 2.1 At
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Fig. 2.3 Effect of force on velocit
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C Force A E Resultant (a) Force B (
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(a) (b) Technical background 29 Fig
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Technical background 31 Fig. 2.11 A
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Technical background 33 Fig. 2.12 (
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Technical background 35 If the volu
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Fig. 2.16 The definition of a radia
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Technical background 39 force would
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Technical background 41 Figure 2.20
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Technical background 43 force where
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Technical background 45 the cosine
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Technical background 47 Fig. 2.28 F
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Technical background 49 Fig. 2.30 T
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Technical background 51 centripetal
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2.17 The gyroscope Technical backgr
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Technical background 55 of oscillat
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Technical background 57 the inertia
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Technical background 59 shut down a
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3 Introduction to helicopter dynami
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Introduction to helicopter dynamics
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(a) (c) (b) Introduction to helicop
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(a) (b) (c) (d) Introduction to hel
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Fig. 3.23 Conditions for hover and
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(a) (b) Introduction to helicopter
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(a) (b) Introduction to helicopter
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4.1 Introduction 4 Rotors in practi
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(a) (b) Rotors in practice 119 Fig.
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Rotors in practice 121 Designers of
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Rotors in practice 123 opposite occ
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Rotors in practice 125 Fig. 4.6 (a)
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Rotors in practice 127 assembly tha
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Rotors in practice 129 Pitch change
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× T=c× D Rotors in practice 131 F
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Rotors in practice 133 In a real he
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Rotors in practice 135 Fig. 4.15 Va
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(a) (b) Rotors in practice 137 Fig.
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Rotors in practice 139 Fig. 4.18 Th
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Rotors in practice 141 swashplate a
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Fig. 4.23 A fixed-pitch tilting hea
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Rotors in practice 145 Fig. 4.25 Bl
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Rotors in practice 147 Fig. 4.27 Ef
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Rotors in practice 149 Fig. 4.29 (a
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Rotors in practice 151 concerned ar
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Rotors in practice 153 and lag damp
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Rotors in practice 155 disappears a
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(d) (e) (f) Rotors in practice 157
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Rotors in practice 159 hull and a v
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Rotors in practice 161 Fig. 4.35 (C
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Rotors in practice 163 Abrasion is
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Rotors in practice 165 There are so
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eing more visible to ground personn
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otates the rod in the screw thread.
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In the case of a rotor having offse
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The tail rotor designer is faced wi
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Fig. 5.5 A right-side wrong-directi
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centre of mass. The solution was to
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safe to start the rotors. However,
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Fig. 5.10 Tail plane locations: (a)
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Fig. 5.12 (a) A top-mounted fin is
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Fig. 5.14 (a) Main rotor lateral ro
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long. The cross-section of the duct
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drag. However, the slots are emitti
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6 Engines and transmissions The pow
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Engines and transmissions 193 the D
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(a) (b) Engines and transmissions 1
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(a) (b) (c) Engines and transmissio
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Fig. 6.5 A typical horizontally opp
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Engines and transmissions 201 the v
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Engines and transmissions 203 The c
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6.9 The oil system Engines and tran
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Engines and transmissions 207 (non-
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(a) (b) Engines and transmissions 2
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Engines and transmissions 211 a hot
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Engines and transmissions 213 Fig.
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Engines and transmissions 215 In wa
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Engines and transmissions 217 is a
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Engines and transmissions 221 own t
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Fig. 6.16 The complex fuel system o
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Engines and transmissions 233 and c
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Engines and transmissions 237 Sensi
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Engines and transmissions 243 the A
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Fig. 6.37 Displays which may be see
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Engines and transmissions 251 slipr
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Engines and transmissions 253 a fau
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Engines and transmissions 255 resul
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Page 274 and 275: Fig. 7.1 (a) A minimal control loop
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Page 278 and 279: fixed point in the hover despite ex
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Page 286 and 287: Fig. 7.7 The remote indicator for a
Page 288 and 289: is set by the use of a control knob
Page 290 and 291: Fig. 7.11 The VSI (vertical speed i
Page 292 and 293: Fig. 7.13 A chaser system which all
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Page 298 and 299: arranged on opposite sides of the p
Page 300 and 301: Fig. 7.19 The turn indicator is spr
Page 302 and 303: 7.17 Airflow-sensing devices The he
Page 304 and 305: Fig. 7.24 Using RADAR signals. At (
Page 306 and 307: Fig. 7.27 Transducers used in signa
Page 308 and 309: Fig. 7.28 In PCM or digital signall
Page 310 and 311: (a) Fig. 7.30 Using slicing and rec
Page 312 and 313: Fig. 7.33 The false codes created i
Page 314 and 315: Fig. 7.35 In a pure binary system,
Page 316 and 317: Fig. 7.38 Producing two’s complem
Page 318 and 319: Fig. 7.40 A power-assisted hydrauli
Page 320 and 321: Fig. 7.42 An electro-hydraulic valv
Page 324 and 325: and autostabilization, it also prov
Page 326 and 327: Fig. 7.47 The Lockheed gyrobar syst
Page 328 and 329: Fig. 7.49 In the Lockheed AMCS, the
Page 330 and 331: Fig. 7.50 With the autopilot diseng
Page 332 and 333: or without the AFCS. Systems of thi
Page 334 and 335: Thus if a VOR receiver detected a 9
Page 336 and 337: 7.29 Fault tolerance In feedback sy
Page 338 and 339: 8 Helicopter performance 8.1 Introd
Page 340 and 341: Helicopter performance 325 column i
Page 342 and 343: Helicopter performance 327 Fig. 8.1
Page 344 and 345: Helicopter performance 329 to skid
Page 346 and 347: (a) (b) Helicopter performance 331
Page 348 and 349: Helicopter performance 333 Fig. 8.7
Page 350 and 351: 8.7 Climbingand descending Helicopt
Page 352 and 353: Helicopter performance 337 In the c
Page 354 and 355: Helicopter performance 339 of its c
Page 356 and 357: 8.10 Stability Helicopter performan
Page 358 and 359: Fig. 8.13 The origin of pitchup ins
Page 360 and 361: Helicopter performance 345 moment f
Page 362 and 363: 9 Other types of rotorcraft Althoug
Page 364 and 365: Other types of rotorcraft 349 De la
Page 366 and 367: Other types of rotorcraft 351 Fig.
Page 368 and 369: Other types of rotorcraft 353 incre
Page 370 and 371: Other types of rotorcraft 355 and c
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Fig. 9.7 The Bell-Boeing Osprey til
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(a) (b) Other types of rotorcraft 3
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Other types of rotorcraft 361 Fig.
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Other types of rotorcraft 365 a low
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Other types of rotorcraft 367 the y
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Other types of rotorcraft 371 the r
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Other types of rotorcraft 373 For e
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Acceleration: and force, 22-5 and v
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Convertiplane, 11-12, 355-8 Bell-Bo
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tanks, 219-20 turbine engines, 237-
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Lockheed flybar system, 309-13 AMCS
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centrifugal stiffening, 71, 100 and
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tail/main rotor interaction, 173 te
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