The Art of the Helicopter John Watkinson - Karatunov.net

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and autostabilization, it also provides power-assisted cyclic control, with the penalty of an increase in drag due to the paddles. The Hiller control system incorporates another unusual feature in that the swashplate works in reverse to that of a conventional helicopter. Figure 7.46(a) shows that in order to simplify the control runs, Hiller took an arm from the non-rotating part of the swashplate straight down to the pilot. The pilot would move the end of this arm in the same way as he would a conventional floor-mounted cyclic stick. In order, for example, to apply aft cyclic, the pilot would pull the end of the arm towards himself. This, however, had the effect of tipping the swashplate down at the front. Hiller solved this problem by connecting the rotating part of the swashplate to the control rotor with a scissors linkage that reverses the action. Figure 7.46(b) shows that when the swashplate tilts forwards, the control axis of the control rotor tilts backwards as required. When the overhead control was replaced by a conventional floor-mounted cyclic in later machines, the reversing swashplate was retained and the cyclic pushrods were simply rigged to make the swashplate move in the correct sense. It is interesting that many examples of the Bell 47 and the Hiller Raven are still flying, although the Bell 47 first flew in 1943 and the Hiller in 1948. The longevity of these designs is testimony to the original concept. The flybar was also adopted in the UH-1 Iroquois, better known as the ‘Huey’ which itself achieved legendary status. 7.26 The Lockheed systems The Bell and Hiller systems are ideal for two-bladed teetering rotors, but it is not easy to apply them to rotors with a larger number of blades. Irven Culver at Lockheed developed stabilizing systems to work with rotors having any number of blades. Culver had rightly concluded that flapping and dragging hinges were not necessary and set out to build hingeless rotors. Without flapping hinges, the cyclic response of a rotor can be extremely rapid and exert huge forces on the hull. Gyroscopic stabilization was essential to contain control response. The Lockheed CL-475 was a flying test bed that sported a variety of rotors and stabilization systems. Initially a two-bladed rotor was used having no flapping hinges and no collective pitch control. Lift was controlled by rotor speed. Cyclic pitch was provided by a single span-wise hinge. A flybar was mounted transversely to the rotor. This superficially resembled a Bell flybar, but only because of the streamlining of the tip weights. The attitude of the flybar with respect to the mast controlled the cyclic pitch of the rotor and the pilot’s cyclic stick applied forces to the flybar via springs and the swashplate to make it precess. As the main rotor changed its attitude, pitch link loads would make the gyro bar follow, serving the same function as the dampers in the Bell system. A second gyro stabilized the yaw axis by controlling the tail rotor pitch. In the Bell system some of the travel of the flybar is lost in the mechanical mixer needed to add in the cyclic control from the swashplate. The direct control of the main rotor by the gyro in the Lockheed system allowed greater loop gain and was thus more stable. However, the two-bladed hingeless rotor suffered from excessive 2P hop in forward flight and work concentrated on hingeless rotors with more than two blades. In 1960 a new three-bladed rotor was designed, again having no flapping hinges. Initially, each blade had its own single-ended flybar known as a gyrobar. This is shown in Figure 7.47. In the gyrobar system, the feathering axis is not parallel to the blade, but instead the feathering axis is swept back with respect to the blade. As was shown in section 4.7, this causes coupling between the flapping and feathering axes. If the rotor Control 309
310 The Art of the Helicopter Fig. 7.46 (a) Early Hiller helicopters had an arm leading directly from the swashplate to the pilot. (b) A reversing mechanism is needed between the swashplate and the flybar to allow the control system of (a) to work in the correct sense.
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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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Engines and transmissions 257 The p
Page 274 and 275: Fig. 7.1 (a) A minimal control loop
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Page 282 and 283: 7.4 Compass errors A magnetic compa
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Page 286 and 287: Fig. 7.7 The remote indicator for a
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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 322 and 323: path axis and the flybar axis diver
Page 326 and 327: Fig. 7.47 The Lockheed gyrobar syst
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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
Page 372 and 373: 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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