The Art of the Helicopter John Watkinson - Karatunov.net

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9 Other types of rotorcraft Although the single main rotor helicopter with a tail rotor predominates, there are many other possibilities, sometimes more complex, which give advantages under certain conditions that outweigh the complexity. This chapter considers those possibilities. Some of these are flawed and have not been developed, whereas some were ahead of their time and deserve to be revisited. Some have been a success from the outset, whereas others have required a great deal of development. 9.1 The gyroplane The gyroplane was the first successful type of rotary wing craft and many of the constructional techniques used in early helicopters were developed there. The rotor is not mechanically driven in normal flight but instead the machine is driven forwards by a conventional aircraft engine and airscrew in either a tractor or pusher arrangement. Figure 1.10 showed that the tip path axis of the gyroplane rotor is tilted aft so that there is an upward component of the relative airflow along the rotor axis. Effectively the rotor is in translational autorotation. This was sometimes called automatic gyration hence the trade name ‘autogyro’ which Juan de la Cierva’s gyroplanes were given. The name is now used almost interchangeably with gyroplane. The aft tilt of the rotor means that the rotor thrust is not vertical and has an aft-facing component comparable to the drag of a wing, and similarly comprising profile drag and induced drag. At constant airspeed in level flight the thrust of the propeller is in equilibrium with the weight, hull drag and the rotor thrust. The propeller is doing work against the induced drag of the rotor and thus delivers power to produce lift. Driving the rotor in this way has the advantages that there is no mechanical transmission and no torque reaction. No tail rotor is necessary. However, the gyroplane is unable to hover because it needs constant upward inflow. If the airspeed is brought to zero, the machine will descend in a vertical autorotation. The gyroplane is an STOL aircraft that cannot stall and in the proper hands it is a very safe form of transport. However, in the absence of a tail rotor, yaw control at very low airspeeds is generally unsatisfactory and some accidents have occurred due to uncorrected yaw on touchdown. A generous amount of vertical tail area is required, for example the triple fins of the Air and Space Model U-18. As the rotor is driven in the same way as a wing, it is quite common for gyroplanes to include a fixed wing. This has the advantage of improving the load factor at high speeds. The inability of the gyroplane to hover is its greatest shortcoming. Before the helicopter was developed, the gyroplane occupied a niche in which fixed-wing aircraft
348 The Art of the Helicopter were unsuitable. Once the true helicopter was developed, the gyroplane could not compete and its market contracted dramatically. The basic problem is that the rotating wings introduce some of the high stress, the mechanical complexity and the high maintenance regime of the helicopter, for which there is no compensating ability to hover. In gyroplanes having pusher propellers, the visibility from the cockpit is truly excellent. It has had some success as a recreational machine and in applications such as aerial photography where slow stable flight is an advantage, but has effectively been eclipsed by the helicopter. The gyroplane rotor experiences the same advancing/retreating and gyroscopic phenomena as the helicopter, in fact most of these were first discovered in the gyroplane. One does, however, tire of reading quite erroneous descriptions of how Juan de la Cierva’s machines rolled over because of the lift difference between advancing and retreating blades. It is well established that the lift difference between advancing and retreating blades may result in a roll couple, but this is subject to the gyroscopic phase lagof90 ◦ that results in flapback. Clearly the advancing/retreating asymmetry was not the origin of de la Cierva’s difficulty. Figure 9.1 shows that de la Cierva’s early machines were basically aeroplanes having conventional aircraft controls but with a rotor added. The early rotors were hingeless and acted like gyroscopes. The problem was simply that when the conventional elevator was operated, a pitching moment was applied, but the rotor would precess this into a roll. Equally the operation of the ailerons would result in a rolling moment that would precess into a pitching motion. This was not a novel phenomenon; some World War I aircraft having rotary engines were notoriously gyroscopic and displayed precession whereby use of the elevator would cause an amount of yaw. Fig. 9.1 An early de la Cierva autogyro having wings and aircraft-type control surfaces.
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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
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Fig. 7.1 (a) A minimal control loop
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Fig. 7.2 (a) When attitude conditio
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fixed point in the hover despite ex
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(a) (b) Fig. 7.4 (a) The earth beha
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7.4 Compass errors A magnetic compa
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In most cases the machine will have
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Fig. 7.7 The remote indicator for a
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is set by the use of a control knob
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Fig. 7.11 The VSI (vertical speed i
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Fig. 7.13 A chaser system which all
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e modified if the gyro is in a movi
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must be in steady flight when the D
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arranged on opposite sides of the p
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Fig. 7.19 The turn indicator is spr
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7.17 Airflow-sensing devices The he
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Fig. 7.24 Using RADAR signals. At (
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Fig. 7.27 Transducers used in signa
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Fig. 7.28 In PCM or digital signall
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(a) Fig. 7.30 Using slicing and rec
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Page 318 and 319: Fig. 7.40 A power-assisted hydrauli
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Page 322 and 323: path axis and the flybar axis diver
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Page 338 and 339: 8 Helicopter performance 8.1 Introd
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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
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Page 356 and 357: 8.10 Stability Helicopter performan
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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
Page 374 and 375: (a) (b) Other types of rotorcraft 3
Page 380 and 381: Other types of rotorcraft 365 a low
Page 382 and 383: Other types of rotorcraft 367 the y
Page 386 and 387: Other types of rotorcraft 371 the r
Page 388 and 389: Other types of rotorcraft 373 For e
Page 394 and 395: Acceleration: and force, 22-5 and v
Page 396 and 397: Convertiplane, 11-12, 355-8 Bell-Bo
Page 398 and 399: tanks, 219-20 turbine engines, 237-
Page 400 and 401: Lockheed flybar system, 309-13 AMCS
Page 402 and 403: centrifugal stiffening, 71, 100 and
Page 404 and 405: tail/main rotor interaction, 173 te
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