The Art of the Helicopter John Watkinson - Karatunov.net

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Engines and transmissions 251 sliprings (2) and carbon brushes. The rotation of the resultant magnetic field causes flux reversals in the stationary magnetic circuit or stator surrounding the rotor. A winding (4) on the stator will produce an alternating voltage. This cannot be used directly in a system using a DC battery, but must be rectified using diodes (5). Clearly rectified alternating current is very irregular, and in practice a more constant current is obtained by mounting three sets of coils on the stator at 120 ◦ . This results in a three-phase alternator and if the output is rectified with six diodes as shown in Figure 6.40 the voltage is much more constant. The diodes are usually incorporated into the alternator body so that they may be cooled by fan. The output voltage is proportional to the field current. The voltage regulator (1) senses the system voltage, and if it is excessive, the field current is reduced. If it is too small, the field current is increased. As a result the system voltage will stabilize at a fixed value even if different loads are switched on and off. A voltage regulator failure could result in full field current being applied. In this case the alternator output current would be limited by the inductance of the windings. The battery would absorb much of this current and eventually boil dry. Some machines have an overvoltage sensor to cut out the alternator if this happens. Fig. 6.40 The alternator of a light helicopter is fitted with a three-phase rectifier to provide DC power.
252 The Art of the Helicopter Fig. 6.41 Electrical system of a light helicopter showing the position of the ammeter and the master switch. The state of the battery and alternator can be assessed using an Ampere meter, always abbreviated to ammeter, which is connected as shown in Figure 6.41. When the engine is stopped, electrical loads are supplied by battery, and current flows out through the ammeter which will register discharge (−). When the engine is started, the battery will have been partially discharged by the starter motor, and current will flow back from the alternator to charge the battery, registering charge (+). As the battery becomes recharged the magnitude of the charging current will fall and the ammeter will return to the null position where it will remain. If the ammeter displays a discharge with flight RPM, the alternator is not supplying enough current, it is switched off or some load has been applied beyond its capacity. A common explanation is that the belt driving the alternator has broken or is slipping. Figure 6.41 also shows that the master switch isolates all electrical devices from the battery (except the clock). In some cases the total electrical load is too large for a switch and a relay or contactor is used. This is a small version of the starter motor solenoid and is controlled by a small current from the switch itself. Generally only one wire feeds current to each device and current returns through the metal frame of the machine. If a failure of the insulation occurs somewhere in the electrical wiring, current could flow direct to the frame with little resistance to stop it. The high fault current could cause a fire in the wiring. This is prevented by splitting the wiring into sections and protecting each with a fuse or circuit breaker. In the case of a fault, the section containing the fault will carry an excessive current that melts the fuse or magnetically trips the breaker. The current is cut off and the fire is prevented. Equally importantly, the supply is maintained to all other sections; only devices using current from the affected section will lose power. A fuse is cheap and effective, but it has to be replaced if it fails. A fuse should only be replaced with one of the same rating. If a fuse is replaced with one of a higher rating, the protection it gives is lost and the wiring could burn in the case of a fault. A circuit breaker pops out when tripped and can be reset by finger pressure. In addition breakers can be used as switches by pulling them out. A tripped breaker does not always indicate
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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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Page 226 and 227: Engines and transmissions 211 a hot
Page 228 and 229: Engines and transmissions 213 Fig.
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Page 238 and 239: Fig. 6.16 The complex fuel system o
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Page 262 and 263: Fig. 6.37 Displays which may be see
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Page 270 and 271: Engines and transmissions 255 resul
Page 272 and 273: 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 300 and 301: Fig. 7.19 The turn indicator is spr
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Page 304 and 305: Fig. 7.24 Using RADAR signals. At (
Page 306 and 307: Fig. 7.27 Transducers used in signa
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Page 312 and 313: Fig. 7.33 The false codes created i
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Fig. 7.38 Producing two’s complem
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Fig. 7.40 A power-assisted hydrauli
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Fig. 7.42 An electro-hydraulic valv
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path axis and the flybar axis diver
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and autostabilization, it also prov
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Fig. 7.47 The Lockheed gyrobar syst
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Fig. 7.49 In the Lockheed AMCS, the
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Fig. 7.50 With the autopilot diseng
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or without the AFCS. Systems of thi
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Thus if a VOR receiver detected a 9
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7.29 Fault tolerance In feedback sy
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8 Helicopter performance 8.1 Introd
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Helicopter performance 325 column i
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Helicopter performance 327 Fig. 8.1
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Helicopter performance 329 to skid
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(a) (b) Helicopter performance 331
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Helicopter performance 333 Fig. 8.7
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8.7 Climbingand descending Helicopt
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Helicopter performance 337 In the c
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Helicopter performance 339 of its c
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8.10 Stability Helicopter performan
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Fig. 8.13 The origin of pitchup ins
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Helicopter performance 345 moment f
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9 Other types of rotorcraft Althoug
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Other types of rotorcraft 349 De la
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Other types of rotorcraft 351 Fig.
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Other types of rotorcraft 353 incre
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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 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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