The Art of the Helicopter John Watkinson - Karatunov.net

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Fig. 7.7 The remote indicator for a flux gate compass works by aligning its rotatable coil at right angles to the resultant flux generate by the three signals from the compass. At all other angles a voltage will be induced in the coil and this will be amplified to drive the motor. The coil also carries the direction indicator. order to cancel out deviation. In this case during swinging of the compass the goal is to find the correct values for these currents. It is also possible to remove the variation in the earth’s magnetic field and obtain a true heading rather than a magnetic heading. This requires a device called a differential transmitter. This contains two sets of windings at 120 ◦ , but one set can be turned by an operator control. If the two sets of windings are aligned, the relative amplitudes of the signals coming out will be the same as those entering, but if the secondary winding is turned, the output signals are effectively rotated. Thus if the differential transmitter is set to the amount of local magnetic variation, the remote display will read true heading. 7.6 Pressure instruments The instruments operated by pressure are the altimeter, the vertical speed indicator (VSI) and the airspeed indicator (ASI). Of these, the first two measure static pressure piped to the instruments from the static vents, whereas the ASI measures the dynamic pressure due to motion sensed as the pressure difference between the pitot head and the static vents. The necessary pipework is shown in Figure 7.8. The static vents are usually installed one each side of the fuselage in order to cancel any effect due to asymmetrical airflow. Each carries a mandatory placard stating that the vent is to be kept clear. The static pipes initially run upwards from the vents to prevent the entry of water. The pitot head is installed facing forward at some point where the airflow is reasonably undisturbed. It may be heated to prevent icing. The pitot should be checked for blockage as part of the pre-flight checks. It is good practice to cap the pitot with a suitable cover when the machine is on the ground, in which case the checks will include the removal and stowage of the cover. 7.7 The altimeter The altimeter is to all intents and purposes an aneroid barometer. The mechanism is shown in Figure 7.9. It contains a sealed capsule that is corrugated to allow it to flex. The capsule is evacuated, hence the term aneroid, and so ambient pressure attempts to crush it. The stiffness of the corrugations and a separate spring oppose the pressure. The capsule will expand as ambient pressure falls with rising altitude, and a system of Control 271
272 The Art of the Helicopter Fig. 7.8 The pipework involved with pressure-sensing instruments. These require a dynamic pressure feed from a forward facing port or pitot head and a static pressure feed typically from ports on the side of the hull. Fig. 7.9 The altimeter is essentially a barometer fitted with a control that can adjust the reference. This allows it to display altitude with respect to a pressure that has been input on the setting scale. Evacuated bellows (a) is sensing element in conjunction with spring (b). Rising air pressure collapses bellows and stretches spring. Falling air pressure allows the spring to expand the capsule. Capsule movement is amplified by lever (c) which operates the display pointers via a system of gears (d). Altimeter is compensated for ambient pressure by turning knob (e) according to subscale setting required on the card (f). Subscale knob is arranged to stretch or relax the spring slightly in order to give zero reading at a range of barometric pressures. The case of the instrument is connected to the static vent pipe. links and gears amplifies the small capsule expansion to move the pointer over a scale. The aneroid altimeter needs no power except to illuminate the scale. A conventional barometer measures absolute pressure for meteorological purposes, whereas the altimeter is required to measure the pressure difference between its present location and some reference pressure in order to compensate for barometric changes. The pressure difference is, however, displayed in feet (or metres). The reference pressure
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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 219 Fig.
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Page 238 and 239: Fig. 6.16 The complex fuel system o
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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 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 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
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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
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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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