The Art of the Helicopter John Watkinson - Karatunov.net

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Other types of rotorcraft 377 Fig. 9.29 UAV with coaxial rotors and a rotationally symmetrical body can attain high speeds by near-axial flight. be used for tasks in which there is a significant risk. Pilotless aircraft are often called drones and the term is also applied to pilotless helicopters. Small remotely controlled helicopters can be used for reconnaissance and may escape detection or prove very difficult targets if they are detected. Small helicopters have also been developed for crop dusting, notably in Japan. However, the limitations of the helicopter apply to small ones equally. Small fixed-wing drones can be launched from a simple ramp and recovered by parachute and will have greater range than the inefficient helicopter. Consequently drone helicopters are very rare indeed and fill extremely specialized niches. The drone helicopter may depend entirely on a remote pilot, or it may be entirely autonomous so that it can complete an entire mission automatically. Early drones were totally pilot controlled and had to stay within sight of the pilot. Subsequently the drone could relay a television picture of the view from the cockpit so that the drone could be flown out of sight. As electronics developed, it became possible to integrate the helicopter controls with autopilot functions and control the whole with a navigation system. This led to the UAV (unmanned air vehicle) concept that can be applied to the helicopter as well as it can to the aeroplane. In the absence of a pilot the UAV designer has much more freedom. The contrarotating coaxial rotor is popular as it avoids the use of very small and delicate tail rotors. Figure 9.29 shows a typical UAV having coaxial rotors. The hull is axially symmetrical and high speed forward flight can be achieved by tilting the whole machine over. Tilt-rotor UAVs have also been developed. 9.11 Radio control principles Radio control is simply the use of radio signals to relay the position of control sticks without any physical connection. In practical applications there will be a need to have several control channels simultaneously available and each one will need to be proportional, which means that small or large movements of the control stick will be remotely reproduced by the movement of a servo. The foundation of this technology was a patent by A.H. Reeves in the 1930s which showed that any type of information could be carried by varying the width or distribution of pulses. In a helicopter, the actual flying controls require four simultaneous
378 The Art of the Helicopter control channels. These will be lateral cyclic, fore-and-aft cyclic, collective and tail rotor. Subsidiary controls will be needed to start the engine and rotors and to adjust RRPM. In an analog or pulse width modulation (PWM) system, each control is connected to a transducer such as a potentiometer or LVDT (see Chapter 7) that controls the length of a pulse. There will be one pulse for each control channel, followed by a reset or synchronizing pulse. The pulse signal is used to amplitude or frequency modulate a carrier wave in a radio transmitter. A receiver tuned to the transmitter will be able to demodulate the carrier signal and recover the pulse train. The reset pulse sets a pulse counter to zero. Each control pulse is then counted so that each pulse is routed to the correct channel. A PWM system is analog because the infinitely variable position of a control stick results in an infinitely variable pulse length. In practical systems the resolution of the system may be reduced because of noise in the radio link. The digital or PCM (pulse code modulation) system converts the position of each control stick to a binary number of fixed word length. In an eight-bit system, there can be 256 different numbers. The binary numbers from the various control channels are multiplexed into a single transmission in which the number corresponding to each channel has a fixed place in the sequence. The start of the sequence is denoted by a fixed synchronizing pattern.
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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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Fig. 7.33 The false codes created i
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Fig. 7.35 In a pure binary system,
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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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Page 348 and 349: Helicopter performance 333 Fig. 8.7
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Page 362 and 363: 9 Other types of rotorcraft Althoug
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Page 366 and 367: Other types of rotorcraft 351 Fig.
Page 368 and 369: Other types of rotorcraft 353 incre
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Page 372 and 373: Fig. 9.7 The Bell-Boeing Osprey til
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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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