The Art of the Helicopter John Watkinson - Karatunov.net

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Engines and transmissions 221 own tanks, but this can be minimized by filling the tanks before leaving the machine overnight. Water does not readily mix with fuel and it is denser, so it will be found at the bottom of tanks. The point where the engine feed is taken from the tank is slightly above the lowest point of the tank so that fuel is drawn from above any water that may settle out in the tank. As a result there will always be a quantity of unusable fuel in the tank, typically about a gallon. The lowest point of the tank is fitted with a drain. This is a spring-loaded valve which is normally closed but which can be pushed open momentarily by hand. Part of the pre-flight check procedure is to operate the tank drains and to catch the fluid that comes out in a transparent container. Any water in the tank will come out first and a clear boundary will be seen in the container between the water and the fuel once all the water has come out. The tanks are also fitted with air vent plumbing to allow air to enter as fuel is used. In the absence of a vent atmospheric pressure would crush the tanks as the fuel was pumped out. The fuel pickup pipes from the two tanks go to the fuel shut-off valve. This is in the engine compartment, but operated by a rod passing through the firewall to a control often mounted near the pilot’s shoulder. The main fuel line runs down from the fuel shut-off valve through the electric boost pump to the main filter; also known as a strainer. The filter contains a fine mesh element that prevents debris entering the carburettor or fuel injection system where it could block the fine jets. Debris is either trapped in the mesh until it is removed during maintenance, or falls into the bowl. Any water that gets past the measures designed into the tanks will also collect in the bowl. The engine feed is from the top of the filter, so water is left behind. A further vital pre-flight check is to open the spring-loaded drain valve on the filter bowl again catching the results in the glass container. Draining is continued until pure fuel flows. The bowl is then free of water and can trap the maximum amount. Fuel from the filter passes next to the engine-driven pump. This is mechanical and only works when the engine is running. The combination of electric and mechanical pump one after the other means that fuel pressure is always available even if one of the pumps fails. In addition the electric pump can run without the engine, and this can be useful in fuel-injected machines to purge the injection pipes of fuel vapour prior to a hot start. The fuel pump contains a pressure regulating mechanism so that constant fuel pressure is available. A pressure switch operates a ‘pressure OK’ light on the instrument panel once fuel pressure exceeds a set threshold. Fuel is then delivered to the carburettor or the fuel injection system. Figure 6.15 shows the fuel system of the JetRanger. Twin electric boost pumps (1) lift fuel from the tank and check valves (2) allow one to carry on if the other fails. The main fuel valve (7) is remote from the cockpit and is motorized. The airframe filter (8) has a pressure drop monitor (9) that operates a warning light (10) if blockage occurs. The engine-driven pump (15) also has a filter (11) and blockage switch (13). The delivery pressure is regulated in the fuel control unit by returning surplus fuel to the inlet side of the gear pump (16). In larger helicopters the fuel system will inevitably become more complex. In order to limit the consequences of damage, for structural reasons and to control the CM position, there may be a large number of smaller tanks, each needing provision for refilling, supply and a quantity gauge. A full fuel tank is heavy and may break free in a crash. A deliberately weak point may be introduced in the pipes along with self-sealing valves so that the tank will not leak if it breaks free. Wiring to pumps and gauges will also be designed to detach. In military machines, self-sealing tanks may be fitted. These are essentially double skinned and between the skins is a compound that expands on
222 The Art of the Helicopter Fig. 6.15 The fuel system of a light turbine-engine helicopter. See text for details. contact with fuel. If a tank is pierced, leaking fuel contacts the compound and this will expand, sealing the hole. Figure 6.16 shows the fuel system of the Chinook. This is complex because there are six tanks, two main engines, an APU and a fuel-burning cabin heater. In addition there is provision for pressure refuelling from a central point as well as connections in the cabin to allow long-range tanks to be carried internally. The fuel is carried in the prominent side sponsons. These cannot contain a single tank for a number of reasons. First, a long single tank would be dangerous because when partially filled all of the fuel could flow to one end and cause a huge trim shift. Second, a single tank would be vulnerable to battle damage. Finally, the front undercarriage leg and its supporting structure occupies some space in the sponson. As a result the Chinook has three tanks along each side. These are not simply interconnected as if one were to be holed this would result in loss of all the fuel on one side. Instead the forward and aft tanks each have a pump which discharges into the main, or centre, tanks. The centre tanks have two pumps in parallel and valves ensure that one can fail without affecting the other.
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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.
Page 186 and 187: In the case of a rotor having offse
Page 188 and 189: The tail rotor designer is faced wi
Page 190 and 191: Fig. 5.5 A right-side wrong-directi
Page 192 and 193: centre of mass. The solution was to
Page 194 and 195: safe to start the rotors. However,
Page 196 and 197: Fig. 5.10 Tail plane locations: (a)
Page 198 and 199: Fig. 5.12 (a) A top-mounted fin is
Page 200 and 201: Fig. 5.14 (a) Main rotor lateral ro
Page 202 and 203: long. The cross-section of the duct
Page 204 and 205: drag. However, the slots are emitti
Page 206 and 207: 6 Engines and transmissions The pow
Page 208 and 209: Engines and transmissions 193 the D
Page 210 and 211: (a) (b) Engines and transmissions 1
Page 212 and 213: (a) (b) (c) Engines and transmissio
Page 214 and 215: Fig. 6.5 A typical horizontally opp
Page 216 and 217: Engines and transmissions 201 the v
Page 218 and 219: Engines and transmissions 203 The c
Page 220 and 221: 6.9 The oil system Engines and tran
Page 222 and 223: Engines and transmissions 207 (non-
Page 224 and 225: (a) (b) Engines and transmissions 2
Page 226 and 227: Engines and transmissions 211 a hot
Page 228 and 229: Engines and transmissions 213 Fig.
Page 230 and 231: Engines and transmissions 215 In wa
Page 232 and 233: Engines and transmissions 217 is a
Page 238 and 239: Fig. 6.16 The complex fuel system o
Page 248 and 249: Engines and transmissions 233 and c
Page 252 and 253: Engines and transmissions 237 Sensi
Page 258 and 259: Engines and transmissions 243 the A
Page 262 and 263: Fig. 6.37 Displays which may be see
Page 266 and 267: Engines and transmissions 251 slipr
Page 268 and 269: Engines and transmissions 253 a fau
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
Page 276 and 277: Fig. 7.2 (a) When attitude conditio
Page 278 and 279: fixed point in the hover despite ex
Page 280 and 281: (a) (b) Fig. 7.4 (a) The earth beha
Page 282 and 283: 7.4 Compass errors A magnetic compa
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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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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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