The Art of the Helicopter John Watkinson - Karatunov.net

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Fig. 1.20 The structure of a light helicopter: Enstrom F-28.See text for details. 1.7 Engine and transmission Introduction to rotorcraft 17 The engine or engines and transmission are generally close together. Piston engines are heavy, and they are almost always placed below the rotor head to balance the machine. Turbines are much smaller and lighter and are often built into the roof of the hull to maximize internal space. Both piston engines and turbines turn much faster than the rotor shaft, and the transmission must incorporate reduction gearing. The gearbox will generate a good deal of heat on a large machine, and require an oil cooler. This will have its own air intake near the rotor shaft; often in the front of the pylon. The gearbox also drives the tail rotor shaft, which runs the length of the tail boom to the tail rotor gearbox. The tail rotor shaft is often mounted outside the tail cone for ease of inspection and maintenance. The rotors may take some time to come to rest after the engines have been shut down, and this may be inconvenient. The civil user wants to disembark passengers with the rotors stopped. The naval user wants to put the machine on the elevator down to the hangar and the army user wants the rotors stopped quickly on a clandestine mission so that the machine can be camouflaged. This can be achieved by fitting a rotor brake on the transmission. Helicopters have also been built with jets at the blade tips, and this has the advantages that no gearbox is required and there is no torque reaction. Unfortunately tip jets have short fatigue life, very high fuel consumption and noise level to match and are little used. They will not be considered further here. As it is a major subject, the whole of Chapter 6 is devoted to helicopter engines and transmissions. 1.8 The fuel system The fuel system can be simple or complex depending on the type of machine. In early piston engine machines using carburettors, the fuel system was little more than a pair of tanks that fed fuel by gravity through the pilot’s cut-off valve and a filter to the engine. The tanks in a gravity fed system are mounted one each side of the mast so that lateral and longitudinal trim is unaffected as fuel is consumed. The tanks are clearly visible on the Bell 47 and the Hughes 300. Larger machines will use the space below
18 The Art of the Helicopter the floor to put tanks close to the CM, in which case pumps will be required to feed the engines. Piston engines burn AVGASor aviation gasoline, which is basically similar to automobile fuel but made to tighter quality standards. Turbines burn AVTUR that has a similar relationship to kerosene. As a piston engine will stop if AVTUR reaches it, pilots like to know they have taken on the right fuel. AVGASfillers are marked red and AVTUR fillers are marked black to help prevent a dangerous mistake. Recently there have been significant advances in the development of Diesel engines, allowing a similar power to weight ratio to a gasoline engine to be obtained. The advantage of the aeroDiesel is that it can burn AVTUR and its improved fuel economy allows better payload or range. A more detailed treatment of fuel systems can be found in Chapter 6. 1.9 The landing gear The landing gear is subject to considerable variation. Utility and training helicopters are invariably fitted with skids to allow a landing on unprepared ground even with forward speed. Small wheels, known as ground handling wheels, can be fitted so the machine can be moved around. Some skids are broader than usual so they can act as skis for landing on snow or soft ground. Inflatable or rigid floats can be attached to the skids to permit operation over water, but there will be a drag and payload penalty. Larger machines invariably have wheels, as skids would make them too difficult to move. Naval helicopters need wheels to allow them to be moved below decks. In many cases the wheels can be locked so as to be tangential to a circle. The machine can be turned into the wind, but will not roll as the ship heels. 1.10Oleos and ground resonance Landing gears often incorporate a telescopic section containing oil and a compressed gas acting as a spring. These are formally known as oleo-pneumatic struts, invariably abbreviated to oleos. When the length of the oleo changes, the oil is forced through a small orifice to damp the movement. The struts that hold up automobile tailgates work on the same principle, but these are sealed units whereas the type of oil and the gas pressure in an oleo may be adjusted to give the correct spring rate and damping. One obvious purpose of the oleo is to absorb the impact of landing, but a more important role is to control ground resonance. Ideally the rotor blades rotate with perfectly even spacing when run up on the ground, but it is possible for them to be disturbed from that condition. This results in the CM of the rotor moving away from the shaft axis and the rotor tries to whirl the top of the hull in a circular orbit. Under certain conditions this motion becomes uncontrollable unless there is damping to dissipate the energy. The origin of ground resonance will be discussed in Chapter 4 where it will be shown that the rotor head may also need dampers to prevent the problem. 1.11 The rotors The main rotor takes the place of the wings of a conventional aircraft, and it is not unrealistic to think of a helicopter as being supported by the lift from wings that rotate instead of flying in a straight line. The main difference between rotor blades and
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Page 4 and 5: The Art of the Helicopter John Watk
Page 6 and 7: Contents Preface xi Acknowledgement
Page 8 and 9: 4.12 Feathering 134 4.13 Pitch cont
Page 10: 8.5 Power management 326 8.6 Flying
Page 13 and 14: xii Preface reader to make sense of
Page 16 and 17: 1 Introduction to rotorcraft 1.1 Ap
Page 18 and 19: Introduction to rotorcraft 3 Fig. 1
Page 24 and 25: Introduction to rotorcraft 9 for th
Page 26 and 27: Introduction to rotorcraft 11 Fig.
Page 28 and 29: (a) (b) (c) (d) Introduction to rot
Page 30 and 31: Fig. 1.18 The contra-rotating coaxi
Page 34 and 35: Introduction to rotorcraft 19 wings
Page 36 and 37: Introduction to rotorcraft 21 a rot
Page 38 and 39: Technical background 23 Fig. 2.1 At
Page 40 and 41: Fig. 2.3 Effect of force on velocit
Page 42 and 43: C Force A E Resultant (a) Force B (
Page 44 and 45: (a) (b) Technical background 29 Fig
Page 46 and 47: Technical background 31 Fig. 2.11 A
Page 48 and 49: Technical background 33 Fig. 2.12 (
Page 50 and 51: Technical background 35 If the volu
Page 52 and 53: Fig. 2.16 The definition of a radia
Page 54 and 55: Technical background 39 force would
Page 56 and 57: Technical background 41 Figure 2.20
Page 58 and 59: Technical background 43 force where
Page 60 and 61: Technical background 45 the cosine
Page 62 and 63: Technical background 47 Fig. 2.28 F
Page 64 and 65: Technical background 49 Fig. 2.30 T
Page 66 and 67: Technical background 51 centripetal
Page 68 and 69: 2.17 The gyroscope Technical backgr
Page 70 and 71: Technical background 55 of oscillat
Page 72 and 73: Technical background 57 the inertia
Page 74 and 75: Technical background 59 shut down a
Page 76 and 77: 3 Introduction to helicopter dynami
Page 78 and 79: Introduction to helicopter dynamics
Page 80 and 81: Introduction to helicopter dynamics
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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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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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