The Art of the Helicopter John Watkinson - Karatunov.net

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Other types of rotorcraft 375 Fig. 9.27 (a) Pitch control increases lift on end of the hull and reduces it on the other. (b) The hull pitches. (c) Flapping hinges cause the rotors to follow the hull attitude. Fig. 9.28 (a) In translational flight the rotors flap back. (b) Forward cyclic is used on each swashplate to reduce flapback and level the hull.
376 The Art of the Helicopter The yaw control is by differential tilt of the rotor thrust and clearly if there is no rotor thrust there will be no yaw couple. If rotor thrust reverses the yaw control will reverse. Whilst this is not a problem in most flight conditions, a zero-g pushover could result in loss of yaw control. A crop-dusting turn or return-to-target manoeuvre is also difficult for a tandem because when the hull is pointing straight up after the first quarter loop the rotors need to be set to flat pitch and this removes the yaw authority. Consequently the tandem will perform a variation on the manoeuvre in which the yaw is commenced during the quarter loop. Momentum carries the yaw on during the flat pitch phase. The tandem is generally designed to have a level cabin in translational flight and when at rest on the ground. This means that in the hover the cabin will slope down to the rear and the machine must touch down with the rear wheels first. This allows an interesting taxi mode where the rear wheels are carrying a significant weight but the front wheels are clear of the ground. Forward speed can be controlled by rear wheel brake and steering is possible by applying the brakes differentially. The waterborne characteristics of a tandem are worth a few comments. The contrarotation means that the rotors can be started and stopped whilst afloat without the machine rotating as a single main rotor machine would. The built-in tip path plane tilt causes a tendency to forward motion when the hull is floating level. When afloat the acrylic cockpit chin windows are partially submerged, and whilst this is not a problem whilst stationary, water taxiing at speed will put them under tremendous stress. To avoid this, pilots will lift the nose in a water taxi. The floor of the cabin is sealed to act as a raft for use on water and the ramp can be lowered whilst afloat to deploy or recover small boats or swimmers. In the tandem rotor helicopter the rotor heads are designed to meet different requirements. The yaw control is obtained by tilting the two rotor discs laterally in opposite directions. Effective yaw requires that the tip path axes actually make a significant tilt and the flapping hinges are needed to allow this to happen. If conventional heads with significant flapping hinge offset are used, the result of an application of the yaw control is a serious twisting couple applied to the fuselage. Thus for a tandem rotor helicopter, the flapping hinge offset needs to be significantly reduced. This need not reduce the roll response, because a roll is obtained by applying lateral cyclic to both rotors in the same sense. As there are two rotors, each rotor only needs to apply half the roll moment. In order to prevent heavy underslung loads reducing the lateral cyclic authority the main load hook is on rollers and can traverse a curved lateral beam whose centre of curvature is near a line joining the rotorheads. In the Chinook, the flapping hinges are provided with a relatively small offset for the above reasons. If the dragging hinges were coincident with the flapping hinges there would be a large drag angle change between the power-on and autorotation states and there would be little space for drag dampers. Instead the dragging hinges are placed outboard of the feathering hinges. This arrangement works very well and the only drawback is that when the blades are stationary gravity causes them to swing about the dragging bearing. These are not necessarily vertical, being outboard of the feathering bearings. 9.10 Remotely piloted and radio-controlled helicopters In some cases putting a pilot in a helicopter is not the right thing to do. Without a pilot the helicopter can be much smaller, or it can lift more. The pilotless helicopter can also
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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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Page 342 and 343: Helicopter performance 327 Fig. 8.1
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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.
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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
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Page 388 and 389: Other types of rotorcraft 373 For e
Page 394 and 395: Acceleration: and force, 22-5 and v
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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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