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130 Engine Group 17-1.2 Performance at Power Required The engine performance (mass flow, fuel flow, and gross jet thrust) is calculated for a specified power required Pq, flight condition, and engine rating. The flight condition includes the altitude, temperature, flight speed, and primary rotor speed; and engine, drive system, and IRS states. The engine turbine speed is N = rengΩprim. The engine model deals with a single engine. The power required of a single engine is obtained by dividing the engine group power by the number of engines operational (total number of engines less inoperable engines): Preq = PreqEG/(Neng − Ninop) In the engine model, installation losses Ploss are added to Preq (Pq = Preq + Ploss). The engine model gives the performance of a single engine. The performance of the engine group is obtained by multiplying the single-engine characteristics by the number of engines operational (total number of engines less inoperable engines): ˙mreqEG =(Neng − Ninop) ˙mreq ˙wreqEG =(Neng − Ninop) ˙wreqKffd FNEG =(Neng − Ninop)FN DauxEG =(Neng − Ninop)Daux The fuel flow has also been multiplied by a factor accounting for deterioration of the engine efficiency. 17-1.3 Installation The difference between installed and uninstalled power is the inlet and exhaust losses Ploss: Pav = Pa − Ploss and Preq = Pq − Ploss. The inlet ram recovery efficiency ηd is included in the engine-model calculations. The inlet and exhaust losses are modeled as fractions of power available or power required: Ploss =(ℓin+ℓex)Pa or Ploss =(ℓin+ℓex)Pq. Installation effects on the jet thrust are included in the engine model. The momentum drag of the auxiliary-air flow is a function of the mass flow ˙maux = faux ˙mreq: Daux =(1− ηaux) ˙mauxV =(1− ηaux)faux ˙mreqV where ηaux is the ram recovery efficiency. Exhaust losses (ℓex) and auxiliary-air-flow parameters (ηaux, faux) are defined for IRS on and off. Inlet particle-separator loss is added to the inlet losses (ℓin). 17–2 Control and Loads The engine orientation is specified by selecting a nominal direction ef0 in body axes (positive or negative x, y, orz-axis; usually thrust forward, hence positive x-axis); and then applying a yaw angle ψ, then an incidence or tilt angle i (table 17-1). The yaw and incidence angles can be connected to the aircraft controls cAC: ψ = ψ0 + TψcAC i = i0 + TicAC with ψ0 and i0 zero, constant, or a function of flight speed (piecewise linear input). Hence the incidence and yaw angles can be fixed orientation or can be control variables. Optionally the lateral position of the engine group can be set equal to that of a designed rotor (useful for tiltrotors when the rotor hub lateral position is calculated from the clearance or wing geometry).
Engine Group 131 The engine group produces a jet thrust FN, acting in the direction of the engine; a momentum drag Daux, acting in the wind direction; and a nacelle drag Dnac, acting in the wind direction. The engine group is at location z F . The force and moment acting on the aircraft in body axes are thus: F F = ef FN + edDaux + edDnac M F = Δz F F F where Δz F = z F −z F cg, ef is the engine-thrust direction and ed is the drag direction. The velocity relative to the air gives ed = −v F /|v F | (no interference). The engine axes are C BF = UiVψ, where U and V depend on the nominal direction, as described in table 17-1. The engine direction is ef = C FB ef0. For a tiltrotor aircraft, one of the aircraft controls is the nacelle angle, with the convention αtilt =0 for cruise and αtilt =90degree for helicopter mode. The engine incidence angle is then connected to αtilt by defining the matrix Ti appropriately. If the engine nominal direction is defined for airplane mode (+x), then i = αtilt should be used; if the engine nominal direction is defined for helicopter mode (−z), then i = αtilt − 90 should be used. Table 17-1. Engine orientation. nominal (F axes) ef0 incidence, + for force yaw, + for force CBF = UiVψ x forward i up right YiZψ −x aft −i up right Y−iZ−ψ y right j aft up ZiX−ψ −y left −j aft up Z−iXψ z down k aft right Y−iX−ψ −z up −k aft right YiXψ 17–3 Nacelle Drag The engine group includes a nacelle, which contributes to the aircraft drag. The component drag contributions must be consistent. The pylon is the rotor support and the nacelle is the engine support. The drag model for a tiltrotor aircraft with tilting engines would use the pylon drag (and no nacelle drag), since the pylon is connected to the rotor-shaft axes; with non-tilting engines it would use the nacelle drag as well. The nacelle drag acts at the engine location z F . The nacelle axes are the engine axes, hence C BF is calculated as described previously (see table 17-1). For the engine nominal direction forward (+x-axis), the nacelle z-axis is downward and the x-axis is forward; zero incidence angle corresponds to zero angle-of-attack; and 90 degree incidence angle corresponds to 90 degree angle-of-attack (vertical drag). The velocity, angle-of-attack, and dynamic pressure are calculated at the nacelle (without interference). The reference area for the nacelle drag coefficient is the nacelle wetted area. The wetted area per engine is input, or calculated either from the engine system (engine, exhaust, and accessories) weight or from the engine-system plus drive-system weight: Swet = k 2/3 w/Neng where w = WES or w = WES + Wgbrs/NEG and the units of k are feet 2 /pound 2/3 or meter 2 /kilogram 2/3 . The reference area is then Snac = NengSwet. The nacelle area is included in the aircraft wetted area if
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NASA/TP-2009-215402 NDARC NASA Desi
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NASA/TP-2009-215402 NDARC NASA Desi
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TABLE OF CONTENTS CHAPTER 1 - INTRO
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TABLE OF CONTENTS (cont.) CHAPTER 1
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viii LIST OF FIGURES (cont.) Figure
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Chapter 1 Introduction The NASA Des
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Introduction 3 of rotorcraft config
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Introduction 5 previous case DESIGN
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Introduction 7 4) Scully, M.; and F
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Chapter 2 Nomenclature The nomencla
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Nomenclature 11 Fuel Tanks Power Na
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Nomenclature 13 Motion aF AC aircra
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Chapter 3 Tasks The NDARC code perf
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Tasks 17 engine group is found (inc
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Tasks 19 3-4 Maps 3-4.1 Engine Perf
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Chapter 4 Operation 4-1 Flight Cond
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Operation 23 e) Input payload weigh
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Operation 25 Table 4-1. Mission seg
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Operation 27 horizontal ground dist
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Operation 29 climb for zero power m
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Operation 31 a) Horizontal velocity
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Operation 33 From the pressure p =
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Chapter 5 Solution Procedures The N
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Solution Procedures 37 Sizing Task
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Solution Procedures 39 relaxation i
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Solution Procedures 41 Table 5-4. T
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Solution Procedures 43 successive s
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Solution Procedures 45 initialize e
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Chapter 6 Cost Costs are estimated
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Cost 49 Table 6-1. DoD and CPI infl
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Cost 51 predicted base price (1994$
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Chapter 7 Aircraft The aircraft con
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Aircraft 55 The tilt control variab
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Aircraft 57 forward axes for descri
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Aircraft 59 For steady-state flight
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Aircraft 61 where Δz F = z F − z
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Aircraft 63 disk area); or the drag
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Aircraft 65 7-10 Performance Indice
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Aircraft 67 WEIGHT EMPTY STRUCTURE
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Chapter 8 Systems The systems compo
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Chapter 9 Fuselage There is one fus
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Fuselage 73 αe = αfus − αzl, w
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Chapter 10 Landing Gear There is on
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Chapter 11 Rotor The aircraft can h
Page 91 and 92: Rotor 79 propulsion group. The driv
Page 93 and 94: Rotor 81 plane command. The collect
Page 95 and 96: Rotor 83 or just CSF = WCHF with no
Page 97 and 98: Rotor 85 If μ is zero, the equatio
Page 99 and 100: Rotor 87 The velocity ratio is fW =
Page 101 and 102: Rotor 89 T/T ∞ 1.3 1.2 1.1 1.0 Ha
Page 103 and 104: Rotor 91 TPP tilt / cyclic magnitud
Page 105 and 106: Rotor 93 with an average over the r
Page 107 and 108: Rotor 95 (all equal to 1 for μz =0
Page 109 and 110: Rotor 97 κ 1.30 1.25 1.20 1.15 1.1
Page 111 and 112: Rotor 99 (C T /σ) s c d mean 0.20
Page 113 and 114: Rotor 101 11-5.1.3 Twin Rotors For
Page 115 and 116: Rotor 103 The wake is a skewed cyli
Page 117 and 118: Rotor 105 weight per lifting rotor;
Page 119 and 120: Chapter 12 Force The force componen
Page 121 and 122: Chapter 13 Wing The aircraft can ha
Page 123 and 124: Wing 111 denotes outboard edge, sub
Page 125 and 126: Wing 113 13-3.1 Lift The wing lift
Page 127 and 128: Wing 115 The wing interference at t
Page 129 and 130: Chapter 14 Empennage The aircraft c
Page 131 and 132: Empennage 119 14-4 Weights The tail
Page 133 and 134: Chapter 15 Fuel Tank 15-1 Fuel Capa
Page 135 and 136: Fuel Tank 123 if Wfuel >Wfuel−max
Page 137 and 138: Chapter 16 Propulsion The propulsio
Page 139 and 140: Propulsion 127 If the sum of the fi
Page 141: Chapter 17 Engine Group The engine
Page 145 and 146: Engine Group 133 specific fuel cons
Page 147 and 148: Chapter 18 Referred Parameter Turbo
Page 149 and 150: Referred Parameter Turboshaft Engin
Page 159 and 160: Chapter 19 AFDD Weight Models This
Page 161 and 162: AFDD Weight Models 149 The spar-cap
Page 163 and 164: AFDD Weight Models 151 19-1.2 Aircr
Page 165 and 166: AFDD Weight Models 153 where w = nz
Page 167 and 168: AFDD Weight Models 155 units as use
Page 169 and 170: AFDD Weight Models 157 Table 19-9.
Page 171 and 172: AFDD Weight Models 159 where fP = f
Page 173 and 174: AFDD Weight Models 161 The conversi
Page 175 and 176: AFDD Weight Models 163 19-12 Foldin
Page 177 and 178: AFDD Weight Models 165 error (%) er
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