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136 Referred Parameter Turboshaft Engine Model The inlet ram air temperature ratio and pressure ratio are obtained then from M and the inlet ram recovery efficiency ηd: γ − 1 2 θM = 1+ M = 2 1+0.2M 2 γ − 1 δM = 1+ ηdM 2 2 γ γ−1 = 1+0.2ηdM 23.5 where the ratio of specific heats γ =1.4. 18–2 Engine Ratings The power available from a turboshaft engine depends on the engine rating. Each engine rating has specific operating limitations, most importantly an operating time limit intended to avoid damage to the engine. Typical engine ratings are given in table 18-1. Engine power is generally specified in terms of SLS static MCP. Takeoff typically uses MRP. CRP or ERP are restricted to use in one-engine inoperative (OEI) emergencies. Table 18-1. Typical engine ratings. rating description time limit MCP maximum continuous power ∞ IRP intermediate rated power 30 min MRP maximum rated power 10 min CRP contingency rated power 2.5 min ERP emergency rated power 1.0 min 18–3 Performance Characteristics The engine performance is described by: the power available Pa, at each engine rating and the specification engine-turbine speed Nspec; the mass flow ˙m and fuel flow ˙w required to produce power required Pq at engine-turbine speed N; and the gross jet thrust F at a given power required Pq. Then the specific power is SP = P/ ˙m, and the specific fuel consumption is sfc = ˙w/P. The reference performance is at sea-level-standard static conditions (subscript 0), and MCP (subscript C). Referred or corrected engine parameters are used in the model: power mass flow specific power P δ √ θ ˙m δ/ √ θ P/ ˙m θ fuel flow thrust turbine speed For each rating R, the performance is characterized by the following quantities for sea-level-standard static conditions: power P0R, specific power SP0R, and mechanical power limit PmechR. The mass flow ˙w δ √ θ F δ N √ θ
Referred Parameter Turboshaft Engine Model 137 is then ˙m0R = P0R/SP0R. The gross jet thrust Fg0C is given at MCP. These characteristics are at the specification turbine speed Nspec. The installed power required Preq and power available Pav >Preq are measured at the engine output shaft. In addition to shaft power, the engine exhaust produces a net jet thrust FN, from mass flow that goes through the engine core. The fuel flow and mass flow are the total required to produce the shaft power and jet thrust. The forces produced by mass flow that does not go through the engine core (such as IR suppressor or cooling air) are treated as momentum drag Daux. The difference between net and gross jet thrust is the momentum drag: Fn = Fg − ˙mreqV = ˙mreq(Vj − V ), where Vj is the engine-jet-exhaust velocity. Note that traditional units for mass flow are pound/sec (pps), while this equation requires slug/sec ( ˙mreq/g replaces ˙mreq). The uninstalled power required is Pq, the power available Pa, the gross jet thrust Fg, and net jet thrust Fn. The engine model calculates Pa as a function of flight condition and engine rating; or calculates engine mass flow, fuel flow, and jet thrust at Pq. 18–4 Installation The difference between installed and uninstalled power is the inlet and exhaust losses Ploss: Pav = Pa − Ploss Preq = Pq − Ploss The inlet ram-recovery efficiency ηd (through δM) 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. So Pav = Pa(1 − ℓin − ℓex) Pq = Preq/(1 − ℓin − ℓex) The engine model gives uninstalled power and the gross thrust Fg for a nominal exhaust nozzle area. The gross jet thrust FG and exhaust power loss (ℓex) are both functions of the exhaust-nozzle area. Smaller exhaust-nozzle areas increase exhaust losses and increase gross thrust. Thus the ratio of installed to uninstalled thrust is approximated by a function of the exhaust power loss: so the net installed jet thrust is FG/Fg = Kfgr = Kfgr0 + Kfgr1ℓex + Kfgr2ℓ 2 ex + Kfgr3ℓ 3 ex FN = KfgrFg − ˙mreqV 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 IR suppressor on and off. Inlet particle separator loss is added to the inlet losses (ℓin). 18–5 Power-Turbine Speed The shaft power available is a function of the gas power available PG and the power-turbine efficiency ηt: Pa = ηtPG. Generally the power-turbine speed N has a significant effect on ηt, but almost
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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
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Rotor 79 propulsion group. The driv
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Rotor 81 plane command. The collect
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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 and 142: Chapter 17 Engine Group The engine
Page 143 and 144: Engine Group 131 The engine group p
Page 145 and 146: Engine Group 133 specific fuel cons
Page 147: Chapter 18 Referred Parameter Turbo
Page 151 and 152: 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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