X-Git-Url: https://git.mxchange.org/?a=blobdiff_plain;f=src%2FFDM%2FIO360.cxx;h=c75b9b3f2fea84f37ca9d4ac62a46a1444b9474d;hb=ee98995d30e75cda88c9866f3cb6a761fda7d078;hp=f4e1f29eec3d5769937b172bcc6a4e2a5d18891e;hpb=5d423a94b0f6421af87817c006c515fec1953ca2;p=flightgear.git diff --git a/src/FDM/IO360.cxx b/src/FDM/IO360.cxx index f4e1f29ee..c75b9b3f2 100644 --- a/src/FDM/IO360.cxx +++ b/src/FDM/IO360.cxx @@ -1,10 +1,9 @@ -// Module: 10520c.c -// Author: Phil Schubert -// Date started: 12/03/99 -// Purpose: Models a Continental IO-520-M Engine -// Called by: FGSimExec -// -// Copyright (C) 1999 Philip L. Schubert (philings@ozemail.com.au) +// IO360.cxx - a piston engine model currently for the IO360 engine fitted to the C172 +// but with the potential to model other naturally aspirated piston engines +// given appropriate config input. +// +// Written by David Luff, started 2000. +// Based on code by Phil Schubert, started 1999. // // This program is free software; you can redistribute it and/or // modify it under the terms of the GNU General Public License as @@ -18,201 +17,23 @@ // // You should have received a copy of the GNU General Public License // along with this program; if not, write to the Free Software -// Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA -// 02111-1307, USA. -// -// Further information about the GNU General Public License can also -// be found on the world wide web at http://www.gnu.org. -// -// FUNCTIONAL DESCRIPTION -// ------------------------------------------------------------------------ -// Models a Continental IO-520-M engine. This engine is used in Cessna -// 210, 310, Beechcraft Bonaza and Baron C55. The equations used below -// were determined by a first and second order curve fits using Excel. -// The data is from the Cessna Aircraft Corporations Engine and Flight -// Computer for C310. Part Number D3500-13 -// -// ARGUMENTS -// ------------------------------------------------------------------------ -// -// -// HISTORY -// ------------------------------------------------------------------------ -// 12/03/99 PLS Created -// 07/03/99 PLS Added Calculation of Density, and Prop_Torque -// 07/03/99 PLS Restructered Variables to allow easier implementation -// of Classes -// 15/03/99 PLS Added Oil Pressure, Oil Temperature and CH Temp -// ------------------------------------------------------------------------ -// INCLUDES -// ------------------------------------------------------------------------ -// -// -///////////////////////////////////////////////////////////////////// -// -// Modified by Dave Luff (david.luff@nottingham.ac.uk) September 2000 -// -// Altered manifold pressure range to add a minimum value at idle to simulate the throttle stop / idle bypass valve, -// and to reduce the maximum value whilst the engine is running to slightly below ambient to account for CdA losses across the throttle -// -// Altered it a bit to model an IO360 from C172 - 360 cubic inches, 180 HP max, fixed pitch prop -// Added a simple fixed pitch prop model by Nev Harbor - this is not intended as a final model but simply a hack to get it running for now -// I used Phil's ManXRPM correlation for power rather than do a new one for the C172 for now, but altered it a bit to reduce power at the low end -// -// Added EGT model based on combustion efficiency and an energy balance with the exhaust gases -// -// Added a mixture - power correlation based on a curve in the IO360 operating manual -// -// I've tried to match the prop and engine model to give roughly 600 RPM idle and 180 HP at 2700 RPM -// but it is by no means currently at a completed stage - DCL 15/9/00 -// -// DCL 28/9/00 - Added estimate of engine and prop inertia and changed engine speed calculation to be calculated from Angular acceleration = Torque / Inertia. -// Requires a timestep to be passed to FGNewEngine::init and currently assumes this timestep does not change. -// Could easily be altered to pass a variable timestep to FGNewEngine::update every step instead if required. -// -// DCL 27/10/00 - Added first stab at cylinder head temperature model -// See the comment block in the code for details -// -// DCL 02/11/00 - Modified EGT code to reduce values to those more representative of a sensor downstream -// -// DCL 02/02/01 - Changed the prop model to one based on efficiency and co-efficient of power curves from McCormick instead of the -// blade element method we were using previously. This works much better, and is similar to how Jon is doing it in JSBSim. -// -////////////////////////////////////////////////////////////////////// +// Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. #include -#include -#include #include -#include "IO360.hxx" - -FG_USING_STD(cout); - -float FGNewEngine::Lookup_Combustion_Efficiency(float thi_actual) -{ - const int NUM_ELEMENTS = 11; - float thi[NUM_ELEMENTS] = {0.0, 0.9, 1.0, 1.05, 1.1, 1.15, 1.2, 1.3, 1.4, 1.5, 1.6}; //array of equivalence ratio values - float neta_comb[NUM_ELEMENTS] = {0.98, 0.98, 0.97, 0.95, 0.9, 0.85, 0.79, 0.7, 0.63, 0.57, 0.525}; //corresponding array of combustion efficiency values - //combustion efficiency values from Heywood: ISBN 0-07-100499-8 - float neta_comb_actual; - float factor; - - int i; - int j = NUM_ELEMENTS; //This must be equal to the number of elements in the lookup table arrays - - for(i=0;i thi[i]) && (thi_actual < thi[i + 1])) - { - //do linear interpolation between the two points - factor = (thi_actual - thi[i]) / (thi[i+1] - thi[i]); - neta_comb_actual = (factor * (neta_comb[i+1] - neta_comb[i])) + neta_comb[i]; - return neta_comb_actual; - } - } - - //if we get here something has gone badly wrong - cout << "ERROR: error in FGNewEngine::Lookup_Combustion_Efficiency\n"; - return neta_comb_actual; -} - - -// Calculate Manifold Pressure based on Throttle lever Position -static float Calc_Manifold_Pressure ( float LeverPosn, float MaxMan, float MinMan) -{ - float Inches; - // if ( x < = 0 ) { - // x = 0.00001; - // } - - //Note that setting the manifold pressure as a function of lever position only is not strictly accurate - //MAP is also a function of engine speed. (and ambient pressure if we are going for an actual MAP model) - Inches = MinMan + (LeverPosn * (MaxMan - MinMan) / 100); - - //allow for idle bypass valve or slightly open throttle stop - if(Inches < MinMan) - Inches = MinMan; - - return Inches; -} - - - - -// Calculate Oil Temperature -static float Oil_Temp (float Fuel_Flow, float Mixture, float IAS) -{ - float Oil_Temp = 85; - - return (Oil_Temp); -} - -// Calculate Oil Pressure -static float Oil_Press (float Oil_Temp, float Engine_RPM) -{ - float Oil_Pressure = 0; //PSI - float Oil_Press_Relief_Valve = 60; //PSI - float Oil_Press_RPM_Max = 1800; - float Design_Oil_Temp = 85; //Celsius - float Oil_Viscosity_Index = 0.25; // PSI/Deg C - float Temp_Deviation = 0; // Deg C - - Oil_Pressure = (Oil_Press_Relief_Valve / Oil_Press_RPM_Max) * Engine_RPM; - - // Pressure relief valve opens at Oil_Press_Relief_Valve PSI setting - if (Oil_Pressure >= Oil_Press_Relief_Valve) - { - Oil_Pressure = Oil_Press_Relief_Valve; - } +#include STL_FSTREAM +#include STL_IOSTREAM - // Now adjust pressure according to Temp which affects the viscosity - - Oil_Pressure += (Design_Oil_Temp - Oil_Temp) * Oil_Viscosity_Index; - - return Oil_Pressure; -} +#if !defined(SG_HAVE_NATIVE_SGI_COMPILERS) +SG_USING_STD(cout); +#endif +#include "IO360.hxx" +#include "LaRCsim/ls_constants.h" -// Calculate Density Ratio -static float Density_Ratio ( float x ) -{ - float y ; - y = ((3E-10 * x * x) - (3E-05 * x) + 0.9998); - return(y); -} - - -// Calculate Air Density - Rho -static float Density ( float x ) -{ - float y ; - y = ((9E-08 * x * x) - (7E-08 * x) + 0.0024); - return(y); -} - - -// Calculate Speed in FPS given Knots CAS -static float IAS_to_FPS (float x) -{ - float y; - y = x * 1.68888888; - return y; -} - +#include
//************************************************************************************* // Initialise the engine model @@ -229,149 +50,456 @@ void FGNewEngine::init(double dt) { rho_fuel = 800; // kg/m^3 - an estimate for now R_air = 287.3; - // Control and environment inputs - IAS = 0; + // environment inputs + p_amb_sea_level = 101325; // Pascals + + // Control inputs - ARE THESE NEEDED HERE??? Throttle_Lever_Pos = 75; Propeller_Lever_Pos = 75; Mixture_Lever_Pos = 100; + //misc + IAS = 0; time_step = dt; - // Engine Specific Variables. - // Will be set in a parameter file to be read in to create - // and instance for each engine. + // Engine Specific Variables that should be read in from a config file + MaxHP = 200; //Lycoming IO360 -A-C-D series +// MaxHP = 180; //Current Lycoming IO360 ? +// displacement = 520; //Continental IO520-M + displacement = 360; //Lycoming IO360 + displacement_SI = displacement * CONVERT_CUBIC_INCHES_TO_METERS_CUBED; + engine_inertia = 0.2; //kgm^2 - value taken from a popular family saloon car engine - need to find an aeroengine value !!!!! + prop_inertia = 0.05; //kgm^2 - this value is a total guess - dcl + Max_Fuel_Flow = 130; // Units??? Do we need this variable any more?? + + // Engine specific variables that maybe should be read in from config but are pretty generic and won't vary much for a naturally aspirated piston engine. Max_Manifold_Pressure = 28.50; //Inches Hg. An approximation - should be able to find it in the engine performance data Min_Manifold_Pressure = 6.5; //Inches Hg. This is a guess corresponding to approx 0.24 bar MAP (7 in Hg) - need to find some proper data for this Max_RPM = 2700; Min_RPM = 600; //Recommended idle from Continental data sheet - Max_Fuel_Flow = 130; Mag_Derate_Percent = 5; -// MaxHP = 285; //Continental IO520-M - MaxHP = 180; //Lycoming IO360 -// displacement = 520; //Continental IO520-M - displacement = 360; //Lycoming IO360 - displacement_SI = displacement * CONVERT_CUBIC_INCHES_TO_METERS_CUBED; - engine_inertia = 0.2; //kgm^2 - value taken from a popular family saloon car engine - need to find an aeroengine value !!!!! - prop_inertia = 0.03; //kgm^2 - this value is a total guess - dcl Gear_Ratio = 1; + n_R = 2; // Number of crank revolutions per power cycle - 2 for a 4 stroke engine. - started = true; + // Various bits of housekeeping describing the engines initial state. + running = false; cranking = false; - + crank_counter = false; + starter = false; // Initialise Engine Variables used by this instance + if(running) + RPM = 600; + else + RPM = 0; Percentage_Power = 0; - Manifold_Pressure = 29.00; // Inches - RPM = 600; + Manifold_Pressure = 29.96; // Inches Fuel_Flow_gals_hr = 0; - Torque = 0; +// Torque = 0; Torque_SI = 0; - CHT = 298.0; //deg Kelvin - CHT_degF = (CHT * 1.8) - 459.67; //deg Fahrenheit + CHT = 298.0; //deg Kelvin + CHT_degF = (CHT_degF * 1.8) - 459.67; //deg Fahrenheit Mixture = 14; Oil_Pressure = 0; // PSI Oil_Temp = 85; // Deg C + current_oil_temp = 298.0; //deg Kelvin + /**** one of these is superfluous !!!!***/ HP = 0; RPS = 0; Torque_Imbalance = 0; // Initialise Propellor Variables used by this instance - FGProp1_Angular_V = 0; - FGProp1_Coef_Drag = 0.6; - FGProp1_Torque = 0; - FGProp1_Thrust = 0; FGProp1_RPS = 0; - FGProp1_Coef_Lift = 0.1; - Alpha1 = 13.5; - FGProp1_Blade_Angle = 13.5; - FGProp_Fine_Pitch_Stop = 13.5; - - // Other internal values - Rho = 0.002378; + // Hardcode propellor for now - the following two should be read from config eventually + prop_diameter = 1.8; // meters + blade_angle = 23.0; // degrees } - -//***************************************************************************** //***************************************************************************** // update the engine model based on current control positions void FGNewEngine::update() { - // Declare local variables -// int num = 0; - // const int num2 = 500; // default is 100, number if iterations to run -// const int num2 = 5; // default is 100, number if iterations to run - float ManXRPM = 0; - float Vo = 0; - float V1 = 0; +/* + // Hack for testing - should output every 5 seconds + static int count1 = 0; + if(count1 == 0) { +// cout << "P_atmos = " << p_amb << " T_atmos = " << T_amb << '\n'; +// cout << "Manifold pressure = " << Manifold_Pressure << " True_Manifold_Pressure = " << True_Manifold_Pressure << '\n'; +// cout << "p_amb_sea_level = " << p_amb_sea_level << '\n'; +// cout << "equivalence_ratio = " << equivalence_ratio << '\n'; +// cout << "combustion_efficiency = " << combustion_efficiency << '\n'; +// cout << "AFR = " << 14.7 / equivalence_ratio << '\n'; +// cout << "Mixture lever = " << Mixture_Lever_Pos << '\n'; +// cout << "n = " << RPM << " rpm\n"; +// cout << "T_amb = " << T_amb << '\n'; +// cout << "running = " << running << '\n'; + cout << "fuel = " << fgGetFloat("/consumables/fuel/tank[0]/level-gal_us") << '\n'; +// cout << "Percentage_Power = " << Percentage_Power << '\n'; +// cout << "current_oil_temp = " << current_oil_temp << '\n'; + cout << "EGT = " << EGT << '\n'; + } + count1++; + if(count1 == 100) + count1 = 0; +*/ - // Set up the new variables - float Blade_Station = 30; - float FGProp_Area = 1.405/3; - float PI = 3.1428571; + // Check parameters that may alter the operating state of the engine. + // (spark, fuel, starter motor etc) + + // Check for spark + bool Magneto_Left = false; + bool Magneto_Right = false; + // Magneto positions: + // 0 -> off + // 1 -> left only + // 2 -> right only + // 3 -> both + if(mag_pos != 0) { + spark = true; + } else { + spark = false; + } // neglects battery voltage, master on switch, etc for now. + if((mag_pos == 1) || (mag_pos > 2)) + Magneto_Left = true; + if(mag_pos > 1) + Magneto_Right = true; + + // crude check for fuel + if((fgGetFloat("/consumables/fuel/tank[0]/level-gal_us") > 0) || (fgGetFloat("/consumables/fuel/tank[1]/level-gal_us") > 0)) { + fuel = true; + } else { + fuel = false; + } // Need to make this better, eg position of fuel selector switch. + + // Check if we are turning the starter motor + if(cranking != starter) { + // This check saves .../cranking from getting updated every loop - they only update when changed. + cranking = starter; + crank_counter = 0; + } + // Note that although /engines/engine[0]/starter and /engines/engine[0]/cranking might appear to be duplication it is + // not since the starter may be engaged with the battery voltage too low for cranking to occur (or perhaps the master + // switch just left off) and the sound manager will read .../cranking to determine wether to play a cranking sound. + // For now though none of that is implemented so cranking can be set equal to .../starter without further checks. + +// int Alternate_Air_Pos =0; // Off = 0. Reduces power by 3 % for same throttle setting + // DCL - don't know what this Alternate_Air_Pos is - this is a leftover from the Schubert code. + + //Check mode of engine operation + if(cranking) { + crank_counter++; + if(RPM <= 480) { + RPM += 100; + if(RPM > 480) + RPM = 480; + } else { + // consider making a horrible noise if the starter is engaged with the engine running + } + } + if((!running) && (spark) && (fuel) && (crank_counter > 120)) { + // start the engine if revs high enough + if(RPM > 450) { + // For now just instantaneously start but later we should maybe crank for a bit + running = true; +// RPM = 600; + } + } + if( (running) && ((!spark)||(!fuel)) ) { + // Cut the engine + // note that we only cut the power - the engine may continue to spin if the prop is in a moving airstream + running = false; + } - // Input Variables + // Now we've ascertained whether the engine is running or not we can start to do the engine calculations 'proper' - // 0 = Closed, 100 = Fully Open - // float Throttle_Lever_Pos = 75; - // 0 = Full Course 100 = Full Fine - // float Propeller_Lever_Pos = 75; - // 0 = Idle Cut Off 100 = Full Rich - // float Mixture_Lever_Pos = 100; + // Calculate Sea Level Manifold Pressure + Manifold_Pressure = Calc_Manifold_Pressure( Throttle_Lever_Pos, Max_Manifold_Pressure, Min_Manifold_Pressure ); + // cout << "manifold pressure = " << Manifold_Pressure << endl; - // Environmental Variables + //Then find the actual manifold pressure (the calculated one is the sea level pressure) + True_Manifold_Pressure = Manifold_Pressure * p_amb / p_amb_sea_level; - // Temp Variation from ISA (Deg F) - float FG_ISA_VAR = 0; - // Pressure Altitude 1000's of Feet - float FG_Pressure_Ht = 0; + //Do the fuel flow calculations + Calc_Fuel_Flow_Gals_Hr(); - // Parameters that alter the operation of the engine. - int Fuel_Available = 1; // Yes = 1. Is there Fuel Available. Calculated elsewhere - int Alternate_Air_Pos =0; // Off = 0. Reduces power by 3 % for same throttle setting - int Magneto_Left = 1; // 1 = On. Reduces power by 5 % for same power lever settings - int Magneto_Right = 1; // 1 = On. Ditto, Both of the above though do not alter fuel flow + //Calculate engine power + Calc_Percentage_Power(Magneto_Left, Magneto_Right); + HP = Percentage_Power * MaxHP / 100.0; + Power_SI = HP * CONVERT_HP_TO_WATTS; + // FMEP calculation. For now we will just use this during motored operation. + // Eventually we will calculate IMEP and use the FMEP all the time to give BMEP (maybe!) + if(!running) { + // This FMEP data is from the Patton paper, assumes fully warm conditions. + FMEP = 1e-12*pow(RPM,4) - 1e-8*pow(RPM,3) + 5e-5*pow(RPM,2) - 0.0722*RPM + 154.85; + // Gives FMEP in kPa - now convert to Pa + FMEP *= 1000; + } else { + FMEP = 0.0; + } + // Is this total FMEP or friction FMEP ??? - //================================================================== - // Engine & Environmental Inputs from elsewhere + Torque_FMEP = (FMEP * displacement_SI) / (2.0 * LS_PI * n_R); - // Calculate Air Density (Rho) - In FG this is calculated in - // FG_Atomoshere.cxx + // Calculate Engine Torque. Check for div by zero since percentage power correlation does not guarantee zero power at zero rpm. + // However this is problematical since there is a resistance to movement even at rest + // Ie this is a dynamics equation not a statics one. This can be solved by going over to MEP based torque calculations. + if(RPM == 0) { + Torque_SI = 0 - Torque_FMEP; + } + else { + Torque_SI = ((Power_SI * 60.0) / (2.0 * LS_PI * RPM)) - Torque_FMEP; //Torque = power / angular velocity + // cout << Torque << " Nm\n"; + } - Rho = Density(FG_Pressure_Ht); // In FG FG_Pressure_Ht is "h" - // cout << "Rho = " << Rho << endl; + //Calculate Exhaust gas temperature + if(running) + Calc_EGT(); + else + EGT = 298.0; + + // Calculate Cylinder Head Temperature + Calc_CHT(); + + // Calculate oil temperature + current_oil_temp = Calc_Oil_Temp(current_oil_temp); + + // Calculate Oil Pressure + Oil_Pressure = Calc_Oil_Press( Oil_Temp, RPM ); + + // Now do the Propeller Calculations + Do_Prop_Calcs(); + +// Now do the engine - prop torque balance to calculate final RPM + + //Calculate new RPM from torque balance and inertia. + Torque_Imbalance = Torque_SI - prop_torque; //This gives a +ve value when the engine torque exeeds the prop torque + // (Engine torque is +ve when it acts in the direction of engine revolution, prop torque is +ve when it opposes the direction of engine revolution) + + angular_acceleration = Torque_Imbalance / (engine_inertia + prop_inertia); + angular_velocity_SI += (angular_acceleration * time_step); + // Don't let the engine go into reverse + if(angular_velocity_SI < 0) + angular_velocity_SI = 0; + RPM = (angular_velocity_SI * 60) / (2.0 * LS_PI); + + // And finally a last check on the engine state after doing the torque balance with the prop - have we stalled? + if(running) { + //Check if we have stalled the engine + if (RPM == 0) { + running = false; + } else if((RPM <= 480) && (cranking)) { + //Make sure the engine noise dosn't play if the engine won't start due to eg mixture lever pulled out. + running = false; + EGT = 298.0; + } + } - // Calculate Manifold Pressure (Engine 1) as set by throttle opening + // And finally, do any unit conversions from internal units to output units + EGT_degF = (EGT * 1.8) - 459.67; + CHT_degF = (CHT * 1.8) - 459.67; +} - Manifold_Pressure = - Calc_Manifold_Pressure( Throttle_Lever_Pos, Max_Manifold_Pressure, Min_Manifold_Pressure ); - // cout << "manifold pressure = " << Manifold_Pressure << endl; +//***************************************************************************************************** -//**************************FIXME******************************************* - //DCL - hack for testing - fly at sea level - T_amb = 298.0; - p_amb = 101325; - p_amb_sea_level = 101325; +// FGNewEngine member functions - //DCL - next calculate m_dot_air and m_dot_fuel into engine +//////////////////////////////////////////////////////////////////////////////////////////// +// Return the combustion efficiency as a function of equivalence ratio +// +// Combustion efficiency values from Heywood, +// "Internal Combustion Engine Fundamentals", ISBN 0-07-100499-8 +//////////////////////////////////////////////////////////////////////////////////////////// +float FGNewEngine::Lookup_Combustion_Efficiency(float thi_actual) +{ + const int NUM_ELEMENTS = 11; + float thi[NUM_ELEMENTS] = {0.0, 0.9, 1.0, 1.05, 1.1, 1.15, 1.2, 1.3, 1.4, 1.5, 1.6}; //array of equivalence ratio values + float neta_comb[NUM_ELEMENTS] = {0.98, 0.98, 0.97, 0.95, 0.9, 0.85, 0.79, 0.7, 0.63, 0.57, 0.525}; //corresponding array of combustion efficiency values + float neta_comb_actual = 0.0f; + float factor; - //calculate actual ambient pressure and temperature from altitude - //Then find the actual manifold pressure (the calculated one is the sea level pressure) - True_Manifold_Pressure = Manifold_Pressure * p_amb / p_amb_sea_level; + int i; + int j = NUM_ELEMENTS; //This must be equal to the number of elements in the lookup table arrays - // RPM = Calc_Engine_RPM(Propeller_Lever_Pos); - // RPM = 600; - // cout << "Initial engine RPM = " << RPM << endl; + for(i=0;i thi[i]) && (thi_actual < thi[i + 1])) { + //do linear interpolation between the two points + factor = (thi_actual - thi[i]) / (thi[i+1] - thi[i]); + neta_comb_actual = (factor * (neta_comb[i+1] - neta_comb[i])) + neta_comb[i]; + return neta_comb_actual; + } + } + + //if we get here something has gone badly wrong + cout << "ERROR: error in FGNewEngine::Lookup_Combustion_Efficiency\n"; + return neta_comb_actual; +} -// Desired_RPM = RPM; +//////////////////////////////////////////////////////////////////////////////////////////// +// Return the percentage of best mixture power available at a given mixture strength +// +// Based on data from "Technical Considerations for Catalysts for the European Market" +// by H S Gandi, published 1988 by IMechE +// +// Note that currently no attempt is made to set a lean limit on stable combustion +//////////////////////////////////////////////////////////////////////////////////////////// +float FGNewEngine::Power_Mixture_Correlation(float thi_actual) +{ + float AFR_actual = 14.7 / thi_actual; + // thi and thi_actual are equivalence ratio + const int NUM_ELEMENTS = 13; + // The lookup table is in AFR because the source data was. I added the two end elements to make sure we are almost always in it. + float AFR[NUM_ELEMENTS] = {(14.7/1.6), 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, (14.7/0.6)}; //array of equivalence ratio values + float mixPerPow[NUM_ELEMENTS] = {78, 86, 93.5, 98, 100, 99, 96.4, 92.5, 88, 83, 78.5, 74, 58}; //corresponding array of combustion efficiency values + float mixPerPow_actual = 0.0f; + float factor; + float dydx; -//************** + int i; + int j = NUM_ELEMENTS; //This must be equal to the number of elements in the lookup table arrays + + for(i=0;i AFR[i]) && (AFR_actual < AFR[i + 1])) { + //do linear interpolation between the two points + factor = (AFR_actual - AFR[i]) / (AFR[i+1] - AFR[i]); + mixPerPow_actual = (factor * (mixPerPow[i+1] - mixPerPow[i])) + mixPerPow[i]; + return mixPerPow_actual; + } + } + //if we get here something has gone badly wrong + cout << "ERROR: error in FGNewEngine::Power_Mixture_Correlation\n"; + return mixPerPow_actual; +} + +// Calculate Cylinder Head Temperature +// Crudely models the cylinder head as an arbitary lump of arbitary size and area with one third of combustion energy +// as heat input and heat output as a function of airspeed and temperature. Could be improved!!! +void FGNewEngine::Calc_CHT() +{ + float h1 = -95.0; //co-efficient for free convection + float h2 = -3.95; //co-efficient for forced convection + float h3 = -0.05; //co-efficient for forced convection due to prop backwash + float v_apparent; //air velocity over cylinder head in m/s + float v_dot_cooling_air; + float m_dot_cooling_air; + float temperature_difference; + float arbitary_area = 1.0; + float dqdt_from_combustion; + float dqdt_forced; //Rate of energy transfer to/from cylinder head due to forced convection (Joules) (sign convention: to cylinder head is +ve) + float dqdt_free; //Rate of energy transfer to/from cylinder head due to free convection (Joules) (sign convention: to cylinder head is +ve) + float dqdt_cylinder_head; //Overall energy change in cylinder head + float CpCylinderHead = 800.0; //FIXME - this is a guess - I need to look up the correct value + float MassCylinderHead = 8.0; //Kg - this is a guess - it dosn't have to be absolutely accurate but can be varied to alter the warm-up rate + float HeatCapacityCylinderHead; + float dCHTdt; + + // The above values are hardwired to give reasonable results for an IO360 (C172 engine) + // Now adjust to try to compensate for arbitary sized engines - this is currently untested + arbitary_area *= (MaxHP / 180.0); + MassCylinderHead *= (MaxHP / 180.0); + + temperature_difference = CHT - T_amb; + + v_apparent = IAS * 0.5144444; //convert from knots to m/s + v_dot_cooling_air = arbitary_area * v_apparent; + m_dot_cooling_air = v_dot_cooling_air * rho_air; + + //Calculate rate of energy transfer to cylinder head from combustion + dqdt_from_combustion = m_dot_fuel * calorific_value_fuel * combustion_efficiency * 0.33; + + //Calculate rate of energy transfer from cylinder head due to cooling NOTE is calculated as rate to but negative + dqdt_forced = (h2 * m_dot_cooling_air * temperature_difference) + (h3 * RPM * temperature_difference); + dqdt_free = h1 * temperature_difference; + + //Calculate net rate of energy transfer to or from cylinder head + dqdt_cylinder_head = dqdt_from_combustion + dqdt_forced + dqdt_free; + + HeatCapacityCylinderHead = CpCylinderHead * MassCylinderHead; + + dCHTdt = dqdt_cylinder_head / HeatCapacityCylinderHead; + + CHT += (dCHTdt * time_step); +} + +// Calculate exhaust gas temperature +void FGNewEngine::Calc_EGT() +{ + combustion_efficiency = Lookup_Combustion_Efficiency(equivalence_ratio); //The combustion efficiency basically tells us what proportion of the fuels calorific value is released + + //now calculate energy release to exhaust + //We will assume a three way split of fuel energy between useful work, the coolant system and the exhaust system + //This is a reasonable first suck of the thumb estimate for a water cooled automotive engine - whether it holds for an air cooled aero engine is probably open to question + //Regardless - it won't affect the variation of EGT with mixture, and we can always put a multiplier on EGT to get a reasonable peak value. + enthalpy_exhaust = m_dot_fuel * calorific_value_fuel * combustion_efficiency * 0.33; + heat_capacity_exhaust = (Cp_air * m_dot_air) + (Cp_fuel * m_dot_fuel); + delta_T_exhaust = enthalpy_exhaust / heat_capacity_exhaust; + + EGT = T_amb + delta_T_exhaust; + + //The above gives the exhaust temperature immediately prior to leaving the combustion chamber + //Now derate to give a more realistic figure as measured downstream + //For now we will aim for a peak of around 400 degC (750 degF) + + EGT *= 0.444 + ((0.544 - 0.444) * Percentage_Power / 100.0); +} + +// Calculate Manifold Pressure based on Throttle lever Position +float FGNewEngine::Calc_Manifold_Pressure ( float LeverPosn, float MaxMan, float MinMan) +{ + float Inches; + + //Note that setting the manifold pressure as a function of lever position only is not strictly accurate + //MAP is also a function of engine speed. (and ambient pressure if we are going for an actual MAP model) + Inches = MinMan + (LeverPosn * (MaxMan - MinMan) / 100); + + //allow for idle bypass valve or slightly open throttle stop + if(Inches < MinMan) + Inches = MinMan; + + //Check for stopped engine (crudest way of compensating for engine speed) + if(RPM == 0) + Inches = 29.92; + + return Inches; +} + +// Calculate fuel flow in gals/hr +void FGNewEngine::Calc_Fuel_Flow_Gals_Hr() +{ //DCL - calculate mass air flow into engine based on speed and load - separate this out into a function eventually //t_amb is actual temperature calculated from altitude //calculate density from ideal gas equation rho_air = p_amb / ( R_air * T_amb ); - rho_air_manifold = rho_air * Manifold_Pressure / 29.6; + rho_air_manifold = rho_air * Manifold_Pressure / 29.6; //This is a bit of a roundabout way of calculating this but it works !! If we put manifold pressure into SI units we could do it simpler. //calculate ideal engine volume inducted per second swept_volume = (displacement_SI * (RPM / 60)) / 2; //This equation is only valid for a four stroke engine //calculate volumetric efficiency - for now we will just use 0.8, but actually it is a function of engine speed and the exhaust to manifold pressure ratio @@ -382,32 +510,25 @@ void FGNewEngine::update() { //Now calculate mass flow rate of air into engine m_dot_air = v_dot_air * rho_air_manifold; - //cout << "air = " << m_dot_air; - // cout << "rho air manifold " << rho_air_manifold << '\n'; - // cout << "Swept volume " << swept_volume << '\n'; - //************** //DCL - now calculate fuel flow into engine based on air flow and mixture lever position - //assume lever runs from no flow at fully out to thi = 1.6 at fully in at sea level - //***TODO*** - MUST try and get some real idea of the actual full rich sea level mixture - this is important !!! + //assume lever runs from no flow at fully out to thi = 1.3 at fully in at sea level //also assume that the injector linkage is ideal - hence the set mixture is maintained at a given altitude throughout the speed and load range - thi_sea_level = 1.6 * ( Mixture_Lever_Pos / 100.0 ); + thi_sea_level = 1.3 * ( Mixture_Lever_Pos / 100.0 ); equivalence_ratio = thi_sea_level * p_amb_sea_level / p_amb; //ie as we go higher the mixture gets richer for a given lever position m_dot_fuel = m_dot_air / 14.7 * equivalence_ratio; Fuel_Flow_gals_hr = (m_dot_fuel / rho_fuel) * 264.172 * 3600.0; // Note this assumes US gallons +} - //cout << "fuel " << m_dot_fuel; << "kg/s " << Fuel_Flow_gals_hr << "gals/hr" - //cout << " air " << m_dot_air << '\n'; - -//*********************************************************************** -//Engine power and torque calculations - +// Calculate the percentage of maximum rated power delivered as a function of Manifold pressure multiplied by engine speed (rpm) +// This is not necessarilly the best approach but seems to work for now. +// May well need tweaking at the bottom end if the prop model is changed. +void FGNewEngine::Calc_Percentage_Power(bool mag_left, bool mag_right) +{ // For a given Manifold Pressure and RPM calculate the % Power // Multiply Manifold Pressure by RPM - ManXRPM = Manifold_Pressure * RPM; - // cout << ManXRPM; - // cout << endl; + float ManXRPM = True_Manifold_Pressure * RPM; /* // Phil's %power correlation @@ -425,328 +546,155 @@ void FGNewEngine::update() { // Calculate %power for DCL prop model Percentage_Power = (7e-9 * ManXRPM * ManXRPM) + (7e-4 * ManXRPM) - 1.0; - // cout << Percentage_Power << "%" << "\t"; - + // Power de-rating for altitude has been removed now that we are basing the power + // on the actual manifold pressure, which takes air pressure into account. However - this fails to + // take the temperature into account - this is TODO. + // Adjust power for temperature - this is temporary until the power is done as a function of mass flow rate induced // Adjust for Temperature - Temperature above Standard decrease - // power % by 7/120 per degree F increase, and incease power for + // power by 7/120 % per degree F increase, and incease power for // temps below at the same ratio - Percentage_Power = Percentage_Power - (FG_ISA_VAR * 7 /120); - // cout << Percentage_Power << "%" << "\t"; - -//******DCL - this bit will need altering or removing if I go to true altitude adjusted manifold pressure - // Adjust for Altitude. In this version a linear variation is - // used. Decrease 1% for each 1000' increase in Altitde - Percentage_Power = Percentage_Power + (FG_Pressure_Ht * 12/10000); - // cout << Percentage_Power << "%" << "\t"; - + float T_amb_degF = (T_amb * 1.8) - 459.67; + float T_amb_sea_lev_degF = (288 * 1.8) - 459.67; + Percentage_Power = Percentage_Power + ((T_amb_sea_lev_degF - T_amb_degF) * 7 /120); //DCL - now adjust power to compensate for mixture - //uses a curve fit to the data in the IO360 / O360 operating manual - //due to the shape of the curve I had to use a 6th order fit - I am sure it must be possible to reduce this in future, - //possibly by using separate fits for rich and lean of best power mixture - //first adjust actual mixture to abstract mixture - this is a temporary hack in order to account for the fact that the data I have - //dosn't specify actual mixtures and I want to be able to change what I think they are without redoing the curve fit each time. - //y=10x-12 for now - abstract_mixture = 10.0 * equivalence_ratio - 12.0; - float m = abstract_mixture; //to simplify writing the next equation - Percentage_of_best_power_mixture_power = ((-0.0012*pow(m,6)) + (0.021*pow(m,5)) + (-0.1425*pow(m,4)) + (0.4395*pow(m,3)) + (-0.8909*m*m) + (-0.5155*m) + 100.03); + Percentage_of_best_power_mixture_power = Power_Mixture_Correlation(equivalence_ratio); Percentage_Power = Percentage_Power * Percentage_of_best_power_mixture_power / 100.0; - //cout << " %POWER = " << Percentage_Power << '\n'; - -//***DCL - FIXME - this needs altering - for instance going richer than full power mixture decreases the %power but increases the fuel flow - // Now Calculate Fuel Flow based on % Power Best Power Mixture -// Fuel_Flow = Percentage_Power * Max_Fuel_Flow / 100.0; - // cout << Fuel_Flow << " lbs/hr"<< endl; - // Now Derate engine for the effects of Bad/Switched off magnetos - if (Magneto_Left == 0 && Magneto_Right == 0) { + //if (Magneto_Left == 0 && Magneto_Right == 0) { + if(!running) { // cout << "Both OFF\n"; Percentage_Power = 0; - } else if (Magneto_Left && Magneto_Right) { + } else if (mag_left && mag_right) { // cout << "Both On "; - } else if (Magneto_Left == 0 || Magneto_Right== 0) { + } else if (mag_left == 0 || mag_right== 0) { // cout << "1 Magneto Failed "; - - Percentage_Power = Percentage_Power * - ((100.0 - Mag_Derate_Percent)/100.0); + Percentage_Power = Percentage_Power * ((100.0 - Mag_Derate_Percent)/100.0); // cout << FGEng1_Percentage_Power << "%" << "\t"; } - - HP = Percentage_Power * MaxHP / 100.0; - - Power_SI = HP * CONVERT_HP_TO_WATTS; - - // Calculate Engine Torque. Check for div by zero since percentage power correlation does not guarantee zero power at zero rpm. - if(RPM == 0) { - Torque_SI = 0; - } - else { - Torque_SI = (Power_SI * 60.0) / (2.0 * PI * RPM); //Torque = power / angular velocity - // cout << Torque << " Nm\n"; - } - -//********************************************************************** -//Calculate Exhaust gas temperature - - // cout << "Thi = " << equivalence_ratio << '\n'; - - combustion_efficiency = Lookup_Combustion_Efficiency(equivalence_ratio); //The combustion efficiency basically tells us what proportion of the fuels calorific value is released - - // cout << "Combustion efficiency = " << combustion_efficiency << '\n'; - - //now calculate energy release to exhaust - //We will assume a three way split of fuel energy between useful work, the coolant system and the exhaust system - //This is a reasonable first suck of the thumb estimate for a water cooled automotive engine - whether it holds for an air cooled aero engine is probably open to question - //Regardless - it won't affect the variation of EGT with mixture, and we con always put a multiplier on EGT to get a reasonable peak value. - enthalpy_exhaust = m_dot_fuel * calorific_value_fuel * combustion_efficiency * 0.33; - heat_capacity_exhaust = (Cp_air * m_dot_air) + (Cp_fuel * m_dot_fuel); - delta_T_exhaust = enthalpy_exhaust / heat_capacity_exhaust; -// delta_T_exhaust = Calculate_Delta_T_Exhaust(); - - // cout << "T_amb " << T_amb; - // cout << " dT exhaust = " << delta_T_exhaust; - - EGT = T_amb + delta_T_exhaust; - - //The above gives the exhaust temperature immediately prior to leaving the combustion chamber - //Now derate to give a more realistic figure as measured downstream - //For now we will aim for a peak of around 400 degC (750 degF) - - EGT *= 0.444 + ((0.544 - 0.444) * Percentage_Power / 100.0); - - EGT_degF = (EGT * 1.8) - 459.67; - - //cout << " EGT = " << EGT << " degK " << EGT_degF << " degF";// << '\n'; - -//*************************************************************************************** -// Calculate Cylinder Head Temperature - -/* DCL 27/10/00 - -This is a somewhat rough first attempt at modelling cylinder head temperature. The cylinder head -is assumed to be at uniform temperature. Obviously this is incorrect, but it simplifies things a -lot, and we're just looking for the behaviour of CHT to be correct. Energy transfer to the cylinder -head is assumed to be one third of the energy released by combustion at all conditions. This is a -reasonable estimate, although obviously in real life it varies with different conditions and possibly -with CHT itself. I've split energy transfer from the cylinder head into 2 terms - free convection - -ie convection to stationary air, and forced convection, ie convection into flowing air. The basic -free convection equation is: dqdt = -hAdT Since we don't know A and are going to set h quite arbitarily -anyway I've knocked A out and just wrapped it up in h - the only real significance is that the units -of h will be different but that dosn't really matter to us anyway. In addition, we have the problem -that the prop model I'm currently using dosn't model the backwash from the prop which will add to the -velocity of the cooling air when the prop is turning, so I've added an extra term to try and cope -with this. - -In real life, forced convection equations are genarally empirically derived, and are quite complicated -and generally contain such things as the Reynolds and Nusselt numbers to various powers. The best -course of action would probably to find an empirical correlation from the literature for a similar -situation and try and get it to fit well. However, for now I am using my own made up very simple -correlation for the energy transfer from the cylinder head: - -dqdt = -(h1.dT) -(h2.m_dot.dT) -(h3.rpm.dT) - -where dT is the temperature different between the cylinder head and the surrounding air, m_dot is the -mass flow rate of cooling air through an arbitary volume, rpm is the engine speed in rpm (this is the -backwash term), and h1, h2, h3 are co-efficients which we can play with to attempt to get the CHT -behaviour to match real life. - -In order to change the values of CHT that the engine settles down at at various conditions, -have a play with h1, h2 and h3. In order to change the rate of heating/cooling without affecting -equilibrium values alter the cylinder head mass, which is really quite arbitary. Bear in mind that -altering h1, h2 and h3 will also alter the rate of heating or cooling as well as equilibrium values, -but altering the cylinder head mass will only alter the rate. It would I suppose be better to read -the values from file to avoid the necessity for re-compilation every time I change them. - +/* + //DCL - stall the engine if RPM drops below 450 - this is possible if mixture lever is pulled right out + //This is a kludge that I should eliminate by adding a total fmep estimation. + if(RPM < 450) + Percentage_Power = 0; */ - //CHT = Calc_CHT( Fuel_Flow, Mixture, IAS); - // cout << "Cylinder Head Temp (F) = " << CHT << endl; - float h1 = -95.0; //co-efficient for free convection - float h2 = -3.95; //co-efficient for forced convection - float h3 = -0.05; //co-efficient for forced convection due to prop backwash - float v_apparent; //air velocity over cylinder head in m/s - float v_dot_cooling_air; - float m_dot_cooling_air; - float temperature_difference; - float arbitary_area = 1.0; - float dqdt_from_combustion; - float dqdt_forced; //Rate of energy transfer to/from cylinder head due to forced convection (Joules) (sign convention: to cylinder head is +ve) - float dqdt_free; //Rate of energy transfer to/from cylinder head due to free convection (Joules) (sign convention: to cylinder head is +ve) - float dqdt_cylinder_head; //Overall energy change in cylinder head - float CpCylinderHead = 800.0; //FIXME - this is a guess - I need to look up the correct value - float MassCylinderHead = 8.0; //Kg - this is a guess - it dosn't have to be absolutely accurate but can be varied to alter the warm-up rate - float HeatCapacityCylinderHead; - float dCHTdt; - - temperature_difference = CHT - T_amb; - - v_apparent = IAS * 0.5144444; //convert from knots to m/s - v_dot_cooling_air = arbitary_area * v_apparent; - m_dot_cooling_air = v_dot_cooling_air * rho_air; - - //Calculate rate of energy transfer to cylinder head from combustion - dqdt_from_combustion = m_dot_fuel * calorific_value_fuel * combustion_efficiency * 0.33; - - //Calculate rate of energy transfer from cylinder head due to cooling NOTE is calculated as rate to but negative - dqdt_forced = (h2 * m_dot_cooling_air * temperature_difference) + (h3 * RPM * temperature_difference); - dqdt_free = h1 * temperature_difference; - - //Calculate net rate of energy transfer to or from cylinder head - dqdt_cylinder_head = dqdt_from_combustion + dqdt_forced + dqdt_free; + if(Percentage_Power < 0) + Percentage_Power = 0; +} - HeatCapacityCylinderHead = CpCylinderHead * MassCylinderHead; +// Calculate Oil Temperature in degrees Kelvin +float FGNewEngine::Calc_Oil_Temp (float oil_temp) +{ + float idle_percentage_power = 2.3; // approximately + float target_oil_temp; // Steady state oil temp at the current engine conditions + float time_constant; // The time constant for the differential equation + if(running) { + target_oil_temp = 363; + time_constant = 500; // Time constant for engine-on idling. + if(Percentage_Power > idle_percentage_power) { + time_constant /= ((Percentage_Power / idle_percentage_power) / 10.0); // adjust for power + } + } else { + target_oil_temp = 298; + time_constant = 1000; // Time constant for engine-off; reflects the fact that oil is no longer getting circulated + } - dCHTdt = dqdt_cylinder_head / HeatCapacityCylinderHead; + float dOilTempdt = (target_oil_temp - oil_temp) / time_constant; - CHT += (dCHTdt * time_step); + oil_temp += (dOilTempdt * time_step); - CHT_degF = (CHT * 1.8) - 459.67; + return (oil_temp); +} - //cout << " CHT = " << CHT_degF << " degF\n"; +// Calculate Oil Pressure +float FGNewEngine::Calc_Oil_Press (float Oil_Temp, float Engine_RPM) +{ + float Oil_Pressure = 0; //PSI + float Oil_Press_Relief_Valve = 60; //PSI + float Oil_Press_RPM_Max = 1800; + float Design_Oil_Temp = 85; //Celsius + float Oil_Viscosity_Index = 0.25; // PSI/Deg C +// float Temp_Deviation = 0; // Deg C + Oil_Pressure = (Oil_Press_Relief_Valve / Oil_Press_RPM_Max) * Engine_RPM; -// End calculate Cylinder Head Temperature + // Pressure relief valve opens at Oil_Press_Relief_Valve PSI setting + if (Oil_Pressure >= Oil_Press_Relief_Valve) { + Oil_Pressure = Oil_Press_Relief_Valve; + } + // Now adjust pressure according to Temp which affects the viscosity -//*************************************************************************************** -// Oil pressure calculation + Oil_Pressure += (Design_Oil_Temp - Oil_Temp) * Oil_Viscosity_Index; - // Calculate Oil Pressure - Oil_Pressure = Oil_Press( Oil_Temp, RPM ); - // cout << "Oil Pressure (PSI) = " << Oil_Pressure << endl; - -//************************************************************************************** -// Now do the Propeller Calculations - -#ifdef NEVS_PROP_MODEL - - // Nev's prop model - - num_elements = 6.0; - number_of_blades = 2.0; - blade_length = 0.95; - allowance_for_spinner = blade_length / 12.0; - prop_fudge_factor = 1.453401525; - forward_velocity = IAS; - - theta[0] = 25.0; - theta[1] = 20.0; - theta[2] = 15.0; - theta[3] = 10.0; - theta[4] = 5.0; - theta[5] = 0.0; - - angular_velocity_SI = 2.0 * PI * RPM / 60.0; - - allowance_for_spinner = blade_length / 12.0; - //Calculate thrust and torque by summing the contributions from each of the blade elements - //Assumes equal length elements with numbered 1 inboard -> num_elements outboard - prop_torque = 0.0; - prop_thrust = 0.0; - int i; -// outfile << "Rho = " << Rho << '\n\n'; -// outfile << "Drag = "; - for(i=1;i<=num_elements;i++) - { - element = float(i); - distance = (blade_length * (element / num_elements)) + allowance_for_spinner; - element_drag = 0.5 * rho_air * ((distance * angular_velocity_SI)*(distance * angular_velocity_SI)) * (0.000833 * ((theta[int(element-1)] - (atan(forward_velocity/(distance * angular_velocity_SI))))*(theta[int(element-1)] - (atan(forward_velocity/(distance * angular_velocity_SI)))))) - * (0.1 * (blade_length / element)) * number_of_blades; - - element_lift = 0.5 * rho_air * ((distance * angular_velocity_SI)*(distance * angular_velocity_SI)) * (0.036 * (theta[int(element-1)] - (atan(forward_velocity/(distance * angular_velocity_SI))))+0.4) - * (0.1 * (blade_length / element)) * number_of_blades; - element_torque = element_drag * distance; - prop_torque += element_torque; - prop_thrust += element_lift; -// outfile << "Drag = " << element_drag << " n = " << element << '\n'; - } + return Oil_Pressure; +} -// outfile << '\n'; - -// outfile << "Angular velocity = " << angular_velocity_SI << " rad/s\n"; - - // cout << "Thrust = " << prop_thrust << '\n'; - prop_thrust *= prop_fudge_factor; - prop_torque *= prop_fudge_factor; - prop_power_consumed_SI = prop_torque * angular_velocity_SI; - prop_power_consumed_HP = prop_power_consumed_SI / 745.699; - - -#endif //NEVS_PROP_MODEL - -#ifdef DCL_PROP_MODEL - - double prop_diameter = 1.8; // meters - double J; // advance ratio - dimensionless - double Cp_20; // coefficient of power for 20 degree blade angle - double Cp_25; // coefficient of power for 25 degree blade angle - double Cp; // our actual coefficient of power - double blade_angle = 23.0; // degrees - double neta_prop_20; - double neta_prop_25; - double neta_prop; // prop efficiency - - Gear_Ratio = 1.0; - FGProp1_RPS = RPM * Gear_Ratio / 60.0; // Borrow this variable from Phils model for now !! - angular_velocity_SI = 2.0 * PI * RPM / 60.0; - forward_velocity = IAS * 0.514444444444; // Convert to m/s - - //cout << "Gear_Ratio = " << Gear_Ratio << '\n'; - //cout << "IAS = " << IAS << '\n'; - //cout << "forward_velocity = " << forward_velocity << '\n'; - //cout << "FGProp1_RPS = " << FGProp1_RPS << '\n'; - //cout << "prop_diameter = " << prop_diameter << '\n'; - if(FGProp1_RPS == 0) - J = 0; - else - J = forward_velocity / (FGProp1_RPS * prop_diameter); - //cout << "advance_ratio = " << J << '\n'; - - //Cp correlations based on data from McCormick - Cp_20 = 0.0342*J*J*J*J - 0.1102*J*J*J + 0.0365*J*J - 0.0133*J + 0.064; - Cp_25 = 0.0119*J*J*J*J - 0.0652*J*J*J + 0.018*J*J - 0.0077*J + 0.0921; - - //cout << "Cp_20 = " << Cp_20 << '\n'; - //cout << "Cp_25 = " << Cp_25 << '\n'; - - //Assume that the blade angle is between 20 and 25 deg - reasonable for fixed pitch prop but won't hold for variable one !!! - Cp = Cp_20 + ( (Cp_25 - Cp_20) * ((blade_angle - 20)/(25 - 20)) ); - //cout << "Cp = " << Cp << '\n'; - //cout << "RPM = " << RPM << '\n'; - //cout << "angular_velocity_SI = " << angular_velocity_SI << '\n'; - - prop_power_consumed_SI = Cp * rho_air * pow(FGProp1_RPS,3.0) * pow(prop_diameter,5.0); - //cout << "prop HP consumed = " << prop_power_consumed_SI / 745.699 << '\n'; - if(angular_velocity_SI == 0) - prop_torque = 0; - else - prop_torque = prop_power_consumed_SI / angular_velocity_SI; - - // calculate neta_prop here - neta_prop_20 = 0.1328*J*J*J*J - 1.3073*J*J*J + 0.3525*J*J + 1.5591*J + 0.0007; - neta_prop_25 = -0.3121*J*J*J*J + 0.4234*J*J*J - 0.7686*J*J + 1.5237*J - 0.0004; - neta_prop = neta_prop_20 + ( (neta_prop_25 - neta_prop_20) * ((blade_angle - 20)/(25 - 20)) ); - - //FIXME - need to check for zero forward velocity to avoid divide by zero - if(forward_velocity < 0.0001) - prop_thrust = 0.0; - else - prop_thrust = neta_prop * prop_power_consumed_SI / forward_velocity; //TODO - rename forward_velocity to IAS_SI - //cout << "prop_thrust = " << prop_thrust << '\n'; - -#endif //DCL_PROP_MODEL - - //Calculate new RPM from torque balance and inertia. - Torque_Imbalance = Torque_SI - prop_torque; //This gives a +ve value when the engine torque exeeds the prop torque - - angular_acceleration = Torque_Imbalance / (engine_inertia + prop_inertia); - angular_velocity_SI += (angular_acceleration * time_step); - RPM = (angular_velocity_SI * 60) / (2.0 * PI); - - //DCL - stall the engine if RPM drops below 550 - this is possible if mixture lever is pulled right out - if(RPM < 550) - RPM = 0; +// Propeller calculations. +void FGNewEngine::Do_Prop_Calcs() +{ + float Gear_Ratio = 1.0; + float forward_velocity; // m/s + float prop_power_consumed_SI; // Watts + double J; // advance ratio - dimensionless + double Cp_20; // coefficient of power for 20 degree blade angle + double Cp_25; // coefficient of power for 25 degree blade angle + double Cp; // Our actual coefficient of power + double neta_prop_20; + double neta_prop_25; + double neta_prop; // prop efficiency + + FGProp1_RPS = RPM * Gear_Ratio / 60.0; + angular_velocity_SI = 2.0 * LS_PI * RPM / 60.0; + forward_velocity = IAS * 0.514444444444; // Convert to m/s + + if(FGProp1_RPS == 0) + J = 0; + else + J = forward_velocity / (FGProp1_RPS * prop_diameter); + //cout << "advance_ratio = " << J << '\n'; + + //Cp correlations based on data from McCormick + Cp_20 = 0.0342*J*J*J*J - 0.1102*J*J*J + 0.0365*J*J - 0.0133*J + 0.064; + Cp_25 = 0.0119*J*J*J*J - 0.0652*J*J*J + 0.018*J*J - 0.0077*J + 0.0921; + + //cout << "Cp_20 = " << Cp_20 << '\n'; + //cout << "Cp_25 = " << Cp_25 << '\n'; + + //Assume that the blade angle is between 20 and 25 deg - reasonable for fixed pitch prop but won't hold for variable one !!! + Cp = Cp_20 + ( (Cp_25 - Cp_20) * ((blade_angle - 20)/(25 - 20)) ); + //cout << "Cp = " << Cp << '\n'; + //cout << "RPM = " << RPM << '\n'; + //cout << "angular_velocity_SI = " << angular_velocity_SI << '\n'; + + prop_power_consumed_SI = Cp * rho_air * pow(FGProp1_RPS,3.0f) * pow(float(prop_diameter),5.0f); + //cout << "prop HP consumed = " << prop_power_consumed_SI / 745.699 << '\n'; + if(angular_velocity_SI == 0) + prop_torque = 0; + // However this can give problems - if rpm == 0 but forward velocity increases the prop should be able to generate a torque to start the engine spinning + // Unlikely to happen in practice - but I suppose someone could move the lever of a stopped large piston engine from feathered to windmilling. + // This *does* give problems - if the plane is put into a steep climb whilst windmilling the engine friction will eventually stop it spinning. + // When put back into a dive it never starts re-spinning again. Although it is unlikely that anyone would do this in real life, they might well do it in a sim!!! + else + prop_torque = prop_power_consumed_SI / angular_velocity_SI; + + // calculate neta_prop here + neta_prop_20 = 0.1328*J*J*J*J - 1.3073*J*J*J + 0.3525*J*J + 1.5591*J + 0.0007; + neta_prop_25 = -0.3121*J*J*J*J + 0.4234*J*J*J - 0.7686*J*J + 1.5237*J - 0.0004; + neta_prop = neta_prop_20 + ( (neta_prop_25 - neta_prop_20) * ((blade_angle - 20)/(25 - 20)) ); + + // Check for zero forward velocity to avoid divide by zero + if(forward_velocity < 0.0001) + prop_thrust = 0.0; + // I don't see how this works - how can the plane possibly start from rest ??? + // Hmmmm - it works because the forward_velocity at present never drops below about 0.03 even at rest + // We can't really rely on this in the future - needs fixing !!!! + // The problem is that we're doing this calculation backwards - we're working out the thrust from the power consumed and the velocity, which becomes invalid as velocity goes to zero. + // It would be far more natural to work out the power consumed from the thrust - FIXME!!!!!. + else + prop_thrust = neta_prop * prop_power_consumed_SI / forward_velocity; //TODO - rename forward_velocity to IAS_SI + //cout << "prop_thrust = " << prop_thrust << '\n'; } -