2 // Author: Phil Schubert
3 // Date started: 12/03/99
4 // Purpose: Models a Continental IO-520-M Engine
5 // Called by: FGSimExec
7 // Copyright (C) 1999 Philip L. Schubert (philings@ozemail.com.au)
9 // This program is free software; you can redistribute it and/or
10 // modify it under the terms of the GNU General Public License as
11 // published by the Free Software Foundation; either version 2 of the
12 // License, or (at your option) any later version.
14 // This program is distributed in the hope that it will be useful, but
15 // WITHOUT ANY WARRANTY; without even the implied warranty of
16 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
17 // General Public License for more details.
19 // You should have received a copy of the GNU General Public License
20 // along with this program; if not, write to the Free Software
21 // Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
24 // Further information about the GNU General Public License can also
25 // be found on the world wide web at http://www.gnu.org.
27 // FUNCTIONAL DESCRIPTION
28 // ------------------------------------------------------------------------
29 // Models a Continental IO-520-M engine. This engine is used in Cessna
30 // 210, 310, Beechcraft Bonaza and Baron C55. The equations used below
31 // were determined by a first and second order curve fits using Excel.
32 // The data is from the Cessna Aircraft Corporations Engine and Flight
33 // Computer for C310. Part Number D3500-13
36 // ------------------------------------------------------------------------
40 // ------------------------------------------------------------------------
41 // 12/03/99 PLS Created
42 // 07/03/99 PLS Added Calculation of Density, and Prop_Torque
43 // 07/03/99 PLS Restructered Variables to allow easier implementation
45 // 15/03/99 PLS Added Oil Pressure, Oil Temperature and CH Temp
46 // ------------------------------------------------------------------------
48 // ------------------------------------------------------------------------
51 /////////////////////////////////////////////////////////////////////
53 // Modified by Dave Luff (david.luff@nottingham.ac.uk) September 2000
55 // Altered manifold pressure range to add a minimum value at idle to simulate the throttle stop / idle bypass valve,
56 // and to reduce the maximum value whilst the engine is running to slightly below ambient to account for CdA losses across the throttle
58 // Altered it a bit to model an IO360 from C172 - 360 cubic inches, 180 HP max, fixed pitch prop
59 // 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
60 // 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
62 // Added EGT model based on combustion efficiency and an energy balance with the exhaust gases
64 // Added a mixture - power correlation based on a curve in the IO360 operating manual
66 // I've tried to match the prop and engine model to give roughly 600 RPM idle and 180 HP at 2700 RPM
67 // but it is by no means currently at a completed stage - DCL 15/9/00
69 // DCL 28/9/00 - Added estimate of engine and prop inertia and changed engine speed calculation to be calculated from Angular acceleration = Torque / Inertia.
70 // Requires a timestep to be passed to FGNewEngine::init and currently assumes this timestep does not change.
71 // Could easily be altered to pass a variable timestep to FGNewEngine::update every step instead if required.
73 // DCL 27/10/00 - Added first stab at cylinder head temperature model
74 // See the comment block in the code for details
76 // DCL 02/11/00 - Modified EGT code to reduce values to those more representative of a sensor downstream
78 //////////////////////////////////////////////////////////////////////
80 #include <simgear/compiler.h>
90 // ------------------------------------------------------------------------
92 // ------------------------------------------------------------------------
95 // Calculate Engine RPM based on Propellor Lever Position
96 float FGNewEngine::Calc_Engine_RPM (float LeverPosition)
98 // Calculate RPM as set by Prop Lever Position. Assumes engine
99 // will run at 1000 RPM at full course
102 RPM = LeverPosition * Max_RPM / 100.0;
103 // * ((FGEng_Max_RPM + FGEng_Min_RPM) / 100);
105 if ( RPM >= Max_RPM ) {
113 float FGNewEngine::Lookup_Combustion_Efficiency(float thi_actual)
115 float thi[11]; //array of equivalence ratio values
116 float neta_comb[11]; //corresponding array of combustion efficiency values
117 float neta_comb_actual;
120 //thi = (0.0,0.9,1.0,1.05,1.1,1.15,1.2,1.3,1.4,1.5,1.6);
124 thi[3] = 1.05; //There must be an easier way of doing this !!!!!!!!
132 //neta_comb = (0.98,0.98,0.97,0.95,0.9,0.85,0.79,0.7,0.63,0.57,0.525);
143 neta_comb[10] = 0.525;
144 //combustion efficiency values from Heywood: ISBN 0-07-100499-8
148 j = 11; //This must be equal to the number of elements in the lookup table arrays
154 //this is just to avoid crashing the routine is we are bigger than the last element - for now just return the last element
155 //but at some point we will have to extrapolate further
156 neta_comb_actual = neta_comb[i];
157 return neta_comb_actual;
159 if(thi_actual == thi[i])
161 neta_comb_actual = neta_comb[i];
162 return neta_comb_actual;
164 if((thi_actual > thi[i]) && (thi_actual < thi[i + 1]))
166 //do linear interpolation between the two points
167 factor = (thi_actual - thi[i]) / (thi[i+1] - thi[i]);
168 neta_comb_actual = (factor * (neta_comb[i+1] - neta_comb[i])) + neta_comb[i];
169 return neta_comb_actual;
173 //if we get here something has gone badly wrong
174 cout << "ERROR: error in FGNewEngine::Lookup_Combustion_Efficiency\n";
176 return neta_comb_actual; //keeps the compiler happy
179 float FGNewEngine::Calculate_Delta_T_Exhaust(void)
182 heat_capacity_exhaust = (Cp_air * m_dot_air) + (Cp_fuel * m_dot_fuel);
183 dT_exhaust = enthalpy_exhaust / heat_capacity_exhaust;
189 // Calculate Manifold Pressure based on Throttle lever Position
190 static float Calc_Manifold_Pressure ( float LeverPosn, float MaxMan, float MinMan)
197 //Note that setting the manifold pressure as a function of lever position only is not strictly accurate
198 //MAP is also a function of engine speed.
199 Inches = MinMan + (LeverPosn * (MaxMan - MinMan) / 100);
201 //allow for idle bypass valve or slightly open throttle stop
209 // set initial default values
210 void FGNewEngine::init(double dt) {
212 CONVERT_CUBIC_INCHES_TO_METERS_CUBED = 1.638706e-5;
213 // Control and environment inputs
215 Throttle_Lever_Pos = 75;
216 Propeller_Lever_Pos = 75;
217 Mixture_Lever_Pos = 100;
218 Cp_air = 1005; // J/KgK
219 Cp_fuel = 1700; // J/KgK
220 calorific_value_fuel = 47.3e6; // W/Kg Note that this is only an approximate value
224 // Engine Specific Variables used by this program that have limits.
225 // Will be set in a parameter file to be read in to create
226 // and instance for each engine.
227 Max_Manifold_Pressure = 28.50; //Inches Hg. An approximation - should be able to find it in the engine performance data
228 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
230 Min_RPM = 600; //Recommended idle from Continental data sheet
232 Mag_Derate_Percent = 5;
233 // MaxHP = 285; //Continental IO520-M
234 MaxHP = 180; //Lycoming IO360
235 // displacement = 520; //Continental IO520-M
236 displacement = 360; //Lycoming IO360
237 engine_inertia = 0.2; //kgm^2 - value taken from a popular family saloon car engine - need to find an aeroengine value !!!!!
238 prop_inertia = 0.03; //kgm^2 - this value is a total guess - dcl
239 displacement_SI = displacement * CONVERT_CUBIC_INCHES_TO_METERS_CUBED;
245 CONVERT_HP_TO_WATTS = 745.6999;
247 // outfile.open(ios::out|ios::trunc);
249 // Initialise Engine Variables used by this instance
250 Percentage_Power = 0;
251 Manifold_Pressure = 29.00; // Inches
253 Fuel_Flow = 0; // lbs/hour
255 CHT = 298.0; //deg Kelvin
256 CHT_degF = (CHT * 1.8) - 459.67; //deg Fahrenheit
258 Oil_Pressure = 0; // PSI
259 Oil_Temp = 85; // Deg C
262 Torque_Imbalance = 0;
263 Desired_RPM = 2500; //Recommended cruise RPM from Continental datasheet
265 // Initialise Propellor Variables used by this instance
266 FGProp1_Angular_V = 0;
267 FGProp1_Coef_Drag = 0.6;
271 FGProp1_Coef_Lift = 0.1;
273 FGProp1_Blade_Angle = 13.5;
274 FGProp_Fine_Pitch_Stop = 13.5;
276 // Other internal values
281 // Calculate Oil Pressure
282 static float Oil_Press (float Oil_Temp, float Engine_RPM)
284 float Oil_Pressure = 0; //PSI
285 float Oil_Press_Relief_Valve = 60; //PSI
286 float Oil_Press_RPM_Max = 1800;
287 float Design_Oil_Temp = 85; //Celsius
288 float Oil_Viscosity_Index = 0.25; // PSI/Deg C
289 float Temp_Deviation = 0; // Deg C
291 Oil_Pressure = (Oil_Press_Relief_Valve / Oil_Press_RPM_Max) * Engine_RPM;
293 // Pressure relief valve opens at Oil_Press_Relief_Valve PSI setting
294 if (Oil_Pressure >= Oil_Press_Relief_Valve)
296 Oil_Pressure = Oil_Press_Relief_Valve;
299 // Now adjust pressure according to Temp which affects the viscosity
301 Oil_Pressure += (Design_Oil_Temp - Oil_Temp) * Oil_Viscosity_Index;
308 // Calculate Cylinder Head Temperature
309 static float Calc_CHT (float Fuel_Flow, float Mixture, float IAS, float rhoair, float tamb)
318 //Calculate Exhaust Gas Temperature
319 //For now we will simply adjust this as a function of mixture
320 //It may be necessary to consider fuel flow rates and CHT in the calculation in the future
321 static float Calc_EGT (float Mixture)
323 float EGT = 1000; //off the top of my head !!!!
324 //Now adjust for mixture strength
330 // Calculate Density Ratio
331 static float Density_Ratio ( float x )
334 y = ((3E-10 * x * x) - (3E-05 * x) + 0.9998);
339 // Calculate Air Density - Rho
340 static float Density ( float x )
343 y = ((9E-08 * x * x) - (7E-08 * x) + 0.0024);
348 // Calculate Speed in FPS given Knots CAS
349 static float IAS_to_FPS (float x)
357 //*****************************************************************************
358 //*****************************************************************************
359 // update the engine model based on current control positions
360 void FGNewEngine::update() {
361 // Declare local variables
363 // const int num2 = 500; // default is 100, number if iterations to run
364 // const int num2 = 5; // default is 100, number if iterations to run
370 // Set up the new variables
371 float Blade_Station = 30;
372 float FGProp_Area = 1.405/3;
373 float PI = 3.1428571;
377 // 0 = Closed, 100 = Fully Open
378 // float Throttle_Lever_Pos = 75;
379 // 0 = Full Course 100 = Full Fine
380 // float Propeller_Lever_Pos = 75;
381 // 0 = Idle Cut Off 100 = Full Rich
382 // float Mixture_Lever_Pos = 100;
384 // Environmental Variables
386 // Temp Variation from ISA (Deg F)
387 float FG_ISA_VAR = 0;
388 // Pressure Altitude 1000's of Feet
389 float FG_Pressure_Ht = 0;
391 // Parameters that alter the operation of the engine.
392 int Fuel_Available = 1; // Yes = 1. Is there Fuel Available. Calculated elsewhere
393 int Alternate_Air_Pos =0; // Off = 0. Reduces power by 3 % for same throttle setting
394 int Magneto_Left = 1; // 1 = On. Reduces power by 5 % for same power lever settings
395 int Magneto_Right = 1; // 1 = On. Ditto, Both of the above though do not alter fuel flow
398 //==================================================================
399 // Engine & Environmental Inputs from elsewhere
401 // Calculate Air Density (Rho) - In FG this is calculated in
404 Rho = Density(FG_Pressure_Ht); // In FG FG_Pressure_Ht is "h"
405 // cout << "Rho = " << Rho << endl;
407 // Calculate Manifold Pressure (Engine 1) as set by throttle opening
410 Calc_Manifold_Pressure( Throttle_Lever_Pos, Max_Manifold_Pressure, Min_Manifold_Pressure );
411 // cout << "manifold pressure = " << Manifold_Pressure << endl;
413 //**************************FIXME*******************************************
414 //DCL - hack for testing - fly at sea level
417 p_amb_sea_level = 101325;
419 //DCL - next calculate m_dot_air and m_dot_fuel into engine
421 //calculate actual ambient pressure and temperature from altitude
422 //Then find the actual manifold pressure (the calculated one is the sea level pressure)
423 True_Manifold_Pressure = Manifold_Pressure * p_amb / p_amb_sea_level;
425 // RPM = Calc_Engine_RPM(Propeller_Lever_Pos);
427 // cout << "Initial engine RPM = " << RPM << endl;
429 // Desired_RPM = RPM;
433 //DCL - calculate mass air flow into engine based on speed and load - separate this out into a function eventually
434 //t_amb is actual temperature calculated from altitude
435 //calculate density from ideal gas equation
436 rho_air = p_amb / ( R_air * T_amb );
437 rho_air_manifold = rho_air * Manifold_Pressure / 29.6;
438 //calculate ideal engine volume inducted per second
439 swept_volume = (displacement_SI * (RPM / 60)) / 2; //This equation is only valid for a four stroke engine
440 //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
441 volumetric_efficiency = 0.8;
442 //Now use volumetric efficiency to calculate actual air volume inducted per second
443 v_dot_air = swept_volume * volumetric_efficiency;
444 //Now calculate mass flow rate of air into engine
445 m_dot_air = v_dot_air * rho_air_manifold;
447 // cout << "rho air manifold " << rho_air_manifold << '\n';
448 // cout << "Swept volume " << swept_volume << '\n';
452 //DCL - now calculate fuel flow into engine based on air flow and mixture lever position
453 //assume lever runs from no flow at fully out to thi = 1.6 at fully in at sea level
454 //also assume that the injector linkage is ideal - hence the set mixture is maintained at a given altitude throughout the speed and load range
455 thi_sea_level = 1.6 * ( Mixture_Lever_Pos / 100.0 );
456 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
457 m_dot_fuel = m_dot_air / 14.7 * equivalence_ratio;
459 // cout << "fuel " << m_dot_fuel;
460 // cout << " air " << m_dot_air << '\n';
462 //***********************************************************************
463 //Calculate percentage power
465 // For a given Manifold Pressure and RPM calculate the % Power
466 // Multiply Manifold Pressure by RPM
467 ManXRPM = Manifold_Pressure * RPM;
472 // Phil's %power correlation
474 Percentage_Power = (+ 7E-09 * ManXRPM * ManXRPM) + ( + 7E-04 * ManXRPM) - 0.1218;
475 // cout << Percentage_Power << "%" << "\t";
478 // DCL %power correlation - basically Phil's correlation modified to give slighty less power at the low end
479 // might need some adjustment as the prop model is adjusted
480 // My aim is to match the prop model and engine model at the low end to give the manufacturer's recommended idle speed with the throttle closed - 600rpm for the Continental IO520
482 Percentage_Power = (+ 6E-09 * ManXRPM * ManXRPM) + ( + 8E-04 * ManXRPM) - 1.8524;
483 // cout << Percentage_Power << "%" << "\t";
486 // Adjust for Temperature - Temperature above Standard decrease
487 // power % by 7/120 per degree F increase, and incease power for
488 // temps below at the same ratio
489 Percentage_Power = Percentage_Power - (FG_ISA_VAR * 7 /120);
490 // cout << Percentage_Power << "%" << "\t";
492 //******DCL - this bit will need altering or removing if I go to true altitude adjusted manifold pressure
493 // Adjust for Altitude. In this version a linear variation is
494 // used. Decrease 1% for each 1000' increase in Altitde
495 Percentage_Power = Percentage_Power + (FG_Pressure_Ht * 12/10000);
496 // cout << Percentage_Power << "%" << "\t";
499 //DCL - now adjust power to compensate for mixture
500 //uses a curve fit to the data in the IO360 / O360 operating manual
501 //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,
502 //possibly by using separate fits for rich and lean of best power mixture
503 //first adjust actual mixture to abstract mixture - this is a temporary hack in order to account for the fact that the data I have
504 //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.
506 abstract_mixture = 10.0 * equivalence_ratio - 12.0;
507 float m = abstract_mixture; //to simplify writing the next equation
508 Percentage_of_best_power_mixture_power = ((-0.0012*m*m*m*m*m*m) + (0.021*m*m*m*m*m) + (-0.1425*m*m*m*m) + (0.4395*m*m*m) + (-0.8909*m*m) + (-0.5155*m) + 100.03);
509 Percentage_Power = Percentage_Power * Percentage_of_best_power_mixture_power / 100.0;
511 //cout << " %POWER = " << Percentage_Power << '\n';
513 //***DCL - FIXME - this needs altering - for instance going richer than full power mixture decreases the %power but increases the fuel flow
514 // Now Calculate Fuel Flow based on % Power Best Power Mixture
515 Fuel_Flow = Percentage_Power * Max_Fuel_Flow / 100.0;
516 // cout << Fuel_Flow << " lbs/hr"<< endl;
518 // Now Derate engine for the effects of Bad/Switched off magnetos
519 if (Magneto_Left == 0 && Magneto_Right == 0) {
520 // cout << "Both OFF\n";
521 Percentage_Power = 0;
522 } else if (Magneto_Left && Magneto_Right) {
523 // cout << "Both On ";
524 } else if (Magneto_Left == 0 || Magneto_Right== 0) {
525 // cout << "1 Magneto Failed ";
527 Percentage_Power = Percentage_Power *
528 ((100.0 - Mag_Derate_Percent)/100.0);
529 // cout << FGEng1_Percentage_Power << "%" << "\t";
534 //**********************************************************************
535 //Calculate Exhaust gas temperature
537 // cout << "Thi = " << equivalence_ratio << '\n';
539 combustion_efficiency = Lookup_Combustion_Efficiency(equivalence_ratio); //The combustion efficiency basically tells us what proportion of the fuels calorific value is released
541 // cout << "Combustion efficiency = " << combustion_efficiency << '\n';
543 //now calculate energy release to exhaust
544 //We will assume a three way split of fuel energy between useful work, the coolant system and the exhaust system
545 //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
546 //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.
547 enthalpy_exhaust = m_dot_fuel * calorific_value_fuel * combustion_efficiency * 0.33;
548 heat_capacity_exhaust = (Cp_air * m_dot_air) + (Cp_fuel * m_dot_fuel);
549 delta_T_exhaust = enthalpy_exhaust / heat_capacity_exhaust;
550 // delta_T_exhaust = Calculate_Delta_T_Exhaust();
552 // cout << "T_amb " << T_amb;
553 // cout << " dT exhaust = " << delta_T_exhaust;
555 EGT = T_amb + delta_T_exhaust;
557 //The above gives the exhaust temperature immediately prior to leaving the combustion chamber
558 //Now derate to give a more realistic figure as measured downstream
559 //For now we will aim for a peak of around 400 degC (750 degF)
561 EGT *= 0.444 + ((0.544 - 0.444) * Percentage_Power / 100.0);
563 EGT_degF = (EGT * 1.8) - 459.67;
565 //cout << " EGT = " << EGT << " degK " << EGT_degF << " degF";// << '\n';
567 //***************************************************************************************
568 // Calculate Cylinder Head Temperature
572 This is a somewhat rough first attempt at modelling cylinder head temperature. The cylinder head
573 is assumed to be at uniform temperature. Obviously this is incorrect, but it simplifies things a
574 lot, and we're just looking for the behaviour of CHT to be correct. Energy transfer to the cylinder
575 head is assumed to be one third of the energy released by combustion at all conditions. This is a
576 reasonable estimate, although obviously in real life it varies with different conditions and possibly
577 with CHT itself. I've split energy transfer from the cylinder head into 2 terms - free convection -
578 ie convection to stationary air, and forced convection, ie convection into flowing air. The basic
579 free convection equation is: dqdt = -hAdT Since we don't know A and are going to set h quite arbitarily
580 anyway I've knocked A out and just wrapped it up in h - the only real significance is that the units
581 of h will be different but that dosn't really matter to us anyway. In addition, we have the problem
582 that the prop model I'm currently using dosn't model the backwash from the prop which will add to the
583 velocity of the cooling air when the prop is turning, so I've added an extra term to try and cope
586 In real life, forced convection equations are genarally empirically derived, and are quite complicated
587 and generally contain such things as the Reynolds and Nusselt numbers to various powers. The best
588 course of action would probably to find an empirical correlation from the literature for a similar
589 situation and try and get it to fit well. However, for now I am using my own made up very simple
590 correlation for the energy transfer from the cylinder head:
592 dqdt = -(h1.dT) -(h2.m_dot.dT) -(h3.rpm.dT)
594 where dT is the temperature different between the cylinder head and the surrounding air, m_dot is the
595 mass flow rate of cooling air through an arbitary volume, rpm is the engine speed in rpm (this is the
596 backwash term), and h1, h2, h3 are co-efficients which we can play with to attempt to get the CHT
597 behaviour to match real life.
599 In order to change the values of CHT that the engine settles down at at various conditions,
600 have a play with h1, h2 and h3. In order to change the rate of heating/cooling without affecting
601 equilibrium values alter the cylinder head mass, which is really quite arbitary. Bear in mind that
602 altering h1, h2 and h3 will also alter the rate of heating or cooling as well as equilibrium values,
603 but altering the cylinder head mass will only alter the rate. It would I suppose be better to read
604 the values from file to avoid the necessity for re-compilation every time I change them.
607 //CHT = Calc_CHT( Fuel_Flow, Mixture, IAS);
608 // cout << "Cylinder Head Temp (F) = " << CHT << endl;
609 float h1 = -95.0; //co-efficient for free convection
610 float h2 = -3.95; //co-efficient for forced convection
611 float h3 = -0.05; //co-efficient for forced convection due to prop backwash
612 float v_apparent; //air velocity over cylinder head in m/s
613 float v_dot_cooling_air;
614 float m_dot_cooling_air;
615 float temperature_difference;
616 float arbitary_area = 1.0;
617 float dqdt_from_combustion;
618 float dqdt_forced; //Rate of energy transfer to/from cylinder head due to forced convection (Joules) (sign convention: to cylinder head is +ve)
619 float dqdt_free; //Rate of energy transfer to/from cylinder head due to free convection (Joules) (sign convention: to cylinder head is +ve)
620 float dqdt_cylinder_head; //Overall energy change in cylinder head
621 float CpCylinderHead = 800.0; //FIXME - this is a guess - I need to look up the correct value
622 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
623 float HeatCapacityCylinderHead;
626 temperature_difference = CHT - T_amb;
628 v_apparent = IAS * 0.5144444; //convert from knots to m/s
629 v_dot_cooling_air = arbitary_area * v_apparent;
630 m_dot_cooling_air = v_dot_cooling_air * rho_air;
632 //Calculate rate of energy transfer to cylinder head from combustion
633 dqdt_from_combustion = m_dot_fuel * calorific_value_fuel * combustion_efficiency * 0.33;
635 //Calculate rate of energy transfer from cylinder head due to cooling NOTE is calculated as rate to but negative
636 dqdt_forced = (h2 * m_dot_cooling_air * temperature_difference) + (h3 * RPM * temperature_difference);
637 dqdt_free = h1 * temperature_difference;
639 //Calculate net rate of energy transfer to or from cylinder head
640 dqdt_cylinder_head = dqdt_from_combustion + dqdt_forced + dqdt_free;
642 HeatCapacityCylinderHead = CpCylinderHead * MassCylinderHead;
644 dCHTdt = dqdt_cylinder_head / HeatCapacityCylinderHead;
646 CHT += (dCHTdt * time_step);
648 CHT_degF = (CHT * 1.8) - 459.67;
650 //cout << " CHT = " << CHT_degF << " degF\n";
653 // End calculate Cylinder Head Temperature
656 //***************************************************************************************
657 // Engine Power & Torque Calculations
662 // Calculate Engine Horsepower
664 HP = Percentage_Power * MaxHP / 100.0;
666 Power_SI = HP * CONVERT_HP_TO_WATTS;
668 // Calculate Engine Torque
670 Torque = HP * 5252 / RPM;
671 // cout << Torque << "Ft/lbs" << "\t";
673 Torque_SI = (Power_SI * 60.0) / (2.0 * PI * RPM); //Torque = power / angular velocity
674 // cout << Torque << " Nm\n";
677 // Calculate Oil Pressure
678 Oil_Pressure = Oil_Press( Oil_Temp, RPM );
679 // cout << "Oil Pressure (PSI) = " << Oil_Pressure << endl;
681 //==============================================================
683 // Now do the Propellor Calculations
685 #ifdef PHILS_PROP_MODEL
688 FGProp1_RPS = RPM * Gear_Ratio / 60.0;
689 // cout << FGProp1_RPS << " RPS" << endl;
691 //Radial Flow Vector (V2) Ft/sec at Ref Blade Station (usually 30")
692 FGProp1_Angular_V = FGProp1_RPS * 2 * PI * (Blade_Station / 12);
693 // cout << FGProp1_Angular_V << "Angular Velocity " << endl;
695 // Axial Flow Vector (Vo) Ft/sec
696 // Some further work required here to allow for inflow at low speeds
697 // Vo = (IAS + 20) * 1.688888;
698 Vo = IAS_to_FPS(IAS + 20);
699 // cout << "Feet/sec = " << Vo << endl;
701 // cout << Vo << "Axial Velocity" << endl;
703 // Relative Velocity (V1)
704 V1 = sqrt((FGProp1_Angular_V * FGProp1_Angular_V) +
706 // cout << V1 << "Relative Velocity " << endl;
708 // cout << FGProp1_Blade_Angle << " Prop Blade Angle" << endl;
710 // Blade Angle of Attack (Alpha1)
712 /* cout << " Alpha1 = " << Alpha1
713 << " Blade angle = " << FGProp1_Blade_Angle
715 << " FGProp1_Angular_V = " << FGProp1_Angular_V << endl;*/
716 Alpha1 = FGProp1_Blade_Angle -(atan(Vo / FGProp1_Angular_V) * (180/PI));
717 // cout << Alpha1 << " Alpha1" << endl;
719 // Calculate Coefficient of Drag at Alpha1
720 FGProp1_Coef_Drag = (0.0005 * (Alpha1 * Alpha1)) + (0.0003 * Alpha1)
722 // cout << FGProp1_Coef_Drag << " Coef Drag" << endl;
724 // Calculate Coefficient of Lift at Alpha1
725 FGProp1_Coef_Lift = -(0.0026 * (Alpha1 * Alpha1)) + (0.1027 * Alpha1)
727 // cout << FGProp1_Coef_Lift << " Coef Lift " << endl;
729 // Covert Alplha1 to Radians
730 // Alpha1 = Alpha1 * PI / 180;
732 // Calculate Prop Torque
733 FGProp1_Torque = (0.5 * Rho * (V1 * V1) * FGProp_Area
734 * ((FGProp1_Coef_Lift * sin(Alpha1 * PI / 180))
735 + (FGProp1_Coef_Drag * cos(Alpha1 * PI / 180))))
736 * (Blade_Station/12);
737 // cout << FGProp1_Torque << " Prop Torque" << endl;
739 // Calculate Prop Thrust
740 // cout << " V1 = " << V1 << " Alpha1 = " << Alpha1 << endl;
741 FGProp1_Thrust = 0.5 * Rho * (V1 * V1) * FGProp_Area
742 * ((FGProp1_Coef_Lift * cos(Alpha1 * PI / 180))
743 - (FGProp1_Coef_Drag * sin(Alpha1 * PI / 180)));
744 // cout << FGProp1_Thrust << " Prop Thrust " << endl;
746 // End of Propeller Calculations
747 //==============================================================
749 #endif //PHILS_PROP_MODEL
751 #ifdef NEVS_PROP_MODEL
756 number_of_blades = 2.0;
758 allowance_for_spinner = blade_length / 12.0;
759 prop_fudge_factor = 1.453401525;
760 forward_velocity = IAS;
769 angular_velocity_SI = 2.0 * PI * RPM / 60.0;
771 allowance_for_spinner = blade_length / 12.0;
772 //Calculate thrust and torque by summing the contributions from each of the blade elements
773 //Assumes equal length elements with numbered 1 inboard -> num_elements outboard
777 // outfile << "Rho = " << Rho << '\n\n';
778 // outfile << "Drag = ";
779 for(i=1;i<=num_elements;i++)
782 distance = (blade_length * (element / num_elements)) + allowance_for_spinner;
783 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))))))
784 * (0.1 * (blade_length / element)) * number_of_blades;
786 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)
787 * (0.1 * (blade_length / element)) * number_of_blades;
788 element_torque = element_drag * distance;
789 prop_torque += element_torque;
790 prop_thrust += element_lift;
791 // outfile << "Drag = " << element_drag << " n = " << element << '\n';
796 // outfile << "Angular velocity = " << angular_velocity_SI << " rad/s\n";
798 // cout << "Thrust = " << prop_thrust << '\n';
799 prop_thrust *= prop_fudge_factor;
800 prop_torque *= prop_fudge_factor;
801 prop_power_consumed_SI = prop_torque * angular_velocity_SI;
802 prop_power_consumed_HP = prop_power_consumed_SI / 745.699;
805 #endif //NEVS_PROP_MODEL
809 #ifdef PHILS_PROP_MODEL //Do Torque calculations in Ft/lbs - yuk :-(((
810 Torque_Imbalance = FGProp1_Torque - Torque;
812 if (Torque_Imbalance > 5) {
814 // FGProp1_RPM -= 25;
815 // FGProp1_Blade_Angle -= 0.75;
818 if (Torque_Imbalance < -5) {
820 // FGProp1_RPM += 25;
821 // FGProp1_Blade_Angle += 0.75;
826 #ifdef NEVS_PROP_MODEL //use proper units - Nm
827 Torque_Imbalance = Torque_SI - prop_torque; //This gives a +ve value when the engine torque exeeds the prop torque
829 angular_acceleration = Torque_Imbalance / (engine_inertia + prop_inertia);
830 angular_velocity_SI += (angular_acceleration * time_step);
831 RPM = (angular_velocity_SI * 60) / (2.0 * PI);
837 if( RPM > (Desired_RPM + 2)) {
838 FGProp1_Blade_Angle += 0.75; //This value could be altered depending on how far from the desired RPM we are
841 if( RPM < (Desired_RPM - 2)) {
842 FGProp1_Blade_Angle -= 0.75;
845 if (FGProp1_Blade_Angle < FGProp_Fine_Pitch_Stop) {
846 FGProp1_Blade_Angle = FGProp_Fine_Pitch_Stop;
853 //end constant speed prop
856 //DCL - stall the engine if RPM drops below 550 - this is possible if mixture lever is pulled right out
860 // outfile << "RPM = " << RPM << " Blade angle = " << FGProp1_Blade_Angle << " Engine torque = " << Torque << " Prop torque = " << FGProp1_Torque << '\n';
861 // outfile << "RPM = " << RPM << " Engine torque = " << Torque_SI << " Prop torque = " << prop_torque << '\n';
863 // cout << FGEng1_RPM << " Blade_Angle " << FGProp1_Blade_Angle << endl << endl;
867 // cout << "Final engine RPM = " << RPM << '\n';
875 // Calculate Oil Temperature
877 static float Oil_Temp (float Fuel_Flow, float Mixture, float IAS)