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 float FGNewEngine::Lookup_Combustion_Efficiency(float thi_actual)
92 const int NUM_ELEMENTS = 11;
93 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
94 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
95 //combustion efficiency values from Heywood: ISBN 0-07-100499-8
96 float neta_comb_actual;
101 j = NUM_ELEMENTS; //This must be equal to the number of elements in the lookup table arrays
107 //this is just to avoid crashing the routine is we are bigger than the last element - for now just return the last element
108 //but at some point we will have to extrapolate further
109 neta_comb_actual = neta_comb[i];
110 return neta_comb_actual;
112 if(thi_actual == thi[i])
114 neta_comb_actual = neta_comb[i];
115 return neta_comb_actual;
117 if((thi_actual > thi[i]) && (thi_actual < thi[i + 1]))
119 //do linear interpolation between the two points
120 factor = (thi_actual - thi[i]) / (thi[i+1] - thi[i]);
121 neta_comb_actual = (factor * (neta_comb[i+1] - neta_comb[i])) + neta_comb[i];
122 return neta_comb_actual;
126 //if we get here something has gone badly wrong
127 cout << "ERROR: error in FGNewEngine::Lookup_Combustion_Efficiency\n";
128 return neta_comb_actual;
132 // Calculate Manifold Pressure based on Throttle lever Position
133 static float Calc_Manifold_Pressure ( float LeverPosn, float MaxMan, float MinMan)
140 //Note that setting the manifold pressure as a function of lever position only is not strictly accurate
141 //MAP is also a function of engine speed. (and ambient pressure if we are going for an actual MAP model)
142 Inches = MinMan + (LeverPosn * (MaxMan - MinMan) / 100);
144 //allow for idle bypass valve or slightly open throttle stop
154 // Calculate Oil Temperature
155 static float Oil_Temp (float Fuel_Flow, float Mixture, float IAS)
162 // Calculate Oil Pressure
163 static float Oil_Press (float Oil_Temp, float Engine_RPM)
165 float Oil_Pressure = 0; //PSI
166 float Oil_Press_Relief_Valve = 60; //PSI
167 float Oil_Press_RPM_Max = 1800;
168 float Design_Oil_Temp = 85; //Celsius
169 float Oil_Viscosity_Index = 0.25; // PSI/Deg C
170 float Temp_Deviation = 0; // Deg C
172 Oil_Pressure = (Oil_Press_Relief_Valve / Oil_Press_RPM_Max) * Engine_RPM;
174 // Pressure relief valve opens at Oil_Press_Relief_Valve PSI setting
175 if (Oil_Pressure >= Oil_Press_Relief_Valve)
177 Oil_Pressure = Oil_Press_Relief_Valve;
180 // Now adjust pressure according to Temp which affects the viscosity
182 Oil_Pressure += (Design_Oil_Temp - Oil_Temp) * Oil_Viscosity_Index;
188 // Calculate Density Ratio
189 static float Density_Ratio ( float x )
192 y = ((3E-10 * x * x) - (3E-05 * x) + 0.9998);
197 // Calculate Air Density - Rho
198 static float Density ( float x )
201 y = ((9E-08 * x * x) - (7E-08 * x) + 0.0024);
206 // Calculate Speed in FPS given Knots CAS
207 static float IAS_to_FPS (float x)
215 //*************************************************************************************
216 // Initialise the engine model
217 void FGNewEngine::init(double dt) {
219 // These constants should probably be moved eventually
220 CONVERT_CUBIC_INCHES_TO_METERS_CUBED = 1.638706e-5;
221 CONVERT_HP_TO_WATTS = 745.6999;
223 // Properties of working fluids
224 Cp_air = 1005; // J/KgK
225 Cp_fuel = 1700; // J/KgK
226 calorific_value_fuel = 47.3e6; // W/Kg Note that this is only an approximate value
229 // Control and environment inputs
231 Throttle_Lever_Pos = 75;
232 Propeller_Lever_Pos = 75;
233 Mixture_Lever_Pos = 100;
237 // Engine Specific Variables.
238 // Will be set in a parameter file to be read in to create
239 // and instance for each engine.
240 Max_Manifold_Pressure = 28.50; //Inches Hg. An approximation - should be able to find it in the engine performance data
241 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
243 Min_RPM = 600; //Recommended idle from Continental data sheet
245 Mag_Derate_Percent = 5;
246 // MaxHP = 285; //Continental IO520-M
247 MaxHP = 180; //Lycoming IO360
248 // displacement = 520; //Continental IO520-M
249 displacement = 360; //Lycoming IO360
250 displacement_SI = displacement * CONVERT_CUBIC_INCHES_TO_METERS_CUBED;
251 engine_inertia = 0.2; //kgm^2 - value taken from a popular family saloon car engine - need to find an aeroengine value !!!!!
252 prop_inertia = 0.03; //kgm^2 - this value is a total guess - dcl
259 // Initialise Engine Variables used by this instance
260 Percentage_Power = 0;
261 Manifold_Pressure = 29.00; // Inches
263 Fuel_Flow = 0; // lbs/hour
266 CHT = 298.0; //deg Kelvin
267 CHT_degF = (CHT * 1.8) - 459.67; //deg Fahrenheit
269 Oil_Pressure = 0; // PSI
270 Oil_Temp = 85; // Deg C
273 Torque_Imbalance = 0;
275 // Initialise Propellor Variables used by this instance
276 FGProp1_Angular_V = 0;
277 FGProp1_Coef_Drag = 0.6;
281 FGProp1_Coef_Lift = 0.1;
283 FGProp1_Blade_Angle = 13.5;
284 FGProp_Fine_Pitch_Stop = 13.5;
286 // Other internal values
291 //*****************************************************************************
292 //*****************************************************************************
293 // update the engine model based on current control positions
294 void FGNewEngine::update() {
295 // Declare local variables
297 // const int num2 = 500; // default is 100, number if iterations to run
298 // const int num2 = 5; // default is 100, number if iterations to run
304 // Set up the new variables
305 float Blade_Station = 30;
306 float FGProp_Area = 1.405/3;
307 float PI = 3.1428571;
311 // 0 = Closed, 100 = Fully Open
312 // float Throttle_Lever_Pos = 75;
313 // 0 = Full Course 100 = Full Fine
314 // float Propeller_Lever_Pos = 75;
315 // 0 = Idle Cut Off 100 = Full Rich
316 // float Mixture_Lever_Pos = 100;
318 // Environmental Variables
320 // Temp Variation from ISA (Deg F)
321 float FG_ISA_VAR = 0;
322 // Pressure Altitude 1000's of Feet
323 float FG_Pressure_Ht = 0;
325 // Parameters that alter the operation of the engine.
326 int Fuel_Available = 1; // Yes = 1. Is there Fuel Available. Calculated elsewhere
327 int Alternate_Air_Pos =0; // Off = 0. Reduces power by 3 % for same throttle setting
328 int Magneto_Left = 1; // 1 = On. Reduces power by 5 % for same power lever settings
329 int Magneto_Right = 1; // 1 = On. Ditto, Both of the above though do not alter fuel flow
332 //==================================================================
333 // Engine & Environmental Inputs from elsewhere
335 // Calculate Air Density (Rho) - In FG this is calculated in
338 Rho = Density(FG_Pressure_Ht); // In FG FG_Pressure_Ht is "h"
339 // cout << "Rho = " << Rho << endl;
341 // Calculate Manifold Pressure (Engine 1) as set by throttle opening
344 Calc_Manifold_Pressure( Throttle_Lever_Pos, Max_Manifold_Pressure, Min_Manifold_Pressure );
345 // cout << "manifold pressure = " << Manifold_Pressure << endl;
347 //**************************FIXME*******************************************
348 //DCL - hack for testing - fly at sea level
351 p_amb_sea_level = 101325;
353 //DCL - next calculate m_dot_air and m_dot_fuel into engine
355 //calculate actual ambient pressure and temperature from altitude
356 //Then find the actual manifold pressure (the calculated one is the sea level pressure)
357 True_Manifold_Pressure = Manifold_Pressure * p_amb / p_amb_sea_level;
359 // RPM = Calc_Engine_RPM(Propeller_Lever_Pos);
361 // cout << "Initial engine RPM = " << RPM << endl;
363 // Desired_RPM = RPM;
367 //DCL - calculate mass air flow into engine based on speed and load - separate this out into a function eventually
368 //t_amb is actual temperature calculated from altitude
369 //calculate density from ideal gas equation
370 rho_air = p_amb / ( R_air * T_amb );
371 rho_air_manifold = rho_air * Manifold_Pressure / 29.6;
372 //calculate ideal engine volume inducted per second
373 swept_volume = (displacement_SI * (RPM / 60)) / 2; //This equation is only valid for a four stroke engine
374 //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
375 volumetric_efficiency = 0.8;
376 //Now use volumetric efficiency to calculate actual air volume inducted per second
377 v_dot_air = swept_volume * volumetric_efficiency;
378 //Now calculate mass flow rate of air into engine
379 m_dot_air = v_dot_air * rho_air_manifold;
381 // cout << "rho air manifold " << rho_air_manifold << '\n';
382 // cout << "Swept volume " << swept_volume << '\n';
386 //DCL - now calculate fuel flow into engine based on air flow and mixture lever position
387 //assume lever runs from no flow at fully out to thi = 1.6 at fully in at sea level
388 //also assume that the injector linkage is ideal - hence the set mixture is maintained at a given altitude throughout the speed and load range
389 thi_sea_level = 1.6 * ( Mixture_Lever_Pos / 100.0 );
390 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
391 m_dot_fuel = m_dot_air / 14.7 * equivalence_ratio;
393 // cout << "fuel " << m_dot_fuel;
394 // cout << " air " << m_dot_air << '\n';
396 //***********************************************************************
397 //Engine power and torque calculations
399 // For a given Manifold Pressure and RPM calculate the % Power
400 // Multiply Manifold Pressure by RPM
401 ManXRPM = Manifold_Pressure * RPM;
406 // Phil's %power correlation
408 Percentage_Power = (+ 7E-09 * ManXRPM * ManXRPM) + ( + 7E-04 * ManXRPM) - 0.1218;
409 // cout << Percentage_Power << "%" << "\t";
412 // DCL %power correlation - basically Phil's correlation modified to give slighty less power at the low end
413 // might need some adjustment as the prop model is adjusted
414 // 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
415 // Calculate % Power for Nev's prop model
416 //Percentage_Power = (+ 6E-09 * ManXRPM * ManXRPM) + ( + 8E-04 * ManXRPM) - 1.8524;
418 // Calculate %power for DCL prop model
419 Percentage_Power = (7e-9 * ManXRPM * ManXRPM) + (7e-4 * ManXRPM) - 1.0;
421 // cout << Percentage_Power << "%" << "\t";
424 // Adjust for Temperature - Temperature above Standard decrease
425 // power % by 7/120 per degree F increase, and incease power for
426 // temps below at the same ratio
427 Percentage_Power = Percentage_Power - (FG_ISA_VAR * 7 /120);
428 // cout << Percentage_Power << "%" << "\t";
430 //******DCL - this bit will need altering or removing if I go to true altitude adjusted manifold pressure
431 // Adjust for Altitude. In this version a linear variation is
432 // used. Decrease 1% for each 1000' increase in Altitde
433 Percentage_Power = Percentage_Power + (FG_Pressure_Ht * 12/10000);
434 // cout << Percentage_Power << "%" << "\t";
437 //DCL - now adjust power to compensate for mixture
438 //uses a curve fit to the data in the IO360 / O360 operating manual
439 //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,
440 //possibly by using separate fits for rich and lean of best power mixture
441 //first adjust actual mixture to abstract mixture - this is a temporary hack in order to account for the fact that the data I have
442 //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.
444 abstract_mixture = 10.0 * equivalence_ratio - 12.0;
445 float m = abstract_mixture; //to simplify writing the next equation
446 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);
447 Percentage_Power = Percentage_Power * Percentage_of_best_power_mixture_power / 100.0;
449 //cout << " %POWER = " << Percentage_Power << '\n';
451 //***DCL - FIXME - this needs altering - for instance going richer than full power mixture decreases the %power but increases the fuel flow
452 // Now Calculate Fuel Flow based on % Power Best Power Mixture
453 Fuel_Flow = Percentage_Power * Max_Fuel_Flow / 100.0;
454 // cout << Fuel_Flow << " lbs/hr"<< endl;
456 // Now Derate engine for the effects of Bad/Switched off magnetos
457 if (Magneto_Left == 0 && Magneto_Right == 0) {
458 // cout << "Both OFF\n";
459 Percentage_Power = 0;
460 } else if (Magneto_Left && Magneto_Right) {
461 // cout << "Both On ";
462 } else if (Magneto_Left == 0 || Magneto_Right== 0) {
463 // cout << "1 Magneto Failed ";
465 Percentage_Power = Percentage_Power *
466 ((100.0 - Mag_Derate_Percent)/100.0);
467 // cout << FGEng1_Percentage_Power << "%" << "\t";
470 HP = Percentage_Power * MaxHP / 100.0;
472 Power_SI = HP * CONVERT_HP_TO_WATTS;
474 // Calculate Engine Torque. Check for div by zero since percentage power correlation does not guarantee zero power at zero rpm.
479 Torque_SI = (Power_SI * 60.0) / (2.0 * PI * RPM); //Torque = power / angular velocity
480 // cout << Torque << " Nm\n";
483 //**********************************************************************
484 //Calculate Exhaust gas temperature
486 // cout << "Thi = " << equivalence_ratio << '\n';
488 combustion_efficiency = Lookup_Combustion_Efficiency(equivalence_ratio); //The combustion efficiency basically tells us what proportion of the fuels calorific value is released
490 // cout << "Combustion efficiency = " << combustion_efficiency << '\n';
492 //now calculate energy release to exhaust
493 //We will assume a three way split of fuel energy between useful work, the coolant system and the exhaust system
494 //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
495 //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.
496 enthalpy_exhaust = m_dot_fuel * calorific_value_fuel * combustion_efficiency * 0.33;
497 heat_capacity_exhaust = (Cp_air * m_dot_air) + (Cp_fuel * m_dot_fuel);
498 delta_T_exhaust = enthalpy_exhaust / heat_capacity_exhaust;
499 // delta_T_exhaust = Calculate_Delta_T_Exhaust();
501 // cout << "T_amb " << T_amb;
502 // cout << " dT exhaust = " << delta_T_exhaust;
504 EGT = T_amb + delta_T_exhaust;
506 //The above gives the exhaust temperature immediately prior to leaving the combustion chamber
507 //Now derate to give a more realistic figure as measured downstream
508 //For now we will aim for a peak of around 400 degC (750 degF)
510 EGT *= 0.444 + ((0.544 - 0.444) * Percentage_Power / 100.0);
512 EGT_degF = (EGT * 1.8) - 459.67;
514 //cout << " EGT = " << EGT << " degK " << EGT_degF << " degF";// << '\n';
516 //***************************************************************************************
517 // Calculate Cylinder Head Temperature
521 This is a somewhat rough first attempt at modelling cylinder head temperature. The cylinder head
522 is assumed to be at uniform temperature. Obviously this is incorrect, but it simplifies things a
523 lot, and we're just looking for the behaviour of CHT to be correct. Energy transfer to the cylinder
524 head is assumed to be one third of the energy released by combustion at all conditions. This is a
525 reasonable estimate, although obviously in real life it varies with different conditions and possibly
526 with CHT itself. I've split energy transfer from the cylinder head into 2 terms - free convection -
527 ie convection to stationary air, and forced convection, ie convection into flowing air. The basic
528 free convection equation is: dqdt = -hAdT Since we don't know A and are going to set h quite arbitarily
529 anyway I've knocked A out and just wrapped it up in h - the only real significance is that the units
530 of h will be different but that dosn't really matter to us anyway. In addition, we have the problem
531 that the prop model I'm currently using dosn't model the backwash from the prop which will add to the
532 velocity of the cooling air when the prop is turning, so I've added an extra term to try and cope
535 In real life, forced convection equations are genarally empirically derived, and are quite complicated
536 and generally contain such things as the Reynolds and Nusselt numbers to various powers. The best
537 course of action would probably to find an empirical correlation from the literature for a similar
538 situation and try and get it to fit well. However, for now I am using my own made up very simple
539 correlation for the energy transfer from the cylinder head:
541 dqdt = -(h1.dT) -(h2.m_dot.dT) -(h3.rpm.dT)
543 where dT is the temperature different between the cylinder head and the surrounding air, m_dot is the
544 mass flow rate of cooling air through an arbitary volume, rpm is the engine speed in rpm (this is the
545 backwash term), and h1, h2, h3 are co-efficients which we can play with to attempt to get the CHT
546 behaviour to match real life.
548 In order to change the values of CHT that the engine settles down at at various conditions,
549 have a play with h1, h2 and h3. In order to change the rate of heating/cooling without affecting
550 equilibrium values alter the cylinder head mass, which is really quite arbitary. Bear in mind that
551 altering h1, h2 and h3 will also alter the rate of heating or cooling as well as equilibrium values,
552 but altering the cylinder head mass will only alter the rate. It would I suppose be better to read
553 the values from file to avoid the necessity for re-compilation every time I change them.
556 //CHT = Calc_CHT( Fuel_Flow, Mixture, IAS);
557 // cout << "Cylinder Head Temp (F) = " << CHT << endl;
558 float h1 = -95.0; //co-efficient for free convection
559 float h2 = -3.95; //co-efficient for forced convection
560 float h3 = -0.05; //co-efficient for forced convection due to prop backwash
561 float v_apparent; //air velocity over cylinder head in m/s
562 float v_dot_cooling_air;
563 float m_dot_cooling_air;
564 float temperature_difference;
565 float arbitary_area = 1.0;
566 float dqdt_from_combustion;
567 float dqdt_forced; //Rate of energy transfer to/from cylinder head due to forced convection (Joules) (sign convention: to cylinder head is +ve)
568 float dqdt_free; //Rate of energy transfer to/from cylinder head due to free convection (Joules) (sign convention: to cylinder head is +ve)
569 float dqdt_cylinder_head; //Overall energy change in cylinder head
570 float CpCylinderHead = 800.0; //FIXME - this is a guess - I need to look up the correct value
571 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
572 float HeatCapacityCylinderHead;
575 temperature_difference = CHT - T_amb;
577 v_apparent = IAS * 0.5144444; //convert from knots to m/s
578 v_dot_cooling_air = arbitary_area * v_apparent;
579 m_dot_cooling_air = v_dot_cooling_air * rho_air;
581 //Calculate rate of energy transfer to cylinder head from combustion
582 dqdt_from_combustion = m_dot_fuel * calorific_value_fuel * combustion_efficiency * 0.33;
584 //Calculate rate of energy transfer from cylinder head due to cooling NOTE is calculated as rate to but negative
585 dqdt_forced = (h2 * m_dot_cooling_air * temperature_difference) + (h3 * RPM * temperature_difference);
586 dqdt_free = h1 * temperature_difference;
588 //Calculate net rate of energy transfer to or from cylinder head
589 dqdt_cylinder_head = dqdt_from_combustion + dqdt_forced + dqdt_free;
591 HeatCapacityCylinderHead = CpCylinderHead * MassCylinderHead;
593 dCHTdt = dqdt_cylinder_head / HeatCapacityCylinderHead;
595 CHT += (dCHTdt * time_step);
597 CHT_degF = (CHT * 1.8) - 459.67;
599 //cout << " CHT = " << CHT_degF << " degF\n";
602 // End calculate Cylinder Head Temperature
605 //***************************************************************************************
606 // Oil pressure calculation
608 // Calculate Oil Pressure
609 Oil_Pressure = Oil_Press( Oil_Temp, RPM );
610 // cout << "Oil Pressure (PSI) = " << Oil_Pressure << endl;
612 //**************************************************************************************
613 // Now do the Propeller Calculations
615 #ifdef NEVS_PROP_MODEL
620 number_of_blades = 2.0;
622 allowance_for_spinner = blade_length / 12.0;
623 prop_fudge_factor = 1.453401525;
624 forward_velocity = IAS;
633 angular_velocity_SI = 2.0 * PI * RPM / 60.0;
635 allowance_for_spinner = blade_length / 12.0;
636 //Calculate thrust and torque by summing the contributions from each of the blade elements
637 //Assumes equal length elements with numbered 1 inboard -> num_elements outboard
641 // outfile << "Rho = " << Rho << '\n\n';
642 // outfile << "Drag = ";
643 for(i=1;i<=num_elements;i++)
646 distance = (blade_length * (element / num_elements)) + allowance_for_spinner;
647 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))))))
648 * (0.1 * (blade_length / element)) * number_of_blades;
650 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)
651 * (0.1 * (blade_length / element)) * number_of_blades;
652 element_torque = element_drag * distance;
653 prop_torque += element_torque;
654 prop_thrust += element_lift;
655 // outfile << "Drag = " << element_drag << " n = " << element << '\n';
660 // outfile << "Angular velocity = " << angular_velocity_SI << " rad/s\n";
662 // cout << "Thrust = " << prop_thrust << '\n';
663 prop_thrust *= prop_fudge_factor;
664 prop_torque *= prop_fudge_factor;
665 prop_power_consumed_SI = prop_torque * angular_velocity_SI;
666 prop_power_consumed_HP = prop_power_consumed_SI / 745.699;
669 #endif //NEVS_PROP_MODEL
671 #ifdef DCL_PROP_MODEL
673 double prop_diameter = 1.8; // meters
674 double J; // advance ratio - dimensionless
675 double Cp_20; // coefficient of power for 20 degree blade angle
676 double Cp_25; // coefficient of power for 25 degree blade angle
677 double Cp; // our actual coefficient of power
678 double blade_angle = 23.0; // degrees
681 double neta_prop; // prop efficiency
684 FGProp1_RPS = RPM * Gear_Ratio / 60.0; // Borrow this variable from Phils model for now !!
685 angular_velocity_SI = 2.0 * PI * RPM / 60.0;
686 forward_velocity = IAS * 0.514444444444; // Convert to m/s
688 //cout << "Gear_Ratio = " << Gear_Ratio << '\n';
689 //cout << "IAS = " << IAS << '\n';
690 //cout << "forward_velocity = " << forward_velocity << '\n';
691 //cout << "FGProp1_RPS = " << FGProp1_RPS << '\n';
692 //cout << "prop_diameter = " << prop_diameter << '\n';
696 J = forward_velocity / (FGProp1_RPS * prop_diameter);
697 //cout << "advance_ratio = " << J << '\n';
699 //Cp correlations based on data from McCormick
700 Cp_20 = 0.0342*J*J*J*J - 0.1102*J*J*J + 0.0365*J*J - 0.0133*J + 0.064;
701 Cp_25 = 0.0119*J*J*J*J - 0.0652*J*J*J + 0.018*J*J - 0.0077*J + 0.0921;
703 //cout << "Cp_20 = " << Cp_20 << '\n';
704 //cout << "Cp_25 = " << Cp_25 << '\n';
706 //Assume that the blade angle is between 20 and 25 deg - reasonable for fixed pitch prop but won't hold for variable one !!!
707 Cp = Cp_20 + ( (Cp_25 - Cp_20) * ((blade_angle - 20)/(25 - 20)) );
708 //cout << "Cp = " << Cp << '\n';
709 //cout << "RPM = " << RPM << '\n';
710 //cout << "angular_velocity_SI = " << angular_velocity_SI << '\n';
712 prop_power_consumed_SI = Cp * rho_air * pow(FGProp1_RPS,3.0) * pow(prop_diameter,5.0);
713 //cout << "prop HP consumed = " << prop_power_consumed_SI / 745.699 << '\n';
714 if(angular_velocity_SI == 0)
717 prop_torque = prop_power_consumed_SI / angular_velocity_SI;
719 // calculate neta_prop here
720 neta_prop_20 = 0.1328*J*J*J*J - 1.3073*J*J*J + 0.3525*J*J + 1.5591*J + 0.0007;
721 neta_prop_25 = -0.3121*J*J*J*J + 0.4234*J*J*J - 0.7686*J*J + 1.5237*J - 0.0004;
722 neta_prop = neta_prop_20 + ( (neta_prop_25 - neta_prop_20) * ((blade_angle - 20)/(25 - 20)) );
724 //FIXME - need to check for zero forward velocity to avoid divide by zero
725 if(forward_velocity < 0.0001)
728 prop_thrust = neta_prop * prop_power_consumed_SI / forward_velocity; //TODO - rename forward_velocity to IAS_SI
729 //cout << "prop_thrust = " << prop_thrust << '\n';
731 #endif //DCL_PROP_MODEL
733 //Calculate new RPM from torque balance and inertia.
734 Torque_Imbalance = Torque_SI - prop_torque; //This gives a +ve value when the engine torque exeeds the prop torque
736 angular_acceleration = Torque_Imbalance / (engine_inertia + prop_inertia);
737 angular_velocity_SI += (angular_acceleration * time_step);
738 RPM = (angular_velocity_SI * 60) / (2.0 * PI);
740 //DCL - stall the engine if RPM drops below 550 - this is possible if mixture lever is pulled right out