src/FDM/UIUCModel/uiuc_engine.cpp

   1 /**********************************************************************
   2
   3  FILENAME:     uiuc_engine.cpp
   4
   5 ----------------------------------------------------------------------
   6
   7  DESCRIPTION:  determine the engine forces and moments
   8
   9 ----------------------------------------------------------------------
  10
  11  STATUS:       alpha version
  12
  13 ----------------------------------------------------------------------
  14
  15  REFERENCES:   simple and c172 models based on portions of
  16                c172_engine.c, called from ls_model;
  17                cherokee model based on cherokee_engine.c
  18
  19 ----------------------------------------------------------------------
  20
  21  HISTORY:      01/30/2000   initial release
  22
  23 ----------------------------------------------------------------------
  24
  25  AUTHOR(S):    Bipin Sehgal       <bsehgal@uiuc.edu>
  26                Jeff Scott         <jscott@mail.com>
  27                Michael Selig      <m-selig@uiuc.edu>
  28
  29 ----------------------------------------------------------------------
  30
  31  VARIABLES:
  32
  33 ----------------------------------------------------------------------
  34
  35  INPUTS:       -engine model
  36
  37 ----------------------------------------------------------------------
  38
  39  OUTPUTS:      -F_X_engine
  40                -F_Z_engine
  41                -M_m_engine
  42
  43 ----------------------------------------------------------------------
  44
  45  CALLED BY:   uiuc_wrapper.cpp
  46
  47 ----------------------------------------------------------------------
  48
  49  CALLS TO:     none
  50
  51 ----------------------------------------------------------------------
  52
  53  COPYRIGHT:    (C) 2000 by Michael Selig
  54
  55  This program is free software; you can redistribute it and/or
  56  modify it under the terms of the GNU General Public License
  57  as published by the Free Software Foundation.
  58
  59  This program is distributed in the hope that it will be useful,
  60  but WITHOUT ANY WARRANTY; without even the implied warranty of
  61  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  62  GNU General Public License for more details.
  63
  64  You should have received a copy of the GNU General Public License
  65  along with this program; if not, write to the Free Software
  66  Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
  67  USA or view http://www.gnu.org/copyleft/gpl.html.
  68
  69 **********************************************************************/
  70 #include <simgear/compiler.h>
  71
  72 #include "uiuc_engine.h"
  73
  74 #if !defined (SG_HAVE_NATIVE_SGI_COMPILERS)
  75 SG_USING_STD(cerr);
  76 #endif
  77
  78 void uiuc_engine()
  79 {
  80   stack command_list;
  81   string linetoken1;
  82   string linetoken2;
  83
  84   Throttle[3] = Throttle_pct;
  85
  86   command_list = engineParts -> getCommands();
  87
  88   /*
  89   if (command_list.begin() == command_list.end())
  90   {
  91         cerr << "ERROR: Engine not specified. Aircraft cannot fly without the engine" << endl;
  92         exit(-1);
  93   }
  94   */
  95
  96   for (LIST command_line = command_list.begin(); command_line!=command_list.end(); ++command_line)
  97     {
  98       //cout << *command_line << endl;
  99
 100       linetoken1 = engineParts -> getToken(*command_line, 1);
 101       linetoken2 = engineParts -> getToken(*command_line, 2);
 102
 103       switch(engine_map[linetoken2])
 104         {
 105         case simpleSingle_flag:
 106           {
 107             F_X_engine = Throttle[3] * simpleSingleMaxThrust;
 108             break;
 109           }
 110         case c172_flag:
 111           {
 112             //c172 engine lines ... looks like 0.83 is just a thrust increase
 113             F_X_engine = Throttle[3] * 350 / 0.83;
 114             F_Z_engine = Throttle[3] * 4.9 / 0.83;
 115             M_m_engine = F_X_engine * 0.734 * cbar;
 116             break;
 117           }
 118         case cherokee_flag:
 119           {
 120             static float
 121               dP = (180.0-117.0)*745.7,   // Watts
 122               dn = (2700.0-2350.0)/60.0,  // d_rpm (I mean d_rps, in seconds)
 123               D  = 6.17*0.3048,           // prop diameter
 124               dPh = (58.0-180.0)*745.7,   // change of power as function of height
 125               dH = 25000.0*0.3048;
 126
 127             float
 128               n,   // [rps]
 129               H,   // altitude [m]
 130               J,   // advance ratio (ratio of horizontal speed to prop tip speed)
 131               T,   // thrust [N]
 132               V,   // velocity [m/s]
 133               P,   // power [W]
 134               eta_engine; // engine efficiency
 135
 136             /* assumption -> 0.0 <= Throttle[3] <=1.0 */
 137             P = fabs(Throttle[3]) * 180.0 * 745.7; /*180.0*745.7 ->max avail power [W]*/
 138             n = dn/dP * (P-117.0*745.7) + 2350.0/60.0;
 139
 140             /*  V  [m/s]   */
 141             V = (V_rel_wind < 10.0 ? 10.0 : V_rel_wind*0.3048);
 142             J = V / n / D;
 143
 144             /* Propeller efficiency */
 145             eta_engine = (J < 0.7 ? ((0.8-0.55)/(.7-.3)*(J-0.3) + 0.55) :
 146                           (J > 0.85 ? ((0.6-0.8)/(1.0-0.85)*(J-0.85) + 0.8) : 0.8));
 147
 148             /* power on Altitude */
 149             H = Altitude * 0.3048;       /* H == Altitude [m] */
 150             P *= (dPh/dH * H + 180.0*745.7) / (180.0*745.7);
 151             T = eta_engine * P/V;        /* Thrust [N] */
 152
 153             /*assumption: Engine's line of thrust passes through cg */
 154             F_X_engine = T * 0.2248;     /* F_X_engine in lb */
 155             F_Y_engine = 0.0;
 156             F_Z_engine = 0.0;
 157             break;
 158           }
 159         };
 160     }
 161   return;
 162 }
 163
 164 // end uiuc_engine.cpp