src/FDM/LaRCsim/cherokee_engine.c

   1 /*
   2 cherokee_engine.c
   3
   4 very rough model of Lycoming engine built in PA-28 Cherokee
   5 Only "AD" characteristics are modelled, no transient behaviour,
   6 meaning that there is no time delay, engine acts as gain only.
   7
   8
   9
  10                 Based upon book:
  11                                 Barnes W. McCormick,
  12                                 "Aerodynamics, Aeronautics and Flight Mechanics",
  13                                 John Wiley & Sons,1995, ISBN 0-471-11087-6
  14
  15         any suggestions, corrections, aditional data, flames, everything to
  16         Gordan Sikic
  17         gsikic@public.srce.hr
  18
  19
  20 This source is not checked in this configuration in any way.
  21
  22
  23 */
  24
  25
  26
  27 #include <float.h>
  28 #include <math.h>
  29 #include "ls_types.h"
  30 #include "ls_constants.h"
  31 #include "ls_generic.h"
  32 #include "ls_cockpit.h"
  33 #include "ls_sim_control.h"
  34
  35
  36
  37
  38
  39 void cherokee_engine( SCALAR dt, int init )
  40 {
  41
  42         static float
  43                 dP = (180.0-117.0)*745.7,   // in Wats
  44                 dn = (2700.0-2350.0)/60.0,  // d_rpm (I mean d_rps, in seconds)
  45                 D  = 6.17*0.3048,                       // propeller diameter
  46                 dPh = (58.0-180.0)*745.7,       // change of power as f-cn of height
  47                 dH = 25000.0*0.3048;
  48
  49         float   n,                      // rps
  50                         H,
  51                         J,                      // advance ratio (ratio of horizontal speed to speed of propeller's tip)
  52                         eta,            // iskoristivost elise
  53                         T,
  54                         V,
  55                         P;
  56
  57 /* copied from  navion_engine.c */
  58     if (init || sim_control_.sim_type != cockpit)
  59         Throttle[3] = Throttle_pct;
  60
  61         /*assumption -> 0.0 <= Throttle[3] <=1.0 */
  62         P = fabs(Throttle[3])*180.0*745.7;              /*180.0*745.5 ->max avail power in W */
  63         n = dn/dP*(P-117.0*745.7) + 2350.0/60.0;
  64
  65 /*  V  [m/s]   */
  66         V = (V_rel_wind < 10.0*0.3048 ? 10.0 : V_rel_wind*0.3048);
  67
  68         J = V/n/D;
  69
  70
  71 /*
  72         propeller efficiency
  73
  74 if J >0.7 & J < .85
  75         eta = 0.8;
  76 elseif J < 0.7
  77         eta = (0.8-0.55)/(.7-.3)*(J-0.3) + 0.55;
  78 else
  79         eta = (0.6-0.8)/(1.0-0.85)*(J-0.85) + 0.8;
  80 end
  81 */
  82         eta = (J < 0.7 ? ((0.8-0.55)/(.7-.3)*(J-0.3) + 0.55) :
  83                         (J > 0.85 ? ((0.6-0.8)/(1.0-0.85)*(J-0.85) + 0.8) : 0.8));
  84
  85
  86
  87 /* power on Altitude  (I mean Altitude, not Attitude...)*/
  88
  89         H = Altitude/0.3048; /* H == Altitude in [m] */
  90
  91         P *= (dPh/dH*H + 180.0*745.7)/(180.0*745.7);
  92
  93         T = eta*P/V;    /* T in N (Thrust in Newtons) */
  94
  95 /*assumption: Engine's line of thrust passes through cg */
  96
  97     F_X_engine = T*0.2248;      /* F_X_engine in lb */
  98     F_Y_engine = 0.0;
  99     F_Z_engine = 0.0;
 100
 101 /* copied from  navion_engine.c */
 102     Throttle_pct = Throttle[3];
 103
 104 }