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flightgear/src/FDM/LaRCsim/c172_aero.c
curt 06b966ee53 Added flaps support to c172 model.
1999-10-29 18:08:31 +00:00

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/***************************************************************************
TITLE: c172_aero
----------------------------------------------------------------------------
FUNCTION: aerodynamics model based on constant stability derivatives
----------------------------------------------------------------------------
MODULE STATUS: developmental
----------------------------------------------------------------------------
GENEALOGY: Based on data from:
Part 1 of Roskam's S&C text
The FAA type certificate data sheet for the 172
Various sources on the net
John D. Anderson's Intro to Flight text (NACA 2412 data)
UIUC's airfoil data web site
----------------------------------------------------------------------------
DESIGNED BY: Tony Peden
CODED BY: Tony Peden
MAINTAINED BY: Tony Peden
----------------------------------------------------------------------------
MODIFICATION HISTORY:
DATE PURPOSE BY
6/10/99 Initial test release
----------------------------------------------------------------------------
REFERENCES:
Aero Coeffs:
CL lift
Cd drag
Cm pitching moment
Cy sideforce
Cn yawing moment
Croll,Cl rolling moment (yeah, I know. Shoot me.)
Subscripts
o constant i.e. not a function of alpha or beta
a alpha
adot d(alpha)/dt
q pitch rate
qdot d(q)/dt
beta sideslip angle
p roll rate
r yaw rate
da aileron deflection
de elevator deflection
dr rudder deflection
s stability axes
----------------------------------------------------------------------------
CALLED BY:
----------------------------------------------------------------------------
CALLS TO:
----------------------------------------------------------------------------
INPUTS:
----------------------------------------------------------------------------
OUTPUTS:
--------------------------------------------------------------------------*/
#include "ls_generic.h"
#include "ls_cockpit.h"
#include "ls_constants.h"
#include "ls_types.h"
#include "c172_aero.h"
#include <math.h>
#include <stdio.h>
#define NCL 11
#define Ndf 4
#define DYN_ON_SPEED 33 /*20 knots*/
#ifdef USENZ
#define NZ generic_.n_cg_body_v[2]
#else
#define NZ 1
#endif
extern COCKPIT cockpit_;
SCALAR interp(SCALAR *y_table, SCALAR *x_table, int Ntable, SCALAR x)
{
SCALAR slope;
int i=1;
float y;
/* if x is outside the table, return value at x[0] or x[Ntable-1]*/
if(x <= x_table[0])
{
y=y_table[0];
/* printf("x smaller than x_table[0]: %g %g\n",x,x_table[0]); */
}
else if(x >= x_table[Ntable-1])
{
slope=(y_table[Ntable-1]-y_table[Ntable-2])/(x_table[Ntable-1]-x_table[Ntable-2]);
y=slope*(x-x_table[Ntable-1]) +y_table[Ntable-1];
/* printf("x larger than x_table[N]: %g %g %d\n",x,x_table[NCL-1],Ntable-1);
*/ }
else /*x is within the table, interpolate linearly to find y value*/
{
while(x_table[i] <= x) {i++;}
slope=(y_table[i]-y_table[i-1])/(x_table[i]-x_table[i-1]);
/* printf("x: %g, i: %d, cl[i]: %g, cl[i-1]: %g, slope: %g\n",x,i,y_table[i],y_table[i-1],slope); */
y=slope*(x-x_table[i-1]) +y_table[i-1];
}
return y;
}
void aero( SCALAR dt, int Initialize ) {
static int init = 0;
static int flap_dir=0;
static SCALAR lastFlapHandle=0;
static SCALAR trim_inc = 0.0002;
static SCALAR alpha_ind[NCL]={-0.087,0,0.175,0.209,0.24,0.262,0.278,0.303,0.314,0.332,0.367};
static SCALAR CLtable[NCL]={-0.14,0.31,1.21,1.376,1.51249,1.591,1.63,1.60878,1.53712,1.376,1.142};
static SCALAR flap_ind[Ndf]={0,10,20,30};
static SCALAR dCLf[Ndf]={0,0.20,0.30,0.35};
static SCALAR dCdf[Ndf]={0,0.0021,0.0085,0.0191};
static SCALAR dCmf[Ndf]={0,-0.186,-0.28,-0.325};
static SCALAR flap_transit_rate=2.5;
/* printf("Initialize= %d\n",Initialize); */
/* printf("Initializing aero model...Initialize= %d\n", Initialize);
*/
/*nondimensionalization quantities*/
/*units here are ft and lbs */
cbar=4.9; /*mean aero chord ft*/
b=35.8; /*wing span ft */
Sw=174; /*wing planform surface area ft^2*/
rPiARe=0.054; /*reciprocal of Pi*AR*e*/
lbare=3.682; /*elevator moment arm / MAC*/
CLadot=1.7;
CLq=3.9;
CLob=0;
Cdob=0.031;
Cda=0.13; /*Not used*/
Cdde=0.06;
Cma=-1.8;
Cmadot=-5.2;
Cmq=-12.4;
Cmob=-0.00;
Cmde=-1.00;
CLde=-Cmde / lbare; /* kinda backwards, huh? */
Clbeta=-0.089;
Clp=-0.47;
Clr=0.096;
Clda=-0.09;
Cldr=0.0147;
Cnbeta=0.065;
Cnp=-0.03;
Cnr=-0.099;
Cnda=-0.053;
Cndr=-0.0657;
Cybeta=-0.31;
Cyp=-0.037;
Cyr=0.21;
Cyda=0.0;
Cydr=0.187;
MaxTakeoffWeight=2550;
EmptyWeight=1500;
Zcg=0.51;
/*
LaRCsim uses:
Cm > 0 => ANU
Cl > 0 => Right wing down
Cn > 0 => ANL
so:
elevator > 0 => AND -- aircraft nose down
aileron > 0 => right wing up
rudder > 0 => ANL
*/
/*do weight & balance here since there is no better place*/
Weight=Mass / INVG;
if(Weight > 2550)
{ Weight=2550; }
else if(Weight < 1500)
{ Weight=1500; }
if(Dx_cg > 0.5586)
{ Dx_cg = 0.5586; }
else if(Dx_cg < -0.4655)
{ Dx_cg = -0.4655; }
Cg=Dx_cg/cbar +0.25;
Dz_cg=Zcg*cbar;
if(Flap_handle < flap_ind[0])
{
Flap_handle=flap_ind[0];
Flap_Position=flap_ind[0];
}
else if(Flap_handle > flap_ind[3])
{
Flap_handle=flap_ind[3];
Flap_Position=flap_ind[3];
}
else
{
if((Flap_handle != lastFlapHandle) && (dt > 0))
Flaps_In_Transit=1;
else if(dt <= 0)
Flap_Position=Flap_handle;
lastFlapHandle=Flap_handle;
if((Flaps_In_Transit) && (dt > 0))
{
if(Flap_Position < 10)
flap_transit_rate = 2.5;
else
flap_transit_rate=5;
if(Flaps_In_Transit)
{
if(Flap_Position < Flap_handle)
flap_dir=1;
else
flap_dir=-1;
if(fabs(Flap_Position - Flap_handle) > dt*flap_transit_rate)
Flap_Position+=flap_dir*flap_transit_rate*dt;
if(fabs(Flap_Position - Flap_handle) < dt*flap_transit_rate)
{
Flaps_In_Transit=0;
Flap_Position=Flap_handle;
}
}
}
}
long_trim=0;
if(Aft_trim) long_trim = long_trim - trim_inc;
if(Fwd_trim) long_trim = long_trim + trim_inc;
/* printf("Long_control: %7.4f, long_trim: %7.4f,DEG_TO_RAD: %7.4f, RAD_TO_DEG: %7.4f\n",Long_control,long_trim,DEG_TO_RAD,RAD_TO_DEG);
*/ /*scale pct control to degrees deflection*/
if ((Long_control+long_trim) <= 0)
elevator=(Long_control+long_trim)*28*DEG_TO_RAD;
else
elevator=(Long_control+long_trim)*23*DEG_TO_RAD;
aileron = -1*Lat_control*17.5*DEG_TO_RAD;
rudder = -1*Rudder_pedal*16*DEG_TO_RAD;
/*
The aileron travel limits are 20 deg. TEU and 15 deg TED
but since we don't distinguish between left and right we'll
use the average here (17.5 deg)
*/
/*calculate rate derivative nondimensionalization (is that a word?) factors */
/*hack to avoid divide by zero*/
/*the dynamic terms might be negligible at low ground speeds anyway*/
/* printf("Vinf: %g, Span: %g\n",V_rel_wind,b);
*/
if(V_rel_wind > DYN_ON_SPEED)
{
cbar_2V=cbar/(2*V_rel_wind);
b_2V=b/(2*V_rel_wind);
}
else
{
cbar_2V=0;
b_2V=0;
}
/*calcuate the qS nondimensionalization factors*/
qS=Dynamic_pressure*Sw;
qScbar=qS*cbar;
qSb=qS*b;
/* printf("aero: Wb: %7.4f, Ub: %7.4f, Alpha: %7.4f, elev: %7.4f, ail: %7.4f, rud: %7.4f, long_trim: %7.4f\n",W_body,U_body,Alpha*RAD_TO_DEG,elevator*RAD_TO_DEG,aileron*RAD_TO_DEG,rudder*RAD_TO_DEG,long_trim*RAD_TO_DEG);
printf("aero: Theta: %7.4f, Gamma: %7.4f, Beta: %7.4f, Phi: %7.4f, Psi: %7.4f\n",Theta*RAD_TO_DEG,Gamma_vert_rad*RAD_TO_DEG,Beta*RAD_TO_DEG,Phi*RAD_TO_DEG,Psi*RAD_TO_DEG);
*/
/* sum coefficients */
CLwbh = interp(CLtable,alpha_ind,NCL,Alpha);
CLo = CLob + interp(dCLf,flap_ind,Ndf,Flap_Position);
Cdo = Cdob + interp(dCdf,flap_ind,Ndf,Flap_Position);
Cmo = Cmob + interp(dCmf,flap_ind,Ndf,Flap_Position);
/* printf("FP: %g\n",Flap_Position);
printf("CLo: %g\n",CLo);
printf("Cdo: %g\n",Cdo);
printf("Cmo: %g\n",Cmo);
*/
CL = CLo + CLwbh + (CLadot*Alpha_dot + CLq*Theta_dot)*cbar_2V + CLde*elevator;
cd = Cdo + rPiARe*CL*CL + Cdde*elevator;
cy = Cybeta*Beta + (Cyp*P_body + Cyr*R_body)*b_2V + Cyda*aileron + Cydr*rudder;
cm = Cmo + Cma*Alpha + (Cmq*Q_body + Cmadot*Alpha_dot)*cbar_2V + Cmde*(elevator);
cn = Cnbeta*Beta + (Cnp*P_body + Cnr*R_body)*b_2V + Cnda*aileron + Cndr*rudder;
croll=Clbeta*Beta + (Clp*P_body + Clr*R_body)*b_2V + Clda*aileron + Cldr*rudder;
/* printf("aero: CL: %7.4f, Cd: %7.4f, Cm: %7.4f, Cy: %7.4f, Cn: %7.4f, Cl: %7.4f\n",CL,cd,cm,cy,cn,croll);
*/
/*calculate wind axes forces*/
F_X_wind=-1*cd*qS;
F_Y_wind=cy*qS;
F_Z_wind=-1*CL*qS;
/* printf("V_rel_wind: %7.4f, Fxwind: %7.4f Fywind: %7.4f Fzwind: %7.4f\n",V_rel_wind,F_X_wind,F_Y_wind,F_Z_wind);
*/
/*calculate moments and body axis forces */
/* requires ugly wind-axes to body-axes transform */
F_X_aero = F_X_wind*Cos_alpha*Cos_beta - F_Y_wind*Cos_alpha*Sin_beta - F_Z_wind*Sin_alpha;
F_Y_aero = F_X_wind*Sin_beta + F_Y_wind*Cos_beta;
F_Z_aero = F_X_wind*Sin_alpha*Cos_beta - F_Y_wind*Sin_alpha*Sin_beta + F_Z_wind*Cos_alpha;
/*no axes transform here */
M_l_aero = croll*qSb;
M_m_aero = cm*qScbar;
M_n_aero = cn*qSb;
/* printf("I_yy: %7.4f, qScbar: %7.4f, qbar: %7.4f, Sw: %7.4f, cbar: %7.4f, 0.5*rho*V^2: %7.4f\n",I_yy,qScbar,Dynamic_pressure,Sw,cbar,0.5*0.0023081*V_rel_wind*V_rel_wind);
*/
/* printf("Fxaero: %7.4f Fyaero: %7.4f Fzaero: %7.4f Weight: %7.4f\n",F_X_aero,F_Y_aero,F_Z_aero,Weight);
*/
/* printf("Maero: %7.4f Naero: %7.4f Raero: %7.4f\n",M_m_aero,M_n_aero,M_l_aero);
*/
}
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