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flightgear/src/FDM/JSBSim/FGLGear.cpp
david 5d8a04291c Latest JSBSim changes.
2001-12-24 13:54:55 +00:00

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/*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Module: FGLGear.cpp
Author: Jon S. Berndt
Norman H. Princen
Date started: 11/18/99
Purpose: Encapsulates the landing gear elements
Called by: FGAircraft
------------- Copyright (C) 1999 Jon S. Berndt (jsb@hal-pc.org) -------------
This program is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free Software
Foundation; either version 2 of the License, or (at your option) any later
version.
This program is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
details.
You should have received a copy of the GNU General Public License along with
this program; if not, write to the Free Software Foundation, Inc., 59 Temple
Place - Suite 330, Boston, MA 02111-1307, USA.
Further information about the GNU General Public License can also be found on
the world wide web at http://www.gnu.org.
FUNCTIONAL DESCRIPTION
--------------------------------------------------------------------------------
HISTORY
--------------------------------------------------------------------------------
11/18/99 JSB Created
01/30/01 NHP Extended gear model to properly simulate steering and braking
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
INCLUDES
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
#include "FGLGear.h"
#include <algorithm>
/*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
DEFINITIONS
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
/*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
GLOBAL DATA
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
static const char *IdSrc = "$Id$";
static const char *IdHdr = ID_LGEAR;
/*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
CLASS IMPLEMENTATION
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
FGLGear::FGLGear(FGConfigFile* AC_cfg, FGFDMExec* fdmex) : Exec(fdmex)
{
string tmp;
*AC_cfg >> tmp >> name >> vXYZ(1) >> vXYZ(2) >> vXYZ(3)
>> kSpring >> bDamp>> dynamicFCoeff >> staticFCoeff
>> rollingFCoeff >> sSteerType >> sBrakeGroup
>> maxSteerAngle >> sRetractable;
if (sBrakeGroup == "LEFT" ) eBrakeGrp = bgLeft;
else if (sBrakeGroup == "RIGHT" ) eBrakeGrp = bgRight;
else if (sBrakeGroup == "CENTER") eBrakeGrp = bgCenter;
else if (sBrakeGroup == "NOSE" ) eBrakeGrp = bgNose;
else if (sBrakeGroup == "TAIL" ) eBrakeGrp = bgTail;
else if (sBrakeGroup == "NONE" ) eBrakeGrp = bgNone;
else {
cerr << "Improper braking group specification in config file: "
<< sBrakeGroup << " is undefined." << endl;
}
if (sSteerType == "STEERABLE") eSteerType = stSteer;
else if (sSteerType == "FIXED" ) eSteerType = stFixed;
else if (sSteerType == "CASTERED" ) eSteerType = stCaster;
else {
cerr << "Improper steering type specification in config file: "
<< sSteerType << " is undefined." << endl;
}
if ( sRetractable == "RETRACT" ) {
isRetractable = true;
} else {
isRetractable = false;
}
GearUp = false;
GearDown = true;
// Add some AI here to determine if gear is located properly according to its
// brake group type ??
State = Exec->GetState();
Aircraft = Exec->GetAircraft();
Position = Exec->GetPosition();
Rotation = Exec->GetRotation();
FCS = Exec->GetFCS();
MassBalance = Exec->GetMassBalance();
WOW = lastWOW = false;
ReportEnable = true;
FirstContact = false;
Reported = false;
DistanceTraveled = 0.0;
MaximumStrutForce = MaximumStrutTravel = 0.0;
SinkRate = GroundSpeed = 0.0;
vWhlBodyVec = (vXYZ - MassBalance->GetXYZcg()) / 12.0;
vWhlBodyVec(eX) = -vWhlBodyVec(eX);
vWhlBodyVec(eZ) = -vWhlBodyVec(eZ);
vLocalGear = State->GetTb2l() * vWhlBodyVec;
Debug(0);
}
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
FGLGear::FGLGear(const FGLGear& lgear)
{
State = lgear.State;
Aircraft = lgear.Aircraft;
Position = lgear.Position;
Rotation = lgear.Rotation;
Exec = lgear.Exec;
FCS = lgear.FCS;
MassBalance = lgear.MassBalance;
vXYZ = lgear.vXYZ;
vMoment = lgear.vMoment;
vWhlBodyVec = lgear.vWhlBodyVec;
vLocalGear = lgear.vLocalGear;
WOW = lgear.WOW;
lastWOW = lgear.lastWOW;
ReportEnable = lgear.ReportEnable;
FirstContact = lgear.FirstContact;
DistanceTraveled = lgear.DistanceTraveled;
MaximumStrutForce = lgear.MaximumStrutForce;
MaximumStrutTravel = lgear.MaximumStrutTravel;
kSpring = lgear.kSpring;
bDamp = lgear.bDamp;
compressLength = lgear.compressLength;
compressSpeed = lgear.compressSpeed;
staticFCoeff = lgear.staticFCoeff;
dynamicFCoeff = lgear.dynamicFCoeff;
rollingFCoeff = lgear.rollingFCoeff;
brakePct = lgear.brakePct;
maxCompLen = lgear.maxCompLen;
SinkRate = lgear.SinkRate;
GroundSpeed = lgear.GroundSpeed;
Reported = lgear.Reported;
name = lgear.name;
sSteerType = lgear.sSteerType;
sRetractable = lgear.sRetractable;
eSteerType = lgear.eSteerType;
sBrakeGroup = lgear.sBrakeGroup;
eBrakeGrp = lgear.eBrakeGrp;
maxSteerAngle = lgear.maxSteerAngle;
isRetractable = lgear.isRetractable;
GearUp = lgear.GearUp;
GearDown = lgear.GearDown;
}
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
FGLGear::~FGLGear()
{
Debug(1);
}
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
FGColumnVector3& FGLGear::Force(void)
{
vForce.InitMatrix();
vMoment.InitMatrix();
if (isRetractable) {
if (FCS->GetGearPos() < 0.01) {
GearUp = true;
GearDown = false;
} else if (FCS->GetGearPos() > 0.99) {
GearDown = true;
GearUp = false;
} else {
GearUp = false;
GearDown = false;
}
} else {
GearUp = false;
GearDown = true;
}
if (GearDown) {
double SteerGain = 0;
double SinWheel, CosWheel, SideWhlVel, RollingWhlVel;
double RollingForce, SideForce, FCoeff;
double WheelSlip;
vWhlBodyVec = (vXYZ - MassBalance->GetXYZcg()) / 12.0;
vWhlBodyVec(eX) = -vWhlBodyVec(eX);
vWhlBodyVec(eZ) = -vWhlBodyVec(eZ);
// vWhlBodyVec now stores the vector from the cg to this wheel
vLocalGear = State->GetTb2l() * vWhlBodyVec;
// vLocalGear now stores the vector from the cg to the wheel in local coords.
compressLength = vLocalGear(eZ) - Position->GetDistanceAGL();
// The compression length is currently measured in the Z-axis, only, at this time.
// It should be measured along the strut axis. If the local-frame gear position
// "hangs down" below the CG greater than the altitude, then the compressLength
// will be positive - i.e. the gear will have made contact.
if (compressLength > 0.00) {
WOW = true;// Weight-On-Wheels is true
// The next equation should really use the vector to the contact patch of the tire
// including the strut compression and not vWhlBodyVec. Will fix this later.
// As it stands, now, the following equation takes the aircraft body-frame
// rotational rate and calculates the cross-product with the vector from the CG
// to the wheel, thus producing the instantaneous velocity vector of the tire
// in Body coords. The frame is also converted to local coordinates. When the
// aircraft local-frame velocity is added to this quantity, the total velocity of
// the wheel in local frame is then known. Subsequently, the compression speed
// (used for calculating damping force) is found by taking the Z-component of the
// wheel velocity.
vWhlVelVec = State->GetTb2l() * (Rotation->GetPQR() * vWhlBodyVec);
vWhlVelVec += Position->GetVel();
compressSpeed = vWhlVelVec(eZ);
// If this is the first time the wheel has made contact, remember some values
// for later printout.
if (!FirstContact) {
FirstContact = true;
SinkRate = compressSpeed;
GroundSpeed = Position->GetVel().Magnitude();
}
// The following needs work regarding friction coefficients and braking and
// steering The BrakeFCoeff formula assumes that an anti-skid system is used.
// It also assumes that we won't be turning and braking at the same time.
// Will fix this later.
// [JSB] The braking force coefficients include normal rolling coefficient +
// a percentage of the static friction coefficient based on braking applied.
switch (eBrakeGrp) {
case bgLeft:
SteerGain = -0.10;
BrakeFCoeff = rollingFCoeff*(1.0 - FCS->GetBrake(bgLeft)) +
staticFCoeff*FCS->GetBrake(bgLeft);
break;
case bgRight:
SteerGain = -0.10;
BrakeFCoeff = rollingFCoeff*(1.0 - FCS->GetBrake(bgRight)) +
staticFCoeff*FCS->GetBrake(bgRight);
break;
case bgCenter:
SteerGain = -0.10;
BrakeFCoeff = rollingFCoeff*(1.0 - FCS->GetBrake(bgCenter)) +
staticFCoeff*FCS->GetBrake(bgCenter);
break;
case bgNose:
SteerGain = 0.10;
BrakeFCoeff = rollingFCoeff;
break;
case bgTail:
SteerGain = -0.10;
BrakeFCoeff = rollingFCoeff;
break;
case bgNone:
SteerGain = -0.10;
BrakeFCoeff = rollingFCoeff;
break;
default:
cerr << "Improper brake group membership detected for this gear." << endl;
break;
}
switch (eSteerType) {
case stSteer:
SteerAngle = SteerGain*FCS->GetDrPos();
break;
case stFixed:
SteerAngle = 0.0;
break;
case stCaster:
// Note to Jon: This is not correct for castering gear. I'll fix it later.
SteerAngle = 0.0;
break;
default:
cerr << "Improper steering type membership detected for this gear." << endl;
break;
}
// Transform the wheel velocities from the local axis system to the wheel axis system.
// For now, steering angle is assumed to happen in the Local Z axis,
// not the strut axis as it should be. Will fix this later.
SinWheel = sin(Rotation->Getpsi() + SteerAngle);
CosWheel = cos(Rotation->Getpsi() + SteerAngle);
RollingWhlVel = vWhlVelVec(eX)*CosWheel + vWhlVelVec(eY)*SinWheel;
SideWhlVel = vWhlVelVec(eY)*CosWheel - vWhlVelVec(eX)*SinWheel;
// Calculate tire slip angle.
if (RollingWhlVel == 0.0 && SideWhlVel == 0.0) {
WheelSlip = 0.0;
} else {
WheelSlip = radtodeg*atan2(SideWhlVel, RollingWhlVel);
}
// The following code normalizes the wheel velocity vector, reverses it, and zeroes out
// the z component of the velocity. The question is, should the Z axis velocity be zeroed
// out first before the normalization takes place or not? Subsequent to that, the Wheel
// Velocity vector now points as a unit vector backwards and parallel to the wheel
// velocity vector. It acts AT the wheel.
// Note to Jon: I commented out this line because I wasn't sure we want to do this.
// vWhlVelVec = -1.0 * vWhlVelVec.Normalize();
// vWhlVelVec(eZ) = 0.00;
// Compute the sideforce coefficients using similar assumptions to LaRCSim for now.
// Allow a maximum of 10 degrees tire slip angle before wheel slides. At that point,
// transition from static to dynamic friction. There are more complicated formulations
// of this that avoid the discrete jump. Will fix this later.
if (fabs(WheelSlip) <= 10.0) {
FCoeff = staticFCoeff*WheelSlip/10.0;
} else {
FCoeff = dynamicFCoeff*fabs(WheelSlip)/WheelSlip;
}
// Compute the vertical force on the wheel using square-law damping (per comment
// in paper AIAA-2000-4303 - see header prologue comments). We might consider
// allowing for both square and linear damping force calculation. Also need to
// possibly give a "rebound damping factor" that differs from the compression
// case. NOTE: SQUARE LAW DAMPING NO GOOD!
vLocalForce(eZ) = min(-compressLength * kSpring
- compressSpeed * bDamp, (double)0.0);
MaximumStrutForce = max(MaximumStrutForce, fabs(vLocalForce(eZ)));
MaximumStrutTravel = max(MaximumStrutTravel, fabs(compressLength));
// Compute the forces in the wheel ground plane.
RollingForce = 0;
if (fabs(RollingWhlVel) > 1E-3) {
RollingForce = vLocalForce(eZ) * BrakeFCoeff * fabs(RollingWhlVel)/RollingWhlVel;
}
SideForce = vLocalForce(eZ) * FCoeff;
// Transform these forces back to the local reference frame.
vLocalForce(eX) = RollingForce*CosWheel - SideForce*SinWheel;
vLocalForce(eY) = SideForce*CosWheel + RollingForce*SinWheel;
// Note to Jon: At this point the forces will be too big when the airplane is
// stopped or rolling to a stop. We need to make sure that the gear forces just
// balance out the non-gear forces when the airplane is stopped. That way the
// airplane won't start to accelerate until the non-gear/ forces are larger than
// the gear forces. I think that the proper fix should go into FGAircraft::FMGear.
// This routine would only compute the local strut forces and return them to
// FMGear. All of the gear forces would get adjusted in FMGear using the total
// non-gear forces. Then the gear moments would be calculated. If strange things
// start happening to the airplane during testing as it rolls to a stop, then we
// need to implement this change. I ran out of time to do it now but have the
// equations.
// Transform the forces back to the body frame and compute the moment.
vForce = State->GetTl2b() * vLocalForce;
vMoment = vWhlBodyVec * vForce;
} else {
WOW = false;
if (Position->GetDistanceAGL() > 200.0) {
FirstContact = false;
Reported = false;
DistanceTraveled = 0.0;
MaximumStrutForce = MaximumStrutTravel = 0.0;
}
compressLength = 0.0; // reset compressLength to zero for data output validity
}
if (FirstContact) {
DistanceTraveled += Position->GetVel().Magnitude()*State->Getdt()*Aircraft->GetRate();
}
if (ReportEnable && Position->GetVel().Magnitude() <= 0.05 && !Reported) {
if (debug_lvl > 0) Report();
}
if (lastWOW != WOW) {
PutMessage("GEAR_CONTACT", WOW);
}
lastWOW = WOW;
// Crash detection logic (really out-of-bounds detection)
if (compressLength > 500.0 ||
vForce.Magnitude() > 100000000.0 ||
vMoment.Magnitude() > 5000000000.0 ||
SinkRate > 1.4666*30)
{
PutMessage("Crash Detected");
Exec->Freeze();
}
}
return vForce;
}
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
void FGLGear::Report(void)
{
cout << endl << "Touchdown report for " << name << endl;
cout << " Sink rate at contact: " << SinkRate << " fps, "
<< SinkRate*0.3408 << " mps" << endl;
cout << " Contact ground speed: " << GroundSpeed*.5925 << " knots, "
<< GroundSpeed*0.3408 << " mps" << endl;
cout << " Maximum contact force: " << MaximumStrutForce << " lbs, "
<< MaximumStrutForce*4.448 << " Newtons" << endl;
cout << " Maximum strut travel: " << MaximumStrutTravel*12.0 << " inches, "
<< MaximumStrutTravel*30.48 << " cm" << endl;
cout << " Distance traveled: " << DistanceTraveled << " ft, "
<< DistanceTraveled*0.3408 << " meters" << endl;
Reported = true;
}
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
// The bitmasked value choices are as follows:
// unset: In this case (the default) JSBSim would only print
// out the normally expected messages, essentially echoing
// the config files as they are read. If the environment
// variable is not set, debug_lvl is set to 1 internally
// 0: This requests JSBSim not to output any messages
// whatsoever.
// 1: This value explicity requests the normal JSBSim
// startup messages
// 2: This value asks for a message to be printed out when
// a class is instantiated
// 4: When this value is set, a message is displayed when a
// FGModel object executes its Run() method
// 8: When this value is set, various runtime state variables
// are printed out periodically
// 16: When set various parameters are sanity checked and
// a message is printed out when they go out of bounds
void FGLGear::Debug(int from)
{
if (debug_lvl <= 0) return;
if (debug_lvl & 1) { // Standard console startup message output
if (from == 0) { // Constructor
cout << " Name: " << name << endl;
cout << " Location: " << vXYZ << endl;
cout << " Spring Constant: " << kSpring << endl;
cout << " Damping Constant: " << bDamp << endl;
cout << " Dynamic Friction: " << dynamicFCoeff << endl;
cout << " Static Friction: " << staticFCoeff << endl;
cout << " Rolling Friction: " << rollingFCoeff << endl;
cout << " Steering Type: " << sSteerType << endl;
cout << " Grouping: " << sBrakeGroup << endl;
cout << " Max Steer Angle: " << maxSteerAngle << endl;
cout << " Retractable: " << sRetractable << endl;
}
}
if (debug_lvl & 2 ) { // Instantiation/Destruction notification
if (from == 0) cout << "Instantiated: FGLGear" << endl;
if (from == 1) cout << "Destroyed: FGLGear" << endl;
}
if (debug_lvl & 4 ) { // Run() method entry print for FGModel-derived objects
}
if (debug_lvl & 8 ) { // Runtime state variables
}
if (debug_lvl & 16) { // Sanity checking
}
if (debug_lvl & 64) {
if (from == 0) { // Constructor
cout << IdSrc << endl;
cout << IdHdr << endl;
}
}
}
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