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