1 /*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
7 Purpose: Encapsulates the landing gear elements
10 ------------- Copyright (C) 1999 Jon S. Berndt (jsb@hal-pc.org) -------------
12 This program is free software; you can redistribute it and/or modify it under
13 the terms of the GNU General Public License as published by the Free Software
14 Foundation; either version 2 of the License, or (at your option) any later
17 This program is distributed in the hope that it will be useful, but WITHOUT
18 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
19 FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
22 You should have received a copy of the GNU General Public License along with
23 this program; if not, write to the Free Software Foundation, Inc., 59 Temple
24 Place - Suite 330, Boston, MA 02111-1307, USA.
26 Further information about the GNU General Public License can also be found on
27 the world wide web at http://www.gnu.org.
29 FUNCTIONAL DESCRIPTION
30 --------------------------------------------------------------------------------
33 --------------------------------------------------------------------------------
35 01/30/01 NHP Extended gear model to properly simulate steering and braking
37 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
39 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
44 /*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
46 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
48 /*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
50 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
53 static const char *IdSrc = "$Id$";
54 static const char *IdHdr = ID_LGEAR;
56 /*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
58 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
60 FGLGear::FGLGear(FGConfigFile* AC_cfg, FGFDMExec* fdmex) : Exec(fdmex)
64 *AC_cfg >> tmp >> name >> vXYZ(1) >> vXYZ(2) >> vXYZ(3)
65 >> kSpring >> bDamp>> dynamicFCoeff >> staticFCoeff
66 >> rollingFCoeff >> sSteerType >> sBrakeGroup
67 >> maxSteerAngle >> sRetractable;
69 if (sBrakeGroup == "LEFT" ) eBrakeGrp = bgLeft;
70 else if (sBrakeGroup == "RIGHT" ) eBrakeGrp = bgRight;
71 else if (sBrakeGroup == "CENTER") eBrakeGrp = bgCenter;
72 else if (sBrakeGroup == "NOSE" ) eBrakeGrp = bgNose;
73 else if (sBrakeGroup == "TAIL" ) eBrakeGrp = bgTail;
74 else if (sBrakeGroup == "NONE" ) eBrakeGrp = bgNone;
76 cerr << "Improper braking group specification in config file: "
77 << sBrakeGroup << " is undefined." << endl;
80 if (sSteerType == "STEERABLE") eSteerType = stSteer;
81 else if (sSteerType == "FIXED" ) eSteerType = stFixed;
82 else if (sSteerType == "CASTERED" ) eSteerType = stCaster;
84 cerr << "Improper steering type specification in config file: "
85 << sSteerType << " is undefined." << endl;
88 if ( sRetractable == "RETRACT" ) {
91 isRetractable = false;
97 // Add some AI here to determine if gear is located properly according to its
98 // brake group type ??
100 State = Exec->GetState();
101 Aircraft = Exec->GetAircraft();
102 Position = Exec->GetPosition();
103 Rotation = Exec->GetRotation();
104 FCS = Exec->GetFCS();
105 MassBalance = Exec->GetMassBalance();
107 WOW = lastWOW = false;
109 FirstContact = false;
111 DistanceTraveled = 0.0;
112 MaximumStrutForce = MaximumStrutTravel = 0.0;
113 SinkRate = GroundSpeed = 0.0;
115 vWhlBodyVec = (vXYZ - MassBalance->GetXYZcg()) / 12.0;
116 vWhlBodyVec(eX) = -vWhlBodyVec(eX);
117 vWhlBodyVec(eZ) = -vWhlBodyVec(eZ);
119 vLocalGear = State->GetTb2l() * vWhlBodyVec;
121 compressLength = 0.0;
129 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
131 FGLGear::FGLGear(const FGLGear& lgear)
134 Aircraft = lgear.Aircraft;
135 Position = lgear.Position;
136 Rotation = lgear.Rotation;
139 MassBalance = lgear.MassBalance;
142 vMoment = lgear.vMoment;
143 vWhlBodyVec = lgear.vWhlBodyVec;
144 vLocalGear = lgear.vLocalGear;
147 lastWOW = lgear.lastWOW;
148 ReportEnable = lgear.ReportEnable;
149 FirstContact = lgear.FirstContact;
150 DistanceTraveled = lgear.DistanceTraveled;
151 MaximumStrutForce = lgear.MaximumStrutForce;
152 MaximumStrutTravel = lgear.MaximumStrutTravel;
154 kSpring = lgear.kSpring;
156 compressLength = lgear.compressLength;
157 compressSpeed = lgear.compressSpeed;
158 staticFCoeff = lgear.staticFCoeff;
159 dynamicFCoeff = lgear.dynamicFCoeff;
160 rollingFCoeff = lgear.rollingFCoeff;
161 brakePct = lgear.brakePct;
162 maxCompLen = lgear.maxCompLen;
163 SinkRate = lgear.SinkRate;
164 GroundSpeed = lgear.GroundSpeed;
165 Reported = lgear.Reported;
167 sSteerType = lgear.sSteerType;
168 sRetractable = lgear.sRetractable;
169 eSteerType = lgear.eSteerType;
170 sBrakeGroup = lgear.sBrakeGroup;
171 eBrakeGrp = lgear.eBrakeGrp;
172 maxSteerAngle = lgear.maxSteerAngle;
173 isRetractable = lgear.isRetractable;
174 GearUp = lgear.GearUp;
175 GearDown = lgear.GearDown;
178 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
185 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
187 FGColumnVector3& FGLGear::Force(void)
189 double SteerGain = 0;
190 double SinWheel, CosWheel;
193 vMoment.InitMatrix();
196 if (FCS->GetGearPos() < 0.01) {
199 } else if (FCS->GetGearPos() > 0.99) {
213 vWhlBodyVec = (vXYZ - MassBalance->GetXYZcg()) / 12.0;
214 vWhlBodyVec(eX) = -vWhlBodyVec(eX);
215 vWhlBodyVec(eZ) = -vWhlBodyVec(eZ);
217 // vWhlBodyVec now stores the vector from the cg to this wheel
219 vLocalGear = State->GetTb2l() * vWhlBodyVec;
221 // vLocalGear now stores the vector from the cg to the wheel in local coords.
223 compressLength = vLocalGear(eZ) - Position->GetDistanceAGL();
225 // The compression length is currently measured in the Z-axis, only, at this time.
226 // It should be measured along the strut axis. If the local-frame gear position
227 // "hangs down" below the CG greater than the altitude, then the compressLength
228 // will be positive - i.e. the gear will have made contact.
230 if (compressLength > 0.00) {
232 WOW = true;// Weight-On-Wheels is true
234 // The next equation should really use the vector to the contact patch of the tire
235 // including the strut compression and not vWhlBodyVec. Will fix this later.
236 // As it stands, now, the following equation takes the aircraft body-frame
237 // rotational rate and calculates the cross-product with the vector from the CG
238 // to the wheel, thus producing the instantaneous velocity vector of the tire
239 // in Body coords. The frame is also converted to local coordinates. When the
240 // aircraft local-frame velocity is added to this quantity, the total velocity of
241 // the wheel in local frame is then known. Subsequently, the compression speed
242 // (used for calculating damping force) is found by taking the Z-component of the
245 vWhlVelVec = State->GetTb2l() * (Rotation->GetPQR() * vWhlBodyVec);
247 vWhlVelVec += Position->GetVel();
249 compressSpeed = vWhlVelVec(eZ);
251 // If this is the first time the wheel has made contact, remember some values
252 // for later printout.
256 SinkRate = compressSpeed;
257 GroundSpeed = Position->GetVel().Magnitude();
260 // The following needs work regarding friction coefficients and braking and
261 // steering The BrakeFCoeff formula assumes that an anti-skid system is used.
262 // It also assumes that we won't be turning and braking at the same time.
263 // Will fix this later.
264 // [JSB] The braking force coefficients include normal rolling coefficient +
265 // a percentage of the static friction coefficient based on braking applied.
270 BrakeFCoeff = rollingFCoeff*(1.0 - FCS->GetBrake(bgLeft)) +
271 staticFCoeff*FCS->GetBrake(bgLeft);
275 BrakeFCoeff = rollingFCoeff*(1.0 - FCS->GetBrake(bgRight)) +
276 staticFCoeff*FCS->GetBrake(bgRight);
280 BrakeFCoeff = rollingFCoeff*(1.0 - FCS->GetBrake(bgCenter)) +
281 staticFCoeff*FCS->GetBrake(bgCenter);
285 BrakeFCoeff = rollingFCoeff;
289 BrakeFCoeff = rollingFCoeff;
293 BrakeFCoeff = rollingFCoeff;
296 cerr << "Improper brake group membership detected for this gear." << endl;
300 switch (eSteerType) {
302 SteerAngle = SteerGain*FCS->GetDrPos();
308 // Note to Jon: This is not correct for castering gear. I'll fix it later.
312 cerr << "Improper steering type membership detected for this gear." << endl;
316 // Transform the wheel velocities from the local axis system to the wheel axis system.
317 // For now, steering angle is assumed to happen in the Local Z axis,
318 // not the strut axis as it should be. Will fix this later.
320 SinWheel = sin(Rotation->Getpsi() + SteerAngle);
321 CosWheel = cos(Rotation->Getpsi() + SteerAngle);
322 RollingWhlVel = vWhlVelVec(eX)*CosWheel + vWhlVelVec(eY)*SinWheel;
323 SideWhlVel = vWhlVelVec(eY)*CosWheel - vWhlVelVec(eX)*SinWheel;
325 // Calculate tire slip angle.
327 if (RollingWhlVel == 0.0 && SideWhlVel == 0.0) {
330 WheelSlip = radtodeg*atan2(SideWhlVel, RollingWhlVel);
333 // Compute the sideforce coefficients using similar assumptions to LaRCSim for now.
334 // Allow a maximum of 10 degrees tire slip angle before wheel slides. At that point,
335 // transition from static to dynamic friction. There are more complicated formulations
336 // of this that avoid the discrete jump. Will fix this later.
338 if (fabs(WheelSlip) <= 10.0) {
339 FCoeff = staticFCoeff*WheelSlip/10.0;
341 FCoeff = dynamicFCoeff*fabs(WheelSlip)/WheelSlip;
344 // Compute the vertical force on the wheel using square-law damping (per comment
345 // in paper AIAA-2000-4303 - see header prologue comments). We might consider
346 // allowing for both square and linear damping force calculation. Also need to
347 // possibly give a "rebound damping factor" that differs from the compression
350 vLocalForce(eZ) = min(-compressLength * kSpring
351 - compressSpeed * bDamp, (double)0.0);
353 MaximumStrutForce = max(MaximumStrutForce, fabs(vLocalForce(eZ)));
354 MaximumStrutTravel = max(MaximumStrutTravel, fabs(compressLength));
356 // Compute the forces in the wheel ground plane.
359 if (fabs(RollingWhlVel) > 1E-3) {
360 RollingForce = vLocalForce(eZ) * BrakeFCoeff * fabs(RollingWhlVel)/RollingWhlVel;
362 SideForce = vLocalForce(eZ) * FCoeff;
364 // Transform these forces back to the local reference frame.
366 vLocalForce(eX) = RollingForce*CosWheel - SideForce*SinWheel;
367 vLocalForce(eY) = SideForce*CosWheel + RollingForce*SinWheel;
369 // Note to Jon: At this point the forces will be too big when the airplane is
370 // stopped or rolling to a stop. We need to make sure that the gear forces just
371 // balance out the non-gear forces when the airplane is stopped. That way the
372 // airplane won't start to accelerate until the non-gear/ forces are larger than
373 // the gear forces. I think that the proper fix should go into FGAircraft::FMGear.
374 // This routine would only compute the local strut forces and return them to
375 // FMGear. All of the gear forces would get adjusted in FMGear using the total
376 // non-gear forces. Then the gear moments would be calculated. If strange things
377 // start happening to the airplane during testing as it rolls to a stop, then we
378 // need to implement this change. I ran out of time to do it now but have the
381 // Transform the forces back to the body frame and compute the moment.
383 vForce = State->GetTl2b() * vLocalForce;
384 vMoment = vWhlBodyVec * vForce;
390 if (Position->GetDistanceAGL() > 200.0) {
391 FirstContact = false;
393 DistanceTraveled = 0.0;
394 MaximumStrutForce = MaximumStrutTravel = 0.0;
397 compressLength = 0.0; // reset compressLength to zero for data output validity
401 DistanceTraveled += Position->GetVel().Magnitude()*State->Getdt()*Aircraft->GetRate();
404 if (ReportEnable && Position->GetVel().Magnitude() <= 0.05 && !Reported) {
405 if (debug_lvl > 0) Report();
408 if (lastWOW != WOW) {
409 PutMessage("GEAR_CONTACT", WOW);
414 // Crash detection logic (really out-of-bounds detection)
416 if (compressLength > 500.0 ||
417 vForce.Magnitude() > 100000000.0 ||
418 vMoment.Magnitude() > 5000000000.0 ||
419 SinkRate > 1.4666*30)
421 PutMessage("Crash Detected: Simulation FREEZE.");
428 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
430 void FGLGear::Report(void)
432 cout << endl << "Touchdown report for " << name << endl;
433 cout << " Sink rate at contact: " << SinkRate << " fps, "
434 << SinkRate*0.3408 << " mps" << endl;
435 cout << " Contact ground speed: " << GroundSpeed*.5925 << " knots, "
436 << GroundSpeed*0.3408 << " mps" << endl;
437 cout << " Maximum contact force: " << MaximumStrutForce << " lbs, "
438 << MaximumStrutForce*4.448 << " Newtons" << endl;
439 cout << " Maximum strut travel: " << MaximumStrutTravel*12.0 << " inches, "
440 << MaximumStrutTravel*30.48 << " cm" << endl;
441 cout << " Distance traveled: " << DistanceTraveled << " ft, "
442 << DistanceTraveled*0.3408 << " meters" << endl;
446 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
447 // The bitmasked value choices are as follows:
448 // unset: In this case (the default) JSBSim would only print
449 // out the normally expected messages, essentially echoing
450 // the config files as they are read. If the environment
451 // variable is not set, debug_lvl is set to 1 internally
452 // 0: This requests JSBSim not to output any messages
454 // 1: This value explicity requests the normal JSBSim
456 // 2: This value asks for a message to be printed out when
457 // a class is instantiated
458 // 4: When this value is set, a message is displayed when a
459 // FGModel object executes its Run() method
460 // 8: When this value is set, various runtime state variables
461 // are printed out periodically
462 // 16: When set various parameters are sanity checked and
463 // a message is printed out when they go out of bounds
465 void FGLGear::Debug(int from)
467 if (debug_lvl <= 0) return;
469 if (debug_lvl & 1) { // Standard console startup message output
470 if (from == 0) { // Constructor
471 cout << " Name: " << name << endl;
472 cout << " Location: " << vXYZ << endl;
473 cout << " Spring Constant: " << kSpring << endl;
474 cout << " Damping Constant: " << bDamp << endl;
475 cout << " Dynamic Friction: " << dynamicFCoeff << endl;
476 cout << " Static Friction: " << staticFCoeff << endl;
477 cout << " Rolling Friction: " << rollingFCoeff << endl;
478 cout << " Steering Type: " << sSteerType << endl;
479 cout << " Grouping: " << sBrakeGroup << endl;
480 cout << " Max Steer Angle: " << maxSteerAngle << endl;
481 cout << " Retractable: " << sRetractable << endl;
484 if (debug_lvl & 2 ) { // Instantiation/Destruction notification
485 if (from == 0) cout << "Instantiated: FGLGear" << endl;
486 if (from == 1) cout << "Destroyed: FGLGear" << endl;
488 if (debug_lvl & 4 ) { // Run() method entry print for FGModel-derived objects
490 if (debug_lvl & 8 ) { // Runtime state variables
492 if (debug_lvl & 16) { // Sanity checking
494 if (debug_lvl & 64) {
495 if (from == 0) { // Constructor
496 cout << IdSrc << endl;
497 cout << IdHdr << endl;