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 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
45 /*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
47 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
49 /*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
51 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
53 static const char *IdSrc = "$Id$";
54 static const char *IdHdr = ID_LGEAR;
56 /*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
58 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
60 FGLGear::FGLGear(FGConfigFile* AC_cfg, FGFDMExec* fdmex, int number) : Exec(fdmex)
64 *AC_cfg >> 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;
98 // Add some AI here to determine if gear is located properly according to its
99 // brake group type ??
101 State = Exec->GetState();
102 Aircraft = Exec->GetAircraft();
103 Propagate = Exec->GetPropagate();
104 Auxiliary = Exec->GetAuxiliary();
105 FCS = Exec->GetFCS();
106 MassBalance = Exec->GetMassBalance();
108 WOW = lastWOW = true; // should the value be initialized to true?
110 FirstContact = false;
111 StartedGroundRun = false;
112 TakeoffReported = LandingReported = false;
113 LandingDistanceTraveled = TakeoffDistanceTraveled = TakeoffDistanceTraveled50ft = 0.0;
114 MaximumStrutForce = MaximumStrutTravel = 0.0;
115 SideForce = RollingForce = 0.0;
116 SinkRate = GroundSpeed = 0.0;
118 vWhlBodyVec = MassBalance->StructuralToBody(vXYZ);
120 vLocalGear = Propagate->GetTb2l() * vWhlBodyVec;
122 compressLength = 0.0;
127 WheelSlip = lastWheelSlip = 0.0;
129 compressLength = 0.0;
134 TirePressureNorm = 1.0;
139 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
141 FGLGear::FGLGear(const FGLGear& lgear)
143 GearNumber = lgear.GearNumber;
146 Aircraft = lgear.Aircraft;
147 Propagate = lgear.Propagate;
148 Auxiliary = lgear.Auxiliary;
151 MassBalance = lgear.MassBalance;
154 vMoment = lgear.vMoment;
155 vWhlBodyVec = lgear.vWhlBodyVec;
156 vLocalGear = lgear.vLocalGear;
159 lastWOW = lgear.lastWOW;
160 ReportEnable = lgear.ReportEnable;
161 FirstContact = lgear.FirstContact;
162 StartedGroundRun = lgear.StartedGroundRun;
163 LandingDistanceTraveled = lgear.LandingDistanceTraveled;
164 TakeoffDistanceTraveled = lgear.TakeoffDistanceTraveled;
165 TakeoffDistanceTraveled50ft = lgear.TakeoffDistanceTraveled50ft;
166 MaximumStrutForce = lgear.MaximumStrutForce;
167 MaximumStrutTravel = lgear.MaximumStrutTravel;
168 SideForce = lgear.SideForce;
169 RollingForce = lgear.RollingForce;
171 kSpring = lgear.kSpring;
173 compressLength = lgear.compressLength;
174 compressSpeed = lgear.compressSpeed;
175 staticFCoeff = lgear.staticFCoeff;
176 dynamicFCoeff = lgear.dynamicFCoeff;
177 rollingFCoeff = lgear.rollingFCoeff;
178 brakePct = lgear.brakePct;
179 maxCompLen = lgear.maxCompLen;
180 SinkRate = lgear.SinkRate;
181 GroundSpeed = lgear.GroundSpeed;
182 LandingReported = lgear.LandingReported;
183 TakeoffReported = lgear.TakeoffReported;
185 sSteerType = lgear.sSteerType;
186 sRetractable = lgear.sRetractable;
187 eSteerType = lgear.eSteerType;
188 sBrakeGroup = lgear.sBrakeGroup;
189 eBrakeGrp = lgear.eBrakeGrp;
190 maxSteerAngle = lgear.maxSteerAngle;
191 isRetractable = lgear.isRetractable;
192 GearUp = lgear.GearUp;
193 GearDown = lgear.GearDown;
194 WheelSlip = lgear.WheelSlip;
195 lastWheelSlip = lgear.lastWheelSlip;
196 TirePressureNorm = lgear.TirePressureNorm;
197 Servicable = lgear.Servicable;
200 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
207 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
209 FGColumnVector3& FGLGear::Force(void)
211 double SinWheel, CosWheel;
212 double deltaT = State->Getdt()*Exec->GetGroundReactions()->GetRate();
215 vMoment.InitMatrix();
218 if (FCS->GetGearPos() < 0.01) {
221 } else if (FCS->GetGearPos() > 0.99) {
233 // Compute the steering angle in any case.
234 // Will make shure that animations will look right.
235 switch (eSteerType) {
237 SteerAngle = degtorad * FCS->GetSteerPosDeg(GearNumber);
243 // Note to Jon: This is not correct for castering gear. I'll fix it later.
247 cerr << "Improper steering type membership detected for this gear." << endl;
252 double t = Exec->GetState()->Getsim_time();
254 vWhlBodyVec = MassBalance->StructuralToBody(vXYZ);
256 // vWhlBodyVec now stores the vector from the cg to this wheel
258 vLocalGear = Propagate->GetTb2l() * vWhlBodyVec;
260 // vLocalGear now stores the vector from the cg to the wheel in local coords.
262 FGColumnVector3 normal, cvel;
264 FGLocation gearLoc = Propagate->GetLocation().LocalToLocation(vLocalGear);
265 compressLength = - Exec->GetGroundCallback()->GetAGLevel(t, gearLoc, contact, normal, cvel);
267 // The compression length is currently measured in the Z-axis, only, at this time.
268 // It should be measured along the strut axis. If the local-frame gear position
269 // "hangs down" below the CG greater than the altitude, then the compressLength
270 // will be positive - i.e. the gear will have made contact.
272 if (compressLength > 0.00) {
274 WOW = true; // Weight-On-Wheels is true
276 // The next equation should really use the vector to the contact patch of the tire
277 // including the strut compression and not vWhlBodyVec. Will fix this later.
278 // As it stands, now, the following equation takes the aircraft body-frame
279 // rotational rate and calculates the cross-product with the vector from the CG
280 // to the wheel, thus producing the instantaneous velocity vector of the tire
281 // in Body coords. The frame is also converted to local coordinates. When the
282 // aircraft local-frame velocity is added to this quantity, the total velocity of
283 // the wheel in local frame is then known. Subsequently, the compression speed
284 // (used for calculating damping force) is found by taking the Z-component of the
287 vWhlVelVec = Propagate->GetTb2l() * (Propagate->GetPQR() * vWhlBodyVec);
288 vWhlVelVec += Propagate->GetVel() - cvel;
289 compressSpeed = vWhlVelVec(eZ);
291 // If this is the first time the wheel has made contact, remember some values
292 // for later printout.
296 SinkRate = compressSpeed;
297 GroundSpeed = Propagate->GetVel().Magnitude();
298 TakeoffReported = false;
301 // If the takeoff run is starting, initialize.
303 if ((Propagate->GetVel().Magnitude() > 0.1) &&
304 (FCS->GetBrake(bgLeft) == 0) &&
305 (FCS->GetBrake(bgRight) == 0) &&
306 (FCS->GetThrottlePos(0) == 1) && !StartedGroundRun)
308 TakeoffDistanceTraveled = 0;
309 TakeoffDistanceTraveled50ft = 0;
310 StartedGroundRun = true;
313 // The following needs work regarding friction coefficients and braking and
314 // steering The BrakeFCoeff formula assumes that an anti-skid system is used.
315 // It also assumes that we won't be turning and braking at the same time.
316 // Will fix this later.
317 // [JSB] The braking force coefficients include normal rolling coefficient +
318 // a percentage of the static friction coefficient based on braking applied.
322 BrakeFCoeff = ( rollingFCoeff*(1.0 - FCS->GetBrake(bgLeft)) +
323 staticFCoeff*FCS->GetBrake(bgLeft) );
326 BrakeFCoeff = ( rollingFCoeff*(1.0 - FCS->GetBrake(bgRight)) +
327 staticFCoeff*FCS->GetBrake(bgRight) );
330 BrakeFCoeff = ( rollingFCoeff*(1.0 - FCS->GetBrake(bgCenter)) +
331 staticFCoeff*FCS->GetBrake(bgCenter) );
334 BrakeFCoeff = ( rollingFCoeff*(1.0 - FCS->GetBrake(bgCenter)) +
335 staticFCoeff*FCS->GetBrake(bgCenter) );
338 BrakeFCoeff = ( rollingFCoeff*(1.0 - FCS->GetBrake(bgCenter)) +
339 staticFCoeff*FCS->GetBrake(bgCenter) );
342 BrakeFCoeff = rollingFCoeff;
345 cerr << "Improper brake group membership detected for this gear." << endl;
349 // Transform the wheel velocities from the local axis system to the wheel axis system.
350 // For now, steering angle is assumed to happen in the Local Z axis,
351 // not the strut axis as it should be. Will fix this later.
353 SinWheel = sin(Propagate->GetEuler(ePsi) + SteerAngle);
354 CosWheel = cos(Propagate->GetEuler(ePsi) + SteerAngle);
355 RollingWhlVel = vWhlVelVec(eX)*CosWheel + vWhlVelVec(eY)*SinWheel;
356 SideWhlVel = vWhlVelVec(eY)*CosWheel - vWhlVelVec(eX)*SinWheel;
358 // Calculate tire slip angle.
360 if (RollingWhlVel == 0.0 && SideWhlVel == 0.0) {
362 } else if (fabs(RollingWhlVel) < 1.0) {
363 WheelSlip = 0.05*radtodeg*atan2(SideWhlVel, fabs(RollingWhlVel)) + 0.95*WheelSlip;
365 WheelSlip = radtodeg*atan2(SideWhlVel, fabs(RollingWhlVel));
368 double maxdeltaSlip = 0.5*deltaT;
370 if (RollingWhlVel == 0.0 && SideWhlVel == 0.0) {
372 } else if (RollingWhlVel < 1.0) {
373 WheelSlip = radtodeg*atan2(SideWhlVel, RollingWhlVel);
374 deltaSlip = WheelSlip - lastWheelSlip;
375 if (fabs(deltaSlip) > maxdeltaSlip) {
376 if (WheelSlip > lastWheelSlip) {
377 WheelSlip = lastWheelSlip + maxdeltaSlip;
378 } else if (WheelSlip < lastWheelSlip) {
379 WheelSlip = lastWheelSlip - maxdeltaSlip;
383 WheelSlip = radtodeg*atan2(SideWhlVel, RollingWhlVel);
386 if ((WheelSlip < 0.0 && lastWheelSlip > 0.0) ||
387 (WheelSlip > 0.0 && lastWheelSlip < 0.0))
392 lastWheelSlip = WheelSlip;
394 // Compute the sideforce coefficients using similar assumptions to LaRCSim for now.
395 // Allow a maximum of 10 degrees tire slip angle before wheel slides. At that point,
396 // transition from static to dynamic friction. There are more complicated formulations
397 // of this that avoid the discrete jump (similar to Pacejka). Will fix this later.
399 if (fabs(WheelSlip) <= 20.0) {
400 FCoeff = staticFCoeff*WheelSlip/20.0;
401 } else if (fabs(WheelSlip) <= 40.0) {
402 // FCoeff = dynamicFCoeff*fabs(WheelSlip)/WheelSlip;
403 FCoeff = (dynamicFCoeff*(fabs(WheelSlip) - 20.0)/20.0 +
404 staticFCoeff*(40.0 - fabs(WheelSlip))/20.0)*fabs(WheelSlip)/WheelSlip;
406 FCoeff = dynamicFCoeff*fabs(WheelSlip)/WheelSlip;
409 // Compute the vertical force on the wheel using square-law damping (per comment
410 // in paper AIAA-2000-4303 - see header prologue comments). We might consider
411 // allowing for both square and linear damping force calculation. Also need to
412 // possibly give a "rebound damping factor" that differs from the compression
415 vLocalForce(eZ) = min(-compressLength * kSpring
416 - compressSpeed * bDamp, (double)0.0);
418 MaximumStrutForce = max(MaximumStrutForce, fabs(vLocalForce(eZ)));
419 MaximumStrutTravel = max(MaximumStrutTravel, fabs(compressLength));
421 // Compute the forces in the wheel ground plane.
424 if (fabs(RollingWhlVel) > 1E-3) {
425 double badPresResis = (1.0 - TirePressureNorm) * 30;
426 RollingForce = (badPresResis * min(fabs(RollingWhlVel), 1.0)
427 + vLocalForce(eZ) * BrakeFCoeff)
428 * fabs(RollingWhlVel)/RollingWhlVel;
430 SideForce = vLocalForce(eZ) * FCoeff;
432 // Transform these forces back to the local reference frame.
434 vLocalForce(eX) = RollingForce*CosWheel - SideForce*SinWheel;
435 vLocalForce(eY) = SideForce*CosWheel + RollingForce*SinWheel;
437 // Note to Jon: At this point the forces will be too big when the airplane is
438 // stopped or rolling to a stop. We need to make sure that the gear forces just
439 // balance out the non-gear forces when the airplane is stopped. That way the
440 // airplane won't start to accelerate until the non-gear/ forces are larger than
441 // the gear forces. I think that the proper fix should go into FGAircraft::FMGear.
442 // This routine would only compute the local strut forces and return them to
443 // FMGear. All of the gear forces would get adjusted in FMGear using the total
444 // non-gear forces. Then the gear moments would be calculated. If strange things
445 // start happening to the airplane during testing as it rolls to a stop, then we
446 // need to implement this change. I ran out of time to do it now but have the
449 // Transform the forces back to the body frame and compute the moment.
451 vForce = Propagate->GetTl2b() * vLocalForce;
452 vMoment = vWhlBodyVec * vForce;
454 } else { // Gear is NOT compressed
458 // Return to neutral position between 1.0 and 0.8 gear pos.
459 SteerAngle *= max(FCS->GetGearPos()-0.8, 0.0)/0.2;
461 if (Propagate->GetDistanceAGL() > 200.0) {
462 FirstContact = false;
463 StartedGroundRun = false;
464 LandingReported = false;
465 LandingDistanceTraveled = 0.0;
466 MaximumStrutForce = MaximumStrutTravel = 0.0;
469 compressLength = 0.0; // reset compressLength to zero for data output validity
472 if (FirstContact) LandingDistanceTraveled += Auxiliary->GetVground()*deltaT;
474 if (StartedGroundRun) {
475 TakeoffDistanceTraveled50ft += Auxiliary->GetVground()*deltaT;
476 if (WOW) TakeoffDistanceTraveled += Auxiliary->GetVground()*deltaT;
479 if (ReportEnable && Auxiliary->GetVground() <= 0.05 && !LandingReported) {
480 if (debug_lvl > 0) Report(erLand);
483 if (ReportEnable && !TakeoffReported &&
484 (vLocalGear(eZ) - Propagate->GetDistanceAGL()) < -50.0)
486 if (debug_lvl > 0) Report(erTakeoff);
489 if (lastWOW != WOW) {
490 PutMessage("GEAR_CONTACT: " + name, WOW);
495 // Crash detection logic (really out-of-bounds detection)
497 if (compressLength > 500.0 ||
498 vForce.Magnitude() > 100000000.0 ||
499 vMoment.Magnitude() > 5000000000.0 ||
500 SinkRate > 1.4666*30)
502 PutMessage("Crash Detected: Simulation FREEZE.");
509 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
511 void FGLGear::Report(ReportType repType)
515 cout << endl << "Touchdown report for " << name << endl;
516 cout << " Sink rate at contact: " << SinkRate << " fps, "
517 << SinkRate*0.3048 << " mps" << endl;
518 cout << " Contact ground speed: " << GroundSpeed*.5925 << " knots, "
519 << GroundSpeed*0.3048 << " mps" << endl;
520 cout << " Maximum contact force: " << MaximumStrutForce << " lbs, "
521 << MaximumStrutForce*4.448 << " Newtons" << endl;
522 cout << " Maximum strut travel: " << MaximumStrutTravel*12.0 << " inches, "
523 << MaximumStrutTravel*30.48 << " cm" << endl;
524 cout << " Distance traveled: " << LandingDistanceTraveled << " ft, "
525 << LandingDistanceTraveled*0.3048 << " meters" << endl;
526 LandingReported = true;
529 cout << endl << "Takeoff report for " << name << endl;
530 cout << " Distance traveled: " << TakeoffDistanceTraveled
531 << " ft, " << TakeoffDistanceTraveled*0.3048 << " meters" << endl;
532 cout << " Distance traveled (over 50'): " << TakeoffDistanceTraveled50ft
533 << " ft, " << TakeoffDistanceTraveled50ft*0.3048 << " meters" << endl;
534 TakeoffReported = true;
539 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
540 // The bitmasked value choices are as follows:
541 // unset: In this case (the default) JSBSim would only print
542 // out the normally expected messages, essentially echoing
543 // the config files as they are read. If the environment
544 // variable is not set, debug_lvl is set to 1 internally
545 // 0: This requests JSBSim not to output any messages
547 // 1: This value explicity requests the normal JSBSim
549 // 2: This value asks for a message to be printed out when
550 // a class is instantiated
551 // 4: When this value is set, a message is displayed when a
552 // FGModel object executes its Run() method
553 // 8: When this value is set, various runtime state variables
554 // are printed out periodically
555 // 16: When set various parameters are sanity checked and
556 // a message is printed out when they go out of bounds
558 void FGLGear::Debug(int from)
560 if (debug_lvl <= 0) return;
562 if (debug_lvl & 1) { // Standard console startup message output
563 if (from == 0) { // Constructor
564 cout << " Name: " << name << endl;
565 cout << " Location: " << vXYZ << endl;
566 cout << " Spring Constant: " << kSpring << endl;
567 cout << " Damping Constant: " << bDamp << endl;
568 cout << " Dynamic Friction: " << dynamicFCoeff << endl;
569 cout << " Static Friction: " << staticFCoeff << endl;
570 cout << " Rolling Friction: " << rollingFCoeff << endl;
571 cout << " Steering Type: " << sSteerType << endl;
572 cout << " Grouping: " << sBrakeGroup << endl;
573 cout << " Max Steer Angle: " << maxSteerAngle << endl;
574 cout << " Retractable: " << sRetractable << endl;
577 if (debug_lvl & 2 ) { // Instantiation/Destruction notification
578 if (from == 0) cout << "Instantiated: FGLGear" << endl;
579 if (from == 1) cout << "Destroyed: FGLGear" << endl;
581 if (debug_lvl & 4 ) { // Run() method entry print for FGModel-derived objects
583 if (debug_lvl & 8 ) { // Runtime state variables
585 if (debug_lvl & 16) { // Sanity checking
587 if (debug_lvl & 64) {
588 if (from == 0) { // Constructor
589 cout << IdSrc << endl;
590 cout << IdHdr << endl;
595 } // namespace JSBSim