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) : 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;
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 Position = Exec->GetPosition();
104 Rotation = Exec->GetRotation();
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 = State->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)
144 Aircraft = lgear.Aircraft;
145 Position = lgear.Position;
146 Rotation = lgear.Rotation;
149 MassBalance = lgear.MassBalance;
152 vMoment = lgear.vMoment;
153 vWhlBodyVec = lgear.vWhlBodyVec;
154 vLocalGear = lgear.vLocalGear;
157 lastWOW = lgear.lastWOW;
158 ReportEnable = lgear.ReportEnable;
159 FirstContact = lgear.FirstContact;
160 StartedGroundRun = lgear.StartedGroundRun;
161 LandingDistanceTraveled = lgear.LandingDistanceTraveled;
162 TakeoffDistanceTraveled = lgear.TakeoffDistanceTraveled;
163 TakeoffDistanceTraveled50ft = lgear.TakeoffDistanceTraveled50ft;
164 MaximumStrutForce = lgear.MaximumStrutForce;
165 MaximumStrutTravel = lgear.MaximumStrutTravel;
166 SideForce = lgear.SideForce;
167 RollingForce = lgear.RollingForce;
169 kSpring = lgear.kSpring;
171 compressLength = lgear.compressLength;
172 compressSpeed = lgear.compressSpeed;
173 staticFCoeff = lgear.staticFCoeff;
174 dynamicFCoeff = lgear.dynamicFCoeff;
175 rollingFCoeff = lgear.rollingFCoeff;
176 brakePct = lgear.brakePct;
177 maxCompLen = lgear.maxCompLen;
178 SinkRate = lgear.SinkRate;
179 GroundSpeed = lgear.GroundSpeed;
180 LandingReported = lgear.LandingReported;
181 TakeoffReported = lgear.TakeoffReported;
183 sSteerType = lgear.sSteerType;
184 sRetractable = lgear.sRetractable;
185 eSteerType = lgear.eSteerType;
186 sBrakeGroup = lgear.sBrakeGroup;
187 eBrakeGrp = lgear.eBrakeGrp;
188 maxSteerAngle = lgear.maxSteerAngle;
189 isRetractable = lgear.isRetractable;
190 GearUp = lgear.GearUp;
191 GearDown = lgear.GearDown;
192 WheelSlip = lgear.WheelSlip;
193 lastWheelSlip = lgear.lastWheelSlip;
194 TirePressureNorm = lgear.TirePressureNorm;
195 Servicable = lgear.Servicable;
198 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
205 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
207 FGColumnVector3& FGLGear::Force(void)
209 double SteerGain = 0;
210 double SinWheel, CosWheel;
212 double deltaT = State->Getdt()*Aircraft->GetRate();
215 vMoment.InitMatrix();
218 if (FCS->GetGearPos() < 0.01) {
221 } else if (FCS->GetGearPos() > 0.99) {
235 vWhlBodyVec = MassBalance->StructuralToBody(vXYZ);
237 // vWhlBodyVec now stores the vector from the cg to this wheel
239 vLocalGear = State->GetTb2l() * vWhlBodyVec;
241 // vLocalGear now stores the vector from the cg to the wheel in local coords.
243 compressLength = vLocalGear(eZ) - Position->GetDistanceAGL();
245 // The compression length is currently measured in the Z-axis, only, at this time.
246 // It should be measured along the strut axis. If the local-frame gear position
247 // "hangs down" below the CG greater than the altitude, then the compressLength
248 // will be positive - i.e. the gear will have made contact.
250 if (compressLength > 0.00) {
252 WOW = true; // Weight-On-Wheels is true
254 // The next equation should really use the vector to the contact patch of the tire
255 // including the strut compression and not vWhlBodyVec. Will fix this later.
256 // As it stands, now, the following equation takes the aircraft body-frame
257 // rotational rate and calculates the cross-product with the vector from the CG
258 // to the wheel, thus producing the instantaneous velocity vector of the tire
259 // in Body coords. The frame is also converted to local coordinates. When the
260 // aircraft local-frame velocity is added to this quantity, the total velocity of
261 // the wheel in local frame is then known. Subsequently, the compression speed
262 // (used for calculating damping force) is found by taking the Z-component of the
265 vWhlVelVec = State->GetTb2l() * (Rotation->GetPQR() * vWhlBodyVec);
266 vWhlVelVec += Position->GetVel();
267 compressSpeed = vWhlVelVec(eZ);
269 // If this is the first time the wheel has made contact, remember some values
270 // for later printout.
274 SinkRate = compressSpeed;
275 GroundSpeed = Position->GetVel().Magnitude();
276 TakeoffReported = false;
279 // If the takeoff run is starting, initialize.
281 if ((Position->GetVel().Magnitude() > 0.1) &&
282 (FCS->GetBrake(bgLeft) == 0) &&
283 (FCS->GetBrake(bgRight) == 0) &&
284 (FCS->GetThrottlePos(0) == 1) && !StartedGroundRun)
286 TakeoffDistanceTraveled = 0;
287 TakeoffDistanceTraveled50ft = 0;
288 StartedGroundRun = true;
291 // The following needs work regarding friction coefficients and braking and
292 // steering The BrakeFCoeff formula assumes that an anti-skid system is used.
293 // It also assumes that we won't be turning and braking at the same time.
294 // Will fix this later.
295 // [JSB] The braking force coefficients include normal rolling coefficient +
296 // a percentage of the static friction coefficient based on braking applied.
300 BrakeFCoeff = ( rollingFCoeff*(1.0 - FCS->GetBrake(bgLeft)) +
301 staticFCoeff*FCS->GetBrake(bgLeft) );
304 BrakeFCoeff = ( rollingFCoeff*(1.0 - FCS->GetBrake(bgRight)) +
305 staticFCoeff*FCS->GetBrake(bgRight) );
308 BrakeFCoeff = ( rollingFCoeff*(1.0 - FCS->GetBrake(bgCenter)) +
309 staticFCoeff*FCS->GetBrake(bgCenter) );
312 BrakeFCoeff = ( rollingFCoeff*(1.0 - FCS->GetBrake(bgCenter)) +
313 staticFCoeff*FCS->GetBrake(bgCenter) );
316 BrakeFCoeff = ( rollingFCoeff*(1.0 - FCS->GetBrake(bgCenter)) +
317 staticFCoeff*FCS->GetBrake(bgCenter) );
320 BrakeFCoeff = rollingFCoeff;
323 cerr << "Improper brake group membership detected for this gear." << endl;
327 switch (eSteerType) {
329 SteerAngle = -maxSteerAngle * FCS->GetDrCmd() * 0.01745;
335 // Note to Jon: This is not correct for castering gear. I'll fix it later.
339 cerr << "Improper steering type membership detected for this gear." << endl;
343 // Transform the wheel velocities from the local axis system to the wheel axis system.
344 // For now, steering angle is assumed to happen in the Local Z axis,
345 // not the strut axis as it should be. Will fix this later.
347 SinWheel = sin(Rotation->Getpsi() + SteerAngle);
348 CosWheel = cos(Rotation->Getpsi() + SteerAngle);
349 RollingWhlVel = vWhlVelVec(eX)*CosWheel + vWhlVelVec(eY)*SinWheel;
350 SideWhlVel = vWhlVelVec(eY)*CosWheel - vWhlVelVec(eX)*SinWheel;
352 // Calculate tire slip angle.
354 if (RollingWhlVel == 0.0 && SideWhlVel == 0.0) {
356 } else if (fabs(RollingWhlVel) < 1.0) {
357 WheelSlip = 0.05*radtodeg*atan2(SideWhlVel, RollingWhlVel) + 0.95*WheelSlip;
359 WheelSlip = radtodeg*atan2(SideWhlVel, RollingWhlVel);
362 double maxdeltaSlip = 0.5*deltaT;
364 if (RollingWhlVel == 0.0 && SideWhlVel == 0.0) {
366 } else if (RollingWhlVel < 1.0) {
367 WheelSlip = radtodeg*atan2(SideWhlVel, RollingWhlVel);
368 deltaSlip = WheelSlip - lastWheelSlip;
369 if (fabs(deltaSlip) > maxdeltaSlip) {
370 if (WheelSlip > lastWheelSlip) {
371 WheelSlip = lastWheelSlip + maxdeltaSlip;
372 } else if (WheelSlip < lastWheelSlip) {
373 WheelSlip = lastWheelSlip - maxdeltaSlip;
377 WheelSlip = radtodeg*atan2(SideWhlVel, RollingWhlVel);
380 if ((WheelSlip < 0.0 && lastWheelSlip > 0.0) ||
381 (WheelSlip > 0.0 && lastWheelSlip < 0.0))
386 lastWheelSlip = WheelSlip;
388 // Compute the sideforce coefficients using similar assumptions to LaRCSim for now.
389 // Allow a maximum of 10 degrees tire slip angle before wheel slides. At that point,
390 // transition from static to dynamic friction. There are more complicated formulations
391 // of this that avoid the discrete jump. Will fix this later.
393 if (fabs(WheelSlip) <= 20.0) {
394 FCoeff = staticFCoeff*WheelSlip/20.0;
395 } else if (fabs(WheelSlip) <= 40.0) {
396 // FCoeff = dynamicFCoeff*fabs(WheelSlip)/WheelSlip;
397 FCoeff = (dynamicFCoeff*(fabs(WheelSlip) - 20.0)/20.0 +
398 staticFCoeff*(40.0 - fabs(WheelSlip))/20.0)*fabs(WheelSlip)/WheelSlip;
400 FCoeff = dynamicFCoeff*fabs(WheelSlip)/WheelSlip;
403 // Compute the vertical force on the wheel using square-law damping (per comment
404 // in paper AIAA-2000-4303 - see header prologue comments). We might consider
405 // allowing for both square and linear damping force calculation. Also need to
406 // possibly give a "rebound damping factor" that differs from the compression
409 vLocalForce(eZ) = min(-compressLength * kSpring
410 - compressSpeed * bDamp, (double)0.0);
412 MaximumStrutForce = max(MaximumStrutForce, fabs(vLocalForce(eZ)));
413 MaximumStrutTravel = max(MaximumStrutTravel, fabs(compressLength));
415 // Compute the forces in the wheel ground plane.
418 if (fabs(RollingWhlVel) > 1E-3) {
419 RollingForce = (1.0 - TirePressureNorm) * 30
420 + vLocalForce(eZ) * BrakeFCoeff
421 * fabs(RollingWhlVel)/RollingWhlVel;
423 SideForce = vLocalForce(eZ) * FCoeff;
425 // Transform these forces back to the local reference frame.
427 vLocalForce(eX) = RollingForce*CosWheel - SideForce*SinWheel;
428 vLocalForce(eY) = SideForce*CosWheel + RollingForce*SinWheel;
430 // Note to Jon: At this point the forces will be too big when the airplane is
431 // stopped or rolling to a stop. We need to make sure that the gear forces just
432 // balance out the non-gear forces when the airplane is stopped. That way the
433 // airplane won't start to accelerate until the non-gear/ forces are larger than
434 // the gear forces. I think that the proper fix should go into FGAircraft::FMGear.
435 // This routine would only compute the local strut forces and return them to
436 // FMGear. All of the gear forces would get adjusted in FMGear using the total
437 // non-gear forces. Then the gear moments would be calculated. If strange things
438 // start happening to the airplane during testing as it rolls to a stop, then we
439 // need to implement this change. I ran out of time to do it now but have the
442 // Transform the forces back to the body frame and compute the moment.
444 vForce = State->GetTl2b() * vLocalForce;
445 vMoment = vWhlBodyVec * vForce;
447 } else { // Gear is NOT compressed
451 if (Position->GetDistanceAGL() > 200.0) {
452 FirstContact = false;
453 StartedGroundRun = false;
454 LandingReported = false;
455 LandingDistanceTraveled = 0.0;
456 MaximumStrutForce = MaximumStrutTravel = 0.0;
459 compressLength = 0.0; // reset compressLength to zero for data output validity
462 if (FirstContact) LandingDistanceTraveled += Position->GetVground()*deltaT;
464 if (StartedGroundRun) {
465 TakeoffDistanceTraveled50ft += Position->GetVground()*deltaT;
466 if (WOW) TakeoffDistanceTraveled += Position->GetVground()*deltaT;
469 if (ReportEnable && Position->GetVground() <= 0.05 && !LandingReported) {
470 if (debug_lvl > 0) Report(erLand);
473 if (ReportEnable && !TakeoffReported &&
474 (vLocalGear(eZ) - Position->GetDistanceAGL()) < -50.0)
476 if (debug_lvl > 0) Report(erTakeoff);
479 if (lastWOW != WOW) {
480 PutMessage("GEAR_CONTACT: " + name, WOW);
485 // Crash detection logic (really out-of-bounds detection)
487 if (compressLength > 500.0 ||
488 vForce.Magnitude() > 100000000.0 ||
489 vMoment.Magnitude() > 5000000000.0 ||
490 SinkRate > 1.4666*30)
492 PutMessage("Crash Detected: Simulation FREEZE.");
499 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
501 void FGLGear::Report(ReportType repType)
505 cout << endl << "Touchdown report for " << name << endl;
506 cout << " Sink rate at contact: " << SinkRate << " fps, "
507 << SinkRate*0.3048 << " mps" << endl;
508 cout << " Contact ground speed: " << GroundSpeed*.5925 << " knots, "
509 << GroundSpeed*0.3048 << " mps" << endl;
510 cout << " Maximum contact force: " << MaximumStrutForce << " lbs, "
511 << MaximumStrutForce*4.448 << " Newtons" << endl;
512 cout << " Maximum strut travel: " << MaximumStrutTravel*12.0 << " inches, "
513 << MaximumStrutTravel*30.48 << " cm" << endl;
514 cout << " Distance traveled: " << LandingDistanceTraveled << " ft, "
515 << LandingDistanceTraveled*0.3048 << " meters" << endl;
516 LandingReported = true;
519 cout << endl << "Takeoff report for " << name << endl;
520 cout << " Distance traveled: " << TakeoffDistanceTraveled
521 << " ft, " << TakeoffDistanceTraveled*0.3048 << " meters" << endl;
522 cout << " Distance traveled (over 50'): " << TakeoffDistanceTraveled50ft
523 << " ft, " << TakeoffDistanceTraveled50ft*0.3048 << " meters" << endl;
524 TakeoffReported = true;
529 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
530 // The bitmasked value choices are as follows:
531 // unset: In this case (the default) JSBSim would only print
532 // out the normally expected messages, essentially echoing
533 // the config files as they are read. If the environment
534 // variable is not set, debug_lvl is set to 1 internally
535 // 0: This requests JSBSim not to output any messages
537 // 1: This value explicity requests the normal JSBSim
539 // 2: This value asks for a message to be printed out when
540 // a class is instantiated
541 // 4: When this value is set, a message is displayed when a
542 // FGModel object executes its Run() method
543 // 8: When this value is set, various runtime state variables
544 // are printed out periodically
545 // 16: When set various parameters are sanity checked and
546 // a message is printed out when they go out of bounds
548 void FGLGear::Debug(int from)
550 if (debug_lvl <= 0) return;
552 if (debug_lvl & 1) { // Standard console startup message output
553 if (from == 0) { // Constructor
554 cout << " Name: " << name << endl;
555 cout << " Location: " << vXYZ << endl;
556 cout << " Spring Constant: " << kSpring << endl;
557 cout << " Damping Constant: " << bDamp << endl;
558 cout << " Dynamic Friction: " << dynamicFCoeff << endl;
559 cout << " Static Friction: " << staticFCoeff << endl;
560 cout << " Rolling Friction: " << rollingFCoeff << endl;
561 cout << " Steering Type: " << sSteerType << endl;
562 cout << " Grouping: " << sBrakeGroup << endl;
563 cout << " Max Steer Angle: " << maxSteerAngle << endl;
564 cout << " Retractable: " << sRetractable << endl;
567 if (debug_lvl & 2 ) { // Instantiation/Destruction notification
568 if (from == 0) cout << "Instantiated: FGLGear" << endl;
569 if (from == 1) cout << "Destroyed: FGLGear" << endl;
571 if (debug_lvl & 4 ) { // Run() method entry print for FGModel-derived objects
573 if (debug_lvl & 8 ) { // Runtime state variables
575 if (debug_lvl & 16) { // Sanity checking
577 if (debug_lvl & 64) {
578 if (from == 0) { // Constructor
579 cout << IdSrc << endl;
580 cout << IdHdr << endl;
585 } // namespace JSBSim