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 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
46 /*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
48 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
50 /*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
52 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
54 static const char *IdSrc = "$Id$";
55 static const char *IdHdr = ID_LGEAR;
57 /*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
59 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
61 FGLGear::FGLGear(FGConfigFile* AC_cfg, FGFDMExec* fdmex) : Exec(fdmex)
65 *AC_cfg >> tmp >> name >> vXYZ(1) >> vXYZ(2) >> vXYZ(3)
66 >> kSpring >> bDamp>> dynamicFCoeff >> staticFCoeff
67 >> rollingFCoeff >> sSteerType >> sBrakeGroup
68 >> maxSteerAngle >> sRetractable;
70 if (sBrakeGroup == "LEFT" ) eBrakeGrp = bgLeft;
71 else if (sBrakeGroup == "RIGHT" ) eBrakeGrp = bgRight;
72 else if (sBrakeGroup == "CENTER") eBrakeGrp = bgCenter;
73 else if (sBrakeGroup == "NOSE" ) eBrakeGrp = bgNose;
74 else if (sBrakeGroup == "TAIL" ) eBrakeGrp = bgTail;
75 else if (sBrakeGroup == "NONE" ) eBrakeGrp = bgNone;
77 cerr << "Improper braking group specification in config file: "
78 << sBrakeGroup << " is undefined." << endl;
81 if (sSteerType == "STEERABLE") eSteerType = stSteer;
82 else if (sSteerType == "FIXED" ) eSteerType = stFixed;
83 else if (sSteerType == "CASTERED" ) eSteerType = stCaster;
85 cerr << "Improper steering type specification in config file: "
86 << sSteerType << " is undefined." << endl;
89 if ( sRetractable == "RETRACT" ) {
92 isRetractable = false;
99 // Add some AI here to determine if gear is located properly according to its
100 // brake group type ??
102 State = Exec->GetState();
103 Aircraft = Exec->GetAircraft();
104 Position = Exec->GetPosition();
105 Rotation = Exec->GetRotation();
106 FCS = Exec->GetFCS();
107 MassBalance = Exec->GetMassBalance();
109 WOW = lastWOW = true; // should the value be initialized to true?
111 FirstContact = false;
112 StartedGroundRun = false;
113 TakeoffReported = LandingReported = false;
114 LandingDistanceTraveled = TakeoffDistanceTraveled = TakeoffDistanceTraveled50ft = 0.0;
115 MaximumStrutForce = MaximumStrutTravel = 0.0;
116 SinkRate = GroundSpeed = 0.0;
118 vWhlBodyVec = (vXYZ - MassBalance->GetXYZcg()) / 12.0;
119 vWhlBodyVec(eX) = -vWhlBodyVec(eX);
120 vWhlBodyVec(eZ) = -vWhlBodyVec(eZ);
122 vLocalGear = State->GetTb2l() * vWhlBodyVec;
124 compressLength = 0.0;
129 WheelSlip = lastWheelSlip = 0.0;
131 compressLength = 0.0;
136 TirePressureNorm = 1.0;
141 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
143 FGLGear::FGLGear(const FGLGear& lgear)
146 Aircraft = lgear.Aircraft;
147 Position = lgear.Position;
148 Rotation = lgear.Rotation;
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;
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;
214 vMoment.InitMatrix();
217 if (FCS->GetGearPos() < 0.01) {
220 } else if (FCS->GetGearPos() > 0.99) {
234 vWhlBodyVec = (vXYZ - MassBalance->GetXYZcg()) / 12.0;
235 vWhlBodyVec(eX) = -vWhlBodyVec(eX);
236 vWhlBodyVec(eZ) = -vWhlBodyVec(eZ);
238 // vWhlBodyVec now stores the vector from the cg to this wheel
240 vLocalGear = State->GetTb2l() * vWhlBodyVec;
242 // vLocalGear now stores the vector from the cg to the wheel in local coords.
244 compressLength = vLocalGear(eZ) - Position->GetDistanceAGL();
246 // The compression length is currently measured in the Z-axis, only, at this time.
247 // It should be measured along the strut axis. If the local-frame gear position
248 // "hangs down" below the CG greater than the altitude, then the compressLength
249 // will be positive - i.e. the gear will have made contact.
251 if (compressLength > 0.00) {
253 WOW = true;// Weight-On-Wheels is true
255 // The next equation should really use the vector to the contact patch of the tire
256 // including the strut compression and not vWhlBodyVec. Will fix this later.
257 // As it stands, now, the following equation takes the aircraft body-frame
258 // rotational rate and calculates the cross-product with the vector from the CG
259 // to the wheel, thus producing the instantaneous velocity vector of the tire
260 // in Body coords. The frame is also converted to local coordinates. When the
261 // aircraft local-frame velocity is added to this quantity, the total velocity of
262 // the wheel in local frame is then known. Subsequently, the compression speed
263 // (used for calculating damping force) is found by taking the Z-component of the
266 vWhlVelVec = State->GetTb2l() * (Rotation->GetPQR() * vWhlBodyVec);
268 vWhlVelVec += Position->GetVel();
270 compressSpeed = vWhlVelVec(eZ);
272 // If this is the first time the wheel has made contact, remember some values
273 // for later printout.
277 SinkRate = compressSpeed;
278 GroundSpeed = Position->GetVel().Magnitude();
279 TakeoffReported = false;
282 // If the takeoff run is starting, initialize.
284 if ((Position->GetVel().Magnitude() > 0.1) &&
285 (FCS->GetBrake(bgLeft) == 0) &&
286 (FCS->GetBrake(bgRight) == 0) &&
287 (FCS->GetThrottlePos(0) == 1) && !StartedGroundRun)
289 TakeoffDistanceTraveled = 0;
290 TakeoffDistanceTraveled50ft = 0;
291 StartedGroundRun = true;
294 // The following needs work regarding friction coefficients and braking and
295 // steering The BrakeFCoeff formula assumes that an anti-skid system is used.
296 // It also assumes that we won't be turning and braking at the same time.
297 // Will fix this later.
298 // [JSB] The braking force coefficients include normal rolling coefficient +
299 // a percentage of the static friction coefficient based on braking applied.
304 BrakeFCoeff = ( rollingFCoeff*(1.0 - FCS->GetBrake(bgLeft)) +
305 staticFCoeff*FCS->GetBrake(bgLeft) );
309 BrakeFCoeff = ( rollingFCoeff*(1.0 - FCS->GetBrake(bgRight)) +
310 staticFCoeff*FCS->GetBrake(bgRight) );
314 BrakeFCoeff = ( rollingFCoeff*(1.0 - FCS->GetBrake(bgCenter)) +
315 staticFCoeff*FCS->GetBrake(bgCenter) );
319 BrakeFCoeff = rollingFCoeff;
323 BrakeFCoeff = rollingFCoeff;
327 BrakeFCoeff = rollingFCoeff;
330 cerr << "Improper brake group membership detected for this gear." << endl;
334 switch (eSteerType) {
336 SteerAngle = SteerGain*FCS->GetDrCmd()*0.349; // 20 deg
342 // Note to Jon: This is not correct for castering gear. I'll fix it later.
346 cerr << "Improper steering type membership detected for this gear." << endl;
350 // Transform the wheel velocities from the local axis system to the wheel axis system.
351 // For now, steering angle is assumed to happen in the Local Z axis,
352 // not the strut axis as it should be. Will fix this later.
354 SinWheel = sin(Rotation->Getpsi() + SteerAngle);
355 CosWheel = cos(Rotation->Getpsi() + SteerAngle);
356 RollingWhlVel = vWhlVelVec(eX)*CosWheel + vWhlVelVec(eY)*SinWheel;
357 SideWhlVel = vWhlVelVec(eY)*CosWheel - vWhlVelVec(eX)*SinWheel;
359 // Calculate tire slip angle.
361 if (RollingWhlVel == 0.0 && SideWhlVel == 0.0) {
363 } else if (fabs(RollingWhlVel) < 0.10) {
364 WheelSlip = 0.05*radtodeg*atan2(SideWhlVel, RollingWhlVel) + 0.95*WheelSlip;
366 WheelSlip = radtodeg*atan2(SideWhlVel, RollingWhlVel);
369 if ((WheelSlip < 0.0 && lastWheelSlip > 0.0) ||
370 (WheelSlip > 0.0 && lastWheelSlip < 0.0))
375 lastWheelSlip = WheelSlip;
377 // Compute the sideforce coefficients using similar assumptions to LaRCSim for now.
378 // Allow a maximum of 10 degrees tire slip angle before wheel slides. At that point,
379 // transition from static to dynamic friction. There are more complicated formulations
380 // of this that avoid the discrete jump. Will fix this later.
382 if (fabs(WheelSlip) <= 20.0) {
383 FCoeff = staticFCoeff*WheelSlip/20.0;
384 } else if (fabs(WheelSlip) <= 40.0) {
385 // FCoeff = dynamicFCoeff*fabs(WheelSlip)/WheelSlip;
386 FCoeff = (dynamicFCoeff*(fabs(WheelSlip) - 20.0)/20.0 +
387 staticFCoeff*(40.0 - fabs(WheelSlip))/20.0)*fabs(WheelSlip)/WheelSlip;
389 FCoeff = dynamicFCoeff*fabs(WheelSlip)/WheelSlip;
392 // Compute the vertical force on the wheel using square-law damping (per comment
393 // in paper AIAA-2000-4303 - see header prologue comments). We might consider
394 // allowing for both square and linear damping force calculation. Also need to
395 // possibly give a "rebound damping factor" that differs from the compression
398 vLocalForce(eZ) = min(-compressLength * kSpring
399 - compressSpeed * bDamp, (double)0.0);
401 MaximumStrutForce = max(MaximumStrutForce, fabs(vLocalForce(eZ)));
402 MaximumStrutTravel = max(MaximumStrutTravel, fabs(compressLength));
404 // Compute the forces in the wheel ground plane.
407 if (fabs(RollingWhlVel) > 1E-3) {
408 RollingForce = (1.0 - TirePressureNorm) * 30
409 + vLocalForce(eZ) * BrakeFCoeff
410 * fabs(RollingWhlVel)/RollingWhlVel;
412 SideForce = vLocalForce(eZ) * FCoeff;
414 // Transform these forces back to the local reference frame.
416 vLocalForce(eX) = RollingForce*CosWheel - SideForce*SinWheel;
417 vLocalForce(eY) = SideForce*CosWheel + RollingForce*SinWheel;
419 // Note to Jon: At this point the forces will be too big when the airplane is
420 // stopped or rolling to a stop. We need to make sure that the gear forces just
421 // balance out the non-gear forces when the airplane is stopped. That way the
422 // airplane won't start to accelerate until the non-gear/ forces are larger than
423 // the gear forces. I think that the proper fix should go into FGAircraft::FMGear.
424 // This routine would only compute the local strut forces and return them to
425 // FMGear. All of the gear forces would get adjusted in FMGear using the total
426 // non-gear forces. Then the gear moments would be calculated. If strange things
427 // start happening to the airplane during testing as it rolls to a stop, then we
428 // need to implement this change. I ran out of time to do it now but have the
431 // Transform the forces back to the body frame and compute the moment.
433 vForce = State->GetTl2b() * vLocalForce;
434 vMoment = vWhlBodyVec * vForce;
440 if (Position->GetDistanceAGL() > 200.0) {
441 FirstContact = false;
442 StartedGroundRun = false;
443 LandingReported = false;
444 LandingDistanceTraveled = 0.0;
445 MaximumStrutForce = MaximumStrutTravel = 0.0;
448 compressLength = 0.0; // reset compressLength to zero for data output validity
451 deltaT = State->Getdt()*Aircraft->GetRate();
453 if (FirstContact) LandingDistanceTraveled += Position->GetVground()*deltaT;
455 if (StartedGroundRun) {
456 TakeoffDistanceTraveled50ft += Position->GetVground()*deltaT;
457 if (WOW) TakeoffDistanceTraveled += Position->GetVground()*deltaT;
460 if (ReportEnable && Position->GetVground() <= 0.05 && !LandingReported) {
461 if (debug_lvl > 0) Report(erLand);
464 if (ReportEnable && !TakeoffReported &&
465 (vLocalGear(eZ) - Position->GetDistanceAGL()) < -50.0)
467 if (debug_lvl > 0) Report(erTakeoff);
470 if (lastWOW != WOW) {
471 PutMessage("GEAR_CONTACT: " + name, WOW);
476 // Crash detection logic (really out-of-bounds detection)
478 if (compressLength > 500.0 ||
479 vForce.Magnitude() > 100000000.0 ||
480 vMoment.Magnitude() > 5000000000.0 ||
481 SinkRate > 1.4666*30)
483 PutMessage("Crash Detected: Simulation FREEZE.");
490 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
492 void FGLGear::Report(ReportType repType)
496 cout << endl << "Touchdown report for " << name << endl;
497 cout << " Sink rate at contact: " << SinkRate << " fps, "
498 << SinkRate*0.3048 << " mps" << endl;
499 cout << " Contact ground speed: " << GroundSpeed*.5925 << " knots, "
500 << GroundSpeed*0.3048 << " mps" << endl;
501 cout << " Maximum contact force: " << MaximumStrutForce << " lbs, "
502 << MaximumStrutForce*4.448 << " Newtons" << endl;
503 cout << " Maximum strut travel: " << MaximumStrutTravel*12.0 << " inches, "
504 << MaximumStrutTravel*30.48 << " cm" << endl;
505 cout << " Distance traveled: " << LandingDistanceTraveled << " ft, "
506 << LandingDistanceTraveled*0.3048 << " meters" << endl;
507 LandingReported = true;
510 cout << endl << "Takeoff report for " << name << endl;
511 cout << " Distance traveled: " << TakeoffDistanceTraveled
512 << " ft, " << TakeoffDistanceTraveled*0.3048 << " meters" << endl;
513 cout << " Distance traveled (over 50'): " << TakeoffDistanceTraveled50ft
514 << " ft, " << TakeoffDistanceTraveled50ft*0.3048 << " meters" << endl;
515 TakeoffReported = true;
520 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
521 // The bitmasked value choices are as follows:
522 // unset: In this case (the default) JSBSim would only print
523 // out the normally expected messages, essentially echoing
524 // the config files as they are read. If the environment
525 // variable is not set, debug_lvl is set to 1 internally
526 // 0: This requests JSBSim not to output any messages
528 // 1: This value explicity requests the normal JSBSim
530 // 2: This value asks for a message to be printed out when
531 // a class is instantiated
532 // 4: When this value is set, a message is displayed when a
533 // FGModel object executes its Run() method
534 // 8: When this value is set, various runtime state variables
535 // are printed out periodically
536 // 16: When set various parameters are sanity checked and
537 // a message is printed out when they go out of bounds
539 void FGLGear::Debug(int from)
541 if (debug_lvl <= 0) return;
543 if (debug_lvl & 1) { // Standard console startup message output
544 if (from == 0) { // Constructor
545 cout << " Name: " << name << endl;
546 cout << " Location: " << vXYZ << endl;
547 cout << " Spring Constant: " << kSpring << endl;
548 cout << " Damping Constant: " << bDamp << endl;
549 cout << " Dynamic Friction: " << dynamicFCoeff << endl;
550 cout << " Static Friction: " << staticFCoeff << endl;
551 cout << " Rolling Friction: " << rollingFCoeff << endl;
552 cout << " Steering Type: " << sSteerType << endl;
553 cout << " Grouping: " << sBrakeGroup << endl;
554 cout << " Max Steer Angle: " << maxSteerAngle << endl;
555 cout << " Retractable: " << sRetractable << endl;
558 if (debug_lvl & 2 ) { // Instantiation/Destruction notification
559 if (from == 0) cout << "Instantiated: FGLGear" << endl;
560 if (from == 1) cout << "Destroyed: FGLGear" << endl;
562 if (debug_lvl & 4 ) { // Run() method entry print for FGModel-derived objects
564 if (debug_lvl & 8 ) { // Runtime state variables
566 if (debug_lvl & 16) { // Sanity checking
568 if (debug_lvl & 64) {
569 if (from == 0) { // Constructor
570 cout << IdSrc << endl;
571 cout << IdHdr << endl;
576 } // namespace JSBSim