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)
65 *AC_cfg >> tmp >> name >> vXYZ(1) >> vXYZ(2) >> vXYZ(3)
66 >> kSpring >> bDamp>> dynamicFCoeff >> staticFCoeff
67 >> rollingFCoeff >> sSteerType >> sBrakeGroup
68 >> maxSteerAngle >> Retractable;
71 cout << " Name: " << name << endl;
72 cout << " Location: " << vXYZ << endl;
73 cout << " Spring Constant: " << kSpring << endl;
74 cout << " Damping Constant: " << bDamp << endl;
75 cout << " Dynamic Friction: " << dynamicFCoeff << endl;
76 cout << " Static Friction: " << staticFCoeff << endl;
77 cout << " Rolling Friction: " << rollingFCoeff << endl;
78 cout << " Steering Type: " << sSteerType << endl;
79 cout << " Grouping: " << sBrakeGroup << endl;
80 cout << " Max Steer Angle: " << maxSteerAngle << endl;
81 cout << " Retractable: " << Retractable << endl;
84 if (sBrakeGroup == "LEFT" ) eBrakeGrp = bgLeft;
85 else if (sBrakeGroup == "RIGHT" ) eBrakeGrp = bgRight;
86 else if (sBrakeGroup == "CENTER") eBrakeGrp = bgCenter;
87 else if (sBrakeGroup == "NOSE" ) eBrakeGrp = bgNose;
88 else if (sBrakeGroup == "TAIL" ) eBrakeGrp = bgTail;
89 else if (sBrakeGroup == "NONE" ) eBrakeGrp = bgNone;
91 cerr << "Improper braking group specification in config file: "
92 << sBrakeGroup << " is undefined." << endl;
95 if (sSteerType == "STEERABLE") eSteerType = stSteer;
96 else if (sSteerType == "FIXED" ) eSteerType = stFixed;
97 else if (sSteerType == "CASTERED" ) eSteerType = stCaster;
99 cerr << "Improper steering type specification in config file: "
100 << sSteerType << " is undefined." << endl;
103 if( Retractable == "RETRACT" ) {
109 GearUp=false; GearDown=true;
111 // Add some AI here to determine if gear is located properly according to its
112 // brake group type ??
114 State = Exec->GetState();
115 Aircraft = Exec->GetAircraft();
116 Position = Exec->GetPosition();
117 Rotation = Exec->GetRotation();
118 FCS = Exec->GetFCS();
119 MassBalance = Exec->GetMassBalance();
121 WOW = lastWOW = false;
123 FirstContact = false;
125 DistanceTraveled = 0.0;
126 MaximumStrutForce = MaximumStrutTravel = 0.0;
127 SinkRate = GroundSpeed = 0.0;
129 vWhlBodyVec = (vXYZ - MassBalance->GetXYZcg()) / 12.0;
130 vWhlBodyVec(eX) = -vWhlBodyVec(eX);
131 vWhlBodyVec(eZ) = -vWhlBodyVec(eZ);
133 vLocalGear = State->GetTb2l() * vWhlBodyVec;
135 if (debug_lvl & 2) cout << "Instantiated: FGLGear" << endl;
138 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
140 FGLGear::FGLGear(const FGLGear& lgear)
143 Aircraft = lgear.Aircraft;
144 Position = lgear.Position;
145 Rotation = lgear.Rotation;
148 MassBalance = lgear.MassBalance;
151 vMoment = lgear.vMoment;
152 vWhlBodyVec = lgear.vWhlBodyVec;
153 vLocalGear = lgear.vLocalGear;
156 lastWOW = lgear.lastWOW;
157 ReportEnable = lgear.ReportEnable;
158 FirstContact = lgear.FirstContact;
159 DistanceTraveled = lgear.DistanceTraveled;
160 MaximumStrutForce = lgear.MaximumStrutForce;
161 MaximumStrutTravel = lgear.MaximumStrutTravel;
163 kSpring = lgear.kSpring;
165 compressLength = lgear.compressLength;
166 compressSpeed = lgear.compressSpeed;
167 staticFCoeff = lgear.staticFCoeff;
168 dynamicFCoeff = lgear.dynamicFCoeff;
169 rollingFCoeff = lgear.rollingFCoeff;
170 brakePct = lgear.brakePct;
171 maxCompLen = lgear.maxCompLen;
172 SinkRate = lgear.SinkRate;
173 GroundSpeed = lgear.GroundSpeed;
174 Reported = lgear.Reported;
176 sSteerType = lgear.sSteerType;
177 eSteerType = lgear.eSteerType;
178 sBrakeGroup = lgear.sBrakeGroup;
179 eBrakeGrp = lgear.eBrakeGrp;
180 maxSteerAngle = lgear.maxSteerAngle;
181 isRetractable = lgear.isRetractable;
182 GearUp = lgear.GearUp;
183 GearDown = lgear.GearDown;
186 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
190 if (debug_lvl & 2) cout << "Destroyed: FGLGear" << endl;
193 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
195 FGColumnVector3& FGLGear::Force(void)
198 vMoment.InitMatrix();
201 if (FCS->GetGearPos() < 0.01) {
204 } else if (FCS->GetGearPos() > 0.99) {
217 double SteerGain = 0;
218 double SinWheel, CosWheel, SideWhlVel, RollingWhlVel;
219 double RollingForce, SideForce, FCoeff;
222 vWhlBodyVec = (vXYZ - MassBalance->GetXYZcg()) / 12.0;
223 vWhlBodyVec(eX) = -vWhlBodyVec(eX);
224 vWhlBodyVec(eZ) = -vWhlBodyVec(eZ);
226 // vWhlBodyVec now stores the vector from the cg to this wheel
228 vLocalGear = State->GetTb2l() * vWhlBodyVec;
230 // vLocalGear now stores the vector from the cg to the wheel in local coords.
232 compressLength = vLocalGear(eZ) - Position->GetDistanceAGL();
234 // The compression length is currently measured in the Z-axis, only, at this time.
235 // It should be measured along the strut axis. If the local-frame gear position
236 // "hangs down" below the CG greater than the altitude, then the compressLength
237 // will be positive - i.e. the gear will have made contact.
239 if (compressLength > 0.00) {
241 WOW = true;// Weight-On-Wheels is true
243 // The next equation should really use the vector to the contact patch of the tire
244 // including the strut compression and not vWhlBodyVec. Will fix this later.
245 // As it stands, now, the following equation takes the aircraft body-frame
246 // rotational rate and calculates the cross-product with the vector from the CG
247 // to the wheel, thus producing the instantaneous velocity vector of the tire
248 // in Body coords. The frame is also converted to local coordinates. When the
249 // aircraft local-frame velocity is added to this quantity, the total velocity of
250 // the wheel in local frame is then known. Subsequently, the compression speed
251 // (used for calculating damping force) is found by taking the Z-component of the
254 vWhlVelVec = State->GetTb2l() * (Rotation->GetPQR() * vWhlBodyVec);
256 vWhlVelVec += Position->GetVel();
258 compressSpeed = vWhlVelVec(eZ);
260 // If this is the first time the wheel has made contact, remember some values
261 // for later printout.
265 SinkRate = compressSpeed;
266 GroundSpeed = Position->GetVel().Magnitude();
269 // The following needs work regarding friction coefficients and braking and
270 // steering The BrakeFCoeff formula assumes that an anti-skid system is used.
271 // It also assumes that we won't be turning and braking at the same time.
272 // Will fix this later.
273 // [JSB] The braking force coefficients include normal rolling coefficient +
274 // a percentage of the static friction coefficient based on braking applied.
279 BrakeFCoeff = rollingFCoeff*(1.0 - FCS->GetBrake(bgLeft)) +
280 staticFCoeff*FCS->GetBrake(bgLeft);
284 BrakeFCoeff = rollingFCoeff*(1.0 - FCS->GetBrake(bgRight)) +
285 staticFCoeff*FCS->GetBrake(bgRight);
289 BrakeFCoeff = rollingFCoeff*(1.0 - FCS->GetBrake(bgCenter)) +
290 staticFCoeff*FCS->GetBrake(bgCenter);
294 BrakeFCoeff = rollingFCoeff;
298 BrakeFCoeff = rollingFCoeff;
302 BrakeFCoeff = rollingFCoeff;
305 cerr << "Improper brake group membership detected for this gear." << endl;
309 switch (eSteerType) {
311 SteerAngle = SteerGain*FCS->GetDrPos();
317 // Note to Jon: This is not correct for castering gear. I'll fix it later.
321 cerr << "Improper steering type membership detected for this gear." << endl;
325 // Transform the wheel velocities from the local axis system to the wheel axis system.
326 // For now, steering angle is assumed to happen in the Local Z axis,
327 // not the strut axis as it should be. Will fix this later.
329 SinWheel = sin(Rotation->Getpsi() + SteerAngle);
330 CosWheel = cos(Rotation->Getpsi() + SteerAngle);
331 RollingWhlVel = vWhlVelVec(eX)*CosWheel + vWhlVelVec(eY)*SinWheel;
332 SideWhlVel = vWhlVelVec(eY)*CosWheel - vWhlVelVec(eX)*SinWheel;
334 // Calculate tire slip angle.
336 if (RollingWhlVel == 0.0 && SideWhlVel == 0.0) {
339 WheelSlip = radtodeg*atan2(SideWhlVel, RollingWhlVel);
342 // The following code normalizes the wheel velocity vector, reverses it, and zeroes out
343 // the z component of the velocity. The question is, should the Z axis velocity be zeroed
344 // out first before the normalization takes place or not? Subsequent to that, the Wheel
345 // Velocity vector now points as a unit vector backwards and parallel to the wheel
346 // velocity vector. It acts AT the wheel.
348 // Note to Jon: I commented out this line because I wasn't sure we want to do this.
349 // vWhlVelVec = -1.0 * vWhlVelVec.Normalize();
350 // vWhlVelVec(eZ) = 0.00;
352 // Compute the sideforce coefficients using similar assumptions to LaRCSim for now.
353 // Allow a maximum of 10 degrees tire slip angle before wheel slides. At that point,
354 // transition from static to dynamic friction. There are more complicated formulations
355 // of this that avoid the discrete jump. Will fix this later.
357 if (fabs(WheelSlip) <= 10.0) {
358 FCoeff = staticFCoeff*WheelSlip/10.0;
360 FCoeff = dynamicFCoeff*fabs(WheelSlip)/WheelSlip;
363 // Compute the vertical force on the wheel using square-law damping (per comment
364 // in paper AIAA-2000-4303 - see header prologue comments). We might consider
365 // allowing for both square and linear damping force calculation. Also need to
366 // possibly give a "rebound damping factor" that differs from the compression
367 // case. NOTE: SQUARE LAW DAMPING NO GOOD!
369 vLocalForce(eZ) = min(-compressLength * kSpring
370 - compressSpeed * bDamp, (double)0.0);
372 MaximumStrutForce = max(MaximumStrutForce, fabs(vLocalForce(eZ)));
373 MaximumStrutTravel = max(MaximumStrutTravel, fabs(compressLength));
375 // Compute the forces in the wheel ground plane.
378 if (fabs(RollingWhlVel) > 1E-3) {
379 RollingForce = vLocalForce(eZ) * BrakeFCoeff * fabs(RollingWhlVel)/RollingWhlVel;
381 SideForce = vLocalForce(eZ) * FCoeff;
383 // Transform these forces back to the local reference frame.
385 vLocalForce(eX) = RollingForce*CosWheel - SideForce*SinWheel;
386 vLocalForce(eY) = SideForce*CosWheel + RollingForce*SinWheel;
388 // Note to Jon: At this point the forces will be too big when the airplane is
389 // stopped or rolling to a stop. We need to make sure that the gear forces just
390 // balance out the non-gear forces when the airplane is stopped. That way the
391 // airplane won't start to accelerate until the non-gear/ forces are larger than
392 // the gear forces. I think that the proper fix should go into FGAircraft::FMGear.
393 // This routine would only compute the local strut forces and return them to
394 // FMGear. All of the gear forces would get adjusted in FMGear using the total
395 // non-gear forces. Then the gear moments would be calculated. If strange things
396 // start happening to the airplane during testing as it rolls to a stop, then we
397 // need to implement this change. I ran out of time to do it now but have the
400 // Transform the forces back to the body frame and compute the moment.
402 vForce = State->GetTl2b() * vLocalForce;
403 vMoment = vWhlBodyVec * vForce;
409 if (Position->GetDistanceAGL() > 200.0) {
410 FirstContact = false;
412 DistanceTraveled = 0.0;
413 MaximumStrutForce = MaximumStrutTravel = 0.0;
416 compressLength = 0.0;// reset compressLength to zero for data output validity
422 DistanceTraveled += Position->GetVel().Magnitude()*State->Getdt()*Aircraft->GetRate();
425 if (ReportEnable && Position->GetVel().Magnitude() <= 0.05 && !Reported) {
426 if (debug_lvl > 0) Report();
429 if (lastWOW != WOW) {
430 PutMessage("GEAR_CONTACT", WOW);
435 // Crash detection logic (really out-of-bounds detection)
437 if (compressLength > 500.0 ||
438 vForce.Magnitude() > 100000000.0 ||
439 vMoment.Magnitude() > 5000000000.0 ||
440 SinkRate > 1.4666*30)
442 PutMessage("Crash Detected");
451 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
453 void FGLGear::Report(void)
455 cout << endl << "Touchdown report for " << name << endl;
456 cout << " Sink rate at contact: " << SinkRate << " fps, "
457 << SinkRate*0.3408 << " mps" << endl;
458 cout << " Contact ground speed: " << GroundSpeed*.5925 << " knots, "
459 << GroundSpeed*0.3408 << " mps" << endl;
460 cout << " Maximum contact force: " << MaximumStrutForce << " lbs, "
461 << MaximumStrutForce*4.448 << " Newtons" << endl;
462 cout << " Maximum strut travel: " << MaximumStrutTravel*12.0 << " inches, "
463 << MaximumStrutTravel*30.48 << " cm" << endl;
464 cout << " Distance traveled: " << DistanceTraveled << " ft, "
465 << DistanceTraveled*0.3408 << " meters" << endl;
469 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
471 void FGLGear::Debug(void)
473 // TODO: Add user code here