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) : vXYZ(3),
69 *AC_cfg >> tmp >> name >> vXYZ(1) >> vXYZ(2) >> vXYZ(3)
70 >> kSpring >> bDamp>> dynamicFCoeff >> staticFCoeff
71 >> rollingFCoeff >> sSteerType >> sBrakeGroup >> maxSteerAngle;
74 cout << " Name: " << name << endl;
75 cout << " Location: " << vXYZ << endl;
76 cout << " Spring Constant: " << kSpring << endl;
77 cout << " Damping Constant: " << bDamp << endl;
78 cout << " Dynamic Friction: " << dynamicFCoeff << endl;
79 cout << " Static Friction: " << staticFCoeff << endl;
80 cout << " Rolling Friction: " << rollingFCoeff << endl;
81 cout << " Steering Type: " << sSteerType << endl;
82 cout << " Grouping: " << sBrakeGroup << endl;
83 cout << " Max Steer Angle: " << maxSteerAngle << endl;
86 if (sBrakeGroup == "LEFT" ) eBrakeGrp = bgLeft;
87 else if (sBrakeGroup == "RIGHT" ) eBrakeGrp = bgRight;
88 else if (sBrakeGroup == "CENTER") eBrakeGrp = bgCenter;
89 else if (sBrakeGroup == "NOSE" ) eBrakeGrp = bgNose;
90 else if (sBrakeGroup == "TAIL" ) eBrakeGrp = bgTail;
91 else if (sBrakeGroup == "NONE" ) eBrakeGrp = bgNone;
93 cerr << "Improper braking group specification in config file: "
94 << sBrakeGroup << " is undefined." << endl;
97 if (sSteerType == "STEERABLE") eSteerType = stSteer;
98 else if (sSteerType == "FIXED" ) eSteerType = stFixed;
99 else if (sSteerType == "CASTERED" ) eSteerType = stCaster;
101 cerr << "Improper steering type specification in config file: "
102 << sSteerType << " is undefined." << endl;
105 // Add some AI here to determine if gear is located properly according to its
106 // brake group type ??
108 State = Exec->GetState();
109 Aircraft = Exec->GetAircraft();
110 Position = Exec->GetPosition();
111 Rotation = Exec->GetRotation();
112 FCS = Exec->GetFCS();
113 MassBalance = Exec->GetMassBalance();
117 FirstContact = false;
119 DistanceTraveled = 0.0;
120 MaximumStrutForce = MaximumStrutTravel = 0.0;
121 SinkRate = GroundSpeed = 0.0;
123 vWhlBodyVec = (vXYZ - MassBalance->GetXYZcg()) / 12.0;
124 vWhlBodyVec(eX) = -vWhlBodyVec(eX);
125 vWhlBodyVec(eZ) = -vWhlBodyVec(eZ);
127 vLocalGear = State->GetTb2l() * vWhlBodyVec;
129 if (debug_lvl & 2) cout << "Instantiated: FGLGear" << endl;
132 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
134 FGLGear::FGLGear(const FGLGear& lgear)
137 Aircraft = lgear.Aircraft;
138 Position = lgear.Position;
139 Rotation = lgear.Rotation;
142 MassBalance = lgear.MassBalance;
145 vMoment = lgear.vMoment;
146 vWhlBodyVec = lgear.vWhlBodyVec;
147 vLocalGear = lgear.vLocalGear;
150 ReportEnable = lgear.ReportEnable;
151 FirstContact = lgear.FirstContact;
152 DistanceTraveled = lgear.DistanceTraveled;
153 MaximumStrutForce = lgear.MaximumStrutForce;
154 MaximumStrutTravel = lgear.MaximumStrutTravel;
156 kSpring = lgear.kSpring;
158 compressLength = lgear.compressLength;
159 compressSpeed = lgear.compressSpeed;
160 staticFCoeff = lgear.staticFCoeff;
161 dynamicFCoeff = lgear.dynamicFCoeff;
162 rollingFCoeff = lgear.rollingFCoeff;
163 brakePct = lgear.brakePct;
164 maxCompLen = lgear.maxCompLen;
165 SinkRate = lgear.SinkRate;
166 GroundSpeed = lgear.GroundSpeed;
167 Reported = lgear.Reported;
169 sSteerType = lgear.sSteerType;
170 eSteerType = lgear.eSteerType;
171 sBrakeGroup = lgear.sBrakeGroup;
172 eBrakeGrp = lgear.eBrakeGrp;
173 maxSteerAngle = lgear.maxSteerAngle;
176 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
180 if (debug_lvl & 2) cout << "Destroyed: FGLGear" << endl;
183 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
185 FGColumnVector3& FGLGear::Force(void)
188 float SinWheel, CosWheel, SideWhlVel, RollingWhlVel;
189 float RudderPedal, RollingForce, SideForce, FCoeff;
192 vWhlBodyVec = (vXYZ - MassBalance->GetXYZcg()) / 12.0;
193 vWhlBodyVec(eX) = -vWhlBodyVec(eX);
194 vWhlBodyVec(eZ) = -vWhlBodyVec(eZ);
196 // vWhlBodyVec now stores the vector from the cg to this wheel
198 vLocalGear = State->GetTb2l() * vWhlBodyVec;
200 // vLocalGear now stores the vector from the cg to the wheel in local coords.
202 compressLength = vLocalGear(eZ) - Position->GetDistanceAGL();
204 // The compression length is currently measured in the Z-axis, only, at this time.
205 // It should be measured along the strut axis. If the local-frame gear position
206 // "hangs down" below the CG greater than the altitude, then the compressLength
207 // will be positive - i.e. the gear will have made contact.
209 if (compressLength > 0.00) {
211 WOW = true; // Weight-On-Wheels is true
213 // The next equation should really use the vector to the contact patch of the tire
214 // including the strut compression and not vWhlBodyVec. Will fix this later.
215 // As it stands, now, the following equation takes the aircraft body-frame
216 // rotational rate and calculates the cross-product with the vector from the CG
217 // to the wheel, thus producing the instantaneous velocity vector of the tire
218 // in Body coords. The frame is also converted to local coordinates. When the
219 // aircraft local-frame velocity is added to this quantity, the total velocity of
220 // the wheel in local frame is then known. Subsequently, the compression speed
221 // (used for calculating damping force) is found by taking the Z-component of the
224 vWhlVelVec = State->GetTb2l() * (Rotation->GetPQR() * vWhlBodyVec);
226 vWhlVelVec += Position->GetVel();
228 compressSpeed = vWhlVelVec(eZ);
230 // If this is the first time the wheel has made contact, remember some values
231 // for later printout.
235 SinkRate = compressSpeed;
236 GroundSpeed = Position->GetVel().Magnitude();
239 // The following needs work regarding friction coefficients and braking and
240 // steering The BrakeFCoeff formula assumes that an anti-skid system is used.
241 // It also assumes that we won't be turning and braking at the same time.
242 // Will fix this later.
243 // [JSB] The braking force coefficients include normal rolling coefficient +
244 // a percentage of the static friction coefficient based on braking applied.
249 BrakeFCoeff = rollingFCoeff*(1.0 - FCS->GetBrake(bgLeft)) +
250 staticFCoeff*FCS->GetBrake(bgLeft);
254 BrakeFCoeff = rollingFCoeff*(1.0 - FCS->GetBrake(bgRight)) +
255 staticFCoeff*FCS->GetBrake(bgRight);
259 BrakeFCoeff = rollingFCoeff*(1.0 - FCS->GetBrake(bgCenter)) +
260 staticFCoeff*FCS->GetBrake(bgCenter);
264 BrakeFCoeff = rollingFCoeff;
268 BrakeFCoeff = rollingFCoeff;
272 BrakeFCoeff = rollingFCoeff;
275 cerr << "Improper brake group membership detected for this gear." << endl;
279 switch (eSteerType) {
281 SteerAngle = SteerGain*FCS->GetDrPos();
287 // Note to Jon: This is not correct for castering gear. I'll fix it later.
291 cerr << "Improper steering type membership detected for this gear." << endl;
295 // Transform the wheel velocities from the local axis system to the wheel axis system.
296 // For now, steering angle is assumed to happen in the Local Z axis,
297 // not the strut axis as it should be. Will fix this later.
299 SinWheel = sin(Rotation->Getpsi() + SteerAngle);
300 CosWheel = cos(Rotation->Getpsi() + SteerAngle);
301 RollingWhlVel = vWhlVelVec(eX)*CosWheel + vWhlVelVec(eY)*SinWheel;
302 SideWhlVel = vWhlVelVec(eY)*CosWheel - vWhlVelVec(eX)*SinWheel;
304 // Calculate tire slip angle.
306 if (RollingWhlVel == 0.0 && SideWhlVel == 0.0) {
309 WheelSlip = RADTODEG*atan2(SideWhlVel, RollingWhlVel);
312 // The following code normalizes the wheel velocity vector, reverses it, and zeroes out
313 // the z component of the velocity. The question is, should the Z axis velocity be zeroed
314 // out first before the normalization takes place or not? Subsequent to that, the Wheel
315 // Velocity vector now points as a unit vector backwards and parallel to the wheel
316 // velocity vector. It acts AT the wheel.
318 // Note to Jon: I commented out this line because I wasn't sure we want to do this.
319 // vWhlVelVec = -1.0 * vWhlVelVec.Normalize();
320 // vWhlVelVec(eZ) = 0.00;
322 // Compute the sideforce coefficients using similar assumptions to LaRCSim for now.
323 // Allow a maximum of 10 degrees tire slip angle before wheel slides. At that point,
324 // transition from static to dynamic friction. There are more complicated formulations
325 // of this that avoid the discrete jump. Will fix this later.
327 if (fabs(WheelSlip) <= 10.0) {
328 FCoeff = staticFCoeff*WheelSlip/10.0;
330 FCoeff = dynamicFCoeff*fabs(WheelSlip)/WheelSlip;
333 // Compute the vertical force on the wheel using square-law damping (per comment
334 // in paper AIAA-2000-4303 - see header prologue comments). We might consider
335 // allowing for both square and linear damping force calculation. Also need to
336 // possibly give a "rebound damping factor" that differs from the compression
337 // case. NOTE: SQUARE LAW DAMPING NO GOOD!
339 vLocalForce(eZ) = min(-compressLength * kSpring
340 - compressSpeed * bDamp, (float)0.0);
342 MaximumStrutForce = max(MaximumStrutForce, fabs(vLocalForce(eZ)));
343 MaximumStrutTravel = max(MaximumStrutTravel, fabs(compressLength));
345 // Compute the forces in the wheel ground plane.
348 if (fabs(RollingWhlVel) > 1E-3) {
349 RollingForce = vLocalForce(eZ) * BrakeFCoeff * fabs(RollingWhlVel)/RollingWhlVel;
351 SideForce = vLocalForce(eZ) * FCoeff;
353 // Transform these forces back to the local reference frame.
355 vLocalForce(eX) = RollingForce*CosWheel - SideForce*SinWheel;
356 vLocalForce(eY) = SideForce*CosWheel + RollingForce*SinWheel;
358 // Note to Jon: At this point the forces will be too big when the airplane is
359 // stopped or rolling to a stop. We need to make sure that the gear forces just
360 // balance out the non-gear forces when the airplane is stopped. That way the
361 // airplane won't start to accelerate until the non-gear/ forces are larger than
362 // the gear forces. I think that the proper fix should go into FGAircraft::FMGear.
363 // This routine would only compute the local strut forces and return them to
364 // FMGear. All of the gear forces would get adjusted in FMGear using the total
365 // non-gear forces. Then the gear moments would be calculated. If strange things
366 // start happening to the airplane during testing as it rolls to a stop, then we
367 // need to implement this change. I ran out of time to do it now but have the
370 // Transform the forces back to the body frame and compute the moment.
372 vForce = State->GetTl2b() * vLocalForce;
373 vMoment = vWhlBodyVec * vForce;
379 if (Position->GetDistanceAGL() > 200.0) {
380 FirstContact = false;
382 DistanceTraveled = 0.0;
383 MaximumStrutForce = MaximumStrutTravel = 0.0;
386 compressLength = 0.0; // reset compressLength to zero for data output validity
389 vMoment.InitMatrix();
393 DistanceTraveled += Position->GetVel().Magnitude()*State->Getdt()*Aircraft->GetRate();
396 if (ReportEnable && Position->GetVel().Magnitude() <= 0.05 && !Reported) {
397 if (debug_lvl > 0) Report();
403 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
405 void FGLGear::Report(void)
407 cout << endl << "Touchdown report for " << name << endl;
408 cout << " Sink rate at contact: " << SinkRate << " fps, "
409 << SinkRate*0.3408 << " mps" << endl;
410 cout << " Contact ground speed: " << GroundSpeed*.5925 << " knots, "
411 << GroundSpeed*0.3408 << " mps" << endl;
412 cout << " Maximum contact force: " << MaximumStrutForce << " lbs, "
413 << MaximumStrutForce*4.448 << " Newtons" << endl;
414 cout << " Maximum strut travel: " << MaximumStrutTravel*12.0 << " inches, "
415 << MaximumStrutTravel*30.48 << " cm" << endl;
416 cout << " Distance traveled: " << DistanceTraveled << " ft, "
417 << DistanceTraveled*0.3408 << " meters" << endl;
421 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
423 void FGLGear::Debug(void)
425 // TODO: Add user code here