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 extern short debug_lvl;
58 /*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
60 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
62 FGLGear::FGLGear(FGConfigFile* AC_cfg, FGFDMExec* fdmex) : vXYZ(3),
68 *AC_cfg >> tmp >> name >> vXYZ(1) >> vXYZ(2) >> vXYZ(3)
69 >> kSpring >> bDamp>> dynamicFCoeff >> staticFCoeff
70 >> rollingFCoeff >> sSteerType >> sBrakeGroup >> maxSteerAngle;
73 cout << " Name: " << name << endl;
74 cout << " Location: " << vXYZ << endl;
75 cout << " Spring Constant: " << kSpring << endl;
76 cout << " Damping Constant: " << bDamp << endl;
77 cout << " Dynamic Friction: " << dynamicFCoeff << endl;
78 cout << " Static Friction: " << staticFCoeff << endl;
79 cout << " Rolling Friction: " << rollingFCoeff << endl;
80 cout << " Steering Type: " << sSteerType << endl;
81 cout << " Grouping: " << sBrakeGroup << endl;
82 cout << " Max Steer Angle: " << maxSteerAngle << endl;
85 if (sBrakeGroup == "LEFT" ) eBrakeGrp = bgLeft;
86 else if (sBrakeGroup == "RIGHT" ) eBrakeGrp = bgRight;
87 else if (sBrakeGroup == "CENTER") eBrakeGrp = bgCenter;
88 else if (sBrakeGroup == "NOSE" ) eBrakeGrp = bgNose;
89 else if (sBrakeGroup == "TAIL" ) eBrakeGrp = bgTail;
90 else if (sBrakeGroup == "NONE" ) eBrakeGrp = bgNone;
92 cerr << "Improper braking group specification in config file: "
93 << sBrakeGroup << " is undefined." << endl;
96 if (sSteerType == "STEERABLE") eSteerType = stSteer;
97 else if (sSteerType == "FIXED" ) eSteerType = stFixed;
98 else if (sSteerType == "CASTERED" ) eSteerType = stCaster;
100 cerr << "Improper steering type specification in config file: "
101 << sSteerType << " is undefined." << endl;
104 // Add some AI here to determine if gear is located properly according to its
105 // brake group type ??
107 State = Exec->GetState();
108 Aircraft = Exec->GetAircraft();
109 Position = Exec->GetPosition();
110 Rotation = Exec->GetRotation();
111 FCS = Exec->GetFCS();
112 MassBalance = Exec->GetMassBalance();
116 FirstContact = false;
118 DistanceTraveled = 0.0;
119 MaximumStrutForce = MaximumStrutTravel = 0.0;
120 SinkRate = GroundSpeed = 0.0;
122 vWhlBodyVec = (vXYZ - MassBalance->GetXYZcg()) / 12.0;
123 vWhlBodyVec(eX) = -vWhlBodyVec(eX);
124 vWhlBodyVec(eZ) = -vWhlBodyVec(eZ);
126 vLocalGear = State->GetTb2l() * vWhlBodyVec;
128 if (debug_lvl & 2) cout << "Instantiated: FGLGear" << endl;
131 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
133 FGLGear::FGLGear(const FGLGear& lgear)
136 Aircraft = lgear.Aircraft;
137 Position = lgear.Position;
138 Rotation = lgear.Rotation;
141 MassBalance = lgear.MassBalance;
144 vMoment = lgear.vMoment;
145 vWhlBodyVec = lgear.vWhlBodyVec;
146 vLocalGear = lgear.vLocalGear;
149 ReportEnable = lgear.ReportEnable;
150 FirstContact = lgear.FirstContact;
151 DistanceTraveled = lgear.DistanceTraveled;
152 MaximumStrutForce = lgear.MaximumStrutForce;
153 MaximumStrutTravel = lgear.MaximumStrutTravel;
155 kSpring = lgear.kSpring;
157 compressLength = lgear.compressLength;
158 compressSpeed = lgear.compressSpeed;
159 staticFCoeff = lgear.staticFCoeff;
160 dynamicFCoeff = lgear.dynamicFCoeff;
161 rollingFCoeff = lgear.rollingFCoeff;
162 brakePct = lgear.brakePct;
163 maxCompLen = lgear.maxCompLen;
164 SinkRate = lgear.SinkRate;
165 GroundSpeed = lgear.GroundSpeed;
166 Reported = lgear.Reported;
168 sSteerType = lgear.sSteerType;
169 eSteerType = lgear.eSteerType;
170 sBrakeGroup = lgear.sBrakeGroup;
171 eBrakeGrp = lgear.eBrakeGrp;
172 maxSteerAngle = lgear.maxSteerAngle;
175 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
179 if (debug_lvl & 2) cout << "Destroyed: FGLGear" << endl;
182 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
184 FGColumnVector FGLGear::Force(void)
186 float SteerGain, SteerAngle, BrakeFCoeff;
187 float SinWheel, CosWheel, SideWhlVel, RollingWhlVel;
188 float RudderPedal, RollingForce, SideForce, FCoeff;
191 FGColumnVector vForce(3);
192 FGColumnVector vLocalForce(3);
193 FGColumnVector vWhlVelVec(3); // Velocity of this wheel (Local)
195 vWhlBodyVec = (vXYZ - MassBalance->GetXYZcg()) / 12.0;
196 vWhlBodyVec(eX) = -vWhlBodyVec(eX);
197 vWhlBodyVec(eZ) = -vWhlBodyVec(eZ);
199 // vWhlBodyVec now stores the vector from the cg to this wheel
201 vLocalGear = State->GetTb2l() * vWhlBodyVec;
203 // vLocalGear now stores the vector from the cg to the wheel in local coords.
205 compressLength = vLocalGear(eZ) - Position->GetDistanceAGL();
207 // The compression length is currently measured in the Z-axis, only, at this time.
208 // It should be measured along the strut axis. If the local-frame gear position
209 // "hangs down" below the CG greater than the altitude, then the compressLength
210 // will be positive - i.e. the gear will have made contact.
212 if (compressLength > 0.00) {
214 WOW = true; // Weight-On-Wheels is true
216 // The next equation should really use the vector to the contact patch of the tire
217 // including the strut compression and not vWhlBodyVec. Will fix this later.
218 // As it stands, now, the following equation takes the aircraft body-frame
219 // rotational rate and calculates the cross-product with the vector from the CG
220 // to the wheel, thus producing the instantaneous velocity vector of the tire
221 // in Body coords. The frame is also converted to local coordinates. When the
222 // aircraft local-frame velocity is added to this quantity, the total velocity of
223 // the wheel in local frame is then known. Subsequently, the compression speed
224 // (used for calculating damping force) is found by taking the Z-component of the
227 vWhlVelVec = State->GetTb2l() * (Rotation->GetPQR() * vWhlBodyVec);
228 vWhlVelVec += Position->GetVel();
230 compressSpeed = vWhlVelVec(eZ);
232 // If this is the first time the wheel has made contact, remember some values
233 // for later printout.
237 SinkRate = compressSpeed;
238 GroundSpeed = Position->GetVel().Magnitude();
241 // The following needs work regarding friction coefficients and braking and
242 // steering The BrakeFCoeff formula assumes that an anti-skid system is used.
243 // It also assumes that we won't be turning and braking at the same time.
244 // Will fix this later.
245 // [JSB] The braking force coefficients include normal rolling coefficient +
246 // a percentage of the static friction coefficient based on braking applied.
250 SteerGain = -maxSteerAngle;
251 BrakeFCoeff = rollingFCoeff*(1.0 - FCS->GetBrake(bgLeft)) +
252 staticFCoeff*FCS->GetBrake(bgLeft);
255 SteerGain = -maxSteerAngle;
256 BrakeFCoeff = rollingFCoeff*(1.0 - FCS->GetBrake(bgRight)) +
257 staticFCoeff*FCS->GetBrake(bgRight);
260 SteerGain = -maxSteerAngle;
261 BrakeFCoeff = rollingFCoeff*(1.0 - FCS->GetBrake(bgCenter)) +
262 staticFCoeff*FCS->GetBrake(bgCenter);
265 SteerGain = maxSteerAngle;
266 BrakeFCoeff = rollingFCoeff;
269 SteerGain = -maxSteerAngle;
270 BrakeFCoeff = rollingFCoeff;
273 SteerGain = -maxSteerAngle;
274 BrakeFCoeff = rollingFCoeff;
277 cerr << "Improper brake group membership detected for this gear." << endl;
281 switch (eSteerType) {
283 SteerAngle = SteerGain*FCS->GetDrCmd();
289 // Note to Jon: This is not correct for castering gear. I'll fix it later.
293 cerr << "Improper steering type membership detected for this gear." << endl;
297 // Transform the wheel velocities from the local axis system to the wheel axis system.
298 // For now, steering angle is assumed to happen in the Local Z axis,
299 // not the strut axis as it should be. Will fix this later.
301 SinWheel = sin(Rotation->Getpsi() + SteerAngle*DEGTORAD);
302 CosWheel = cos(Rotation->Getpsi() + SteerAngle*DEGTORAD);
303 RollingWhlVel = vWhlVelVec(eX)*CosWheel + vWhlVelVec(eY)*SinWheel;
304 SideWhlVel = vWhlVelVec(eY)*CosWheel - vWhlVelVec(eX)*SinWheel;
306 // Calculate tire slip angle.
308 if (RollingWhlVel == 0.0 && SideWhlVel == 0.0) {
311 WheelSlip = RADTODEG*atan2(SideWhlVel, RollingWhlVel);
314 // The following code normalizes the wheel velocity vector, reverses it, and zeroes out
315 // the z component of the velocity. The question is, should the Z axis velocity be zeroed
316 // out first before the normalization takes place or not? Subsequent to that, the Wheel
317 // Velocity vector now points as a unit vector backwards and parallel to the wheel
318 // velocity vector. It acts AT the wheel.
320 // Note to Jon: I commented out this line because I wasn't sure we want to do this.
321 // vWhlVelVec = -1.0 * vWhlVelVec.Normalize();
322 // vWhlVelVec(eZ) = 0.00;
324 // Compute the sideforce coefficients using similar assumptions to LaRCSim for now.
325 // Allow a maximum of 10 degrees tire slip angle before wheel slides. At that point,
326 // transition from static to dynamic friction. There are more complicated formulations
327 // of this that avoid the discrete jump. Will fix this later.
329 if (fabs(WheelSlip) <= 10.0) {
330 FCoeff = staticFCoeff*WheelSlip/10.0;
332 FCoeff = dynamicFCoeff*fabs(WheelSlip)/WheelSlip;
335 // Compute the vertical force on the wheel using square-law damping (per comment
336 // in paper AIAA-2000-4303 - see header prologue comments). We might consider
337 // allowing for both square and linear damping force calculation. Also need to
338 // possibly give a "rebound damping factor" that differs from the compression
339 // case. NOTE: SQUARE LAW DAMPING NO GOOD!
341 vLocalForce(eZ) = min(-compressLength * kSpring
342 - compressSpeed * bDamp, (float)0.0);
344 MaximumStrutForce = max(MaximumStrutForce, fabs(vLocalForce(eZ)));
345 MaximumStrutTravel = max(MaximumStrutTravel, fabs(compressLength));
347 // Compute the forces in the wheel ground plane.
350 if (fabs(RollingWhlVel) > 1E-3) {
351 RollingForce = vLocalForce(eZ) * BrakeFCoeff * fabs(RollingWhlVel)/RollingWhlVel;
353 SideForce = vLocalForce(eZ) * FCoeff;
355 // Transform these forces back to the local reference frame.
357 vLocalForce(eX) = RollingForce*CosWheel - SideForce*SinWheel;
358 vLocalForce(eY) = SideForce*CosWheel + RollingForce*SinWheel;
360 // Note to Jon: At this point the forces will be too big when the airplane is
361 // stopped or rolling to a stop. We need to make sure that the gear forces just
362 // balance out the non-gear forces when the airplane is stopped. That way the
363 // airplane won't start to accelerate until the non-gear/ forces are larger than
364 // the gear forces. I think that the proper fix should go into FGAircraft::FMGear.
365 // This routine would only compute the local strut forces and return them to
366 // FMGear. All of the gear forces would get adjusted in FMGear using the total
367 // non-gear forces. Then the gear moments would be calculated. If strange things
368 // start happening to the airplane during testing as it rolls to a stop, then we
369 // need to implement this change. I ran out of time to do it now but have the
372 // Transform the forces back to the body frame and compute the moment.
374 vForce = State->GetTl2b() * vLocalForce;
375 vMoment = vWhlBodyVec * vForce;
381 if (Position->GetDistanceAGL() > 200.0) {
382 FirstContact = false;
384 DistanceTraveled = 0.0;
385 MaximumStrutForce = MaximumStrutTravel = 0.0;
388 compressLength = 0.0; // reset compressLength to zero for data output validity
391 vMoment.InitMatrix();
395 DistanceTraveled += Position->GetVel().Magnitude()*State->Getdt()*Aircraft->GetRate();
398 if (ReportEnable && Position->GetVel().Magnitude() <= 0.05 && !Reported) {
399 if (debug_lvl > 0) Report();
405 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
407 void FGLGear::Report(void)
409 cout << endl << "Touchdown report for " << name << endl;
410 cout << " Sink rate at contact: " << SinkRate << " fps, "
411 << SinkRate*0.3408 << " mps" << endl;
412 cout << " Contact ground speed: " << GroundSpeed*.5925 << " knots, "
413 << GroundSpeed*0.3408 << " mps" << endl;
414 cout << " Maximum contact force: " << MaximumStrutForce << " lbs, "
415 << MaximumStrutForce*4.448 << " Newtons" << endl;
416 cout << " Maximum strut travel: " << MaximumStrutTravel*12.0 << " inches, "
417 << MaximumStrutTravel*30.48 << " cm" << endl;
418 cout << " Distance traveled: " << DistanceTraveled << " ft, "
419 << DistanceTraveled*0.3408 << " meters" << endl;
423 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
425 void FGLGear::Debug(void)
427 // TODO: Add user code here