1 /*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
7 ------------- Copyright (C) 1999 Jon S. Berndt (jon@jsbsim.org) -------------
9 This program is free software; you can redistribute it and/or modify it under
10 the terms of the GNU Lesser General Public License as published by the Free Software
11 Foundation; either version 2 of the License, or (at your option) any later
14 This program is distributed in the hope that it will be useful, but WITHOUT
15 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
16 FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
19 You should have received a copy of the GNU Lesser General Public License along with
20 this program; if not, write to the Free Software Foundation, Inc., 59 Temple
21 Place - Suite 330, Boston, MA 02111-1307, USA.
23 Further information about the GNU Lesser General Public License can also be found on
24 the world wide web at http://www.gnu.org.
27 --------------------------------------------------------------------------------
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32 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
37 /*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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41 #include "models/propulsion/FGForce.h"
42 #include "models/FGPropagate.h"
43 #include "math/FGColumnVector3.h"
46 /*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
48 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
50 #define ID_LGEAR "$Id: FGLGear.h,v 1.40 2010/07/30 11:50:01 jberndt Exp $"
52 /*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
54 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
67 /*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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71 /** Landing gear model.
72 Calculates forces and moments due to landing gear reactions. This is done in
73 several steps, and is dependent on what kind of gear is being modeled. Here
74 are the parameters that can be specified in the config file for modeling
77 <h3>Physical Characteristics</h3>
79 <li>X, Y, Z location, in inches in structural coordinate frame</li>
80 <li>Spring constant, in lbs/ft</li>
81 <li>Damping coefficient, in lbs/ft/sec</li>
82 <li>Dynamic Friction Coefficient</li>
83 <li>Static Friction Coefficient</li>
85 <h3>Operational Properties</h3>
88 <li>Brake Group Membership {one of LEFT | CENTER | RIGHT | NOSE | TAIL | NONE}</li>
89 <li>Max Steer Angle, in degrees</li>
92 <h3>Algorithm and Approach to Modeling</h3>
94 <li>Find the location of the uncompressed landing gear relative to the CG of
95 the aircraft. Remember, the structural coordinate frame that the aircraft is
96 defined in is: X positive towards the tail, Y positive out the right side, Z
97 positive upwards. The locations of the various parts are given in inches in
99 <li>The vector giving the location of the gear (relative to the cg) is
100 rotated 180 degrees about the Y axis to put the coordinates in body frame (X
101 positive forwards, Y positive out the right side, Z positive downwards, with
102 the origin at the cg). The lengths are also now given in feet.</li>
103 <li>The new gear location is now transformed to the local coordinate frame
104 using the body-to-local matrix. (Mb2l).</li>
105 <li>Knowing the location of the center of gravity relative to the ground
106 (height above ground level or AGL) now enables gear deflection to be
107 calculated. The gear compression value is the local frame gear Z location
108 value minus the height AGL. [Currently, we make the assumption that the gear
109 is oriented - and the deflection occurs in - the Z axis only. Additionally,
110 the vector to the landing gear is currently not modified - which would
111 (correctly) move the point of contact to the actual compressed-gear point of
112 contact. Eventually, articulated gear may be modeled, but initially an
113 effort must be made to model a generic system.] As an example, say the
114 aircraft left main gear location (in local coordinates) is Z = 3 feet
115 (positive) and the height AGL is 2 feet. This tells us that the gear is
116 compressed 1 foot.</li>
117 <li>If the gear is compressed, a Weight-On-Wheels (WOW) flag is set.</li>
118 <li>With the compression length calculated, the compression velocity may now
119 be calculated. This will be used to determine the damping force in the
120 strut. The aircraft rotational rate is multiplied by the vector to the wheel
121 to get a wheel velocity in body frame. That velocity vector is then
122 transformed into the local coordinate frame.</li>
123 <li>The aircraft cg velocity in the local frame is added to the
124 just-calculated wheel velocity (due to rotation) to get a total wheel
125 velocity in the local frame.</li>
126 <li>The compression speed is the Z-component of the vector.</li>
127 <li>With the wheel velocity vector no longer needed, it is normalized and
128 multiplied by a -1 to reverse it. This will be used in the friction force
130 <li>Since the friction force takes place solely in the runway plane, the Z
131 coordinate of the normalized wheel velocity vector is set to zero.</li>
132 <li>The gear deflection force (the force on the aircraft acting along the
133 local frame Z axis) is now calculated given the spring and damper
134 coefficients, and the gear deflection speed and stroke length. Keep in mind
135 that gear forces always act in the negative direction (in both local and
136 body frames), and are not capable of generating a force in the positive
137 sense (one that would attract the aircraft to the ground). So, the gear
138 forces are always negative - they are limited to values of zero or less. The
139 gear force is simply the negative of the sum of the spring compression
140 length times the spring coefficient and the gear velocity times the damping
142 <li>The lateral/directional force acting on the aircraft through the landing
144 gear (along the local frame X and Y axes) is calculated next. First, the
145 friction coefficient is multiplied by the recently calculated Z-force. This
146 is the friction force. It must be given direction in addition to magnitude.
147 We want the components in the local frame X and Y axes. From step 9, above,
148 the conditioned wheel velocity vector is taken and the X and Y parts are
149 multiplied by the friction force to get the X and Y components of friction.
151 <li>The wheel force in local frame is next converted to body frame.</li>
152 <li>The moment due to the gear force is calculated by multiplying r x F
153 (radius to wheel crossed into the wheel force). Both of these operands are
157 <h3>Configuration File Format:</h3>
159 <contact type="{BOGEY | STRUCTURE}" name="{string}">
160 <location unit="{IN | M}">
165 <orientation unit="{RAD | DEG}">
166 <pitch> {number} </pitch>
167 <roll> {number} </roll>
168 <yaw> {number} </yaw>
170 <static_friction> {number} </static_friction>
171 <dynamic_friction> {number} </dynamic_friction>
172 <rolling_friction> {number} </rolling_friction>
173 <spring_coeff unit="{LBS/FT | N/M}"> {number} </spring_coeff>
174 <damping_coeff [type="SQUARE"] unit="{LBS/FT/SEC | N/M/SEC}"> {number} </damping_coeff>
175 <damping_coeff_rebound [type="SQUARE"] unit="{LBS/FT/SEC | N/M/SEC}"> {number} </damping_coeff_rebound>
176 <max_steer unit="DEG"> {number | 0 | 360} </max_steer>
177 <brake_group> {NONE | LEFT | RIGHT | CENTER | NOSE | TAIL} </brake_group>
178 <retractable>{0 | 1}</retractable>
179 <table type="{CORNERING_COEFF}">
183 @author Jon S. Berndt
184 @version $Id: FGLGear.h,v 1.40 2010/07/30 11:50:01 jberndt Exp $
185 @see Richard E. McFarland, "A Standard Kinematic Model for Flight Simulation at
186 NASA-Ames", NASA CR-2497, January 1975
187 @see Barnes W. McCormick, "Aerodynamics, Aeronautics, and Flight Mechanics",
188 Wiley & Sons, 1979 ISBN 0-471-03032-5
189 @see W. A. Ragsdale, "A Generic Landing Gear Dynamics Model for LASRS++",
193 /*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
195 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
197 class FGLGear : public FGForce
200 /// Brake grouping enumerators
201 enum BrakeGroup {bgNone=0, bgLeft, bgRight, bgCenter, bgNose, bgTail };
202 /// Steering group membership enumerators
203 enum SteerType {stSteer, stFixed, stCaster};
204 /// Contact point type
205 enum ContactType {ctBOGEY, ctSTRUCTURE};
206 /// Report type enumerators
207 enum ReportType {erNone=0, erTakeoff, erLand};
209 enum DampType {dtLinear=0, dtSquare};
211 enum FrictionType {ftRoll=0, ftSide, ftDynamic};
213 @param el a pointer to the XML element that contains the CONTACT info.
214 @param Executive a pointer to the parent executive object
215 @param number integer identifier for this instance of FGLGear
217 FGLGear(Element* el, FGFDMExec* Executive, int number);
221 /// The Force vector for this gear
222 FGColumnVector3& GetBodyForces(void);
224 /// Gets the location of the gear in Body axes
225 FGColumnVector3& GetBodyLocation(void) { return vWhlBodyVec; }
226 double GetBodyLocation(int idx) const { return vWhlBodyVec(idx); }
228 FGColumnVector3& GetLocalGear(void) { return vLocalGear; }
229 double GetLocalGear(int idx) const { return vLocalGear(idx); }
231 /// Gets the name of the gear
232 string GetName(void) const {return name; }
233 /// Gets the Weight On Wheels flag value
234 bool GetWOW(void) const {return WOW; }
235 /// Gets the current compressed length of the gear in feet
236 double GetCompLen(void) const {return compressLength;}
237 /// Gets the current gear compression velocity in ft/sec
238 double GetCompVel(void) const {return compressSpeed; }
239 /// Gets the gear compression force in pounds
240 double GetCompForce(void) const {return StrutForce; }
241 double GetBrakeFCoeff(void) const {return BrakeFCoeff;}
243 /// Gets the current normalized tire pressure
244 double GetTirePressure(void) const { return TirePressureNorm; }
245 /// Sets the new normalized tire pressure
246 void SetTirePressure(double p) { TirePressureNorm = p; }
248 /// Sets the brake value in percent (0 - 100)
249 void SetBrake(double bp) {brakePct = bp;}
251 /// Sets the weight-on-wheels flag.
252 void SetWOW(bool wow) {WOW = wow;}
254 /** Set the console touchdown reporting feature
255 @param flag true turns on touchdown reporting, false turns it off */
256 void SetReport(bool flag) { ReportEnable = flag; }
257 /** Get the console touchdown reporting feature
258 @return true if reporting is turned on */
259 bool GetReport(void) const { return ReportEnable; }
260 double GetSteerNorm(void) const { return radtodeg/maxSteerAngle*SteerAngle; }
261 double GetDefaultSteerAngle(double cmd) const { return cmd*maxSteerAngle; }
262 double GetstaticFCoeff(void) const { return staticFCoeff; }
264 int GetBrakeGroup(void) const { return (int)eBrakeGrp; }
265 int GetSteerType(void) const { return (int)eSteerType; }
267 bool GetSteerable(void) const { return eSteerType != stFixed; }
268 bool GetRetractable(void) const { return isRetractable; }
269 bool GetGearUnitUp(void) const { return GearUp; }
270 bool GetGearUnitDown(void) const { return GearDown; }
271 double GetWheelRollForce(void) {
272 FGColumnVector3 vForce = mTGear.Transposed() * FGForce::GetBodyForces();
273 return vForce(eX)*cos(SteerAngle) + vForce(eY)*sin(SteerAngle); }
274 double GetWheelSideForce(void) {
275 FGColumnVector3 vForce = mTGear.Transposed() * FGForce::GetBodyForces();
276 return vForce(eY)*cos(SteerAngle) - vForce(eX)*sin(SteerAngle); }
277 double GetWheelRollVel(void) const { return vWhlVelVec(eX)*cos(SteerAngle)
278 + vWhlVelVec(eY)*sin(SteerAngle); }
279 double GetWheelSideVel(void) const { return vWhlVelVec(eY)*cos(SteerAngle)
280 - vWhlVelVec(eX)*sin(SteerAngle); }
281 double GetWheelSlipAngle(void) const { return WheelSlip; }
282 double GetWheelVel(int axis) const { return vWhlVelVec(axis);}
283 bool IsBogey(void) const { return (eContactType == ctBOGEY);}
284 double GetGearUnitPos(void);
285 double GetSteerAngleDeg(void) const { return radtodeg*SteerAngle; }
286 FGPropagate::LagrangeMultiplier* GetMultiplierEntry(int entry);
287 void SetLagrangeMultiplier(double lambda, int entry);
288 FGColumnVector3& UpdateForces(void);
294 static const FGMatrix33 Tb2s;
296 FGColumnVector3 vGearOrient;
297 FGColumnVector3 vWhlBodyVec;
298 FGColumnVector3 vLocalGear;
299 FGColumnVector3 vWhlVelVec, vLocalWhlVel; // Velocity of this wheel
300 FGColumnVector3 normal, cvel, vGroundNormal;
301 FGLocation contact, gearLoc;
302 FGTable *ForceY_Table;
308 double compressLength;
309 double compressSpeed;
310 double staticFCoeff, dynamicFCoeff, rollingFCoeff;
311 double Stiffness, Shape, Peak, Curvature; // Pacejka factors
317 double TakeoffDistanceTraveled;
318 double TakeoffDistanceTraveled50ft;
319 double LandingDistanceTraveled;
320 double MaximumStrutForce, StrutForce;
321 double MaximumStrutTravel;
324 double TirePressureNorm;
330 bool StartedGroundRun;
331 bool LandingReported;
332 bool TakeoffReported;
335 bool GearUp, GearDown;
340 std::string sSteerType;
341 std::string sBrakeGroup;
342 std::string sRetractable;
343 std::string sContactType;
345 BrakeGroup eBrakeGrp;
346 ContactType eContactType;
347 SteerType eSteerType;
349 DampType eDampTypeRebound;
350 double maxSteerAngle;
352 FGPropagate::LagrangeMultiplier LMultiplier[3];
354 FGAuxiliary* Auxiliary;
355 FGPropagate* Propagate;
357 FGMassBalance* MassBalance;
358 FGGroundReactions* GroundReactions;
360 void ComputeRetractionState(void);
361 void ComputeBrakeForceCoefficient(void);
362 void ComputeSteeringAngle(void);
363 void ComputeSlipAngle(void);
364 void ComputeSideForceCoefficient(void);
365 void ComputeVerticalStrutForce(void);
366 void ComputeGroundCoordSys(void);
367 void ComputeJacobian(const FGColumnVector3& vWhlContactVec);
368 void CrashDetect(void);
369 void InitializeReporting(void);
370 void ResetReporting(void);
371 void ReportTakeoffOrLanding(void);
372 void Report(ReportType rt);
373 void Debug(int from);
377 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%