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 --------------------------------------------------------------------------------
30 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
32 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
37 /*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
39 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
41 #include "models/propulsion/FGForce.h"
42 #include "math/FGColumnVector3.h"
45 /*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
47 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
49 #define ID_LGEAR "$Id$"
51 /*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
53 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
66 /*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
68 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
70 /** Landing gear model.
71 Calculates forces and moments due to landing gear reactions. This is done in
72 several steps, and is dependent on what kind of gear is being modeled. Here
73 are the parameters that can be specified in the config file for modeling
76 <h3>Physical Characteristics</h3>
78 <li>X, Y, Z location, in inches in structural coordinate frame</li>
79 <li>Spring constant, in lbs/ft</li>
80 <li>Damping coefficient, in lbs/ft/sec</li>
81 <li>Dynamic Friction Coefficient</li>
82 <li>Static Friction Coefficient</li>
84 <h3>Operational Properties</h3>
87 <li>Steerability attribute {one of STEERABLE | FIXED | CASTERED}</li>
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}">
181 <relaxation_velocity>
182 <rolling unit="{FT/SEC | KTS | M/S}"> {number} </rolling>
183 <side unit="{FT/SEC | KTS | M/S}"> {number} </side>
184 </relaxation_velocity>
186 <rolling> {number} </rolling>
187 <side> {number} </side>
189 <wheel_slip_filter> {number} </wheel_slip_filter>
192 @author Jon S. Berndt
194 @see Richard E. McFarland, "A Standard Kinematic Model for Flight Simulation at
195 NASA-Ames", NASA CR-2497, January 1975
196 @see Barnes W. McCormick, "Aerodynamics, Aeronautics, and Flight Mechanics",
197 Wiley & Sons, 1979 ISBN 0-471-03032-5
198 @see W. A. Ragsdale, "A Generic Landing Gear Dynamics Model for LASRS++",
202 /*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
204 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
206 class FGLGear : public FGForce
209 /// Brake grouping enumerators
210 enum BrakeGroup {bgNone=0, bgLeft, bgRight, bgCenter, bgNose, bgTail };
211 /// Steering group membership enumerators
212 enum SteerType {stSteer, stFixed, stCaster};
213 /// Contact point type
214 enum ContactType {ctBOGEY, ctSTRUCTURE};
215 /// Report type enumerators
216 enum ReportType {erNone=0, erTakeoff, erLand};
218 enum DampType {dtLinear=0, dtSquare};
220 @param el a pointer to the XML element that contains the CONTACT info.
221 @param Executive a pointer to the parent executive object
222 @param number integer identifier for this instance of FGLGear
224 FGLGear(Element* el, FGFDMExec* Executive, int number);
228 /// The Force vector for this gear
229 FGColumnVector3& GetBodyForces(void);
231 /// Gets the location of the gear in Body axes
232 FGColumnVector3& GetBodyLocation(void) { return vWhlBodyVec; }
233 double GetBodyLocation(int idx) const { return vWhlBodyVec(idx); }
235 FGColumnVector3& GetLocalGear(void) { return vLocalGear; }
236 double GetLocalGear(int idx) const { return vLocalGear(idx); }
238 /// Gets the name of the gear
239 string GetName(void) const {return name; }
240 /// Gets the Weight On Wheels flag value
241 bool GetWOW(void) const {return WOW; }
242 /// Gets the current compressed length of the gear in feet
243 double GetCompLen(void) const {return compressLength;}
244 /// Gets the current gear compression velocity in ft/sec
245 double GetCompVel(void) const {return compressSpeed; }
246 /// Gets the gear compression force in pounds
247 double GetCompForce(void) const {return StrutForce; }
248 double GetBrakeFCoeff(void) const {return BrakeFCoeff;}
250 /// Gets the current normalized tire pressure
251 double GetTirePressure(void) const { return TirePressureNorm; }
252 /// Sets the new normalized tire pressure
253 void SetTirePressure(double p) { TirePressureNorm = p; }
255 /// Sets the brake value in percent (0 - 100)
256 void SetBrake(double bp) {brakePct = bp;}
258 /// Sets the weight-on-wheels flag.
259 void SetWOW(bool wow) {WOW = wow;}
261 /** Set the console touchdown reporting feature
262 @param flag true turns on touchdown reporting, false turns it off */
263 void SetReport(bool flag) { ReportEnable = flag; }
264 /** Get the console touchdown reporting feature
265 @return true if reporting is turned on */
266 bool GetReport(void) const { return ReportEnable; }
267 double GetSteerNorm(void) const { return radtodeg/maxSteerAngle*SteerAngle; }
268 double GetDefaultSteerAngle(double cmd) const { return cmd*maxSteerAngle; }
269 double GetstaticFCoeff(void) const { return staticFCoeff; }
271 int GetBrakeGroup(void) const { return (int)eBrakeGrp; }
272 int GetSteerType(void) const { return (int)eSteerType; }
274 bool GetSteerable(void) const { return eSteerType != stFixed; }
275 bool GetRetractable(void) const { return isRetractable; }
276 bool GetGearUnitUp(void) const { return GearUp; }
277 bool GetGearUnitDown(void) const { return GearDown; }
278 double GetWheelRollForce(void) {
279 FGColumnVector3 vForce = mTGear.Transposed() * FGForce::GetBodyForces();
280 return vForce(eX)*cos(SteerAngle) + vForce(eY)*sin(SteerAngle); }
281 double GetWheelSideForce(void) {
282 FGColumnVector3 vForce = mTGear.Transposed() * FGForce::GetBodyForces();
283 return vForce(eY)*cos(SteerAngle) - vForce(eX)*sin(SteerAngle); }
284 double GetWheelRollVel(void) const { return vWhlVelVec(eX)*cos(SteerAngle)
285 + vWhlVelVec(eY)*sin(SteerAngle); }
286 double GetWheelSideVel(void) const { return vWhlVelVec(eY)*cos(SteerAngle)
287 - vWhlVelVec(eX)*sin(SteerAngle); }
288 double GetWheelSlipAngle(void) const { return WheelSlip; }
289 double GetWheelVel(int axis) const { return vWhlVelVec(axis);}
290 bool IsBogey(void) const { return (eContactType == ctBOGEY);}
291 double GetGearUnitPos(void);
297 static const FGMatrix33 Tb2s;
299 FGColumnVector3 vGearOrient;
300 FGColumnVector3 vWhlBodyVec;
301 FGColumnVector3 vLocalGear;
302 FGColumnVector3 vWhlVelVec, vLocalWhlVel; // Velocity of this wheel
303 FGColumnVector3 normal, cvel, vGroundNormal;
304 FGLocation contact, gearLoc;
305 FGTable *ForceY_Table;
311 double compressLength;
312 double compressSpeed;
313 double staticFCoeff, dynamicFCoeff, rollingFCoeff;
314 double Stiffness, Shape, Peak, Curvature; // Pacejka factors
320 double TakeoffDistanceTraveled;
321 double TakeoffDistanceTraveled50ft;
322 double LandingDistanceTraveled;
323 double MaximumStrutForce, StrutForce;
324 double MaximumStrutTravel;
327 double TirePressureNorm;
333 bool StartedGroundRun;
334 bool LandingReported;
335 bool TakeoffReported;
338 bool GearUp, GearDown;
341 std::string sSteerType;
342 std::string sBrakeGroup;
343 std::string sRetractable;
344 std::string sContactType;
346 BrakeGroup eBrakeGrp;
347 ContactType eContactType;
348 SteerType eSteerType;
350 DampType eDampTypeRebound;
351 double maxSteerAngle;
352 double RFRV; // Rolling force relaxation velocity
353 double SFRV; // Side force relaxation velocity
354 double LongForceLagFilterCoeff; // Longitudinal Force Lag Filter Coefficient
355 double LatForceLagFilterCoeff; // Lateral Force Lag Filter Coefficient
356 double WheelSlipLagFilterCoeff; // Wheel slip angle lag filter coefficient
358 Filter LongForceFilter;
359 Filter LatForceFilter;
360 Filter WheelSlipFilter;
363 FGAircraft* Aircraft;
364 FGPropagate* Propagate;
365 FGAuxiliary* Auxiliary;
367 FGMassBalance* MassBalance;
369 void ComputeRetractionState(void);
370 void ComputeBrakeForceCoefficient(void);
371 void ComputeSteeringAngle(void);
372 void ComputeSlipAngle(void);
373 void ComputeSideForceCoefficient(void);
374 void ComputeVerticalStrutForce(void);
375 void ComputeGroundCoordSys(void);
376 void CrashDetect(void);
377 void InitializeReporting(void);
378 void ResetReporting(void);
379 void ReportTakeoffOrLanding(void);
380 void Report(ReportType rt);
381 void Debug(int from);
385 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%