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 "models/FGPropagate.h"
43 #include "math/FGColumnVector3.h"
46 /*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
48 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
50 #define ID_LGEAR "$Id: FGLGear.h,v 1.41 2010/09/22 11:33:40 jberndt Exp $"
52 /*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
54 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
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>Brake Group Membership {one of LEFT | CENTER | RIGHT | NOSE | TAIL | NONE}</li>
88 <li>Max Steer Angle, in degrees</li>
91 <h3>Algorithm and Approach to Modeling</h3>
93 <li>Find the location of the uncompressed landing gear relative to the CG of
94 the aircraft. Remember, the structural coordinate frame that the aircraft is
95 defined in is: X positive towards the tail, Y positive out the right side, Z
96 positive upwards. The locations of the various parts are given in inches in
98 <li>The vector giving the location of the gear (relative to the cg) is
99 rotated 180 degrees about the Y axis to put the coordinates in body frame (X
100 positive forwards, Y positive out the right side, Z positive downwards, with
101 the origin at the cg). The lengths are also now given in feet.</li>
102 <li>The new gear location is now transformed to the local coordinate frame
103 using the body-to-local matrix. (Mb2l).</li>
104 <li>Knowing the location of the center of gravity relative to the ground
105 (height above ground level or AGL) now enables gear deflection to be
106 calculated. The gear compression value is the local frame gear Z location
107 value minus the height AGL. [Currently, we make the assumption that the gear
108 is oriented - and the deflection occurs in - the Z axis only. Additionally,
109 the vector to the landing gear is currently not modified - which would
110 (correctly) move the point of contact to the actual compressed-gear point of
111 contact. Eventually, articulated gear may be modeled, but initially an
112 effort must be made to model a generic system.] As an example, say the
113 aircraft left main gear location (in local coordinates) is Z = 3 feet
114 (positive) and the height AGL is 2 feet. This tells us that the gear is
115 compressed 1 foot.</li>
116 <li>If the gear is compressed, a Weight-On-Wheels (WOW) flag is set.</li>
117 <li>With the compression length calculated, the compression velocity may now
118 be calculated. This will be used to determine the damping force in the
119 strut. The aircraft rotational rate is multiplied by the vector to the wheel
120 to get a wheel velocity in body frame. That velocity vector is then
121 transformed into the local coordinate frame.</li>
122 <li>The aircraft cg velocity in the local frame is added to the
123 just-calculated wheel velocity (due to rotation) to get a total wheel
124 velocity in the local frame.</li>
125 <li>The compression speed is the Z-component of the vector.</li>
126 <li>With the wheel velocity vector no longer needed, it is normalized and
127 multiplied by a -1 to reverse it. This will be used in the friction force
129 <li>Since the friction force takes place solely in the runway plane, the Z
130 coordinate of the normalized wheel velocity vector is set to zero.</li>
131 <li>The gear deflection force (the force on the aircraft acting along the
132 local frame Z axis) is now calculated given the spring and damper
133 coefficients, and the gear deflection speed and stroke length. Keep in mind
134 that gear forces always act in the negative direction (in both local and
135 body frames), and are not capable of generating a force in the positive
136 sense (one that would attract the aircraft to the ground). So, the gear
137 forces are always negative - they are limited to values of zero or less. The
138 gear force is simply the negative of the sum of the spring compression
139 length times the spring coefficient and the gear velocity times the damping
141 <li>The lateral/directional force acting on the aircraft through the landing
143 gear (along the local frame X and Y axes) is calculated next. First, the
144 friction coefficient is multiplied by the recently calculated Z-force. This
145 is the friction force. It must be given direction in addition to magnitude.
146 We want the components in the local frame X and Y axes. From step 9, above,
147 the conditioned wheel velocity vector is taken and the X and Y parts are
148 multiplied by the friction force to get the X and Y components of friction.
150 <li>The wheel force in local frame is next converted to body frame.</li>
151 <li>The moment due to the gear force is calculated by multiplying r x F
152 (radius to wheel crossed into the wheel force). Both of these operands are
156 <h3>Configuration File Format:</h3>
158 <contact type="{BOGEY | STRUCTURE}" name="{string}">
159 <location unit="{IN | M}">
164 <orientation unit="{RAD | DEG}">
165 <pitch> {number} </pitch>
166 <roll> {number} </roll>
167 <yaw> {number} </yaw>
169 <static_friction> {number} </static_friction>
170 <dynamic_friction> {number} </dynamic_friction>
171 <rolling_friction> {number} </rolling_friction>
172 <spring_coeff unit="{LBS/FT | N/M}"> {number} </spring_coeff>
173 <damping_coeff [type="SQUARE"] unit="{LBS/FT/SEC | N/M/SEC}"> {number} </damping_coeff>
174 <damping_coeff_rebound [type="SQUARE"] unit="{LBS/FT/SEC | N/M/SEC}"> {number} </damping_coeff_rebound>
175 <max_steer unit="DEG"> {number | 0 | 360} </max_steer>
176 <brake_group> {NONE | LEFT | RIGHT | CENTER | NOSE | TAIL} </brake_group>
177 <retractable>{0 | 1}</retractable>
178 <table type="{CORNERING_COEFF}">
182 @author Jon S. Berndt
183 @version $Id: FGLGear.h,v 1.41 2010/09/22 11:33:40 jberndt Exp $
184 @see Richard E. McFarland, "A Standard Kinematic Model for Flight Simulation at
185 NASA-Ames", NASA CR-2497, January 1975
186 @see Barnes W. McCormick, "Aerodynamics, Aeronautics, and Flight Mechanics",
187 Wiley & Sons, 1979 ISBN 0-471-03032-5
188 @see W. A. Ragsdale, "A Generic Landing Gear Dynamics Model for LASRS++",
192 /*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
194 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
196 class FGLGear : public FGForce
199 /// Brake grouping enumerators
200 enum BrakeGroup {bgNone=0, bgLeft, bgRight, bgCenter, bgNose, bgTail };
201 /// Steering group membership enumerators
202 enum SteerType {stSteer, stFixed, stCaster};
203 /// Contact point type
204 enum ContactType {ctBOGEY, ctSTRUCTURE};
205 /// Report type enumerators
206 enum ReportType {erNone=0, erTakeoff, erLand};
208 enum DampType {dtLinear=0, dtSquare};
210 enum FrictionType {ftRoll=0, ftSide, ftDynamic};
212 @param el a pointer to the XML element that contains the CONTACT info.
213 @param Executive a pointer to the parent executive object
214 @param number integer identifier for this instance of FGLGear
216 FGLGear(Element* el, FGFDMExec* Executive, int number);
220 /// The Force vector for this gear
221 FGColumnVector3& GetBodyForces(void);
223 /// Gets the location of the gear in Body axes
224 FGColumnVector3& GetBodyLocation(void) { return vWhlBodyVec; }
225 double GetBodyLocation(int idx) const { return vWhlBodyVec(idx); }
227 FGColumnVector3& GetLocalGear(void) { return vLocalGear; }
228 double GetLocalGear(int idx) const { return vLocalGear(idx); }
230 /// Gets the name of the gear
231 string GetName(void) const {return name; }
232 /// Gets the Weight On Wheels flag value
233 bool GetWOW(void) const {return WOW; }
234 /// Gets the current compressed length of the gear in feet
235 double GetCompLen(void) const {return compressLength;}
236 /// Gets the current gear compression velocity in ft/sec
237 double GetCompVel(void) const {return compressSpeed; }
238 /// Gets the gear compression force in pounds
239 double GetCompForce(void) const {return StrutForce; }
240 double GetBrakeFCoeff(void) const {return BrakeFCoeff;}
242 /// Gets the current normalized tire pressure
243 double GetTirePressure(void) const { return TirePressureNorm; }
244 /// Sets the new normalized tire pressure
245 void SetTirePressure(double p) { TirePressureNorm = p; }
247 /// Sets the brake value in percent (0 - 100)
248 void SetBrake(double bp) {brakePct = bp;}
250 /// Sets the weight-on-wheels flag.
251 void SetWOW(bool wow) {WOW = wow;}
253 /** Set the console touchdown reporting feature
254 @param flag true turns on touchdown reporting, false turns it off */
255 void SetReport(bool flag) { ReportEnable = flag; }
256 /** Get the console touchdown reporting feature
257 @return true if reporting is turned on */
258 bool GetReport(void) const { return ReportEnable; }
259 double GetSteerNorm(void) const { return radtodeg/maxSteerAngle*SteerAngle; }
260 double GetDefaultSteerAngle(double cmd) const { return cmd*maxSteerAngle; }
261 double GetstaticFCoeff(void) const { return staticFCoeff; }
263 int GetBrakeGroup(void) const { return (int)eBrakeGrp; }
264 int GetSteerType(void) const { return (int)eSteerType; }
266 bool GetSteerable(void) const { return eSteerType != stFixed; }
267 bool GetRetractable(void) const { return isRetractable; }
268 bool GetGearUnitUp(void) const { return GearUp; }
269 bool GetGearUnitDown(void) const { return GearDown; }
270 double GetWheelRollForce(void) {
271 FGColumnVector3 vForce = mTGear.Transposed() * FGForce::GetBodyForces();
272 return vForce(eX)*cos(SteerAngle) + vForce(eY)*sin(SteerAngle); }
273 double GetWheelSideForce(void) {
274 FGColumnVector3 vForce = mTGear.Transposed() * FGForce::GetBodyForces();
275 return vForce(eY)*cos(SteerAngle) - vForce(eX)*sin(SteerAngle); }
276 double GetWheelRollVel(void) const { return vWhlVelVec(eX)*cos(SteerAngle)
277 + vWhlVelVec(eY)*sin(SteerAngle); }
278 double GetWheelSideVel(void) const { return vWhlVelVec(eY)*cos(SteerAngle)
279 - vWhlVelVec(eX)*sin(SteerAngle); }
280 double GetWheelSlipAngle(void) const { return WheelSlip; }
281 double GetWheelVel(int axis) const { return vWhlVelVec(axis);}
282 bool IsBogey(void) const { return (eContactType == ctBOGEY);}
283 double GetGearUnitPos(void);
284 double GetSteerAngleDeg(void) const { return radtodeg*SteerAngle; }
285 FGPropagate::LagrangeMultiplier* GetMultiplierEntry(int entry);
286 void SetLagrangeMultiplier(double lambda, int entry);
287 FGColumnVector3& UpdateForces(void);
293 static const FGMatrix33 Tb2s;
295 FGColumnVector3 vGearOrient;
296 FGColumnVector3 vWhlBodyVec;
297 FGColumnVector3 vLocalGear;
298 FGColumnVector3 vWhlVelVec, vLocalWhlVel; // Velocity of this wheel
299 FGColumnVector3 normal, cvel, vGroundNormal;
300 FGLocation contact, gearLoc;
301 FGTable *ForceY_Table;
307 double compressLength;
308 double compressSpeed;
309 double staticFCoeff, dynamicFCoeff, rollingFCoeff;
310 double Stiffness, Shape, Peak, Curvature; // Pacejka factors
316 double TakeoffDistanceTraveled;
317 double TakeoffDistanceTraveled50ft;
318 double LandingDistanceTraveled;
319 double MaximumStrutForce, StrutForce;
320 double MaximumStrutTravel;
323 double TirePressureNorm;
329 bool StartedGroundRun;
330 bool LandingReported;
331 bool TakeoffReported;
334 bool GearUp, GearDown;
339 std::string sSteerType;
340 std::string sBrakeGroup;
341 std::string sRetractable;
342 std::string sContactType;
344 BrakeGroup eBrakeGrp;
345 ContactType eContactType;
346 SteerType eSteerType;
348 DampType eDampTypeRebound;
349 double maxSteerAngle;
351 FGPropagate::LagrangeMultiplier LMultiplier[3];
353 FGAuxiliary* Auxiliary;
354 FGPropagate* Propagate;
356 FGMassBalance* MassBalance;
357 FGGroundReactions* GroundReactions;
359 void ComputeRetractionState(void);
360 void ComputeBrakeForceCoefficient(void);
361 void ComputeSteeringAngle(void);
362 void ComputeSlipAngle(void);
363 void ComputeSideForceCoefficient(void);
364 void ComputeVerticalStrutForce(void);
365 void ComputeGroundCoordSys(void);
366 void ComputeJacobian(const FGColumnVector3& vWhlContactVec);
367 void CrashDetect(void);
368 void InitializeReporting(void);
369 void ResetReporting(void);
370 void ReportTakeoffOrLanding(void);
371 void Report(ReportType rt);
372 void Debug(int from);
376 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%