1 /*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
7 ------------- Copyright (C) 1999 Jon S. Berndt (jsb@hal-pc.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 <FGJSBBase.h>
42 #include <FGFDMExec.h>
43 #include <input_output/FGXMLElement.h>
44 #include <math/FGColumnVector3.h>
45 #include <math/FGTable.h>
48 /*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
50 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
52 #define ID_LGEAR "$Id$"
54 /*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
56 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
67 /*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
69 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
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>Steerability attribute {one of STEERABLE | FIXED | CASTERED}</li>
89 <li>Brake Group Membership {one of LEFT | CENTER | RIGHT | NOSE | TAIL | NONE}</li>
90 <li>Max Steer Angle, in degrees</li>
93 <h3>Algorithm and Approach to Modeling</h3>
95 <li>Find the location of the uncompressed landing gear relative to the CG of
96 the aircraft. Remember, the structural coordinate frame that the aircraft is
97 defined in is: X positive towards the tail, Y positive out the right side, Z
98 positive upwards. The locations of the various parts are given in inches in
100 <li>The vector giving the location of the gear (relative to the cg) is
101 rotated 180 degrees about the Y axis to put the coordinates in body frame (X
102 positive forwards, Y positive out the right side, Z positive downwards, with
103 the origin at the cg). The lengths are also now given in feet.</li>
104 <li>The new gear location is now transformed to the local coordinate frame
105 using the body-to-local matrix. (Mb2l).</li>
106 <li>Knowing the location of the center of gravity relative to the ground
107 (height above ground level or AGL) now enables gear deflection to be
108 calculated. The gear compression value is the local frame gear Z location
109 value minus the height AGL. [Currently, we make the assumption that the gear
110 is oriented - and the deflection occurs in - the Z axis only. Additionally,
111 the vector to the landing gear is currently not modified - which would
112 (correctly) move the point of contact to the actual compressed-gear point of
113 contact. Eventually, articulated gear may be modeled, but initially an
114 effort must be made to model a generic system.] As an example, say the
115 aircraft left main gear location (in local coordinates) is Z = 3 feet
116 (positive) and the height AGL is 2 feet. This tells us that the gear is
117 compressed 1 foot.</li>
118 <li>If the gear is compressed, a Weight-On-Wheels (WOW) flag is set.</li>
119 <li>With the compression length calculated, the compression velocity may now
120 be calculated. This will be used to determine the damping force in the
121 strut. The aircraft rotational rate is multiplied by the vector to the wheel
122 to get a wheel velocity in body frame. That velocity vector is then
123 transformed into the local coordinate frame.</li>
124 <li>The aircraft cg velocity in the local frame is added to the
125 just-calculated wheel velocity (due to rotation) to get a total wheel
126 velocity in the local frame.</li>
127 <li>The compression speed is the Z-component of the vector.</li>
128 <li>With the wheel velocity vector no longer needed, it is normalized and
129 multiplied by a -1 to reverse it. This will be used in the friction force
131 <li>Since the friction force takes place solely in the runway plane, the Z
132 coordinate of the normalized wheel velocity vector is set to zero.</li>
133 <li>The gear deflection force (the force on the aircraft acting along the
134 local frame Z axis) is now calculated given the spring and damper
135 coefficients, and the gear deflection speed and stroke length. Keep in mind
136 that gear forces always act in the negative direction (in both local and
137 body frames), and are not capable of generating a force in the positive
138 sense (one that would attract the aircraft to the ground). So, the gear
139 forces are always negative - they are limited to values of zero or less. The
140 gear force is simply the negative of the sum of the spring compression
141 length times the spring coefficient and the gear velocity times the damping
143 <li>The lateral/directional force acting on the aircraft through the landing
145 gear (along the local frame X and Y axes) is calculated next. First, the
146 friction coefficient is multiplied by the recently calculated Z-force. This
147 is the friction force. It must be given direction in addition to magnitude.
148 We want the components in the local frame X and Y axes. From step 9, above,
149 the conditioned wheel velocity vector is taken and the X and Y parts are
150 multiplied by the friction force to get the X and Y components of friction.
152 <li>The wheel force in local frame is next converted to body frame.</li>
153 <li>The moment due to the gear force is calculated by multiplying r x F
154 (radius to wheel crossed into the wheel force). Both of these operands are
158 <h3>Configuration File Format:</h3>
160 <contact type="{BOGEY | STRUCTURE}" name="{string}">
161 <location unit="{IN | M}">
166 <static_friction> {number} </static_friction>
167 <dynamic_friction> {number} </dynamic_friction>
168 <rolling_friction> {number} </rolling_friction>
169 <spring_coeff unit="{LBS/FT | N/M}"> {number} </spring_coeff>
170 <damping_coeff unit="{LBS/FT/SEC | N/M/SEC}"> {number} </damping_coeff>
171 <damping_coeff_rebound unit="{LBS/FT/SEC | N/M/SEC}"> {number} </damping_coeff_rebound>
172 <max_steer unit="DEG"> {number | 0 | 360} </max_steer>
173 <brake_group> {NONE | LEFT | RIGHT | CENTER | NOSE | TAIL} </brake_group>
174 <retractable>{0 | 1}</retractable>
175 <table type="{CORNERING_COEFF}">
177 <relaxation_velocity>
178 <rolling unit="{FT/SEC | KTS | M/S}"> {number} </rolling>
179 <side unit="{FT/SEC | KTS | M/S}"> {number} </side>
180 </relaxation_velocity>
182 <rolling> {number} </rolling>
183 <side> {number} </side>
185 <wheel_slip_filter> {number} </wheel_slip_filter>
188 @author Jon S. Berndt
190 @see Richard E. McFarland, "A Standard Kinematic Model for Flight Simulation at
191 NASA-Ames", NASA CR-2497, January 1975
192 @see Barnes W. McCormick, "Aerodynamics, Aeronautics, and Flight Mechanics",
193 Wiley & Sons, 1979 ISBN 0-471-03032-5
194 @see W. A. Ragsdale, "A Generic Landing Gear Dynamics Model for LASRS++",
198 /*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
200 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
202 class FGLGear : public FGJSBBase
205 /// Brake grouping enumerators
206 enum BrakeGroup {bgNone=0, bgLeft, bgRight, bgCenter, bgNose, bgTail };
207 /// Steering group membership enumerators
208 enum SteerType {stSteer, stFixed, stCaster};
209 /// Contact point type
210 enum ContactType {ctBOGEY, ctSTRUCTURE, ctUNKNOWN};
211 /// Report type enumerators
212 enum ReportType {erNone=0, erTakeoff, erLand};
214 @param el a pointer to the XML element that contains the CONTACT info.
215 @param Executive a pointer to the parent executive object
216 @param number integer identifier for this instance of FGLGear
218 FGLGear(Element* el, FGFDMExec* Executive, int number);
220 @param lgear a reference to an existing FGLGear object */
221 FGLGear(const FGLGear& lgear);
226 /// The Force vector for this gear
227 FGColumnVector3& Force(void);
228 /// The Moment vector for this gear
229 FGColumnVector3& Moment(void) {return vMoment;}
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 inline string GetName(void) const {return name; }
240 /// Gets the Weight On Wheels flag value
241 inline bool GetWOW(void) const {return WOW; }
242 /// Gets the current compressed length of the gear in feet
243 inline double GetCompLen(void) const {return compressLength;}
244 /// Gets the current gear compression velocity in ft/sec
245 inline double GetCompVel(void) const {return compressSpeed; }
246 /// Gets the gear compression force in pounds
247 inline double GetCompForce(void) const {return vForce(eZ); }
248 inline double GetBrakeFCoeff(void) const {return BrakeFCoeff;}
250 /// Gets the current normalized tire pressure
251 inline double GetTirePressure(void) const { return TirePressureNorm; }
252 /// Sets the new normalized tire pressure
253 inline void SetTirePressure(double p) { TirePressureNorm = p; }
255 /// Sets the brake value in percent (0 - 100)
256 inline void SetBrake(double bp) {brakePct = bp;}
258 /** Set the console touchdown reporting feature
259 @param flag true turns on touchdown reporting, false turns it off */
260 inline void SetReport(bool flag) { ReportEnable = flag; }
261 /** Get the console touchdown reporting feature
262 @return true if reporting is turned on */
263 inline bool GetReport(void) const { return ReportEnable; }
264 double GetSteerNorm(void) const { return radtodeg/maxSteerAngle*SteerAngle; }
265 double GetDefaultSteerAngle(double cmd) const { return cmd*maxSteerAngle; }
266 double GetstaticFCoeff(void) const { return staticFCoeff; }
268 inline int GetBrakeGroup(void) const { return (int)eBrakeGrp; }
269 inline int GetSteerType(void) const { return (int)eSteerType; }
271 inline double GetZPosition(void) const { return vXYZ(3); }
272 inline void SetZPosition(double z) { vXYZ(3) = z; }
274 bool GetSteerable(void) const { return eSteerType != stFixed; }
275 inline bool GetRetractable(void) const { return isRetractable; }
276 inline bool GetGearUnitUp(void) const { return GearUp; }
277 inline bool GetGearUnitDown(void) const { return GearDown; }
278 inline double GetWheelSideForce(void) const { return SideForce; }
279 inline double GetWheelRollForce(void) const { return RollingForce; }
280 inline double GetWheelSideVel(void) const { return SideWhlVel; }
281 inline double GetWheelRollVel(void) const { return RollingWhlVel; }
282 inline double GetBodyXForce(void) const { return vLocalForce(eX); }
283 inline double GetBodyYForce(void) const { return vLocalForce(eY); }
284 inline double GetWheelSlipAngle(void) const { return WheelSlip; }
285 double GetWheelVel(int axis) const { return vWhlVelVec(axis);}
286 bool IsBogey(void) const { return (eContactType == ctBOGEY);}
287 double GetGearUnitPos(void);
293 FGColumnVector3 vXYZ;
294 FGColumnVector3 vMoment;
295 FGColumnVector3 vWhlBodyVec;
296 FGColumnVector3 vLocalGear;
297 FGColumnVector3 vForce;
298 FGColumnVector3 last_vForce; // remove this
299 FGColumnVector3 vLocalForce;
300 FGColumnVector3 vWhlVelVec; // Velocity of this wheel (Local)
301 FGColumnVector3 normal, cvel;
302 FGColumnVector3 prevOut, prevIn;
303 FGLocation contact, gearLoc;
304 FGTable *ForceY_Table;
310 double compressLength;
311 double compressSpeed;
312 double staticFCoeff, dynamicFCoeff, rollingFCoeff;
318 double TakeoffDistanceTraveled;
319 double TakeoffDistanceTraveled50ft;
320 double LandingDistanceTraveled;
321 double MaximumStrutForce;
322 double MaximumStrutTravel;
323 double SideWhlVel, RollingWhlVel;
324 double RollingForce, SideForce, FCoeff;
328 double TirePressureNorm;
329 double SinWheel, CosWheel;
335 bool StartedGroundRun;
336 bool LandingReported;
337 bool TakeoffReported;
340 bool GearUp, GearDown;
348 BrakeGroup eBrakeGrp;
349 ContactType eContactType;
350 SteerType eSteerType;
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
360 FGAircraft* Aircraft;
361 FGPropagate* Propagate;
362 FGAuxiliary* Auxiliary;
364 FGMassBalance* MassBalance;
366 void ComputeRetractionState(void);
367 void ComputeBrakeForceCoefficient(void);
368 void ComputeSteeringAngle(void);
369 void ComputeSlipAngle(void);
370 void ComputeSideForceCoefficient(void);
371 void ComputeVerticalStrutForce(void);
372 void CrashDetect(void);
373 void InitializeReporting(void);
374 void ResetReporting(void);
375 void ReportTakeoffOrLanding(void);
376 void Report(ReportType rt);
377 void Debug(int from);
380 #include "FGAircraft.h"
381 #include "FGPropagate.h"
382 #include "FGAuxiliary.h"
384 #include "FGMassBalance.h"
387 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%