-/*******************************************************************************
+/*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Header: FGLGear.h
Author: Jon S. Berndt
--------------------------------------------------------------------------------
11/18/99 JSB Created
-********************************************************************************
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
SENTRY
-*******************************************************************************/
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
#ifndef FGLGEAR_H
#define FGLGEAR_H
-/*******************************************************************************
-COMMENTS, REFERENCES, and NOTES
-********************************************************************************
-
-[1] Cooke, Zyda, Pratt, and McGhee, "NPSNET: Flight Simulation Dynamic Modeling
- Using Quaternions", Presence, Vol. 1, No. 4, pp. 404-420 Naval Postgraduate
- School, January 1994
-[2] D. M. Henderson, "Euler Angles, Quaternions, and Transformation Matrices",
- JSC 12960, July 1977
-[3] Richard E. McFarland, "A Standard Kinematic Model for Flight Simulation at
- NASA-Ames", NASA CR-2497, January 1975
-[4] Barnes W. McCormick, "Aerodynamics, Aeronautics, and Flight Mechanics",
- Wiley & Sons, 1979 ISBN 0-471-03032-5
-[5] Bernard Etkin, "Dynamics of Flight, Stability and Control", Wiley & Sons,
- 1982 ISBN 0-471-08936-2
-
-********************************************************************************
+/*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
INCLUDES
-*******************************************************************************/
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
#ifdef FGFS
# include <simgear/compiler.h>
#include "FGFDMExec.h"
#include "FGState.h"
-/*******************************************************************************
+/*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
DEFINITIONS
-*******************************************************************************/
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
#define ID_LGEAR "$Header"
-/*******************************************************************************
-CLASS DECLARATION
-*******************************************************************************/
+/*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+FORWARD DECLARATIONS
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
class FGAircraft;
class FGPosition;
class FGRotation;
+/*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+COMMENTS, REFERENCES, and NOTES [use "class documentation" below for API docs]
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+CLASS DOCUMENTATION
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
+
+/** Landing gear model.
+ Calculates forces and moments due to landing gear reactions. This is done in
+ several steps, and is dependent on what kind of gear is being modeled. Here
+ are the parameters that can be specified in the config file for modeling
+ landing gear:
+ <p>
+ <b><u>Physical Characteristics</u></b><br>
+ <ol>
+ <li>X, Y, Z location, in inches in structural coordinate frame</li>
+ <li>Spring constant, in lbs/ft</li>
+ <li>Damping coefficient, in lbs/ft/sec</li>
+ <li>Dynamic Friction Coefficient</li>
+ <li>Static Friction Coefficient</li>
+ </ol></p><p>
+ <b><u>Operational Properties</b></u><br>
+ <ol>
+ <li>Name</li>
+ <li>Steerability attribute {one of STEERABLE | FIXED | CASTERED}</li>
+ <li>Brake Group Membership {one of LEFT | CENTER | RIGHT | NOSE | TAIL | NONE}</li>
+ <li>Max Steer Angle, in degrees</li>
+ </ol></p>
+ <p>
+ <b><u>Algorithm and Approach to Modeling</u></b><br>
+ <ol>
+ <li>Find the location of the uncompressed landing gear relative to the CG of
+ the aircraft. Remember, the structural coordinate frame that the aircraft is
+ defined in is: X positive towards the tail, Y positive out the right side, Z
+ positive upwards. The locations of the various parts are given in inches in
+ the config file.</li>
+ <li>The vector giving the location of the gear (relative to the cg) is
+ rotated 180 degrees about the Y axis to put the coordinates in body frame (X
+ positive forwards, Y positive out the right side, Z positive downwards, with
+ the origin at the cg). The lengths are also now given in feet.</li>
+ <li>The new gear location is now transformed to the local coordinate frame
+ using the body-to-local matrix. (Mb2l).</li>
+ <li>Knowing the location of the center of gravity relative to the ground
+ (height above ground level or AGL) now enables gear deflection to be
+ calculated. The gear compression value is the local frame gear Z location
+ value minus the height AGL. [Currently, we make the assumption that the gear
+ is oriented - and the deflection occurs in - the Z axis only. Additionally,
+ the vector to the landing gear is currently not modified - which would
+ (correctly) move the point of contact to the actual compressed-gear point of
+ contact. Eventually, articulated gear may be modeled, but initially an
+ effort must be made to model a generic system.] As an example, say the
+ aircraft left main gear location (in local coordinates) is Z = 3 feet
+ (positive) and the height AGL is 2 feet. This tells us that the gear is
+ compressed 1 foot.</li>
+ <li>If the gear is compressed, a Weight-On-Wheels (WOW) flag is set.</li>
+ <li>With the compression length calculated, the compression velocity may now
+ be calculated. This will be used to determine the damping force in the
+ strut. The aircraft rotational rate is multiplied by the vector to the wheel
+ to get a wheel velocity in body frame. That velocity vector is then
+ transformed into the local coordinate frame.</li>
+ <li>The aircraft cg velocity in the local frame is added to the
+ just-calculated wheel velocity (due to rotation) to get a total wheel
+ velocity in the local frame.</li>
+ <li>The compression speed is the Z-component of the vector.</li>
+ <li>With the wheel velocity vector no longer needed, it is normalized and
+ multiplied by a -1 to reverse it. This will be used in the friction force
+ calculation.</li>
+ <li>Since the friction force takes place solely in the runway plane, the Z
+ coordinate of the normalized wheel velocity vector is set to zero.</li>
+ <li>The gear deflection force (the force on the aircraft acting along the
+ local frame Z axis) is now calculated given the spring and damper
+ coefficients, and the gear deflection speed and stroke length. Keep in mind
+ that gear forces always act in the negative direction (in both local and
+ body frames), and are not capable of generating a force in the positive
+ sense (one that would attract the aircraft to the ground). So, the gear
+ forces are always negative - they are limited to values of zero or less. The
+ gear force is simply the negative of the sum of the spring compression
+ length times the spring coefficient and the gear velocity times the damping
+ coefficient.</li>
+ <li>The lateral/directional force acting on the aircraft through the landing
+ gear (along the local frame X and Y axes) is calculated next. First, the
+ friction coefficient is multiplied by the recently calculated Z-force. This
+ is the friction force. It must be given direction in addition to magnitude.
+ We want the components in the local frame X and Y axes. From step 9, above,
+ the conditioned wheel velocity vector is taken and the X and Y parts are
+ multiplied by the friction force to get the X and Y components of friction.
+ </li>
+ <li>The wheel force in local frame is next converted to body frame.</li>
+ <li>The moment due to the gear force is calculated by multiplying r x F
+ (radius to wheel crossed into the wheel force). Both of these operands are
+ in body frame.</li>
+ </ol>
+ @author Jon S. Berndt
+ @version $Id$
+ @see Richard E. McFarland, "A Standard Kinematic Model for Flight Simulation at
+ NASA-Ames", NASA CR-2497, January 1975
+ @see Barnes W. McCormick, "Aerodynamics, Aeronautics, and Flight Mechanics",
+ Wiley & Sons, 1979 ISBN 0-471-03032-5
+*/
+
+/*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+CLASS DECLARATION
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
+
class FGLGear
{
public:
- FGLGear(FGConfigFile*, FGFDMExec*);
+ /// Brake grouping enumerators
+ enum eBrakeGroup {bgNone=0, bgLeft, bgRight, bgCenter, bgNose, bgTail };
+ /** Constructor
+ @param Executive a pointer to the parent executive object
+ @param File a pointer to the config file instance */
+ FGLGear(FGConfigFile* File, FGFDMExec* Executive);
+ /** Constructor
+ @param lgear a reference to an existing FGLGear object */
+ FGLGear(const FGLGear& lgear);
+ /// Destructor
~FGLGear(void);
+
+ /// The Force vector for this gear
FGColumnVector Force(void);
+ /// The Moment vector for this gear
FGColumnVector Moment(void) {return vMoment;}
+ /// Gets the location of the gear in Body axes
FGColumnVector GetBodyLocation(void) { return vWhlBodyVec; }
+
+ FGColumnVector GetLocalGear(void) { return vLocalGear; }
+ /// Gets the name of the gear
inline string GetName(void) {return name; }
+ /// Gets the Weight On Wheels flag value
inline bool GetWOW(void) {return WOW; }
+ /// Gets the current compressed length of the gear in feet
inline float GetCompLen(void) {return compressLength;}
+ /// Gets the current gear compression velocity in ft/sec
inline float GetCompVel(void) {return compressSpeed; }
+ /// Gets the gear compression force in pounds
inline float GetCompForce(void) {return Force()(3); }
+ /// Sets the brake value in percent (0 - 100)
inline void SetBrake(double bp) {brakePct = bp;}
-
- inline void SetReport(bool bb) { ReportEnable=bb; }
+
+ /** Set the console touchdown reporting feature
+ @param flag true turns on touchdown reporting, false turns it off */
+ inline void SetReport(bool flag) { ReportEnable = flag; }
+ /** Get the console touchdown reporting feature
+ @return true if reporting is turned on */
inline bool GetReport(void) { return ReportEnable; }
-
private:
enum {eX=1, eY, eZ};
FGColumnVector vXYZ;
FGColumnVector vMoment;
FGColumnVector vWhlBodyVec;
+ FGColumnVector vLocalGear;
float kSpring;
float bDamp;
float compressLength;
bool Reported;
bool ReportEnable;
string name;
- string BrakeType;
string SteerType;
- string GroupMember;
+ string BrakeGroup;
+ eBrakeGroup eBrakeGrp;
float maxSteerAngle;
FGFDMExec* Exec;
#include "FGPosition.h"
#include "FGRotation.h"
-/******************************************************************************/
+//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
#endif
projects / flightgear.git / blobdiff