uavsim.flightdynamicsmodel
Class AircraftModel

java.lang.Object
  uavsim.flightdynamicsmodel.AircraftModel

public class AircraftModel
extends java.lang.Object

Defines a fixed-wing aircraft as a finite-element model consisting of ailerons, flaps, an elevator, a rudder, and a fuselage. It is derived from Physics for Game Developers by David Bourg.

Author:

Dan Tappan [18.08.11]

Field Summary

(package private) AircraftRigidBody	_airplane the rigid-body model of the aircraft
private double	_airspeedPrevious zzz
private Vector	_attitudeEulerPrevious the attitude velocity in Euler angles zzz
private AircraftModelController	_controller the controller interface that provides input to the flight-control surfaces
(package private) AircraftRigidBodyElement[]	_elements the mass, inertia, and lifting-surface properties of the rigid body
(package private) boolean	_isStalled whether any part of the wing is stalled
(package private) boolean	_isStalling whether any part of the wing is nearing a stall
(package private) double	_liftCoefficient the average coefficient of lift of the wing based on the flaps and ailerons
(package private) int	_stepNumber the current simulation step number
(package private) double	_thrust the thrust force in RPM, ranging from THRUST_MIN to THRUST_MAX, inclusively.
(package private) Vector	_thrustVector the thrust vector, which is assumed to act through the center of gravity of the plane
(package private) Time	_timeAbsolute the absolute running time in seconds
(package private) Time	_timeRelative the relative time in seconds from the previous simulation update
private Vector	_velocityPrevious the attitude velocity in Euler angles zzz
(package private) static int	ELEMENT_AILERON_PORT the index of the finite element for the port aileron
(package private) static int	ELEMENT_AILERON_STARBOARD the index of the finite element for the starboard aileron
(package private) static int	ELEMENT_ELEVATOR_PORT the index of the finite element for the port elevator.
(package private) static int	ELEMENT_ELEVATOR_STARBOARD the index of the finite element for the starboard elevator.
(package private) static int	ELEMENT_FLAP_PORT the index of the finite element for the port flap.
(package private) static int	ELEMENT_FLAP_STARBOARD the index of the finite element for the starboard flap.
(package private) static int	ELEMENT_FUSELAGE the index of the finite element for the fuselage
(package private) static int	ELEMENT_RUDDER the index of the finite element for the combined vertical stabilizer and rudder
static double	ENCODED_UTM_TO_INTERNAL_SCALE the conversion factor between the UTM (Universal Transverse Mercator latitude/longitude) system of the world coordinates and the internal system for the flight-dynamics model zzz??? not quite; it's a scale on the UTM __encoding__
private static double	G the gravitational acceleration constant is feet per second squared
static double	IMMINENT_STALL_LIFT_COEFFICIENT the coefficient of lift corresponding to an imminent stall
private static double	RHO the air density (units to be determined zzz???; see page 130)

Constructor Summary

AircraftModel(CoordinateWorld3D position, AttitudeYaw heading, Airspeed airspeed, RevolutionsPerMinute rpm)
Creates an aircraft model.

Method Summary

private void	calculateAirspeedAcceleration() Calculates the instantaneous change in position per second squared.
private void	calculateAttitudeVelocityAndAcceleration() Calculates the instantaneous change in attitude in degrees per second.
private double	calculateCoefficientOfDragGeneral(double angleOfAttack, int controlSurfacePosition) Calculates the coefficient of drag on a horizontal control surface (flap, aileron, or elevator).
private double	calculateCoefficientOfDragRudder(double angleOfAttack) Calculates the coefficient of drag on a combined vertical stabilizer and rudder.
private double	calculateCoefficientOfLiftGeneral(double angleOfAttack, int controlSurfacePosition) Calculates the coefficient of lift on a horizontal control surface (flap, aileron, or elevator).
private double	calculateCoefficientOfLiftRudder(double angleOfAttack) Calculates the coefficient of lift on a combined vertical stabilizer and rudder.
private void	calculateLoads() Calculates all the forces and moments acting on the plane based on its current state.
private void	calculatePositionAcceleration() Calculates the instantaneous change in position per second squared.
private double	clamp(double value) Clamps a value to the interval [-1,+1].
private void	defineFiniteElements() Defines the discrete finite elements that together form the rigid-body model of the aircraft.
AircraftModelController	getController() Returns the controller interface that provides input to the flight-control surfaces.
private void	initialize(Vector position, double angleYaw, double airspeed, double rpm) Initializes the state of the airplane as indicated and configures its finite-element model.
private double	interpolate(double domainValue, double[] domain, double[] range, double offDomainValue) Interpolates a value in a two-dimensional table.
void	update(double deltaTime) Updates the simulation as a discrete-event time step by using Euler's method of approximation.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

_airplane

final AircraftRigidBody _airplane

the rigid-body model of the aircraft

_airspeedPrevious

private double _airspeedPrevious

zzz

_attitudeEulerPrevious

private Vector _attitudeEulerPrevious

the attitude velocity in Euler angles zzz

_controller

private final AircraftModelController _controller

the controller interface that provides input to the flight-control surfaces

_elements

final AircraftRigidBodyElement[] _elements

the mass, inertia, and lifting-surface properties of the rigid body

_isStalled

boolean _isStalled

whether any part of the wing is stalled

_isStalling

boolean _isStalling

whether any part of the wing is nearing a stall

_liftCoefficient

double _liftCoefficient

the average coefficient of lift of the wing based on the flaps and ailerons

_stepNumber

int _stepNumber

the current simulation step number

_thrust

double _thrust

the thrust force in RPM, ranging from THRUST_MIN to THRUST_MAX, inclusively. Technically, thrust is a function of RPM, but for simplicity, they are considered equivalent for this model because the thrust range in pounds conveniently corresponds to the RPM range

_thrustVector

Vector _thrustVector

the thrust vector, which is assumed to act through the center of gravity of the plane

_timeAbsolute

Time _timeAbsolute

the absolute running time in seconds

_timeRelative

Time _timeRelative

the relative time in seconds from the previous simulation update

_velocityPrevious

private Vector _velocityPrevious

the attitude velocity in Euler angles zzz

ELEMENT_AILERON_PORT

static final int ELEMENT_AILERON_PORT

the index of the finite element for the port aileron

See Also:

Constant Field Values

ELEMENT_AILERON_STARBOARD

static final int ELEMENT_AILERON_STARBOARD

the index of the finite element for the starboard aileron

See Also:

Constant Field Values

ELEMENT_ELEVATOR_PORT

static final int ELEMENT_ELEVATOR_PORT

the index of the finite element for the port elevator. Both elevators are always synchronized

See Also:

Constant Field Values

ELEMENT_ELEVATOR_STARBOARD

static final int ELEMENT_ELEVATOR_STARBOARD

the index of the finite element for the starboard elevator. Both elevators are always synchronized

See Also:

Constant Field Values

ELEMENT_FLAP_PORT

static final int ELEMENT_FLAP_PORT

the index of the finite element for the port flap. Both flaps are always synchronized

See Also:

Constant Field Values

ELEMENT_FLAP_STARBOARD

static final int ELEMENT_FLAP_STARBOARD

the index of the finite element for the starboard flap. Both flaps are always synchronized

See Also:

Constant Field Values

ELEMENT_FUSELAGE

static final int ELEMENT_FUSELAGE

the index of the finite element for the fuselage

See Also:

Constant Field Values

ELEMENT_RUDDER

static final int ELEMENT_RUDDER

the index of the finite element for the combined vertical stabilizer and rudder

See Also:

Constant Field Values

ENCODED_UTM_TO_INTERNAL_SCALE

public static final double ENCODED_UTM_TO_INTERNAL_SCALE

the conversion factor between the UTM (Universal Transverse Mercator latitude/longitude) system of the world coordinates and the internal system for the flight-dynamics model zzz??? not quite; it's a scale on the UTM __encoding__

See Also:

Constant Field Values

G

private static final double G

the gravitational acceleration constant is feet per second squared

See Also:

Constant Field Values

IMMINENT_STALL_LIFT_COEFFICIENT

public static final double IMMINENT_STALL_LIFT_COEFFICIENT

the coefficient of lift corresponding to an imminent stall

See Also:

Constant Field Values

RHO

private static final double RHO

the air density (units to be determined zzz???; see page 130)

See Also:

Constant Field Values

Constructor Detail

AircraftModel

public AircraftModel(CoordinateWorld3D position,
                     AttitudeYaw heading,
                     Airspeed airspeed,
                     RevolutionsPerMinute rpm)

Creates an aircraft model.

Parameters:

position - - the position

heading - - the heading

airspeed - - the airspeed

rpm - - the thrust in revolutions per minute. The range depends on the model configuration, but 0 to 2500 is reasonable

Method Detail

calculateAirspeedAcceleration

private void calculateAirspeedAcceleration()

Calculates the instantaneous change in position per second squared. zzz

calculateAttitudeVelocityAndAcceleration

private void calculateAttitudeVelocityAndAcceleration()

Calculates the instantaneous change in attitude in degrees per second. zzz

calculateCoefficientOfDragGeneral

private double calculateCoefficientOfDragGeneral(double angleOfAttack,
                                                 int controlSurfacePosition)

Calculates the coefficient of drag on a horizontal control surface (flap, aileron, or elevator). The drag table is based on a cambered airfoil with a plain trailing-edge flap having a +/- 15 degree deflection. Proportional input is not implemented yet.

Parameters:

angleOfAttack - - the angle of attack in degrees

controlSurfacePosition - - the control-surface position (-1,0,+1 for up, neutral, down, respectively)

Returns:

the coefficient

calculateCoefficientOfDragRudder

private double calculateCoefficientOfDragRudder(double angleOfAttack)

Calculates the coefficient of drag on a combined vertical stabilizer and rudder. The drag table is based on a symmetric (no camber) airfoil without flaps. In other words, the entire stabilizer rotates.

Parameters:

angleOfAttack - - the angle of attack in degrees

Returns:

the coefficient

calculateCoefficientOfLiftGeneral

private double calculateCoefficientOfLiftGeneral(double angleOfAttack,
                                                 int controlSurfacePosition)

Calculates the coefficient of lift on a horizontal control surface (flap, aileron, or elevator). The lift table is based on a cambered airfoil with a plain trailing-edge flap having a +/- 15 degree deflection. Proportional input is not implemented yet.

Parameters:

angleOfAttack - - the angle of attack in degrees

controlSurfacePosition - - (-1,0,+1 for up, neutral, down, respectively)

Returns:

the coefficient

calculateCoefficientOfLiftRudder

private double calculateCoefficientOfLiftRudder(double angleOfAttack)

Calculates the coefficient of lift on a combined vertical stabilizer and rudder. The lift table is based on a symmetric (no camber) airfoil without flaps. In other words, the entire stabilizer rotates.

Parameters:

angleOfAttack - - the angle of attack in degrees

Returns:

the coefficient

calculateLoads

private void calculateLoads()

Calculates all the forces and moments acting on the plane based on its current state.

calculatePositionAcceleration

private void calculatePositionAcceleration()

Calculates the instantaneous change in position per second squared. zzz

clamp

private double clamp(double value)

Clamps a value to the interval [-1,+1].

Parameters:

value - - the value

Returns:

the clamped value

defineFiniteElements

private void defineFiniteElements()

Defines the discrete finite elements that together form the rigid-body model of the aircraft.

getController

public AircraftModelController getController()

Returns the controller interface that provides input to the flight-control surfaces.

Returns:

the controller

initialize

private void initialize(Vector position,
                        double angleYaw,
                        double airspeed,
                        double rpm)

Initializes the state of the airplane as indicated and configures its finite-element model.

Parameters:

position - - encoded longitude as x, encoded latitude as y, and altitude as z in feet

angleYaw - - the yaw in mathematical degrees

airspeed - - the airspeed in feet per second

rpm - - the rpm

interpolate

private double interpolate(double domainValue,
                           double[] domain,
                           double[] range,
                           double offDomainValue)

Interpolates a value in a two-dimensional table. This is not a general-purpose interpolator because of the way it handles off-scale conditions.

Parameters:

domainValue - - the independent value

domain - - the domain of the independent value

range - - the range of the dependent value to find

offDomainValue - - the value to return if the independent value is off-scale low or high

Returns:

the interpolated dependent value

update

public void update(double deltaTime)

Updates the simulation as a discrete-event time step by using Euler's method of approximation.

Parameters:

deltaTime - - the change in time in seconds from the previous update. A reasonable value is around 0.0025.