Wing.java

package uk.co.flyingsquirrels.aero;

import org.jbox2d.common.Vec2;

import uk.co.flyingsquirrels.models.AirDataSource;
import uk.co.flyingsquirrels.models.Control;
import uk.co.flyingsquirrels.models.ControllableComponentTemplate;
import uk.co.flyingsquirrels.utils.MathUtils;

/**
 * Calculates lift/drag vectors and moments for an airfoil of a certain size
 */
public class Wing extends ControllableComponentTemplate {

	private static final float RHO = 1.2f;
	
	private final Airfoil airfoil;
	private final float wingArea;
	private final AirDataSource airData;

	private float incidence;
	
	private float lift;
	private float drag;
	private float moment;

	public Wing(Airfoil airfoil, float wingArea, float incidence, Vec2 localPosition, AirDataSource airData) {
		super(localPosition, null);
		this.airfoil = airfoil;
		this.wingArea = wingArea;
		this.incidence = incidence;
		this.airData = airData;
	}

	public Wing(Airfoil airfoil, float wingArea, float incidence, Vec2 localPosition, AirDataSource airData, Control control) {
		super(localPosition, control);
		this.airfoil = airfoil;
		this.wingArea = wingArea;
		this.incidence = incidence;
		this.airData = airData;
	}
	
	/**
	 * Returns the lift+drag vector perpendicular to the direction of airflow
	 */
	public Vec2 getForce() {
		return new Vec2(-drag, lift);
	}
	
	/**
	 * Returns the moment about 1/4 chord
	 */
	public float getMoment() {
		return moment;
	}
	
	public void updateInternal(float seconds) {
		if (getControl() != null) {
			incidence = getControl().getValue();
		}
		Vec2 v = airData.getVelocity();
		float qWingArea = 0.5f * getAirDensity() * v.lengthSquared() * wingArea;
		float pitch = airData.getPitch();
		float airflowDirection = MathUtils.clampAngle(Double.valueOf(Math.atan2(v.y, v.x)).floatValue());
		float alpha = MathUtils.clampAngle(pitch + incidence - airflowDirection);
		
		lift = Double.valueOf(airfoil.getCl(alpha) * qWingArea).floatValue();
		drag = Double.valueOf(airfoil.getCd(alpha) * qWingArea).floatValue();
		moment = Double.valueOf(airfoil.getCm(alpha) * qWingArea).floatValue();
	}
	
	private float getAirDensity() {
		airData.getAltitude(); // do something with this
		return RHO;
	}

}