void FixedUpdate()
{
/* Determine relative wind. */
Vector3 windDirection = atmosphere.WindVelocityAt(transform.position);
relativeVelocity = GetComponent <Rigidbody>().velocity - windDirection;
trueAirspeed = relativeVelocity.magnitude;
/* Determine angle of attack. (keep in mind that forward direction is the Up/Y axis, not Z) */
Vector3 forward = transform.TransformDirection(Vector3.up);
Vector3 right = transform.TransformDirection(Vector3.right);
Vector3 up = transform.TransformDirection(Vector3.down);
Vector3 horizontalRight = new Vector3(right.x, 0f, right.z);
angleOfAttackPitch = Mathx.AngleAroundAxis(forward, relativeVelocity, right);
angleOfAttackYaw = Mathx.AngleAroundAxis(right, relativeVelocity, up);
// Angle of attack falls off to 0 based on the amount of sideslip (not being aligned to direction of flight)
float alphaSideFalloff = Mathx.ClampAngle(angleOfAttackYaw + 90f, -360f, 360f, 180f);
alphaSideFalloff = sideFalloffCurve.Evaluate(alphaSideFalloff);
float airDensity = atmosphere.AirDensityAt(transform.position);
/* Determine lift around pitch axis based on angle of attack, using coefficient lookup. */
cLift = cLiftCurve.Evaluate(angleOfAttackPitch) * alphaSideFalloff;
lift = .5f * airDensity * Mathf.Pow(trueAirspeed, 2f) * surfaceArea * cLift * liftMultiplier;
// Determine lift vector as perpendicular to the relative airflow
liftVector = Vector3.Cross(relativeVelocity, right).normalized *lift;
/* Determine profile drag around the pitch axis. */
float cDrag = cDragCurve.Evaluate(angleOfAttackPitch);
drag = .5f * airDensity * trueAirspeed * trueAirspeed * surfaceArea * cDrag;
dragVector = -relativeVelocity.normalized * drag;
/* Add some simple lateral drag to minimize sideslip, convert a portion of it to forward speed like in Wipeout */
sideSlip = Vector3.Project(relativeVelocity, horizontalRight);
Vector3 sideSlipNegation = -sideSlip * 25f;
sideSlipNegation += forward * sideSlipNegation.magnitude * 0.65f;
/* Apply the forces. */
GetComponent <Rigidbody>().AddForceAtPosition(liftVector + dragVector + sideSlipNegation, transform.TransformPoint(centerOfPressure));
}