Airfoil.cs

Airfoil.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using DG.Tweening;

public class Airfoil
    : MonoBehaviour
{
    [Range(0.0f, 5.0f)]
    public float liftCoefficient = 1.0f;
    [Range(0.0f, 5.0f)]
    public float dragCoefficient = 0.25f;

    // used to superficially decrease thrust 
    [ReadOnly]
    public float thrustOffset = 0.0f;

    [Range(0.5f, 4.0f)]
    public float velocitySquareFactor = 2.0f;

    // 0.0f = flat plane, so when flying into wind there is 0 drag
    // 1.0f = cube, so when flying into the wind there is still 100% drag, in addition to lift
    public float aerodynamicRatio = 0.3f;

    private Rigidbody targetBody = null;

    public void OnEnable()
    {
        targetBody = GetComponent<Rigidbody>();
    }

    public void FixedUpdate()
    {
        var wind = Vector3.zero;

        var velocity = targetBody.velocity;
        var velocityDir = targetBody.velocity.SafeNormalize();
        var velocityLen = targetBody.velocity.SafeMagnitude();
        var velocitySq = Mathf.Pow(velocityLen, velocitySquareFactor);

        var windRelative = wind - targetBody.velocity;
        var windRelativeDir = windRelative.SafeNormalize();
        var windRelativeForce = windRelative.SafeMagnitude();
        var windRelativeForceSq = windRelativeForce * windRelativeForce;

        var coeffDrag = Mathf.Abs(Vector3.Dot(targetBody.transform.up, velocityDir));
        var coeffLift = -Vector3.Dot(targetBody.transform.up, velocityDir);

        var dragDirection = -velocityDir;

        coeffDrag = Mathf.Max(coeffDrag, aerodynamicRatio);

        // handle thrusting
        coeffLift = coeffLift * Mathf.Lerp(1.0f, 0.6f, thrustOffset);
        coeffDrag = coeffDrag * Mathf.Lerp(1.0f, 0.6f, thrustOffset);

        // i know not physically correct, but feels good in-game
        var liftDirection = targetBody.transform.up;

        var liftForce = coeffLift * liftDirection * velocitySq * liftCoefficient;
        var dragForce = coeffDrag * dragDirection * velocitySq * dragCoefficient;

        targetBody.AddForce(liftForce, ForceMode.Acceleration);
        targetBody.AddForce(dragForce, ForceMode.Acceleration);

        //Debug.DrawLine(transform.position, transform.position + liftForce * 5.0f, Color.green, 0.1f);
        //Debug.DrawLine(transform.position, transform.position + dragForce * 5.0f, Color.red, 0.1f);
    }
}