Unity(C#)で飛行機が滑空するような物理演算の方法教えてください。

        float direction = 40.0f; // 角度
        float speed = 30.0f; //スピード

                Vector2 v;
        v.x = Mathf.Cos(Mathf.Deg2Rad * direction) * speed;
        v.y = Mathf.Sin(Mathf.Deg2Rad * direction) * speed;
        GetComponent<Rigidbody2D>().velocity = v;

void FixedUpdate(){
    private float pyAngle;
    private Vector2 pyAngleV;
    private Vector2 pyAngleV2;


        if (transform.localEulerAngles.z > 0 && transform.localEulerAngles.z < 90) {

            GetComponent<Rigidbody2D>().AddForce(Vector2.left * (transform.localEulerAngles.z * GetComponent<Rigidbody2D>().velocity.y) / 80);

            if (GetComponent<Rigidbody2D> ().velocity.x > 22.0f) {
                GetComponent<Rigidbody2D> ().AddForce (Vector2.up * (transform.localEulerAngles.z * GetComponent<Rigidbody2D> ().velocity.x) / 20);
            }

//            pyAngleV.x = Mathf.Cos(Mathf.Deg2Rad * transform.localEulerAngles.z) * -((transform.localEulerAngles.z + GetComponent<Rigidbody2D>().velocity.y) / 2);
//            pyAngleV.y = Mathf.Sin(Mathf.Deg2Rad * transform.localEulerAngles.z) * ((transform.localEulerAngles.z + GetComponent<Rigidbody2D>().velocity.x) );
//            GetComponent<Rigidbody2D> ().AddForce (pyAngleV); //加算

        } else if (transform.localEulerAngles.z >= 270 && transform.localEulerAngles.z < 360) {

            pyAngle = (360.0f - transform.localEulerAngles.z); // 0 - 90

            GetComponent<Rigidbody2D>().AddForce(Vector2.right * -(transform.localEulerAngles.z * GetComponent<Rigidbody2D>().velocity.y) / 80);
            GetComponent<Rigidbody2D>().AddForce(Vector2.down * (transform.localEulerAngles.z * GetComponent<Rigidbody2D>().velocity.x) / 40);

//            pyAngleV2.x = Mathf.Cos(Mathf.Deg2Rad * transform.localEulerAngles.z) * ((pyAngle + GetComponent<Rigidbody2D>().velocity.y) / 2);
//            pyAngleV2.y = Mathf.Sin(Mathf.Deg2Rad * transform.localEulerAngles.z) * ((pyAngle + GetComponent<Rigidbody2D>().velocity.x) / 2);
//            GetComponent<Rigidbody2D> ().AddForce (pyAngleV2); //加算

        }
}