How can I create a working and semi-realistic lift force?

I was experimenting with making a flight simulator in Unity Engine and was coming across a problem where the plane would suddenly disappear due to floating-point and "direction normalized" errors. I think that this error has something to do with my lift equation in my PlaneController Script. My reasoning for this is that the errors occur when I try to do a loop in the plane, however it works fine if the plane is moving at slow speeds. One thing that I noticed about my simulator is that an unrealistically large amount of lift is generated. Since the lift equation takes into account the angle of the plane in radians, it seems to me that trying to do a loop just makes the lift force insanely large. I was wondering if anyone had any ideas as to how I could improve my thrust, drag, or lift equations. I posted my plane controller script below. As a heads up, the thrust, lift, and drag forces are added in the Fixed update section at the bottom of the script.

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class PlaneController : MonoBehaviour {
     private Rigidbody plane;
 
     public float throttle;
     public float maxThrust;
     public float thrust;
 
     public float WingArea;
     public float WingSurfaceArea;
 
     private float yawRotation;
     private float airDensity;
     
     public float throttleAcceleration;
 
     // Use this for initialization
     void Start () {
         yawRotation = 0;
         plane = this.GetComponent<Rigidbody>();
         throttle = 0f;
     }
     
     // Update is called once per frame
     void Update () {
         if (Input.GetKey(KeyCode.UpArrow))
         {
             if (throttle >= 100) throttle = 100;
             else throttle += 0.15f;
         }
         if (Input.GetKey(KeyCode.DownArrow))
         {
             if (throttle <= 0) throttle = 0;
             else throttle -= 0.15f;
         }
         if (Input.GetKey(KeyCode.A))
         {
             this.transform.Rotate(new Vector3(0, 0, 0.60f), Space.Self);
         }
         if (Input.GetKey(KeyCode.D))
         {
             this.transform.Rotate(new Vector3(0, 0, -0.60f), Space.Self);
         }
         if (Input.GetKey(KeyCode.W))
         {
             this.transform.Rotate(new Vector3(-0.60f, 0, 0), Space.Self);
         }
         if (Input.GetKey(KeyCode.S))
         {
             this.transform.Rotate(new Vector3(0.60f, 0, 0), Space.Self);
         }
         if (Input.GetKey(KeyCode.Q))
         {
             yawRotation -= 0.15f;
             if (yawRotation > -25f) this.transform.Rotate(new Vector3(0, -0.15f, 0), Space.Self);
             if (yawRotation <= -25f) yawRotation = -25f;
 
         }
         if (Input.GetKey(KeyCode.E))
         {
             yawRotation += 0.15f;
             if (yawRotation < 25f) this.transform.Rotate(new Vector3(0, 0.15f, 0), Space.Self);
             if (yawRotation >= 25) yawRotation = 25f;
         }
         else if (!Input.GetKey(KeyCode.Q) && !Input.GetKey(KeyCode.E))
         {
             if (yawRotation < 0)
             {
                 this.transform.Rotate(new Vector3(0, 0.15f, 0), Space.Self);
                 yawRotation += 0.15f;
             }
             if (yawRotation > 0)
             {
                 yawRotation -= 0.15f;
                 this.transform.Rotate(new Vector3(0, -0.15f, 0), Space.Self);
             }
         }
     }
 
     void FixedUpdate() 
     {
         plane.AddRelativeForce(Vector3.forward * thrust * 0.02f, ForceMode.Impulse);
         float xzVelocity = Mathf.Abs(this.GetComponent<Rigidbody>().velocity.z) + Mathf.Abs(this.GetComponent<Rigidbody>().velocity.x);
         plane.AddRelativeForce(Vector3.back * 0.02f * (1.229f * (xzVelocity + Mathf.Abs(this.GetComponent<Rigidbody>().velocity.y)) * (xzVelocity + Mathf.Abs(this.GetComponent<Rigidbody>().velocity.y))/2) * WingArea * 0.02f, ForceMode.Impulse);
         plane.AddForce((Vector3.up * 2 * 3.141f * Mathf.Deg2Rad * -plane.rotation.x * (xzVelocity * xzVelocity * 1.229f/2) * WingSurfaceArea)* 0.02f * 2, ForceMode.Impulse);
         if(thrust < maxThrust) thrust += throttleAcceleration * throttle / 100 * 0.02f;
     }
 }

Thanks for reading my post.