[c# hover car script] Change time till fullspeed

Hello,
I'm trying to change the time it takes until the car reaches maximum speed. Currently, it takes ~1 second until the car reaches maximum speed. I would like to change it to 2 or 3 seconds in the script. So the hover car should slowly gather some speed. I have tried to change the rigidbody drag, but it changes top speed only. The time it takes until it reaches top speed stays almost the same with any drag value. Here is my current hover script :

Code (CSharp):

1. using UnityEngine;
2. using System.Collections;
3.  
4. [RequireComponent(typeof(Rigidbody))]
5. public class HoverCarControl : MonoBehaviour
6. {
7.   Rigidbody m_body;
8.   float m_deadZone = 0.1f;
9.  
10.   public float m_hoverForce = 9.0f;
11.   public float m_hoverHeight = 2.0f;
12.   public GameObject[] m_hoverPoints;
13.  
14.   public float m_forwardAcl = 100.0f;
15.   public float m_backwardAcl = 25.0f;
16.   float m_currThrust = 0.0f;
17.  
18.   public float m_turnStrength = 10f;
19.   float m_currTurn = 0.0f;
20.  
21.   public GameObject m_leftAirBrake;
22.   public GameObject m_rightAirBrake;
23.  
24.   int m_layerMask;
25.  
26.   void Start()
27.   {
28.     m_body = GetComponent<Rigidbody>();
29.  
30.     m_layerMask = 1 << LayerMask.NameToLayer("Characters");
31.     m_layerMask = ~m_layerMask;
32.   }
33.  
34.   void OnDrawGizmos()
35.   {
36.  
37.     //  Hover Force
38.     RaycastHit hit;
39.     for (int i = 0; i < m_hoverPoints.Length; i++)
40.     {
41.       var hoverPoint = m_hoverPoints [i];
42.       if (Physics.Raycast(hoverPoint.transform.position,
43.                           -Vector3.up, out hit,
44.                           m_hoverHeight,
45.                           m_layerMask))
46.       {
47.         Gizmos.color = Color.blue;
48.         Gizmos.DrawLine(hoverPoint.transform.position, hit.point);
49.         Gizmos.DrawSphere(hit.point, 0.5f);
50.       } else
51.       {
52.         Gizmos.color = Color.red;
53.         Gizmos.DrawLine(hoverPoint.transform.position,
54.                        hoverPoint.transform.position - Vector3.up * m_hoverHeight);
55.       }
56.     }
57. }
58.  
59.   void Update()
60.   {
61.  
62.     // Main Thrust
63.     m_currThrust = 0.0f;
64.     float aclAxis = Input.GetAxis("Vertical");
65.     if (aclAxis > m_deadZone)
66.       m_currThrust = aclAxis * m_forwardAcl;
67.     else if (aclAxis < -m_deadZone)
68.       m_currThrust = aclAxis * m_backwardAcl;
69.  
70.     // Turning
71.     m_currTurn = 0.0f;
72.     float turnAxis = Input.GetAxis("Horizontal");
73.     if (Mathf.Abs(turnAxis) > m_deadZone)
74.       m_currTurn = turnAxis;
75.     }
76.  
77.   void FixedUpdate()
78.   {
79.  
80.     //  Hover Force
81.     RaycastHit hit;
82.     for (int i = 0; i < m_hoverPoints.Length; i++)
83.     {
84.       var hoverPoint = m_hoverPoints [i];
85.       if (Physics.Raycast(hoverPoint.transform.position,
86.                           -Vector3.up, out hit,
87.                           m_hoverHeight,
88.                           m_layerMask))
89.         m_body.AddForceAtPosition(Vector3.up
90.           * m_hoverForce
91.           * (1.0f - (hit.distance / m_hoverHeight)),
92.                                   hoverPoint.transform.position);
93.       else
94.       {
95.         if (transform.position.y > hoverPoint.transform.position.y)
96.           m_body.AddForceAtPosition(
97.             hoverPoint.transform.up * m_hoverForce,
98.             hoverPoint.transform.position);
99.         else
100.           m_body.AddForceAtPosition(
101.             hoverPoint.transform.up * -m_hoverForce,
102.             hoverPoint.transform.position);
103.       }
104.     }
105.  
106.     // Forward
107.     if (Mathf.Abs(m_currThrust) > 0)
108.       m_body.AddForce(transform.forward * m_currThrust);
109.  
110.     // Turn
111.     if (m_currTurn > 0)
112.     {
113.       m_body.AddRelativeTorque(Vector3.up * m_currTurn * m_turnStrength);
114.     } else if (m_currTurn < 0)
115.     {
116.       m_body.AddRelativeTorque(Vector3.up * m_currTurn * m_turnStrength);
117.     }
118.     }
119. }
120.  

Would be cool, if someone could point me into the right direction.

 

Drop down the "m_forwardAcl" ?