You can create new helper if require. A user define class generally extends appRain_Base_Objects or any Module class. We have to follow below steps to create a new helper:
1.Create New file in /development/helper/, For example userdefine.php.
2.Create below class in the file.
3.Now you are ready to call the helper like: App::Helper('UserDefine')
Example:
class Development_Helper_UserDefine extends appRain_Base_Objects
{
}