rails: use class_name - same model multiple times

gistfile1

class AirplaneClass < ActiveRecord::Base
  attr_accessible :name, :description, :organization_id, :stations_attributes,
    :ifr_certified, :currency_if_over_150, :min_hours_to_qualify, 
    :max_wind_limitation, :min_weight, :max_weight, :datapoints_attributes,
    :cruise_performance_chart_id, :landing_distance_chart_id, 
    :takeoff_distance_chart_id

  belongs_to :organization
  has_many :airplanes
  has_many :stations
  has_many :rental_requests
  has_many :datapoints

  belongs_to :cruise_performance_chart, class_name: "Chart", foreign_key: "cruise_performance_chart_id"
  belongs_to :landing_distance_chart, class_name: "Chart", foreign_key: "landing_distance_chart_id"
  belongs_to :takeoff_distance_chart, class_name: "Chart", foreign_key: "takeoff_distance_chart_id"

  accepts_nested_attributes_for :stations, allow_destroy: true
  accepts_nested_attributes_for :datapoints, allow_destroy: true

  validates :name, :presence => true, :uniqueness => {:scope => :organization_id}

  default_scope order: "name"
end