How to render XML template and then use SEND_DATA in Ruby on Rails 3.2.8?

Copying the answer from the edited question body in order to remove this question from the "Unanswered" filter:

format.xml do  
  stream = render_to_string(:template=>"calculations/show" )  
  send_data(stream, :type=>"text/xml",:filename => "test.xml")
end

~ answer per Dmitry