title_body: Flying a UAV with a banner?
upvoted_answer: It should be possible so long as the aircraft has enough spare thrust and lift to counteract the drag and weight. Many model aircraft have good power-to-weight compared to their full size equivalent.
  
  
  For the banner attachment, you need a secure point to attach it to the aircraft, well away from any propellers or control surfaces. Usually this is on the bottom rear of the fuselage.
  It is a good idea to include a 'weak link', which will break if the banner snags; this leaves the banner behind, but saves the aircraft being pulled from the sky.
  You will also need to weight the banner to hang in the correct orientation - making the vertical part of the banner support bottom heavy should suffice.
  
  
  You can fly banners from both fixed-wing or rotary wing aircraft, in slightly different ways. Fixed wing banner extends behing the aircraft, whereas on a helicopter or multirotor the banner hangs below.
  
  Image source