Headscratchers / Gift of the Night Fury

• Why didn't Hiccup rebuild Toothless' autonomous tail?
  If Toothless was able to fly on his own, Hiccup could still ride him like the other dragon riders ride their dragons. Toothless destroyed the first one because he must have concluded, "Now that I can fly on my own, Hiccup can't fly with me anymore," but it would have only taken one ride or two before he learned, "Oh, even though I can fly alone now, Hiccup can still fly with me whenever we want." There are too many moments to count in the Sequel Series and sequel film where Toothless being able to fly on his own would have made things a lot easier and safer for dragon, rider, and others.
  • I doubt this thought crossed either Hiccup's or Toothless' minds. Plus even if Hiccup did eventually think of that, he might not get the message through to Toothless. He'd probably smash every following autonomous tailfin afterwards.
  • Fridge Brilliance here - that mechanism looks to be noticeably heavier than the pull string tail used in the movies and the TV series. Ask any aeronautical engineer what they think of adding weight to the extreme tail of an aircraft. it's a bad because it shifts the center of gravity. The autonomous tail was likely a case of Awesome, but Impractical.
    • Plus, that mechanism didn't look very comfortable.
    • There is also the issue that the design of the tail would actually limit Toothless' aerial capabilities; some of his flight manoeuvres work by having each tail-fin do its own thing, whereas the autonomous tail works by mimicking its counterpart