So a friend of mine came up with an interesting question. Considering the fairly universal following facts about western-style fantasy dragons:
a) dragons can breath fire
b) dragons themselves are fireproof
c) dragons have large wings, allowing them to fly (though the actual science of this is well-known to be fishy, let's for now pretend a dragon such as Toothless or Smaug can actually fly. Super light bones or whatever.)
d) hot air rises and creates lift
If the dragon can produce a large quantity/sizable blast of extremely high heat, could it be useful to the dragon for it napalm/torch the ground beneath it as it was taking off, in order to create additional lift for itself? Or would the effect of doing this be so negligible that it wouldn't be worth it to bother?