Dragon flight was explained...
In the cartoon documentary, "Flight of Dragons," it was explained that dragons eat limestone. It is crushed in their craw and swallowed to mix with stomach acids to form hydrogen. When the dragon expands its chest, it eventually achieves a degree of weightlessness and can fly. The wings are meant for propulsion and stearing. The thick skin was needed to contain the hydrogen.
Should the dragon wish to descend, it simply lets the gas out ... burps, in effect. The gas passes, "Thors Thimble" in the mouth, which generates an amount of natural static electricity and ignites the gas and gives dragon fire, hence the ability to breathe fire. Should a dragon expel all its gas, it has to eat more limestone and/or allow time for more gas build up.
This is why dragons rob dwarf mines ... they didn't eat the dwarves themselves as the meat wasn't worth picking off the bones; the threat was enough to get the lime stone.
Simple, possible physics when you come down to it. None of this scientists mumbo jumbo and farcical presumption.
I think this reference was also observed by Terry Pratchet in his various Discworld novels. Young dragons whos stomachs weren't yet thick enouch to properly contain hydrogen, had a propensity towards spontanious combustion ... contributing towards the scarcity and ultimately death of the species.