Actually, I don't care what it's called officially. It has been and always will be The Flying Castle to me.
If that's "being difficult," then I plead guilty.
Okers. 30 lashes with a wet noodle.
Traditionally, in Gaelic as in English, castles tend to be named, and often for various characteristics. Dunvegan Castle on Skye was not particularly large so they named it "Dun Bheagan" (nearly the same pronunciation as "Dunvegan"), in English "Little Fort." Similarly, Edinburgh Castle was built near Edin (thus "Edin-borough"), so it was called Dunedin (pn doon'each"-in) or "Fort Edin."
So, I tried this with teichidh (pn. cha'key, of flight), and it didn't look good -- Dunchakey?
With sgitheaneich (ski'an-ake, of wings) it looks frightening to Anglophones. Dunskianeich?
So how about Dunàile, Fort of Air (Dunaala)?
Or Dunneul, Fort of Cloud (Dunnale)?
Very lovely in Gaelic imagery is Dun a'Cheo" (Dunakyo) Fort of/in Mist.
Or maybe, given the form of propulsion, we call it Dunrychettain (Dun Raicheittein, Fort of Rockets), or quite carelessly rendered into English orthography but picking up another aspect along the way, though only in English: Dunracketten ("Fort of Noise"?).
Okay, bad ideas all. But not for want of trying... *\;-)