Why is d flat such a horrible sounding note? Mine always sounds terribly airy.

For the D flat in the staff? It's just an awful note. Try using your low D key as well. That sometimes stabilizes it a bit. Also, sometimes the trill key fingering sounds better - it does on my horn so I often use it instead.

*shudders*
Goodness, I hate that Db as well. Sometimes I will have problems getting the note to come out just right. Then again, I've been playing for only a couple months...

Which D-flat are you talking about? Actually, all of them have issues .
There are many alternate fingerings for the top three that can help, though!