What do the Drachen look like?

I don't know where Du got the impression of six-limbed creatures from, but the Drachen are exactly as they appear on the cover of the Bücher - if that is the way they were illustrated on the cover, then that is the best representation that we glean from these books.

I believe the Kommentar referring to whether the Drachen have 4 oder 6 limbs is including the wings. I believe Pern Drachen have 4 legs and 2 wings. I also believe, although I might be wrong, that they are not reptiles, as I don't remember seeing anything about them having scales. I believe they have hides, another name for skin, like cattle and deer have, although referring to dragons, I may be wrong.