How was the continuous looping of tape in an old-school mechanical cockpit voice recorder physically implemented? 30 minutes seems like a lot of tape to loop continuously, did it move more slowly than a normal audio tape?
Most looped tape mechanisms are a variation of this:
(this is an 8-track audio cassette)
The tape is pulled from the center of the spool, and fed back to the outside of the spool.
Some CVRs use two spools and autoreverse instead.
On the right, an example of a flight data recorder. (on the left, the digital storage of a modern FDR).