schrieb:

but what's the very best anyone has managed, presumably using some
wildly experimental airframe?

Johan,
At operating altitude, the space shuttle 'flies' thousands of
miles without losing any altitude. So they have an glide ratio
approaching infinity until they put the bakes on.


As would any object placed at the same speed at that altitude...

If wildly experimental airframes had ever achieved an L/D of something
above 40 they would probably have been used as gliders.
Come to think of it - they have: LS4,6,8, ASW20,24,27, ASH25,...

Regards
Marcel Duenner