Richard Foster asked in MMD 11.02.22 how to tune the three ranks of his
Black Forest flute clock.  He mentioned, "Three octaves would mean the
top register would have pipes less than a centimeter long, or that the
bottom would have pipes that fold twice."

I'm trying hard to understand this problem.  The only explanation would
be that Richard uses only stopped pipes or only open pipes for all the
three ranks, i.e., the ratio of the pipes lengths over three octaves
would be 3:1.  When using stopped pipes for one or two ranks, and open
pipes for the third rank, the ratio becomes 2:1.  Using stopped pipes
as well as open pipes not only avoids geometrical problems but also
results in much better sound because of the different harmonics of
stopped and open pipes.

As an example I looked at the measures of my just restored Black Forest
clock:

  basic octave: Pipe G1, stopped, is 190 mm in length
  next octave: Pipe G2, stopped, is 95 mm in length
  next octave: Pipe G3, open, is 88 mm in length

If you have more questions, don't hesitate to contact me.  I am an
amateur restorer but I have gathered some experience from restoring
more than fifteen self-playing organ-pipe instruments.

Greetings from Germany,
Christian Greinacher