can somebody (or better: wants to) give me a clue how to understand / practice torifune as a method of internal training?
Do you do it? Or is it (in oyur eyes) just part of a spiritual way which doesn't belong to aikido?
How do you do it?
not spiritual. quite practical from an IS training perspective. it starts with two directions: forward and backward.
forward: push from the back leg, send the energy up to your hara/dantien, then down to the front leg
backward: push from the front leg, send the energy up to your hara/dantien, then down to the back leg
couple of things: curve your tail bone slightly so your lower back can relax, keep hip joint creases relax and soft, use the Buddha breathing pattern (kokyu power). for the advance, you add something called dantien rotation which you need to talk to Sigman or Dan or one of the Chen taichi masters. actually, you need to get your hand on one of those guys to learn how to do things the correct way.
the aunkai guys have something they called push-out. that's the forward portion of torifune (even though the aunkai folks don't move forward, but their internal energy do; thus, internal, right?). might want to talk to Rob John about that.
for taiji, if you know silk reeling, where you normally do it in a horse stand. just turn your body 90 degree either left or right and you would have torifune.
practice without a partner: rig up a bungee cord horizontally around solar plex level. grab the thing with both hands and do torifune.
*standard disclaimer of IS idiots*