ROBERT M. Wrote:
-------------------------------------------------------
> SnakeDoc, et al:
>
> The torpedo piston has guides that travel in
> machined grooves on the inside wall of the torpedo
> tube. Toward the breech end, these grooves taper
> until they disappear near the muzzle end of the
> tube, limiting the travel of the piston; this
> allows the impulse air to remain inside the boat.
> By opening the tube vent, the impulse air is
> now bled off, allowing the piston to return to the
> breech end. You wrote. "During whole launch..."
> Do you mean during a salvo launch? Was there a
> torpedoman shortage, necessitating the waiting
> until the salvo was complete to vent and flood
> the tubes?

Well, in fact, I must correct myself - the vent valve was
opened when air pressure in the launching air flask has
dropped down to ~5 atm. So in result, it behaved almost
the same as mechanism with poppet-valve (except the fact,
that there was no case of "incorrect timing" ).

The whole process - from releasing firing rod to full
withdrawal of piston had taken about 2 sec. In this time,
the weight decreased by 1,8 ton (1406 kg of torpedo and 426 kg of
surrounding water) and then increased back to 1,6 ton.
In "Bootskunde für U Boote Bauart VII C" [uboatarchive.net] states, that trim
moment during shot from forward torpedo tube is -3885 mkg.
It seems, that during salvo, there is a need to manualy compensate about 800 kg.

> The U.S. boats used a "poppet-valve" mechanism to
> capture the impulse air after a
> launch. There was a roller assembly that came in
> contact with the outer skin of the torpedo and was
> linked to the poppet valve itself. When the
> torpedo was launched, the roller followed the
> contour of the torpedo's after body, permitting
> the valve to open, allowing the impulse air and some seawater
> to drain into the bilges. This venting operation
> had to be timed (3 to 5 seconds at periscope
> depth) just right or excessive seawater would
> enter the boat. This was the only "automatic
> feature" the boat had, there were no "automatic gears."

Well, I exactly mean the this automatic feature of poppet
valve as "automatic gear".

--
Thanks, regards
Maciek


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