Sounds okay, but why not just build a couple of K-style VBTs and mount them inside the mains, fore and aft? You can get stamped elliptical heads in 304 or 316 SS, so they won't weigh as much as George's, and won't effect your payload all that much. Control them seperately, and you can run a small pump if you want to transfer back and forth for trim changes. I have to tell you, however, that a sub the size of our Ks probably won't get much use out of such a rig. It takes a fair old shift of weight to do a pitch change. And when you get down to it, why bother?
You might consider a change in drop weight design. Put it on a long acme screw, or on a captive track of some sort with hydraulics to shift the weight fore and aft. Again, it seems like you may be thinking a minor problem almost to death. Your aft thruster will drive the stern down as you get underweigh, but you can't really trim against that as any change in prop speed will equate to a change in pitch. You'd spend all your time fiddling with trim instead of peering out the window.
Personally, I'd pitch trim with weights inside, control vertical water column movement on transects with dive planes (if you use the aft main thruster)--or ditch all that and use pivoting side thrusters with enough guts to do all the work for you. Have a look at what Joe has been working on for his Alvin Jr. and what Karl did on his Roataan sub. Come to think of it, have a look at Delta. Those subs have done thousands and thousands of dives, and you can't argue with that kind of success. And guess what? They don't even USE a vbt anymore. Just dive a little heavy and hold a bubble in one of the MBTs like we did for umpty-thousand dives in the oil fields. Trust me, it works like the proverbial charm.
Vance
-----Original Message-----
From: Recon1st@aol.com
To: personal_submersibles@psubs.org
Sent: Sun, 8 Jul 2007 7:44 pm
Subject: Re: [PSUBS-MAILIST] hard vbt sytems
Guys I have been reading all the archives on vbt systems etc and have
not really gotten the answer to my idea.
What I am looking at is using 3 to 4 SCBA tanks on each side for vbt's
these are 40 or 45 cuft hp cylinders. I am thinking on valving both the
water in let and the air blow, and the ability to give a pre measured amount
of blow air which equals water quanity.
The tanks will run horizontal and piped to have a upward u shape connection
so water does not slosh from one tank to the other.
I guess what I am trying to accomplish is more fully blown floatation (freeboard)
and I am trying to fine balance so when I point the nose down using dive planes and
vectored thrust, once the water in these tanks moves forward I would like to
stay at that attitude and neutral the controls and stay pointed down.
I just bet I am dreaming of obtaining this kind of balance, but really like being
ignorant. Like alot of you my first plans was a sea vue flying sub heheh
any ideas
Dean Ackman