Understanding compressed air.

[don prince]

Hi Safrole,

Your last demonsteration... It

Hi Safrole,

Your last demonsteration... It looks OK to me! As you say, some reduce the volume, and others increase the ballast. I believe we are saying the same thing, just from a different prospective.

It doesn't matter if we reduce the volume by flooding the ballast tank, or increase the weight by flooding the ballast tank. Hey... Our sub will acheiver neutral bouyancy on both sides of the Atlantic!

Best regards,
Don_

[don prince]

Hi Beserk,

I wonder why they

Hi Beserk,

I wonder why they list the weight of the Type VIIC at the surface as one weight, and the submerged weight as something greater? The books never mention a change in volume? I can understand both principles, but never considered the volume decrease until this discussion.

Regards,
Don_



Edited By Don Prince on 1128296489

[berserk]

One thing to the VII

One thing to the VII subs. The "Negative Buoyancy Tank", in German Untertriebszelle, was build to get the sub submerged at rough sea. The wave valleys prevent the floating of the superstructure. After the boat submerged, this tank was fully evacuated with compressed air. Then it was possible to hover the boat.

The Captains of those boats find out the possibility to use this tank as a quick dive tank. So this tank was always floated at surfaced drive. But primary, this tank was build for other purposes. And believe me, it was possible to submerge a Type VII faster than 30 seconds.

[stoene]

Hello Gents,

I am officially coming

Hello Gents,

I am officially coming over to the volume team. After considering all that has been said on the subject I realized I was mistaken. Weight can be used if and only if the densities of the superstructure are equal to water. Since this isn't usually the case a larger dive tank wold be need than necessary. These words are a reflection of an earlier post, forget who. I thought very hard on how to pictorilly explain the topic and here is my picture.

But first
1. I'm not a member yet so had to use that other site, sorry.
2. The spheres can be seen as density compensators. This means they can both be lighter that water or heavier than water dependent upon the superstructure ( picture is lighter than water)
3. The smaller empty box can been considered the buoyancy compensator.
4. Lastly, I've had a great time talking this kind of stuff with you guys. Many of my friends here have no interest in subs and their eyes usually glaze over after a few seconds of sub talk.

My Picture

[Guest]

Dont know if going over

Dont know if going over old ground, but "displacement" is equal to to weight of water a vessel displaces. (ie surface trim)
When dived the whole volume of the vessel (sub) is under water and so an amount of water equal to the total volume of the sub (WTC and wet hull) will be displaced.

Therefore the difference between these two amounts must surely be the size of the ballast tank required to perform a static dive, non

[yabbie1]

I would like to make

I would like to make the observation that this has been a vital discussion that lies at the very core of the hobby. The contributions and number of viewings support this.

I do not agree with those who have suggested (some by e-mail) that it is all too academic and that we should stick to practical tips and tricks of building model subs. What could be more basic than an understanding of how our model submarines work? Image going to a model aircraft flying field and finding that no-one can properly explain how an aircraft flies! You would not be impressed. We need to be able to explain these things as simply as possible to newcomers - get our act together - or they may be turned away in confusion. That is why I attempted to summarise the findings in an earlier post.

It is not anti-KISS - you might not need a full grasp of the theory to build a kit or more or less duplicate what many others have done before, but if you want to design and scratch build your own sub (as many do), then being able to calculate the size and position of the ballast tank is absolutely vital. It dominates the design layout. It empowers you to KISS.

Sorry, Skip, but I cannot let an earlier comment of yours pass unscathed! In quoting Bruggen as a "higher authority", this was meant as a general expression, not as a direct comparison to Archimedes! If Archimedes were alive today (and read these postings) he'd turn in his grave...

Regards to all,

Yabbie1

[Guest]

"but if you want to

"but if you want to design and scratch build your own sub (as many do), then being able to calculate the size and position of the ballast tank is absolutely vital"

I don't agree with that. It's entirely a practical proposition to be able to build a perfect working boat without ever resorting to pen and paper, or a calculator.

The hobby can be as simple, or as complex as you want it to be.

Just make sure you enjoy it.

Andy

[berserk]

Hi!

Here in Germany you can

Hi!

Here in Germany you can find only a few WTC boats. The most boats have a piston dive system. Here you can easily resize and/or move your tank.

Some of them dive with a bag dive system. Same as above.

But the bigger subs dive mostly with a compressed air system in combination with 2 piston trim tanks. In this case it’s absolutely necessary to calculate the size and the position of the main ballast tank. Because the ballast tank is insoluble attached to the tube. If the calculations are wrong, you have to start over.

Sure, with a little experience you haven’t calculate everything at all. But that’s not the point. For myself, I have much more time than money. I draw the most parts for my sub with CAD. Here I can see in the run-up if it’s working or not.

Calculation isn’t a must, but it helps to see if you’re on track.

[don prince]

Hi Berserk,

I agree with you

Hi Berserk,

I agree with you on both points; I don't have the time or money to burn on experiments that will not work, and I want to understand all the technical aspects of both real and model subs. I have completed my OTW Type VIIC hull, but I have decided to build my own dive system, and WTC.

I would like to take this discussion off-line from the Subcommettee Bulletin board, and get your opinion about my WTC design, High Pressure water pump control board electronic circuit design, and the over-all sub layout.

Regards,
Don_

don.prince@ncr.com

[mylo]

Yab,

Kudos to you. I

Yab,

Kudos to you. I couldn't agree more. I am new to R/C subs. I am also the kind of guy that will sketch and draw / re draw and re sketch plans using mathematical formulas and exacting science. I very much enjoy this process of the hobby. For me, building something that I planned from scratch and actually having it work....because the math and science is right, is equally as rewarding as playing with the thing.

This thread has confused me more than anything. I am resorting to other reference materials and information to formulate my own ideas for design.

....but, as Yab stated very well, this should be available here. If I was the type that was easily intimidated by "technical" things, I would have said, "Screw the R/C sub thing, too complicated. I think I'll take up flying helicopters instead."

I would have like to have seen guys just post what THEIR experiences are and how they do stuff, may it be KISS ...or, not so KISS, as long as it worked for them. Perhaps people new could pick little bits and pieces from each moddeler and come up with something of their own. Or, they might like someones approach so much they won't "re invent the wheel." I think the point being, the community should argue about it.

......I still think that everybody has been right in what they are saying. They are just saying it in different ways.

Mylo

[mylo]

Oooopsss.....hee hee....I meant to say,

Oooopsss.....hee hee....I meant to say, "the community SHOULDN'T argue".....uh......ya *embarrassed*

Mylo

[berserk]

Moin!

I don’t know how you

Moin!

I don’t know how you handle this in America. In Germany, you get any support you need. No matter which type of sub you build. And of course, no one has to invent the wheel. Because there are many years of experience available.
I agree, some guys will be deterred building a sub because they think it’s to complicate. But its not!

You don’t have to know how it works, if you’re not interessted in. If you buy an Engel sub you just build the sub and it will work fine. It’s an entrance in this hobby. And maybe sometime you will look behind the curtain. The community should help in this case.

Mylo, the point of this discussion was given from Gotland. And if someone has the heart to ask, maybe he gets an answer from the community. There are no stupid questions…