LARGE SCALE RCABS info needed

[dhffr]

Im looking at putting an RCABS system in my OTW S class. I am thinking of using 2 of the 12.5 x 6 bag or 2 of the 8.5 x 4.5. I am looking for the inflated dimensions of these and an air pump (or 2) that can fill them up in a timely manner. This S class is no Hotrod. I want a scale surfacing speed.

The S class beam is about 8" so I can get 2 (side by side) 3.0" or 3.5" clear tubes to house the bags in. Any help would be appreciated. I need to get this boat in the water.


Darrin

[wayne frey]

Experiance speaks well. Art Broader,

Experiance speaks well. Art Broader, or Dave Welch know thier stuff on the subject. Ask them! I don't expect it will be a big problem at all, though. That would be a neat build!!!

[JWLaRue]

I would love to see

I would love to see Art or Dave provide some volume measurements for the various pressure cuff bags that are typically used for RCABS. That would go a long way towards seeing RCABS take a greater hold in the larger boats that some of us build.......

Regarding pumps, the Smart Products company that makes the pumps that Dave sells has a larger/faster pump. Here's the web url for the product brochure: http://www.smartproducts.com/pumps_s..._air_pumps.php

I like the greater maximum psi of this pump and am considering using it for my 1/32nd scale Type II. For now, I'm going to try one of the smaller pumps that I got from Dave.

-Jeff

[Guest]

Bladder displacement volume

Each bladder manufacturer has a slightly different size and shape for their infant, child, adult and thigh size designations. I suggest that modelers do what I did with different sample bladders: inflate to a firm fullness and dunk them in a full container of water sitting in a larger empty container. Pour the water displaced into the larger pan into a measuring cup and you get the volume measurement for that bladder.
Sorry I can't be more specific in volume measurements, but to give you a reference, I downsized from an adult bladder in my 40" Alfa to a child size for my 60" L.A., and the smaller bladder was all that was needed. An advantage of RCABS is that the bladder size and position can be changed empirically, during the final trimming of the model, without changing the size or position of the WTC.

[tmsmalley]

Eureka! The Archimedes method. I

Eureka! The Archimedes method. I love it when BC science can be applied to modern day questions.

[JWLaRue]

I hear you Art, but

I hear you Art, but asking folks to buy multiple cuff sizes is no the answer for a lot of folks. That's why I'd like those selling these things to provide guidance. After all, how hard can it be for a vendor to take the 3 or 4 cuff sizes that they sell (and stock, yes?) and figure out how much water they hold?

It would be a big boost to the adoption of RCABS.

-Jeff

[Guest]

Gee Jeff, I am a

Gee Jeff, I am a scientist of sorts, and I understand that some guidelines are needed for specific almost ready to run models, but practically speaking, for scratch builders, or hull only kits, I would make these generalizatios for RCABS; subs 60" or smaller, use a child size bladder. For a larger sub, use an adult bladder. If you have an adult bladder and a small model, use it. Just don't fill it all the way. If you have a child size bladder and build a larger sub, buy a second child size bladder, and connect it to the first one with a T connector. If you don't have room (height) for a small bladder to fully inflate for the needed water displacement, use a larger bladder and partially inflate it, to displace the needed amount of water.
I'm not about to calculate the number of cc's of water needed to be displaced by the bladder until I have the sub ready for the water, and see if it floats or sinks, without the bladder being inflated. The size of the bladder really isn't that critical, as long as you have room, foam, and lead weights.

[petn7]

I hear you Art, but

I hear you Art, but asking folks to buy multiple cuff sizes is no the answer for a lot of folks. That's why I'd like those selling these things to provide guidance. After all, how hard can it be for a vendor to take the 3 or 4 cuff sizes that they sell (and stock, yes?) and figure out how much water they hold?

It would be a big boost to the adoption of RCABS.

-Jeff

It would be pretty easy to do and it annoys me when stores/vendors don't really know much about what they're actually selling, but still charge high prices. However, using the displacement method is pretty easy to do as long as you stay in metric units.

For smaller sized bladders, where's what I do:

1. Fill a Solo cup to the top with water.
2. Inflate the bladder to the amount you anticipate. For me, I folded the bladder into the perforated WTC, inflated fully, then pinched the tube and removed the bladder.
3. Put the bladder into the Solo cup so that only the bladder is submerged (try to avoid submerging the tube and your finger tips).
4. Remove the bladder
5. Fill a measuring cup with a predetermined amount of water (say...300ml).
6. Pour the water from the measuring cup into the partially emptied Solo cup until its full again. 300ml - the amount of water left in the measuring cup = estimated bladder displacement.

If you want, you can also calculate the displacement of a completely empty bladder using a similar method as above, then subtract that from your value from step 6. The bladder I'm using for my Seafox/Seawolf (that's housed in a 2.5 inch perforated WTC) displaces roughly 265 grams, but I think that value includes the displacement from the bladder itself, in addition to the air inside it. I estimated the bladder itself to displace roughly 45 grams of water.

[JWLaRue]

Art,

Guidelines are always good...but those

Art,

Guidelines are always good...but those that you have provided do not work with WW2 era boats.

Curtis,

One could just fill the bladder with water until full and then empty into a measuring cup and note how many ounces or mililiters the bladder held.....

-Jeff

[bigdave]

I have had a few

I have had a few requests for the amount of water the bladders I use will displace.
I finally made some time to do the calculating and have the figures.
First let me say that I do not run my bladders at max displacement in my designs except for my 3.0-R cylinder prototype.

These amounts are at full inflation. (Not stressed beyond its size or blown up like a balloon)
Just filled with air till it is a rounder shape.
I use three sizes of bladder.
I call them small, medium, and large. (Go figure) Duhh!!
These are all approximate figures.
Small is 4”x 2”= 3 CUIN or 1.6 OZ
Medium is 3.5”x 6.75” =10 CUIN or 5.5 OZ
Large is 4.5”x 9” = 30 CUIN or 16.6 OZ
I hope this helps.
Now go out there and fill those bladders.
I find a good Ale or Stout does the job nicely!! BD.

[petn7]

Art,

Guidelines are always good...but those

Art,

Guidelines are always good...but those that you have provided do not work with WW2 era boats.

Curtis,

One could just fill the bladder with water until full and then empty into a measuring cup and note how many ounces or mililiters the bladder held.....

-Jeff

Hahaha, I suppose so. Might take a while to get all the water out, though. That would probably be good for those with many bladders on hand.

[Guest]

Jeff and others,
For those long

Jeff and others,
For those long and narrow WW2 boats you can make custom size and capacity bladders by cutting old bicycle inner tubes. I get them free from my local bicycle repair shop. Cut on both sides of the valve to the desired length and choose the European, or any suitable width American inner tube, and seal the ends with rubber cement and fold over and clamp ends. You can even put them in saddle tanks.
Heck you can make anything into a submersible with RCABS;
http://smg.photobucket.com/albums/v313/ ... 207-19-08/

[JWLaRue]

Dave,

You're the man! This will

Dave,

You're the man! This will be *very* helpful for those of us looking to build the larger RCABS type systems.

-many thanks,

Jeff (who's very much in favor of no longer passing gas!)

p.s. just checked what my ballast displacement needs to be....and it looks like I will need to run *two* of the large bags!