Dave Welch new 3 inch WTC - DW-RCABS-R 3 inch

[crazy ivan]

SteveUK,

The pressure in fresh

SteveUK,

The pressure in fresh water increases by .432 PSI for every foot of depth. These air pumps are rated at 11 PSI (the one I installed in my prototype version this summer measures 15 PSI max). The volume of the pressure vessel is calculated relative to the bladder such that the full 11 PSI is attained when the bladder is fully deflated. Dividing 11 by .432 shows that a depth of 25.46 feet must be reached before the bladder will be kept deflated. If you want to run deeper than that, better stick to gas systems. Of course, your seals or WTC integrety may come into question at those depths.

Within the 25 foot theoretical operational range of Dave's system, all it takes is a small bubble of air in the bladder to start the boat surfacing, provided it is properly trimmed. That is to say, just slightly negative with the bladder deflated. As the boat rises, external pressure drops, and the bladder expands even more. It's a positive feedback system. At 8 foot down, a mere 3.456 PSI is all that need be overcome... well within the operational parameters of the system.

[anonymous]

SteveUK,

The pressure in fresh

SteveUK,

The pressure in fresh water increases by .432 PSI for every foot of depth. These air pumps are rated at 11 PSI (the one I installed in my prototype version this summer measures 15 PSI max). The volume of the pressure vessel is calculated relative to the bladder such that the full 11 PSI is attained when the bladder is fully deflated. Dividing 11 by .432 shows that a depth of 25.46 feet must be reached before the bladder will be kept deflated. If you want to run deeper than that, better stick to gas systems. Of course, your seals or WTC integrety may come into question at those depths.

Within the 25 foot theoretical operational range of Dave's system, all it takes is a small bubble of air in the bladder to start the boat surfacing, provided it is properly trimmed. That is to say, just slightly negative with the bladder deflated. As the boat rises, external pressure drops, and the bladder expands even more. It's a positive feedback system. At 8 foot down, a mere 3.456 PSI is all that need be overcome... well within the operational parameters of the system.

And there you go.

Steve

[bigdave]

Hi Sam,
The two prototypes

Hi Sam,
The two prototypes I have made so far just have outputs for rudder and rear planes but I will look into bow planes as a possibility.

George,
Thank you my crazy friend for the excellent explanation. Your great idea was my inspiration.

Steve,
I am glad your tests are going well. I can't wait to see the video. BD.

[sam reichart]

just curious-
using one of these

just curious-
using one of these systems, do you all use a small hand pump, or a sports ball pump, to inflate the bladder??

[anonymous]

No we use Dave's filler

No we use Dave's filler hose. You can see it in the third picture. Attach to the tire valve at the forward compartment, open up the valve with the servo and blow! Works perfect.

Steve



Edited By U812 on 1132806755

[steveuk]

Thanks for the facts and

Thanks for the facts and figures. That is reassuring. I have often wondered.. but never knew the maths and science behind it till now.

[sam reichart]

No we use Dave's filler

No we use Dave's filler hose. You can see it in the third picture. Attach to the tire valve at the forward compartment, open up the valve with the servo and blow! Works perfect.

Steve

cool. I like being able to use readily available equipment... (fingers, lungs, you know; those sort of tools...)

[liftmys10]

wow that looks great! Will

wow that looks great! Will it work in a 1/72 scale Permit?

[bigdave]

Not sure, The size is

Not sure, The size is 24"x 3" plus the output connections. BD.

[chuck chesney]

Big Dave...
Your variant of the

Big Dave...
Your variant of the RCABS looks great. I've been using the original RCABS for over a year, and love it. My homebuilt WTC is exactly the same size as your new one, and is fitted in a converted (to wet hull) Engels Patrick Henry hull that is the same size (give or take a skosh for the metric to imperial converson) as Steve's George Washington test boat.
The only issue I've ever had was a few drops of water that got past the SubTech seals when the bladder was inflated. Cured that by adding a bulkhead that devides the motor, rudder and plane servos from everything else. No vacuum,no strain on the seals.

All that being said, I think that I'll convert the whole thing to your RCABS-R system. Better to have a slight positive pressure in the WTC than a slight vacuum, me's thinks. If nothing else, the chance of seeing any leaks will be increased. Air bubbling out, not water being sucked in. I believe that the RCABS-R gets closer to the Fail Safe goal, too.

Congratulations ! Art Broder and you have developed a system that is heads and sholders better than anything else thats out there. What a rare find ! Something that is not only cheaper, but MUCH better than gas, pistons and water pumps. Thanks for your post, and for spreading the word.

Chuck
P.S. Your endcaps and bulkheads look terriffic...where did you get them?

[bigdave]

Hi Chuck,
Thanks for the

Hi Chuck,
Thanks for the nice words. The end caps and bulkheads are mine. I mold them myself. In my design there is no + or - pressure in the WTC. The areas with output seals do not see pressure from the ballast system. The seals only have to keep the water out like in a non-RCABS-R system. It is similar to what you did by putting in your bulkhead. One safety factor I keep forgetting to mention is you can't over fill the bladder. It only gets refilled with the same amount of air it started with. BD.

[chuck chesney]

BigDave...

The fear of possibly over

BigDave...

The fear of possibly over inflating the bladder has always lurked in the back of my mind, even though it hasn't happened... yet. Your system eliminates the possibility entirely.
Brilliant !! One less thing to worry about.

Chuck

[liftmys10]

Will it work on a

Will it work on a 1/72 scale scale shipyard Permit?

[bigdave]

I can only go by

I can only go by the size for the Permit. At about 47"x 5.5" it should fit with no problem as the WTC is 24"x 3". I would say it should work fine, but this is only a guess. BD.



Edited By Bigdave on 1133100508

[tmsmalley]

BD - I hope you

BD - I hope you can do a write up on this for the SCR. There are tons (most?) of the SubCommittee members who don't frequent this site. This is too good to keep secret
Tim