RickK's 170 rebuild

[Capt. Bob]

To realize where the tank will expand, one must understand what causes the expansion.

When the material used to construct the tank comes in contact with fuel, the material absorbs (think sponge on a much smaller scale) a portion of the fuel and that is the cause for expansion. Areas that have continued contact with the fuel tend to reach full absorption and therefore expand the greatest. Also, this absorption is what leads to the plastic/poly type tank fuel smell that can occur. That stated, if the tank were completely full, it would expand (again like a sponge) in all directions.

The 2% (Moeller uses 3%) is the calculated size increase based on (a guess here) the surface area and wall thickness of the tank. As was stated earlier, using fuel and filling the tank would be the proper procedure to test expansion. Other factors like ambient temperature can also play a part in this equation but I'd bet the design engineer doesn't attach as much weight to that as he does the chemical properties of his design.

So where does that leave Rick?

Well I doubt that the expansion will damage his stringers or bulkheads. I would be more concerned (as BA stated) with the possibility of damage (over time) to the tank itself. I agree that the tank structure will fail way before the resin and glass do. The corners would be what I'd address not so much for the expansion itself but for the chafing that could occur because of it. Grind it back just a bit, add some neoprene and let the four winds blow.

[gran398]

Great explanation CB. Learned something new today

[pzart]

Great explanation CB. Learned something new today

X2....great info to know

[CLM65]

Rick,

I've been doing some searching on the web for additional installation information for these poly tanks (I bought one for my rebuild too).  I came across something for Kracor tanks.  They are made of crosslinked polyethylene, just like our Incas, and their expansion is very close to what Inca reports (about 1/4" per 12", or about 2%).  What really stood out was the statement "This swelling will occur during the first 30-45 days after being filled and will then stabilize".

So, unless you can fill the tank and let it sit for a month or so, I'm not so sure the "gas fill" test is going to be meaningful.

Here is a link to the Kracor document:

http://4wings.com/lib/files/fueltanks.pdf

[RickK]

Thanks Craig - a super sleuth   Wonder if that means only if you leave a full tank?
I need to spend some time grinding out the corners a bit and regain the clearance I once had.  I want to add the cushioning that it needs.  My buddy Dave gave me a neoprene "square" about 2'x2'x 1/2".  I will cushion anywhere this tank sits against something hard and in the corners.  Not for another 2 weekends though  

[CLM65]

 

[RickK]

My how time flies...
I had to either cut the tank shorter or make the coffin larger. Harbor freight didn't have a plastic welder of that magnitude so the coffin lost out.
I cut, added on and then scarf jointed the connections and laid in about 6 layers of glass.  It's solid and I gained 1-1/2" more clearance.


Then I glassed in the bulkheads


Next I glassed in the outer tank supports


This morning I drilled some drain holes for the coffin into the main pipe going thru per Fernando's suggestion  




Then I cut high density foam and contact cemented it in place anywhere the tank would touch the coffin or could touch it.




I then set the tank in.  It's hard to see the foam but I now have about an inch on each end of the tank - 1/2" from the foam on each end the foam is 1/2".  Let the swelling begin.  I'll also leave room for that swell in the strapping across the top of the tank.












Plenty of room still.


Next is laying out the fill/vent and starting to think about routing power forward and everything else aft.

[CLM65]

Looks great Rick.  Fits like a (loose) glove !

[Callyb]

Geez Rick. That is some first class work right there.

[GoneFission]

Nice!!!    

[Capt. Bob]

Kinda hard to see the silver nitrate embedded in the HD foam with the blue filter lens but I'll assume it's there.

Lookin' good.

PS... Trust you had enough left for the hoof.

[Blue Agave]

Looks great Rick!  Do you have an estimated launch date for the 170?

[gran398]

It looks GREAT.

That little beefcake is gonna outlast everyone here by a long shot.

[Callyb]

[dirtwheelsfl]

Looks great Rick!  Do you have an estimated launch date for the 170?

Isnt it bad karma to answer that?!   Haha