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Date: Fri, 02 Dec 2011 11:45:47 -0500
From: Chad Robinson <crobinson@medialantern.com>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
CC: Ernest Christley <echristley@att.net>
Subject: Re: [FlyRotary] Re: Steve Brooks Cozy
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I looked into what it would take to get these blow-molded, maybe with a 
group buy from other builders. The complication is that the strakes are 
a lifting body and are structural. The ribs are part of that structure. 
They also serve as anti-slosh plates inside the tanks. Any solution 
needs to include both of them. It's do-able: you just need a tank 
blow-molded for each of the individual tank sections, then you 
plastic-weld them together around the strake ribs. But it means you need 
a bunch of molds...

At the time, I had already bought a batch of ProSeal, so I went with 
that. It looks pretty good - guess we'll see how it holds up (it sure 
wasn't cheap.) So I never finished the research.

The issue is there's a large group of rotary builders but a smaller 
group of Cozy MKIV builders. Cozy builders with aircraft engines don't 
need to deal with this - so it's an even smaller group. I'd be surprised 
if you could get even 25 people together on an order, and you'd need 
several hundred to make it economical to build the blow-molds.

One alternate plan I had tinkered with involved making a very 
rudimentary mold in the shop, then heating a standard 5-gallon red 
plastic gas can and using compressed air to "inflate/reshape" it. A very 
thin wall is just fine (preferable, even). The structure comes from the 
Cozy's strake structure - you're just making a liner. But it's a lot of 
work and finicky to get it right. I also looked into bladders, but there 
are maintenance and reliability concerns with them filling/deflating 
properly in odd-shaped spaces.

Regards,
Chad

On 12/2/2011 10:48 AM, Ernest Christley wrote:
> I reluctantly made a decision to not trust sealing a gas tank to any petrochemical that is shipped to me in a liquid
> form.  You never know what all those petrochemical engineers in Congress will decide mandate to be put into our fuel
> next.  So I welded a fuel tank and glassed that into the place that was designed for a fiberglass tank.  I would have
> preferred buying a premade poly-ethylene or aluminum racing tank, but I couldn't find one that even came close to fitting.
>
> Aren't the Cozy tanks just big cubes sitting inside the wing roots?  Would it be safer, and possibly easier, to buy a
> tank, sit it in the, and glass it into place?
>