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Date: Fri, 02 Dec 2011 13:24:20 -0600
From: Charlie England <ceengland@bellsouth.net>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: Steve Brooks Cozy
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I think that the RV-x tank skins are .030, & they have to both carry the 
fuel weight (at 6g+safety margin) and do structural duty as the wing 
root end D-cell. The newer polysulfide (I think that's the right term) 
sealants seem to work fine exposed to ethanol. (The older stuff can't 
handle even non-E auto gas.)

There are companies selling 'slosh' for automotive/motorcycle tank use, 
so odds are high that they are fine with alcohol.

I think that a lot depends on how late in the evolutionary chain the 
particular sealant came into being. A few days ago, I had a long and 
interesting conversation with an engineer at Precision (fuel injection, 
fuel pumps, Marvel-Schebler carbs, etc). I asked him about replacing any 
needed parts in an MA4 a/c carb to allow safe use of ethanol mogas. He 
said that if you ignore the issues of water capture & subsequent 
corrosion issues, the 'soft' stuff in the carb wouldn't have any 
problems with E-gas. My take on the conversation was that newer fuel 
pumps wouldn't have any deterioration issues, because the 'rubber' 
suppliers have changed their materials formulations in response to 
E-gas, & the aviation products got the benefit.

We didn't discuss Jefco, though...

Charlie

On 12/02/2011 11:44 AM, Ernest Christley wrote:
> My research lead me to "roto molding".  You build a cheap, sheet metal form, that the molder fills with a calculated
> amount of powdered plastic, and then puts on the end of a rotating arm that goes in an oven.  As the form is heated, it
> is rotated on all axis.
>
> I was willing to make the form, but couldn't find a molder.  I ended up just welding the seems to make a tank.  The
> number of Dyke Delta rotary builders is an even smaller subset than the Cozy rotary builders 8*).  I used .050" for my
> tank since it has to actually hold the weight of the fuel.  If I were going to be burying it in a wing where it would be
> supported on all sides, I would have used the thinnest material I could have reasonably worked with (.020" maybe?)
>
> Chad Robinson wrote:
>> 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?
>>>
>>
>> -- 
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>
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