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Yo! Fuel Tank!



 
 
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  #1  
Old October 21st 03, 06:09 AM
Veeduber
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Posts: n/a
Default Yo! Fuel Tank!


Riveted aluminum fuel tanks are smart. They're easy to build and superbly
practical for the homebuilder since she can make them in whatever shape she
needs.

Most folks shy away from this fabrication technique due to the high cost of
Pro-Seal, still listed at more than $8/oz in the Aircraft Spruce catalog (P/N
09-38500 "2oz sealant" $17.85). But now that Thiokol's patents on polysulfide
sealants have expired seam-sealers that do equally well are available for
pennies per pound instead of dollars per ounce. Life Industries is one such
source. They make a line of polysulfide sealants for marine applications,
including a two-part fuel-proof formulation used to calk fuel tanks & bilges.

With aluminum, the sealant-bonding question - getting the stuff to stick - is a
no-brainer. Go to your local Home Depot and buy a quart of JASCO ‘Prep &
Primer.' Or buy a quart of ‘AlumaPrep' from Aircraft Spruce. Same stuff,
chemically speaking. Of course, the aviation-grade' alumaprep is dramatically
more expensive.

Degrease then etch the panels you want the sealant to adhere to for thirty
minutes in a solution of ‘Prep & Primer.' (The strength of the solution isn't
critical. Anything from 1:1 to 3:1 works fine on clean aluminum. If using
Alumaprep, follow their dilution instructions.) ‘Prep & Primer' is a
phosphoric acid etchant made specifically for galvanized and aluminum surfaces.
Scrub the etched surface with a Scotch-brite pad and neutralize with boiling
water. The result will be a matte white finish.

To insure greater integrity of your rivet line, you may wish to use countersunk
rivets. The dimple adds depth to the rivet line, making it stiffer without
increasing its weight. The 120 degree dies you need for poppers are available
from Airparts in Kansas City (www.airpartsinc.com) for about six dollars. And
from other folks, too. The dies are used with your regular pop-rivet gun. Of
course, if you have a lathe it takes only a few minutes to make such a set of
dies and even un-hardened they'll last for several plane's-worth of dimples.

If you've never used flush-head poppers, run a few rows of sets before tackling
the tank. The dimpling process ENLARGES the hole. The geometry here is subtle
so be cool, work at the pilot-hole level, opening up the hole to rivet-size
after you've dimpled & fitted the row. If you don't, the rivet will be too
loose to pop; it'll just pull out. Be VERY careful when deburring as you'll be
working on a corner instead of a flat. A file may be a better choice than a
regular deburring tool. (These factors have probably contributed to the
Conventional Wisdom that sez flush-head poppers don't work very well. They work
just fine, but only when they fit the hole.)

With a pitch of about an inch aluminum poppers provide more than adequate
strength for this application. Indeed, the stiffness of steel flush-head
poppers dictates a minimum metal-depth of about forty thou. Anything thinner
and you're liable to pull the popper through the hole before it can form a
large enough shop-head to snap the mandrel.

You can buy flush-head aluminum poppers from J.C.Whitney in boxes of 500 for
about $12. (JCW item# 14xx4090A, box of 500, $12.19) The short ones do fine for
this type of job.

As with all poppers, be sure to wash them good in MEK prior to use. The
manufacture of pop rivets always leaves some amount of lubricant on the
finished product. That tiny trace of oil will interfere with the adhesion of
the sealant (and of your zinc chromate, when using steel poppers on your other
panels).

Steel poppers may be a wiser choice for attaching the flanged aluminum fitting
for the tank's outlet. You may of course use steel button-head poppers for the
entire tank if you wish. I like the flush-head aluminum jobbies for the
seam-lines because they give me a stiffer joint at less weight.

If you prefer to use solid rivets you'll need to provide access for bucking the
things. Wag Aero still sells sealed blind-nuts for a reasonable price (Cat#
L-676-000 Pkg of 50 for $10.95) Sealed blind nuts are standard for fuel tanks.
The threads of the screw are sealed away from the contents of the tank inside a
little dome. Slosh the tank, you can still remove the access panel.

Tanks tend to violate the rule for panel size vs edge support so you'll
probably want to pound an ‘X' bead into the four sides and the bottom. If
the top of the tank is curved it will already be stiff enough but the sides &
bottom will tend to be pretty wimpy, especially if you're using soft aluminum.
(Almost anything will do for making a tank. Don't tell anyone but I've made
tanks out of siding aluminum. )

If you don't understand what I'm talking about here, take a look at a steel
Jerry can. Some guys like to roll such flutes into the panel but you can do
perfectly well by making up a suitable groove or gap in a board, laying the
panel across it and making several light passes along the groove with your
rubber mallet.

Fuel tank is usually an irregular box. Occasionally an irregular cylinder.
Cylinders support themselves but boxes don't. If the thing has corners, plan
on adding a couple of baffles, not only to control the slosh but to stiffen the
structure.

Rivet-on flanges for the filler and outlet are available from aircraft
suppliers but since they are simple turnings they are easy enough to make if
you have a lathe. And even if you don't. There are thousands of
hobby-machinists on the Internet, their weapon of choice a little 7x10 lathe
that's plenty big enough to whip out a set of fuel tank fittings. To track down
such folks just go to the appropriate Newsgroup – rec.crafts.metalworking is
but one of dozens of such groups – post a message having ‘Help!' as the
subject line, describe the job and tell them where you're located. The
squeaking wheel gets the grease - keep shouting until you connect with someone
in your area. Like all machinists - which is what these folks are... the size
of the machine has nothing to do with it - he'll need an accurately dimensioned
drawing to work from and you'll probably need to provide him with the stock.
Applying sealants is messy as hell, especially Pro-Seal and the other
polysulfides. Masking off the area to be sealed/riveted will help and you might
want to consider PK's instead of clecos. Polysulfide sealant is close to the
perfect adhesive, it'll stick to ANYTHING... and doesn't like to come off. (For
dimpled holes you'll need the longer (ie, 3/8") PK's.) Grubby-up a PK, throw it
away. You're out maybe two cents.

Give the surface to be sealed a final wipe-down with MEK (or whatever solvent
is recommended for you sealant). Allow it to evaporate. Apply the sealant
according to the instructions. Most call for a smooth, uniform coating on both
surfaces. Not too thick, a few thousandths is all you'll need if your
rivet-line is a good fit. And not too wide, about three-quarter of an inch,
max. Most of this stuff cures by reaction with water vapor in the air,
something present everywhere on our particular planet. Cure time is a function
of the width of the sealant-line and the humidity in the air. (That's why the
stuff is so popular with boaters – it cures underwater faster than out of
it.) The two-part formulation cures faster than the no-mix stuff.

You only need about three ounces of sealant for a ten gallon tank, most of
which will go on the flanges, your tools and your clothes. (If you've never
used Pro-Seal before, buy a pint :-)

If you use the 2oz kits, the little tubes can be hard to handle without the
matching gun, a $75 item. (Aircraft certified, right? :-) A dime's worth of
Bondo will allow you to modify a regular calking gun to accept the 2oz
aircraft-certified cartridges. If you want to go that route, I'll tell you how
to make an adapter.

Aircraft Spruce also lists the stuff in pints [$37] and quarts [$74] but the
secret to using bulk-packaged sealants is how to mix & apply the stuff without
gluing yourself to the wall. The usual mix ratio is 10:1 and is fairly
critical. The use of a ratio'd balance beam, baggies for one component and a
Teflon cup for the other is a fairly common procedure. Once you've balanced the
beam, pour the One-stuff from the Teflon cup into the Ten-stuff in the plastic
baggie then seal up the baggie and mix the stuff by squishing the baggie, like
colorizing oleomargarine in days of yore. (That's my yore, not your yore.) Once
the color is uniform, snip a corner of the baggie and squeeze the stuff out
like decorating a cake, using a scrap of metal as a palette knife to smooth the
bead to a uniform thickness across the bond line.

Standard practice when using poppers with a sealed structure is to dip the
degreased popper in the sealant just before you stick it in the hole and give
it a little twist. Don't get too far ahead with the sticking & twisting before
coming back and doing the popping. The structure should be perfectly secured
with a PK in about every fourth hole giving you three poppers in a row. When
you pop, always do the middle one first. Once it's popped some guys butter a
smear of sealant into the mandrel hole but it's not necessary if you're going
to slosh the tank.

After your tank is fabricated leave it alone for about three days, until the
sealant is cured. After it has cured you can provide yourself with virtual
100% leak-free assurance by sloshing the tank with a PVA fuel tank sealant. J.
C. Whitney will sell you a quart of the stuff for about thirty bucks. You need
less than a pint but I haven't found anyone who'll sell me that small a
quantity. As with the polysulfides, there are only a few companies that make
fuel tank sealants and most use functionally identical formulations. The thirty
dollar stuff from J.C.Whitney appears to be the same as the hundred dollar
stuff with ‘aircraft-certified' on the label. Maybe it's not but it works the
same.

Since your tank was already etched, the sloshing sealant is going to form a
perfect bond. Plug the outlet, pour in the sloshing sealant (it's a creamy
white stuff; the vehicle is MEK) seal up the inlet (I use a hose clamp and
piece of inner tube) then commence rolling the tank over and around and up and
down... but in a logical fashion. What you want to do is to flow the sloshing
sealer over every part of the interior surface.

After sloshing the tank, drain the sealant back into its can and seal it up
good. Remove whatever is plugging the drain so air can circulate through the
tank, prop it so it can drip out then leave the thing to cure.

Takes about 24 ours.

When it's cured, get your light wand and your bore scope and whatever else you
need and inspect the interior surface. It should have a uniform white coating.

The sealant is a form of PVA – polyvinylalcohol. Once cured, it is impervious
to virtually all solvents, including gasoline, alcohol and water. I've used the
J.C.Whitney stuff on steel, aluminum and fiberglas with excellent results (JCW
"Alcohol resistant Gas Tank Sealer" item# 12xx8316Y each $28.99). How well it
works depends largely on how well you've prepped the surface. Basic rule is to
have it perfectly free of grease, including fingerprints. For aluminum, you
need to provide some ‘tooth' to the surface, which is accomplished by the
etchant (ie, the Prep & Primer stuff).

Lots of ‘expert' homebuilders damn such tanks with faint praise. Sure it
works... but REAL fuel tanks are ALWAYS welded, yadayadayada... Sure they are,
Mr. Expert. (I invite those experts to join me at FlaBob as we refurbish a
P-51... and its riveted, sealed and sloshed fuel tanks.)

Your fuel system should have a strainer in the tank. Smartest one you can get
is to MAKE YOUR OWN using a short length of 3003 aluminum tubing, slit about
every quarter inch with a hobby saw. The typical hobby saw leaves a kerf about
..028" wide, much smaller than the mesh of a cheap finger strainer. Cut enough
slots to insure the thing will flow enough fuel.

The tank should be equipped with a shut-off valve. See the Northern Hydraulics
catalog. Go to the same source for your gascolator. It ain't
aviation-certified but it works and doesn't cost the earth.

Basic fuel tank plumbing is to keep a constant down-ward flow of fairly large
diameter tubing from the tank to the gascolator. The idea here is that
anything large enough to get through the strainer in the tank will NOT block
the fuel line but will simply end up in the gascolator.

If you're flying a VW a primer makes for easier starting. Since you hand-prop
real engines, put the primer near the gascolator; no need to put any more fuel
in the fuselage than absolutely necessary. Great Plains sells a good primer at
a fair price.

For lo-buck builders, riveted, sealed and sloshed fuel tanks are a practical
alternative to other methods of fabrication, their use so common we tend to
forget others may not have heard of them.

-R.S.Hoover

PS - The ‘xx' in the JCW item numbers is different for each catalog but the
basic number stays the same.




  #2  
Old October 21st 03, 04:49 PM
Bob Kuykendall
external usenet poster
 
Posts: n/a
Default

Cool. Good stuff; thanks for the info!

Also, here's an interesting article on fuel tanks from Alfred Scott's
Sequoia Aircraft site:

http://www.seqair.com/skunkworks/Fue.../Problems.html

Note that it's mostly about fairly large, fairly complicated fuel
tanks welded up from untempered aluminum. But the stuff about the
torture test should be of interest to folks who are designing their
own tanks.

Thanks again, and best regards to all

Bob K.
http://www.hpaircraft.com/hp-24
  #3  
Old October 21st 03, 06:04 PM
Kyle Boatright
external usenet poster
 
Posts: n/a
Default

For what it is worth, most of today's RV builders DON'T use slosh in their
tanks. In the old days, some builders were having problems with slosh
coming loose. Imagine having to open up a tank to remove mis-applied slosh
(or risk clogging your fuel filter with the stuff when it flakes off). Some
builders who didn't slosh had a leak or two, but it was easier dealing with
the leaks than with slosh that wasn't staying attached...

In the end, if you do everything right, you don't need slosh. Beyond that,
if you slosh *properly* the slosh won't come loose. It comes down to
following proper fitting, cleaning, and prep procedures all the way through
the process - slosh or not.

KB



  #4  
Old October 21st 03, 10:30 PM
Larry Smith
external usenet poster
 
Posts: n/a
Default


"Veeduber" wrote in message
...

Riveted aluminum fuel tanks are smart. They're easy to build and superbly
practical for the homebuilder since she can make them in whatever shape

she
needs.


[xlnt stuff]
Ah, Mr. Hoover, you've done gone and done it again, posted a wealth of
material. It's a keeper. Thanks.

I just tried to order some rivets, p-lead cable, and epoxy from ACS but
couldn't get their web catalog to work. Hint to J. Irwin: Use a checkout
like Wicks. It works.


  #5  
Old October 21st 03, 11:47 PM
Veeduber
external usenet poster
 
Posts: n/a
Default

To All:

Someone wrote to ask where they might find 'dimensioned drawings' as mentioned
in the post on fuel tanks.

Welll... they aren't all that good but you'll find simple drawings for most of
the stuff I've written about in the FILES archives of the Fly5kfiles mailing
list over on Yahoo, or one of the other mailing lists (FlyVW, etc). The
drawings are in DeltaCAD format. There's a link to the free DeltaCAD reader
software. The drawings are usually supported by a .txt file, an article or a
posted message but the linkage isn't always given.

These drawings are meant mostly for scratch builders trying to fly on the
cheap. If that's you, you probably already know about the drawings and their
related files. If any of this is news to you, you might want to scan the
archives of groups devoted to flying on the cheap and lo-buck building.

-R.S.Hoover
  #6  
Old October 22nd 03, 12:06 AM
Jim Austin
external usenet poster
 
Posts: n/a
Default

Thanks once again for another great post. I have printed it out
and will keep it for future use, as I'm sure many others will. Things
like this are what keeps me checking this group regularly despite the
personal attacks and other garbage I have to wade through.

Regards,
Jim Austin

  #7  
Old October 22nd 03, 01:48 AM
Blueskies
external usenet poster
 
Posts: n/a
Default

Indeed!

--
Dan D.



..
"Jim Austin" wrote in message
...
Thanks once again for another great post. I have printed it out
and will keep it for future use, as I'm sure many others will. Things
like this are what keeps me checking this group regularly despite the
personal attacks and other garbage I have to wade through.

Regards,
Jim Austin



  #8  
Old October 22nd 03, 03:06 AM
Veeduber
external usenet poster
 
Posts: n/a
Default

Dear Jim (and the Group),

The message about fuel tanks was first posted several years ago on another
mailing list. It was reposted here at the request of a subscriber and will now
be available via Google.

The main advantage of a newsgroup appears to be as an archival resource.
Thanks to Google and other search engines anyone interested in riveted fuel
tanks will find at least some information.

Because of the sociopaths who homestead newsgroups most of the real builders
that I know use r.a.h. only as a hailing frequency, communicating privately or
via special-purpose mailing lists once contact has been established.

-R.S.Hoover
  #9  
Old October 23rd 03, 12:16 AM
Bruce E. Butts
external usenet poster
 
Posts: n/a
Default

Great Article, it goes into my saved file for reference. But one
question.... What are PKs?

Thanks,
Bruce

Veeduber wrote:

Riveted aluminum fuel tanks are smart. They're easy to build and superbly
practical for the homebuilder since she can make them in whatever shape she
needs.

Most folks shy away from this fabrication technique due to the high cost of
Pro-Seal, still listed at more than $8/oz in the Aircraft Spruce catalog (P/N
09-38500 "2oz sealant" $17.85). But now that Thiokol's patents on polysulfide
sealants have expired seam-sealers that do equally well are available for
pennies per pound instead of dollars per ounce. Life Industries is one such
source. They make a line of polysulfide sealants for marine applications,
including a two-part fuel-proof formulation used to calk fuel tanks & bilges.

With aluminum, the sealant-bonding question - getting the stuff to stick - is a
no-brainer. Go to your local Home Depot and buy a quart of JASCO ‘Prep &
Primer.' Or buy a quart of ‘AlumaPrep' from Aircraft Spruce. Same stuff,
chemically speaking. Of course, the aviation-grade' alumaprep is dramatically
more expensive.

Degrease then etch the panels you want the sealant to adhere to for thirty
minutes in a solution of ‘Prep & Primer.' (The strength of the solution isn't
critical. Anything from 1:1 to 3:1 works fine on clean aluminum. If using
Alumaprep, follow their dilution instructions.) ‘Prep & Primer' is a
phosphoric acid etchant made specifically for galvanized and aluminum surfaces.
Scrub the etched surface with a Scotch-brite pad and neutralize with boiling
water. The result will be a matte white finish.

To insure greater integrity of your rivet line, you may wish to use countersunk
rivets. The dimple adds depth to the rivet line, making it stiffer without
increasing its weight. The 120 degree dies you need for poppers are available
from Airparts in Kansas City (www.airpartsinc.com) for about six dollars. And
from other folks, too. The dies are used with your regular pop-rivet gun. Of
course, if you have a lathe it takes only a few minutes to make such a set of
dies and even un-hardened they'll last for several plane's-worth of dimples.

If you've never used flush-head poppers, run a few rows of sets before tackling
the tank. The dimpling process ENLARGES the hole. The geometry here is subtle
so be cool, work at the pilot-hole level, opening up the hole to rivet-size
after you've dimpled & fitted the row. If you don't, the rivet will be too
loose to pop; it'll just pull out. Be VERY careful when deburring as you'll be
working on a corner instead of a flat. A file may be a better choice than a
regular deburring tool. (These factors have probably contributed to the
Conventional Wisdom that sez flush-head poppers don't work very well. They work
just fine, but only when they fit the hole.)

With a pitch of about an inch aluminum poppers provide more than adequate
strength for this application. Indeed, the stiffness of steel flush-head
poppers dictates a minimum metal-depth of about forty thou. Anything thinner
and you're liable to pull the popper through the hole before it can form a
large enough shop-head to snap the mandrel.

You can buy flush-head aluminum poppers from J.C.Whitney in boxes of 500 for
about $12. (JCW item# 14xx4090A, box of 500, $12.19) The short ones do fine for
this type of job.

As with all poppers, be sure to wash them good in MEK prior to use. The
manufacture of pop rivets always leaves some amount of lubricant on the
finished product. That tiny trace of oil will interfere with the adhesion of
the sealant (and of your zinc chromate, when using steel poppers on your other
panels).

Steel poppers may be a wiser choice for attaching the flanged aluminum fitting
for the tank's outlet. You may of course use steel button-head poppers for the
entire tank if you wish. I like the flush-head aluminum jobbies for the
seam-lines because they give me a stiffer joint at less weight.

If you prefer to use solid rivets you'll need to provide access for bucking the
things. Wag Aero still sells sealed blind-nuts for a reasonable price (Cat#
L-676-000 Pkg of 50 for $10.95) Sealed blind nuts are standard for fuel tanks.
The threads of the screw are sealed away from the contents of the tank inside a
little dome. Slosh the tank, you can still remove the access panel.

Tanks tend to violate the rule for panel size vs edge support so you'll
probably want to pound an ‘X' bead into the four sides and the bottom. If
the top of the tank is curved it will already be stiff enough but the sides &
bottom will tend to be pretty wimpy, especially if you're using soft aluminum.
(Almost anything will do for making a tank. Don't tell anyone but I've made
tanks out of siding aluminum. )

If you don't understand what I'm talking about here, take a look at a steel
Jerry can. Some guys like to roll such flutes into the panel but you can do
perfectly well by making up a suitable groove or gap in a board, laying the
panel across it and making several light passes along the groove with your
rubber mallet.

Fuel tank is usually an irregular box. Occasionally an irregular cylinder.
Cylinders support themselves but boxes don't. If the thing has corners, plan
on adding a couple of baffles, not only to control the slosh but to stiffen the
structure.

Rivet-on flanges for the filler and outlet are available from aircraft
suppliers but since they are simple turnings they are easy enough to make if
you have a lathe. And even if you don't. There are thousands of
hobby-machinists on the Internet, their weapon of choice a little 7x10 lathe
that's plenty big enough to whip out a set of fuel tank fittings. To track down
such folks just go to the appropriate Newsgroup – rec.crafts.metalworking is
but one of dozens of such groups – post a message having ‘Help!' as the
subject line, describe the job and tell them where you're located. The
squeaking wheel gets the grease - keep shouting until you connect with someone
in your area. Like all machinists - which is what these folks are... the size
of the machine has nothing to do with it - he'll need an accurately dimensioned
drawing to work from and you'll probably need to provide him with the stock.
Applying sealants is messy as hell, especially Pro-Seal and the other
polysulfides. Masking off the area to be sealed/riveted will help and you might
want to consider PK's instead of clecos. Polysulfide sealant is close to the
perfect adhesive, it'll stick to ANYTHING... and doesn't like to come off. (For
dimpled holes you'll need the longer (ie, 3/8") PK's.) Grubby-up a PK, throw it
away. You're out maybe two cents.

Give the surface to be sealed a final wipe-down with MEK (or whatever solvent
is recommended for you sealant). Allow it to evaporate. Apply the sealant
according to the instructions. Most call for a smooth, uniform coating on both
surfaces. Not too thick, a few thousandths is all you'll need if your
rivet-line is a good fit. And not too wide, about three-quarter of an inch,
max. Most of this stuff cures by reaction with water vapor in the air,
something present everywhere on our particular planet. Cure time is a function
of the width of the sealant-line and the humidity in the air. (That's why the
stuff is so popular with boaters – it cures underwater faster than out of
it.) The two-part formulation cures faster than the no-mix stuff.

You only need about three ounces of sealant for a ten gallon tank, most of
which will go on the flanges, your tools and your clothes. (If you've never
used Pro-Seal before, buy a pint :-)

If you use the 2oz kits, the little tubes can be hard to handle without the
matching gun, a $75 item. (Aircraft certified, right? :-) A dime's worth of
Bondo will allow you to modify a regular calking gun to accept the 2oz
aircraft-certified cartridges. If you want to go that route, I'll tell you how
to make an adapter.

Aircraft Spruce also lists the stuff in pints [$37] and quarts [$74] but the
secret to using bulk-packaged sealants is how to mix & apply the stuff without
gluing yourself to the wall. The usual mix ratio is 10:1 and is fairly
critical. The use of a ratio'd balance beam, baggies for one component and a
Teflon cup for the other is a fairly common procedure. Once you've balanced the
beam, pour the One-stuff from the Teflon cup into the Ten-stuff in the plastic
baggie then seal up the baggie and mix the stuff by squishing the baggie, like
colorizing oleomargarine in days of yore. (That's my yore, not your yore.) Once
the color is uniform, snip a corner of the baggie and squeeze the stuff out
like decorating a cake, using a scrap of metal as a palette knife to smooth the
bead to a uniform thickness across the bond line.

Standard practice when using poppers with a sealed structure is to dip the
degreased popper in the sealant just before you stick it in the hole and give
it a little twist. Don't get too far ahead with the sticking & twisting before
coming back and doing the popping. The structure should be perfectly secured
with a PK in about every fourth hole giving you three poppers in a row. When
you pop, always do the middle one first. Once it's popped some guys butter a
smear of sealant into the mandrel hole but it's not necessary if you're going
to slosh the tank.

After your tank is fabricated leave it alone for about three days, until the
sealant is cured. After it has cured you can provide yourself with virtual
100% leak-free assurance by sloshing the tank with a PVA fuel tank sealant. J.
C. Whitney will sell you a quart of the stuff for about thirty bucks. You need
less than a pint but I haven't found anyone who'll sell me that small a
quantity. As with the polysulfides, there are only a few companies that make
fuel tank sealants and most use functionally identical formulations. The thirty
dollar stuff from J.C.Whitney appears to be the same as the hundred dollar
stuff with ‘aircraft-certified' on the label. Maybe it's not but it works the
same.

Since your tank was already etched, the sloshing sealant is going to form a
perfect bond. Plug the outlet, pour in the sloshing sealant (it's a creamy
white stuff; the vehicle is MEK) seal up the inlet (I use a hose clamp and
piece of inner tube) then commence rolling the tank over and around and up and
down... but in a logical fashion. What you want to do is to flow the sloshing
sealer over every part of the interior surface.

After sloshing the tank, drain the sealant back into its can and seal it up
good. Remove whatever is plugging the drain so air can circulate through the
tank, prop it so it can drip out then leave the thing to cure.

Takes about 24 ours.

When it's cured, get your light wand and your bore scope and whatever else you
need and inspect the interior surface. It should have a uniform white coating.

The sealant is a form of PVA – polyvinylalcohol. Once cured, it is impervious
to virtually all solvents, including gasoline, alcohol and water. I've used the
J.C.Whitney stuff on steel, aluminum and fiberglas with excellent results (JCW
"Alcohol resistant Gas Tank Sealer" item# 12xx8316Y each $28.99). How well it
works depends largely on how well you've prepped the surface. Basic rule is to
have it perfectly free of grease, including fingerprints. For aluminum, you
need to provide some ‘tooth' to the surface, which is accomplished by the
etchant (ie, the Prep & Primer stuff).

Lots of ‘expert' homebuilders damn such tanks with faint praise. Sure it
works... but REAL fuel tanks are ALWAYS welded, yadayadayada... Sure they are,
Mr. Expert. (I invite those experts to join me at FlaBob as we refurbish a
P-51... and its riveted, sealed and sloshed fuel tanks.)

Your fuel system should have a strainer in the tank. Smartest one you can get
is to MAKE YOUR OWN using a short length of 3003 aluminum tubing, slit about
every quarter inch with a hobby saw. The typical hobby saw leaves a kerf about
.028" wide, much smaller than the mesh of a cheap finger strainer. Cut enough
slots to insure the thing will flow enough fuel.

The tank should be equipped with a shut-off valve. See the Northern Hydraulics
catalog. Go to the same source for your gascolator. It ain't
aviation-certified but it works and doesn't cost the earth.

Basic fuel tank plumbing is to keep a constant down-ward flow of fairly large
diameter tubing from the tank to the gascolator. The idea here is that
anything large enough to get through the strainer in the tank will NOT block
the fuel line but will simply end up in the gascolator.

If you're flying a VW a primer makes for easier starting. Since you hand-prop
real engines, put the primer near the gascolator; no need to put any more fuel
in the fuselage than absolutely necessary. Great Plains sells a good primer at
a fair price.

For lo-buck builders, riveted, sealed and sloshed fuel tanks are a practical
alternative to other methods of fabrication, their use so common we tend to
forget others may not have heard of them.

-R.S.Hoover

PS - The ‘xx' in the JCW item numbers is different for each catalog but the
basic number stays the same.







  #10  
Old October 23rd 03, 12:27 AM
Veeduber
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What are PKs?

-----------------------------------------------

Hex head sheet metal screws with an attached, non-marring washer. PK's are
what the world used before clecos.

Do a google for 'Riveting 101,' see if you find anything of interest.

-R.S.Hoover
 




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