Drains in Wing Tanks

[flybynightkarmarepair]

Wag-Aero has a special this month on quick drains:
http://www.wicksaircraft.com/catalog/product_cat.php/subid=6879/index.html

I'm building a mongrel dog of a low wing airplane that uses wing tanks,
pretty much like the Hummel Ultracruiser Plus. The tanks themselves
are .032 aluminum. The question of the day is how to mount the drains
to the tanks.

2 styles and several sizes of drains are offered. The use either
tapered pipe thread or straight threads.

Obviously, a doubler will be needed to provide enough meat to fasten
the drains to. The question is to whether to make a fairly thick
doubler, and tap it for the tapererd pipe thread, or to use a somewhat
thinner doubler, tap it for straight threads, and put a shear nut on
the inside of the tank, before pro-sealing it up.

How thick should a piece of 6061-t6 be in order to securely hold 1/8"
NPT threads? I think I'm leaning toward that solution, with the
doubler OUTSIDE the tank skin to keep the un-usable fuel down a bit.
Looking at my "Machinery's Handbook", I'd need 0.2639" for full thread
engagement. Can I live with less than that? What do RV's use in this
area?

OR, am I barking up the wrong tree entirely, and I should grab a
welding flange, drill some holes in it, and slap it on with rivets and
pro-seal, and let it hang down.
http://www.aircraftspruce.com/catalog/appages/alumflange.php

[Drew Dalgleish]

On 2 Apr 2006 23:37:06 -0700, "flybynightkarmarepair" >
wrote:

>Wag-Aero has a special this month on quick drains:
>http://www.wicksaircraft.com/catalog/product_cat.php/subid=6879/index.html
>
>I'm building a mongrel dog of a low wing airplane that uses wing tanks,
>pretty much like the Hummel Ultracruiser Plus. The tanks themselves
>are .032 aluminum. The question of the day is how to mount the drains
>to the tanks.
>
>2 styles and several sizes of drains are offered. The use either
>tapered pipe thread or straight threads.
>
>Obviously, a doubler will be needed to provide enough meat to fasten
>the drains to. The question is to whether to make a fairly thick
>doubler, and tap it for the tapererd pipe thread, or to use a somewhat
>thinner doubler, tap it for straight threads, and put a shear nut on
>the inside of the tank, before pro-sealing it up.
>
>How thick should a piece of 6061-t6 be in order to securely hold 1/8"
>NPT threads? I think I'm leaning toward that solution, with the
>doubler OUTSIDE the tank skin to keep the un-usable fuel down a bit.
>Looking at my "Machinery's Handbook", I'd need 0.2639" for full thread
>engagement. Can I live with less than that? What do RV's use in this
>area?
>
>OR, am I barking up the wrong tree entirely, and I should grab a
>welding flange, drill some holes in it, and slap it on with rivets and
>pro-seal, and let it hang down.
>http://www.aircraftspruce.com/catalog/appages/alumflange.php
>
My murphy rebel uses a welding flange pro-sealed and rivetted on. Pipe
threads are the way to go cuz sooner or later you're going to have to
replace that valve and it would suck if you had to open the tank to do
it.

[Charlie]

flybynightkarmarepair wrote:
> Wag-Aero has a special this month on quick drains:
> http://www.wicksaircraft.com/catalog/product_cat.php/subid=6879/index.html
>
> I'm building a mongrel dog of a low wing airplane that uses wing tanks,
> pretty much like the Hummel Ultracruiser Plus. The tanks themselves
> are .032 aluminum. The question of the day is how to mount the drains
> to the tanks.
>
> 2 styles and several sizes of drains are offered. The use either
> tapered pipe thread or straight threads.
>
> Obviously, a doubler will be needed to provide enough meat to fasten
> the drains to. The question is to whether to make a fairly thick
> doubler, and tap it for the tapererd pipe thread, or to use a somewhat
> thinner doubler, tap it for straight threads, and put a shear nut on
> the inside of the tank, before pro-sealing it up.
>
> How thick should a piece of 6061-t6 be in order to securely hold 1/8"
> NPT threads? I think I'm leaning toward that solution, with the
> doubler OUTSIDE the tank skin to keep the un-usable fuel down a bit.
> Looking at my "Machinery's Handbook", I'd need 0.2639" for full thread
> engagement. Can I live with less than that? What do RV's use in this
> area?
>
> OR, am I barking up the wrong tree entirely, and I should grab a
> welding flange, drill some holes in it, and slap it on with rivets and
> pro-seal, and let it hang down.
> http://www.aircraftspruce.com/catalog/appages/alumflange.php
>
a/c building is like plumbing work; sometimes it pays to just pay
instead of doing it yourself.

Van's a/c has pipe threaded flanges, predrilled with rivet holes just
for this purpose. s&h will probably cost more than the parts.

[Lou]

Seeing how I'm near this stage: How would you handle this in a
fiberglass tank?

[flybynightkarmarepair]

You could:
+ ignore the problem. Most fiberglass homebuilt tanks I've seen don't
have quick drains; they're relying on the gascolator to stop the water.
+ use the aluminum welding flanges, and either embed them in the layup,
or flox them in place, after drilling holes in the flange for the flox
"rivets" to squeze through.
+ use polysulfide (Pro-Seal is one (un)popular brand) to glue a welding
flange onto a completed tank, again, after drilling holes in the
flange.

I'm going to take the previous posters advice and rivet some flanges on
my tanks, with closed end pop rivets, dipped in MEK to degrease them
first, and everything slathered in Pro-Seal.

[Morgans]

"flybynightkarmarepair" > wrote

> I'm going to take the previous posters advice and rivet some flanges on
> my tanks, with closed end pop rivets, dipped in MEK to degrease them
> first, and everything slathered in Pro-Seal.

Forgive my ignorance, but is this proseal safe to use with alcohol in the
gas? If not, nowadays, that seems to be taking a very big risk.
--
Jim in NC

[Lou]

What sealent would you recommend?

[Richard Lamb]

Lou wrote:
> What sealent would you recommend?
>

google "Fuel tank sealant" +Alcohol

About 100 hits

this was the first one...
http://www.motoroilcompanies.com/fueltank/fueltanksealer/

[Morgans]

"Lou" > wrote in message
oups.com...
> What sealent would you recommend?

Good welding?
--
Jim in NC

[flybynightkarmarepair]

Polysulfides like Pro-Seal are resistant to fuel and alcohol.

Poly Vinyl Alcohol used to be the favored pour-in fuel tank sealer; no
more since alcohol has creapt into gas many places.