Moose fuel tanks

[Mike Davis]

Wanted to run an idea I had past everyone... I originally placed the order
for my Moose kit with 80 gallon tanks... it was tempting to order the 120
gallon tanks, but the thought of keeping 720 lbs. of fuel on board to keep
the tanks full just didn't seem like the way to go. But Alaska sure is a
big place, and I'd love to be able to carry that much fuel.

Then I had a thought... what about splitting the wing tanks in two? Why
couldn't you just leave the middle rib whole, and put a check valve in it at
the bottom rear corner, to allow fuel to flow from the outer compartment to
the inner compartment, but not back out. You could use the typical ram air
fed into the outer tank to provide positive pressure. This way you could
normally fly only filling the inner tanks which would give you 60 gallons.
But on those occasions when you wanted the extra fuel you could also fill
the outer tanks to get the full 120 gallons. This could easily be split
80/40 or any other combination also since all the ribs start out solid, and
you would drill out only those you needed.

Having the ram air feed into the outer tank should cause the outer tank to
drain completely into the inner tank before the inner tank level started to
fall. Once the outer tank was empty air would start passing through the
check valve and the inner tank would
empty normally so your site gauges would still be accurate from the 60
gallon point down. I suppose an electronic sending unit could be installed
in the outboard tanks for monitoring, or with a little additional plumbing a
second set of site gauges.

I've drawn a simple picture of what I have in mind and loaded it to the web
site in area 58, Super Rebel Wing, or click here:

http://rebel:builder@www.dcsol.com:81/f ... altank.jpg

I'd love some feedback from everyone... let me know if you think this would
work alright. I've sent the idea to Murphy too, and will let you know what
they think. I think it would be great to keep it full at 60 gallons, and
still be able to load it to 120 for that big moose hunting trip.

Mike
195SR




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[Robert Johnson]

Not being an expert, this is what I see could be a problem. 1/ I doubt you
would get enough ram air pressure to force the outboard tank empty while
still maintaining a quantity of fuel in the inboard. 2/ If the inboard tank
only is full, and sealed with the check valve like you describe this means
there is no vent in this tank and what do you think would happen sitting in
the hot sun ??? 3/ If the outboard tank was empty a lot of the time, I would
be concerned about condensation (water) build up when sitting, and this
would be the first thing sucked into the inboard tank when running. ( if of
course you had enough suction to open the check valve without collapsing the
wing section first.) Just MHO -Bob J Rebel "652"




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[Mike Davis]

Hi Bob, I had not thought about expansion on the inboard tanks, but had
considered plumbing the ram air into both tanks and placing a small valve on
the inboard tank that could be turned off (shut of the vent) when using the
outboard tanks... this would take care of pressure normalization. As for
ram air alone moving the fuel from outboard to inboard, my thought was that
the ram air only has to help since the system would still work as a gravity
based system as fuel was burned out of the inner portion... I see what you
mean though if the inboard was full it would be working against gravity
after a while. I thought my uncle's tip tanks on his Comanche transferred
using pressure only, and I know he burns those off first, while the tank
they transfer to remains full... I'll have to check with him and see for
sure how those work.

Water condensation is the main reason I'm interested in separate tanks... it
would be much worse with one big tank if I didn't keep it full. The
outboard portion of the tank would need it's own pencil drain of course, but
again long range tanks are fairly common on a lot of aircraft and I'm not
aware of any increased tendency for water collecting in the tanks when
empty.

One of the local builders has two separate tanks in each wing, but he ran
separate plumbing from each into the cabin, and then has two small valves
mounted in the cabin in each wing root to turn them on and off, then runs
them both down the same line into the cabin to a central andair selector on
the floor. I'm not sure what he is going to use for a quantity indicator on
the outboard tanks. I was hoping for something simpler than this though.

Thanks, Mike
195SR

----- Original Message -----
From: "Robert Johnson" <ob.johnson@sympatico.ca>
To: <murphy-rebel@dcsol.com>
Sent: Thursday, April 11, 2002 4:31 AM
Subject: Re: Moose fuel tanks

Not being an expert, this is what I see could be a problem. 1/ I doubt you
would get enough ram air pressure to force the outboard tank empty while
still maintaining a quantity of fuel in the inboard. 2/ If the inboard

tank

only is full, and sealed with the check valve like you describe this means
there is no vent in this tank and what do you think would happen sitting

in

the hot sun ??? 3/ If the outboard tank was empty a lot of the time, I

would

be concerned about condensation (water) build up when sitting, and this
would be the first thing sucked into the inboard tank when running. ( if

of

course you had enough suction to open the check valve without collapsing

the

wing section first.) Just MHO -Bob J Rebel "652"

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[Warren Montgomery]

Mike,

As you may know I went through all the options to increase my 80s to 120s for the upgrade. This included the option of tip tanks. In the end I ripped apart my 80s when doing the upgrade and increased to 120s. I was able to buy the stock cut to size
for under 300USD from metalmart.com. They sell by the sq" so in this case were by far the cheapest. I'm used to lots of tanks on big aircraft so if I had to do again I would consider seperating each wing into 2x30s then running an aluminum tube from
the outter tank to a secondary outlet on the root rib. I'd then mount a westac capacidene probe on the root rib and a secondary one on the outter most rib of the outter tank .I'd also run a through vent from/to each outter tank. I'm not sure why I
did't do it this way for my retofit. Oh well, not going to do my tanks a third time!

This would mean 4 fuel caps/ probes/outlets etc. Damn, and I had a spare set of probes.

Good luck.
Warren
Dubai, UAE
SR029




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