Dual tanks... ?
 

Hi All,

On my Goldberg Extra 300 I am ready to mount the fuel tank and I have a question.

The engine chosen for this aircraft is an ASP 1.08, and the fuel tank space is only large enough for a 12oz tank if I use a regular Sullivan/Dubro/Great Planes tank. The 14 and 16oz tanks are all about 1/2" too long to fit. According to everything I have heard, a 12oz tank will only give about 6-8 minutes of time with this engine. I would like more than 10-12 minutes.

So, one thing that comes to mind is a dual tank arrangement, with a smaller (10oz?) tank up behind the firewall, and a larger tank (12-16oz?) near the CG. The engine does not have a pump. Muffler pressure will be available. Can this type of setup be made to work with what I have to work with? Do you have any other ideas that may work for this aircraft?

I was thinking of using something other than a real hobby fuel tank as a fuel tank, but I have not found a suitable substitute that fits the space. I was also thinking it would be good to keep all that weight (if I was able to get 20oz or so to fit) closer to the CG instead of way up front.

I should add that the stock tank location is on the engine centerline, and this version of the Extra is the early one with the shoulder mounted wing. So the location of the second tank would be almost directly behind the front tank and the top of the rear tank would be about 3/4 of an inch below the bottom of the front tank.

Thanks in advance!

Dual tanks... ?
 

I've used two 10 oz tanks in this plane....

Put them side by side in the stock location....taped together...
Pluming can be fun...but works quite well..

Dual tanks... ?
 

i have two kraft hayes 11 oz tanks side by side in a sig extra 300 on the cg and it works great.a real bear to get in there to plumb it but worth it

Dual tanks... ?
 

Thanks for the input, guys! :) I will pick up two tanks tomorrow and plumb 'em in.

I imagine the routing is:
Pressure fitting in tank 1 to muffler pressure.
Suction (clunk) fitting in tank 1 routed to pressure fitting on tank 2.
Suction (clunk) fitting in tank 2 to needle valve.

If this is correct then all I have to do is figure out how to get the lines out the firewall hole. :rolleyes:

To fill the tanks you fill tank 2 (the one routed to needle) through the clunk line as normal, as it fills it then overflows to tank 1 (the pressurized tank) and fill it 'til fuel comes out the pressure fitting?

Thanks again,

Dual tanks... ?
 

Lets seeeeee

Carb line to clunk in tank one....
Overflow from tank one to to clunk in tank two...
Overflow from tank two to muffler pressure...

Yep, that sounds right...

If I remember right I used one of those quick fill fittings to fill the tanks mounted to the fire wall...

Dual tanks... ?
 

I have 3 tanks in my GP F-14 with a Cline Pump. Works better than some of my single tank planes.

mark

Dual tanks... ?
 

You have it right, here's a pic for a visual.

Also, go with the two tanks side-by-side. Without a pump, you'll have problems with having one of them on the CG.

Dual tanks... ?
 

Sweet! Thanks again guys. Off to earn some $$, then to the LHS for a couple o' tanks. :D

Dual tanks... ?
 

I've never had any trouble having the rear tank far aft..the engine only "sees" the tank it is drawing from...the other tank just feeds into it. Also works if you want to run a small tank near the engine with a large tank feeding it..the head pressure changes in the small tank are small, making for very consistant runs.

Dual tanks... ?
 

The problem will come during sustained nose-high attitude, once the engine has used some of the "local" fuel (which basically has slightly collapsed the tank) it is now pulling fuel from the local tank, which is pulling fuel from the aft tank. Of course, the TANK is not doing the pulling, the engine is.

I don't know if I got the point across, but trust me, it's a physics thing.

Oh..physics..
 

Yeah, you're right. I don't know anything about physics.

The muffler pressure will make the fuel flow from the rear tank to the front tank (unless it is some extreme distance and the hydrostatic head of the column of fuel in the line is too great for the muffler pressure to overcome). The front tank is never depleted of fuel, and it never has to "suck" fuel from the rear tank. It is fed fuel from the rear tank.

A good example where you can actually watch this happen is a heli running a header tank. Some helis have the main fuel tank quite a bit below the optimum elevation for the engine to maintain a consistant neddle throughout the tank. They run small headers close to the engine and at a level that allow a consistant needle. This set-up draws fuel "uphill" for extended periods and the mixture does not change until the header tank gets close to empty.

I've run this system on both helis and planes, and it works just dandy.

But then I don't know anything about physics..maybe that is why it works for me, I am just too stupid to know any better.

Dual tanks... ?
 

Hey, don't get upset, if it works, it works. But drawing fuel from tank "A" is going to require the exact amount of vacuum as drawing from "C" (providing it is a closed system).

Dual tanks... ?
 

If you use the side by side 10oz tanks I think you have to put them bottom to bottom to get them to fit into the fuse...

Mine had a OS91FX and could get 12 minute flights easy...
Full throttle was balistic....tooooo fast for me eyeballs....

Have a happy...

Dual tanks... ?
 

I'm not upset...whatever the explaination, from my experience I have found that running a header tank close to the engine and another tank farther away does not require a pump, does not produce the extreme fuel draw problems associated with running a single tank over the CG, and makes for very nice running engines altogether. YMMV

But I don't want to continue to drive this poor fellows thread off topic any longer.

Dual Tanks
 

As stated above a dual tank system is fine. Us heli guys use it often. The 1st tank that the motor draws fuel from stays full until the aft tank is fully depleated. Because of this I would advise you use the bigger tank in front of the CG and the smaller one aft. Additionally, make sure the main tank for the motor is the one in front of the cg. If you did it reversed the motor would drain the front tank first, causing a rearward CG change (not good).

Good Luck!

Here is a pic of the setup on my heli (Courtesy of DJ Vegh's site):

Phil (Mesa, AZ)

Dual tanks... ?
 

How about a twin-engine, scale plane with a high wing, like a PBY or a CL215? I'm imagining two header tanks in the engine nacelles fed by a large main tank in the fuse. And I figure that you'd need check valves in the supply lines to the header tanks and in the twin pressure lines to the main tank.

I'm thinking of the plumbing on a future project...