Extended range fuel tanks

[jclark]

Originally Posted by airguy

Here you go - 7.5 gallon tanks that can fit behind either seat in the 7/9 and extend about 3" into the baggage compartment. There's 2 hours of range for you without removing the passenger seat.

https://www.smoke-system-helper.com/tanks-only

I helped Marvin in the design of the "7.5 gallons" behind the seat tanks. I have two installed in an RV6.

They have been used as separate fuel and smoke oil tanks as well as two (plumbed together) fuel tanks.

The way **I** use them (your mileage may vary) is to plumb them to the "center" position of the standard Van's fuel selector. So I have "Left", "Aux", and "Right" positions.

Startup and takeoff on "Left" tank, fly 15 minutes (which is usually enough to get me to altitude) and then switch to the "Aux" tank. Assuming **ONE** tank, I fly for 45 minutes. At 15 minutes into this tank, I get my 30-minute interval timer saying change tanks. I fly for another 30 minutes and THEN change to "Right" tank. After that, I continue to fly as normal on my standard tanks. SO, this gives me 45 minutes of time, assuming 10 gallons per hour. It makes the RV6 have about 45 gallons and this allows me to travel with RV7's having 42 gallons.

IMPORTANT: Each tank is VENTED to the outside and I have clear tuning on the side of each as a "sight tube".

I have not had any troubles with the tanks.

I may be able to dig up some old photos and video if anyone is interested.

[DeeCee 57]

interesting stuff here...

James, what is the weight of those 2 7.5G tanks?
How are they secured?
Vented outside, flex line to the bottom or side fuse?
Since I don?t have a spare port on my fuel selector, the plan is to T into the line from the right Wing tank. Gravity + suction should alleviate the need for an additional pump?

Thanks

[Bicyclops]

Originally Posted by DeeCee 57

interesting stuff here...

James, what is the weight of those 2 7.5G tanks?
How are they secured?
Vented outside, flex line to the bottom or side fuse?
Since I don?t have a spare port on my fuel selector, the plan is to T into the line from the right Wing tank. Gravity + suction should alleviate the need for an additional pump?

Thanks

Think about that one before you do it. Much of the capacity of the tank is going to be higher than the wing tank. You might vent some of it overboard. I mounted a Facet pump with a built in check valve under the floorboard of the baggage compartment. The pump prevents flow either direction when not in use. I make sure that I've used enough fuel out of the tank I'm pumping into before I start the transfer.

I teed my vent into that of one of the mains and haven't had any problems with that.

The tank comes with tabs welded on that will attach to the seat belt anchors. There is another tab at the top that attaches to the seat back cross brace. It's pretty rigid.

Ed Holyoke

[jclark]

Originally Posted by DeeCee 57

interesting stuff here...

James, what is the weight of those 2 7.5G tanks?
How are they secured?
Vented outside, flex line to the bottom or side fuse?
Since I don?t have a spare port on my fuel selector, the plan is to T into the line from the right Wing tank. Gravity + suction should alleviate the need for an additional pump?

Thanks

What fuel selector do you have?
I would not merge with another tank.

I vent via INDIVIDUAL LINES to a 90 degree fuel fitting attached to the bottom of the fuselage right near where the flap extension rod enters the fuselage.

I don't recall the weight. I suspect the actual weight is on Marvins web site. This weight is not that far aft CG if you look closely as some of it is just below YOUR BACK.

For more dialog contact me at the gmail place. jclarkmail over there :-). Or call me 8 OH 3, 238, 2ll3.

[Walt]

Just a thought from a maintenance guy, I have a customer with the behind the seat tanks in his 7. Working in the aft fuselage or under the panel is nearly impossible without removing the tanks which is not a 5 min job.

[DeeCee 57]

I have an Andair duplex selector, so no way to add a line here... and the reason I will have to Tee into an existing line.
Now whatever system I install will of course have a tap. Once say the right tank would be near empty, I would open said tap to xfer the fuel in that tank, whilst feeding the engine with the other one.
Not sure gravity would suffice for the transfer though...

Intended are a couple of longer flights for which additional capacity would be welcome, but no need for a permanent system.

Side note: usually flying my -6 at about 43% power (19/2000) returns a TAS of 130 kts at a fuel burn of about 5.5 usg. Longest flight to date 5:40 at the end of which I still had 6.5 usg left, indication verified upon subsequent refueling. So my endurance at those settings is almost 7 hours no reserve.

[airguy]

Originally Posted by DeeCee 57

I have an Andair duplex selector, so no way to add a line here... and the reason I will have to Tee into an existing line.
Now whatever system I install will of course have a tap. Once say the right tank would be near empty, I would open said tap to xfer the fuel in that tank, whilst feeding the engine with the other one.
Not sure gravity would suffice for the transfer though...

I've got the same setup, what I have in mind is tapping into the return line from the fuel pumps (dual electric with a pressure regulator - excess returns to the tanks) and feeding the ferry into that return line. That way the duplex selector can be used to move the fuel into the wing tank of choice since it's merging with the pump overflow upstream of the duplex.

I'm going to use a Facet fuel pump with check valve for positive stop on flow either way unless it's energized to move the fuel from the ferry tanks to the wings.

[acroflyrgirl]

So from reading here it sounds like there might be a way that I could use my 4.25 gal smoke tank as an occasional fuel tank. I have the Van's fuel valve, so an extra port.

I would love to have that little extra fuel for those 1200 mile trips that usually require two fuel stops. Just wonder if it's a safe install and if it can be easily returned to smoke when needed.

What I've read was dedicated fuel rather than interchangeable to fuel then to smoke.

Cathy

[Bicyclops]

Originally Posted by acroflyrgirl

So from reading here it sounds like there might be a way that I could use my 4.25 gal smoke tank as an occasional fuel tank. I have the Van's fuel valve, so an extra port.

I would love to have that little extra fuel for those 1200 mile trips that usually require two fuel stops. Just wonder if it's a safe install and if it can be easily returned to smoke when needed.

What I've read was dedicated fuel rather than interchangeable to fuel then to smoke.

Cathy

Howdy Cathy,

I'd be a little nervous about getting a slug of smoke oil in with the gas. Mixed into the fuel in a tank, it would lower the octane rating and possibly cause you detonation. A slug of oil right into the carb or fuel servo might be immediately catastrophic. You would need a positive way to know that the tank and lines were completely flushed out with fuel and the flushed fuel disposed of when you convert the system. Going back to smoke would be easier. You probably wouldn't want to pump a whole lot of fuel right into your pipes, but at least you wouldn't be as worried about failing the engine.

Ed Holyoke