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  #1  
Old 01-11-2021, 05:38 PM
blaplante blaplante is offline
 
Join Date: Jan 2010
Location: Southern California
Posts: 181
Default Aux Tank (temporary) - for side by side RVs

This is mostly a brainstorm that probably won't ever get to the front of the list

Feel free to (politely please) poke holes in this.

Goal: ways to add significant temporary extra fuel to the RV6 (could work in the 7 etc. as well). Significant being 12-15 gallons. Not required when flying with a passenger. It seems to me that a solution could be as follows:

Take out the passenger seat pads. Build a tank to sit on the floor and lean back on the seat back. Dimensions could be 15.5" wide, 27" high, and around 8.5" fore/aft. Weight all up is about 100 pounds. Use the harnesses to retain it. Probably additional hold down mounted to the seat cross-bar.

Vent overboard via hose and a new vent (location TBD).

Ground strap from tank to airframe.

Use a small electric fuel pump to pump from the tank into a Tee in the feed line from the right tank to the selector valve.

Use: Once the right tank is down (let's say to 6 gallons), switch to the left tank.
Engage the aux tank pump, verify the number of gallons pumped by looking at the right tank gauge. Most likely you'd do this in two rounds - pump 7 gallons to the right tank, and repeat later with the remainder.

Some advantages I see:
By pumping into the right tank we can drain the aux tank. Any un-porting of the fuel pump only interrupts flow to the right tank, not to the engine.
Pretty simple to install.
Weight is located at a fairly good position for w&b.
No need for fuel sender or gauge as the gauge in this scenario (dipstick to record starting fuel is all that's needed).

Downside is that I can't find a suitable size pre-made tank, so it would need to be scratchbuild, similar to an RV12 tank.

Some inspiration at https://www.kitplanes.com/adding-an-...nk-to-an-rv-8/

A low mounted tank like in the link above is another possibility, but strikes me as harder to tie down in the RV6.
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  #2  
Old 01-11-2021, 07:36 PM
Taltruda Taltruda is offline
 
Join Date: Oct 2017
Location: Las Vegas, NV
Posts: 637
Default

Iíve seen a plastic fuel cell that is kind of torso shaped.. itís meant to be secured into a seat with the regular harness. I donít know where my friend got it, but it would fit your needs perfectly..
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RV-8 empenage finished 10-2020

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  #3  
Old 01-11-2021, 08:15 PM
larrynew's Avatar
larrynew larrynew is online now
 
Join Date: Oct 2007
Location: In New Braunfels, ist das Leben schŲn!
Posts: 899
Default Turtlepac

Turtlepac might have what youíre looking for. https://www.turtlepac.com/products/c...an-fuel-tanks/
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RV-7A - Built, flew 900+ hrs, sold
RV-10 - Built, flying 100+ hrs
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  #4  
Old 01-11-2021, 08:57 PM
Kyle Boatright Kyle Boatright is online now
 
Join Date: Aug 2005
Location: Atlanta, GA
Posts: 4,434
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In addition to other ideas, I'd try Summit Racing. They have a number of different fuel cells for sale.
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  #5  
Old 01-11-2021, 09:23 PM
mbauer mbauer is offline
 
Join Date: Nov 2015
Location: Nikiski, AK
Posts: 430
Default

Quote:
Originally Posted by blaplante View Post
This is mostly a brainstorm that probably won't ever get to the front of the list

Feel free to (politely please) poke holes in this.

Goal: ways to add significant temporary extra fuel to the RV6 (could work in the 7 etc. as well). Significant being 12-15 gallons. Not required when flying with a passenger. It seems to me that a solution could be as follows:

Take out the passenger seat pads. Build a tank to sit on the floor and lean back on the seat back. Dimensions could be 15.5" wide, 27" high, and around 8.5" fore/aft. Weight all up is about 100 pounds. Use the harnesses to retain it. Probably additional hold down mounted to the seat cross-bar.

Vent overboard via hose and a new vent (location TBD).

Ground strap from tank to airframe.

Use a small electric fuel pump to pump from the tank into a Tee in the feed line from the right tank to the selector valve.

Use: Once the right tank is down (let's say to 6 gallons), switch to the left tank.
Engage the aux tank pump, verify the number of gallons pumped by looking at the right tank gauge. Most likely you'd do this in two rounds - pump 7 gallons to the right tank, and repeat later with the remainder.

Some advantages I see:
By pumping into the right tank we can drain the aux tank. Any un-porting of the fuel pump only interrupts flow to the right tank, not to the engine.
Pretty simple to install.
Weight is located at a fairly good position for w&b.
No need for fuel sender or gauge as the gauge in this scenario (dipstick to record starting fuel is all that's needed).

Downside is that I can't find a suitable size pre-made tank, so it would need to be scratchbuild, similar to an RV12 tank.

Some inspiration at https://www.kitplanes.com/adding-an-...nk-to-an-rv-8/

A low mounted tank like in the link above is another possibility, but strikes me as harder to tie down in the RV6.
I have an aluminum tank that holds 22-22.5 gallons, sits in the passenger seat of my RV-6 and works great. It does not use a pump, plumbed into Vans standard three-way fuel valve using 1/2" Rubber Marine fuel line, a short section of clear Tygon tubing (designed for fuel-not the cheap vinyl stuff you can buy at most hardware stores), Use head pressure to supply fuel to the regular system through the standard 3-way valve from Vans.

Tilt the seat all the back, strap in using the seat belt-have abrasion protection that was added, the vent line needs to go up front, not out the back. My AP/IA had me install it into the NACA inlet.

Bought a roll over protected vent valve from ebay.

Plumbing starts as 1/2" NPT-the stainless steel valve has NPT on the inlet, 8AN outlet to the filter, once past the filter it uses the rubber marine fuel line. Before using 8AN fittings again, have a section of the clear Tygon tubing to verify fuel flow. If bubbles show: know that it is getting low and I switch to the mains. You will need to verify accurate fuel flow at your cruise RPM so that you know when to start watching closely and more often if you want to burn the fuel to the empty level.

I've tested the system up to 17,500 to verify no problems. 1-gallon unusable.

Was able to complete a 1009-mile leg from Petersburg, Alaska to Hermiston, Oregon in 9-hours. Still had over an hour of fuel in the mains.

A friend who made marine fuel tanks for forty years TIG welded it up for me, he knew enough to add a filler neck/tube to about 2" from the bottom so that the filling is not just spraying fuel around inside.

Used .090 weldable type of aluminum (5200 series if I remember right).

Use two alligator clipped cables for the ground strap, portable and easy to remove or clamp into position. One on my side the other near the fuselage wall.

Fuel cap and neck came from Aircraft Spruce & Specialty.

Size:

15-1/2" Wide to fit between back seat angle-makes a nice fit and doesn't move around. Supported on both sides by the seat cushion angles.

Front to back is 12-3/4", this gives plenty of room for full deflection of the passenger seat control stick-no mechanical stop which could be real bad...

Height is 28", plenty of clearance just in case of turbulence, wouldn't want it making a hole in the canopy...

I stop filling at 22-gallons, there is more room, but 22-gal works just fine. No, splash that way.

The seat belt and shoulder harness lock it into place. Has handles for easy removal.

Weighs in at 25.2lbs including fittings valves, filters, fuel line.

Per my AP/IA he said to use the Permatex AVIATION Form-A-Gasket to seal the NPT fittings.

Also use the fuel line hose clamps instead of normal hose clamps you buy in a hardware store. They are designed to bite into the rubber hose, locking it into position better than the other cheaper style.

The AN "bulkhead" fitting for the vent line is located facing forward into the airstream to supply positive air flow to the tank. To mount this bulkhead, drilled a hole in the NACA inlet used for the cabin ventilation.

A final note-Make sure you label the Vans fuel control valve with Left/Right/AUX/Off, and keep an AN plug to plug off the fuel valve, if you leave it open, big possibility that you will dump fuel in the cockpit, when changing main tanks.

Weight of fuel 6lbs x 22 gallons = 132lbs + 25.2lbs = 157.2lbs or less than a 170lb passenger. Has not has any effect on the normal CG for weight and balance.

Planning to add some retention cable straps to be bolted down, holding it tighter to the seat frame, the seatbelt shoulder harness does allow a little vertical movement.

I have the fuel tank here at the house, could take some photos for you if that would help.

Best regards,
Mike Bauer
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N999SN 1998 Syd Nelson RV-6 (purchased 2017)
UTC -09:00 Alaska

Last edited by mbauer : 01-11-2021 at 10:01 PM.
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  #6  
Old 01-11-2021, 10:26 PM
blaplante blaplante is offline
 
Join Date: Jan 2010
Location: Southern California
Posts: 181
Default .090 tank?

Mike, interesting post! I'm surprised at the thickness of your tank though. IIRC, our wing tank skins are just 0.032" ... OK, a portable / removable tank is going to get more of a beating, and your capacity is a bit more than I was considering. I was thinking that 40 or 50 thou plate would be plenty. But 90 thou? Wow.

Also any comment on why the vent needs to be forward? Maybe this is because of your gravity feed?
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  #7  
Old 01-11-2021, 11:59 PM
mbauer mbauer is offline
 
Join Date: Nov 2015
Location: Nikiski, AK
Posts: 430
Default Aluminum Thickness

After reading an on-line article about aluminum tanks by Tony Bingelis (EAA Sport Aviation-Dec. 1986) decided to go for it.

The article mentions .040 to .050 aluminum for the tank. This is for a permanent mounted tank.

Thinking a portable tank might get banged around some; went with the .090. Besides an installed main tank will have supports, this portable needs to rely on itself. Bulging sides (hydraulic action) could flex and cause cracks in my mind.

Since it is temporary, the extra thickness doesn't really make a difference. Plenty strong and the aluminum is a little easier to weld. The extra weight is a non-issue for a temp.

Kevin, the TIG guy, did say the .090 was a perfect choice. Had already bought it getting ready to do my own welding. (Not very good on aluminum yet)

My tank had Zero leaks when Kevin was done TIG Welding it. I spent two days cleaning the mill off of the aluminum, then in about 45-minutes he TIG welded the whole thing using vertical welds.

Here is a view of how he put the pieces together before doing the TIG welding.


AP/IA did say it could create a vacuum if vented towards the rear. Not sure if this was because of no pump. Didn't ask any more questions as I trust him to know what is needed. He is out of the country at this time, not able to get in touch, would call and ask.

Tank photos:

Tank front with top abrasion "round" and seat belt loops. Added a plastic tube to show the vent and the bulkhead for the NACA intake vent. This is a spare-just like the one on my RV-6 in use.


Here is the Right side that is nearest the fuselage wall on the passenger side
Note the Top carry handle and the plumbing, biggest thing to pay attention to is the Doublers used for any through the tank wall fittings, gas cap, vent and fuel outlet!:


Closeup of the fuel outlet. Stainless steel ball valve, Filter, and seat belt abrasion resistance round.


Internal: besides the Filler neck to the bottom of tank, it has baffles, to slow down the hydraulic action that could be encountered if it gets bumpy. Don't want to blow a seam if the fuel starts moving around!

Look at the welds to see that Kevin knows how to TIG. This is an incredibly strong fuel tank!

BTW- I was wrong about the hose clamps, they are smooth on the inside so that they don't bite the rubber or plastic.


Final photo of tank:

Best regards,
Mike Bauer
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N999SN 1998 Syd Nelson RV-6 (purchased 2017)
UTC -09:00 Alaska

Last edited by mbauer : 01-12-2021 at 12:39 AM. Reason: get photo to work
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  #8  
Old 01-12-2021, 02:21 AM
DeeCee 57's Avatar
DeeCee 57 DeeCee 57 is offline
 
Join Date: Sep 2018
Location: LSZF
Posts: 594
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here's my inflated F/O

25USG drum from TurtlePac, see link in post #3... also available in 33USG, though you'd have to check on dimensions. Too big for my ship since I have manual flaps which function I want to retain.
I mounted a T fitting with a quick disconnect on the R wing tank supply line.

The feed plan is as follows, fill both wing tank + Turtle, fly and feed from the R wing tank till empty, switch to L wing tank, switch the Turtle elec pump on to transfer fuel until R wing tank full (I have, believe it or not, very accurate fuel indications), repeat until Turtle empty...

The TurtlePac is "light", foldable, quickly installed/removed, and above all doesn't require a vent line.

A little pricey, but hey, it's only money
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  #9  
Old 02-09-2021, 06:17 PM
Radioflyer Radioflyer is offline
 
Join Date: Nov 2009
Location: Boston
Posts: 163
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Hi DeeCee, I was wondering if you could relate more information about how the turtle pac behaves as the fuel is used. Does the seatbelt tend to cause the pac to fold over as fuel is used such that some duel might be trapped in an upper fold and thereby require some manipulation to unfold? Obviously, the pac will collapse, so does this require some monitoring in flight? Can the pac be plumbed into the selector valve directly obviating the pump entirely?
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  #10  
Old 02-10-2021, 07:07 AM
QuixoteAg QuixoteAg is offline
 
Join Date: Mar 2017
Location: Titusville, NJ
Posts: 19
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Hi Dan - by "a little pricey", how many aircraft monetary units does it take for one?
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