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More Fuel

David Shelton

David Shelton

Well Known Member
I noticed that a lot of builders are increasing their fuel capacity. I'm thinking about designing an aux fuel cell to put in our cargo pods. Since the pods are already designed to carry a motorcycle, they are properly ventillated and fitted with drainage grommets in the event of a fuel spill.

How many gallons do you think it should carry? The pod has a useful load of 250 pounds so we should be able to carry up to 40 gallons. I'm tempted to make it a little smaller to leave space for some luggage. How often do you guys need more fuel? Do you think it's better to replace the main fuel valve (use one that can select from 3 tanks) or plumb a bipass around the fuel valve with a seperate valve to control the aux tank?

-David
 
How about a transfer pump system with two pumps, one to each wing tank, with a one way check valve to simply refill the wing tanks? No extra valves. Redundancy built into the system (two pumps, two sets of independent feed lines) and simple.
 
G-force said:
How about a transfer pump system with two pumps, one to each wing tank, with a one way check valve to simply refill the wing tanks? No extra valves. Redundancy built into the system (two pumps, two sets of independent feed lines) and simple.
Click to expand...
Getting the lines from the belly to the wing tanks will be an issue.

Best just to keep it simple and plumb it in at the fuel selector. The problem will be raising it in place and connecting the lines. This can be solved by putting a cargo door on the pod. Once it is lifted in place, you can reach through the door to make the conections. Then you can use the door to access a small cargo hold.

Just some random thoughts from a -9 driver.
 
Use a flexible fuel bladder and you get the best of both worlds - room for storage or luggage or both. Just cover it with a tarp.

Definitely plumb a transfer system with redundant pumps (or one electric and one manual) to pump the fuel up to where it can gravity feed. It's a long way up hill to the motor!
 
Never

Try to take off using just your aux tank if you are sucking that far uphil..Especially with mogas as that is asking for vapour lock on take off!

Frank
 
Having not seen the internal workings of the fuel selector, I ask this question of those that have.

Can you plumb the aux fuel pump into the fuel selector and have the fuel flow backwards through the normal main supply line between the tank the fuel selector, to move fuel from the aux tank to the main tank that is selected on the fuel selector? This would allow you to run only one additional fuel line, (aux tank pump to fuel selector) and be able to put the fuel in either tank as desired. Is there a check valve anywhere in the process that would prevent this? You would obviously need a checkvalve between the aux tank pump and the fuel selector to prevent the main tanks from gravity feeding back downhill into the aux tank.
 
That could work if it were a "main/aux/both" type selector and there was a check valve in the "aux" line to prevent dumping the usable fuel in your mains into the aux tank.

You would still have the possibility of over-transferring to deal with, though.
 
frankh said:
Try to take off using just your aux tank if you are sucking that far uphil..Especially with mogas as that is asking for vapour lock on take off!

Frank
Click to expand...

At 12 inches lower than the mains, the aux tank should drop fuel pressure by another 0.04 psi. Since this is small compared with the vapor pressure of 100LL (6.5 psi), I think vapor lock will still be dominated by heat and other factors. However, there are many reasons to favor the main tanks and I'll plan to use them during takeoff and landing.
 
Thanks for all the suggestions.

For the tank construction, I?m leaning towards a rubber fuel cell with articulated foam inside. It would be about 6 cubic feet to carry 40 gallons. I?d make the dimensions 3ft wide (width of the pod) x 1ft tall (height of pod) x 2ft long. I?ll tie it down at the front of the pod where it will have little effect on the CG and it will be held in place on three sides by the sidewalls and front bulkhead. Here is a picture of the pod interior. The white parts are just cradles to carry my motorcycle but I'll pull them out when I carry the aux tank.

IMG_4509small.jpg


Suggestions for the plumbing varied greatly! I like the idea of redundant pumps but I may just plumb directly to the fuel selector (left/right/aux/off) for simplicity. I?m trying to keep it simple because it will be removable and only used occasionally. I can already attach/remove the belly pod in 60 seconds. When I need more range, I basically want to strap a tank into it, hook up a single fuel line and be ready to go.

I guess it would be possible for the fuel selector to fail in a way that would allow fuel to drain from the main tanks into the lower aux tank. I plan to install both a check valve and a shutoff valve between the aux tank and the fuel selector. I?ll keep the aux shutoff valve closed when I?m not using the tank or it isn?t in the airplane. Does anyone know if the Andair check valves ($65) are any better than ACS ($30)?

I?d like to make the aux tank really easy to install or remove so I?m looking for a quick fuel hose connector. Does anyone have any ideas here? I know this stuff is common in auto racing.
 
Yes but

David Shelton said:
At 12 inches lower than the mains, the aux tank should drop fuel pressure by another 0.04 psi. Since this is small compared with the vapor pressure of 100LL (6.5 psi), I think vapor lock will still be dominated by heat and other factors. However, there are many reasons to favor the main tanks and I'll plan to use them during takeoff and landing.
Click to expand...

Vapour lock tends to be something of a linear affair..it sort of happens or it doesn't..I would agree 100LL is far less likely to VL than Mogas...Oh I make it about 0.314psi of extra pressure drop...1/2.3psi (for water)* about 6/8.3 (density correction).

Incidently..It this a completed aircraft?..If not then why not build tuckey tanks ..I.e modify the outboard wing skins..you can then avoid having to take up valuable space in your pod..Particularly as the pod is drag producing, I could see where you might take the pod but have no additional luggage in it..Alternatively you can keep the space in the pod for the gear but still carry the extra fuel in the wings.

Frank
 
How often

Do I need extra fuel?

About every single cross country trip I take..Not because i can't make it to the next stop...More because last Summer the cost of fuel varied so widely that an extra 20 gallons would have made a significant dent in the fuel cost for the trip.

I am still considering Tuckey tanks and I have a design that I can add to my completed painted aircraft with virtually no disturbing of the origional paint.

Its alot of work though and very hard to tear into a completed airplane..But if fuel goes to $6 a gallon again then carrying 80 gallons of auto fuel in the 7a has a lot of appeal!

Frank
 
frankh said:
Do I need extra fuel?

Its alot of work though and very hard to tear into a completed airplane..But if fuel goes to $6 a gallon again then carrying 80 gallons of auto fuel in the 7a has a lot of appeal!
Click to expand...

I'm just visualizing those extra "heavy" seven and one half.......... red five gallon gas cans being loaded onto the plane (approx. 38 gallons). :eek:

I confess, I'd prefer not to be carrying all that extra weight around. Besides, I like coffee and a few sodas once and a while. I'd have to limit those too!
It's the "restroom thing"... :D

L.Adamson --- RV6A
 
True but

With carrying the weigh on the outboard section of the wing its almost ..er..free weight..:)..I.e its not like carrying it at the fuselarge where the extra weight adds to the bending moment of the wing....The only place you need to be careful is rough landing with a lot of fuel in the outboard tanks and taxiiing...as the bending moment is then downwards relative to the fuse/landing gear.

Like I said I would'nt use it to avoid landing to streatch the legs..Just to avoid filling up at spendy airports.

Frank
 
we made our own Aluminium tip tanks which fit inside the fibre glass tips, secured and reinforced the fibreglass joint with an Aluminium strip.

This yields about 27 to 28 Litres per side.

Ohhh a translation for all you nice chaps who speak funny :D

Aluminium....the correct word and spelling if you refer to the periodic table is known as ALOOMINUM ;) and around 7 1/4 Gallons per side :)

Cheers from down here!

DB:cool:
 
Don't worry DB

RV10inOz said:
we made our own Aluminium tip tanks which fit inside the fibre glass tips, secured and reinforced the fibreglass joint with an Aluminium strip.

This yields about 27 to 28 Litres per side.

Ohhh a translation for all you nice chaps who speak funny :D

Aluminium....the correct word and spelling if you refer to the periodic table is known as ALOOMINUM ;) and around 7 1/4 Gallons per side :)

Cheers from down here!

DB:cool:
Click to expand...

I'm trying to educate the ones that speak funny..:)
 
Can we get

Some pics of your tip tanks?..An extra 15 gallons of petrol is pretty significant and I suspect less work than retrofiting Tuckey tanks

Frank
 
We have quick connectors on the fuel lines to the trolling motor (15HP) on our boat. Large outboard (200HP) can use portable tanks also. There must be an appropriate connector already out there specifically for fuel.
 
RJBrown said:
We have quick connectors on the fuel lines to the trolling motor (15HP) on our boat. Large outboard (200HP) can use portable tanks also. There must be an appropriate connector already out there specifically for fuel.
Click to expand...

Size is not the issue here, this is an case where the fuel is transferred from the aux to a wing tank, I would never think of running direct from an aux tank, strapped on the belly.

Dont forget proper venting, and filtering.
 
For the -10,

I was wondering about fabbing a set of aluminum (aluminium) tanks using riveted aluminum and fuel tank sealant. It would fit in the passenger floor area for those times when you're using the plane as a two place airplane. You could build in the mounting brackets similar to seat belt brackets and have a quick connect fuel line plumbed in nearby, with a quick connect vent line to the outside. You'd have to make it stout enough you could walk on it, because that might happen.
I haven't taken any measurements, but seems like it'd be possible to fit a four gallon tank on each side. It would be near centerline and give you close to another hour in cruise...or enough to have a little extra margin.
 
Transfer or run direct?

Most of my hours are in sailplanes so I?m not a fuel expert and I appreciate all the advice. A lot of folks clearly don?t want to run directly off an aux tank and prefer to transfer fuel into the main tanks. I believe transferring fuel would require additional complexity (more tubing, check valves, pumps, power cables, switches, etc.) and might actually have more modes of failure. I also hate to touch the plumbing for the main tanks for fear of compromising their reliability? for example; the failure of a check valve might allow a main tank to drain into the aux.

I plan to use the main tanks during takeoff and landing but what is so risky about running off the aux tank during cruise? I would imagine the aux tank will be fairly reliable and I can switch to either main tank if it stops feeding.

My buddy argued that air would be sucked into the fuel lines if I ran the aux tank dry? but wouldn?t the same thing happen if I run a main tank dry?
 
David Shelton said:
My buddy argued that air would be sucked into the fuel lines if I ran the aux tank dry… but wouldn’t the same thing happen if I run a main tank dry?
Click to expand...

The aux tank would be plumbed to a fuel selector just like the right and left tanks. As long as the selector valve is not trying to draw from a empty tank as well as one with fuel, you'll have no problem. It's like sticking two straws in your mouth, and pulling one straw out of a glass of water. At that point the water flow ceases. It's also the reason we just don't use fuel selectors with "both" for low wings.

P.S. --- P-51 Mustangs use to run off auxilary tanks in the fuselage behind the pilot's seat just fine. Since this tank effected the CG, it was used first, before switching to wing tanks.

L.Adamson --- RV6A
 
I think

L.Adamson said:
P.S. --- P-51 Mustangs use to run off auxilary tanks in the fuselage behind the pilot's seat just fine. Since this tank effected the CG, it was used first, before switching to wing tanks.

L.Adamson --- RV6A
Click to expand...


it was probably more about not getting into a dogfight with 75 gallons of fuel behind your back..:)
 
L.Adamson said:
...P.S. --- P-51 Mustangs use to run off auxilary tanks in the fuselage behind the pilot's seat just fine. Since this tank effected the CG, it was used first, before switching to wing tanks.

L.Adamson --- RV6A
Click to expand...
Somewhere I read that the fuselage tank so impacted the CG that when it was full the pilots had to push forward on the stick to make a turn.

CG? We don't need no stinking CG!
 
No bueno Amigo!

frankh said:
Try to take off using just your aux tank if you are sucking that far uphil..Especially with mogas as that is asking for vapour lock on take off!

Frank
Click to expand...

The last guy I saw do that in a Bonanza had all his blood removed upon impact,his flesh totally gray just minutes after stall/snap when engine quit.
Poor Judgement. poor Pilot, Poor family:(:(:(
 
frankh

Good luck..... its an up hill battle in your part of the world. But it does entertain those of us who are cheeky enough to play with their minds! ;)

Ok here is a pic of our tanks. I made three sets as two friends needed some too. The build is not easy as there are a lot of compound curves involved so it was easiest to draw it up and plot out the templates and in the end we made patterns and jigs for welding. It worked REALLY well. But it came at a price. There are two baffles internally also.

So just to make a set of tanks, no fittings etc I would say around AUD$1200 which is about $900. And thats after we have done a few.

If you asked me to build a set, I can not promise you they will be that cheap. So do not get your hopes up. Plus you need to freight them etc.

If you have a GOOD TIG welder available to you, or are yourself, give it a go. But it was no easy task. Remember you need to make space for lights etc and the rear of the tip is where the flaps cut in so you can not capture the whole tip.

Good Luck!

DB:cool:

4525920200a10822593628l.jpg
 
Safeair1 is still offering their tip tank kit that adds approx. 15 gallons capacity on the RV-10. I have it on my airplane and am very satisfied with the quality of the kit. I see that Safeair1 sells a lot of their products through Avery Tools, but the tip tanks come from Safeair1 directly.
 
The guy selling this Aircraft has managed to put 120 gallons in the wings. I dont know how he did it, but he confirmed it was all in the wings.

N9826S
 
I am getting an Andair valve that has Left/Aux/Right selection directly from Andair in England. I will plug the Aux end. I will use a bladder type tank when needed and use a flexible line to hook them up.
 
J E Ursin said:
The guy selling this Aircraft has managed to put 120 gallons in the wings. I dont know how he did it, but he confirmed it was all in the wings.

N9826S
Click to expand...

He did it by purchasing another set of fuel tanks and putting them outboard. I've seen one. The big unknown is if it's had a landing with more than 60 gallons on board....
John
 
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