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Leading edge tanks

srt

Member
It seems that I will have more time than money for my RV-8 project in the near term. I was thinking of converting some of the outboard LE to extended range tanks as I've seen some others do. Any insight from anyone else who has done it? Would you do it again? Any major reason not to do it?

At least one specific question that I haven't seen addressed: The way to do this that I have in mind, and what I've seen from others, the extra tank is not (easily) removable. How leak-free does a well-built tank tend to be?

Thanks in advance.

Scott
 
Scott,

I've read of it being done both ways. I made three bays wet in each wing of my -7. I left the bay next to the original tank and the outermost bay dry. The spar is the 'back baffle' in my aux tanks. I did add stiffeners in each wet bay, mimicing the main tanks.

No engineering study was done by me; I just followed the example of two -9 builders who went before. Not yet flying, so I can't comment on that, but I can tell you that 1. it's a LOT of extra work, and 2. it's almost certainly the lightest way to do it. I weighed all the bits & pieces to add mine, and IIRC, it was under 2 pounds. Don't remember if that included the extra fuel line, but I doubt it.

edit:To answer your actual question, they should be as leak free (or not) as your regular tanks, if you build both.

Charlie
 
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Just about everything you want to know can be found here.

There is a link there to another compete and flying RV-8 that has "Extra Capacity" fuel tanks.
 
I would advise against the mod. I've seen serious safety and build problems after doing tech inspections on rv wings that have had the outboard tanks added. Unless you plan to perminantly rivet them to the spar web. Every extended range tank mod that I've seen done has had nut plates added to the spar web where the out board skin normally rivets in place. The problem with this is edge distances can't be met on a pre punched structure. The fuel tank skin on an rv is thicker (.032) than the leading edge skin outboard of the tank. So to save time people use the inboard skin on the out board section of the wing as well. So now you have prepunched holes in the spar web and pre punched holes for screws in the tank skin. Both of them competing for space. The result is a series of holes left open in the spar web with improper edge distance. This will eventually lead to spar cracking. My advice is to land for fuel one extra time on your cross country and enjoy all of the small airports we have at our disposal.

BK
 
Thanks for the tips. I've found some good write ups by Pat Tuckey and Ron Duren and was planning on following that concept. I was going to do 3 bays in the middle, leaving 1 bay between the inboard tank and the outboard tank for plumbing and pump, and 1 bay outboard for landing lights.

If I do this, I will be riveting to the spar flange in the prepunched holes, not adding nutplates. I would also add a back baffle like the stock tanks. If I do this, I'll be thinking carefully about any structural or operational detriments that it could cause. Definitely don't want to introduce any problems.

How about longer term use? How often do RV (stock or modified) tanks develop leaks or need removal for maintenance? (If you were to take a guess on average...)

Thanks again!
 
Here's a few of the reasons I wouldn't opt for additional outboard leading edge tanks.

1. There's no point in having additional tanks if you can't 100% reliably access the fuel in them. I've seen builders tackle auxiliary fuel supply numerous ways but all of them have some shortcomings, and all of them add to the complexity of the fuel system which makes it less reliable.

2. Vans wing spars are not engineered for the loads that might arise with outboard fuel tanks. In particular, landing with the outboard tanks full or partly full of fuel could easily overstress the wing spar. You might think that you won't land with outboard fuel but there are many reasons why you might HAVE to land.

3. Outboard leading edge tanks are a MAJOR structural and systems modification and when you come to sell this aircraft many potential buyers will be very wary of what you have done, particularly given that Vans would not approve it and you are unlikely to have any approved engineering calculations. It might thus be wise to consider resale value of the aircraft.

Vans used to sell the Jon Johansen auxiliary tip tanks but they discontinued selling them many years ago. It might be constructive to speculate as to why they made that decision.
 
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... I was going to do 3 bays in the middle, leaving 1 bay between the inboard tank and the outboard tank for plumbing and pump, and 1 bay outboard for landing lights..

Im not familiar with the structural details of the pre punched wings so take the following with a grain of salt, but its a fairly common mod on Rockets to simply extend the tank one more bay. That brings it from 42 to 58 gallons total. That would be a LOT of gas for a 4 banger. Not sure why you would want to add a second discrete tank (with plumbing and a pump no less) when you could simply build a slightly bigger tank.
 
I would advise against the mod. I've seen serious safety and build problems after doing tech inspections on rv wings that have had the outboard tanks added. Unless you plan to perminantly rivet them to the spar web. Every extended range tank mod that I've seen done has had nut plates added to the spar web where the out board skin normally rivets in place. The problem with this is edge distances can't be met on a pre punched structure. The fuel tank skin on an rv is thicker (.032) than the leading edge skin outboard of the tank. So to save time people use the inboard skin on the out board section of the wing as well. So now you have prepunched holes in the spar web and pre punched holes for screws in the tank skin. Both of them competing for space. The result is a series of holes left open in the spar web with improper edge distance. This will eventually lead to spar cracking. My advice is to land for fuel one extra time on your cross country and enjoy all of the small airports we have at our disposal.

BK

I have done the mod on my 9A, and BK's warning above is valid. I chose to build the tanks as well as I possibly could, slather on a metric ton (or close to it) of proseal on the seams to ward off leaks, and I riveted the outboard tanks in place using the original prepunched holes. I also put the Z-brackets between the tank baffle and the spar, just the same as the main tanks. Those tanks are now non-removable, and if I ever develop a serious leak in them I will simply abandon them in place and discontinue their use.

Here's a few of the reasons I wouldn't opt for additional outboard leading edge tanks.

1. There's no point in having additional tanks if you can't 100% reliably access the fuel in them. I've seen builders tackle auxiliary fuel supply numerous ways but all of them have some shortcomings, and all of them add to the complexity of the fuel system which makes it less reliable.

2. Vans wing spars are not engineered for the loads that might arise with outboard fuel tanks. In particular, landing with the outboard tanks full or partly full of fuel could easily overstress the wing spar. You might think that you won't land with outboard fuel but there are many reasons why you might HAVE to land.

3. Outboard leading edge tanks are a MAJOR structural and systems modification and when you come to sell this aircraft many potential buyers will be very wary of what you have done, particularly given that Vans would not approve it and you are unlikely to have any approved engineering calculations. It might thus be wise to consider resale value of the aircraft.

Vans used to sell the Jon Johansen auxiliary tip tanks but they discontinued selling them many years ago. It might be constructive to speculate as to why they made that decision.

This is also a valid comment - but there are some other considerations as well. With respect to #1, I put a small non-fuel bay between my main and outboard tanks, and put a Facet fuel transfer pump between them for positive transfer. I also have flow-through venting on my tanks (see my builders site for more, or PM me) so I actually have a passive and an active method for transferring fuel from the outboard to the inboards. Proper design is critical here, fuel system mods have the highest likelihood of inducing an emergency in the air of any mods I can think of. Caution is advised, but it can be done.

With respect to #2 - this is also absolutely true. Landing with any fuel at all in the outboard tanks should be considered an emergency condition, requiring a wing spar inspection before further flight. The wing spars are NOT engineered to take that kind of load on a landing. Taxi and takeoff with those tanks filled should be OK as long as you taxi gingerly and have good smooth pavement for the taxiway and runway. The bending loads on the spar at the root are greatly amplified during ground ops with fuel in the outboard tanks.

With respect to #3 - this is also true - Vans won't approve it. BUT there are quite a few people who have already done it, a lot more that ask about it, and many that want it. I discount the probability that you couldn't find a buyer fairly heavily. It's certainly true that most buyers would turn away - but some will actually prefer the aircraft BECAUSE it has longer range tanks. YMMV.


No engineering study was done by me; I just followed the example of two -9 builders who went before. Not yet flying, so I can't comment on that, but I can tell you that 1. it's a LOT of extra work, and 2. it's almost certainly the lightest way to do it. I weighed all the bits & pieces to add mine, and IIRC, it was under 2 pounds. Don't remember if that included the extra fuel line, but I doubt it.

Yep, I'll agree to all that as well. I followed Pat Tuckey's design, with a few tweaks specific to the 9A wing and change to the vent system. No "proper" engineering study has been done to support this, it's not recommended or supported by Vans, and you're going to be a member of a very small club of people that have done it, which means if you break it you own both pieces. No guarantees anywhere.

I spent about 50 hours and maybe a couple hundred dollars extra on my outboard tanks, adding 15.5 gallons each side, and I love having them. I will caution you again - it's something that can be done, but tinkering with the fuel system as I have done is NOT a thing to approach lightly. It's the quickest way I know to snap your fingers in the mousetrap if you're not very careful. Caution is advised.

You might also consider this as an alternative - http://www.vansairforce.com/community/showthread.php?t=142539&highlight=smoke+oil+tank you'll still need to figure out some plumbing and fuel transfer issues, but this is removable and leaves the wing structure as-designed. He has tanks available in a variety of sizes, including some that are hidden behind the seat backs and don't interfere with the baggage space. He also has some that give 7 gallons on each side behind the seats and only chew up 3" of baggage space.
 
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Structure question is answered in my mind.

Mike Stewart installed his version of the Tuckey Tanks on his RV-Super 8 wings several years ago. He used the stock tank skins and drilled the holes for the screws wherever they hit. You might suspect there would be a risk of flange failure, but it has not happened with Mike.

It would be difficult to imagine any RV-8 with more structural loads imparted to its wings than Mike's plane. He has a 6 cylinder Lycoming engine and he flies aerobatic routines on a regular and recurring basis. If any wings were to fail because of this modification, surely Mike's wings would be the first.

At OSH last summer I spoke with Pat Tuckey, the father of the Tuckey Tanks, and he has had no structural issues with his, which have been flying for many years.

As a possible compromise for safety, you could simply order the tank skins un-drilled and drill the holes for the tank screws so that they hit every second or third prepunched rivet hole. In that way, there would be no extra holes drilled or figure 8 holes to deal with. Instead of using traditional nut plates (which require you to drill 2 additional holes for the positioning rivets) you could use Click Bond nut plates (that are epoxied in).

At the last OSH, I spoke with Gus, who said it should not be a problem ordering an unpunched (but pre-bent) tank skin.

I have done a bit of research into this mod because I plan on flying my 8A around the world and the extra 42 gallons in the wings would make it possible to negotiate that pesky Hilo, HI to Oakland, CA leg.

Pat Tuckey said he likes the extra 42 gallons because he can fill up on cheap gas when he gets the chance.

Everyone should make up their own minds, but seeing that Mike Stewart's wings have held firm gives me all the empirical data I need.
 
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It's worth pointing out that if you intend to rivet the leading edge tanks (as I did), then adding van's back baffle make the task significantly more complicated. You must cut off the back flange of each rib & 're-flange', you must add another line of rivets top & bottom to the skin for the back baffle, and you would then need to add the z-brackets. Much simpler to just use the spar as the back baffle. IIRC, I had to cover one or two lightening holes in the spar and that was it. Adding the back baffle also adds that much more weight.

I tried to keep fuel delivery as close to 'stock' as possible, with only a transfer port added to each main tank. Main tank venting & delivery is as designed. I'm very uncomfortable with the technique some have used which combines the main tank vent with fuel transfer, & vents only the aux. That technique depends on a perfect seal of the main filler cap to supply transfer vacuum to the aux, and is a major mod to the original delivery system.

Charlie
 
It's worth pointing out that if you intend to rivet the leading edge tanks (as I did), then adding van's back baffle make the task significantly more complicated. You must cut off the back flange of each rib & 're-flange', you must add another line of rivets top & bottom to the skin for the back baffle, and you would then need to add the z-brackets. Much simpler to just use the spar as the back baffle. IIRC, I had to cover one or two lightening holes in the spar and that was it. Adding the back baffle also adds that much more weight.

Charlie

Oh man, you did it the hard way. I removed the 5 original structural ribs, and replaced them with 7 fuel tank ribs I bought from Vans and a new baffle plate. They were already perfectly sized for the purpose. It's true that you gain more tankage space using the rear spar as the baffle, if I ever build another set of outboards I'll probably follow that route.

I tried to keep fuel delivery as close to 'stock' as possible, with only a transfer port added to each main tank. Main tank venting & delivery is as designed. I'm very uncomfortable with the technique some have used which combines the main tank vent with fuel transfer, & vents only the aux. That technique depends on a perfect seal of the main filler cap to supply transfer vacuum to the aux, and is a major mod to the original delivery system.

Charlie

That's why I put the Facet transfer pumps in as well - if I do have a leak on the inboard fuel caps, I can still push fuel from the outboard to the inboard tanks.
 
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Thanks for the discussion, everyone. Good points being made. I don't have my mind made up about this yet.

I would not try to add additional fastener holes in the spar flange, as noted, no room for proper edge distance. Another possibility that I haven't explored yet would be to rivet a narrow strip to the spar flange and add a joint plate parallel to the spar, similar to the one between the tank and leading edge. I can think of a couple of things I don't like about that, and I'm not even sure if there is room for it.

As mentioned, ground handling loads with extra fuel outboard is a concern. I would consider landing with fuel there an emergency only situation. However, I'm thinking 3 extra bays of fuel, my quick calculation was something like 13 gallons. That's a couple of hours to empty them vs 4 or so for the stock tanks.

Extra complexity in the fuel system is definitely a concern. Anything comparable in the certified world?

I'm not too worried about resale, but how hard/expensive would it be to convert back to the per-plans configuration if it became an issue?
 
LRT

Scott

I have a 64 gallon capacity in my RV-8.

All I did was to increase the main tank size. Bought two extra tank skins, some tank ribs and two baffles. Joined each to the main tank with a lap strip.

No extra plumbing and no extra pumps. Had to buy some more Z brackets.

You don't have to use the extra capacity all the time, but it's sure nice to load up on cheaper fuel when you can. And if you're solo, go a long way.

Go for it.

Carr
 
I tend to find that builders contemplating auxiliary tanks tend to be focused on the logistics of installing the actual tanks but fail to comprehend the potential pitfalls in their fuel transfer system. And it's the fuel transfer system that will likely kill you. Here's a couple of typical examples:

1. A friend of mine installed a system whereby there was a one-way check valve between the outboard and inboard tanks and the fuel flow was by gravity feed. This is a common system and is the standard system for Jon Johanson tip tanks. However my friend had concerns about the system from the outset because he suspected that fuel was occasionally venting overboard on descent and setting up a siphoning effect.

But my friend completely lost confidence in the system when he landed one day and discovered that his right outboard tank was still half full (and it should have been completely empty). Then he installed Stewart Warner fuel gauges in the auxiliary tanks so he could see that they were being fully used. But he rarely used the auxiliary tanks and the Stewart Warner sensors did not like being out of fuel continuously so they were problematic and unreliable.

So my friend, who was something of an electronics guru, decided on a more complex system. He installed a Facet fuel pump to transfer the fuel. But then he became concerned that he did not know when all the fuel was transferred and he was concerned with damaging the Facet pump by running it dry (definitely not recommended). So he installed an optical fuel sensor in the outboard tank that cut off the facet pump when there was no fuel in the tank. And then eventually he started to worry about pumping fuel into the main tank when there was insufficient empty volume to accommodate it. That would of course caused fuel to be pumped overboard though the tank vent. So my friend installed a second optical sensor in the main tank that cut off the Facet pump if there was no reasonable space available for fuel in the main tank.

Then my friend started to worry about the logistics of getting the fuel as quickly as possible from the outboard tanks to the inboard tanks so that he could land at the earliest possible time without damaging the wing spar. That resulted in him installing an automatic fuel transfer mode whereby the moment there was some reasonable space available in the main tank the Facet pump would come on automatically and transfer fuel from the auxiliary tank until either the optical sensor in the main tank or the optical sensor in the auxiliary tank cut off the pump. As some fuel was used out of the main tank this system would continue to cycle on and off automatically ensuring that the main tank was always relatively full.

I think you can see where this is going. My friend went from a system that was so simple it was a dangerous oversimplification to end up with a system that was dangerous because it was so complex.

In the end my friend became reluctant to use the auxiliary fuel system. And over the years I have found that many of my friends with auxiliary tanks never use them because they are not entirely comfortable that they will get the extra fuel when they need it. The nagging doubt undermines them.

2. And now for case 2 (this is much shorter) involving another friend. He simply installed a 5 way Andair fuel valve and so he had a separate port to each of his 4 tanks. He was absolutely convinced it would be foolproof. But because he had no indication of remaining fuel in the auxiliary tanks he promptly ran one dry and when he switched to a main tank he found it took almost 12 seconds for the engine to re-light so the event was very stressful. At a lower altitude it could have been a very bad outcome. After that he was reluctant to use the auxiliary tanks.
 
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Thanks for the insight, Bob. I would not be satisfied with any of the situations you describe. If I'm not convinced that this can be a simple and reliable system, it won't be done. Either way, I have a little time to study it before making a decision.

Carr, the issue I have with just using 1 larger tank on each wing is when implemented that way, you cannot operate in the as-designed configuration. Even if you only fill each tank to 21 gallons, that fuel weight is now farther outboard. That gives higher moments from ground handling loads, and an unknown (to me) effect on things like spin recovery. If I go for aux tanks, I want to be able to easily revert to the designed/tested configuration. I hope your setup is working well for you though! :D
 
2. And now for case 2 (this is much shorter) involving another friend. He simply installed a 5 way Andair fuel valve and so he had a separate port to each of his 4 tanks. He was absolutely convinced it would be foolproof. But because he had no indication of remaining fuel in the auxiliary tanks he promptly ran one dry and when he switched to a main tank he found it took almost 12 seconds for the engine to re-light so the event was very stressful. At a lower altitude it could have been a very bad outcome. After that he was reluctant to use the auxiliary tanks.
I regularly run a tank dry in flight. I see no issue in doing so either, so long as you actually intend to do it! Having tested both left and right tanks, it takes about 4 seconds from that first stumble back to cruise RPM. I wouldn't necessarily recommend it in the circuit, but if you do it there, you're doin' it wrong!
 
I regularly run a tank dry in flight. I see no issue in doing so either, so long as you actually intend to do it! Having tested both left and right tanks, it takes about 4 seconds from that first stumble back to cruise RPM. I wouldn't necessarily recommend it in the circuit, but if you do it there, you're doin' it wrong!

Just an FYI from the AFP manual (the "standard" Van's FI pump):

WARNING
Airflow Performance and Bendix/Precision fuel injection systems are non-returning systems. In the event that a tank is run dry in flight, an air lock will be formed on the out let of the pumps. It is possible that the auxiliary pump will not pick up fuel, as the auxiliary pump cannot create enough air pressure to over come the flow divider opening pressure, thus displacing the air and resume pumping fuel. It is not recommended to run a fuel tank dry in flight without adequate testing and proper documentation of the procedure for this operation.
 
How about the Pat Tuckey transfer.

Seems simple without the possibility of pumping fuel overboard. Main tank vents to aux tank. Aux tank vented out. Pump in between the two. I would also add capacitance senders on all 4 tanks. Watch the fuel level ensuring the outboard levels go to empty before the inboard levels decrease.
 
You will definitely need quantity senders in each tank - main and auxiliary. I have capacitance senders in my main and float senders in the aux, along with a fuel flow transducer that tracks the engine burn and feeds that to the Dynon Skyview. The transducer has turned out to be surprisingly accurate, often to within .1 gallon (and never more than .4 gallon) of actual usage across a 30-40 gallon burn on a long cross country. I use the fuel computer more than I use the quantity senders as it turns out to be more accurate by quite a margin.

Every builder will have a different approach to it, but as Captain Avgas pointed out there is danger in too simple or too complex. I prefer having the tools to implement a change, the data to indicate what changes need to be made, and let my wet noodle decide what to do and when, rather than trying to automate it.

At my age, I have nothing but awe for RVators whose bladders can last longer than the fuel in their stock tanks.

It's not always about that, though that is certainly part of it. I can carry easily 8 hours of fuel and use that capacity frequently - but my longest leg so far was 4.5 hours from Reno to Denver. There are a lot of other reasons to carry that much fuel, it doesn't have to be burned in one hop.
 
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At my age, I have nothing but awe for RVators whose bladders can last longer than the fuel in their stock tanks.

Hi Bob, Most of the guys I know with long range tanks use them so that they can fly to places with no fuel, or places where the fuel is exorbitantly expensive, or places where the fuel is only in drums. Most of them aren't flying huge distances in one leg.

PS Sorry to hear about your medical condition deteriorating.
 
... leaving 1 bay between the inboard tank and the outboard tank for plumbing and pump, and 1 bay outboard for landing lights....
I have seen a number of different ways to move the fuel to the engine

1. Electric pumps to move the fuel from the outboard to inboard tanks
2. Electric pumps with optic sensors so when the inboard tanks can hold all the fuel in the outboard tank, it automatically moves the fuel and turns the pumps off, when full
3. Syphon the fuel from the outboard tanks to the inboard one, as the level in the inboard tank drops. This requires the vent line be plumbed to the outboard tanks.
4. Use a five-way Andair fuel valve; Left Outboard, Left Inboard, Off, Right Inboard, Right Outboard.
5. If a cockpit aux tank is installed, the standard Van's valve has an unused position that can be plumbed to the aux tank. No additional wiring or plumbing is required.

There may be a few other options but of the four I have listed, if I were going to add LR tanks to my RV, I would go with option number four, a five way fuel valve. This has the advantage that you burn fuel from whatever tank you want and don't have to wait for a given tank runs down. It doesn't require two extra fuel pumps, breakers, etc. And it is simple.

The only drawback that I can think of is you have to manage your fuel. I don't see this as a drawback but rather an advantage. Your biggest challenge is that you should (must?) install a level sender in each tank. If you don't, you could have a leak and expect to have that extra fuel available when you need it most.

Good luck and let us know what you are going to do.
 
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I too wanted to install additional fuel tanks in the wings but here in Germany we have to prove all kinds of changes are safe. Vans does not recommend it. And some issues are spin recovery and different mass concentrations and so different flutter characteristics.
I ended up installing a 10 Gal Aux tank in the rear baggage area with a Facet Pump and a 3-way fuel selector. The tank is easily removable when not needed. When installed I loose the rear baggage area and of course have limited pax weight. So no ideal solution but for me it´s acceptable. I had to prove some of the JAR/FAR 23 requirements for fuel tank installations like fuel spillage, drainage and venting as well as crashloads.
 
I still have not seen a good argument against the most reliable method of all - make the tanks bigger. Ive seen the talk about possible spin issues, but having separate tanks out near the tips is certainly going to drive the moment of inertia much higher than just extending the stock tanks a bay or two, so you are even worse off. Besides, you are going to have to demonstate spins in Phase 1 if you intend to do them in phase 2 anyway, so what does that buy you?.

I'm not trying to convince anyone here... I'm just curious why you guys are making this so much harder than it needs to be. To the OP: how much extra fuel meets your requirement?
 
Toolbuilder,

Enlarging the stock tanks a bay or two puts more weight further out on the wing. So the spin issues arrise. I don't know about you but I sure don't want to test spins with more weight out further. With adding outboard tanks, with the outboard tanks empty, the spin characteristics will be the same as stock.
 
I have seen a number of different ways to move the fuel to the engine

1. Electric pumps to move the fuel from the outboard to inboard tanks
2. Electric pumps with optic sensors so when the inboard tanks can hold all the fuel in the outboard tank, it automatically moves the fuel and turns the pumps off, when full
3. Syphon the fuel from the outboard tanks to the inboard one, as the level in the inboard tank drops. This requires the vent line be plumbed to the outboard tanks.
4. Use a five-way Andair fuel valve; Left Outboard, Left Inboard, Off, Right Inboard, Right Outboard.

I favor option 1. With this option you can turn the pump on for a certain length of time and monitor your onboard tank levels to make sure you are getting the fuel. Even better if you have level senders in both tanks. Also, this way you can pump the outboard tank dry. With 4 options on your fuel selector, you have 4 tanks that you have unusable fuel in, the level if which depends on your comfort level on how low you will run a tank before considering it empty.
 
Toolbuilder,

Enlarging the stock tanks a bay or two puts more weight further out on the wing. So the spin issues arrise. I don't know about you but I sure don't want to test spins with more weight out further. With adding outboard tanks, with the outboard tanks empty, the spin characteristics will be the same as stock.

Fair enough, but I'm curious how an airplane is going to be tested in phase 1 and documented for Phase 2.

Also depends on the amount of fuel desired and the mission of the airplane. If you want to double the fuel capacity and retain the ability to perform spins, then yes, separate tanks make sense. However, if you are just trying to add 5-10 gallons per side, then one should do a MMOI calculation between bigger mains and the same added capacity out at the tips. Despite the same total tankage, there will be a huge inertia difference between the two.
 
I favor option 1. With this option you can turn the pump on for a certain length of time and monitor your onboard tank levels to make sure you are getting the fuel. Even better if you have level senders in both tanks. Also, this way you can pump the outboard tank dry. With 4 options on your fuel selector, you have 4 tanks that you have unusable fuel in, the level if which depends on your comfort level on how low you will run a tank before considering it empty.

Jesse, This is such a great debate and will only be settled by one's comfort level, as you pointed out.

Running a tank dry is something I was taught never to do because you can suck up "gunk" that may have collected in the tank. Truth is, you are sucking this stuff up all the time because the pickup is in the bottom of the tank.

What I have subsequently been taught is to watch the fuel pressure when the tank gets close to empty. When it starts to waiver, change tanks before sound of silence becomes defining (usually as your passenger starts screaming).

Either way, the fuel feed options are something every builder must take into account.
 
I favor option 1. With this option you can turn the pump on for a certain length of time and monitor your onboard tank levels to make sure you are getting the fuel. Even better if you have level senders in both tanks. Also, this way you can pump the outboard tank dry. With 4 options on your fuel selector, you have 4 tanks that you have unusable fuel in, the level if which depends on your comfort level on how low you will run a tank before considering it empty.

FYI - I added a 5th bullet to my list above. I forgot about fuselage tanks and while I'm not a fan of this option, some others are.
 
I have seen a number of different ways to move the fuel to the engine

1. Electric pumps to move the fuel from the outboard to inboard tanks
2. Electric pumps with optic sensors so when the inboard tanks can hold all the fuel in the outboard tank, it automatically moves the fuel and turns the pumps off, when full
3. Syphon the fuel from the outboard tanks to the inboard one, as the level in the inboard tank drops. This requires the vent line be plumbed to the outboard tanks.
4. Use a five-way Andair fuel valve; Left Outboard, Left Inboard, Off, Right Inboard, Right Outboard.
5. If a cockpit aux tank is installed, the standard Van's valve has an unused position that can be plumbed to the aux tank. No additional wiring or plumbing is required.

There may be a few other options but of the four I have listed, if I were going to add LR tanks to my RV, I would go with option number four, a five way fuel valve. This has the advantage that you burn fuel from whatever tank you want and don't have to wait for a given tank runs down. It doesn't require two extra fuel pumps, breakers, etc. And it is simple.

The only drawback that I can think of is you have to manage your fuel. I don't see this as a drawback but rather an advantage. Your biggest challenge is that you should (must?) install a level sender in each tank. If you don't, you could have a leak and expect to have that extra fuel available when you need it most.

Good luck and let us know what you are going to do.

I went with a combination of 1 and 3, because as pointed out earlier if the seal on the inboard tank filler cap fails you can't pull a vacuum in the inboard, and it won't automatically siphon-transfer from the outboards. I considered the minor weight of a pair of Facet pumps to be worth the peace of mind when I'm out over the big water and wondering if they'll stay sealed...
 
Pat Tuckey wing plan

Sorry to continue this old thread I am trying to find the drawing and details for the Pat Tuckey wing tanks. The website napwars does not work for me, as I can't reach the page (maybe a location issue). Would anyone have details on these tanks from the website.

Kind regards Simon
 
Sorry to continue this old thread I am trying to find the drawing and details for the Pat Tuckey wing tanks. The website napwars does not work for me, as I can't reach the page (maybe a location issue). Would anyone have details on these tanks from the website.

Kind regards Simon

Send me a PM with an email address and I'll forward you my copy of the drawings. They are designed for a RV-8 so you may have to modify a few of the dimensions to fit a different wing.
 
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