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Extra fuel for the RV-4

It seems adding fuel capacity to the RV-4 is a common desire due to the fact that in its "standard condition" it holds less than the other RV's and many people use them for travel as opposed to the "local sport plane" that Van probably envisioned.

In addition to the considerable forum activity this topic has gotten in the past, and various options out there for adding fuel to the RV-4, I'll add the following:
(Disclaimer - I'm not an engineer nor have I had my ideas reviewed by or tested by anyone with credentials so this info is worth what I'm charging for it....)

I wanted to add fuel without adding complexity, valves, more complicated fuel management, etc. Fuel interruption to the engine is the/a leading cause of power failures and I didn't want to create too many "unknowns" in adding the fuel to my plane. So.... I just built bigger fuel tanks.

Before embarking on this I looked at the plans and pictures and peeked through that inspection/access cover on the bottom of the wing with flashlight and mirror and mirrors to try to determine if I would run into some "unforseen" obstacle or structural problem in my plan or create "debris" (rivet heads, etc.) in the wing that I would not be able to remove. When I was pretty sure I had a plan I removed a fuel tank so I could see a LOT more in the wing. If at this point I saw a problem with my plan I would just put the tank back on. It still looked like my plan would work and the needed work would be "accessible" without cutting holes in the wing, so it was time to start drilling rivets.
It was hard to drill out that first rivet and commit to repairs/mods. I lined the drill up with the rivet, then chickened out. I went to lunch and to the park, and thought about it for an hour or so, then came back and drilled out that rivet. It was easy after that!! I cut the leading edge of the wing back to allow for a bigger tank. How far to go???? To the wingtip? How much fuel did I want? I didn't want fuel sloshing around "way out there" and have it handle like a Cessna 310 with full tip tanks along with numerous other structural and stability issues. I didn't want to get "too experimental" and thought doing something like an RV-8 was "more or less tested". There was a "natural stopping point" (relating to tank attachment) one rib beyond where the RV-8 tank ends. This turns out to be the same size as my friends F1 Rocket tank, so it seemed "proven" in at least some aspects.......

All said and done here are the high points:

It holds 54 gallons total. The project was not really that much worse than building fuel tanks in the first place, which is not really that much fun, and considering the Pro-Seal... uggghh But, the fact that I was doing it to a "finished airplane" did not really add that much extra work and trouble. The mods to the wing (creating the extra space and facilitating the mounts) only took me a few days on each side, it was the tank construction that took up most of the time. Fitting it to the existing wing was not really that much trouble. The tanks had to be painted to match, of course, but the wing required no painting and no extra holes except that one row of rivets just outboard of the tank (the row that holds the "doubler strip" at the tank/wing joint) had to be replaced so were unpainted. (I just left them that way and they more or less match all the new screws that hold the tanks on which are also unpainted. All the painting was on the fuel tanks so I had them painted before installation (it matches pretty good) and did not have to get the plane to a paint shop. All "construction debris" was removed from the wing.

It was not practical to extend the "fuel tank mounting channel" outboard of its original end point as it is attached with the big 3/16" rivets that hold the spar together. I was going to mess with those and there would be no driving and bucking new ones in a finished wing. The tank mounts in the standard RV-4 fashion out to its original end point and then mounts using a slightly modified version of the brackets that attach the RV-8 tank to the spar the rest of the way out to the tank tip. At the tank/wing joint it is identical to what it was before, which involves putting the new "undersized rib" and doubler strip in the wing at what is now the inboard most leading edge rib. I did replace the fuel vent line in the fuselage with new ones that "loop up higher" in the fuselage to be sure it was still higher than the high point of the fuel, which of course keeps rising as you move outboard due to wing dihedral.

I ordered new fuel tank components from Vans where possible. The parts that were not possible to get from Vans were the primary tank skin (as they don't have any that long) and the aft baffle (same reason). The aft baffle/channel is easy to make with a break and sheer and the tank leading edge skin is surprisingly easy to form using a shop vac, a pvc pipe and a sheet of plastic (Thanks Kelly for turning me onto this method!!) The RV-4 fuel tank design changed slightly in 1986 and the ribs are now different. Mine is the old style and I used almost all of the "pre 1986" fuel tank ribs that Vans has. They have a few left but not nearly a complete set. You can get ribs for the new style and modify them, but it is extra work. If you have a post 86 RV-4 and want to do this it can be done just as I did it, and Vans has the ribs!

This mod probably counts as a "major change or alteration" and depending on when your "operating limitations" were issued they probably say either a major change voids them or that notice must be given to the FAA and their response received prior to further flight. To each his own, but I contacted a DAR and went through the "by the book" process which was pretty easy.

I've flown 25 - 30 hours since the mod, including one 6 hour leg, and all seems to work well, except I can't get up and walk back to the lavatory.....

If anyone is interested I can provide pics and "how to" technical details, tips and hints I learned in doing it. I did find several tricks that would have been handy to know the first time......... Oh, speaking of which - I nearly had my tanks done and I pulled off the protective PVC coating (that comes on new aluminum) and exposed for the first time the "mill stamp" on the tank skin. It was stamped 6061-T6 !!! I'd ordered 2024-T3. They shipped me the wrong stuff! They re-shipped me T3 for free but I had to scrap them and build another set of tanks out of the right stuff. Yeah...... really!!

Here are some pics of the Vacuum Forming of the Leading Edge: https://picasaweb.google.com/117608675674478183490/VacForming

and some pics of the Construction Process: https://picasaweb.google.com/117608675674478183490/FuelTanks
 
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Follow Up

If I recall my discussion with Vans it seems the RV-6 skins would have been an option - I just wanted even longer than that. The RV-8 skins are all said to be pre-punched so the holes would not line up with my existing wing or I'd probably have settled for 45 gallons. As it turned out making the skins from "scratch" was no problem at all.......... Except of course for making them from the wrong alloy the first time.

OK, I'll figure out how to post pics here and add some for the interested parties. Give me a day or two - or some helpful advice on posting pics here ???

-Steve
 
Extra Fuel for the RV4 and RV7

If I recall my discussion with Vans it seems the RV-6 skins would have been an option - I just wanted even longer than that. The RV-8 skins are all said to be pre-punched so the holes would not line up with my existing wing or I'd probably have settled for 45 gallons. As it turned out making the skins from "scratch" was no problem at all.......... Except of course for making them from the wrong alloy the first time.

OK, I'll figure out how to post pics here and add some for the interested parties. Give me a day or two - or some helpful advice on posting pics here ???

-Steve

Fastwind,

I would be very interested (as would many) in viewing photos of your build. I have been researching extended fuel options for the RV 7 and am in the position you found yourself not to long ago.

My question, and please to anyone else who can provide input is as follows:

Can the RV 7 wing (or RV 4) support:

1. Aux + mains (total 84 Gallon) - In essence Tuckey Tanks
2. Plus - tip tanks (similar to Johanson's- total 25 Gallons).
3. Plus - Wet wing smoke tank (situated wing root area) - total 26 Gallons.
(see: http://www.mstewart.net/super8/smoketank/index.htm)

Total = 135 Gallons / or 67.5 Gallons per side.


I know via Sam Stewart's design that 1 + 3 to a large extent proven.

Is 1+2+3 feasible? (specifically for long distance flight - without the 2nd seat being used to accomodate an additonal ferry tank). If it is, would someone be willing to to give advice w.r.t plumbing.

- Simon
 
Can the RV 7 wing (or RV 4) support:

1. Aux + mains (total 84 Gallon) - In essence Tuckey Tanks
2. Plus - tip tanks (similar to Johanson's- total 25 Gallons).
3. Plus - Wet wing smoke tank (situated wing root area) - total 26 Gallons.
(see: http://www.mstewart.net/super8/smoketank/index.htm)

Total = 135 Gallons / or 67.5 Gallons per side.


I know via Sam Stewart's design that 1 + 3 to a large extent proven.

Is 1+2+3 feasible? (specifically for long distance flight - without the 2nd seat being used to accomodate an additonal ferry tank). If it is, would someone be willing to to give advice w.r.t plumbing.

- Simon

This guy did 1+2 on a -9: http://www3.telus.net/haywire/RV-9/C-FSTB.htm

That's a heck of a lot of fuel, though. What are you planning to do with it all?
 
OK, I'll figure out how to post pics here and add some for the interested parties. Give me a day or two - or some helpful advice on posting pics here ???

-Steve

Steve,
The easiest way is to open a Picasa account (free), put all of the photos into a folder there, make the folder accessible by all, and then copy and paste the link to the folder into your message here. This allows you to put as many photos as you want in the folder (there is a 10 photo per post limit here on the forums), add captions, etc.

www.picasa.google.com

If you want to post photos here, the instructions are here:
http://www.vansairforce.net/articles/ImagesInForums/images.htm
 
Pics

OK, thanks for the pointer to Picasa.

I've posted a link to pics on the original post above. There are pics of the wing work as well as of the Vacuum Forming process that was asked about.
 
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