Fuel Tank

[dz1sfb]

While I am chomping at the bit to get started, I was thinking about the possibility of a fuselage mounted fuel tank. The obvious advantage to the wing tank is the gravity feed. So, here comes my question;
How much space is between the wing root ribs? I have noticed the wing center fairing and am thinking there might be enough space for a fuel tank of sufficient volume to take up the gap. Kind of like a motorcycle fuel tank that straddles the frame. Maybe I am just dreaming too much, but you could have a nice airfoil shaped aluminum tank there that would not necessitate opening the fuel system to remove the wings and have the benefit of gravity flow.

A second question is; if the space is too tight to sufficient volume, what about spreading the wings apart just a skosh more to get the volume?

This may be all purely academic, but I can see this one in my minds eye.

Ken

[Tom XL-7]

I plan on doing the same. You can fit 5 gallons in there between the wing mounts front and back and between the wings without modifications.
My aircraft will live in a trailer for part of it's life. Anything I can leave hooked up and on the fuselage is time saved.
tom xl-7

.

[scottiniowa]

I plan on doing the same. You can fit 5 gallons in there between the wing mounts front and back and between the wings without modifications.
My aircraft will live in a trailer for part of it's life. Anything I can leave hooked up and on the fuselage is time saved.
tom xl-7

.

Tom, where are you getting this much volume?  what width are you using for your calculations? and are you using just between the attach points or using space fore and aft as well.  I am not saying this can't be done, but rather my calculations of using tank the shape of the wing, and 1" in between the fore and aft attach points, with width of 4" was giving me only 3.3 gal. 

Of course adding slightly in height, or lower (head clearance) or somehow adding ahead or rear of attach points can make a big difference very quickly.  or even the width. ( every .500" wider gives me .4 gal more space)

Am curious in the calculations used.

[Tom XL-7]

Scott , Ken 
 Did some calculations and yes my statement "with no modifications" is full of something and it is not fuel.  Page 53(XL) shows 10 inches for a gap cover  so I may have allowed as much as 8 inches width if I needed it. Page 7A shows the mount  2.5 inches wide and page 35 shows the root fitting sticking out of the wing 2.75 which I have changed to 2 in red ink.
2 root fittings plus wing mount should yield a 6 inch gap.  Assumption time:  rib drawings not in hand-28 inches overall length. 
 231 cu inches in a gallon times 5gallons needs 1155 cu inches of volume. 1155 / 28 / 6 =6.875 height which I don't have easily. Ken suggested a motorcycle type tank which would hang beside and below the top fuse tube. I would rather not go that route (more fittings -two sumps) but one side lower could act as a useful sump. 
I sketched it long ago just as a proof of concept. I would not extend the root fitting but have little problem lengthening the wing mount. 
If I had used the original numbers on page 35 that would have given me 7.5 inch gap which reduces needed height to a more workable 5.5 inch  average height.
 I probably used 8 inches and that is what memory was coming up with. 8 wide 28 long.
 Good catch - doable regardless. 
Tom XL-7

[Tom XL-7]

Maybe not so bad after all If I did use 2.5 for wing mount plus two root mounts at 2.75 (which was the original drawing) that does equal 8 inches.  Stock dwgs.
That may be where I came up with 8 inches to begin with. The power of another cup of coffee!
tom xl-7

[scottiniowa]

Well certainly good talk on this subject... I'm going to have to sharpen my pencil and calculate a few of my measurements as I am basing my calculations on one set of numbers and Tom is using others.

So first I will compare mine with with Tom's-  As the old saying goes, I have certainly been wrong once.   if I took my present calculation of max width of 6.2" and go out to Tom's 8" I would easily have enough gal/space.
As present I am still under 5 gals.

Now for the sump/style/motor cycle way..  If I am understanding this correctly..the tank being slung saddle style over the top frame frame bar where the wing attach points are. this would create two low parts of the tank. Easy enough for all to picture.  Under low fuel levels, (Just in these two lower cavities) one would need a sump hole each side- and front and back.  For landing and take off- to keep from un-porting. This has always been the problem with long narrow tanks with flat bottoms with the long axis in direction of travel. (think climb out angle and decent angle and where the last gal would be)   And of course we would certainly fall into this. I don't know if this would warrant a cross over tube, if so, it would be needed front and back. This of course could reduce sump requirements to one in front and one in rear..but your still adding an extra hole for the cross over..unless done with fittings alone- all about the same for matter of work.

That being said, this is still well worth considering.  I will keep working on it, to either prove or disprove the idea.  Presently I would estimate this a 80%+ possibility.

[Terry Lundby]

Hi, Guys.
I've finished the ribs and am waiting for things to warm up here in Minnesota.  I had this idea a few months ago.  If my math is correct, (no promises here) a FOUR gallon airfoil shaped tank can be built to the dimensions of 24" L, 6" W, 6.4"H. I built to the inaccurate rib drawings provided in the plans, so I gain a bit in the height dimension.  A ONE gallon header tank is placed in the forward fuselage.  From what I've read this should allow for a cleaner routing of the fuel line and minimal CG issues.  Is it worth the trouble and extra complexity?  Maybe not...  A 5 gallon fuselage fuel tank doesn't seem to be problem on Sam Buchanan's XL.  Les Homan says in a video that there is trim change but his plane seems to fly fine. I have no idea how this would be mounted to the airframe, also, I am in no way an engineer so take this all with a grain of salt.

[scottiniowa]

Hi, Guys.
I've finished the ribs and am waiting for things to warm up here in Minnesota.  I had this idea a few months ago.  If my math is correct, (no promises here) a FOUR gallon airfoil shaped tank can be built to the dimensions of 24" L, 6" W, 6.4"H. I built to the inaccurate rib drawings provided in the plans, so I gain a bit in the height dimension.  A ONE gallon header tank is placed in the forward fuselage.  From what I've read this should allow for a cleaner routing of the fuel line and minimal CG issues.  Is it worth the trouble and extra complexity?  Maybe not...  A 5 gallon fuselage fuel tank doesn't seem to be problem on Sam Buchanan's XL.  Les Homan says in a video that there is trim change but his plane seems to fly fine. I have no idea how this would be mounted to the airframe, also, I am in no way an engineer so take this all with a grain of salt.

Just thoughts Terry-

•     one gallon header tanks-   certainly easily do-able and if you use the Tube method of building, very easy to make.
• Cleaner routing of fuel lines-  Cleaner than what? Leonards way vs the top center tank or Sam's tank?  Sam's would be far the simplest, after that, there is not much difference.
• Trim change- a few seconds of work per gal of fuel burned off, no problem.
• No idea how mounted to airframe-  To which are you referring?  Sam's tank used the under lying frame work of the main frame and a few easily made tabs. And the top center tank can easily use the front and rear wing attach bars. They are there and handy.  Pretty easy to use/make these tabs as well.

[Tom XL-7]

• I have checked my rib jig and  the 28 inch length is wrong. 27.5 between the spars. General clearance needs plus one has to leave space for bolt heads or nuts, tools will reduce that a bit.

The idea of a header is something I have been interested in. Would it solve the problem of a rear drain losing fuel in a descent.   I realize your not to plan on running out of fuel but if you saw air in your fuel tubing it would be nice to know the fuel was in the header.
How many times has that reserve position on a motorcycle petcock come in handy.
Don't know where that No. 1 that starts this post came from but I can't get rid of it.

Tom XL-7

[Dan_]

The idea of a header is something I have been interested in. Would it solve the problem of a rear drain losing fuel in a descent.   I realize your not to plan on running out of fuel but if you saw air in your fuel tubing it would be nice to know the fuel was in the header.
Tom XL-7

Tom,
Leonard had a small header tank in the prototype LE for a while.  I don't remember why he took it out...  Probably to save weight.  A header tank is basically a wide place in your fuel line...

He had the zenith carb on there for a while too but changed to the dual Mikunis.  I don't know if that had anything to do with getting rid of the header tank or not.

You got the 1. in your post by clicking the "ordered list" Icon in the editor above your post box.

To get rid of it put your cursor just to the right of it and hit the back space key, as I did when I trimmed your quote above.

Attached is another tank possibility.  Looks like an aftermarket dirt bike tank.

[Terry Lundby]

Hi, Scott.

I think the way Sam mounted his tank is the simplest and I like to keep things simple.   I haven't abandoned the idea of a center tank but I do favor the location used by Sam B. and Les H.  A header tank would not be difficult to install but no matter how easy to install, it does complicate the matter.  

Cleaner fuel line routing...  I could have been clearer.  I'm not a fan of the fuel line suspended in the pilot's line of sight to the right, it just bugs me.  It's just a matter of opinion, I've never flown a L.E. and it doesn't appear to be a problem with anyone who has completed and flown their A/C.

Again, I should have been clearer about the CG. I was concerned about flying qualities of a plane without a trim system.   A quick and dirty trim system from days gone by was a small independent tab located above or below the stab.  A simple retrofit if required but I doubt that it would needed.

Yes, it would be easy to mount the tank between the wings or on the fuselage diagonal as Sam did.  I just hadn't put any thought as to how it would be done.  

I've been reading your posts, much good information!

Best regards, Terry.

[Steve]

If you are looking for another tank location - the Sam Buchanan fabrication will challenge you skills... His fus location is about the lowest you can feed the dual Mikuni's with the (large orifice) gravity flow carb float inlet valves... IIRC Les has a tank that is a little less than 5 gallons... On a big tight 1/2 motor you can see nearly 3 gallons an hour consumption with a rich mixture... Fly away from the home field down wind and find you are too far out when you start grinding your way back...

If you want to fly soon put the Team ready made tank in the wing... A tank over the tube between the front and back wing mount is a head room limiter, a bear to fabricate and the first thing your head rams in a roll over... An inch clearance between head and wing is common, the shoulder harness has to be really cinched to maintain that clearance... Carefully mock up the wing tank clearances if you are determined to go this way... The wing tank is a safety measure and a few minutes work to drain into a 5 gallon can when u take the wings off... Unlike the plans; put the tank in the right wing half and enter the cab from the left - no pilot fuel line interference and you can watch the evil fuel line air bubbles if they develop...

[Terry Lundby]

If you are looking for another tank location - the Sam Buchanan fabrication will challenge you skills... His fus location is about the lowest you can feed the dual Mikuni's with the (large orifice) gravity flow carb float inlet valves... IIRC Les has a tank that is a little less than 5 gallons... On a big tight 1/2 motor you can see nearly 3 gallons an hour consumption with a rich mixture... Fly away from the home field down wind and find you are too far out when you start grinding your way back...

If you want to fly soon put the Team ready made tank in the wing... A tank over the tube between the front and back wing mount is a head room limiter, a bear to fabricate and the first thing your head rams in a roll over... An inch clearance between head and wing is common, the shoulder harness has to be really cinched to maintain that clearance... Carefully mock up the wing tank clearances if you are determined to go this way... The wing tank is a safety measure and a few minutes work to drain into a 5 gallon can when u take the wings off... Unlike the plans; put the tank in the right wing half and enter the cab from the left - no pilot fuel line interference and you can watch the evil fuel line air bubbles if they develop...

Hi, Steve.  Thanks for the great site.  

I've looked into the center fuselage wing tank because I'll most likely be removing the wings fairly often.  I too don't like this position in the case of a nose over but I guess the fuse is not a lot better.  The fuel line is a small issue, looks more than function.  I think my best bet for improving trailering will be procedural, such as attaching wing bolts with an electric drill/wrench, some type of wing support attached to the trailer.  Or...  I'll probably pay hanger fees.

[dz1sfb]

Well this certainly stirred some response. I like the idea of a small header tank. If you have some welding skills, you can fabricate from aluminum, or mock up in foam, fiberglass it, then put in some gas to eat out the foam and viola`.

Having sumps on each side of the top tube it would be good to have a crossover. Also you could go above the wing profile some ala Tiger Moth and maintain the headroom below.

Ken

[dz1sfb]

Okay, after seeing Charles Deboer's LE here , there would be no need or desire to have the center tank saddle over the top tube. This further supports the possibility for ample fuel volume.

Ken