KF3 minimize unusable fuel level

[NotSoAmish]

My KF3 kit has the wing fuel tank pickups at the trailing edge of the tanks. What is the best place to relocate these for minimizing unusable tank volume? Know that landing approach decents take away usable volume with a rear pickup location.
I also want to go to brass compression fittings made for nylon tubing and clear nylon tubing for tank sight level indicators and fuel pickup. Any thoughts on this?

[kitfoxnick]

Do you have a header tank?

[NotSoAmish]

Yes. A poly header tank will go behind the seats.

[HighWing]

There are several considerations if you decide to move the pick-up fittings. In the rear position, the fuel line is straight out and through the butt rib. This makes periodic inspection of the finger strainer a pretty routine project. If you move the pick up forward, it will be more difficult as the fuel lines will have to be in a tight 90° bend to accommodate the space and the need for the line to actually exit the wing at the aft edge for wing folding. You will need an inpection panel in the fabric below the pick up so you can unscrew the "Ell" for access to the finger strainer. The Ell is just too long to unscrew without impacting the fabric. I worked on this on 5 Outback for a friend. The original builder apparently planned on exiting straight out from the mid tank location and I don't know what his thinking was regarding wing folding. Another issue there was that he took up all the slack between wing tank and the 1st and 3rd ribs by snugging the tank right up to the no.1 rib and it required a modified elbow to fit between tank side and rib web (picture below). It was a real challenge, and not much fun undoing what proved to be some poor planning to restore a maintenance friendly version - sort of like flying out of a box canyon. With all that, I just went to the original plan on my current Model IV project. I flew 900 yours over nine years with the origanal design and only once did I find a porting issue and that was during a flight with a long downhill flight to home when I purposely tried to unport the tank. I still had six or so gallons of fuel, so when the low fuel light came on, it was a few seconds after raising the nose a bit that the light went off and I saw the fuel flowing again in the Purelator filters.
Lowell

[Dave S]

I really like Lowell's modified fitting for the finger strainer/ell. Neat fabricated part.

Here is an attached photo of one solution to an access area between the #1 rib and fuel tank for the 13 gallon wing tank. The cutout is reinforced/polytacked with a "C" shaped piece of aluminum and covered with another aluminum plate held by 2 screws.

I did have an earlier post on the subject of nose down vs unusable fuel and found that the tanks would old 6 gallons unusable on each side with a 10 degree nose down pitch (which is not anywhere near a normal pitch down). Going to 5 degrees basically cut the unusable to 3 gallons on each side. Level pretty much cuts the unusable to a few ounces in the tank depression/sump by the fuel pickup.

Sincerely,

Dave S
KF7 Trigear
912ULS Warp

[kitfoxnick]

You can go straight out with a mid tank hose. The new tanks from kitfox has the output in the middle, at the output location there is a well. The reason I asked about the header is that with a header you have about 15 min worth gas in the header. I would recommend installing a low fuel switch in the top of the header. If you get air in the header you'll know immediately that you have a fuel issue, weather you forgot to turn on your fuel at the tank or you've been on a long decent or whatever at least you have some time to figure out what's going on. You can get just about all of the gas out of the older style tanks by slipping with the nose a little high.

[NotSoAmish]

Dave,
Is the acess port just to put a wrench on the strainer fitting for removal? Has anyone tried making a tool the would eliminate the need for the lower access cover? I think I can mill out a socket to fit over the square brass elbow. If the elbow comes out first then a standard socket may fit over the strainer hex provided it is not too far behind a rib strut.

Kitfoxnick,
Well? a lower sump region of the tank?

The McMaster Carr fitting shown is made for nylon tubing and in a 90 degree version should nest in between the root and butt ribs OK. My tanks can be slid outboard since there are not installed yet. I have 2.25" between tank and root rib if I slide it outboard. Thanks to all for allerting me on the issues of having the tank close to the root rib.

So if the fuel pickup is forward you have to worry about climbouts when fuel is low. Would be even more a concern since fuel consumpsion is higher rate then. I see a fuel level warning system is my future from the discussions here. I drive a VW tdi and routinely take it to 1 gallon of diesel fuel remaining but the consequences are much different from a low fuel condition in a plane.

[HighWing]

You can go straight out with a mid tank hose.

That is what was on the Outback I helped with. For wing folding, I can't visualize this without either having a very large loop of fuel line hanging overhead or disconnecting for every wing fold. For those in hangars, I did fold once a year for my annual as I always removed the finger strainer for inspection. And yes, I did find some junk there one time - a piece of rubber from a card lock avgas pump (I always used a Mr Funnel when fueling with mogas). So wing folding is definitely in my plans.

Regarding the modified socket - I did that for the throttle nut, but in this case the port being right on the bottom of the tank, the clearance between port and fabric makes it impossible to rotate the Elbow past the fabric. When I did the Outback, I used the Rans method of gluing a Lexan U shape on the back of the fabric and using quarter inch #5 sheet metal screws to secure the .016 aluminum cover. Lexan cuts without a memory so it always lays flat, bonds very well and is thicker for the sheet metal screw bite.

Dave's comment on unusable fuel is exactly as suggested by my real life experience. Unless you have a habit of flying under bridges or wires, raising the nose to re-port the wing tank is pretty much a non issue. In my experience, I was finishing a non stop from Idaho and descending from my 10,500 clearance altitude over the Sierras to home when this happened. I expected it and watched the whole think unfold. Reporting the tank and reducing the descent was all it took to make the ramaining fifteen minutes to my hangar and there was indeed three gallons in each tank when I got home.
Lowell

[Dorsal]

Dave,
Is the acess port just to put a wrench on the strainer fitting for removal? Has anyone tried making a tool the would eliminate the need for the lower access cover? I think I can mill out a socket to fit over the square brass elbow. If the elbow comes out first then a standard socket may fit over the strainer hex provided it is not too far behind a rib strut.


I also put an access plate in just as shown in the picture, I concluded it would be necessary if I ever needed to remove the 90 degree fitting (the fitting itself needs the clearance).

[NotSoAmish]

I also put an access plate in just as shown in the picture, I concluded it would be necessary if I ever needed to remove the 90 degree fitting (the fitting itself needs the clearance).


I am thinking that a 1/4" NPT (into strainer) x 1/4" compression, then a 90 degree compression fitting off the first fitting would get you back to tubing without having to rotate a 90 degree fitting into the fabric. The 90 degree compression would be removed without rotating it.
I know it's adding fittings and potential leak points but I have found the compression fittings I purchase for work to be very reliable and are routinely used for vacuum and pressure hold testing with air or nitrogen as the media. just need to get a handle on the flow rates from tanks to see if the I.D. on 1/4" compression fittings will provide enough flow. The minumum ID should be 1/4" if I remember right.

[kitfoxnick]

I didn't say it would be as nice of a fit and finish as you have done with your 90 deg fitting but you can go straight out, mine has a loop.
I will try to post a pic later.


Well? a lower sump region of the tank?
Yes

I would recommend not using compression fittings for gas lines.

My personal opinion is that you could get more fuel out of your old style tanks by leaving your strainer setup the way it is.

[DanB]

While on the subject...this is an interesting application of a banjo bolt/fitting I ran across. You can't see clearly, but the fuel tank was tapped at the under-side near the rear of the tank. It looks a bit "dragy" as far as the aerodynamics go, but as I said...interesting.


3478

[Dave S]

[quote=NotSoAmish;23613]Dave,
Is the acess port just to put a wrench on the strainer fitting for removal? Has anyone tried making a tool the would eliminate the need for the lower access cover? I think I can mill out a socket to fit over the square brass elbow. If the elbow comes out first then a standard socket may fit over the strainer hex provided it is not too far behind a rib strut.

Barry,

I found that the right angle barb end of the fitting would not clear the lower surface of the wing/fabric - other installations may work out differently - I used the fittings that came with the kit - If I ever change it - probably do something like Lowell did with the modified fitting.

Basically the access point permits: 1) the angle fitting to swing all the way around without hitting anything, 2) a place to get in there with wrenches, 3) easy access for dealing with the hose/barb fitting connection and clamp.

Sincerely,

Dave S