Fuel Line Routing

[noema]

I am a bit puzzled as to what's the best way to route the fuel lines. Specifically I am trying to figure out the details behind the pilot door. I am coming through the aft former and then possible have to go through two stringers. This seems to be very hard to do as one piece of fuel line. I would basically have to delay mounting the the formers, slide them on the already perfectly bent fuel. This would also make it very hard to replace the fuel line later.

How did you do this? Split up the line with a coupling? Completely bypass and just go around the inside? Then build some kind of protective cover over it?

Anybody has some good photos (preferably for the Patrol but I assume the 4-Place has a similar detail).

Screenshot 2022-08-08 230029.jpgScreenshot 2022-08-08 230054.jpg

[bkyser]

The builder of my Patrol put a bulkhead fitting in the lower stringer, thus splitting the line in two.

[noema]

That makes sense. Is it a 90deg bulkhead?

[bkyser]

I couldn't figure out how to add a picture to a comment, so I edit my original post with a picture.

[N3UW]

Noema, I am out of town at the present but I will post some pictures of what I did later this week if others have not yet. What I did is run it as two pieces with a union in the area between the lower section of window and the lower stringer. I protected the tubing with double wall heat shrink with sealant. I ran the tube between the rear door jam and tabs as tight to the vertical fuselage tube as possible. I notched the stringers as necessary to pass. I then passed through holes in the lower door jam with edge protection on the hole. The hole was large enough to allow the tube and nut to pass through. The same was done on forward jam.

your second photo appears to show a tab on the lower stringer that is almost against the door jam. I believe my tab was rear enough to allow the tube to pass between the tab and the rear portion of the door jam.

[noema]

I think I understand. Some photos would be great.

[Mark Goldberg]

Apart from the routing of the fuel lines - start the lines up as high as you can next to the seat back of the pilot as they come down hill in the front. This is to try to keep the fuel going down hill with no low spots in the lines where water can be trapped. Mark

[noema]

Got it. Seems to be a challenge with large wheels.

[Bcone1381]

Noema, Your concern for replacement of the fuel line later is a constraint that I intentionally did not include in my fuel line build. It's a non-moving part. I used the hard 5052 aluminum tubing. It's well protected. Its' covered now on both sides with fabric.

[noema]

Did you run one line without union from wing to T-fitting?

[spinningwrench]

BB6B5342-1E44-4973-9609-5317ACF4F53A.jpg46EC20F9-1AB6-4B0E-8C38-81FB0DF6E920.jpg045971D3-B89F-40B4-8466-74BD3F336F26.jpg I followed Brooks lead on this and did a single 5052 line with no unions to leak. I doubt one would ever have to replace this line. Brooks developed a good technique for bending and cutting the line. Here is my Patrol install.

[Paul Johnston]

I used the rubber grommets in the formers also . But I did two unions in that run -just below window and one below the door- Much easier. Never seen a leak at a flare nut

[N3UW]

Stefan,
I finally got back in town. I took some photos of my fuel line installation in the Patrol. It is important to make sure the fuel always runs downhill and does not have a place for water to collect and potentially freeze. Also make sure you keep the fuel lines as low as possible on the tube at the wing root where it will attach to the fuel tank. On the lines to the fuel valve, I was not able to use the supplied fuel valve bracket because it placed the fuel valve too high. It would have cause the fuel line to bend up to the valve creating a low spot as the fuel line crossed over the tube to the valve. I created a new mount that lowered the valve about 9mm to allow a straight line. To protect the fuel line I used a combination of heat shrink and cloth friction tape sealed with shellac. I made the holes through the door jams large enough to pass the nuts on the AN fittings. I also protected them with split grommet material that I will glue in.

[Bcone1381]

I like the 9 photos John provides and his advice. I see vibration and I see things rubbing and I worry a bit. SO, I don't have my fuel lines in direct contact with any fuselage component except where it might be secured like with an Adel cushion tube clamp. AC43.13 says to secure them every 18 inches. If they are close to anything like a former, it also got a piece of rubber tubing for protection. John's look better than mine. I have no experience with shellac coated friction tape. I'd run it through the stringer if I cant control the contact issue that might be shown in photo #4.

[noema]

Thanks John for posting more pics. It helps a lot to look at all those reference solutions. I will probably be using a 45 deg elbow in the corner because I already have it. Will post once I got it done.

Bcone1381 is right the entire span under the door probably needs two attachment point if strictly adhering to AC43.13.

I was wondering about the fuel lines into the fuel valve too. It clearly creates a small low point (see attached photo). Is this gradual enough to wash out any water buildup. Asking because with my kit there is really no other way of mounting it other than redoing the entire assembly.

[noema]

Actually, I could probably mount the triangle assembly at the bottom of the tabs (possibly with spacers). This way I could lower the entry ports as desired. This would also move the drain valve closer to the bottom skin.

Any reason not to do that?

[N3UW]

I have not completed the attachment of the fuel lines yet. I planned to add a few adel clamps and weld a few tabs once I had all the windows, doors and stringers fitted. I may be a bit over cautious on the low spot but I had a friend have an engine stoppage in flight due to a low spot in the fuel line where water collected and it froze. I wanted to make sure that my fuel system always had positive slope while on the ground and in normal flight attitude. It may be overkill. I simply lowered the fuel valve about 3/8". I had a series of rings laser cut out of 1/4" AL to make the adapter. I then spaced down the fuel strainer. That gave me a slight downward slope. I also have the QB fuselage and I made this change after I had originally installed using the factory bracket. I had the rings cut out by oshcut.com. There were 3 different sized rings stacked together then polished. It also created a nice mounting point for valve.

The cloth tape I use is 3M black cotton cloth electrical tape that after I install it I cover it with shellac to lock it in and seal it. It is how Piper used to protect lines. It is nice because you can do it after the fitting are on and build it up to the thickness you need.

[noema]

This looks great!

With shellac do you mean nail paint? Any resin would work, right?

[N3UW]

noema, One of my other hobbies is furniture making and Shellac is a finish I often use. I make my shellac from dried flakes mixed with denatured alcohol. It is actually the secretion of the lac bug that is collected and dried. Actually any kind of sealing finish like clear lacquer or varnish would probably work. Shellac is nice because use a fairly thin mixture thinned out with alcohol. You just want it to soak into the cotton friction tape so that it does not peal off with age and heat and it hardens it a bit..

[Bcone1381]

I"ll echo what John wrote about slope of fuel lines. I like how he lowered the selector valve/gascolator to get that slope. (That might be something the factory could modify for future builders.) I live in Michigan, so I figure a tablespoon of water will enter my fuel system and freeze....freeze in the gascolator. No problem.

And so the right aft line under the door was kept as high as I could like John and Bruce and was terminated as low as I could to keep the slope going down. With the tail on the ground with 600x6 tires its good but its close!! That line will not have a downslope if I go bigger tires....like 28" tires. No way.

The Left side has a far more generous slope. So that left fuel tank is my primary tank, and I'll label it Primary, and maybe place a limitation of some kind in the POH.

[noema]

Brooks, I was wondering about bigger wheels too. I like the solution of at least having one fuel line with plenty of gradient and then noting the OPs in the POH.

[noema]

I looked closer into the fuel line slope and big wheels. The angle change for bigger wheels is actually less than I have initially thought. You get 3.58in gear height for every degree the line is sloped forward in relation to the ref longeron (h = l*tan(alpha)). The gear without wheels is about 21in, with 35s this results in 38.5in gear height. Therefore you need a slope of at least 11 degree (angle between fuel line and reference longeron) to be compatible with the biggest Bushweels.

On the right aft fuel line I can get a 13 degrees delta from the reference longeron. I think this is pretty much the maximum slope without doing any mods. Happy to have figured out this is a comfortable margin for the wheels I plan to put on.

[Bcone1381]

Awesome! Thanks for that. Good Data!! I just eyed it up when I did my lines and made a non-data driven conclusion.....that was a long time ago!