Fuel Line Routing

[Archer39J]

I'm routing the fuel lines and have run into an issue. I've positioned the fuselage to the 3-point ground attitude of 13 degrees and it seems the fuel line fwd of STA C runs slightly uphill. Though you can't tell from the photo, the red section is sloped up maybe 1/2 or 1 degree or so. The pass through point I chose through the boot cowl former is even lower than most examples I've seen, even in the manual.

This is in line with the attach tab you see in photo 2, but it looks like many folks chose to go even higher.

Have others addressed this, or folks taxiing around with low points in their fuel system and it just hasn't been an issue? I've also seen examples of lines running uphill out of the fuel valve (though mine faces aft) and apparently that hasn't been a problem either.

Fuel1.PNG
Fuel 2.PNG
Fuel 3.PNG

[Mark Goldberg]

If you have the aft of the line as high as possible, and the forward side as low as possible - then it is about as good as it can get. I do not know of any problems resulting from this on all the planes out there. Mark

[Archer39J]

If you have the aft of the line as high as possible, and the forward side as low as possible - then it is about as good as it can get. I do not know of any problems resulting from this on all the planes out there. Mark

Yeah that’s about what I figured, if it hasn’t been an issue I’ll move on.

[marcusofcotton]

Thanks for bringing this up Dave. For me, I see this as a significant issue as I live in a freezing climate and am planning on maximizing angle of attack for short field ops. I'm also planning on a raised threshold to eliminate the mouse door so I'll likely be able to keep the fuel line higher at the door midpoint to address it.

Sure is good having this group to share details, thanks all!

[AKKen07]

Well I routed my lines normally then had an IA come take a peek and he was not happy with my default low point at the rear corners of the door frames. Point is we have lots of poor fuel sources and plenty of moisture and lots of cold for it to freeze at these corners. He suggested that I run a line off of a T at that spot with a drain line going down to a quick drain on both sides. I suppose I could link up both sides in the middle and just have one drain, but still, kind of a bummer. What are the forum’s thoughts on this? Assuming that I cannot improve on the angle of the line here without remodeling my door frame (not an option) would you put in some new low point drains? That means with aux tanks I’ll have SEVEN places to sump! Sheesh.

[svyolo]

I thought the low spot requirement was for level flight. If you are on big tires I don't think it is possible to route the rear lines under the door in such a way that there is not a low spot.

[AKKen07]

The concern is that on the ground, water will sink to the low point and accumulate where it can not be drained. In this case, the door corner. There it can freeze and become an obstruction to fuel flow or worse bust a line/fitting. In flight the circulating fuel will drag the water through the gascolator and/or filter and low points won’t be an issue.
The objective of putting the gascolator at the low point is for this purpose. The door corner problem complicates that.

[jaredyates]

Post us up a photo of how you have it set up Ken!

[AKKen07]

Good idea

[AKKen07]

So on the rotisserie there is no apparent problem. But, once I put it on its gear the slope becomes positive under the door.

[whee]

I think it looks good Ken. I wouldn't change it. Plenty of BHs flying with the same, or not quite as good, routing with no issues related to that possible low point. On normal sized tires there won't be a low point; it will be down hill all the way to the fuel valve. Install bush wheels and you will likely have a low spot there but so far the other guys on big tires haven't had any issues.

[AKKen07]

Thanks John, that was my thought when I built the lines. The IA I had over just made me doubt my decision.

[AKKen07]

Update: had another A&P look at it and he thinks I need to have drain(s) too... He keeps his 170 outside all year and gets enough water to freeze his wing sumps regularly. Having the extra lines/drain should keep the ice from blocking the system theoretically.

[Mark Goldberg]

Ypu have the fuel line as far up as possible where it starts on the aft side of the door sill. Hard to say if you have the forward side as low as it could go but it looks pretty close. And if the problem the AI's see is on the aft side then lowering the front would not help anyway. I do not know of anyone who has had a problem like your friends are concerned about. But I suppose it could happen. It is very hard to keep all the lines flowing down hill when you have big tires. Mark

[AKKen07]

Thanks Mark. Between the added complexity and weirdness of the “fix” I am not sure what to do or not do. I would have to run lines through the floor between the rear seat and rudder cables which would be exposed and vulnerable to baggage when the seat is out. Putting drains and extra lines for the drains might cause other issues. If I catch water in these lines as the de facto line points, and have an inline pre boost pump filter, why do I have a gascolator? Will the vulnerability to leaks and damage from baggage over the exposed sections of this line be more of a risk than the unlikely event of water freezing in the lines? I suppose I could build an aluminum cover for that section. Argh!

[svyolo]

One thing I re-did was make the holes in the formers big enough to pass the flare nuts. I used a big snap bushing, and two layers of clear fuel tubing over the fuel line to fit the bushing.

[Bcone1381]

Murphy's law.....Whatever can happen will happen. So it is important to consider all the possibilities that could go wrong during flight and act to counter them.

-Could a limitation be written to prevent adding a sump? (A minimum of X gallons with takeoff and landing on Both tanks with temperatures below freezing.)
-Could the aircraft be stored in cold weather with the tail placed on a platform to allow the aft line to slop downward.
-Adding a sump is not Murphy proof unless its exercised.

If the aft fuel line on one side got plugged up with ice.....
-will ice (or water) be present in the fuel sample at the tank? (My fuel sumping experience dates back to the prior decade....I cant recall if I ever saw ice in a fuel sample.)
-will problem be masked by the tanks front sump's fuel supply for the entire flight?
-will the problem be masked by the selecting BOTH tanks?
-If we still took off with 1 tank selected, is there enough fuel in the forward line to run up, take off, and raise the tail to cover that front bung and provide a fuel supply? How often do we takeoff with less than half tanks? But doing so still masks the problem.

The above illustration is not justification for not adding a sump, rather it should show us how a problem can be hidden and mysterious, and issues arise when switching to Tundra Tires, or shows why no one has had a problem yet.

The Patrol has the same issue on the right tank only. Its slope is good with 800 x 6 tires, but larger tires will cause an issue. The left tank fuel supply is steeper because there is no door to go under.

[JimParker256]

Ken,

I'm not sure what good a drain would do, if the water in those lines is frozen... You can open the drains all you want, but the "ice" is not going to come out until the line is warmed to the point the it melts and becomes liquid again. Seems like you'd have to make a habit of pre-heating that area somehow, and then immediately opening the drain, for the drain to have any real benefit to you in that situation.

I think that a "real" solution would require some kind of a "sump" at that low point (like another gascolator - or two, one on each side). Is it worth it? You're the builder and only you can decide.

[AKKen07]

Jim, good point for sure. The advantage of these drain lines in this scenario would be another 18” of line on each side to catch wanted outside the main feed to the engine. It will function as a sort of gascolator in that respect. If you look at a Citabria there is a lot of line going to the low point in the aft fuselage to a drain while the gascolator is on the firewall. In my case (I’m not sure about the Citabria) the primary fuel flow would then bypass this frozen cache of water unless there was so much water that it overflowed to the main line. If these lower lines freeze I would now now where the water was and would necessarily heat the area until all water was drained from the system. None could escape this procedure as it would otherwise with an undrainable low point. Clearly I’ve chosen my route here and will post pics when I finish.

[JimParker256]

Yeah, I can see how that would work pretty well. I wasn't thinking about having an 18" column for the fuel/water to flow into. That SHOULD do the trick. I've never sumped more than a few thimbles worth of fuel out of a tank, but I've heard tales of aircraft sitting out in rainstorms where they took on a 1/2 gallon of water... But you're right – if nothing came out of that drain when the temperature was below freezing, it would be a dead giveaway that you have some water in that line. Thawing and draining until only fuel emerged should resolve the issue. Guess I've got another item to think about. I'm only planning for 8:50x6:00 tires, but I'm already thinking there might be a low point behind the door, no matter how careful I am with routing the fuel lines...

[kestrel]

Mine is equipped with 7 drains. One for each of 4 tanks, the gascolator and one at each low point behind the doors on the belly.

[AKKen07]

Aha! I’m not the first! I am curious how you have routed and secured your door corner drains. Any chance we can glean some details from you? I’ve been trying to figure the best fittings etc to use.

[kestrel]

I didn't build the plane, but I'll see if I can get a few photos to hint at how it was done.

[AKKen07]

Thanks! Definitely appreciate it.

[kestrel]

They're not much, but here is a few photos. Looks like there is a T (not visible) under the rear edge of the door. The bottom of the T goes down to the belly and a quick drain. Note that this one was built with an additional T-fitting to install a ferry tank. I don't believe it was ever used. The headset jacks that are visible are for the rear seats.

[JimParker256]

I like the idea of including a T-fitting for a possible ferry tank connection. Cheap insurance "just in case".

[schu]

Ferry tank? A bearhawk in super economy cruise can already go 4-5 hours with standard tanks and 5-7 hours with aux tanks. I'd be installing a urinal before a ferry tank.

[JimParker256]

And the Patrol I'm building can likely go almost 10 hours at super-economy cruise speeds (AKA "Max Cruise for a SuperCub", LOL). But there might be times I want to go somewhere as fast as possible, with as few stops as possible. (Hmmm. Dallas to OSH non-stop might be do-able with a 20-gallon ferry tank...) Just kidding on that one. But the idea of flying out to the back country, and having enough fuel to fly around a while, spend the night at a remote strip somewhere, then fly back to civilization is pretty appealing to me.