Fuel Line Routing

[Battson]

Personally I think this is an issue which gets overstated.

I have a drain per tank and the gascolator, if any water gets into small low points then it will not be enough to cause trouble. I have tested this.

See attached photo of the water taken from the gascolator. Other water sitting in the minor sumps in fuel lines, fittings, etc. all passed through the engine with nothing more than a cough. This happened on the ground before I even got to the runway.

IMG_20180116_195937.jpg

[AKKen07]

I think you’re absolutely right so long as it doesn’t freeze into a line blockage. That’s an impressive amount of water too!

[AKKen07]

410BDB09-A35F-446B-BFA1-D887CF4AB730.jpeg96A498AB-9412-4C04-995C-BC473662D202.jpeg This is my “fix” (or unnecessary mod depending on your POV.)

[zkelley2]

410BDB09-A35F-446B-BFA1-D887CF4AB730.jpeg96A498AB-9412-4C04-995C-BC473662D202.jpeg This is my “fix” (or unnecessary mod depending on your POV.)

It's a little hard to tell, but I think you'll have yet another low point in front of that one. If what I'm imaging the rest looks like, you've isolated that spot with a low point, but the low point in front of it won't send water back up the fuel lines.

[AKKen07]

I don’t follow. I might be a bit slow... where is the new problem spot? Everything from the wing root to the forward T should be downhill to this drain. From the forward T on will be down to the gascolator. I don’t see any low points in between.maybe the angle of the pic is misleading?

[zkelley2]

Ya, I might be confused by the pictures... but from that back T, it's going to T up with the front tank fitting coming down the door frame right? Then under the floor to the gascolator and fuel selector. Those are going to be somewhat isolated from the drain you put in. I'm just not picturing how this solves anything.

I just re-did my whole fuel system from what the previous builder had in place. I really don't like the location of where most people put the gascolater either. I should have taken pictures before heading out on this trip.

[AKKen07]

Yeah, you almost got it, but there is a drain in the gascolator too. From the T it would probably flow to the gascolator but it doesn’t matter if it flows to the front low point (gascolator) or aft (new drains) now because I can detect/get the water out at either location. The only problem was a low point that could not be relieved of water at the back corner of the door, now there are three low points with three drains. Am I making sense?

[Mark Goldberg]

FYI - fuel systems are one of the areas that airplane design engineers do not like builders making changes. What Bob designed has worked well on a LOT of planes. So I would be cautious re-designing the wheel. Mark

[Mark Goldberg]

I just spoke with Bob and asked him about this discussion. He basically feels that not enough water could accumulate in the lines to make the engine quit. He said you can certainly get enough water in a fuel tank to make the engine quit. He said the gascolator would hold more water than could be in a low spot in the fuel system lines. He did mention something that no one has brought up - the possibility of water freezing and breaking a fuel line. It has never happened but perhaps could.

He also said no problem running drains like Ken did - with one caveot. When you have fuel lines on the bottom of a fuselage they can break off and spew/leak fuel everywhere if the plane ever goes down on its belly. Granted - the gascolator is down low where this could also be applicable. Bob once saw a Beech Staggerwing land gear up and all these fuel lines on the belly broke and leaked fuel. The plane burned up. The pilot got out with no injury. But the plane burned up because of fuel lines down low on the fuselage belly. Mark
.

[marcusofcotton]

... He did mention something that no one has brought up - the possibility of water freezing and breaking a fuel line. It has never happened but perhaps could...
.

Actually, freezing has been brought up on this thread by several people many times including on both pages. Freezing might not get heard in Texas.

[zkelley2]

Jim, frozen water will split a steel line, I'm not sure why it wouldn't split aluminum. Aluminum isn't that ductile.

[JimParker256]

zkelley2, I have seen it split larger sizes of PVC, steel, copper, etc. I just have no experience with small-diameter (1/4 inch) aluminum, so I guess I'll have to give it a try when I get some time...

[Russellmn]

As long as there is no check valve built into the system up stream (towards the tank) of the low point, any expansion from freezing would take the path of least resistance- towards the tank. When a water pipe in a house freezes and splits, it is because a section of the pipe is plugged (such as a slug of ice plugging off the open end, and THEN water downstream freezes.

However, I was always under the impression the gascolator should be at the lowest point in the system anyway, which is where the water would collect...

[marcusofcotton]

BTW, if that came across snarky, I apologize, it wasn't meant to be.

Unfortunately, I've seen way too many split lines, tubing, and fittings from freezing. Even if there was no line damage, seems to me that no fuel flowing might not be desirable either.

[Battson]

I would think the small volumes of water we are talking about cannot break the line. Ice often won't even break plastic lines PROVIDED the water is not freezing the entire line solid i.e. the line only contains a relatively small proportion of frozen water compared to liquid fuel / water. If there is room for the ice to expand along the line, then the ice will travel along the line as it freezes.

[zkelley2]

Plastic lines are what we use when you know it's going to freeze. Look at PEX vs copper water lines.

But you're right, unless it froze the whole line it's unlikely it's burst.

[Battson]

Point taken