Fuel System Y-Fitting Attach

[Archer39J]

Instead of your standard AN804 T+Bulkhead fitting I went and got myself a fancy Summit Racing Y-fitting. Two things: now I'll have to bend the attach tab down a bit which shouldn't be a problem, and since it's not a bulkhead fitting I need to find a way to secure it to the tab. When the nut, sleeve, and tube are attached there's maybe 1/16" of play between the fitting and the tab.

Any thoughts about how to go about this? I'm thinking possibly a rubber washer between the nut and tab, or perhaps letting the Y fitting hang free behind the tab and holding the outlet tube with some kind of grommet in the tab? With the washer I'm concerned about affecting the snugness of the flare, but I guess if it's not good you'll know right away so...

[Battson]

You'll need to secure the 3003 or 5052 tube to prevent it from rubbing on the 4130 near that location anyway. I would consider letting the fitting float free?

Edit - you'll be planning to put something there, to stop your feet catching on the fuel lines?

[Archer39J]

You'll need to secure the 3003 or 5052 tube to prevent it from rubbing on the 4130 near that location anyway. I would consider letting the fitting float free?

Edit - you'll be planning to put something there, to stop your feet catching on the fuel lines?

I don't recall having seen any measures to protect the outlet tube as it curves under the floor in photos of other builds. I'm looking at the geometry of adding a cover for the rudder cables which would also cover the fuel line in that area, but I'm not sure it will work out. I'm using 5052 tube also, so free floating may be the easiest.

[mpillor]

Like your floorboards. Info?

[Archer39J]

https://bearhawkforums.com/forum/bearhawk-4-place-quickbuild/33723-honeycomb-panel-floor-boards

I've opted to not pot inserts and just use through holes with nylon washers, seems to work quite well.

[Battson]

I don't recall having seen any measures to protect the outlet tube as it curves under the floor in photos of other builds.

Speaking to a number of licensed & experienced aircraft mechanics, I was told the entire fuel line system does need to be protected anywhere it could touch another part. They cited a number of examples where some certified plane or helicopter had something rubbing on the fuel line leading to a replacement of the fuel line.

I used some plastic wrap to protect the line in that area. Seems to have worked well so far. Mine pass under the floor back near the front door post away from the pedals.

The vibration can wear away at the fuel lines pretty fast, especially the 5052 which normally has the 0.035" wall instead of the thicker and softer 3003 with 0.049".

[Archer39J]

Speaking to a number of licensed & experienced aircraft mechanics, I was told the entire fuel line system does need to be protected anywhere it could touch another part. They cited a number of examples where some certified plane or helicopter had something rubbing on the fuel line leading to a replacement of the fuel line.

I used some plastic wrap to protect the line in that area. Seems to have worked well so far. Mine pass under the floor back near the front door post away from the pedals.

The vibration can wear away at the fuel lines pretty fast, especially the 5052 which normally has the 0.035" wall instead of the thicker and softer 3003 with 0.049".

Oh, yeah sleeving that tube where it could contact the longeron is a good idea. Like you say anywhere it can contact something, like where the fwd line runs down the windshield/door post, Jared talks about that on his blog. I thought you meant a cover for incidental foot contact, which I hadn't seen anyone do.

[Luke68]

This was my solution to the exposed fuel line problem.
i was going to try and bend something up but decided this was faster and looked better, leaves you plenty of room for wiring or static lines also.

[Bdflies]

At first, the 'Y' fitting looks to be a good idea. It should offer a bit less flow resistance than a tee. Then, there's the dilemma of installation. This is a great example of how changes or improvements end up with rabbit hole pursuits. The bulkhead tee attaches firmly and flows fine. Like Archer, I like the idea of the 'Y' fitting. As a practical matter, the bulkhead Tee is an elegant and proven solution to this intersection.
My $0.02.

Bill

[Archer39J]

At first, the 'Y' fitting looks to be a good idea. It should offer a bit less flow resistance than a tee. Then, there's the dilemma of installation. This is a great example of how changes or improvements end up with rabbit hole pursuits. The bulkhead tee attaches firmly and flows fine. Like Archer, I like the idea of the 'Y' fitting. As a practical matter, the bulkhead Tee is an elegant and proven solution to this intersection.
My $0.02.

Bill

Ha, exactly! Seemed like an easy swap, but a good lesson that almost any change leads to a daisy-chain of other changes...

[Bcone1381]

The objective, as I understand it, is to have the fuel line secured in accordance with AC43.13, which IIRC is every 16" for 3/8" fuel line. There are lots of great places to use WDG loop clamps to secure the fuel line to in that area.

I did not find the fuel line "bulkhead" attachment tab helpful. My tab was poorly positioned. A floorboard tab located near it made it nearly impossible to accommodate the fuel line making a 90 degree turn while maintaining the slope downward of the fuel line. Using the rigid aluminum tubing and a tubing bender necessatates a straight section of tubing of about 3 inches after every fitting. There was a fuselage tube above the fuel line 'bulkhead' tab that got in the way as well.

Your Y with MS21919 WDG tube clamps might work out well. I liked my TEE. IMO, the difficult situation for the fuel system flow test is in the nose high attitude with minimum fuel in the tank. Fuel will exit out the rear tank fuel line. So it may benefit positioning the Tee so that it resistance in the fuel system is minimized when flowing thru the rear line.

Ask yourself "If I install Bush wheels, will any water be able to enter the fuel lines and not make it to the gascolator."

IMG_4414.jpg

[Bdflies]

Regarding the fuel flow test; after the usual flow test, before flight, I did an inflight test. The standard Patrol fuel system (with a "Red Cube" flowmeter) will adequately flow full throttle demands of a Lycoming O-360, in a climbout attitude, from either left or right tank, with about 5 gallons in each tank. 10 gallons on board is about as low as I care to takeoff with.

Bill

[Battson]

The objective, as I understand it, is to have the fuel line secured in accordance with AC43.13, which IIRC is every 16" for 3/8" fuel line. There are lots of great places to use WDG loop clamps to secure the fuel line to in that area.

That reminds me, if you are using bulkhead fittings then you might like to leave bends or floating sections between them, to allow for thermal expansion and contraction. The fuel and metal fuselage change temperature and quite different rates, also the steel and aluminium have different coefficients of thermal expansion - meaning they change length and different rates as they heat up / cool down.

[Archer39J]

Thought I'd post an update of my routing with the Y-fitting. Clamping the lines where I did the fitting is very well secured.



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[Archer39J]

And yes the section mid-door will be secured to the fuselage, I just haven't done that yet. I'll also sleeve with that spiral tube HDPE anywhere it can rub.

[svyolo]

Dave and Brooks. You guys are a bad influence. I promised myself a stock build to get er done. Moving the T or Y aft and up a bit might make a header tank under the front seat or seats easier. I see another rabbit hole approaching.

[Archer39J]

Can't speak to the header tank, but in this rare case the mod was time neutral

[svyolo]

By moving the fitting a bit farther aft, I can run the post T (or Y) output directly to a header tank under the right front seat. Simple shutoff valve forward of that. EFI return to the header tank. I haven't been spending any time on this yet. But I think I like it.

[Battson]

Suggest you might like to wrap the line below the Y-fitting, where it's resting near the 4130N tubing, using a plastic spiral wrap. It keeps the alloy line from vibrating against the steel. Worked well for me.

[Archer39J]

Hard to tell from the pics but there's like 1/4" clearance there and it's quite rigid. Though I'll sleeve anyway for good measure, certainly couldn't hurt.

[Battson]

In my case it was rigid too, but the clearance was smaller and everything kinda "settled" over time. Also the floorboards and people's feet get kinda close to them in my install.