Tall narrow fuel tank plumbing
08-14-2018, 08:53 PM
#1
Tall narrow fuel tank plumbing
Hi All,
im in danger of vastly overthinking this, but I’m just putting together my jetlegend PNP F18.
The two fuel tanks are pictured below (photo stolen from another thread), But are effectively tall and narrow with a wide top section.
id normally use a felt clunk, but read about heavy clunks being better.
i couldn’t see how a heavy clunk would help in this situation, it’s likely to be left at the bottom unless your knife edge.
And I also see some threads with metal pipe on the clunk line, but can’t understand the benefit.
so the question is, what’s the “groupthink” on the best way to treat a tall narrow tank?
Is a baffle even an option?
08-15-2018, 04:01 AM
#2
Well, first, the tanks aren't positioned in the F18 as they are sitting on the table as posted. They are positioned as an upside down "L". In the pictures, the outside of the "L" is positioned down into the fuse leaving the large flat area for the vent. In other words, the two red metal connections are vertical in the fuse when mounted. It drains fast into the primary center tank leaving a deep part of the "L" to drain the rest of the fuel. And, you have said this on your post. 95% of the time flying the JL F18 you will be in a positive G force, so the fuel is always at the lowest point. Those clunks are some of the best to use. CARF uses them all of the time in their jets.
As far as the metal pipe on the clunk line, it is to keep the clunk line from going forward and getting stuck a 180 degrees. The metal pipe also is used when there is a baffle inside the tank. The metal pipe is put through the hole in the baffle and keeps the fuel line from getting cut by the baffle. There is no way that you can put a baffle in a sealed tank that doesn't have one. Those tanks are a lot better design, then the ones I had in my JL F18 a few years back.
But, yes, you are over thinking the installation.
As far as the metal pipe on the clunk line, it is to keep the clunk line from going forward and getting stuck a 180 degrees. The metal pipe also is used when there is a baffle inside the tank. The metal pipe is put through the hole in the baffle and keeps the fuel line from getting cut by the baffle. There is no way that you can put a baffle in a sealed tank that doesn't have one. Those tanks are a lot better design, then the ones I had in my JL F18 a few years back.
But, yes, you are over thinking the installation.
08-15-2018, 04:16 AM
#3
For me on tanks like these I use a small header tank. Then when the clunks are not in the fuel you are still drawing from a header tank. I am not a fan of the felt clunks if you are using a UAT also. They add allot of restriction and can cause air bubbles due to cavitation. Felt clunks by them selves are ok but don't use them with an added filter in the UAT.
Also on tanks like these I set them up in series. That way the second tank stays full half the flight so you end up drawing less air. The metal tubing is used incase your clunks can get stuck. You add the tube in the middle to keep the clunk from moving to the front of the tank and possibly getting stuck. This does not always need to be done and probably not needed for your install since you are using that black clunk line.
Also on tanks like these I set them up in series. That way the second tank stays full half the flight so you end up drawing less air. The metal tubing is used incase your clunks can get stuck. You add the tube in the middle to keep the clunk from moving to the front of the tank and possibly getting stuck. This does not always need to be done and probably not needed for your install since you are using that black clunk line.
08-15-2018, 04:54 AM
#5
I would only use that style as a saddle tank, hopefully you have a main. Then just do like states above saddle to mains and main to UAT.
Last edited by FenderBean; 08-15-2018 at 04:56 AM.
08-15-2018, 01:13 PM
#8
They’ve changed the fuel system. As Chris said, I wouldn’t do that set up without a header before the UAT. Or in series. The issue that I see with series, is that your lateral balance will go off center. This will affect your loops and other maneuvers. The gyro will hide it. My F18 was JL and had the two saddle tanks then into about a half of a gallon main tank then to the UAT. The fuselage had to be taken apart in two halves to get to the main tank.
Last edited by RCFlyerDan; 08-15-2018 at 01:22 PM.
