Critique my fuel system layout

(old message removed)

Aren't you missing a bypass tube?

That fuel filter is not going to be easy to service. Build a door in the bottom of the fuse directly under the filter. You will thank me every year at annual time!
I have installed access doors on quite a few RVs and rockets, including a RV10.
They are very similar in construction to all the other access panels on the aircraft.

Looks just fine.

You only need to worry about the rigidity of lines FWF.

As Tom mentioned, an access panel will make life easier. I put one in on the right side of the tunnel. I know folks that have installed them on both sides of the tunnel as well.

I've already had the opportunity to take both the filter and pump out and it was not a problem.

This is even more important if you install a center console, which makes taking the tunnel cover off more difficult.

rleffler said:

...You only need to worry about the rigidity of lines FWF...

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This advice is contrary to standard aircraft practice. Even if there is no perceived relative movement between two fixed points, such as between a fuel selector and a firewall bulkhead fitting, there should be enough degrees of bend along the run to accommodate expansion or flexing of the structure. The key point is to bend the tube enough to make sure it is not a structural element.

That said, the picture shows about 90 degrees (total) in that Z bend, and that's plenty as long as the pump and filter can float slightly in rubber mounts. If they are truly rigidly mounted, then I might be uncomfortable with the line from the selector valve.

I see that the filter is supported, but don't see that the fuel pump is supported. That's a lot of unsupported mass. I would also agree that adding a large removable panel in the right side would be a good idea. I have one, and it is not a problem to remove my filter to inspect it.

Duh on the bypass. Actually I think if your tunnel cover comes off fairly easy you don't need an extra access. Screws are screws and its good to look in there periodically.

Plumbing the new version AFP pumps is a breeze. Looks like you do have enough offset between the valve and the filter. Like Tom and Bob said, the filter in the tunnel is a little bit of a pain. Several customers now are mounting filters in the wing roots to make life alittle easier. Some of our European customers have mounted gascolators in the roots.

I would hate to spill fuel in the tunnel or cabin of an RV10---especially after all the hard work, carpet, leather, consoles etc.

Tom

TS Flightlines said:

I would hate to spill fuel in the tunnel or cabin of an RV10---especially after all the hard work, carpet, leather, consoles etc.

Tom

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Luckily the floor of the tunnel is lower than the floor where the carpet is.

TS Flightlines said:

Plumbing the new version AFP pumps is a breeze.

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I hope it's the same inline configuration for the RV-9. I've got an AFP pump on order, but Van's engineers are currently redesigning some of the sheet metal to accommodate the new pump. The double-decker thing is OK, but it sure requires a lot of odd bends in the tubing.

I am going to keep plugging my floor inspection panel. We are supposed to check these filters at least once a year, more if you fly a lot of hours. Making it EASY to check will greatly improve the odds of this important job being done. There is no sump on this filter as there is with a gascolator and so the only way to know if there is **** in it is to take it out and have a look at it. With a new airplane you should likely do that in the first 5 or 10 hours just to make sure that there is no fuel tank construction residue.
There are quite a few a screws in that tunnel cover and the tunnel cover is underneath the panel. Yes it is doable but it is not a quick job. Also, if the cover is painted you will eventually ruin that nice paint around the screw holes.
It will take one to two hours to make an inspection panel in the bottom of the fuselage. You will get that time back on your first inspection.

For that matter put some extra inspection panels over the step attach points. This will make this inspection very easy.

Inspection panels not only make inspections easy but they make them happen.

I decided against an inspection/maintenance panel to service my AFP filter in the tunnel. I want to remove the forward tunnel cover to inspect all the fuel fittings under there without using mirrors or inspection cameras. I noticed a decrease in my fuel pressure after the first 60 hours. It took me about 30 minutes to remove the seats, tunnel carpet cover, forward tunnel cover and the filter. About the same for reassembly. I was surprised to find quite a bit of junk in the filter screen but happy I could do a thorough inspection of everything while I was doing the service.

Also, i just had my fuel selector fail due to crud that seized the valve. I am thinking about putting a couple of inline fuel filters in each wing root now.

digidocs said:

Hi VAF,

Would the VAF braintrust have a look at my fuel system layout below and let me know what you think?

A few specific questions:

- Is this setup too rigid? There is compliance in the big z-bend tube on the firewall end, but the other tubes are short and straight enough that they are pretty stiff. If I use Van's supplied pipe clamps to lock everything into mounts riveted to the floor, am I locking in stresses due to slight misalignments and flexural stress from vibration?

- If this setup is too rigid, any suggestions on alternate configurations that would be better? The new AFP fuel pump is longer than the old one and my fuel valve is mounted a but more forward, so I'm a bit constrained on space.

- Any other things that could be better?

Thanks for the help!
David

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David:

It looks OK to me. If you want to get rid of the short piece of tubing and the 2 flares between the filter and the pump you can use a swivel coupling like this:
http://www.jegs.com/i/JEGS-Performance-Products/555/100322/10002/-1?parentProductId=752566

I needed the shorter length, because I put my flowmeter in the tunnel too. I just today finished the access panel on the right side. Pictures are as follows:





Good luck on your build.

The inline positioning is certainly clean looking, but before you move on, try and remove just one of the devices in that line. With short pipes, and flared ends, it is like Jenga with"I" shaped blocks.

My 2 cents which is not much when compared to most folks on this site. I used stainless flex lines with the aeroquip fire sleeves on my tunnel fuel lines. It was expensive but gave me great peace of mind. Additionally based on 6 annuals I would install the side access panel. It provides great ease of access to the system.