Vapor Return Line or Not?

jpharrell · #1 10-13-2010, 02:00 PM

My question is should I install vapor return lines in my RV-7A fuel tanks or not? I just started on the tanks and have not yet made a decision on the fuel system for this bird. Is it worth the extra cost, time and weight to install return lines now just in case I need them later? If I don't install them, are there workarounds later if I fall in love with an injection system that needs vapor return lines?

John Harrell
RV-7A under construction, building wings
www.johnsrv7a.wordpress.com

shuttle · #2 10-13-2010, 02:20 PM

Have a read here: http://www.vansairforce.com/communit...ad.php?t=10648

Personally, I'd not do it until I had committed to a fuel injection system that needed it and then I'd tailor the plumbing to the specific requirement.

Neal@F14 · #3 10-13-2010, 03:15 PM

As long as you do not install your fuel tank sending units and sending unit mounting plates onto the tanks before you've settled on a particular fuel injection system, you can wait until later.

We installed the ECI fuel injection system in the RV-8 and that required removing the big round sending unit mounting plates off the tanks to drill and add return ports. Fortunately the wings were still sitting in their cradles and not installed onto the fuselage yet, and we had used Permatex aviation gasket sealer (the brown goop that comes in a plastic jar) on the cork gaskets which was easy to remove. Had the sending unit plates been glued in with proseal like many builders do, it would've been a royal pain to disassemble for adding the return ports.

WingsOnWheels · #4 10-13-2010, 08:46 PM

I went ahead and added an Aux port on my tanks just in case. I just used a couple more of the tank drain flanges. I might never use them, but at least they are there just in case.

David-aviator · #5 10-14-2010, 08:46 AM

Quote:

Originally Posted by jpharrell

My question is should I install vapor return lines in my RV-7A fuel tanks or not? I just started on the tanks and have not yet made a decision on the fuel system for this bird. Is it worth the extra cost, time and weight to install return lines now just in case I need them later? If I don't install them, are there workarounds later if I fall in love with an injection system that needs vapor return lines?

John Harrell
RV-7A under construction, building wings
www.johnsrv7a.wordpress.com

It is more than just the return line to consider. If it will be used later a 6 port valve will also be needed which will require a lot of work installing it.

Might be a good idea to make a decision now as what the fuel system will be down the road.

RVbySDI · #6 10-14-2010, 09:26 AM

David is right on this. There is more to consider than just the return fuel lines.

I have installed the ECI FI system in my 9A. I did make that decision long before I started building my fuel tanks so I knew when I started what I was going to need to do. I would suggest you try and make your decision on whether to use the return lines or not before the build. However, if you are just not ready to make that decision it can be done later on with a little bit of work. You most certainly will need to plumb for the 6 port fuel valve for the return lines. Another thing to consider is the fuel flow monitoring for your instrument(s). If you are planning for a glass panel EFIS that will monitor fuel flow you may need an additional fuel flow transducer in the return line to accurately monitor the fuel flow on your EFIS. I have the GRT HX units in my plane and had to install an additional Red Cube in the return line to get the fuel flow to read accurately. These are just a few more things you need to think about in making your decision.

Concerning the return lines on the tank, ECI changed the routing after I had built my tanks. My return lines run through the Z brackets on the back of the rear baffle of the tanks and run all the way to the outboard end of the tank before a fitting penetrates the tank and dumps the fuel back into the tank. I believe they have changed this routing and are now running the return line through the access plate as others have posted. If so, that would make a retrofit much simpler than my lay out. It would be a fairly simple matter of installing a fitting in the access plate and dealing with the plumbing for the 6 port fuel valve plumbing and all the other stuff between the tank and the engine.

Good luck on whatever you decide. I will say I LOVE my ECI FI. It was interesting to me a few weeks ago when I was at LOE. Sunday morning when we were all prepping to leave out it was rather chilly. It was very interesting to observe how long many of the RV's had to crank before the engine would fire up. As I was standing on the tarmac watching others start their engines I wondered what it would take to get my engine started. Once I finally got in the airplane I found out.

I turned the boost pump on for about 8 seconds, yelled "clear prop" and turned the key. After about 1 1/2 revolutions of the prop the engine immediately fired and began purring. I LOVE THIS PLANE!

Neal@F14 · #7 10-14-2010, 10:52 AM

Quote:

Originally Posted by RVbySDI

Another thing to consider is the fuel flow monitoring for your instrument(s). If you are planning for a glass panel EFIS that will monitor fuel flow you may need an additional fuel flow transducer in the return line to accurately monitor the fuel flow on your EFIS.

We have the Dynon D-120 EMS in the RV-8 and just put the single fuel flow transducer inline between the ECI's engine driven pump and the throttle body unit. That way it measures simply how much the engine is consuming, not how much is flowing thru the pump & return lines.

Quote:

I will say I LOVE my ECI FI.

Ditto. This RV-8 is the easiest-starting fuel injected aircraft engine I've ever seen. Even hot starts in the brutal Texas summer heat were a piece of cake. Although I haven't really tried running it LOP for any extended time, I have noticed that once at high altitude, I can pull back the mixture and the engine stays running glassy smooth all the way down to the point where it basically flames out.

The ECI FI system was expensive to buy, including the Andair duplex valve and all the related plumbing components, complicated to install, and a royal pain to get calibrated correctly at first, but the end result is an extremely easy starting, smooth running, rock-solid reliable FI system.

flyvans.com · #8 10-14-2010, 10:58 AM

great experience so far flying with the eci injection :-)

not very easy nor exactly cheap to install though...
coming up with brackets for the control cables is rather tricky. made one on our own (tech drawing on our website), got one from robbie attaway (attawayair.com)
it's a chicken/egg problem, since you need custom control cables but won't find any control cable specs/throw/distance from rod end to mounting thread from either van's nor spruce. we had the luck of having a sample cable from another builder that had the wrong length. i still can't believe that eci doesn't supply such an important (and safety critical) hardware needed for every integration into an airplane...
also, the instructions regarding the need for a low pressure fuel boost pump are very much cya (cover your a...)...
first, in all the diagrams or their van's install manual, you only find references to the high pressure boost pump as per van's kit and obviously needed for starting/mech pump failure.
yet in the tech install sheet they talk about a need for a low boost pump or an electric pump speed controller...
via email, they however openly admitted that there really shouldn't be a low boost pump as it will actually make the engine run less optimal.

also, the 6port andair valve has a hefty price tag, is very nice though! much better than the default van's faucet style valve.
fabricating the return line itself is rather a piece of cake.

if you can look over these quirks, the system is excellent in a great many respects! read the operating manual where it lists all of the advantages.
operationally, it's awesome.
also, it leaves wide open doors for the use of mogas (less ethanol) or other lower octane fuels due to the much increased margin from vapour lock.

the fuel flow meter however doesn't necessarily need to be installed aft of the firewall (requiring 2 meters and electronic subtraction).
we have ours (afs/e.i. red cube) between the throttle body and the spider mounted to the engine sump with a very rigid bracket. where it works just perfectly.

rgds, bernie

RVbySDI · #9 10-14-2010, 11:56 AM

Quote:

Originally Posted by flyvans.com

the fuel flow meter however doesn't necessarily need to be installed aft of the firewall (requiring 2 meters and electronic subtraction).
we have ours (afs/e.i. red cube) between the throttle body and the spider mounted to the engine sump with a very rigid bracket. where it works just perfectly.

I understand about the installation of the fuel flow meter. In my installation, I felt the best location for the meter was aft of the firewall. Since I did put the unit(s) prior to the fuel pump I needed to have one meter the return fuel.

I can see where it could be beneficial to mount the meter after the fuel pump but it I was concerned about vibration, heat and a secure mounting location for it in the engine compartment after the fuel pump so I decided to go with mounting on the firewall in the cockpit before it goes into the pump.

Andy_RR · #10 10-14-2010, 07:43 PM

I decided to include them in the tanks at least at this stage. My intention is to leave my fuel system options open for the future. I'll consider this again at each stage of the fuse build too.

I made my return line, which migrates its way into the second most inboard bay at the bottom, double as the anti-hangup bracket too, to add some lightness...

Here's the outside of the tank:

In hindsight, I might have put the access plate on the rear baffle instead of the inboard rib to eliminate the need for anti-hangup brackets. A small mod to the rearmost stiffener would also be required