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Fuel return line?

Jasonm

Well Known Member
I'm at the stage of planning my fuel system layout and will be installing the EFII boost pump and prefilter, Red Cube transducer and Andair valve. I'm still undecided on whose fuel injection I'll be using but wanted to understand if I need to plan for a fuel return line. What are other builders doing?


Jason
 
If you use Airflow Performance injection system, return line is optional, but recommended for improved hot starting.

I have the return line with my AFP system, and use it with every hot start. Not sure what hot starts are like without purging, because I have never tried them with this engine, XIO-540 by Barrett.
 
Needed or not

Install the plumbing lines and fittings for a return line no matter what your plans are at this point.
You'll spend less than $50.- in parts and a little extra work but your options
are now wide open.
Among other options you'll be able to set up a mogas fuel system that won't vapor lock.
 
Install the plumbing lines and fittings for a return line no matter what your plans are at this point.
You'll spend less than $50.- in parts and a little extra work but your options
are now wide open.
Among other options you'll be able to set up a mogas fuel system that won't vapor lock.

....... except Mogas is not approved for the IO540.......
 
Like Jim, I have an Airflow Performance FI. The purge line is connected to a t connector at the right seat tunnel wall. You switch to the left tanks, turn the boost on, and warm fuel returns to the right tank. The nice part about this arrangement is that you don't have to plumb all the way back to the tank.

You can't beat the support from Airflow. Give Don a call and discuss your questions with him. I think you'll be sold after your done with that conversation.
 
There are really a couple of options for a return line. One is to do as Bob said and just T it into a line from one tank or the other. For a purge line this works fine. The other option is to buy an double stack Andair fuel valve that returns the fuel to the tank that it is drawing from through separate lines. This is required if you are using the EFII fuel injection, which is constantly returning fuel while running. Of course, with the efii you would want two boost pumps and would not need the red cube.
 
I agree, install the plumbing back to the tank then its there if you need it.

Plumbing back to the tank also eliminates the need for any special "purge procedure" like having to remember to select a particular tank.
 
i am putting a return line in. i picked up some 3/8" tubing and I plan to run it in the tank all the way towards the fuel cap. I figured this will allow a few things. 1) any bubbles will rise out of the fuel by the time it gets to the fuel output & 2) it will allow the fuel to cool down as well.

are these issues now? i don't know but i figure it couldn't hurt.
 
i am putting a return line in. i picked up some 3/8" tubing and I plan to run it in the tank all the way towards the fuel cap. I figured this will allow a few things. 1) any bubbles will rise out of the fuel by the time it gets to the fuel output & 2) it will allow the fuel to cool down as well.

are these issues now? i don't know but i figure it couldn't hurt.

You just need to plumb it into the top half of the root rib. Bubbles will come out anyway and the fuel will cool down. You don't need to run it out towards the fuel cap.
 
....... except Mogas is not approved for the IO540.......

Which really requires a little elaboration, so I'll link an earlier post by you here. But this is off-topic for the current thread. IMHO, which I am putting into practice in my project, it does not hurt to have the return regardless of what fuel you will be using. In my case, I am going to insist on the AFP system anyway, so it's a no-brainer. The 4 cylinder version has been working beautifully in my RV-6A (with 100LL) so I'll stick with what I know.
 
Just plumb for that return line no matter what your plans are at this point.

except Mogas is not approved for the IO540.......

I have approved it in my IO 540 and so have many others.
 
Thanks all

Great info as usual guys! I will install the return line now rather than later.

Jason
 
Please elaborate

I am busy with the fuel lines at present. I have the RSA-5 FI so I do not need the return line. However, with everybody saying it is worth installing during this stage of the build, I must strongly consider doing it now. I am not sure how it is plumbed though. I have the Andair fuel selector with extension but without the "double" selector (needed for EFFI), with Don's electric fuel pump and filter.
Thank you.
Johan
 
I simply added an additional AN832-4D fitting and associated hardware with a rigid line out to the third bay, similar to the fuel vent line. I didn't use the diamond shaped plate that Van's uses for the vent line, but the rest of the setup was the same. If it goes unused, just put the cap on it securely and test the tank that way.
 
I simply added an additional AN832-4D fitting and associated hardware with a rigid line out to the third bay

I don't see any reason for running a line out to the 3rd bay.
Simply terminating the return line at the fitting works just fine.
Unlike a vent line there will always be fuel in that return line.

IMG_3167.JPG


Plumbing the return line via a selector is one option or you can simply return it to the left or right tank.

The 4plex Andair fuel selector is a fine work of art, however it is a tall stack
and a pricey addition. For the RV-10, obstructing the tunnel with such a tall stack makes running the heater hoses almost impossible. Not to mention the
nest of plumbing coming together all in the same place.

Another option and the one I choose was using an Andair fuel selector and using Vans supplied selector for the return plumbing. Clearly not as simple as the 4plex Andair set and forget but way cheaper, and much more convenient to install. An additional benefit is the option to transfer fuel from one tank to the other.
IMG_2746.JPG


IMG_2462.JPG


IMG_0458.JPG


Operation simply requires that you switch both fuel selectors something the 4plex valve does with one hand motion.

I have designed my fuel system to run on 91 octane mogas and chosen a constant flow return line as a means to keep the fuel system cool and prevent
vapor lock. Doing my 3rd annual and over 300 hours of trouble free operation.
Today's mogas price $ 2.43 per Gallon :D
 
Return line

I am using flyefii.com's electronic fuel injection so it was necessary to run a return line. After speaking to Robert at EFII, I ran a return line capable of full flow return, so it is a 3/8" line, just like the supply lines.

It took longer to figure out WHAT to do than actually doing it...

Thanks to all here who answered my questions and sent photos of their installs.

All made possible by this site and D.R..
 
Some folks like the warmer fuel being returned to empty out farther into the tank, away from the pickup point for fresh fuel going to the engine. It gives the return fuel some time to "settle" the bubbles and mix with the cooler fuel a bit more, in theory at least. I don't really see a wrong way, as long as the return line goes back to a tank!
 
Experimental

Experimentals don't need any approval. The engine is 8.5:1 CR, just like the 0-360's....same cylinders and pistons.

That would have been too easy.

Let me first say that I have not broken any new ground by using mogas in an IO-540 with AFP injection and 8:1 CR, 1 Light speed ignition and one impulse coupled slich mag.
I have simply copied what many others have been doing for years.
I did extensive testing during and after phase 1 using mogas in all phases of flight to ensure that my engine runs properly in any and all conditions.
Apart from the constant flow return line there is not much else that is different
from a stock engine installation.
 
After reading this thread, it seems the best idea is to plumb for a return line. I just started building my tanks. Is this something I need to do now? And if so, what do I need to do/add....thanks
 
Lets be clear about the return line.
You don't need to do anything.
If you want to prepare yourself for some future options install an additional fitting in the upper part of the inner tank rib (see pic)
Apparently the EFII requires a full size 3/8" line, for all other returns a 1/4" is fine. If you never need it just put a plug in it and forget about it.
 
Just make sure that the return line location does not interfere with the aileron mechanism in the wing root. Ask me how I know!
 
EFII return line

In past I have gotten great results by just dumping the return fuel into the first bay of the tank, didn't even have an extension on the bulkhead fitting, fuel cooled & degassed just fine. Strongly disagree with 'T"ing into a delivery fuel line.

3/8 line should be used as return flow volume is probably greater than the volume used by the engine & EFII pumps are hi-volume / hi-pressure pumps after all.

Original post stated one Red Cube... You will need a second Red Cube for the return line & your EMS will have to calculate actual fuel flow as a difference between inlet flow & return flow, so plan for 2!

Andair duplex valves are great for the job but expensive. The current project I'm doing will use a V4-3-P-C Newton duplex valve. Some other brand kit manufactures call out for this brand valve so I'm going to give it a try this time around, HALF the price of a comparable Andair!

Hope this helps
 
A newbie perspective

I just went through this, so I will tell you from my perspective something that clarified it for me. Sometimes, when talking to the experts, they forgot that I was a newbie, and it just went over my head.

If you are running a continuous flow FI system, then you either need an Andair duplex selector, or a second selector.

But, if you are just trying to allow a return for a purge line to assist with hot starts (highly recommended), you only need to run upstream of your selector to one tank (lets say left for sake of this discussion). Then when you want to purge, select the right tank, and start it up. One it has started, you can select either tank you wish.

The continuous flow FI systems are common on Continentals, but not very common on Lycomings.

Hope this helps.
 
Bendix RSA-5 or RSA-10 (or Bendix style, i.e Precision): no return line required.

Airflow Performance FM-200: single return line, tee into one tank feed upstream of fuel selector, or return directly to one tank.

Airflow Performance FM-150 or FM-200A: no return line required.

EFii electronic: one return line back through firewall to duplex fuel selector, then a return line to both tanks.

Strongly recommend against separate fuel supply and fuel return selector valves with the EFii system.
 
Sorry for a bit of thread drift here, but I am at a bit of a loss to understand how the US experimental rules can possibly work in your litigation-heavy society.

Lycoming produces a list of approved fuels for their engines. We all know that, with proper precautions, Mogas will run just as well in a 8.5:1 540 as an 8.5:1 360. But if you get vapour lock, crash and bonk someone on the head, how on earth do you not get the *** sued off you?
 
Simple: we use Lyc "clones" experimental aircraft engines.

Vapor lock is generally a problem with the fuel system and part of the airframe.

As to the litigation: It is always about money and most of us built airplanes because we don't have enough of it to buy a finished one.
Lawyers are smart enough not to waste their time chasing a defendant who will simply be bankrupt at the end of the proceedings.
And one more thing, we carry liability insurance.
 
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I don't see any reason for running a line out to the 3rd bay.
Simply terminating the return line at the fitting works just fine.
Unlike a vent line there will always be fuel in that return line.

IMG_3167.JPG

Just curious, what is the flange you used for this return line? Is the fitting attached to it the same diameter as the fuel pickup?

Thanks!
Rodrigo
 
Just curious, what is the flange you used for this return line? Is the fitting attached to it the same diameter as the fuel pickup?

Thanks!
Rodrigo

That looks like the standard flange that Van's sells for the fuel drain port at the bottom of the tank.
 
Data References ..?

Bendix RSA-5 or RSA-10 (or Bendix style, i.e Precision): no return line required.

Airflow Performance FM-200: single return line, tee into one tank feed upstream of fuel selector, or return directly to one tank.

Airflow Performance FM-150 or FM-200A: no return line required.

EFii electronic: one return line back through firewall to duplex fuel selector, then a return line to both tanks.

Strongly recommend against separate fuel supply and fuel return selector valves with the EFii system.

Great thread guys.

I'm still planning my fuel layout and am not ashamed to say that I'm struggling to digest this wealth of knowledge.

I did not make provision for a return line when building my wings (wish I had thought a little deeper now !), so the options for a system that does not require a return line are most appealing.

May I ask where you sourced the above info Dan...? I'm blowed if I can find much online about the technical requirements of each.....maybe I'm just not looking in the right places ! ;o))

Thanks again to one and all..
Chris
 
....... except Mogas is not approved for the IO540.......
What makes you think that? The engine was certified on 91/96 octane, just like the 180hp 4 cylinder engines. Same cylinder, same compression ratio (if you go with stock). What kind of approval are you looking for in an experimental aircraft?? There is no reason the engine shouldn't run fine on 91 or higher octane mogas as long as it does not contain ethanol.
I just double checked...A and D series IO540 is approved for 91/96 or 100LL.
I am planning on trying some, in one tank, to see how it does. In many of the southern states mogas in the summer has same or lower Reid vapor pressure as 100LL, generally 7.0 to 7.5. IIRC 100LL is 7.5.
 
I agree, install the plumbing back to the tank then its there if you need it.

Plumbing back to the tank also eliminates the need for any special "purge procedure" like having to remember to select a particular tank.

I suppose some of the alternative FI systems may need different starting procedures. With stock Bendix RSA injection and Bendix S1200 mags, I have no issue with hot starts. The engine in stock, certified configuration starts pretty easily, hot or cold. Took me a half dozen hot starts to figure out best technique, given that my MT prop has pretty close to zero flywheel effect.
 
Not that simple....

Remember that that 91 number is "motor octane", while car gas 91 is "R+M/2", average of motor and research octane numbers. 91 car gas is about 87 motor octane.
 
AKI (a little thread hijack)

That average is the Anti-Knock Index (AKI) posted on gasoline pumps. Lycoming Service Instruction 1070S, dated 4/24/13, specifically permits use of 93 AKI automotive gas in the IO-540-D series engines. However, alcohol>1% is not allowed.

The Letter also cautions that winter blend automotive fuels often have Reid vapor pressures higher than aviation fuels.

Using such unleaded gas requires Lycoming oil additive LW-16702, an anti-scuff additive, which is in Aeroshell 15W50 and 100W Plus oils.
 
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Remember that that 91 number is "motor octane", while car gas 91 is "R+M/2", average of motor and research octane numbers. 91 car gas is about 87 motor octane.
Well aware of that. Note that most carbureted O-540s have Petersen STC, including those with the same 8.5 compression and parallel valve cylinders, as used in the Comanche 250, and PA-32-260. They did note some material compatibility issues with the gaskets/diaphragms in the Bendix fuel injection as of the mid-late 80's test timeframe. I do not know, but suspect that units overhauled in more recent years are less likely to have those problems. That is their stated reason that they did not try to obtain STCs for any fuel injected Lycoming engines. They did get some of the Continental IO-470s approved as the Continental injection units did not exhibit the problem they found with the Bendix.
 
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