Fuel System Questions

[Battson]

I'm very curious about this. What port what the return line connected to?

As Z pointed out, this is a high flow fuel injection system and I'm guessing most people here don't have experience with a system like that. According to the data I have found the system will be drawing 25gph from the tanks minimum at all times. That's a lot of fuel, more than most of the carbureted systems typically see so what is best for a carb system may not be the best for this system.

First just to clarify, the fuel was flowing from an aux tank, not from a fuel injection return line - but of course the tank does not know the difference, I think the net result would be the same. I expect the flow rate is somewhat comparable.

I believe it was plumbed into the outboard side of the tank using the fitting installed at the factory.

The more I think about it, the less I can understand why the sight gauge was adversely affected. But the problem was clear to see.

[patrickh99]

Did the top of the sight gauge use a Tee fitting with the aux tank feeding it? That would cause the issue described.

[whee]

I'm getting ready to install my fuel lines and am trying to get it right the first time. I drew up a sketch of what I'm currently thinking and am curious what you guys think. I wouldn't say this is my final revision, I have too many unanswered questions, but this where I'm currently at.

Untitled by Jon Whee, on Flickr

Remember: I'll have Continental fuel injection that will see high flow rates, a duplex fuel valve with no "Both" position, a engine driven fuel pump and a electric boost pump from EFII.

We built and installed the right side fuel lines as shown in my sketch and did some preliminary flow testing. Boost pump is not installed so flow tests were gravity feed only right out of the BH gascolator. Remember, these are only preliminary numbers.

Because the Continental IO360 has a pumped fuel system we need 125% of max fuel burn (gravity systems need 150%). According to the book the IO360 model we'll be using burns a max of 18.1gph so we need 22.625gph of flow.

Level flight: 66.6gph
Tail low: 62.1gph
Because of the low ceilings in my garage we were unable to to a tail high test.

The number will decease some because of the 3/8" fittings in the fuel tanks; it will be interesting to see how much they are reduced. It's nice to know that should we ever decide to install a TSIO550 we won't need to redo the fuel system

[Battson]

Did you decide to go for a gascolator, filter, both?

[whee]

Did you decide to go for a gascolator, filter, both?

Installed a gascolator and may install the inline filter as you have done. My preferred method will be to replace the screen supplied with the BH gascolator (appears to be 300micron) with a 90micron screen and not install a inline filter. The EFII boost pump module requires a 90micron prefilter.

[Mark Moyle]

Wee,
I'm going with the duplex valve with"both"....will have two header tanks under the floor and a 1/4" return lines up the front door posts to each wing tank. Will need to weld a couple 1/4" NPT flanges to the tanks for the return lines. On the fuel flow.... I think installing the cube in the fuel line to the fuel spider/distributor will eliminate the need for a second sensor...that is if the sensor can withstand 31 psi.... On the fuel pump I'll be using Lancair's set up for the IO550. The pump is two speed. One for speed for prime and second for emergency should the fuel injection gear pump fail. Will use a gascolator before the fuel selector valve.... Maybe a sump drain in each header tank? And if you do ever decide to install a big bore continental....install 1/2" fuel delivery lines.


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[nichzimmerman]

Whee, your fuel flow numbers are a useful data point. I wonder how much fuel flow would be reduced if it was measured at the approximate carb/injector location rather than at the gascolator? You are obviously concerned with delivering 125% of required fuel to the fuel pump, but if your apparatus is still setup, and you were curious about the improvement given by the 1/2" fuel line over others published measurements, consider re-testing at engine level and posting your results. I have totally selfish motivations, as I'm still up in the air about using 1/2" line in my carb fuel system =).

[whee]

Nic, I'm not curious about the improvement 😉 but I will see if I have the tubing required to run such a test. Honestly, if your running a carbed engine I don't thinking you'll benefit from 1/2" lines. Even the guys at the local FBOs were giving us a hard time about it.

[MattS]

I am flying a 4 place with a Continental IO-360. Purchased recently and learning a lot. The fuel selector does not have BOTH, but all the fuel returns to the right tank. The issue I'm finding is I don't know how I can ever run the Left tank close to empty. Since the amount of fuel returning to the right tank varies and is not measured, I have no way of knowing exactly how much fuel I'm removing when I'm feeding off the LEFT tank. Keep in mind I'm flying hours over the Amazon River or Amazon rainforest. Not excited about running a Continental Injected engine out of fuel ever (even if I do have fuel in the other tank), but for sure not in this situation. I am going to install a Duplex valve (trying to decide between Andair or SPRL) that will return fuel to the tank I'm feeding so I can keep track of fuel burn per tank. After much thought, I am assuming that without a header tank, using BOTH will only put me back into the same situation I am in now-- not knowing EXACTLY how much fuel I've burned per side (because of the variable return rate).

[whee]

Matt, In my opinion BOTH puts you in a worse position than you are now. I think that your system is workable but a duplex valve with return lines to each tank is a nicer solution. I for sure, without a doubt, would go with an Andair valve.

I've never flown with Continental fuel injection so I can't speak from experience. I did research running them out of fuel because I wanted to know how long it took to restart once switched to a tank with fuel in it. As you can imagine Google could only tell me so much, if it is believable at all, and the official documents don't say anything about it. It appears that running a tank dry on a low wing with Continental FI is a serious issue and it may not restart before your on the ground. On a high wing it may not be an issue. It may restart as soon as the selector is moved to a tank with fuel in it just like most carbureted high wings. I want to know the answer so once I have my plane flying I plan to figure it out.

[JimParker256]

Check the BeechTalk forum for information on how long it takes an injected Continental to re-start once you switch to a tank with some fuel in it. I was surprised by how fast they claimed it would re-start. So I ran a test on my IO-540 (260 HP) in my previous airplane (Rockwell Commander 114(, and restart took less probably 3-5 seconds after I switched to the other tank! There is actually a certification requirement for how long a re-start takes when you run a tank dry - I just can't remember with absolute certainty, but I believe it's 10 seconds or less...

Also a great article on this in the "Pelican's Perch" article series written by John Deakin (available online - just Google "Pelican's Perch"). He talks about how every pilot should intentionally run one tank dry during a flight (with plenty of fuel in the other tank, of course), then refill it once back on the ground to find out how much that tank actually holds. Then you repeat the process on a subsequent flight, running the other tank dry and measuring the quantity to refill. That way you know your "actual" maximum usable fuel onboard. (This is especially important for airplanes that use a "bladder-type" fuel system, as wrinkles and folds in the bladder can impact both how much fuel the bladder holds, and how much fuel may be trapped in the tank by those folds... The "bladder" issues are not a consideration for the Bearhawk series (thank you Bob!), but still it's a good idea to find out how much fuel you can actually use from YOUR tanks.

[whee]

The BT forum is a great source of information. I've been a member there for a a while and used to read it regularly.

I've been in the "run each tank dry at least once" camp for a long time. As I've said before that is how I managed the fuel in my Luscombe on cross countries: First 30min on left tank, switch to right tank till dry then back to left tank. I don't have any intention to do that in the BH except the one time to see how the usable in each tank actually is.

[Brad Ripp]

I like the idea mentioned earlier in this post about the aux transfer line feeding into the lower site guage line. Can anyone verify it gives you a good signal of bubbles when the aux tank is empty? One of my wings are complete and the former kit owner ran the transfer in the standard tank to tank format. Sooo, I can either remove that or I can T off of it and run a second line to the site guage for the bubble indication. Anyone see a problem with that? (Other than a couple more connections in an already many connection system?) I figure this way the transfer may flow a little faster also? The only downside I can see is whether the vent lines can keep up with it. The completed tank has the fuel cap vent as well as an under wing vent for the aux tank (so there are two.) Thoughts?

[tailwind]

I need to time mine. The ball in the site gage is pushed up to the top of the site gage so I can tell that the pumps are working but I have not observed bubbles in the gage. Having said that I don’t often use them unless I am making a long trip.

[svyolo]

Whee,
This is a year and a half old thread, but if you don't mind if I ask, how did you route your fuel lines in the end. It seems like the easiest to me is to put the duplex valve up over the cockpit. Keeps all the lines short, and only a single feed and return line going south of the lower skin of the wing. Easy to work on, easy to spot a leak. The bad, is the leak is on me. Every time I work on something, the leak is in the cockpit. So maybe not a good choice. But there are STILL a bunch of connections up there that can leak on the cockpit. The other "best" place seems to be under the front seats. Lots of space, the seats are easily removable and good access to work on it. But now you run 4 fuel lines north and south. What was your choice, and how did it turn out? On a low wing AC the choice is obvious. On a high wing you have more choices. Is an overhead fuel valve verboten?

[jaredyates]

Please don't take lightly changes to the fuel system. It is carefully engineered and a high-risk area for modification.