Return fuel lines

[FFTravism]

For those that ran return fuel lines to the tanks for fuel injection did you run the lines up the front at the window or in the rear? I can see benefits to both. Front is defiantly shorter and less tubing. The rear location would be potentially less visible.
Thanks

[Battson]

Disclaimer - I didn't run return lines, but I did run a lot of stuff down the front door post and wanted it to be out of sight and well protected.

I just used offcut aluminium from the kit to make these box sections you see in the image. They are one piece and slip over the door post, very rigid and strong once secured to the window frame tabs. It also makes a tidy finish for the window and the door seals.

As pictured, the screws aren't installed to hold the frames to the window. I used nut plates on the window tabs, with short truss-head screws.
20130608_163150.jpg

[FFTravism]

Thanks for the picture. I like the concealer trim on the A post.

[Mark Goldberg]

Travis, only some fuel injection systems require a return line to the tank. The legacy injection systems, Bendix & Airflow Performance, do not. While we are free in our planes to do largely whatever we want - I prefer the legacy fuel injection systems for the Bearhawks. If you want fuel injection.

Not trying to start an argument here. Or even a discussion about fuel injection systems and which are best. But I know you are a first time builder. So I thought to chime in. Mark

[Battson]

It's a good comment, simple fuel systems are so important for safety, and return lines do not make the system simpler.
Not to mention the challenges with not overflowing one side, when you want to fill both tanks.

[triumphantduke]

Some passive thoughts to share from my personal decision process, this is not to discourage you..just to share.

My driving reason originally to chase return type fuel injection AND ignition was fuel efficiency, engine longevity(less carbon build up), and cooler fuel (because it returns, so vapor lock is reduced).
-Fuel efficiency is taken care of with a lambda gauge if you want to be precise, this will also reduce chances of carbon buildup from overly rich mixtures(there are tests done comparing carb to fuel injection for efficiency, where the BSFC was essentially equivalent). From what I gathered, the primary factor that makes us “think” fuel injection is way better becomes clearer when there’s a control for the ignition type used for the comparison. So theoretically, after a baseline, I’d like to eventually swap one ignition out to get the majority benefit while keeping a non-electrically dependent setup(mags for the 2nd). This is all thrown out the window if you like negative Gs or are trying to have a performance setup (max hp available no matter the increase in fuel usage)
-cooler fuel/vapor lock risk reduction can be achieved with proper down hill flowing lines, insulation, heat shielding, and a carb if you’re extra concerned (b/c of mechanical injection worries of fuel heating around the spider in the heat of summer after shutdown or at a low idle/taxi)

The appraised value of these thoughts is 2 cents. Just trying to relate, injection is cool though but ended up with too many caveats for my comfort. I think discussion is healthy and reduces the risk of choices made in a vacuum.
I do not have a completed Bearhawk.

[FFTravism]

I am looking at both options. I evaluated my mission with the plane and what we want to do and really the option of running any fuel would be really nice. Mogas/Rec Fuel/100LL and 100GAMA.

[whee]

I ran my return lines up the front door post. Shorter lines, away from passengers that might accidentally damage them, easier routing and easy to cover. Routing my rear supply lines was a little challenging and sharing that space with return lines would have made it more so. I intended to cover the fuel lines and wiring I ran up the front door posts but I never have.

[Pbruce]

One consideration: I believe the bank attitude (in exclusion) doesn’t drive the scenario you describe. In the left turn wouldn’t you would generally be in balanced flight (ball centered)? Theoretically then, the remaining fuel would remain level in the tanks, regardless of the bank attitude. It would require a slipping turn to cause fuel to move to the down-side and un-port the pickup at the wing root for a sustained period.

The slipping turn is of course a common technique, which might need to be avoided at low fuel levels. Conversely, a skidding left turn (which pilots are taught to avoid) would potentially un-port the right pickup. In fact, any unbalanced flight in any normal flight attitude could cause these effects.

Perhaps this is a case for using a “both” selection? Im not arguing against compelling reasons not to use both-just theorizing. Personally, I’ll be careful if I am doing much maneuvering at low fuel levels. I’m going carbureted as another part of my mitigation strategy.

[triumphantduke]

you're totally right - thank you for catching that! (edit made)

[whee]

Poor Travis, looking for an answer to a simple question.

What’s 2+2? Everyone: PURPLE!

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[FFTravism]

You feel me on this. Not to offend any of the answers as the info is good but yes. I know fuel injection is a topic with different opinions. I tried to ask it without creating a big debate.

[schu]

In my not all that humble opinion, the only reason for electronic fuel injection is you want to run completely garbage fuel.

There is no fuel efficiency gains over mechanical injection for tractor engines as those gains are seen in LOP operations and electric ignition which work on either setup.

Here are the cons:

You must return to tank with the extra pluming required.
You don't get a both selector valve, you must manage fuel.
You are going to cycle up to 80gph back to the tank which can be dangerous with low fuel because you can't spit fuel into the tank and immediately feed the pump with it. Header tanks are advised.
You must have 7-8 amps of power to run the system. The ECU and ignition aren't too bad, but the pumps require a bit of power.
You must have a bullet proof power system. There have been bearhawk crashes with EFI when the pilot had an issue, hit the 'emergency' switch and then put it in a field.

I think mechanical injection with electric ignition is the best solution. The SDS CPI2 ignition can maintain it's own light weight battery and if you lose power, the battery will power the ignition system for hours.

Don't be tricked into thinking that EFI is even more bullet proof than those old nasty carbs when the reality is that there is a lot of knowledge needed to adapt the fuel system to work, and you are WAY more of a test pilot with EFI than what is known to work well on these airplanes.

Disclaimer: I'm not going to run a totally stock fuel system, but I understand what I'm doing, I have options to revert to what I know will work, and have accepted that I'm going to be a test pilot.

[FFTravism]

Thank you. There is a few somethings I didn't think about. They do offer the newton dual valves with the both option now. I really wasn't trying to start a big discussion about EFI but I have received some info I have not thought about.

[schu]

Dual (both) valves with a return is a bad idea.

[kestrel]

What’s 2+2? Everyone: PURPLE!

Ha!
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Ha!
Ha!

[kestrel]

Does anyone know the gravity feed flow rate of a Bearhawk with 3/8 inch fuel lines? A 540 burns about 23-24 gal/hr at full power and I think that some people run that without a fuel pump? Mine is equipped with fuel pumps so I can't make any assumptions from aircraft.

EDIT: Maybe I can make some assumptions?

The spec is 125% of flow rate to a pump. On a Bearhawk with feeds from both front and rear of the tank, it really should be 150%, but I should be able to expect that it was tested to at least 30 gph?

[jaredyates]

I never tested it without a fuel flow meter in the circuit, but found on both airplanes around 30gph as I recall. Bob ran his 540 without any pumps but I didn't feel like I could meet the spec without them. Maybe not having a fuel flow meter would help, but for me it's a required item to manage the engine.

[kestrel]

Maybe someone can check my numbers:

A 3/8 inch OD fuel line has a wall thickness of 0.035" (I'm uncertain here, I found the spec for 1/2 line) so and ID of 0.305", an ID cross section area of 0.0731" and an ID circumference of 0.958".

A 1/2 inch OD fuel line has an ID of 0.430", a cross section area of 0.1452" and an ID circumference of 1.351"

The cross sectional area of the 1/2" line is 1.99 times that of the 3/8" line. So, for the same flow "speed", it should flow about twice the GPH.

However, it is going to be somewhat better than that because the circumference is "only" 1.4 times that of the 3/8 line so while it has twice the cross section area, it has only 1.4 times the surface area to slow it down. So, a fuel system made from 1/2 inch line should flow more than 60 gph.

Did I miss anything?

[FFTravism]

Friction loss for each one. It doesn't go up or down at a proportional rate typically. Calculating friction loss is something I have to do for my job.

[AZBearhawk272]

My system flows 78 gpm with 3/8 in lines.
Aircraft at 17 deg nose up with 5 gal in each tank, selector in both, feeding only from the aft feed ports on the tank.

Kevin D
#272
KCHD

[kestrel]

Friction loss for each one. It doesn't go up or down at a proportional rate typically. Calculating friction loss is something I have to do for my job.

I didn't forget friction, but I'm also not expert in it. I tried to address it by pointing out that the ratio of cross section area vs. circumference was more favorable for the 1/2 line.

[FFTravism]

I didn't forget friction, but I'm also not expert in it. I tried to address it by pointing out that the ratio of cross section area vs. circumference was more favorable for the 1/2 line.

That makes sense. I may try to find it but it may not be readily available.

[Battson]

No point calculating it, theory and practice are only the same in theory. Just go with a simple system with 3/8s lines and old school injection - everyone goes through the exact thought process you're doing now, at the start. They all end in the same place... Practically, it just makes sense.

[kestrel]

My system flows 78 gpm with 3/8 in lines.
Aircraft at 17 deg nose up with 5 gal in each tank, selector in both, feeding only from the aft feed ports on the tank.

Kevin D
#272
KCHD

Wow! That's higher than I would have expected. Can you expand what the fuel was flowing through for this? Any chance you tested with fuel in one tank only? ...thinking of uncoordinated flight and or one tank run dry before the other.

Jared's test seemed to include at least the fuel selector valve and fuel flow sensor? I'm not sure where his test point was and if the fuel was flowing through any idle fuel pumps?

For an EFII system, the fuel pump is often under the floor or front seats, so that would be a shorter, less restrictive run than all the way through the firewall to the engine.