Fuel Flow Discussion, Moved from Float Mounting

[Archer39J]

Or they follow the installation instructions without an understanding of the design and how different platforms will affect it's performance.

[Mark Goldberg]

Bob has made some suggestions for flying your planes:

OPERATION OF BEARHAWK FUEL SYSTEM

Take off and land on Both at fuel valve selector.. Be sure
both tanks have fuel in them.

Cruise can be on left or right to insure both tanks have fuel in them.
Both can be used if flow is about even.

In rough air on landing stay high, do not drag it in if fuel is low.

Bob has no problem with any of us adding a vent tube between the two tanks. With a gravity flow system, he does not think it needed. But no harm for sure except the following point. If you do add a cross vent tube, you will have fuel coming out of the gas caps if you park the plane on a slope. Without the cross vent, you can just turn the selector valve to off.

Bob understands that having any fuel pump, especially the higher pressure pumps used with fuel injected engines - will suck air and not fuel if given the opportunity. He thinks the Continental fuel injection system might be a little worse in this regard than the Bendix system used on Lycomings.

He feels with low fuel level in the tanks, slipping or skidding (or even rough air) while on approach to landing can cause an interruption of fuel flow. If you think about being in a bank and slipping or skidding so the fuel in the upper wing tank sloshes outboard could un port the fuel outlets. Mark

[zkelley2]

A lot of efi systems do not get installed correctly leading to loss of power. We can't really say here but it's quite common.

[AKKen07]

Not to keep beating the poor horse but I was just browsing my Bingelis Firewall Forward book when I ran into a paragraph stating that any fuel system with tanks that feed simultaneously MUST have a cross vent to feed equally. I think I’m pretty well convinced at this point.

[Gerhard Rieger]

If you do not have both, then a header tank makes sense. the exact reason I am using a two Gallon header tank. I will not have a problem slipping my aircraft and un porting will not influence it. Having larger vent lines will make sure that the header tank stays filled at all times. put an opened beer can to your mouth upside down. then stab a hole in the bottom which is now on top. hope you can swallow fast. it will be down your throat before you know it. Make sure you vent the header tank well, I have two 1/2 inch vent lines, one to each wing tank. One will always be higher than the other because one is in the front left corner and the other rear right corner. any bubbles from air entering the fuel system because of un-porting the main tank will go up and out the highest vent line and breath back to the main tank, it will also make sure that the header tank stay full as you resume normal flight, if you crash and your aircraft's belly is ripped open ripping of your fuel selector, you will have your two main tanks spilling their fuel out at an alarming rate below the floor and have exactly the same problem I have using the header tank. this is a very interesting read, lots to consider.

[svyolo]

I read the NTSB report a couple of times before. It doesn't seem like the Feds want to spend much time analyzing EAB accidents. Not much useful information. I am pretty sure their description of the "Emergency Power Switch" is way off.

N22GM probably had a complete dual EFII system. It is very redundant (more than I actually require) Other than an electrical feed or fuel problem, the only single failure that makes the engine go quiet is the Crank trigger (Hall Effect Sensor).

Just not enough info in the NTSB report. Too bad. Thats what those reports are for. So the rest of us can learn something.

[yateselden]

As I keep reading posts, this cross vent would be a good safty feature if you should happened to plug a vent with bugs or whatever. And that also reminds me of them damn mud dobbers!

[yateselden]

I would have thought, the gravity of the fuel in the fullest tank would overcome any possible difference in tank pressure.

[yateselden]

Whee, were those experiences in your own Bearhawk? I'm thinking like Battson on this. His revamped experiment with the glass over head, straws on the bottom. This is a very interesting subject, as Im running EFI with returns to the wing tanks and no header tank. There are many different scenarios in these posts with few spelled out. The only things I can see that would cause more fuel in one vented tank is plugged vent, flying uncoordinated and possibly the differences in pressure at the vents due to the prop wash. A long prop like yours might cause less/low pressure on one side for your tank vent. A crossover tank vent would equalize both tanks. Just thinking, and considering here.

[zkelley2]

He had EFII on that right?
Theres a history of electronic fuel injection and improper wiring causing that to happen. It would suddenly shut off if it was the ignition or fuel injection.

[Mark Goldberg]

The owner of that plane told me after the accident that he felt the problem was the electronic ignition. He was not sure, but felt that since the engine did not stumble on its way to shutting off (it was just an immediate and sudden stoppage) that the problem was electrical. Mark

[Bcone1381]

I like data and I like declared known best practices.....standards. Without data problems cant be defined. Can we get more data? Thank you those who fly Bearhawks who contribute. Can the silent of the 100+ Bearhawk owner operators help here?

If BOTH is selected then a significant imbalance between the tanks indicates an air pressure imbalance exists. Is this common? Can we collect data in order to discover if a fuel imbalance is common (when using both)? Can, a value be declared or a limitation set to define a significant imbalance? For example, The max imbalance allowable imbalance when BOTH is selected is 7 gallons.

Fact, It is possible to see the fuel tank pressure and how it changes and what factors effect the pressure inside a tank. It seems like folks could put a TEE at the top sight gage bung and hook up a VSI, Altimeter or a manometer.

Like I said, I like data.

Here is an accident report of N22GM. Next week I'll search more of the FAA data base, but I thought this one relevant.

https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20190327X81141&AKey=1&RType=Prelim&IType=LA

[zkelley2]

Such an airplane would not meet the old FAR 23(or any of the CAR's) and I doubt it'd meet the new one either. So I would venture one does not exist.

[zkelley2]

whee, if you're on a 2 mile final and need to slip, you don't even need the engine at that point! haha.

For left/right say a 40 gal tank burning 10 per hour, you'd takeoff on the Best tank(might on might not be a thing depending on aircraft) lets call that the left. At a safe altitude, switch to the right, burn an hour, back to left, burn an hour, back to right, burn until the engine sputters, then land on the right with a full hours of gas and more fuel in a tank then if you split that 10 gallons into 2 tanks.

[Archer39J]

If I don't like how this one works I can just machine my own, just one more thing to design and test though....