Fuel Flow Discussion, Moved from Float Mounting

[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....

[Archer39J]

Put it near the filler neck. Debating whether to even finish with a tube poking outside, but then this would also be subject to icing. Once I get one in hand and can do some testing I may decide to just have it terminate inside the wing with a weep hole in the skin, of course zero fuel/vapors dumping inside a wing bay would be the requirement.

[JJohnston]

What would you do with that (check valve)?

[Archer39J]

This is what I've been looking at, might be easier than a full cross vent and would work if both caps get clogged. https://www.mcmaster.com/5492k51

[Ray Strickland]

In my first homebuilt I had 1/4” vent tubes with a bulb of screen wire protecting the entrance from insects. No cross vent tube. Ran on both for 400 hrs w/o a problem. However, I have often thought that the small Bearhawk cap vents could be plugged by a direct strike from a fat, juicy bug. While it hasn’t happened in 200 hours (running on both), this discussion has convinced me to install a cross vent tube at the next annual—just to be safe.

[Nev]

This is a very good point you’ve made.

[patrickh99]

No fuel venting system is going to be perfectly symmetrical: different lengths, different bends, bugs, etc. The recommended fuel caps for the Bearhawk have the potential to aggravate the situation if they are not both machined exactly the same AND installed/aligned exactly the same. That is a small airfoil on the top of the cap; turn it slightly and you switch from pressure, to less pressure, to suction. Thank Bernoulli for that. All of the external venting components are affected by the relative wind angle & velocity, so you will never have equal pressure in tanks that do not have an internal cross-vent. Fuel pump presence or absence is irrelevant to this issue.

[schu]

Can someone give a list of planes that have;
1) A fuel system that allows for "BOTH"
AND
2) Does NOT have interconnecting tanks?
AND
3) Requires a fuel pump for normal operations.

I'm sure I could do the research, but without a floatplane I am traveling by speedboat which cuts into my free time!

www.amazonsaltandlight.org

I certainly can't. I doubt such an animal exists.