Fuel flow & Venting

06-10-2009, 05:28 PM

Mike | Fuel flow & Venting

As time goes on we all learn more and more about the seawind and its associated hardware. My fuel system has been re-constructed to mimic what Mike Bowes and the Planemaker’s have done; with a few minor, wee changes.

The other night I was thinking about how I could even out the flow of fuel from the main tanks when they are both feeding fuel to the headers in flight. Yes, I do have the valving so I can turn off and switch tanks, however, if I can keep both tanks on and land with both main tanks at the same level…all the better. I went back thru the old posts and noticed that almost all have the port main tank emptying faster than the starboard main tank. Throughout the past year I have noticed that my port main tank also empties faster than the starboard.

So, what to do…..?

FUEL:

The fuel strainers have been removed from both main tanks. The mains are plumbed with Â½” lines giving me approximately 120GPH gravity flow to the headers. From the headers into the on/off valves and onward to the fuel filter, pumps, and finally to the big rotary fan. In summary, the fuel system hardware is equal from side to side.

VENTS:

The only issue I have not addressed is the venting of the main and tip tanks. The header tanks are vented….or not (electric valve)…. to the starboard side of the pylon. Once again the hardware is of equal lengths from side to side.

The tip tank vents under the wings have the possibility of picking up water during water landings & takeoffs. They also shed fuel depending on the balance of the plane in the water or on the land. Either way, not good, so it has been suggested that the under wing vents be capped off. If this is done then the venting / pressurizing of the tanks will be done thru the ram air port in the front of the pylon. What happens if the port ices up or a BIG bee flies into it and gets stuck? This would require a second ram air port.

As the fuel flows from the main tank to the header the pressure in the main tank will change. Is it possible if one tank starts draining faster than the other then the pressure differential will not let the tanks catch up to each other and will always be out of sync? Could the pressures in the header tanks be different..? If this is the case, I am back to the original question……

With all the hub-bub regarding the fuel system and venting I am wondering what the rest of you have done? Do your tanks feed fuel at the same rate?

06-13-2009, 09:53 PM

kiwi

Filing as per manual worked well for me

Phil

06-15-2009, 11:24 AM

Fred Lohr

nothing like a fuel system question to get things going. My take on this is that my tanks feed slightly faster from the left than right, but i don't care. they both feed into a header tank thru 1/2 inch fittings and it has never been a problem. Especially since i have large diameter, low resistance check valves in line on the way to the header. Filing a different angle on the vent tube might even out your flow which is an easy, no risk fix, if it works.

As far as the vents go, they stick down about 1 1/2 inches below the wing and to scoop up any water the the sponsoon would have to be completely submerged. I have not accumulated any spray up thru the vent into the aux tank in lots of water landings. If you are parked at a real angle, such as the time i ended up stuck on a boat ramp with one gear up, one down waiting for the tide to come in, then some fuel is going to exit that vent. This is not a common occurence. But you should make sure your valves are off when parked on a sloped ramp so that you don't have pressure from the up hill wing pushing fuel out the down side. If you have check valves, that is less of a problem.

in summary, my advice, leave them alone except to file more or less of an angle on one side.

06-24-2009, 07:00 PM

Doug Fir | Fuel flow and venting

Fred,

I too am going with a system in which the mains flow into a header tank (actually a sump tank might be a better description) through 1/2 ID lines and will use manual valves located near each wing roots. All these years of discussions about venting issue really makes me wonder if mud daubber can get into them. This is a constant headache with my Cessna. I just wonder if there is a venting gas cap that would work in our application?

Doug in Japan

06-25-2009, 06:04 PM

Mike

Quote:

Originally Posted by Doug Fir View Post

Fred,

Doug in Japan

I am sure there is a vented cap that can be either made or purchased.

1/2" lines are the only way to go from the tank to the header(s). I assume the manual valves are for main fuel shutoff only and another valve will be installed for switching..?

The question is.....what are you going to do with the rest of the venting..? The vents are also used to pressurize the tanks with ram air.

06-27-2009, 02:10 AM

Doug Fir

Mike,

I am still in the design phase with my fuel system and want to keep it simple without check, or solenoid valves if possible but use the manual's basic sump tank idea. The difference is I want a tall column sump tank with some low level warning sensors wired in.

What follows is the preliminary design idea for everyone's critique. The wet wing is in reality one long tank but divided into chambers made of 1 mm thick welded teflon with built in one way flap valves. I will be running high ethanol content fuels so the by-the-book method will not provide a safe seal for me. The third tank, actually only for long distance flights, is one in the far back seat area on the CG. All three tanks each have one (1) cable operated manual ball valve that double as a safety shut off valve. All three tanks can feed the tall rectangular sump tank.

Now I realize that any fuel tank needs air to be introduced into it to equalize pressure so the fuel can flow out. What confuses me is where to pick up that air? The sump tank can be vented with a 1/2 Teflon line into the tail high up. The wings are the question. If I understand everyone correctly it seems the wings are both vented under the wing and pressurized from a line going from the tail. I don't see why they have to pressurized all the way from the tail if a good static vent line can be provided nearby. For instance a location that is inspectable, can be covered with a 'Remove before flight plug' and one that doesn't injest water in flight or landing, or create a minus pressure in operation. Somewhere appearing behind an aileron?

Cheers

Doug

06-27-2009, 02:15 PM

Mike

Doug,

You might want to consider electric ball valves with a center off switch and position sensing. The ball valve could be opened or closed all the way or you could go to center off to partially open/close the valve to balance the flow between the mains. Currently, pressurization/venting of the tanks happen with the tube in the tail and under the wings.

The question is.....How much ram air or pressurization is needed (if any) to keep the fuel flowing to the headers..?

06-27-2009, 09:44 PM

Doug Fir

Mike,

Thanks for the quick reply. My business for the last 15 years was designing industrial scale ozone water purification systems. The failure modes were numerous as gases had to interact with liquids and there were several pressure differentials to maintain depending on what stage the water was in. Numerous locations had water traps and off gassing vents to ambient atmosphere. Basically a nightmare to orchestrate and balance and heavily technology depended. Some of the tricky challenges only appeared when the hot machine was shut down. As the warm liquids contract in the tank they created a vacuum and tend to pull in cool moisture laden air through the vents. Sometimes a water trap occurs if the line has a bend in it. Forgive me if this information doesn't apply to the Sea Wind, I included it as food for thought. What does apply is the use of solenoids valves. They eventually stick, because of the corrosive environment they live in. Fuel, water, aluminum and air laden with salts is a recipe for corrosion. I guess if you want to use them plan on changing them out every few years as part of a service program. I would rather feed the sump through a quality manual ball valves one tank at a time for 30 minutes and manage my fuel than depending on any electrical valve. I will however have a dual directional electric fuel transfer pump between the wing tanks. Hydraulic valves? same as the LAKE - Manual.

Doug

10-31-2011, 01:17 AM

Rusty

I will however have a dual directional electric fuel transfer pump between the wing tanks. Hydraulic valves? same as the LAKE - Manual.

Doug[/quote]

What are you using for a dual directional electric fuel transfer pump? I contacted the Holley Engineering Dept answer line and learned as I thought that the HP 150 pump has a gearotor element and only needs to reverse the leads to run backwards. The internal bypass valve has to be locked down, though. I received my new Andair boost pump/filter package this week. Now I'm wondering if the Holley could be considered as the backup pump with suitable valving, or if I should bite the bullet for another Andair. The Andair is solid state, cooled and lubed by the fuel flowing through the hardened gearotor element--designed for continuous use. Since most of my failures over the last 20 years of a Cherokee were electrical, I lean toward a hand wobble pump, but see no way to have it up front with me. I used to have a lot of vapor lock problems too, until I realized the @#%$%~ A&Ps had swapped holes beween the plug wires and the fuel pump cooling hose.

I have the Parker hydraulic valves as used on the Lake, too. Not sure how to tie in the backup handpump---two check valves or a shuttle valve. Any thoughts?

11-01-2011, 10:23 AM

Planemakers

Hi Guys;

I know this thread was started 2.5 years ago and was just recently archived in the new ISPA site but I was thinking and could have a little something to add.

Experience has shown us that, for the most part, the port wing empties faster than the starboard wing. I'm going to guess that, for the most part, these aircraft have a header tank on the port side. This means that the fuel coming from the sbrd side has to go across the mid-deck area to get to the header tank. Being a somewhat broad shouldered, moderatly fluffy guy myself, I can see how maybe the plumbing from the sbrd side to the header tank might go ever so slightly uphill or remain flat for a few feet in order to make room for a person laying on their side.

This too may be causeing the different drain rates of the wings.

Just adding another possible cause to think about.

John J

11-02-2011, 01:52 PM

Jack Ardoyno | Check Valves

I can't let a discussion of the fuel system go by without chiming in. I'll be brief. I am and have always been opposed to check valves in the lines to the header tanks. I have seen fuel flows of as low as 3 GPH through these check valves, presumably because of stiffening of the spring over time. If you insist on check valves please, please, please do periodic flow checks on them to make sure you are not getting a significant reduction in flow.

Jack