Fuel Vent Lines

[dust]

OK so i am starting allot of fuel posts, sorry but this seems a little more generic than to just my system

 

fuel vent lines, seem we have a unique situation in the kneeling canard area, TWO distinct high points in the tank

 

one when kneeling

 

one when flying.

 

why not put a "t" or a "y" and vent from both positions, so we always vent air not gas?

 

enjoying the design/tweeking

 

mike

[Jim Sower]

<... why not put a "t" ...>

Some folks seem to be doing this. Personally, I think it's an exercize in Guilding the Lilly or PVORT. If you're climbing, or cruising on a totally full tank (like you air refueled) the fuel will climb up the vent line a couple of inches, but drain right back the instant it can. I don't see why this should be an issue. To be honest, I don't see how it won't climb up the vent from the back of he tank (rear branch of "Y") even if the forward branch was open to the air cavity. After my usual careful analysis I have come to personally regard this mod as an exercize in MM

[dust]

OK so i go on a flight, come back and fill the tanks and park the plane in the hanger.

 

I leave a gallon or 2 empty in the tanks.

 

the fuel heats up, the plane is parked on it's nose, the vent line is submerged in fuel, won't it leak out because the air is not available to vent as the fuel and or the air expand??

 

enjoying the build and closing tank # 1 of 4 next week

 

enjoying the build

 

mike

[Jim Sower]

<... the plane is parked on it's nose, the vent line is submerged in fuel ...>

I thought the vent line terminated at the aft, upper, inboard corner of the tank. If you do that, it will always be in the air bubble when the plane is kneeling won't it?

[dust]

no, it is forward to almost where the, hmmmmmmmmmmmmmmmm, hard to explain, it is forward about 18 or so inches, looks to be where the air buble would be in flight??

 

I am only talking about adding maybe a foot of tube and a 2 to 1 fitting.

 

enjoying the build

 

Mike

[dust]

OK you enggggineers, ifin you have 30 gallons at 40 degrees and heat it to 100 degrees farenheight

 

how much gas will you have???

 

sorry to interupt the poll on server site

 

he he he

 

enjoy the build

 

Mike

[Jim Sower]

<... forward about 18 or so inches ... where the air buble would be in flight ...>

So what if you ran the tube forward 18" - and then cut a notch in it at the aft inboard corner. That would make everyone happy, wouldn't it?

 

How long has the vent halfway up the strake been the design? I'd always heard aft inboard corner - like where it is on my EZ. Was moving it forward a response to an actual documented problem, or just some guy with time on his hands chasing foul balls?

 

Anyway, I can't think of a situation that a notched vent would not be able to handle. Or a vent that stops at the aft inboard corner for that matter. Could someone describe a situation where vent in aft inboard corner would cause a problem? I know that if your only vent is 18" forward and you're kneeling with full tanks you're going to piss all over the tarmac. I can't figure out any negatives with vent in the corner.

[No4]

Hallo Dust,

At 40'f Avgas weighs 5.9 lbs per gallon, 30 gallons would weigh 177 lbs.

177 lbs of Avgas at 100'f weighs 5.6 lbs per gallon.

Which now gives you 31.6 gallons of Avgas.

 

[John Slade]

Jeff Russel at Aerocad recommends a small hole in the vent line in the aft corner. That's what I did.

 

I think the problem with not running the vent line forward is sustained climb on a hot day with the fuel covering the rear vent. The fuel expands and pushes out the vent.

[dust]

This is totally cool, when i fill up i have a max of 1.6 gals of expansion, i can deal with that, asanti(thank you in swahili, spaciba(russian),xia xia, (mandarine), salåmat(tagalo) of course all spelled phoenitacally.

 

We conciderred the hole and of course i will go with the heavyer option

 

enjoy the build

 

Mike

[Jim Sower]

OK girls, let's see here. Someone help me out with the math and physics for a minute. We fill up, kneeling, all of the 40F gas the tanks will hold and go flying. Climbing out, we're burning maybe 9 gph. Looks to me like we're going to open a 1.6 gal void in your tank in about 10 minutes. I'll need some help figuring out where (geographically) you might pump 30 gal of 40F fuel into a bright white insulated tank and have it heat up to 100F in less than 10 min. In less than a several hours for all that. Worried about the non-selected tank? Climb a couple of minutes on one tank, 15 minutes on the other and back to the first to continue your normal tank tramsfer schedule.

 

As for vents, if you have *totally* independent vent plumbing for mid and aft vents, one will have an inch or two of fuel in the vent line under adverse (tank totally full) conditions. The forward vent will have about 2" flooded when kneeling, the aft vent will be flooded an inch when the plane is climbing. But only if the tank is full - which it isn't going to be (for more than a few minutes) if the airplane is flying - which is the object of the exercise.

 

If all we have is an aft vent, as the tank empties during climb, the fuel system will very easily pull air through an inch of fuel to grow the bubble as fuel is consumed. Gravity feeding will not pull air through 7" or 8" of fuel (ask me how I know this), but it WILL pull it through 1" quite easily. And that's all you're asking of it. And you're not gravity feeding anyway - you're pulling (quite hard actually) with the fuel pump.

 

Ladies, I fear that we are pole vaulting over rat turds again ... Jim S.

[Marc Zeitlin]

Originally posted by Jim Sower

OK girls, let's see here. Someone help me out with the math and physics for a minute. We fill up, kneeling, all of the 40F gas the tanks will hold and go flying......

Do you always kneel your plane when filling? Do you never fill your plane AFTER a flight and then park it? Personally, to prevent condensation, I try to have the tanks as full as possible most of the time, which means that I fill them after a flight and while level (or close to it). That means up to 5 or so gallons more per side than filling while kneeling. If I then lower the nose to park, I'll have 10 - 15 gallons above the mid-tank vent line. _I_ have two vent lines per side, per Carl Denk's (oh, wait, he's on the other lists, but not this one) instructions, so I have one vent line at the back of the tank (as dust inquired). I NEVER vent fuel while parked. Also, while climbing at low speed (90 mph, or Vx), the deck angle is such that you'll have many gallons above the vent line - thermal heating can easily push a gallon or so overboard during the climbout, and why should I have to think about switching tanks every few minutes if an easy fix (adding some tubing) can fix the problem?

 

Originally posted by Jim Sower

Ladies, I fear that we are pole vaulting over rat turds again ... Jim S. [/b]

Not hardly, this time.

[Norm M]

I could never figure out the reason for drilling a hole near the rear of the tank. Seems to me that once you open the inside of the tube to the fuel compartment, if there is fuel there, it will vent overboard. I ran two vents in each tank, the lines go up over the top, and one doubles back. I think this is the 'Carl Denk solution' that Marc mentioned. In this manner, if both lines on one side get plugged, the other side can still vent.

 

Even with this system, I found pretty blue streaks on my cowl after my first big cross country, where I filled each tank and departed within 30 minutes.

 

One thing I would do differently- I let the tubes extend into the airstream. This was tough to finish around. I would mount the tubes through a cowl lip after the plane is shaped and finished, or imbed a union so you could use an outlet nipple. Not a big deal, but the aluminum tubes on mine are a bit scruffy. Nobody's going to notice as I fly past, and I didn't build it for the judges anyway...

 

Regards-

Norm Muzzy

[dust]

"and one doubles back"

 

yo no comprendo, señor

 

enjoying the build

 

Mike

[Jim Sower]

<… Do you always kneel your plane when filling …>

Typically yes. So I can check the drains for water in the gas I just loaded.

 

<… Do you never fill your plane AFTER a flight and then park it ... to prevent condensation …>

Sometimes, sometimes not. I agree it's a good practice for the reasons stated. Mostly I fuel going out since I fill it about half with mogas that I brought to the hangar with me, and then go to the pump and top off. It's difficult to do that coming in.

 

<… 5 or so gallons more per side than filling while kneeling …>

That wasn't my experience with my EZ. I was assuming my EZ and your Cozy are very much alike in this regard. Starting to seem as if this may not be the case. In any event, my Cozy will have the fuel receptacles as far aft as is practical.

 

<… _I_ have two vent lines per side, per Carl Denk's instructions …>

I remember a couple of longish threads a year or two ago on the Cozy and the C-A lists. Lots of chatter back and forth. Ended, as I recall, with a good bit of support for forward and aft vents. I could not see it, then or now. What I did not see then (I may have missed it) was documented evidence that all this fuss and bother and back and forth was in response to an ACTUAL PROBLEM, or whether it was someone's speculative brain fart that took on a life of its own. Ever notice how from time to time someone on these lists will invent a problem and then come up with a wonderfully elegant solution that's just the thing to solve this imaginary problem …? I left those threads with the impression that they were one of those deals. Please correct me if there was a genuine documented problem involved (and if so, was it actually documented as solved).

 

<… I NEVER vent fuel while parked …>

Nor does anyone with a vent in the aft corner (as per plans).

 

<… climbing at low speed (90 mph, or Vx), the deck angle is such that you'll have many gallons above the vent line …>

Agreed. But under those circumstances several things happen: 1) the fuel level will be a few of inches above the aft vent inlet; 2) the aft vent will be flooded those few inches; 3) the "bubble" will be waaaay up forward at the leading edge; 4) if you are fully fueled, that bubble will be rather small. Under the stated conditions (typical departure) I am confident that unless your forward vent is also way up at the leading edge, it will also be flooded. I don't know your deck angle, or how close to totally full your tanks get, so I can't quantify precisely how big your bubble is, or exactly how far forward it is, but I am quite certain that in most Cozys (and EZs) it is far enough forward and small enough that any forward vent will be flooded and remain so until significant fuel is burned off. If you have a template or diagram of your strakes near the wing root, you can incline it to your deck angle, mark off where you think the bubble is and mark where you know your forward vent line terminates. I am estimating here, not having any templates or accurate notion of your deck angles or precise location of your forward vent outlet. This is the part where I asked for some help with the math.

 

<… thermal heating can easily push a gallon or so overboard during the climbout …>

Parked on the ground, over time, perhaps. On climbout, I don't think so. This is where I took issue before and asked for help with the math and physics. I figure you're burning about 10 gph on climb. That's about 1/3 of the fuel capacity of the selected tank per hour. I don't think thermal expansion is going to exceed 25% of volume per hour. Is there some huge factor am I missing?

 

<.. why should I have to think about switching tanks every few minutes if an easy fix …>

Fair question. Matter of fact, that is pretty much the whole issue. If your forward vent never floods/cannot flood, you win and I stand corrected (right here in front of God and everybody). Absent the compelling geometry you can provide, I believe that it does flood. If in fact it does, I submit that it serves no useful purpose (which has been my contention all along). Even if it does flood it would be dumb for anyone remove a forward vent. It is harmless. By the same token, why install something that serves no useful purpose?

 

In the end analysis, this discussion has probably consumed more resources of time and effort than it deserves. Ever seen that happen on these lists J

 

Just a theory … Jim S.

[dust]

Ok, what i have learned here is that when I do get my bird flying and visit my daughter/soninlaw/grandkids and maybe nat in scottsdale monthly, when i land I better not fill the tanks to more than 1.6 gallons from the top, I will mark that on the safty chain and remember it

 

Fuel left behind does me no good

 

Plane call for a vent about 18 inches forward from the aft side, ABOUT. So I am going to add a small section of pipe a fitting to put another vent at the reaward section of the tank and be done with it, I WILL WEIGH THEM AND INFORM THE GROUP OF THE ADDED WEIGHT AND THE AMOUNT OF FORWARD BALAST TO COUNTER BALLANCE THIS MAJOR CHANGE TO THE DESIGN.

 

It is a stupid little tweek, to a problem that seems logical to me and my partners.

 

Done deal and thanks to those that left info

 

enjoy the build

 

Mike

[Dave Clifford]

Thanks for your "Theory" Jim. I thinks we got it figured out.

[marbleturtle]

It's not just theory...

 

One of the first Cozy's I had a chance to see in person, I won't mention names, had a fuel vent issue.

 

On a cold morning, he opened up his T hanger and let the Sun shine in on his grazing Cozy IV. Pretty! The conversation was going well until I slipped trying to figure out a graceful entrance to the pilot seat and fell sprawled sideways across both front seats. Then the conversation turned to "I don't give rides", something about liability. After more discussion... I also remember something about letting me use his plane for getting checked out after mine is built. Somehow the liability is different after I build my own plane, or maybe he just figured I would never make it that far.

 

Now for the part you would be interested in. In the middle of ranting about how all the bad information available on unofficial cozy sites on the internet is going to kill someone, fuel started pouring out of the lower cowling.

 

After spending about 40 minutes in the Sun on a cold day, apparently the air in the tanks expanded enough to push the fuel out the vent lines. He scrambled to pop open the gas caps and the waterfall of fuel stopped. He said his was one of the first IV's completed. I don't know if the vents have been relocated to allow for venting in the parked position.

 

It was a good lesson for me though... actually the best kind. One I didn't have to pay for!

[Norm M]

Originally posted by dust

"and one doubles back"

 

yo no comprendo, señor

 

enjoying the build

 

Mike

Here is a picture. I ran my lines on the inside, glassed over them, then filled it with pour foam.

 

http://home.forbin.com/muzzy/cozyweb/cozyimageweb/PIC00496.jpg

 

This picture shows how the lines went from the top of the tank into the turtleback, and exited down to the drain point. The extra line is a return fuel line, which was not used.

 

http://home.forbin.com/muzzy/cozyweb/cozyimageweb/PIC00497.jpg

[Jim Sower]

I don't see how a kneeling Cozy/EZ vented at the aft inboard corner can piss on the tarmac unless the fuel has expanded to where every bit of air is forced out. Of course that can happen if you store the airplane "fully" fueled. Climbing out is another matter. If the vent(s) is/are flooded (and they inevitably will be if the tank is full), the amount of thermal expansion required to dump fuel is the volume of the vent line from tank to inlet. About a teaspoon. That's why I recommended cycling the fuel selector frequently until there is reason to believe the vents are no longer flooded. But it's not a big deal. The consequences of drawing from only one tank on climb is maybe a quart of fuel over the side. I could give no real assurance that you wouldn't lose most of that even if you cycled the selected tank every minute or two.

 

Bottom line, given full tanks, I don't see how you can prevent flooded vents, and flooded vents WILL dump fuel. The good news is that the amount of fuel dumped should usually be neglegible. So put your vent where it will do the most good kneeling, don't park the airplane too full, and take your beating like a man.

 

As best I can visualize it .... Jim S.