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Smilin' Jack

Well Known Member
Paul Dye, Ironman wrote an article about the coiled vent he installed on his awesome RV3.
I sent him an idea and for folks who do not have their wings built via the slow build method perhaps this is an alternate idea on the coiled vent .
Would like any thoughts!
Originally Posted by Smilin' Jack
Paul,
I was reading an article about the coiled vent you used on the RV3, i am not an aeronautical engineer but realizing every jet I have flown has the fuel vents out on the wing tip. I think you could run the vent line outward to the last rib then coil it like you did and drop the vent out the tip and it would be at the highest point of the dihedral on the wing, definately easier and higher coils than squeezing it into the wing root. Understand when building your vent rib of the tank it would be just outboard of the fuel cap. That would be the outboard rib of the tank instead of the inboard most rib of the tank. There would be no reason to run the vent line the entire length of the fuel tank like we currently do and the total run out to the wing tip would only be slightly longer than what we currently doing. This would place the top of the coils above the top of the vent tube in the tank and probably stop any weeping of fuel.
What do you think?.. I am too far out in left field? If I would have thought about this last year when building my wings I might have tried this. I know that in our jets they all incorporate a fuel float test to shut off the single point refueling system when the aircraft tanks are full.

Thus, failure of not testing the fuel vent float results the fuel not shutting off and venting it all overboard at the rate the fuel is being delivered to the aircraft. This type of vent float would not be required since we are visually fueling the aircraft and we can not put more fuel into the tank than the fuel cap opening will allow. If a fellow wanted to install tip tanks the vent is already there.

What do you think?.
Your RV 3 is going to be a show stopper..


Smilin' Jack
Corporate pilot from PDK
 
I would agree with you for the most part, in theory, but it is all about the design compromises.

I can't speak for Van, but there are only 2 reasons that I can think of, why they are designed this way, to put them in the engine outlet/exhaust stream, and easy removal (since the tanks are designed to be removable).

I think the coil is probably the best solution, simple with very little modification. Venting outboard would work as well, but is more work and requires more forethought. Of course, I may be biased, as I am using the coil with a flush mount NACA vent.
 
That's what I did on mine, the vent line has 3 loops just inside the last bay before the wingtip, and is connected to the Bonaco vent with the screen pressed into it.
 
It's always neat to see that someone reads my column! ;)

I do want to point out that that piece was written using the vents as an example of the modification process - it wasn't intended to be a complete treatise on venting systems, and it doesn't necessarily say that the coiled vent is the BEST solution.....the problem is that "best" is a moving target, depending on if you want perfect venting, no spillage, easy installation, etc....the design requirements.

Now that we have flown the airplane for a few months, I would say (anecdotally), that I notice a little more "burping" of fuel with the coiled vents than with the Van's "standpipe" design...so if you don't want to lose ANY fuel, go with the stock. Also - since you don't get a lot of rise with the coils, if you do park on a slope with the wings not level, you could lose more fuel with the coils. Using a tip vent, you'd want to measure the height rise you get and decide if it is adequate.

I'm satisfied with the coil vents so far, but I would describe them as "adequate", and not "superior". They are very easy to fabricate and eliminate extra cockpit plumbing - but they ARE a bit of a compromise. Since the article was written almost a year ago, I thought I'd just add my current experience.

Paul
 
I am collecting ideas for an eventual build, and I like this idea.

I have the stock vents in the -6A and they burp fuel when full. I also don't like the vent lines in the cockpit. Mainly because it doesn't look good.:)

Just a question, why would you need to take the vent to the wing tip? Seems if the wing root coil idea works, a coil on the outboard side of the tank would work just as well.

I have thought about making small NACA ducts for the vent instead of the fitting hanging out in the wind. I have seen this on a few canards, and don't see why it would not work on an RV.

Any more ideas?
 
Don't forget to consider what happens when the plane is inverted in flight or tied down to a non-level ramp.

Dave
 
David Paule said:
Don't forget to consider what happens when the plane is inverted in flight or tied down to a non-level ramp.

Dave
Click to expand...

Inverted in flight, you've got bigger issues to worry about than burping a little fuel out the vents. On a non-level ramp, yeah well, I guess that might be an issue, pick a better parking spot if you're concerned about it or lose a couple gallons of fuel. Fuel up before departure and get over it. In my world the ancillary costs (taxi/rentcar/hotel/cheeseburger/bar-tips/incidentals) cost more than the possibility of dumping a gallon of 100LL on the ramp, and I'm going to utterly fail to panic over that.

If the possibility of dumping a gallon of 100LL on the ramp brings up the risk of an out-of-fuel emergency for you.... well then you've got bigger issues than can be addressed here. No, I'm not picking on you, just saying let's keep it in the proper perspective.
 
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It pains me to dump fuel on the ramp

airguy said:
Inverted in flight, you've got bigger issues to worry about than burping a little fuel out the vents. On a non-level ramp, yeah well, I guess that might be an issue, pick a better parking spot if you're concerned about it or lose a couple gallons of fuel. Fuel up before departure and get over it. In my world the ancillary costs (taxi/rentcar/hotel/cheeseburger/bar-tips/incidentals) cost more than the possibility of dumping a gallon of 100LL on the ramp, and I'm going to utterly fail to panic over that.

If the possibility of dumping a gallon of 100LL on the ramp brings up the risk of an out-of-fuel emergency for you.... well then you've got bigger issues than can be addressed here. No, I'm not picking on you, just saying let's keep it in the proper perspective.
Click to expand...

Civility requirements are being applied in my response.

Bob Axsom
 
Bob, (and others) - sorry if that came across as harsh, I was just trying to get a point across (poorly apparently) that the small loss of fuel from a dripping vent line should NOT be enough volume loss to cause a safety-of-flight issue.

I don't want my airplane dumping fuel on the ramp any more than you do, but all aircraft do it from time to time.

Mea Culpa, backing away slowly....
 
On the Cardinal I used to own, the vent connection was on the outboard side on both left and right fuel tanks. The vent tube for the left tank exited out the right wing tip, and the right tank vent exited out the left wing tip. When parked on an uneven ramp fuel did not leak. More complicated plumbing, but no fuel spill on the ramp.
 
Unless there was something else going on, I'd expect that the combination of a non-level ramp plus full fuel tanks plus some tank heating in the sun would result in some fuel flowing out the vents.

Dave
 
Nothing more than a squirt at most. It is probably less fuel than folks typically pour onto the ramp when they check their sumps!

As Doug would say, "This is a big nothingburger."
 
I coiled the RV8 vents today but just inside the tanks. There was an extra 2" of line after hook up at the inboard rib so it was curved around the filler neck up and aft at the outboard rib, theoretically providing vent at the highest point in the tank. The rest of the system will be as per the plan.
 
Smilin' Jack said:
...but realizing every jet I have flown has the fuel vents out on the wing tip. I think you could run the vent line outward to the last rib then coil it like you did and drop the vent out the tip and it would be at the highest point of the dihedral on the wing...
Click to expand...

If the left tank vent goes out the left wingtip, does fuel flow out of the vent line when in a left bank?

It would seem for this to work right the left tank would have to vent out the right wingtip, and the right tank out the left wingtip. That way regardless of the bank the low tank is venting out the high wingtip.
 
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Bubblehead said:
If the left tank vent goes out the left wingtip, does fuel flow out of the vent line when in a left back?

It would seem for this to work right the left tank would have to vent out the right wingtip, and the right tank out the left wingtip. That way regardless of the bank the low tank is venting out the high wingtip.
Click to expand...

If the turn is coordinated, the tank and vent don't know they aren't flying straight and level.
 
There is another way, run the vent from the Port tank under the cockpit and out to the Starboard wing tip and similar for the other side. I didn't do that on my RV4, but now wish I had done. There is not much extra weight and very little chance of fuel loss.
 
I am doing the wing root coil and using these.
DSC02747.jpg
 
The coil and Van's fuel vent plumbing work but neither are ideal. The reason why is a slug of fuel will always be in the lines so it takes a much higher pressure to move that slug than would be the case if vented to free air. When they do vent fuel overboard its usually a sizable quantity due to the pressure buildup. That and the vents are in a perfect place for the fuel to stream into a spot where the fumes work their way into the cabin. Hundreds of times I've smelt fuel in various RVs after takeoff for this reason. I hate it and so do my passengers!

Most certified aircraft vent to the tip or in the case of Cessnas behind the wing strut. The ones that vent to the tip usually use a small flapper check valve with a small hole drilled in the flapper valve door to allow for a tiny amount of dribble. They tend to stay clear because the lines drain back into the tank downhill. Since the flapper door opens towards the tank, when suction requires venting it can easily meet the demand yet closes and allows the overflow pressure to be relieved via the small hole in the door, thus keeping fuel dribble to a minimum. Parking on an incline is never a problem.

I have two tanks in each wing of my Rocket and both vent to the wingtips with flapper-door check valves oriented horizontally on the tip rib. I fit a new fitting to the outboard tank rib and sealed it and made a wrench to tighten the nut thru the fuel cap. It was a challenge on a finished tank but it works. If I had to do it over I would have just put a small sealed access hole and a fitting thru that. From there its a silicone hose out to the wingtip so that when the tank is installed the hose is tugged from the tip.
 
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I've got dual tanks in my wings (plans-built mains and aux leading edge) and use flow-through venting from the wing tip. The only time this can dump fuel out the vent is if both tanks are completely full, which I would only do just before takeoff on a very long cross country.

Obviously not many people will do this - but the same idea might apply - a small catch tank with the vent attaching on top and the tank line attaching on bottom. It would still equalize pressure but would allow you to accumulate some amount of fuel without dumping it, and that would then find it's way back into the tank. This could be something as simple as a piece of large-diameter torque tube like we use for the elevator push/pull, set at a slight angle in the outboard wing, to provide some additional volume to capture that liquid. A 2" diameter tube 3 feet long will hold a half-gallon.

Just thoughts...
 
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