Coiled vent on RVs

Smilin' Jack · #1 06-01-2012, 07:09 AM

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

RV8RIVETER · #2 06-01-2012, 07:24 AM

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.

airguy · #3 06-01-2012, 07:24 AM

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.

Ironflight · #4 06-01-2012, 08:40 AM

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

Mike D · #5 06-01-2012, 09:53 AM

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?

David Paule · #6 06-01-2012, 11:41 AM

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

Dave

airguy · #7 06-03-2012, 09:46 PM

Quote:

Originally Posted by David Paule

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

Dave

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.

Bob Axsom · #8 06-03-2012, 11:15 PM

Quote:

Originally Posted by airguy

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.

Civility requirements are being applied in my response.

Bob Axsom

airguy · #9 06-04-2012, 08:25 AM

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....

MikeT · #10 06-04-2012, 09:15 AM

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.