handyman

My Feedback: (2)

looking over some pics and i see set ups with extra fuel lines on top of tanks..........why?

JohnBuckner

My Feedback: (1)

Could you explain as little further as to what type of airplanes you saw and what kind of engines, were the fuel tanks exposed?

flyinwalenda

My Feedback: (5)

Perhaps re-post those pics or post links to them.

dant-RCU

My Feedback: (3)

Most likely it is the tank vent line. A loop at the top prevents fuel from being syphoned from the tank.
Since the vent is open to the atmosphere and not pressurized (as in muffler pressure from a glow engine)
most of us use this method of hook up. Usually the line is then routed out the bottom of the fuse.

Dan

Gray Beard

My Feedback: (-1)

Pretty much what Dan said. It's how I set up the gas tank in my gas powered planes. It just keeps the gas from sloshing out. I usually run about two or three loops on the vent line on the top of the tank then vent out the bottom.

sensei

The reason you see allot of fuel tanks with several loops of vent line is simple; improper setup, you don't see this in full scale and there is a reason. Take a look under most R/C airplanes and you will see a fuel line hanging down and in many cases swayed back from and during flying, this causes the the shaken fuel during flight to be scavenged from the vent line during flight because the air rushing past the aft facing vent line creates a vacuum effect and pulling out whatever fuel it can. Remedy: shorten the flexible vent line or go with a hard line and scarf a 45 degree angle facing forward to the airflow just like we did in the old U-Control Airplane fuel tank days, this will add a slight positive pressure to the vent and take care of the problem and you can leave all that fuel line on the ground while your flying.

Bob

invertmast

My Feedback: (23)

true, but you forget one thing... If your vent line is forward of the fuel tank (for whatever reason) and you nose the airplane over, the fuel will drain out of the vent. Putting a loop of line to go aft of the tank and then to the vent will prevent this from happening.

Ernie Misner

It's usually a loop around the tank, then down and out for the vent line. This is a vent, no pressure on gasser tanks, and the loop is simply to keep gas from running out and making a dangerous mess when you turn the plane over inverted. That wouldn't be good at all.

sensei

LOL,

I am talking about loosing fuel during flight guys. This loop thing really started from guys flying IMAC and needing all the fuel to get through the double pattern and back on the ground, so they do not wish to loose any fuel in the air. I don't see many 50cc-50% airplanes standing on there noses or laying on their backs, and if for some reason you need to service your airplanes while on the nose or on its back, just remove the fuel. Again this is an issue during flight...

Bob

handyman

My Feedback: (2)

saw it in a few pics on here,,,,seems to be a long loop across the top of the tank

BarracudaHockey

My Feedback: (11)

Its been said correctly a few times, it keeps the vent pipe which is at the top of the taank, from draining the tank while the plane is flying inverted.

invertmast

My Feedback: (23)

Allot/most of the 1/5 50cc warbirds have a one piece wing and are routinely on the nose or backs for servicing/installation, and for those who still use a bulb pump, they may decide not to remove the fuel from there tanks at the end of the day. For me, i personally like to keep a bit of fuel in the tank and lines to gravity feed to the carb to keep the diaphragms most. That may or may not be happening, but it gives me a lil piece of mind

For turbines, its not as easy to remove the fuel at the end of the day every time, and since we typically run external start and taxi tanks to maximize flight time, we need to be able to get to the vent fitting. On some models (eurofighters, rafale's, etc) its not feasible to put the vent fitting aft of the tanks bc then you could not get to it to hook up and remove the external tank.

So to say it is (generally) a improper setup isnt completely true for every case.

MTK

Hey guy, I don't see many full scale airplanes flying inverted do you? Worse yet, flying inverted and pushing significant g's. That will force fuel out the vent and into the air, every time. Full scale airplanes that do fly that way, for example aerobats and military, are set-up differently than your average common Cessna.

We don't set-up our tanks improperly; we demand that the fuel stay put regardless of what attitude we place the model in

To the OP, we are beginning to see more and more water bottle gas tanks fitted with fittings rather than a stopper, to avoid leaking stoppers. Fittings, like the types I sell, are installed at the top of the water bottle in addition to the cap of the bottle....the cap takes the carb feed line, aka, the clunk line, and the one or two fittings on the top of the tank are the vent and the fill fittings...Hope that helps

Gray Beard

My Feedback: (-1)

Or held by the stab and being pushed to the flight or start up area. As for scavenging fuel out the line? I haven't seen it happening to any of my RC planes but it could happen.
Just another little thing not to dwell on or over think. The looped vent line is just something most people do but I like the idea sensei brought up. If nothing else it would be a cleaner look.

Luchnia

My Feedback: (21)

I run my vent lines on the top of my clear tanks and then out the fuse on the bottom and I have never had an issue with the fuel vacuum effect. As a matter of fact, all the guys I fly gas with have similar vent setups without the above mentioned issue. My setup works great and I don't have a problem with siphoning fuel through the vent. Maybe some guys are plumbing the setup wrong or something.

sensei

I have seen guys use up to 18" of line looping it around, and everything adds weight so when I made the statement of improper setup; if your adding extra weight to correct another problem then to me... But that is just me, I will always search for the lightest functional option I can go with as a solution. Now once again when you 45 degree forward scarf the the vent line the fuel does not come out even inverted as long as the airplane is moving forward because there is positive pressure on the line. Anyway do as you please.

Bob

lrglnman

Most weedeaters use a 1 way valve to prevent extra gas from coming out. there is a supply line to the carb, a return and a vent. why cant we use the vent like on most weedeaters ? u can turn a weedeater upside down with no ill results.

handyman

My Feedback: (2)

i thought the same thing,,air gos in and gas wont come out if turned up-side-down

FlyinTiger

My Feedback: (45)

You'll need an open vent of some kind if you ever fly during a temperature change (everyone does). As it warms up throughout the day (or in your trailer/shop/storage area) and you don't have a vent line that allows air OUT of the tank you'll pop a stopper, tank seam or the cap off the threads of a water bottle tank. Weed eaters have vent lines or vented caps that allow atmospheric changes to relieve the pressure in tanks.

Some portion of your fuel line needs to be higher than the highest point in the tank, or you will siphon fuel out onto the ground after your tank is full. Loop of fuel tubing or just a little rise in the line before going down and out of the bottom of the fuselage.

Fuel all over the ground is not good for the pavement/grass at your field, nor for flying...you might run out of gas before you think. This has caused several dead sticks at events in the heat of the Summer.

warbird addict

Speaking of one way valves , I picked up a 33% extra from a guy and he had installed a really nice aluminum check valve on the vent line, I subsequently raped the gear out of that plane and installed it in my big H-9 pawnee along with that check valve and it works awsome, I stood the plane on it's nose with a full tank and it never lost a drop thru the vent
Don't know who makes the check valve or where to get it LOL the only concern I have with it is if it ever gets stuck shut it will be some bad Joo Joo for sure LOL

sensei

For my style of flying I don't think I would want to have a one way check valve in my vent line, too me it is another critical point of failure waiting to happen at the wrong time, slow low, and maybe vertical with 0 airspeed. Have you ever had a one way check valve stick on you in any application before? It happens from time to time and all it needs is a tiny piece of junk in the fuel/gas to make it stick.

Bob

Gray Beard

My Feedback: (-1)

All YS engines use a check valve and you can get them from Central Hobbies or YS Service. A one way valve will need to be removed before filling the gas tank. Sounds like more work then useful.

sensei

I know they do but I still would never put one in any of my big gassers. Maybe it's just me.

Bob

Gray Beard

My Feedback: (-1)

That was a reply to post 21 and no one is asking you to.

DGrant

My Feedback: (4)

Wow.. record thread on a little vent line question. I had no idea there was so much info on ..... wait.... what was the question again?