What is the reasoning behind putting a loop in the vent line and putting the loop on top of the gas tank on a gas motor?
Years ago we never did this and had no problems that I know of.
Some are saying so the gas doesn’t leak out the tank when you go inverted.
But when you go inverted the bottom of the vent line is well above the height of the tank, so what is the purpose of the loop in the vent line?

Can you say "downlines"?

If you don't put the loop in the vent line and start flying IMAC maneuvers, you'll see the siphoning all over the bottom of the fuselage when you land.....

I'm gonna get the popcorn, Zeeb...you already brought the "salt"....
EVERYONE knows it's really so fuel won't run out when you tilt the airplane over on it's spinner...

Yep, popcorn time. Here we go again....

My two cents: I've never used a loop in the vent line in over 40 years of flying, and never had fuel "siphoning" problems. But that's just me.... The only time I get "crud" on my airplane is if I have my smoke system set up to pump too much smoke oil.

And BTW, as far as maneuvers, if my airplanes spend more than 10 seconds straight and level, it's because I am coming in for a landing or trying to chase a fly away from my face while flying...

I'm outta here!

AV8TOR

Nah, it's so we can brag to our electric flying friends that 10 ozs gasoline lasts 20 minute on a 30 cc engine....LOL!

Whoops, I never admit to having "friends" that fly electric! Perish the thought!!! PPTTUUiii

Edit: I've even let all my cherished magazine subscriptions lapse and not renewed them because I am so sick of all the electric coverage. There MIGHT be, if I'm lucky, one article that actually interests me in any given issue any more. All the rest is electric in one form or another, and foam toy airplanes. I just don't know why they can't leave the electric stuff to dedicated electric magazines, and keep our long loved glow/gas magazines dedicated to "real" planes.... Ok, ok, I'll get off the "soapbox" now.

AV8TOR

Well when I started playing with the RC models and specifically the gassers, I put the loops on top of my tanks because that's the way everyone around here did the gas engine installs. When I put my Comp-Arf together it was much more convenient to just drop the vent line out behind the fuel tank. Trust me, there was fuel all over the belly when I landed and so I put the loop in the vent line and that siphoning went away.

So what can I say? Anecdotal evidence? Sure but it worked for me and the only models I have with smoke systems are the turbines with composite fuselages which are painted inside so when that d*mn smoke oil escapes, there isn't any exposed wood for it to soak into.....

Not sure why? but I do it because most people do it, and I read it on the internet so it must be true

Caramel popcorn anyone?

May I add my two cents?
One can get away without siphoning of fuel (without the loop) while in flight if the vento face is facing forward and in to the airstream. But not when the model is static and you turn the model upside down for some reason.
Have one set up with the brass pipe at the end of line facing forward and one with the loop. Hence can speak for both setups

The loop is handy for when you carry your plane back to the pit area after the engine quits and you landed out there a ways. When the plane is inverted the fuel can dribble out on you. Also when nose down too. Then as mentioned it helps keep fuel from dribbling out in some of the aerobatic maneuvers too. Of course if you have a really big plane trying to carry it back nose down or inverted might not be a problem then.

I keep a "leash" in my flight box. In the rare event I have to land out, I just level the prop, wrap the loop in the soft rope leash around the tail, and walk the airplane back like a good little doggie.

AV8TOR

Me two...The model airplane hobby Coverage in Mags has become something totally different than even 10 years ago.

Bob Hunt, Dean Pappas and I have kicked around ideas on how, what, when, to bring back mag content (perhaps online) of real model airplaning the way it was. With the tinkerer/hobbyist in mind. Of course it won't be for everyone, we know that. But somehow, our hope is that the original allure of modeldom is not lost forever and needs preservation, at minimum as an educational tool.

It might go over quite well. The magazines don't reflect what's going on in the real world as I've seen it. At the three major flying fields here in Tucson, it is maybe, at the most, 10 to 20% electric and the rest glow or gas. The magazines are 90% electric anymore, and only 10% glow or gas if that. Of course it stands to reason.... The magazines make their money from advertising. And who has the most bucks to spend on advertising? The electric clique. Because all they have to do is create a mold, inject it with foam, slap some graphics on it, and sell something that cost them a dollar to make, for 100 bucks plus. A profit margin like that allows quite a few bucks for advertising to keep it going.

If you create something and need contributors, I would seriously consider doing so. I've had a few articles published over the years, including in the good old (tears here....) RC Modeler magazine. Remember those old magazine covers of theirs with the bikini clad models with airplanes? Oh man.... We're supposed to be progressive, but in many ways it seems like we're going backwards.....

AV8TOR

Hay av8tor
I like your altitude, as I do the same thing and with the vent line to.

Cheers Bob T