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Old Aug 31, 2012, 07:25 PM
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United States, TX, Lewisville
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Dle 20 clunk line

I got a prox 260 I'm putting a dle 20 on, have a Sullivan 8oz tank. I was trying to use the standard gas line for a clunk but it's pretty stiff and doesn't let it go to the front, I was gonna load it up with weight but is there a more flexible gas line I could get?
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Old Sep 01, 2012, 03:02 PM
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pilotpete2's Avatar
The Northeast Kingdom, Vermont
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The clunk should never ever go to the front of the tank under normal conditions
As long as the clunk freely touches the bottom, top and sides of the tank as you rotate it, you should be fine.
Pete
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Old Sep 01, 2012, 03:27 PM
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Well right now if the tank was half full and I was noes down it will be sucking air...
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Old Sep 01, 2012, 06:35 PM
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When you push the nose down in flight, the fuel will experience momentary negative G's.
Most dives and spins are not of long enough duration to be a problem, especially for gas engines, where the carb is pumped and has enough of a supply to see you through the maneuver.
I've never setup a tank where the clunk could fall to the front of the tank on it's own. It usually take a run off the runway into grass and nose over to do that, and then you will have a deadstick on the next flight if you don't catch it
Pete
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Old Sep 03, 2012, 05:44 AM
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United States, MD, Elkton
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As much as I hate to say it,those new "space age" tanks are looking mighty good! It's all sealed at the factory,and has a rotating pickup near the center of the tank. Prohibitively expensive,but going in all my prohibitively expensive models from now on !

Very few models run out of fuel during gyrations...the black rubber smoke system lines are very flexible,and could be installed for fuel also.

Fuel doesn't lie still in model airplanes....someone put a camera in one to watch the activity in a tank that was mounted on the CG..At times fuel was at the top of the tank in level flight-it's always moving. Centrifugal/centripetal forces take the pickup along with the fuel,wherever the fuel goes in the tank.
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Old Sep 03, 2012, 06:45 AM
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michael,
As mentioned the engine really doesn't need fuel from the front of the tank, ever. I saw something come off my gas 3D profile one day while playing pretty hard. Not knowing what it was, I cooled it bringing it back around for a slow pass while gently feeling it out for handling issues. Seemed fine, and I didn't see anything wrong? While wondering "what the heck?" the engine quit, telling me immediately what happened. What I had seen was the fuel tank falling! The engine quit a good 45-60 seconds after seeing the tank fall. It had been running on the contents of the 4" fuel line (minus what leaked from that) along with the contents of the carb that entire time!

I run a 6oz tank, and just getting/keeping the clunk able to contact the rear sides of the tank can be a pain because the line's so short. I run extra weight in the form of a 5/16 nut right above the clunk. That seems to work pretty good. -Al
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Last edited by ahicks; Sep 03, 2012 at 08:11 PM.
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Old Sep 03, 2012, 05:21 PM
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Fokker DII's Avatar
USA So. Cal.
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I run viton tubing inside the tank. It costs a bit more but stays flexible for years unlike the yellow stuff.
I also have one of the "space age" tanks from "Rotoflow" in my Giant Big Stik, feeding a Syssa 30cc. The clunk in them does not move fore and aft, only rotates. I have never had it fail to feed fuel no matter what attitude the plane is in. Yep, I love these things since they are maintainence free and have no stuck in the front clunks after a bad landing!
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Old Sep 03, 2012, 06:28 PM
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Been there, done that one Fokker
Those Rotoflow tanks look interesting, but I'll stick with the Tygon F-4040-A (what Dubro sells) and change the clunk line each season.
For gas engines, the Walbro felt filter clunks are da bomb. As long as gas sloshes on them, you'll never suck air. The only issue with using filter clunks is having to use a third line for fill/drain, but NOT with a clunk, just a tube down into the very front of the tank. I just lift the tail to get out the last of the fuel.
Pete
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Old Sep 03, 2012, 07:13 PM
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United States, TX, Leander
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B&B sells a gas fuel line thats more flexible than tygon. I've been using it in 16oz tanks for awhile. Hasnt gotten stiff yet.
Edwin
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Old Sep 03, 2012, 10:07 PM
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Fokker DII's Avatar
USA So. Cal.
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Quote:
Originally Posted by edwin1 View Post
B&B sells a gas fuel line thats more flexible than tygon. I've been using it in 1mcmasters.6oz tanks for awhile. Hasnt gotten stiff yet.
Edwin
I buy my Viton tubing from McMasters industrial supply. A lot cheaper than the hobby suppliers. That stuff is impervious to gasoline and never gets hard. Use Shore 60 for flexability.
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Old Sep 06, 2012, 02:19 PM
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United States, FL, Jacksonville
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Viton and a felt or ceramic clunk
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Old Sep 06, 2012, 06:35 PM
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United States, OR, The Dalles
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The vitron I got from the hobby shop is pretty thick walled. Viteron from the chain saw shop has a slightly thinner wall, and is much more flexible.

I agree, though, you don't want the clunk to go to the front of the tank.
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Old Sep 06, 2012, 07:05 PM
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Fokker DII's Avatar
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Quote:
Originally Posted by JeffinTD View Post
The vitron I got from the hobby shop is pretty thick walled. Viteron from the chain saw shop has a slightly thinner wall, and is much more flexible.

I agree, though, you don't want the clunk to go to the front of the tank.
Viton from McMasters is 1/16" thick wall and comes in many diameters. Shore 60 is the flexible stuff. There is also a stiffer Shore # but it is not good for a clunk line. They sure beat the hobby store prices.

BTW: Be careful buying at the LHS, The black tubing that many carry is "Neoprene". It will get rock hard in less than a year......ask how I know...
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Old Sep 07, 2012, 10:47 AM
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United States, FL, Jacksonville
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Yea, make sure you're buying Viton and not Hayes clunk line for glow fuel.
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Old Sep 18, 2012, 10:08 PM
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I find my tygon doesn't get stiff if I leave the tank full. I only drain it to transport it. I have no idea what other effects that is going to have long term, but my clunk line seems to like it.
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