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Fuel clunk question and fuel tank question - 10/9/2012 9:28 PM   
jetspud



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From: shreveport , LA, USA
Status: offline 		Im trying to plumb my fuel tanks and i had bought the large fuel line fittings from jmp. Well when turning the tank like the plane is in a dive the clunck does not want to fall to the front. I normanlly just tie some fishing weights to the clunk but the hole is to small for any sizeable weights. Will the tygon soften up onces the fuel is in the tank to were i dont have to rack my brain trying to come up with a solution.

Second the jet is a f16 1/6 th scale. Four tanks two infront of the other two futher from the cg should i make those that are furthest from the cg drain first ??

Thanks
David

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RE: Fuel clunk question and fuel tank question - 10/9/2012 11:11 PM   
Vettster


 

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From: BeetonOntario, CANADA
Status: offline 		Doesn't really matter that the clunk does not go forward as the UAT will supply the engine for the very short amount of time that the plane is pointed at the ground. You must also remember that the fuel will not necessarily fall to the front of the tank. It will be in a negative G mode and want to stay to the rear. I got tired of the clunk getting stuck sideways or forward in the tank on my gasser... that now I just use 2" of tygon near the cap and then a length of brass tube with the clunk on the end. The clunk is always at the back of the tank even on my turbines.

As for the four fuel tanks.. Assuming all four tanks are ahead of the CG and the plane was balanced empty(full UAT) as thats what it sounds like your describing... You would want the front tanks to drain first so as to relieve the Nose heavy situation, when the tanks are full. On my F-104 I have a large main tank infront of the CG and two smaller tanks behind the CG. The rear tanks drain first so the CG moves forward, but then moves back again as the main tank drains. Not even noticeable in flight.

If you have two tanks infront of the CG and two tanks behind the CG...Drain the rear tanks first. You dont want to end up with a tail heavy plane.

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RE: Fuel clunk question and fuel tank question - 10/9/2012 11:25 PM   
marc s



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From: farnborough, UNITED KINGDOM
Status: offline 		Fuel tank fitting with a large opening helps along with a good heavy clunk.....

marcs

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RE: Fuel clunk question and fuel tank question - 10/10/2012 1:10 AM   
RAMFlyer



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Status: offline 		You tease us with the pictures, how about a supplier.  And better yet, a supplier in the USA...

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RE: Fuel clunk question and fuel tank question - 10/10/2012 1:28 AM   
G4guy


 

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quote:

ORIGINAL: jetspud

Im trying to plumb my fuel tanks and i had bought the large fuel line fittings from jmp. Well when turning the tank like the plane is in a dive the clunck does not want to fall to the front. I normanlly just tie some fishing weights to the clunk but the hole is to small for any sizeable weights. Will the tygon soften up onces the fuel is in the tank to were i dont have to rack my brain trying to come up with a solution.

Second the jet is a f16 1/6 th scale. Four tanks two infront of the other two futher from the cg should i make those that are furthest from the cg drain first ??

Thanks
David

I never want my fuel clunk to fall towards the front of the tank, not required. I always use a short flexible tube then a piece of brass tubing with clunk attached long enough to reach the rear of the tank. The fuel will be always be there.

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RE: Fuel clunk question and fuel tank question - 10/10/2012 7:38 AM   
marc s



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From: farnborough, UNITED KINGDOM
Status: offline 		Ram, Todd (Dreamworks) carries the 'bullet' clunks, the Pro Filler is new only released at Jetpower last month but its on my web site shop.

Appreciate your interest.

marcs

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RE: Fuel clunk question and fuel tank question - 10/10/2012 12:33 PM   
rcjetsaok



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From: LAGO VISTA, TX, USA
Status: offline 		David,

The problem with the clunk going forwars is that if ( and when ) it gets stuck there, you are screwed. I have seen it happen a number of times over the years. Not a goot deal. Make the pick up hose long enough that it can't go forward. There are only two situations the clunk will go forward if it can, 1 - vertical decelerated flight straight down, and 2 -when it hits the ground/sudden stop.... The first is not too often or for very long, and the second... it doesn't much matter any more. The clunk going forward is bad juju.. IMHO, of course...


See ya soon !!!

Danno

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RE: Fuel clunk question and fuel tank question - 10/10/2012 4:11 PM   
Ragz



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Status: offline 		Marc, The bullet shaped clunks look great.  Are they the same size/dia as the BVM/JMP HD clunks?

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RE: Fuel clunk question and fuel tank question - 10/10/2012 4:41 PM   
highhorse


 

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From: Memphis, TN, USA
Status: offline 		As stated by others, there is no need for a clunk to go forward. The back of the tank won't be full of air unless the fuel goes forward, and that won't happen simply because the jet is pointed down. For the fuel to go forward, the jet must be decelerating, regardless of its attitude. Heck, as far as that goe, one might reasonably worry about the need for a clunk to go forward during UP lines, yet no one does.

My advice is to follow others' advice and relax. Ain't no thang !

Don.

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RE: Fuel clunk question and fuel tank question - 10/10/2012 5:31 PM   
gunradd



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From: Springhill, FL, USA
Status: offline 		My F22 has very long and skinny saddle tanks with baffels installed in the middle. Was getting lots of flame outs so I made it to where the clunks stayed in the back of the tank and added a small 8oz header tank before the UAT and all the problems solved. The clunks would get stuck in the baffels and make the engine flame out before with clunks that made it to the front of the tank.

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RE: Fuel clunk question and fuel tank question - 10/10/2012 5:54 PM   
k12rc



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From: reidsville, NC, USA
Status: online 		As stated by vettster i Also use a tube between. Cap and clunk PSP mfg makes a kit to fit bottles
quote:

ORIGINAL: Vettster

Doesn't really matter that the clunk does not go forward as the UAT will supply the engine for the very short amount of time that the plane is pointed at the ground. You must also remember that the fuel will not necessarily fall to the front of the tank. It will be in a negative G mode and want to stay to the rear. I got tired of the clunk getting stuck sideways or forward in the tank on my gasser... that now I just use 2'' of tygon near the cap and then a length of brass tube with the clunk on the end. The clunk is always at the back of the tank even on my turbines.

As for the four fuel tanks.. Assuming all four tanks are ahead of the CG and the plane was balanced empty(full UAT) as thats what it sounds like your describing... You would want the front tanks to drain first so as to relieve the Nose heavy situation, when the tanks are full. On my F-104 I have a large main tank infront of the CG and two smaller tanks behind the CG. The rear tanks drain first so the CG moves forward, but then moves back again as the main tank drains. Not even noticeable in flight.

If you have two tanks infront of the CG and two tanks behind the CG...Drain the rear tanks first. You dont want to end up with a tail heavy plane.


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RE: Fuel clunk question and fuel tank question - 10/22/2012 12:18 AM   
wl7cpa


 

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Status: offline 		A big glob of plastic formed around a clunk inside a fuel tank. It comepletely surrounded it and plugged the hole. Any ideas where it came from? Is the inside of the tank reacting to the fuel and metal clunk? Any help would be appreciated.

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RE: Fuel clunk question and fuel tank question - 10/22/2012 4:17 AM   
Vettster


 

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Status: offline 		Are you using tygon fuel line or silicone?

It could also be that your fuel has gone bad and growing algi and its collecting around your clunk

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RE: Fuel clunk question and fuel tank question - 10/22/2012 10:45 AM   
BaldEagel



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Status: online 		If its a Kevlar or GRP tank it could be release agent that had not been cleaned out of the tank, Ali and Carsten had a thread about it somewhere on RCU do a search for it.

Mike

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RE: Fuel clunk question and fuel tank question - 10/22/2012 10:51 AM   
wl7cpa


 

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From: Sarasota, FL, USA
Status: offline 		Well, that answers it. Thanks. It was a new tank on my H9 Hellcat. I wish I could post a picture but do not seem to be able to. But Kevlar makes sense and if I was to describe it, Kevlar would be the description. Thanks again Mike for the comeback.

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RE: Fuel clunk question and fuel tank question - 10/23/2012 12:39 AM   
rcand


 

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From: coral springs, FL, USA
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quote:

ORIGINAL: jetspud

Im trying to plumb my fuel tanks and i had bought the large fuel line fittings from jmp. Well when turning the tank like the plane is in a dive the clunck does not want to fall to the front. I normanlly just tie some fishing weights to the clunk but the hole is to small for any sizeable weights. Will the tygon soften up onces the fuel is in the tank to were i dont have to rack my brain trying to come up with a solution.

Second the jet is a f16 1/6 th scale. Four tanks two infront of the other two futher from the cg should i make those that are furthest from the cg drain first ??

I agree with what the others have stated. The fuel will go toward the back of the tank in any situation where there is acceleration, like going down.

Thanks
David



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RE: Fuel clunk question and fuel tank question - 10/23/2012 2:24 AM   
gooseF22


 

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From: Fort Wayne, IN, USA
Status: offline 		another technique is to take a slurpy straw cut shorter and put it over the tygon.. it will still flex but keep center section straight.. then it cannot double back to the front.. easy fix.. really easy..

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RE: Fuel clunk question and fuel tank question - 10/23/2012 3:08 AM   
Pepperpete



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From: Grande Prairie, AB, CANADA
Status: offline 		The slurpy straw doesn't break down over time? And can someone recommend a good place to buy the proper diameter brass tubing? It looks like I've got some replumbing to do.

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