DMichael

My Feedback: (5)

I assembled my first jet about 3 seasons ago and, at that time, I used Tygon for my clunk line. I'm running diesel fuel. I also did not install any kind of tube in the line so that it would not double over on itself. I just inspected the tank and the clunk line and, while now dark in color, the tygon clunk line has not lost any flexibility, unlike when running on a gas plane.

I have two questions:
- Any reason that I should use Viton instead of Tygon?
- Is it a good idea to insert tubing in the clunk line so that it doesn't double back on itself in the tank?

Thanks!

FenderBean

I still use tygon but it it will harden over time and not last as long as the other.

Dave Wilshere

Do not put a hard tube in the line-especially if you are using a non absorption type clunk.

Dave

Dansy

My Feedback: (53)

Viton tubing so I never have to change it....but do inspect the tank during winter time....and hard tube are pretty standard.....no clunk felt for me.

Len Todd

I use tigon all the time down to the UATs. But, I also inspect all fuel tanks every two years. Frequently, during my inspections, I usually replace the internal clunk lines. I usually end up reusing the external lines. However, on my Sprint, I have not replaced the clunk line in at least 4 years and it still moves around O.K.

I have used clunk line with and without hardline installed. Never noticed any difference. I use mostly 3/16ths tigon. I think one would be hard pressed to find an install where 3/16ths tigon doubled back over on itself.

I don't use felt clunks. I frequently can not get them inside the tank anyway due to the clunk being to big to fit the tank's fitting. I stick to BVM's heavy hi-flow clunks. Got them in all my gas planes too.

Viper1GJ

My Feedback: (20)

I agree, I use Viton inside the tank and never have to change it. Hi flow hard clunk with safety wire for security. Never had any issue. I use Tygon outside the tank up to the air trap and pump. I use this system for 45-320N turbines. I use 1/8" ID for 45-160N, 3/16" ID for 180-220N, and 1/4" ID for 230-320N. I get the flexible Viton and Tygon from McMaster Carr. I like Jet Tech fuel fittings for glass and Kevlar tanks and a Dubro stopper for plastic or 3D printed tanks. Just my preference.
Gary

Viper1GJ

My Feedback: (20)

I agree, I use Viton inside the tank and never have to change it. Hi flow hard clunk with safety wire for security. Never had any issue. I use Tygon outside the tank up to the air trap and pump. I use this system for 45-320N turbines. I use 1/8" ID for 45-160N, 3/16" ID for 180-220N, and 1/4" ID for 230-320N. I get the flexible Viton and Tygon from McMaster Carr. I like Jet Tech fuel fittings for glass and Kevlar tanks and a Dubro stopper for plastic or 3D printed tanks. Just my preference.
Gary

DMichael

My Feedback: (5)

Getting a little conflicting opinions on the line in the tube.

Dave- do you recommend against a hard tube in the line barcause you want the clunk to follow the fuel, for instance, when on a downline?

I see some folks saying they use a hard tube in the line or don’t believe the line they’re using is doubling over on itself. Either situation would suggest that on downlines the clunk is not in the fuel. In those cases is the engine being fed by the reserve in the UAT?

Dansy

My Feedback: (53)

‘Don’t forget that on down line your also at idle....

CARS II

My Feedback: (7)

I also inspect and change the fuel tank every two years and use Tygon, I have done it both ways with the fuel tank fuel line, my Reaction's fuel tank line ( 60 oz ) has a hard tube added to it.

( FYI ) During a particular flight I decided to do 4 square loops consecutively, on the second loop I could hear the engine starving because the loops were done with short straight lines, on the third and forth loop I increased the length of the straight lines on the loops and that solved the starvation that was happening.

AEROSHELDON

My Feedback: (99)

Good thread !!

camss69

My Feedback: (46)

I use Viton for the clunk line and use a hard tube in the middle.

I've had an engine out on a 3d plane from a clunk line getting stuck in the front of the tank. That was after a blender though and I don't see a lot of jets doing blenders. I'm not sure the tube is required in a jet installation but I'm not sure it can hurt either. DAVEI'm interested to hear why you don't run the tube in the middle of the clunk line.

I can see no reason to use Tygon as a clunk line when Viton is available. I've literally got a tank that's 7 years old in one of my 3d planes and the Viton still seems to be just fine. Outside of the tank I get because it's so expensive.

Auburn02

My Feedback: (1)

I've had good luck with the BVM clunk line, though I have no idea what material it actually is. I'm sure they didn't invent it.

sewbusy

I think this video, which I am just about sure you have already seen, should give us pause for thought on using that tube in the middle.

Auburn02

My Feedback: (1)

I'm not sold that the brass tube would have much impact one way or the other in that test; even normal fuel tube be it tygon or viton or BVM line is not going to allow the clunk to double over to the front of the tank and stay in the fuel 100% of the time. Also, that video is why we run UATs. And yes, while that extreme scenario might introduce some air into the UAT, most UATs are designed such that you would need a LOT of air to have it reach the engine.

Dave Wilshere

Sorry. Not been on this thread for a while.
I guess it all comes down to fuel. I use nothing but Tygon and felt clunks. Oldest still in my possession is the Instruction manual Classic Flash, I finished the tank for flight in July 2006 and it still has the same Tygon and felt clunks on main and wing tank today. The fuel system works flawlessly with the BVM bubble trap (No MAP at that time!) landing with almost zero air after 8 minutes. CARF Hawk from 2009 same Tygon and felt clunk from day one, also on a BVM trap as it was late that year I got my first MAP Bubble trap, again lands with no air in the UAT. This goes through all my models since I have never changed a clunk line, I’m not aware of any of my team having to either. Several have models in the 10-12 year age still with same Tygon clunk line.
We all use the same Paraffin (Kerosene) green house heater type 28second heating oil bought from the same refinery for 20 years. It’s super clean and water free. It’s expensive compared to JetA and other Kero options...but none of us have turbine issues, I have several JetCat turbines run into 35-40 hours with no service.

Clunk line hard tube. I’m talking about un-baffled open tanks. Anything from 50oz Dubro to the CARF cylinder tanks without a baffle, coke bottles, Derjet Cougar and Vampire all just have a length of Tygon that when hung vertically the clunk sits 10-15mm from the rear of the tank. I always Felt clunks (which should be thought of ‘wet weight’ not dry as they are installed. I have never had a tank clunk line hang up/kink. Yes I want the clunk line to have the chance of following the fuel when nose down (remember G force not static workshop testing) I only use 1/8” (3.2mm) bore Tyron for the clunk lines right up to 220N twin tank set ups like my Mephisto/Bolt.
I buy genuine Tygon 4040 not the half dozen lookalike types.
Dave

sewbusy

Everyone flies differently and everyone has their own reasons to use what they use. A scale jet pilot flies differently from a sport pilot and a pilot who competes in F3S Jet aerobatics also has different requirements. So, there is no “One shot fits all.” Keep using what works for you. If it doesn’t then it’s time to look for other options.

For me, I’ve spent 29 years competing in IMAC and 3 years in F3S. I’ve documented what works for me flying jet sequences in ALL orientations of the aircraft. Some may agree, some may disagree, and that’s fine. https://www.sewbusy.com/jet-aerobatics-blog.html

For those interested in Jet Aerobatics....you can take a look here: https://www.jetaerobatics.org
However, the main thing, is, go out, fly and enjoy yourself with your friends & make new ones! 👍
Wayne

David Gladwin

My BVM F 4 has been flying since 2000 ( see the BVM events site, Florida Jets 2000) with Tygon internal tubing. Its still there, still good to go, at least it was when inspected last month !
Jet A almost exclusively.

David Gladwin

It might be of interest to point out my Phantom has TWO airtraps to ensure the most secure flow of air free fuel to its Pegasus,

Its fuel system consists of its two main tanks. This is preceeded by a 16 ounce round tank feeding equally into the main tanks.

The two main tanks feed in parallel to a16 ounce flat Sullivan tank mounted on its side with Tygon pickup, lightly lead weighted which stops 1 1/2 inches ,or so , short of the tank rear. This means that even with some air in this tank the clunk is unlikely to leave the fuel, even when vertically downwards.

This tank then feeds the final air trap, home made from a JPX oil tank, there was no BVM UAT then, geometrically centered brass tube which then feeds the engine.

i have never seen any air in this tank, proof it works, and never a flameout in 21 years

So, in my fleet, I use PST bubble traps, BVM UATs, GBR tanks, Intairco, , MAP, and home made with JPX oil tanks with just geometrically centered pickup they all work perfectly, so I doubt if there is an ULTIMATE, BEST, airtrap !

gunradd

My Feedback: (9)

I use BVM clunk line on every build. Then use the clear tubing for all fuel lines so I can see problems before they become bad.

for a brass line on the tank.... after I build a tank I move it all around at all angles. If the clunk can get stuck it gets a brass tube. If it’s ok then I don’t. Some of these scale planes have very narrow long tanks. The clunk can find its way to the front then get stuck.

If the clunk does not have a wedge in the tip then I make one with my grinder just incase it tries to suck it self to the side of the tank fuel will still flow.

Dave Wilshere

Doing my beginning season check and here is the Tygon line from inside my fuel station. It’s over 14 years old. I changed the pick up clunk a couple of seasons back, but this shows that with the kerosene fuel and oil I use Tygon stays flexible…

Bob_B

My Feedback: (11)

Dave curious as to what your’e paying for clean kerosene? I have been using pump kero but recently bought the heater kerosene.

Dave Wilshere

Bob it’s going up all the time with the situation in Europe now. It was expensive before, last year around £1.50 a litre. But I have been using the same stuff for 20 years and have never had a drop of water in it and my fuel filters, bubble traps etc even on my oldest models have never been changed or cleaned.
People go on about the cost, but I have never had a flame out that has caused a crash or damage, so the when you factor in that it’s cheap! All my guys do the same thing, none have fuel issues.

Dave

Zeeb

My Feedback: (41)

Sorry but I do not get this mentality, it's like guys looking for the cheapest batteries for their models. WHY would you buy cheap fuel for a model that costs thousands of dollars (or whatever you local currency is) when it could single handedly wreck the thing??????

I don't get it.......

Bob_B

My Feedback: (11)

Doing the conversion it looks like you are paying about $7.50 US per gal, I paid $10 per gal. Still worth it in my opinion on the smaller turbines I have, X45 and X90.