Hi,
Please, could you share your thoughts regarding clunk type setup for aerobatic or 3D plane?
While braking in gas engines on stand I noticed that clunk with filter on it is still providing fuel w/o air bubbles untill the last drop of the fuel in the tank while over 90% of the filter is exposed to the air.
I am wondering why air is not coming through exposed to the air part of the filter ???
Any guess or ideas?

So far I have been using regular clunk and forced to land with 50% fuel in the tank as I see that engine starts coughing after ~ 10-15 min in the flight.
I guess clunk starts picking up air in half empty tank.
What if I will use clunk with filter?
I hope occasional exposure to the air in half empty tank with new clunk may give me bubble free fuel flow.
Then I can reduce tank size and use saved weight for more aggressive 3D ..
Please, share your thoughts on this topic.
Thank you,
AK.

Well I can tell you on the turbine side of this hobbie, one little air bubble can end your fun real quick as some modles of turbines (Jet Cats in my experace) can't take to many air bubbles before they shut off and force you into a dead stick.

Now to prevent this we mainly use a product in the US called a UAT, its a small 6-8oz fuel cell with a mesh materal vs a fuel line and clunk.

But from what I read in the UK, most peaple don't use these little header tanks, but just use the nice felt fuel clunks you can get at Lows, as it basicly dose the same thing, but the small header tanks, just like the jets and Helis use help prevent issue when flying with a lot of suden change of directions as most large (my 110in Krill Katan 60oz tank) dont have baffleing in them to keep the fuel next to the pick up. So the small tank kind of acts like a baffle.

So your options are;

1. make sure your current set up has flexable fuel line to help keep the clunk in the fuel, as some get very stiff qucily and will not touch the top of the tank when enverted.
2. Use a felt/filter pick up clunk
3. Add a header tank, very small tank.
4. stop flying 3D ,,,,, Ya right LOL

OOh yes some peaple reduce the size of the tank for 3D, but really your goal should be to make sure the tank is over the CG as not to cause an CG changes while flying, and if your motor cant handle the exstra few oz of weight for the exstra few oz of fuel, you may need a bigger motor or better set up.

Have fun mike

Thank you Mike.
Yes, I am thinking about updating one of my gas planes with felt/filter clunk and go for extreme 3D until dead stick, but high in the air expecting dead stick situation. I'd like to check how much fuel will be left if any in the tank.
Yes, it is risky, but result can be used to upgrade my over 7 gas planes fleet with more reliable clunk.
You have mentioned jet engine sensitivity to air bubbles.
I can tell you that 4-stroke gas engines as sensitive to the air bubbles as jet engines ... May be even more as they consume almost 3 times less fuel compare to 2-stroke engines.
Among my 7 planes I have 2 with 4-stroke gas engines and they both 3D planes.
I am mostly concern about these 2 planes as I already experienced dead stick on them for a few times.
Thank you for your input.

AK.

AK, the foam/felt type clunk/filter will absorb fuel on its own and at a rate that is faster than our engines burn fuel, appropriately sized clunks that is. Therefore these type clunks will remain wet until there is no fuel in the tank and without the first air bubble.
I have found the ceramic type to be superior in absorption than the other two.

AK, will this be a gasser? If so, I tossed my tank right off the plane (67" Fusion profile w/DLE20) one time, and had power for quite a while while trying to figure out what came off the plane? Fuel line was only maybe 6" long.

Point being, if the clunk comes out of the fuel for a second, a gasser with a pumped carb will not even know it. If you're considering running a felt pick up, go for it.

---------
So far I had dead stick situation only on 4-stroke gassers . Al my 7 planes set for gas powered engines.
4-stroke gasser SAITO consume unbelivable small amount of fuel per minute.
Thus even tiny air bubble kill the engine right away.
Even if I am using heavy APC prop the insertion of this prop is still not enough to run air bubble through the carb.
For 2-stroke gassers such air bubble is not a problem.
Engine will just barble for a sec and then run smooth again.

Also remember that the harder you run your motor the more likely for it to overheat

So check your baffling and tune

Although I don't do any real violent 3D I do want my engine to run as well as I can make it. For me the solution was to use dual 1 liter tanks with felt clunks. Keeping the engine cool is important too and you should baffle around the cylinders as best you can.

Run a header tank like the helicopter models.

On the other forum pilots advised me to use ceramic clunk, which is a filter as well.They highly recommend it even on top of felt clunk as felt one may loose fibre, which clog carb filter.

I have always used the felt clunk, after cleaning/replacing many carb screens over many years I have never found felt in the screen.
The felt does not shed into the line, anyone who tells you that has never used one.
Just buy one of these and your problem will be gone
.

Hello AK, these are good questions you ask and I have wondered about some of them too. Another difference in the 4-strokes is that there is no excess of fuel in the crankcase like a 2 stroke. The 4 stroke intake tract is super lean and clean compared to the delivery in a 2 stroke. I think that is why 2 strokes are a thing of the past for everyday vehicles.... and pollution as well. On 20cc engines where sometimes a 6 oz. glow type tank is used, will a felt clunk even go through the stopper hole? That is a consideration. Also on the small tanks the flexibility of the clunk (gas type) fuel line is important too. The most flexible line I have found is made by Echo for their trimmers and is sold commonly at home improvement stores here in the USA. This tubing is the same basic size as med. glow fuel tubing, is black, and easily as flexible. It is not neoprine like the DuBro black tubing though, and should withstand ethanol okay.

Is it true that a felt type of clunk is the only filter material that will keep a pumper carb clean enough? If a felt clunk won't fit in a glow size tank for 20cc..... is there an in-line type of filter that uses felt material or is fine enough to keep pumper carbs happy?

How many types of felt, gas clunks are you guys talking about? Ceramic and steel? The steel/felt ones are common - does anyone have a link to the ceramic type and who makes it? Thanks!

6 oz tank uses the same hardware the bigger tanks use, will pass the felt clunk. Here's a link to the bronze colored pick up. Will likely jog your memory once you've seen it. I think they're just as effective at removing bubbles from the fuel line.

http://www3.towerhobbies.com/cgi-bin...?&I=LXD741&P=7

Properly installed with a flexible fuel line, the felt clunk works extremely well at keeping the engine supplied with fuel even during violent maneuvers, keeping bubbles out of the fuel supply and keeping it clean, and using up all the fuel in the tank.

However, for even further backup, I've had an eye on this clever new product with interest:

http://www.jlproducts.net/ProductQuikFire.html

This product if used, might be a good argument for using the simpler two line fuel system setup instead of the three line. By the way, I recognize the filter element itself, and you could purchase a replacement if necessary at any auto parts shop.

AV8TOR

If you used the simpler two line system with this product any dirt brought in from fueling would cling to the "wrong side" of the clunk - but that would not matter because of the filter in this product, right? I wonder if this filter is indeed as good as the felt clunk type. (can filter as finely)

Thanks Al. Yes, this sintered bronze clunk sure does look familiar and is cheaper than the OS version as I recall. Is this what we were referring to as a "ceramic" clunk earlier? Thanks.

Well, I have a filter in my fueling can, so I'm not likely too introduce dirt into the system anyway, but yeah, that's the point I was making; anything that did get into the system during fueling would be stopped by the filter in the "QuikFire"" unit. That is a good filter in the QuikFire, and I think it would be more than sufficient to filter the fuel. I would still use a felt clunk myself however, for it's ability to keep air out of the system and to completely empty the tank. Another benefit of the felt clunk is that it is heavy and helps the clunk, "clunk".

AV8TOR

I really don't think we need to over complicate it, the felt clunk works great, if you look in the gas tank of most peoples yard machines you will find all sorts of crap in them, the reason they still run is because of the felt clunks in place.
Combine that with tygothane C210A fuel line and you won't need to touch the tank for years.

I hear the felt clunk works great, but have never tried one myself, I run clear tanks that I can see inside of while using the old normal brass clunks, I do double filter all gas going into my airplanes and have done so for over 3 decades without a single fuel related engine out issue while flying 3D or not.

Yup!

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Thanks, I hadn't seen that one!

Ahicks, I've had the sintered bronze clunks corrode to the point they won't pass fuel or air. It's the only type I won't use, YMMV.

I do 3D with 2- and 4-strokes and use a plain clunk and inline filter, never have a problem. It sounds like the OP has a heat issue, or a fuel line that's too stiff.

Looks like the sintered brass and ceramic are indeed two different types. We're getting some good info here. So what is everyone using for a flexible clunk line? My vote earlier was for the Echo black tubing which is small and super flexible but I don't know if it is big enough to go on the gas type felt clunks.