How to avoid the clunk doubling back....

Hi

I always do it that way, although I tend to use brass tube because: A) I usually have some lying around from old tanks - and B) it is heavier than alloy, therefore the clunk is less likely to "float" - I haven't a clue whether or not this happens in practice, but it sounds a valid theory!!!! 8^)

Regards KGB

That will work, and I see no problems. However, I'd worry about WHY the clunk doubled back. Usually, this is due to a very hard landing or nose-first crash. Normal areobatic maneuvers shouldn't cause it to double back.

Dr1

That will work, and I see no problems. However, I'd worry about WHY the clunk doubled back. Usually, this is due to a very hard landing or nose-first crash. Normal areobatic maneuvers shouldn't cause it to double back.

Dr1

Yes, it will work fine. I use brass tubing, the same size that goes into the tank. Drill out the end of the clunk a bit and solder in the length of tubing. Attach the other end with a 1/2" bit of fuel tubing. Don't make the whole thing so long that it hangs the clunk up in the rear corners of the tank though. Gord Schindler MAAC6694

Usually happens with some of the import ARFs because they use a very thin-wall tube inside the tank. If you replace the thin stuff with Aerotrend or other heavy wall silicone tube the problem goes away.

Depends on the size and shape of the tank. In my biggest plane, I have a one liter tank made from a fuel can. The clunk moves back and forth by its own weight.

I would use aluminium rather than brass - methanol reacts with brass over a period of time - I had a brass clunk dissolve when used in my bulk fuel container. I've had no problem with Al. The bulk container one was replace with stainless steel.

Malcolm

Malcolm>

That sounds pretty good actually, might try this in my 3D models. They're the ones that need it!

Tried that, unfortunately the line is larger in diameter than any straws I have at home. I'd also be worried about the straw disintegrating over time.

Thanks for the advice. I've fitted alloy tubing as that is all I had. A violent shake/rattle/roll test on the tank shows this to work.

Thanks for the advice. I avoided soldering etc and simply grafted some alloy tube into the fuel line. Tank has plastic fuel fittings anyhow. No chance of hanging up, long semi-cylindrical tank with no real corners.

Rather long constant diameter rounded tank, about 6 inches long.

Doh, you just reminded me I didn't measure the tank before refitting it. Wanted to know how much it held.... I know it holds heaps....at least

I'm using standard silicone fuel line which is rather thick but very flexible. Took the tank out of the plane and gave it a shake, easy to double the clunk back.

Was off-centre line during landing in heavy wind. Rather than try to make the runway I gently went to land it in the long grass. Naturally a gust of wind came along and lifted a wing, causing a gentle cartwheel (no damage).

That's what confused me.

I've had my solo rating for less than a month and am now starting to practice some aerobatics. The plane flew fine just after take off and, once I burnt off some fuel (it's sluggish with a full tank), I started some maneouvers.

Hurled it aroung pretty good for high wing trainer and my skill level (not much really) and after a few minutes of this is suddenly died. Did this several times, the last inverted at the top of a loop. Checked the fuel level and the tank was 90% full. Drained the tank and gave it a good shaking, heard the clunk fall back into place.

Cut off a piece of that "fat" plastic straw you get a McDonalds and slip it over most of the fuel pickup tube. Works great.

Phil AMA609

The Raven wrote:

envisaged.

For an easy, lightweight, simple, inexpensive and effective mod which will eliminate your problem - do this.

Get a plastic drinking straw and cut a length/section slightly shorter than the length of fuel tubing to the clunk pickup within the tank. Place the pickup fuel tubing inside it. Make sure the tubing still has sufficient flexibility for the clunk to reach where it should.

Voila, one semi-rigid fuel pickup that won't bend back on itself within the tank.

As a follow up to my original post, I eventually decided to use rigid pipe as the main section of clunk line. Small sections of tubing being the joiners to the clunk and, at the other end, the tank fitting.

Trialed today in some rather nasty weather and several flights involving aerobatics etc only resulted in one dead stick. In this case, the deadstick appears to be a case of low fuel leading to a few bubbles in the fuel line AND a rapid transition from idle to full throttle while in flight.

In other words, no clunk related problems at all.

Thanks everyone for your advice. I'm sure all the methods suggested were valid, I merely chose the one that best matched my first assessment of the problem while also being the one I had suitable materials for.