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8oz tank clunk doesn't move much. Problem in a long dive?

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8oz tank clunk doesn't move much. Problem in a long dive?

Old 03-14-2002, 04:44 PM
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bgi
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Default 8oz tank clunk doesn't move much. Problem in a long dive?

Here's your basic beginner question from an old C/L flier:

I'm building a Sig SE. I got the Dubro 8oz tank as instructed (it fits really nicely). I assembled the brass tubes, stopper, clunk, etc. It becomes immediately obvious that the clunk doesn't move around very much - ESPECIALLY problematic is the fact that when the tank is in a nose-down attitude, the short piece of tubing is too stiff (or the clunk isn't heavy enough) to bring the clunk down anywhere close to the front of the tank.

When I remove the stopper assembly and hold it vertical (clunk up) and the clunk barely tilts to one side. This is with a really short length of brass tube protruding on the inside of the stopper, so the tubing is as long as practical without touching the rear of the tank. Even when it tilts as shown in the photo, it will hit the side of the tank and stop. Shortening the tube to enable it to slip past the side of the tank will only make it bend less.

It looks like any lengthy vertical dive on less than 3/4 tank will kill the engine. Shorter durations in this attitude would at least cause large air bubbles to enter the fuel line.

What's the solution to this problem?

1) Thin walled fuel line?
2) Heavier clunk?

Thanks!

-brad
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Old 03-14-2002, 05:32 PM
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Default 8oz tank clunk doesn't move much. Problem in a long dive?

bgi
You don't want the clunk to fall forward into the front of the tank. I have seen more than a few crashes on take off only to find the clunk in the front of the tank.

I make my clunk lines so that they are 1/8 to 1/4" from the rear of the tank. The line should be able to swing around without hittind the rear of the tank. I will then hold the tank level and rotate it like the plane would be rolling and watch the clunk, it should touch all four sides of the tank without binding up.

You will most likely not be in a 90 vertical dive very long. The plane runs out of altitude real fast coming straight down. If you did have enough altitude and came straight down at full power chances are very good the the plane would flutter and not make it out alive with or without the motor running.

DEG
Old 03-14-2002, 06:22 PM
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Default 8oz tank clunk doesn't move much. Problem in a long dive?

DEG,

Hey, this makes a lot of sense. I had thought about the full-throttle dive and how short that must be before the plane either:

a) has a meeting with mother earth

or

b) flutters

But I was still concerned about bubbles in the fuel line. I suppose that when the bubble reaches the venturi, the pressure will blow the bubble right out the jet quickly and the net result will be a short engine blip. yes?

thanks!

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