After today's flying, I noticed that the tank on my recently acquired Super Staris SV-26 is loose.  Very loose, free to move 1/2" up and down.  We had difficulty getting a consistent engine run.  One click of the Enya NVA got the Enya 60 AAC changing lap times by a full second.

Clearly, securing the tank and starting over with the tank height / needle adjustments is indicated.  Though I remain curious about the expected effect of a loose tank.

Somewhat related, the tank is a "magnum" style, meaning it has long curved uniflow and vent tubes, a design that stresses the solder joint where the tubes enter the tank.  One suggestion I got is to use silicone caulk over the fragile solder joint, making it stronger.  I also have some 3M auto bumper repair epoxy that I could use instead of silicone.  Because that type of joint is so notorious for failure, I was treating it very carefully, handling it so lightly that I did not detect the massive looseness earlier.

Present plan is to test for leaks, secure the tank and try again to dial in the rig.

thanks,

Peter

If the tank is rattling around inside the tank compartment, the fuel could foam up.  I'm not sure how that would translate into such a dramatic difference in lap times, though.

I've never heard of that style tank before.  Is it possible to attach the tubes to the tank right at the point where they turn forward?  Or is the whole point of the tank to hook around something in the fuselage?

Here is a picture of the notorious magnum.  I completely agree that the best tank arrangement is one where the fueling operation uses a separate bracket like Dan describes, attached to the tank tube with a piece of flexible tubing.

I'm glad there's someone else who's both experienced in control line and doesn't understand quite how that tank works in a plane.

Peter, it's off topic (kinda) but could you post a picture of your tank installation?

I'm glad there's someone else who's both experienced in control line and doesn't understand quite how that tank works in a plane.

    That arrangement was extremely common back in the day. The tank just drops in from the bottom, and there is a notch in the cowl interface plane for the tubes to come out. The tubes run up above the top surface of the tank. The lower tube is usually the overflow and the top is the vent.

     It is a bit on the fragile side, but I can tell you that there were thousands and thousands of them just like it in common use from the 70's until now. The tubes are soldered to each other to stiffen up the combination, and sometimes you wrapped copper wire at the very top where they first split off  from each other to keep the solder joint from cracking.

     Brett

 p.s.   I am not sure why it is called a Magnum tank, that design was around for at least 20 years before there was a Magnum kit and I am sure that Mikey will certainly confirm that he did not invent it!

Ah, I can visualize it perfectly now.

It looks like your tank has the tubes soldered together, which would add tons of strength -- it may be worth doing that to the Brodak tank if it's not done already.