stunthanger.com
Engine basics => Engine set up tips => Topic started by: Peter in Fairfax, VA on April 30, 2022, 08:48:00 PM
-
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
-
I think if you use a hard epoxy or Bondo ect, the tubing will break where it ends.
-
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?
-
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?
Tim has the right idea. You just need to support the tube by making up something nice that you can attach to te fuselage side, and then attach the tubes to that with something like a landing gear strap . I have seen some solder a strip of brass to the two tubes, with a hole in between them, and then just run a screw through the hole and into the fuselage. Installing one of those brass threaded inserts at that point and using a 4-40 screw would look nice and just space off the fuselage as far as needed with a small chip. of plywood.
Type at you later,
Dan McEntee
-
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 am having a hard time getting my brain wrapped around a tank with external tubes bouncing around. Back in the day, when I flew slimers the fill and vent tubes were on a separate plate fixed to the fuselage side and connected via flexible tubing to the tank with all tubes coming out the front. The tank was "slide in" to the compartment that was about 1/2" taller than the tank. We used shims of varying thicknesses above and below. To move the tank up, you pull one shim out of the top and put it in the bottom. Used the same arrangement when I switched to clunks. The one in the picture seems to be like the old Green Box cowl that left the tank compartment open from the bottom and the tubes exited through a cutout.
Never understood using a tank with tubes coming out anywhere but the front except on profiles.
ken
-
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?
-
With the tank installed in a SIG Magnum, the cowl separation line goes back and down at an angle, is conveniently at a spot where the metal tubes in the photo can exit the fuselage and go up the fuselage side to get high enough to prevent syphoning. I think Mike Pratt scratch built the tank for the prototypes and tank makers just ran with it. I have seen other models from back in the day with a similar set up. If the engine centerline was high enough in the fuselage it could get difficult to do the copper tubes connected to the tank by fuel line trick . This set up works well, the tubes just tend to act like a tuning fork and just need to be secured to the fuselage side as I already described.
Type at you later,
Dan McEntee
-
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!
-
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?
Yes - hook around the fuselage side. That's also why you can't attach the tubes to the top of the tank, you would have to cut a long slit through the fuselage to clear the support.
It looks a little iffy, the tubes did tend to get bent backards from fueling, and sometimes crack, but I used a nearly identical arrangement for *many years* and thousands of flights with no real problems.
Brett
p.s. Here's one that Ed Robbert made for me in about 1981. Look carefully and you can see the vent tube is bent backwards from putting pressure when attaching the fueling tube.
-
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.
-
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.
I assume it is, and amazed if it wasn't. That wasn't even a lesson learned, as far as I know, everyone took one look and said "we should solder those together". The copper wire wrap, if any, goes right at the top of that solder joint.
Brett