You can easily guess that I think the bubbless tanks are about the best thing that has happened to engines in a long time. I didn’t invent them, but I certainly have championed them for the last 10 or twelve years.
I will not waste space on how they are made, other than to say that they have a bladder lining similar to a baby bottle to keep the air and liquid from actually touching. This prevents foaming. Without foaming, you can run you tank completely empty without the engine changing. In a race, this means you carry less fuel to get the job done and you can run harder from the beginning.
There are two types out there: The Bubble-Jett and the TETTRA ™. You get the Bubble-Jett tanks from me and Darrol Cady, and the Tettra from Dave Shadel at Performance Specialties, and other outlets. They both work about the same in an airplane and once installed you would never know which was which.
One of the best things about these tanks is that you don’t have to worry about how you install them. If the fuel lines are free, they will work. Since they have no air inside the fuel bladder, you don’t need to worry about wrapping the tank for vibration isolation. Stick the tank in, center it in the fuse, and stuff foam or paper around it to keep it from moving. We usually glue or tape an ice cream stick to the front to keep the tank from sliding forward and pinching the fuel lines.
The crap trap part of the article is telling you how to not screw up a foolproof system.
- When you assemble the TETTRA make sure you notch the end of the tubing like a kings crown so that the end of the tubing cannot plug during the run. The bladder can get up against the tubing and get sucked into the opening , plugging the fuel. The Jett is made that way.
- This is about the only thing you can do to screw up a bubbless tank so pay attention!!! During fueling, don’t get sloppy!!! Always empty the tank, and even pump it back and forth to get all the air out. In a closed system, if you don’t fuel it correctly, you can have worse problems then with a standard tank. The bubble you leave in a poorly fueled tank will not stay at the top and away from the clunk like it will in a regular tank. When the airplane accelerates, especially during launch, the bubble will move toward the front and pass over the opening of the fuel tubing and BAM your engine suddenly dies at just the critical point. You crash, or make a very bad landing.
- Don’t connect the muffler pressure line to the fuel inlet to keep the fuel from leaking during storage. Remove fuel from the tank. First, the bladder material in a TETTRA is silicone and slightly susceptible to weakening over time. The Jetts have silicone sealer with the same problem. Second, and much more important, fuel from the bladder will get into the pressure side of the tank, making the tank impossible to fully fill. When you look at a tank like this you think you have a leak in the bladder. Occasionally hold the tank vertically nose down and suck on the pressure side to remove excess fuel and oil from the tank.
- Fill gently and carefully. In a closed system you are filling the tank until you feel the bladder expand against the tank. This is generally ok, but you need to give the bladder time to move about and find its least binding arrangement, plus give the excess fuel and oil a chance to escape the pressure hole, which as you know, is very small. After filling, if you have a good shut-off, you do not need to clamp the fuel tube. If you do not have a tight shut-off, or you are flying Q-500, then be sure to use hemostats or some other type of clamp to avoid air back-filling into the tank. Also, the tank will just set there and siphon itself empty, unlike a clunk tank.
- A ruptured bladder is a disaster, mainly because you do not have a weighted clunk in the system. If you did, the tank would work just like the old type and you might not get a zero. If you do get a rupture and don’t have time to change before the next heat, fill the tank fully and wait until about 15 sec to start (leave the needle in its last position) and hope for the best. If, on the other hand, you develop a very small vacuum leak, noticeable during filling, you are OK for a while. This leak could be due to a small hole in the bladder, bladder seal, or in the tubing. This is not a disaster. You can probably finish the contest without any problem. The reason this is not much of a problem is that a flexible bag cannot hold pressure, meaning that the pressure inside the bag is exactly the same as the pressure outside the bag. When the inside pressure is the same as the outside pressure, you will not have a leak. Just try to keep the fuel drained from the pressure side.
- A final note: the length of tubing in a system is not really an issue. Kinked and bad installations are. Keep you lines as short as possible, but make sure that you have your fuel system set up so that the engine gets free, easy flow.
Food for Thought: Did you ever wonder why we just don’t just put land mines in the areas around the judges cages and supply the 2-3 pylon men with Stinger missiles?
Dub
