|02-27-2008, 11:08 PM||#1|
RCC Junior Contributor
I am: Bill O
Join Date: May 2006
Location: London, ON
Total Props: 0
Second fuel tank?
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In some cases people use a "bladder" type of fuel tank, be it from Jett or whoever. With them, I knowyou need to fuel it a special way, taking certain precautions against unwanted air introduction.
Instead, what about installing a second small tank like I have seen on helicopters?
i.e. - the main tank (your 10 or 12 or 14 oz etc) has the pressurization from the exhaust to it, and it 's then feeding into a small tank (a couple of oz?). The engine draws fuel from the small, always full, without bubbles tank. Of course, both tanks are still wrapped in foam or whatever as usual.
How well does this work in fixed wing planes? Any problems? Is the install with special problems?
I'd hate to see my expensive Dub Jett engine get a lean run, but don't really wish to go to a bladder tank.
Thanks all, for your experienced help.
|02-27-2008, 11:22 PM||#2|
I am: Boolean21
Join Date: Sep 2002
Total Props: 56
I have seen people try a second header tank so to speak with no extra benefit, fuel draw and crank leaks were there main problem...GMS engine
I have also seen people use pumps, those actually helped a consistent fuel flow through out flight.
Jett motors usually have a great fuel draw and consistent runs, but they are very expensive !
Just a couple thoughts.
|02-28-2008, 06:23 AM||#3|
There is of course the inconvenience of filling the tank with a syringe. However used and installed properly the bubbless tank solves all of the usual fuel tank problems. Forget header tanks, forget wrapping it in foam none of that is necessary. When filled correctly the fuel pick up is immersed in a solid blob of fuel. No air can get into the bladder. There will be no bubbles in the line, there will be no frothing of the fuel. You will not get a lean run unless you set the needle so.
See the picture. I do not wrap the tank in foam, it is held in place with velcro. This engines turns at 19,000 rpm with no fuel feed problems.
|02-28-2008, 10:41 AM||#4|
RCC Pro Contributor
I am: Jim Brown
Join Date: Mar 2003
Location: Rockland, Ont.
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As Ed says, using a bladder tank, when properly filled, will pretty much guarantee that you do not get any bubbles. But it is a bit finicky.
DF Jets have been using header tanks for years. And now, turbine jets also use header tanks. I'm not sure I'd want to fill a 100oz fuel tank with a syringe, Ed.
The idea behind the header tank is that it will capture and keep any bubbles coming from the main tank. This is particularly important with turbine jets, as one little bubble can result in a complete flame out of the engine. Glow and Gas engines will tolerate a minor bubble.
The trick is to design the header tank such that it can not pass on any bubbles. The best way to do that is using a geometrically centered pick up tube. The end of the pick up tube is located at the geometric center of the header tank. As long as the header tank is at least half full, it is impossible for it to pick up any bubbles. The second best way is to use a pick up that can be partially exposed to air, but still deliver only fuel. the BVM UAT is one example of that. It uses a membrane that only passes fuel as long as part of it is in fuel.
One point to keep in mind when using a header tank. Your flight should be timed such that you have landed prior to the main tank being emptied. On a glow powered system, this is particularly important because the change in the drag of the fuel draw will change when the main tank is empty, causing the fuel mixture at the carb to change (it will go rich.) This is not the case with a turbine jet because of the use of an electric fuel pump. However, if your main tank is empty, you probably have about 1 minute of fuel in your header tank.
|02-28-2008, 03:57 PM||#5|
Join Date: Nov 2003
Location: Winnipeg Manitoba
Total Props: 0
IVE GOT A C160,BABY BROTHER TO THE C130,ITS A TWIN ENGINE AND I USE TWO OS 25 LA.
I DIDNT LIKE THE TANK SET UP IN THE NAUCELLS,NOT ENOUGH ROOM.
SO WHAT I DID WAS PUT A 2 OZ HEADER TANK IN THE NAUCELLS AND A 5 OZ,I THINK,TANK IN THE FUSE,ONE FOR EACH ENGINE.
YOU RUN A LINE FROM THE PRESSURE NIPPLE ON THE ENGINE MUFFLER TO THE PRESURE.VENT LINE ON THE FUSE ,LARGER TANK.
FROM THE FUEL PICK UP LINE IN THE FUSE TANK YOU RUN A LINE TO THE PRESSURE,VENT LINE ON THE HEADER TANK IN THE NAUCELLS.
THEN FROM THE FUEL PICK UP LINE ON THE HEADER TANK TO THE ENGINE CARB.
I FUEL THROUGH THIS LINE AT THE CARB.
THERE IS APPROX DIFFERENCE OF AT LEAST TWO INCHES IN HEIGHT BETWEEN THE TWO TANKS.
NEVER HAD A PROBLEM,WORKS GREAT ALSO ON 4 STROKES.
THE TANK/CARB ALLIGNMENT,RE NACULEES ARE THE SAME AS USUAL
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