moodier

My Feedback: (1)

Hi;Really wondering on this use of header tanbks.Presently just useing a twinstar but seldom ever completes flite on 2 engines!I really think it is a fuel problem and in view of several other twins I am setting up wonder if should start trying out that system.This is first major problem have had on twin with dead sticks but happens to often.The little tanks are no help either but have tried more padding as they fit so tight think may be foaming fuel from the vibration.Have checked tanks several times balanced props,got rid of the Mag 28s replaced with pair of OS 25s that have been reliable!Just seems that maybe the header system would help out as have 2-PBYs and a B-25 to set up and if works might be better way to go on them.FIgure the twinstar good place to experiment!!These twins never seem to have enough room in nacelles for tank.Just checking the PBY 86" and only room for a 4oz tank!!Thanks for your thoughts!!!

91zulu

My Feedback: (2)

Most times its the position of the tanks. If the center line of the tanks are not in line with the needle valve then you may have to pressurize the tanks. because what happens is when the fuel level reach below the center line there is`nt enough pressure from the muffler to keep fuel flow constant. Sometimes as soon as you reduce the throttle a bit the pressure in the tank drops and hence the fuel flow slows down or stops. This happens due to the distance the fuel now has to travel, usually up hill.
Now how I fix that was reduce the exhaust outlet. If its a twin exhaust close off one of the pipes. creating more back pressure,... insert cooper pipe in the exhaust pipes. Push the cooper into the chamber about half way. Make sure its a snug fit and for good measure grill and tap 2 screws opposite each other to make sure they do not drop out in flight. You could also do this for stock mufflers.
Or do a submerge pressure system. That is instead of curving the cooper to the top of the tank you have two clunks in the tank. One goes to the carb and the other to pressure. Yes I know bubbles in the tank it don`t sound logical, but trust me it works. I have used this system on engines that had over size carbs like the ASP 90s and 108s and never had lean runs. because the pressure stayed in the tank it could not escape back out the pressure tubing due to it being submerge in the fuel. That was the problem with the big ASP engines, the carbs where too big and there wasn`t enough pressure to send the right amount of fuel to the carb and that caused them to run lean and shut off in flight. Some guys added perry pumps to solve this problem. By the way the clunk to the pressure should be shorter than the one to the carb.

moodier

My Feedback: (1)

Thanks for the reply!Hadn't tried the raising the fuel pressure thru restricting the exhaust outlet will try that!Part of my problem also is the lack of room for adequate size tank in the nacelles.The PBY which is a 7'one only has room for a 4oz tank need more fuel that is why thinking of the header system?.Does anyone know a way to use one tank on a twin in the fueslage.Had pair of YS63 thinking of them but no plane large enough,as there pressure system would allow use of only one tank with there check valves!Friend tried using the check valve deal on regular engine blew up the tank!!Apparently build up to much pressure guess the YX must limit the pressure?

91zulu

My Feedback: (2)

Have you timed the engines on the tanks ?

moodier

My Feedback: (1)

Checked the tanks come in with 1/2 fuel left!On it the space is so limited no way to do much in location either!need to do some checking on the klunk in these little tanks!Next time get it out will try restricting the exhaust to increase the fuel pressure!Reason thinking about the header system is that the PBY has only small space for tanks and thinking that would be a way to increase fuel capacity!Thanks!!!

mucksmear

Hi Moodier,

I have a Duellist 2/40 with a 12oz center tank and a couple of 4oz header tanks in the nacelles, for a comfortable capacity of 20oz. Works just fine. OS 46sfp so their pumped. The header tanks are not vented, although each has a fill line installed in the same manner as a vent line. The main tank vents to the underside of the wing.

To fuel the plane, I plug the center tank's vent line, and unplug both header tank fill lines and start filling from one header tank. The fill line on the opposite header tank now acts like an overflow vent. When fuel comes out of it, I know all 3 tanks are full.

To fly, I plug up both header tank fill lines, and unplug the center tank's vent.

-E

moodier

My Feedback: (1)

Hi:That sounds real neat but looks like it requires pumped engines?Hard to find them anymore,Got rid of my YS ones after toany battles with the pumps wonderful engines if you are smart enough to make them work!!Picked up an old Dualist with 2 small frame Fox 40s finally got them loosened up after 10+years of sitting but haven't tried to fly it yet,It has at least room for decent size tanks so many of these twins lack the room!Your system raly sounds like a nice arrangement!!How old are those engines?Didn't know OS had any small pumped engines,are they any less trouble than the other pumped engines such as my YS ones?Have a Clarence Lee Pumped 61 new in box but is big for these smaller planes even if could fins a mate to it!Thanks for the reply!!

jmupilot

Is it always the same engine that quits? I dont know how you adjust your engines but I always adjust the engines separately. the small difference in RPM has never bothered me. I always start one , tune it them shut it off then start the other tune it, then shut if off. The 25 size motors dont swing props big enough to really make a difference in RPM vs. thrust. I fly two different twin OS .25LA powered airplanes and I have never had an engine quit on me. Each engine has its own tank, with normal plumbing. A friend of mine has used the center mounted fuel tanks without any problems on his Jack Stafford B-24. Just remember that on a twin the with a center tank when flying in a prolonged banking turn, one engine is going to go leaner because of it having to pull fuel up hill the other is going to get more fuel flow.. So If your tweaking every last bit of RPM you may be causeing the lean one to starve for fuel and quit. This only applies if your using a center tank and the exhast pressure is not enouth to push the fuel to both engines equally. Using a small header tank should eliminate that. Again small diference in fuel pressure on the small carbs has a greater distrubance on the fuel than you may think. Try making up a test board and mounting the engines at the same distance apart as in the aircraft. Then you can experiment with centerline, header tanks and fuel plumbing and its easy to change and get to everything.

Pete

moodier

My Feedback: (1)

Hi;Thanks for the info!I am usieng mix on throttles running littlew rich etc.Actually will pull tanks did find that line to the klunk was quite stiff tried to find liter line but had none now friend turned up some of that real lite line that comes on some tanks and I found some heavier klunks will try that.Hung it up for awhile will get it out and try again!Intially blamed the Mags but then same with the 25FPs so think not the engines,May try slite restriction of exhaust to raise the pressure?Thanks!!!

airbusdrvr

jmupilot, in a coordinated turn(no side slip) the fuel pressure would be the same to both engines. There is an interesting video about Bob Hoover that demonstrates this, http://www.youtube.com/watch?v=vQpVI...earch=aircraft . Watch specifically at the 2 min 30 second point. You will see that the water(fuel in our discussion) stays level and does not lean to one side or the other.

maxpower1954

Hey Ron, you beat me to it! That's what the ball is showing when it is centered.

On another thread someone kept talking about how his model was "weathervaning" in flight, because of the large vertical tail, but I can't seem to find it now.
I hear that one quite a bit, even saw it in a model review in RCM once!

Did you start on the Dualist? Russ Farris

jmupilot

I wont argue the fact the the fuel will stay level in a tank or that a glass of water with stay put on the dash, I'm a full scale pilot also coordination of the turn has nothing to do with this. You still have to draw fuel up hill if the tank is in the center of the aircraft. Why do you think they always tell you to place the fuel tank even with the carb? You only have to hold a model nose hi without muffler pressure to demonstrate this. its only pulling 1 G then. but if you tweek the needle when level I'll bet it leans when the nose goes up. If the tank is in the center of the airplane then when in a bank the upper engine has to draw fuel uphill.

I've heard of full scale pilots having fuel starvation in Hi-wing aircraft when they were in continuos bank while circling around a point gawking. The fuel in the selected wing tank was less than 1/4 full. They had the fuel selector set to draw from one tank instead from both, it just happened to be the one that was on the low wing. BINGO the engine quit,and they were flying coordinated turns at 1G but the fuel was away from the fuel pick up, it didnt flow uphill.

Pete