Inverted flight problems

I need help from somebody, anybody, please!!!!! The set up is a foam winged Ukey from J and J sales (Joe Just) and an older OS MAX 35 S. The tank is a Brodak Uniflow oval stunt tank (no pressure). The condition of the engine is worn, but seems to run ok. The problem is every time I go inverted, I need to make an inverted landing due to a dead engine!!!, thus going through needles and props like they are free!!!! I have pressure tested the fuel line and tank, no leaks. The tank is mounted on center line of the NVA. One observation is that the engine does not draw fuel very easily, even when I cover the venturi with my finger and flip the prop, probably due to poor compression. I am using SIG 10% nitro and 25% castor at 5000ft altitude. I am not familiar with these older OS engines and don't know if the problem is that this engine is just worn out. If anyone has any ideas I would be glad to hear them. Thanks, Dave Markley

Dave,
Just a guess on my part, I'm not familiar with your tank setup but often engines that are worn will fire up and run great until they get a little warm. Then the cylinder expands and it starts to lose compression also causing lack of fuel draw. You might want to try pressure to see if it makes a difference as it will help with the fuel draw. If you fly level flights with no problem. Then you will have to look elsewhere, mainly at your tank setup. I would run the engine on the ground a couple of tanks and turn the plane over and see if there is a change in the engine run when you invert the plane. Also be sure to check all your fuel lines to be sure there are no leaks or pin holes in the lines etc. These are often hard to find and can drive you nuts. You should be able to flood your engine by putting your finger over the venturi and flipping the prop. Make sure all the fuel lines are clear and your filter is not plugged and causing problems also. Good Luck

Well, Dave, there could be several things here.

First off, I am assuming that you are plugging the overflow tube so that the tank can run in true uniflow fashion. And I am also assuming that you know which is the pickup tube that should hook the tubing to the engine. These oval profile tanks have been plumbed in several different ways over the years. Brodak changed the plumbing from what Taffender had, but Brodak also bought some of Taffender's stock when they bought the business. Some some of the early ones sold by Brodak were made by Taffender. In other words, there were changes in this design. Some had the pickup at the top, some had it at the bottom. But all of the pickups were pretty much in line with the needle.

All that being said, you still may need to move the tank above the center line of the engine. This is quite common on profile planes. What I would do is start the engine, hold the plane upright and set the needle. Check it with the tach. Then invert the plane and see what it does. If it goes lean, you will need to lower the tank. If it goes rich inverted you will need to raise the tank (when upright).

Once you get the engine running in this fashion corrrectly both ways, then try to fly it again. You should be pretty close.

Oh, and we used to put a guard or a skid at the needle location on our old beater profile planes. That way if you had to land inverted you would at least save the needle. Can't help much if the engine is still running when you land but I will admit to putting wheels on both sides of one of my planes when I was in high school (about 50 years ago). I could take off either way and land either way. I wouldn't really recommend that for precision aerobatics, but I have often thought about it. There is nothing against it in the rules. I wonder what the reaction of the judges would be if you had a plane with two sets of landing gear, one on top, one on the bottom. You cold take off "normally" in a counter clockwise direction, fly the pattern, do the required two laps at the end, and then flip it inverted and wait for the fuel to run out and land. Well, I can't say it would win anyone any extra points, but it did enable me to just go out and fly until I ran out of fuel and then land in whatever direction I was heading at the time. Hey, no broken needles, no broken props.

Thanks for the ideas guys, I will give your suggestions a try. Leonard, I actually had a set of wheels mounted on the top of the plane just for this reason and thought it looked so bad that I took them back off, I think I will put them back on until I figure out what is going on. I have not moved the tank up or down as of yet but I can tell you that when I turn the plane over while running the fuel line starts to show tons of bubbles and the engine then of course goes lean and or dies. I think that moving the tank might just do the trick, what do you think of running pressure? I have not been using a muffler, to keep the nose weight down, but I will if it will help, Thanks again, Dave

I am thinking that you have a cracked line in your tank.If you turn it upside down and you get lots of bubbles you are drawing air from somewhere.Run it inverted after filling the tank right up and watch for bubbles well holding it inverted.If after running for a minute or so it starts drawing bubbles I would say you have a cracked pick up line in your fuel tank.Hope this may help.

Pressure can help with fuel draw, but won't help your bubbly problem. You may, also, have a loosly mounted tank that is vibrating more when inverted. Make sure the tank is solidly attached to the plane. It may also help to add defoamer to the fuel. Get some regular Armor-All and add a drop or two (just drops, not squirts) to your gallon of fuel. Shake it first to see if it foams. If it does, add a drop or two and see the difference. If it doesn't foam when you shake it (or mildly but goes away right away) you are OK.

There may be something inside the tank, but I am guessing now it is the way the tank is mounted. Make sure you get good fuel draw right side up and inverted while on the ground before you take it up flying again. If it won't run while holding it on the ground, it won't hold while in the air.

Use a dubro 4, oz clunk tank, modified for uniflow, and muffler pressure.

I'll be darned if that sucker doesn't start behaving on inverted.

Found the problem, I had the fuel line plummed to the vent, not the uniflow. Run's like a champ now, no matter what attitude the plane is in. You guys are great, I can't thank you enough for the help. This site is a live saver for someone like me that does not have much experience, Thanks again, Dave Markley

Great news Dave. Happy flying!!