FlyingMonkey

I started flying my combat spad this weekend. Here is the setup... Hybrid spad dog fighter / DPS, OS46LA, 11x5 prop, 15% fuel. Now the problem. This plane flies really nice, BUT when I start a combat style flight... sharp turns, inverted, loops, rolls etc.. the engine dies. Its acts as if its starving for fuel and at times I can recover it if I get it level fast enough for the engine to get fuel. The fuel tank seems to be sealed with no air leaks. The fuel mixture is fine.. couple clicks rich from peak. It will climb vert without lean stall. Does it sound like my fuel pick up is maybe hanging? Is there any special setup tricks for a combat model? I figured this is still a beginner question so I posted here.



Thanks
Keith

bnorm

The clunk in the fuel tank has fliped foward......Put plane tail down and shake it til you can hear clunk rattle......WIDBL

C_Watkins

My Feedback: (10)

And if that doesn't do it, ensure that the clunk doesn't hit the rear of the tank when
swinging through from upright to inverted. It should clear it by 1/16"-1/8" to be safe.

You might actually remove the tank and put it at every conceivable angle, to make double
sure it doesn't hit or hang at any point. It has to be freely mobile to fly wild and crazy

Edit... note that this is generally more of a problem on "squared off" tank designs.

FlyingMonkey

Thanks for the replies.

I found the culprit I think... I pulled the engine and fuel tank, checked the tank for air leaks again. It was fine, but I replaced the cap assembly anyway. I then tested all the fuel lines for leaks. Wa-la.. the intake feed line had a pin hole. Looks like the brass pipe may had made the damage. I sanded the brass blunt and free of barbs. I replaced all fuel lines. I hope this solves this problem.

I did not rule this out either. See below.

The clunk did clear the tank like you said above. However it was very free to loop forward if it wanted to. I have had this happen after a hard landing or crash. I assembled the take intake clunk with a setup that MinnFlyer had posted a while back with a brass line in-between the intake line in the tank. This will solve that problem. I hope with the mods and replacements this problem is one of the past. I will find out Sat or Sun if it is fixed.

Thanks Again,
Keith

DBCherry

My Feedback: (4)

Looks like you've done everything I would have suggested. I'll be surprised if you still have a problem.
Dennis-

FlyingMonkey

Hey DB,

Well I stand tested it today. It looked like its foaming in the tank, I saw allot of bubbles in the line, I saw the dead spot in the line as it passed to the needle valve when the engine died, and I know I had all the leaks taken care of. So I balanced the prop. It needed it bad. I dont run a spinner. I hope that does it. This leads me to ask this... How much air is expected in the line? Is it that it shouldn't have any air, maybe a few bubbles every few seconds. When it was running like it should I remember seeing a bubble pass through every couple of seconds. I'm getting a headache []

Montague

Ideally, you shouldn't see any air in the line, but if all you get is a standing bubble, or a buddle now and then, you're likely ok.

I have one engine that was doing what you are describing, when I changed engines the problems went away. After closer inspection, it turned out the engine with problems had the carb not-quite-mounted-right. Basically, it was leaking just enough air around the carb that while it pulled fuel fine in normal flight, high-G turns made it starve for fuel. Once I get the carb re-mounted, I'm sure it will be fine (haven't had time to get to it yet though)