mgnostic

I'm dealing with a little bigger engine that is usually discussed in this forum but this still should be right up your alley. The plane is a Pica 1/12 scale zero. The engine is a TT.25 on a four ounce tank. The carb weeps a little fuel around the collar where the fuel line attaches, just enough that you can feel a bit of it in the prop blast. After I wiped out my 1/12 Arsenal I pulled the radio and tried to put the Zero back into the air. The engine fired up easily and held a needle setting holding the nose straight up in the air. It was turning 14900 on an 8-6 prop. I had richened it up a bit from turning 15100. Every thing was going well until I heaved it into the air. About 10 feet out it sagged massively nearly dying. It went for about 1.5 or 2 seconds and then picked back up but by then it had already tip stalled and was headed for the ground. The crash knocked off the wing and the tail. This motor has sagged on launch before. Any thoughts?

richg99

I had a TT .28 that had somewhat similar problems. It wouldn't get up as high in RPM's like yours...but would die whenever I gave it anything over 3/4 throttle. I had two problems. #1 was a tiny hole in the fuel tank lead and #2 was a bit of "stuff" caught in the needle valve. Clearing it out and using my compressor to blow through the orifices fixed my issues. Rich

BMatthews

You're throwing it too hard and the sudden acceleration creates a negative surge in the fuel to the engine. You want to push it firmly but not chuck it like a rock or baseball.

Being a low wing are you using an underhand launch or do you have some finger grips on the lower side? If you can do it over the shoulder then try for a javelin lauch that is more of a long but firm push rather than a sudden whip like throw.

mgnostic

My usual hand launch technique is a short run with an overhand toss. In previous flights this airplane liked about a 15 degree climb on the toss so that it didn't pancake before it got up to flying speed. No grips, Thumb and forefinger on top of the wing gripping the fuse and teh second and ring fingers underneath to hold it steady. I suspect a surge (anti-surge?) is the problem in some manner. I was using the same setup on my Arsenal except for having a .15 engine and launching with the same technique with never a hiccup. In response to Richg99 it holds full throttle just fine even with the plane nose high. Throttle transition is good. it seems to be due to the forces associated with the launch.

blvdbuzzard

I had an issue where the clunk was bottoming out on the back of the tank and that would starve it of fuel. Check the clunk and see if it is far enough away from the bottom.

Dru.

Max_Power

Sounds like the little fuel leak(out) becomes a air leak(in) when the pressure reverses from the fuel g-loading problem others have mentioned. Then you have a nice big air bubble right at the needle that the engine just can't overcome? Sometimes Fixing the issues that are obvious will resolve the little glitches..even if they don't seem related. I'd try to fix the fuel leak and try again. Good luck Todd

combatpigg

My Feedback: (3)

Engines can gradually lose their ability to draw fuel due to blow by or crankcase pressure leakage. If this is the case I would switch to a 8x5 or 9x4 prop and increase the castor%
The engine should also pass a pinch test when you set the needle, even with the nose pointed straight up. With a 9x4 there won't be as much a need for a throw.

The easiest thing to check first is if the fuel tank system, is it air tight from the end of the feed line to the end of the pressure line? If you are trying to needle a system that isn't pumping up, it will be more effected by G forces.