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OS .61 dies when flying inverted

I have a fairly new (less than a year old) OS .61FX mounted upright in

Twist 3D 60 with a 13x6 prop. The engine has been properly broke in an has about 20 flights on it. I'm having a problem that I'm not sure how to solve. When flying the plane at around 1/4 throttle, if I fly inverted, i will die and I have to dead-stick the plane to the ground. It doesn't seem to happen when I do this at 3/4 or higher throttle, bu it does stutter from time to time, it just doesn't quit. I never have a problem whatsoever if I don't fly inverted ... run through a tank of fuel just fine and I can do anything I want with th plane.

At first, I thought the clunk was getting stuck and sucking air, bu this is not the case. The clunk is free and not getting hung up anywhere ... also, when th plane lands dead-stick, upon inspection, there is fuel in the fuel lin all the way to the carb with no air bubbles in it.

Is there a way to correct this problem? Anyone ever had this happe before? I'm not sure where to start, I've never had this issu previously.

I've tried leaning and richening the engine with the main needle valv (no difference - the problem is repeatable), and I've changed to hotter glow plug (from an OS 8 to a 3) so far.

I'm just not sure what's causing the condition, so I'm not sure what t try to fix it.

Could the engine be flooding itself upside down somehow, causing th glow plug to foul out? What would cause that and how can it b corrected?

I pulled the glow plug after one of the dead-stick landings and it wa not wet, but with a hot engine, I thought maybe it had evaporated afte normal level flight had resumed (even though the engine was no running).

Just not sure where to go with this and I'm searching for some ideas t try ...

-- Stormlor

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Stormlord
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IF, when upright, your tank centerline is below the carb jet, then when inverted it will be above the jet by the same amount, for a difference of twice the distance. The fuel mixture, properly adjusted for upright flight, will become rich - possibly too rich - and the engine will load up. Midrange throttle typically is a bit rich anyway. Try raising the tank.

If that's not the problem, try adding landing gear on the top.

-Dave

Reply to
Dave Plumpe

Like the other reply, I think that the fuel tank is probably set too low causing a tank high position when inverted. This can easily drown your engine with an overly rich mixture. I would set the tank up dead centre with the needle valve (had to for pattern flying where there is a lot of inverted and outside manoeuvres). Then very carefully adjust the low end mixture so that it isn't too rich. You have to make adjustments to both the low and high end mixtures as you are tuning. You know that you have the low end mixture pretty close if you have the engine at idle for several seconds and then pinch off the fuel line and the engine dies without a great increase in rpm. There should be a slight rpm increase before dying. Properly tuned there should be little to no hesitation when going from idle to full throttle.

Good luck

Reply to
Worn Out Retread

What Dave and Retread said, plus:

For a diagnostic, why not put the plane on a stand and run it inverted on the ground, at the deadly throttle setting? Then you can see what's going on close up, you can see if you can adjust the mixture to keep it going, you can maybe pinch the fuel tubing to see if it's too rich or lean (if it's too rich pinching the line will make it speed up, too lean it'll sag or die immediately instead of after a bit).

Reply to
Tim Wescott

Ted shuffled out of his cave and grunted these great (and sometimes not so great) words of knowledge:

I agree with the others - the tank is set too low.

Position the tank so that where the fuel line exits the stopper on the tank is even with the SPRAY BAR in the carb. You MAY need to readjust the carb settings.

Reply to
Ted Campanelli

Storm --

I concur with the others that the tank is too low in relation to the carb. However, I'm also aware that you realistically cannot raise the tank on the Twist. Talking to one of our resident experts at the field today, he said his fix was to rotate the engine sidewise; i.e., the cylinder on the right side on the model.

Ideally, the tank center line should be at or no more than 1/2" below the carb spraybar.

If you still prefer to keep your original set up, an alternate solution is to add a Perry Pump in the fuel system.

Cheers -- \_________Lyman Slack________/ \_______Flying Gators R/C___/ \_____AMA 6430 LM____ / \___Gainesville FL_____/ Visit my Web Site at

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"On so-called global warming or climate change, let us not scare ourselves with catastrophic forecasts, or use them to defend and promote irrational interventions in human lives."

Reply to
Lyman Slack

Storm --

I concur with the others that the tank is too low in relation to the carb. However, I'm also aware that you realistically cannot raise the tank on the Twist. Talking to one of our resident experts at the field today, he said his fix was to rotate the engine sidewise; i.e., the cylinder on the right side on the model.

Ideally, the tank center line should be at or no more than 1/2" below the carb spraybar.

If you still prefer to keep your original set up, an alternate solution is to add a Perry Pump in the fuel system.

Cheers -- \_________Lyman Slack________/ \_______Flying Gators R/C___/ \_____AMA 6430 LM____ / \___Gainesville FL_____/ Visit my Web Site at

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"On so-called global warming or climate change, let us not scare ourselves with catastrophic forecasts, or use them to defend and promote irrational interventions in human lives."

Reply to
Lyman Slack

Storm --

Can you rotate the engine so the cylinder is on the right side of the Twist? This will get the carb spraybar in line with the tank CL. If you can't, another option would be to add a Perry pump.

Cheers -- \_________Lyman Slack________/ \_______Flying Gators R/C___/ \_____AMA 6430 LM____ / \___Gainesville FL_____/ Visit my Web Site at

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Reply to
Lyman Slack

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