jdavis

ok, silly question: i have one of those os .50 sx engines mounted inverted in a sig rascal (only way to mount it with out major hacking).

anyway, after it kept flaming out, i installed an onboard glow driver. so, anyway, i go to test the new system out and it will not turn. i flip the plane over, remove the glow plug and i can see a pool of fuel sitting on the cylinder. i try and turn it again, with the glow plug removed and it shoots out! for some reason fuel is REALLY flowing. any ideas? what can i do to stop it?

thanks

TLH101

My Feedback: (90)

Check the level of the fuel tank. The centerline of the tank should be about 1/4-3/8" below the level of the spraybar in the carb.

Kimhoff

My Feedback: (22)

Flip the plane over and start it.

rrragmanliam

My Feedback: (1)

Ditto! Start the plane inverted. Lot's of guys start there inverted engines this way.

Darren

downunder

OK, a silly question from me
Did this only happen after you'd finished installing the glow driver in which case was the fuel tank completely empty? If there was fuel in the tank and you'd had the model nose down for some time then fuel would have run through the vent line, into the muffler and then into the engine.

jdavis

ok, let me clear some stuff up...

first, the plane was flying as is... but i everytime i would come in for a landing, it would flame out, as all my planes that i have tried to invert the engine on... i have learned to avoid inverting, but in the case of the rascal, i didnt have much of a choice.

second, i had drained all the fuel out sometime ago, and yes, the plane sat on its wheels for quite sometime before i was able to get back to it (engine upside down)

so, i get the glow driver installed, and fuel it up to test.

chain it down, turn it on, and try to start it... no go. hydolocked.

flipped it on its back, removed the glow plug, turned it over and got fuel shot into my eyes.

flushed eyes, put glow plug back on, tried to start (still on its back) and fuel was shooting out of the carb. while hand turning. then hydolocked.

put plane away, and started this thread.

the main deal here is, it all worked (as good as an inverted engine could) before. but now, it seems like it is sucking fuel like there is no tomorrow (and there might not be if it doesnt strighten up).

anyother thoughts?

iwannafly

My Feedback: (1)

A guy at the field has this same setup and has been having similiar problems because the tank is too high. Last I saw him he was going to remove the foam rubber to try to get another 1/4 inch lower with the tank. He has to clamp the fuel line when not flying and hold the plane inverted on start. A real pain.

DarZeelon

Jim, EVERYBODY,


First, to set the record straight; a glow engine does not "flame out"!

Neither does any other reciprocating internal combustion engine.

In a reciprocating engine, the burn ends and ceases shortly after ignition takes place.
Most of the power-stroke is driven by residual pressure in the cylinder (although the fuel in a rich running glow engine, could still be burning when the exhaust port opens).

In every cylinder of such an engine, the flame is re-initiated every complete cycle, by the glow plug, or the spark plug, or spontaneous ignition (Diesel).

These engine cut-out, shut-down, quit... But flame-out? NO!


Leave this term only for engines that employ continuous combustion; jet engines and rockets.

There, a flame-out is literally that. Fuel is supplied faster than the flame can consume it and the flame actually exits the engine very visibly, through the tail-pipe. It extinguishes and the engine shuts down by the time it is past the turbine(s)...


Inverted engines are best started upright, by inverting the plane.
Adjust the tank level, so in level flight attitude, its centerline will be level (+ or - 3/8") with the spray-bar in the carburettor, as was said already.

downunder

It seems that somehow you managed to fill not only the cylinder but the crankcase as well. With the engine upright and the plug out you cleared the cylinder but the crankcase was still flooded. This is why fuel spat out the carb when you turned it over. Some of this excess fuel also went back up into the cylinder and locked it up. The easiest way to clear the crankcase is to leave the plug out and spin the engine over with an electric starter but watch what comes out of the plug hole. When very few droplets are coming out it should be fairly well cleared. One thing to be careful of though is that you don't fill the muffler with fuel and then have it run back inside the cylinder.

How it got flooded in the first place is hard to say because it depends on how you refuel, how your tank is plumbed and so on. If I were to take a guess I'd say your muffler pressure line was your vent and you overfilled which forced fuel into the muffler and then into the engine. With an inverted engine you can't flood it from fuel syphoning out of the tank because it just drips straight out and onto the ground.

With an inverted engine you need to set the idle mix much more carefully than you can get away with on an upright engine. It has to be just barely on the rich side because when you come back to idle any excess fuel tends to collect inside the crankcase and any small throttle movement will suddenly flush this extra fuel loose and it'll dump on the plug and cool it down. It wouldn't hurt to try another plug though...just in case.

Dar...
Flameout is a colloquial term for an engine that stops running for some reason other than running out of fuel. Everyone knows what it means and a lecture was uncalled for. But now it's my turn
A flameout on a gas turbine is NOT caused by supplying excess fuel. Excess fuel is the only way that a gas turbine can accelerate and an over-excess causes overtemps and a possibility of overspeed. Gas turbines flameout when there's an interruption to airflow, usually from a compressor stall. This stall can be initiated by having too high an angle of attack of incoming airflow relative to the intake duct, too high ram airflow, too much restriction in the intake duct (for instance, translating cowls closed when they should be open), spikes incorrectly set to control the position of the shockwave at the inlet duct etc. All stalls are actually the compressor blades stalling but there are two types of stall. One is a permanent stall (and the closest to your definition) where airflow drops too low to support the flame and the fuel pump output can't react quickly enough. The other is a pulsing stall where the blades stall then recover only to stall again. The engine then makes a sound like a pulse jet.
End of lecture

DarZeelon

Brian,


All you wrote is very true. I have seen a film demonstrating a compressor stall in an IAF F-15's P&W F-100 engine (actually a turbofan). It is a disturbing sight.

But of all the terms used by modelers, to describe the failure of a piston engine to continue running, 'flame-out' is the most inappropriate. It just sounds all wrong, so I made this correction.

A flame-out should only describe this effect in an engine that supports an 'eternal flame', which our glow engines are not.

'Quit', for example, is so much more appropriate and simpler.
It is very understood and no one will mis-interpret it.

RustyTumbles

who cares, we all no what he means! So lets get back to the engine problem.

blw

My Feedback: (3)

In defense of Dar, you gotta say it right so we all understand what you are talking about. I agree that flameout only refers to turbines.