themicahmachine

My Feedback: (1)

I could use some help narrowing down the cause of my latest frustration. When flying yesterday, two independent engines (a Magnum .46 and a Webra Speed .32) would both tune properly and run well on the ground. During flight, after a few minutes, both would just cut off. This happened at mid-throttle, while cruising around. After the first two dead stick landings, I checked glow plugs, re-tuned, and ran both engines on the ground for several minutes without issue. Took off again with the plane running the Magnum, and about 3 minutes in it dies while cruising slowly around the pattern. I packed it up at that point and came home, not wanting to push my luck and ruin a plane. Any ideas what could cause it? The only common factor between the two engines is the fuel, but that fuel was just fine the last time I few two weeks ago. Can anyone suggest somewhere else I can look to narrow down the possibilities?

hugger-4641

My Feedback: (6)

How exactly did you tune them on the ground? How did you check the glow plugs? Which glow plugs are you using? What fuel ? Did you notice how hot the engines were after you landed?

Assuming you are correct and there is nothing wrong with the fuel or the glow plugs(this is a big assumption!), either a lean or a rich condition can cause what you describe, but usually if too rich you will have trouble in transition from idle to higher rpm. I would try again, tune your engines the same as you did before, but this time turn the HS needle a couple clicks rich before you fly and see if you still have the same problem.

jetmech05

Ok there is only a couple of ways to stop a glow fuel engine once started....shut off the fuel.....shut off the air......or get too hot.....
Since you were flying I think shutting off the air is not an issue.....
So lets look at the fuel......the airplane you flew twice...did it die with about the same amount of fuel in the tank after both flights?.....You know what the heck with this...you wanna fix planes and fly...don't blame you
If it were me I'd change the glow plug and richen the high end an 1/8th of a turn....if that doesn't do it then I'd change the fuel lines...inside the tank too.....
If that doesn't do it then I suspect fuel is bad....I know it happens with 2 airplanes...but a glow plug and richen is cheaper than a gallon of glow fuel

Villa

Let's accept the fact that it happened to two engines. In situations like that I suspect some type of air leak; bad fuel tank, leaking fuel lines. I only use Hayes fuel tanks now because I think they give the least trouble. I also replace ALL of the fuel lines at the first sign of a problem.

JohnBuckner

My Feedback: (1)

All good points by the responders and in particular what Villa is saying above. Of course I also am a strong proponent of the Hayes (0 ring type) tanks.

But first themicamachine I would suggest confirming that you have not inadvertantly crossed your tank pressure (muffler) and feed (carburator) lines.

In addition confirm you do not have internal tank clunk lines that are pinched forward from hard landings or firm arrivals.

John

JohnBuckner

My Feedback: (1)

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LesUyeda

"would both tune properly and run well on the ground."

Sounds to me like that "properly" may very well be in question. Two different engines. The only comonallity is the tuner. I would suggest that perhaps the tuner is tuning the engines in too lean, so that when the prop unloads, and the engines pick up rpm, they are starving; i.e. tuned too lean on the ground.

Les

RCPAUL

My Feedback: (1)

There is probably another element in common - fuel. If the fuel has water in it, it can couse an engine to quite prematurely.

Paul

jester_s1

Both engines ran fine on the ground though, so fuel and glow plugs shouldn't be a factor. I'd pinch test at part throttle and see what you get. It could be that you have a lean spot at the middle of your throttle movement and need to compensate with a richer LSN setting. You didn't say what planes you were flying, but if it's a cowled installation you could have overheated which will cause a shutdown. The fact that you were able to start right back up would support this. As stated above, another possible culprit would be an air leak in your fuel line. At full throttle there is enough muffler pressure to keep air from leaking in, but at certain lower throttle settings you'll have negative pressure in the line which will cause air to leak in. That gives you a too lean mix at the carb and can look like a tuning problem when it's really a fuel supply problem. I'd run the engines on the ground through a full tank and watch for bubbles in the line to eliminate that as a cause. If you see one single bubble coming down the fuel line, you have an air leak and need to replace the clunk line and carb line. Bad bearings and engine air leaks are a possibility too since you didn't say how old these engines are.

themicahmachine

My Feedback: (1)

Jester, the lean spot in the middle of the throttle sounds like the most reasonable suggestion so far. I'll open a fresh can of fuel and start pinch testing at half throttle on the ground. Idoubt they're running lean at full throttle, since Itypically richen up a fair bit when just flying around. My tuning has never been a problem before. It could be that since Iwas spending a lot more time at lower throttle than usual (first flights of the year), a preexisting problem just made itself apparent.

The two planes, btw, are a World Models Sky Raider Mach 2 (running the magnum .46) and an OKHobbies Veltro Sport (running the Webra .32 with a tuned pipe). Neither has a cowl.

carrellh

My brother had an AT-6 that 'ran out of fuel' after flying for just a few minutes. Thought maybe the clunk was stuck at the front of the tank. Shook the plane and heard the clunk rattling around. Ran it on the ground and it did the same. Pulled the tank out and the clunk had fallen off of the line inside the tank. The tank line was sort of 'floating' around the half tank mark.

It seems odd that two very different engines would do exactly the same thing, which makes me think fuel or glow plug. .

I'm not sure how you check a glow plug other than replacing it.

Gray Beard

My Feedback: (-1)

Just a guess but it sounds like you have the engine too lean on the ground and they are leaning out more as they unload in the air. Our weather is starting to change here and this is a normal problem when people start to re-tune for the warmer weather. I lean my engines out as much as I can on the ground then fatten the high end by about 500 rpm. I used to fatten them up between 300 and 400 like most people but I discovered 500 was the magic spot for my engines.
Just a guess though???

tkline

I have had the same problem before and it was my fuel. Don't know if that's your problem but that was what was wrong with mine

da Rock

If the lowspeed needles have never been tuned, they can be a problem.

They affect the midrange operation. Actually, they affect the entire range but have less impact on full throttle, so unless you're running a lot of mid to low range you don't notice.

The pinch test usually works well for diagnosing and adjusting.

ronwc

My Feedback: (404)

It's your fuel - fuel can go bad overnight if you let air in, which condensates water into fuel.

Taken from - http://pages.suddenlink.net/donramsey/Fuel.htm

Contrary to many things you might have read or heard, just about the only thing that adversely affects model fuel is the absorption of moisture from the air. Keep the air away from it, and your fuel will likely be potent longer than you are! Methanol - the major ingredient in model fuel - is hygroscopic. This means it's virtually 100% soluble in water, and absorbs moisture from the air like a vacuum cleaner sucking up dirt.

Most modelers have no idea how rapidly this can - and does - happen, and tend to be rather skeptical about the idea. Let me paint a picture for you: Almost everyone has spilled a little fuel on the top of their fuel can in their flight box. If so, you've no doubt noticed that the shallow film of raw fuel takes on a cloudy, milky look. What you are seeing is the methanol sucking moisture right out of the air. Since the quantity of fuel is thin with a lot of surface area, the absorption is rapid, the water won't mix with the oil and the fuel turns cloudy. Just remember how quickly this happens…..almost immediately….and it might give you an idea of just how quickly your fuel can be ruined if you leave the cap off, allow a vent tube to remain open, etc.

The wide surface area relative to the quantity of the fuel exposed is disproportionate, of course, to leaving the cap off the fuel jug, but I think you get the idea. In a humid condition such as exists in parts of the U.S., it doesn't take very long at all to adversely affect your fuel. And it doesn't take a large opening….a cross-threaded cap, a small vent line, etc. is all that's needed to do the damage.

themicahmachine

My Feedback: (1)

Thank you, that has me convinced it is most probably the fuel. I will try running them again with new fuel prior to changing anything else. The jug of fuel Iwas using had only about 3/4 of an inch left in the bottom, and was about a season old. It also had a very high castor content. I think this will probably have it solved.

Thanks everyone.

LesUyeda

"would both tune properly and run well on the ground"

I cannot reconcile how "bad" fuel would run well on the ground.

Les

da Rock

You'll know when you try the new fuel. That is, unless it was a bad needle setting that caused it. Very seldom will bad fuel run well on the ground.

There is something that can happen to fuel other than water absorption. When nitro is part of the mixture, there is usually an igniter added. They evaporate out faster than anything else does if the can is left open much at all. Then the nitro doesn't want to fire, especially when the engine isn't producing heat enough to keep itself warm. Of course, this also shows up on the ground.

When fuel is the problem, the engine will usually warn you by needing a very different needle setting than usual.

In any case, you're happy with the plan of action. Just let us know how your new fuel works for that engine. And let us know how much of a difference the needle setting is with the new stuff.

jester_s1

The nice thing about trying a new jug of fuel is that if that's not the problem, you still have your old jug to use!