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Test for Glow Engine Experts - 6/29/2012 5:18 AM   
Lightning Fan


 

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From: Hartland, WI, USA
Status: offline 		I had a glow engine problem that stumped a lot of us at the field for a few days.  I've been at this hobby since 1967 flying glow, gas and electric so I thought I'd seen and fixed all the glow problems possible.
I'm presenting this as it appeared to us as an intellectual exercise for your enjoyment - if you are not into puzzles, move on, because this problem is solved and we are not in need of help.

Setup
A friend gave me an OS Max FP 25 for use in a SPAD combat Draco (coroplast construction flying wing, 40 inch span, see spadtothebone.org for plans).  The engine appeared to be well used, and the owner said it ran well right up to the crash it was involved in.  The carb was mounted 180 degrees from the normal stock configuration, and the threaded part of the spraybar that the needle threads to was bent about 5 degrees.  I installed the carb as it was originally designed ... needle on the left looking from the back of the engine.  The carb mounting screws were in good shape, as was the carb to crankcase o ring.  The bent spraybar was straightened using two brass tubes, muscle and eye - the needle appeared to thread in just fine and the needle itself appeared undamaged.

The engine was installed on typical SPAD mounts (cutting board material), with the four oz Dubro rectangular tank just behind the engine, it's centerline about 1/4" below the center of the carb.  The tank is a two line system, with fueling being done by pulling the carb line off the engine.  The tank is held on with zip ties, no foam.  It has a normal muffler pressure tap and line ot the tank.  I made a new muffler gasket from a piece of 3x5 card stock.

Master airscrew 9x5 prop, Byrons 15% nitro sport fuel, 16% oil.

Initial test flights had the usual bugs and were typically short as I got the feel of the plane.  The engine ran well, turning around 12K.  The needle acted normally.  This is an airbleed carb which worked reliably.   More info about the problem to follow in the next post, but here's a pic of the setup:

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< Message edited by Lightning Fan -- 6/30/2012 8:36 AM >

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RE: Test for Glow Engine Experts - 6/29/2012 5:30 AM   
Lightning Fan


 

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Status: offline 		So, continuing on ...
When our first casual combat sessions started, I found that the airplane would only run for about 4 minutes, lean out and die.  This led to several fun deadsticks.  Initially, we thought glow plug, so I changed from the old plug that was in there, an idle bar of all things, to an OS F.
No change.
Tried an A3.
No change.

Observed that the fuel level, at the time it quit, was right at the top of the stopper of the tank.  Initially I was using plastic tubing through the stopper, not brass.  In the deadsticks, the tank had shifted forward a couple of times, flexing that plastic, so I figured it had a hole in it.
Went back home, changed out the plastic lines and all the fuel tubing, inside and outside the tank.  I also noticed that the stopper screw didn't seem to have a lot of bite to compress the stopper, so I fixed that with a bigger diameter screw.

Next week, combat day, and the darn thing did exactly the same thing.  Four minutes, test your deadstick skills with a flying brick.  Sort of takes the joy out of it.
Four of us troubleshooting now, and the only thing we learned was that the problem is repeatable on the ground.  Fill the tank, it runs.  Drain to top of stopper, it quits.
We ran a 1/16" drill bit down the muffler pressure nipple, no obstruction and it blows through fine.  Muffler appears normal, and has baffle installed.
Another set of pics:


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RE: Test for Glow Engine Experts - 6/29/2012 5:37 AM   
MetallicaJunkie



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Status: offline 		i have been into rc since 92 and have not really met an engine i couldnt tune except for airbleed carbs..... im sure an expert here will help

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RE: Test for Glow Engine Experts - 6/29/2012 5:38 AM   
Lightning Fan


 

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Frustrated now.  These problems happen to other people, not me.

At home I changed the stopper, all the lines again, put a fuel line o ring on the needle seat to make a better seal, and changed the carb - crankcase O ring out.
I ran the engine several times on the ground, same old thing ... the Four Minute Failure.

Next week, combat day, I go out there knowing that this engine is nfg.  First flight, four minutes, deadstick.  Then one of the guys suggests running no pressure.  What the heck, we do it, and have to open the needle a bit to compensate for no pressure ... but the darn thing ran to end of tank!  Four flights, no problems at all!  Put the pressure back on, four minute failure again.
More pics: 



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RE: Test for Glow Engine Experts - 6/29/2012 5:44 AM   
Ernie Misner



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Status: offline 		Okay, we give up, what did you find?

Thanks,

Ernie Misner

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RE: Test for Glow Engine Experts - 6/29/2012 5:46 AM   
Lightning Fan


 

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Status: offline 		At home, I am absolutely sure now that this is a tank problem.  That is the only thing that the pressure line could affect.
Replaced all the stuff in the tank again, used brass tubing, carefully faced the tank opening to be sure it would seal, and used a Sullivan stopper assembly this time because their rubber is a bit more compliant.  This HAS to fix it.
Combat day arrives.  Go to the field, it quits after four minutes again.  Fly with no pressure, it drains the tank just fine.
I'm done.  I'm just going to fly it this way even though I know that this makes no sense, and things you do not understand in RC eventually come around and bite you.

But ... a guy makes a suggestion that took me two minutes to do, and which everyone, including the guy, said could not be it.  I did it to humor him, and it worked.  The engine ran much better, the needle adjustments seemed more "normal" and it drained the tank in flight.  Problem solved.

What was it that he suggested?  You have all the information that we had at the time in these posts and pics.



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RE: Test for Glow Engine Experts - 6/29/2012 6:17 AM   
Ernie Misner



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Status: offline 		Simple, the fuel line was laying right on the engine cooling fins and getting too hot which caused (after exactly 4 minutes) a vapor lock situation and lean condition. But wait.... why did it run okay with no pressure line?

Ernie

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RE: Test for Glow Engine Experts - 6/29/2012 6:25 AM   
PatrickCurry



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Status: offline 		Did you take the spinner off?  Could the large spinner have been causing some kind of funky air-flow that was causing the airbleed not to function right?

Edit:  Well, I guess my question to Ernie, makes *my* guess illogical too.....  LOL  If the airbleed was not functioning right, why would it always be at 4 minutes?


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RE: Test for Glow Engine Experts - 6/29/2012 6:30 AM   
PatrickCurry



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Status: offline 		But it did it on the ground and in the air Ernie.... weird that it always happened right at 4 minutes.  Wouldn't the heat have been different running on the ground and in the air?  I'm just guessing.

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RE: Test for Glow Engine Experts - 6/29/2012 6:36 AM   
Lightning Fan


 

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Patrick is the winner.
Took the spinner off, and problem gone.
As you can see from the pics, the spinner blends right into the carb throat.  Really hard to understand exactly what went on here, but we think that the air getting accelerated over the spinner and thus over the top of the carb created a venturi that sucked air out of the carb, making it very sensitive to fuel level. 
Honestly, I don't have a full explanation, but I can tell you for sure that this fixed it.
While the spinner was on, the air bleed screw  position did not seem to matter, and yes, it is checked clear.



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RE: Test for Glow Engine Experts - 6/29/2012 6:43 AM   
Ernie Misner



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Status: offline 		Patrick will you split the prize $ with me just because I tried hard? You deserve it though, your funky answer was right on, way to go!

Ernie Misner

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RE: Test for Glow Engine Experts - 6/29/2012 6:48 AM   
PatrickCurry



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Status: offline 		Awesome!  I love online forums....  seems like I had read somewhere before when someone had a spinner causing some kind of airflow problem and in the pics it looked like there was a lot of fuel all over the place like maybe it was spraying out of the carb somewhere.


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RE: Test for Glow Engine Experts - 6/29/2012 6:49 AM   
PatrickCurry



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Status: offline 		Prize money?!     Nah, if he's flying SPADs, he ain't givin out no prize money.  LOL  I'm a SPAD man myself.   

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RE: Test for Glow Engine Experts - 6/29/2012 6:54 AM   
Ernie Misner



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Status: offline 		We've learned to NTAABCWS. This a test for the OP (original poster) or anyone else. What does that stand for?

Thanks,

Ernie

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RE: Test for Glow Engine Experts - 6/29/2012 12:13 PM   
Kaos Rulz


 

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Status: offline 		I think I have the first part " Not To Assume Anything Because C..W..S.."

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RE: Test for Glow Engine Experts - 6/29/2012 1:08 PM   
summerwind


 

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Status: offline 		LightningFan,

what i really want to know here though (and i know you won't anwser), is why you would have assumed the "glow plug" to be at fault at the very first part of your analysis?



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RE: Test for Glow Engine Experts - 6/29/2012 2:47 PM   
Lamoilleriver


 

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Status: offline 		What size spinner were you using? Trusting the ole' crannial matter, I use a 1 and 3/4" spinner for that size motor. Enjoyed reading this thread, Thanks. When it comes to OS engines, at least to my experience, I use an OS glow plug, a #8 most of the time on the two strokes and always an F with the four strokes.

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RE: Test for Glow Engine Experts - 6/29/2012 3:15 PM   
Mr67Stang



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Status: offline 		Good stuff. Enjoyed the game... just entered to late. I would not have guessed the problem. As I was reading the next thing you checked was what I was thinking was the fault.

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RE: Test for Glow Engine Experts - 6/29/2012 3:29 PM   
Lightning Fan


 

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Status: offline 		summerwind -
Why would you say I would not answer?  Look, this was delivered as entertainment, and I will be the first to acknowledge that the troubleshooting methodology could have been better.  i was the guy that changed out tank hardware three times for no good reason, too.

I tried the glow plug first because the one that was in there was an unknown.  I had no idea what the guy had left in it, and for all I knew it was bad and had caused the crash that HE had.  I have had multiple experiences where a plug that started going bad would lead to an engine quitting at full throttle.  It was an easy thing to try and I really should have changed it before running the engine the first time.
I suspect that you raise this question because plugs are rarely the cause of glow engine problems, particularly with today's plug quality.  I would agree. 

Lam -
You asked spinner size, and someone else said I must be cheap because this is a SPAD.  Sort of right, I have a few 50cc ships, and about ten flyable ships.  This one was built in an effort to get combat going in the club (successful so far) and I used what was in my junk box.  This spinner also faired nicely into the landing skid I put on.  It was about 2 and a quarter inches ... too big!!


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RE: Test for Glow Engine Experts - 6/29/2012 3:58 PM   
Lamoilleriver


 

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Status: offline 		Going combat and being cheap need to go hand in hand. Been known to salvage/recycle parts form the trash bin at the club.

I was leaning towards a small split in the tank myself, spinner problem is new to me, Thanks for the lesson.

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RE: Test for Glow Engine Experts - 6/29/2012 4:05 PM   
Sport_Pilot



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Status: offline 		Is this an ABC engine or the older iron piston FP?  If it is older iron piston then you have too little of the wrong oil in the fuel.  In that case the engine is losing compression from heat which hurts fuel draw then leans out and dies.

< Message edited by Sport_Pilot -- 6/29/2012 6:33 PM >

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RE: Test for Glow Engine Experts - 6/29/2012 5:56 PM   
Kaos Rulz


 

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Status: offline 		I'm good with the spinner. I want to know about the acronym!

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RE: Test for Glow Engine Experts - 6/29/2012 6:59 PM   
Ernie Misner



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Status: offline 		NTAABCWS = never trust an air bleed carb with spinner! lol

Thanks, we're all winners in this fun sport anyway.

Ernie

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RE: Test for Glow Engine Experts - 6/29/2012 9:45 PM   
TCraft Lover


 

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Status: offline 		This was a heck of a lot of fun. I personally would never have figured it out. I still can't make the connection as to why removing muffler pressure made it run to empty. Good stuff though and lots -o- fun.

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RE: Test for Glow Engine Experts - 6/29/2012 10:16 PM   
tony0707


 

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Status: offline 		Hi
Why did the engine run to the end of the tank with the pressure line off the tank ?
Could it be you are turning less RPMS than if the line was onso running cooler at less RPM
I assume the spinner was on then and the engine ran as it should -so why would the spinner air flow be the problem ?
! think the spinner is the problem but not the air flow-its to big ( is it a 2 1/4 size spinner ) loading the engine and causing a heat build up with the low oil percentage you are running

My first thought is that spinner is to big for a 25 size glo engine over loading the enginecausing heat to build up
Just to much for the small engine to turn with your prop of choice
My second thought is that 16 % oil is on the low side17 or 18 would be better mostly for cooling purposes in this case
I run MORGAN OMEGA 15 % in my glo stuff for 20 yearsno engine or bearing wear to speak of
My third thought is your engine could be set too lean as the tank fuel is used the engine will get leaner in the air get hot from being lean and die
The additional air over the engine with the spinner offcould be keeping the crankcase coolerand the engine running being cooler
My thought is that you are dealing with a heat build up issuefrom to much spinner and maybe to much prop
I do not run a 25 size glo engine ( 46 is my smallest ) so not sure if you prop is correct for your set up and plane

From you post you seem very experienced with glo engines
I have been flying ONLY glo from 46 to 1.80 for 26 years
Just my two cents from many years of hands on experience

Regards Tony

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