Japanman

Hi,
I flew the vampire again yesterday, but the engine didn`t run well, and i ended up comming home soon. I found that the plug was aluminium plated. I did a check through of the system, and i can`t find any obvious inputs of aluminium, so maybe the engine is still over compressed (even with .8mm under the plug!)

anyone an expert on plug death?

J.M

matchlessaero

Hey JM,

Certainly not an expert here, but the wallet thinning I have done over the last 2 years definitely speaks about a burnt plug or two...

While running the SuperCaliente, I have tried a lot of different plugs and found a few things....

It runs best on the old flat coil globees, and second best on the Norvel Freedom plug (which I am guessing you are running).

The globees usually failed for me after 2 flights (1 if a bad needle) by damaged coils, and the Norvel plugs get 2 good flights and then progressively worse and worse until the engine won't come up on the pipe readily.

By progressively checking the plug, I found that it became alu plated worse as it was run. Total runs have never gotten past about 12, and some have gone bad as quick as 6.

I am running 35% Norvel fuel with a spike of castor mixed in. No other changes (fuel mix), and the rpm range I am running is 26k on the ground and approx 28-29 unloaded in the air.

One note- I was not alu-fouling plugs before I began running the pipe and getting the engine up to those rpm ranges.

Jim Thomerson

I've had a couple of engines, not 1/2A's, where the rod was dragging somewhere on the crankcase. At the bottom of the stroke in one, up on the sides near the bypasses in another. Both engines suffered some damage before I realized what was going on.

Jim

Japanman

Matchlessareo,
Thats interesting that you too have had the aluminiumised plugs. I wonder if the aluminium is comming from the bigend and crank- i have never had a problem with my other ball bearing engines, or heard of the r/c car guys having this problem- and the race engines certainly do the kind of revs we do... though not constant rpms for long periods like a plane.
for your zeus powered engine, are you having to run much lower compression? I have to run much reduced static compression levels in both my norvels on the pipe I think because of the higher dynamic compression on the pipe. They aren`t stock, both have porting mods to work better with the pipe/ high rpms.

I am going to make an adapter to fit a turbo plug from a car engine as i now have no more plugs! (this also lets me play with the big selection of heat range plugs available for them!)

good to hear from a fellow battler!

J.M

skaliwag

My Feedback: (1)

I remember that there was a big debate back on the SMALLNET posts about this problem.
Many people blamed it on the fuel bottle. Nitro eats EVERYTHUNG.

MR Flyer57

There could also be a problem caused by leaving the glow plug heater attached too long. I have found that a high revving engine will cook the plug very fast if the plug is heated by a battery and by the heat of the engine in combination. Also when they go this way the element will look as if it is coated when it is actually stripped of the very thin platinum layer coating.
I don't know your start up procedure, so I'm just trying to check off things that have happened to me.
An engine that is run lean will act the same way as one over heated as above, and I really don't know what the cure is. I have tried lots of things and sometimes they work and other times it seems that it stays the same.
The other thing I have see is contamination of the plug. It takes almost nothing to get to the little guys.
And last but not least, never use anything but a battery to heat them. Some people use their box and its glow plug panel heater to heat up 1/2 a plugs. This is a bad idea. Though it will work for full size plugs I still think it is a bad idea.
There are other reasons as listed above that could be your problem so
Good luck and remember this is just my opinion,
MR Flyer57

Japanman

Jim, sorry, i meant to reply to you before but got side tracked,
I think that it is aluminium coming from the crankshaft- those extra rpms are bound to be causing extra wear! that or the big end of the rod. I know that there is no internal contact as you mention. I wonder if putting in a bronze bushing might stop this happening.

MR flyer57,
- yes i know what you mean about the lean run plugs- they look a bit sandblasted too. In this case though, it seems to be definatly a coating building up on the plug- the element is VISABLY(!) thicker!! [:-]

J.M

matchlessaero

JM, I also think it is the crankshaft wear. As you break these in, the crankshaft takes a fit that gets progressively better. Without that fit, they won't needle well and they heat up. (thanks to JLeavitt for pointing me in that direction....)

The other thing that backs this up is the fact that my engines all coated plugs more quickly when breaking in than when run for quite some time.

prole

My Feedback: (3)

MR Flyer57- I'd love to hear more about your findings in regards to this. When you say only use a battery but not a power panel what classifies a battery? Is the 12V battery that runs the panel different than the 1.2V battery that is in a glow starter. What about those 1.5V Hobbico batteries, I have used them with much success, but then again I have used all of these with little problems.

I just got a flight line box and a power panel and battery for it, just wondering if that isn' t the way to go. I was sold on it by seeing Bob from Early RC using gator clips to hook up the plug on his Cox engines. The hot on the tip of the plug and the ground to the chassis. Seemed to work pretty well...

thanks Marshall...

as always,
|Timothy|

MR Flyer57

Hi Prole,
Most of this information was gleaned here on this site.

So far what I have learned is that your power panel does not reduce the voltage to 1.5 and just light the glow plug, it actually switches off and on very rapidly and you adjust the frequency by turning the power knob on the panel.

The voltage stays at 12, but since it is switching off and on rapidly it appears to glow properly. This is not what the glow plug likes, it is a little rough on plugs. It seems that the small 1/2 A plugs take a beating with this system, even more than the larger ones
.
A steady 1.2 or 1.5 (depending on if the battery is rechargeable) is what the plug was designed for, and from what I have read, this is a major contributor to plug failure. Plugs were designed (especially 1/2A ones) at a time before rechargeable batteries, and were set up to use a large 1.5 dry cell. I'm not sure if they have redesigned them to keep up with the heating systems we are using, but I doubt it.

Add the oscillating power from a panel to the heat already in a running engine, and I could see where it would over heat the wire, causing problems with the platinum coating or even coating it with aluminum.

I have no reason to believe that what I have read is incorrect, but I also have not independently corroborated this information either.

If this is wrong or there is part of the puzzle that I am missing, please add or revise this and maybe I can learn more.

I have used a power panel most of the time, because it seemed that the cox engines were hard to start and the panel has a continuity checker built in, where you could see if the plug was burnt very easily. It seems that 1.2 volts doesn't get the plugs glowing as well as the 1.5 dry cells did, but I don't know how anyone would get voltage at 1.5 anymore.

Any one out have more info on this?

Hope this explains what I was referring to Tim
MR Flyer57

Jim Thomerson

I use a 2-volt 5 amp hr gel cell and heat Cox plugs up like a flashlight. Really improves the starting and does no damage that I can see. Usually I get a large number of runs out of a plug, but I have had a couple that died after one run. I do find that after 50- 60 runs the performance begins to degrade. I should qualify that I have a pretty good stash of various size Cox plugs and havn't bought one in the last few years.

Jim

ajcoholic

My Feedback: (10)

I ONLY use my power panel to light my plugs for 15 years now, and it never casued me any problems...

AJC

bsindel

Mr Flyer57,

Alkaline cells should deliver about 1.5 volts like the old carbon cells did. If you want to get an idea of what batteries Cox designed their glow heads for just look at one of their starter kits. In it you will find a batterery holder designed to hold two D cell batteries connected in parallel.

Glow heads/plugs are essentially a resistor whose resistance increases as its temperature increases which in turn limits the current flow through the glow plug. What many people fail to take into consideration is that the battery/current source also has a resistance which affects the current flow in the circuit as well. With the old carbon cells their internal resistance was fairly high as compared to nicads and power panel glow drivers which meant that they could not provide as large a current flow into a low resistance load. If you measure the voltage across the glow head when it is connected to a carbon cell battery you will find that the voltage will drop down to less than 1.5 volts usually about 1.2 volts or less. The difference between the battery voltage and the plug voltage is dropped across the internal resistance of the battery, and you can calculate the internal resistance of the battery if you know the current flowing in the circuit. The formula would be R (resistance) = E (voltage) divided by I (current). To overcome the high internal resistance of a single carbon cell a second cell was added in parrallel. This effectively cuts the internal resistance of the current source by half which means that the current source can deliver twice as much current as it could with only one cell. The Cox glow heads were designed to work with this sort of power, and as far as I know their design has not changed.

Nicads have a very low internal resistance and are designed to give up lots of current very quickly. You can get some sense of this if you compare the nicads performance with the carbon cells performance in a glow plug circuit. Using the same glow plug, you will find that the voltage drop across the glow plug will be just about the same as it was with the carbon cell, but you will notice that the difference between the nicads voltage and the voltage across the glow plug is much less which indicates that the internal resistance of the nicad is much less. Figuring the internal resistance of the power panel output is a little bit more difficult to figure because you are using the average voltage of the square wave output of the power panel circuit, but the sharp edges of the square wave output are an idication of the low internal resistance of that current source.

How does this affect plug life? In the case of nicads, the glow element when cold gets a sudden rush of current flow through it before it comes up to temperature and can limit the current flow. If that element for some reason, damage or defect, has a high resistance area on it, it will very likely cause that area to heat quickly and burn out. As for the 12 volt glow driver, when first connected to the glow plug it applies 12 volts with a very high current capability across the glow element, which is likely to be even more stressfull than the nicad. It's sort of like taking off from a stop sign in your car by either slowly applying the throttle or slamming the pedal to the floor. Other things that can shorten plug life are lean engine runs, vibration, and high nitro fuels. I have also heard people claim that starting a flooded engine can cause the glow plug element to become distorted or broken as a result of fuel exploding inside the glow plug element cavity, but I have no way to prove it. I would think that if that were the case then inverted engines would be really hard on glow plugs.

I hope some of this is useful,
Bill Sindel

MR Flyer57

Hey Bill,
Thank you for the insight. I would like to know more about the cause of failures because we all at one time or the other have scratched our head and wondered just what would make three glow plugs in a row go south. It doesn't necessarily have to be our engines experiencing this problem. I have had new members or people who are just new to the sport, ask about it. Though I know a few things that will absolutely kill a glow plug, there are too many cases where one engine is a glow plug eater and for the life of me I can't nail down the cause.
I have use my panel for many years and have had glow plugs last for many many flights, and then come across a plane that eats them at two a day.
Please keep the ideas coming,
MR Flyer57

ajcoholic

My Feedback: (10)

My way of thinking is this (maybe oversimplified but heck its they waymy brain works )

- No matter what the actual voltage or current supplied (whether it is a pulsed system with a higher voltage, an actual 1.5V dry cell, a nicad pack, wetcell, etc) if the glow element lights up but doesnt burn out, how does it know any different?

As to how fast it lights up, well, using a power panel there is an easy fix if you think thats the problem (I dont), just reduce the output untill the plug doesnt even glow(witrh the adjustment knob), then slowly increase the power untill it does. Then it comes up gradually just like when using a worn out carbon cell.

I set my power panel on the hot side of things (I mean I like the element glowing bright) and unless I am running a high performance engine, I seem to go forever on a plug/head. I really dont think that the method of lighting your plug (as long as it is NOT over doing it, I mean, you can expcet the element to last if you are pumping too much through it and it is lighting up like a 100W bulb) is contributing to the failure. Just my opinion though, no disrespect meant to any of you guys with differing opinions

Andrew

Japanman

One other big factor is fuel-
I mix my own here in Japan- well, actually i 'blend' my own from 30% nitro car fuel (the highest% at my LHS) with myown methanol and castor.
This is a bit frustrating because there are no oil type/ content figures on the car fuel- but i assume it is 16% oil- probably synthetic, and mix to get 20-25% total oil.

Have any of you guys had a bad run with any oil type fouling plugs? With castor, i have very ocassionally had a plug suddenly stop working well- i think from a bit of burnt oil. I have found that, left in my plug box for a few weeks they seem to come back too life, often with good timing when i need a new plug

J.M

Jim Thomerson

That's an interesting comment on plugs coming back to life. I've gotten into taking a plug that is beginning to degrade, i.e, starts to drop RPM when the battery is removed, and, instead of throwing it away, putting it away in a 35mm film canister. Most plugs I pull out of the cannister work fine. I wonder if some coating eventually oxidizes.

Jim

MR Flyer57

There is also another possibility, and that is that the plug was not the problem but was changed anyway.
A case could go this way. The engine is running badly and for the life of you and your friends you cannot find out why. You are advised and try a plug change, and low and behold it is running better. Maybe a lot, maybe just a little.

The plug goes into the canister and you forget about it. The problem could be lots of things, like bad fuel or something is the fuel system, or even a lean run that has cooked the engine a little. It could even be a loose back plate or air seeping through any of the gaskets. But a fresh glow plug seems to help.

It is not a bad glow plug and when you are faced with the same problem next time, or a similarly off running day. you might grab one of the discarded plugs and find that it runs fine. There are times when it is deffenatly a glow plug but most of the time I change one out it is not dead, just bad.

Included with the glow plug change is a retweaking of the carb, which changes the sound and perception even though it might not change the problem.

This does happen, but how often?,, well who knows. Also it seems the the blown plugs go into the same holder as the removed ones,, that might be alright. You never know when a marginal one in your bad stash might be the only one you have left, so almost all of us keep them.

more rambling on my part,
MR Flyer57

MR Flyer57

I have been reading all the threads on this subject I can (without going completely blind) and there are a wide range of opinions and options.

To my dismay there has been some flaming in other threads. In an effort to turn down the heat a little please let me say that the best part of this forum is the knowledge base and lively discussion.
I am not a expert on any part of the glow plug issue and stand with the head scratchers going "what the heck" when glow plugs start popping too often. Most know the easy stuff, but knowing what is really going on and how to change it is often very allusive.

As no more that a interested bystander wanting to know more, be aware that what I state here is read somewhere else on this forum and is stuff for discussion, not written is stone and not confirmed by testing, but just using the common sense scale of "Hmm that makes sense!".

It seems that for every idea there is another school of thought and another opinion. I for one think this is great and very informative. So if my opinion seems easily molded, it is! I am listening and learning and having a blast. I hope all of you out there are also.

If anyone has an idea as to how glow plugs collect aluminum and how much it would take to foul them please don't be shy about submitting your own humble thoughts.

Does the transfer of aluminum have to do with the heat of the engine or does it have more to do with the rpm.?
Is it simply a matter of a engine not being burnished in and still shedding small amounts of aluminum?

Still looking for answers,
MR Flyer57

ZAGNUT

My Feedback: (1)

it's pretty much accepted that a plug used for break-in is gonna pick up some aluminium or other junk and shouldn't be used for flying even if it lasts. on big engines i usually burn a plug or two during break-in and i contribute this to the wearing in of the alum piston.

cox plugs have always lasted a long time for me even after the break in. this i believe is from my use of ALL castor fuel that provides much better protection for the alum bearing that the crank runs in, no wear=no alum finding its way to the plug. all castor fuel has its own problem though, it leaves a bit of varnish on the plug element that if left to build up can cause a "hot spot" that'll eventually fry the element. so i check the plug often and if it starts to look dirty i throw it in a film canister with acetone and leave it for a week or two, i alway have a clean plug on hand to swap for the dirty one.

dave

Japanman

Zagnut,
Thats interesting what you say about the castor and acetone- I have read about someone using an industrial carb de-gummer/cleaner to clean plugs- but i have never had one fail due to the filament comming apart, they have always just stopped ignighting the mixture properly.

Flyer57
My guess is aluminium is 'plating' itself onto the filament by simply being in a fine enough powder that it can melt instantly in contact with the filament. Platinum alloys readily, and aluminium is obviously compatibile with it- enough to stick to its surface, anyway.
It seems very similar to metal flame coating processes used in industry.

JM

bsindel

I don't about you guys, but I love hearing all the different ideas that come out on this forum. Zagnuts idea about cleaning plugs sounds so neat that I went out and got one of those film canisters to put in my flight box to keep clean plugs in. Couldn't hurt.

One thing I am not clear on is where would aluminum be coming from so that it could be mixed with the fuel. All of my engines have bushings or bearings on the moving parts. I don't have any abc types so is the aluminum piston the source on these type engines?

Bill Sindel

ZAGNUT

My Feedback: (1)

now that i think about it i'd say the most likely source of aluminium particles would be the backplate being in contact with the rod. the rod will usually ride up against the crank web or backplate, depends on the engine and tolerances in machining.
i've read somewhere about hard chroming the backplate face to prevent this type of wear.

also, once ball bearings start getting worn out they'll allow the crank's main bearing to come into contact with the case around the intake area.

dave

Japanman

I`m wishing i had a lathe right now to make up a bronze bushing for the crank- then I would know for sure either way where the majority of the aluminium is coming from.

Has anyone had one of the litemachines norvels apart? i see they say they have a bronze bushing.. is it all the way through, or just at one end?

J.M

Japanman

O.K,
well, in order to go flying tomorrow, i have made a (car) turbo plug adapter for my .061 The really good thing about this is, if you have a drill press and a few odds and ends, you can make one too, this is because it is made from a defunct norvel plug, drilled out and tapped, with a taper seat cut into the bottom.
well, I have to say, so far my first test with a novarossi cold plug, has been good! I was able to up the compression ratio, and it idles and runs full power everybit as well as the standard plug.. in fact i suspect i am getting a few more rpms- but that is hard to verifiy without a tach- but certainly no power loss!
It is a new plug, so I will be interested how long it lasts.

J.M