Glow Plug Measurements

[frank williams]

The wire element in our glow plugs is platinum, alloyed with either iridium or rhodium for increased strength.  The alloys add hardness to the wire and allow it to be produced or drawn more easily.

I’ve always been told that the platinum is the primary catalytic element that ignites the methanol in our fuel, but I think that either the iridium or the rhodium, are capable of providing a catalytic reaction also.  Chemists?
 
The starting battery heats the platinum wire to make the catalytic action occur more easily to start and once running the platinum / methanol reaction keeps the wire glowing.  (See the demonstration of the catalytic action in the following video.)   
                           

The plug manufacturers mark their plugs as hot, medium, or cold.  I assume the greater the area of the element wire in a particular plug, the hotter the plug, or the greater the catalytic action.
 
As flyers, we know by experience some plugs work better for us.  Presumably the hotter plugs are better for our type of modeling use.  We want to run at slower speeds and richer fuel settings.  The “hotter” plugs are assumed to be less likely to “flame out” or “burp” during loaded maneuvers.

But short of testing every plug with enough flights to assess its usefulness for F2B, we rely on the word of the plug manufacturer and other flyers.  A good article that summarizes glow plug heat ranges from different manufacturers is the following. It is coauthored by our own Brian Gardner.
                          http://www.scootworks.com/rdrcdave/gloplugs.html

But there are other plug models and types (hose nose and big bore) that aren’t addressed in this article.
What I would like to do is to physically test the hot plugs to find the hottest of the hot and to rank them.  But, I’m not sure how to do it.

One thought was to measure the element resistance and compare the resistance with the element in the presence of methanol vapor.  Measuring the resistance with my VOM didn’t yield much information.  Obviously, the wrong tool.

What about measuring minimum idle speed of a test engine in an inverted position, and ranking plugs that way?  The assumption is that the better stunt plug will have the lower idle speed.  I haven’t tried that yet.

Anyone have any thoughts on measuring the “hotness” or “coldness” of a glow plug?  I sure like to see a quantitative assessment of current glow plugs.

[qaz049]

It isn't just Methanol that has the particular catalytic action with the glowplug element. Ethanol and Petrol (Gasoline) and a whole range of other hydrocarbons work as well.

[qaz049]

But there are other plug models and types (hose nose and big bore) that aren’t addressed in this article.
What I would like to do is to physically test the hot plugs to find the hottest of the hot and to rank them.  But, I’m not sure how to do it.

One thought was to measure the element resistance and compare the resistance with the element in the presence of methanol vapor.

I've had some success measuring the relative surface temperature emissions of hot steel using an Infrared photo-transistor and the rather course "Paddle ports" (analog to digital converter) on both the IBM PC and the Apple 2e.

Should be able to do it easily and accurately these days with a much cheaper Arduino or a Raspberry Pi microcomputer.  It would just need a fixture with the glowplug in one end and the transistor in the other with two wires to the computer board.  The result would be a relative Digital number between 0 and 255 for an 8-Bit ADC, 0 to 1023 for a 10-bit or 0-65535 for a 16 bit.

A bit of experimentation with glow plugs of known "heat-range" should determine a baseline for each category.

[Dave Hull]

Frank,

Bill Netzeband did an article years ago on glow plugs. You might find some test methods you can evaluate for further use.  I know I have always wanted to update it with modern plugs....

I found the video attached really interesting. What it also implies is that the cleanliness of the plug during testing may make a difference. A used plug with a coating of oil would likely suppress the reaction due to the lack of exposed surface area.  (I thought the guy was pretty gutsy to have attempted that test the first time. I guess chemists are...until they blow up the lab?)

Dave

ref.:  http://www.airplanesandrockets.com/motors/how-to-select-the-proper-glow-plug-1963-annual-edition-am.htm

[Dan McEntee]

Heat range of the plug is also determined by the size of the "chamber" that the wire coil is in, in addition to the size and length of the wire. There can be long and short hot plugs. Plug length is just determined by how much meat in the head there is to cut threads. You can put a long reach plug in an engine where a short reach belongs by adding a washer or two or some other type of shim. A friend of mine almost lost his first pipe ship because some one told him a shorr reach K&B plug was a hot plug and he tried it in his .40 piped engine. Almost lost it when it flamed out on the first reverse wing over. The plug didn't extend far enough into the combustion chamber. It has all been covered before here on the forums, just gotta find it.
   Type at you later,
  Dan McEntee

[Jim Kraft]

See How we are responsible as model flyers. We had catalytic converters on our engines long before cars. At least we do not need oxygen sensors, yet.

[frank williams]

Ty – There are cold plugs that are long reach and hot plugs that are short reach.  In general long or short doesn’t play a part in plug temperature range.  The idea that a hotter plug is longer may come from the four cycle plugs that have an extended nose or what I call “hose nose”.  Of course a longer element wire will have more surface are and be considered hotter.  Maybe that is where the idea of long being hotter.
 
I use to regularly mill about 60 thou out of the plug seat on the ST60 heads.  This made the plug poke deeper into the combustion chamber.  I felt I got a hotter ignition and a better run on inside maneuvers on the ST. 

Also, catalytic converters are a mixture of platinum, iridium, and rhodium.

Gaz049 – Good idea using a PIC with a IR detector …. Remember it’ not just the temperature of the element with a battery attached, but the change that takes place in the presence of methanol vapor.  What we are looking for is the relative effect of one element  vs another as it catalytically reacts with the fuel.

Dave – thanks for the Netzeband article … I’ve been looking for a copy of it.    I found the video very interesting also, everyone should study it to understand that there is no battery involved to make the platinum wire glow brightly.  He did initially heat it slightly with a torch to warm it up, but after that all the heat came from the catalytic reaction.

Dan – I think the “big bore” plugs with the increased recess for the element probably allow the methanol vapors to more easily circulate around the element wire.  I should add that I did strip out a few ST60 heads when I recessed the seat.  Also, the hard inside turn into a wingover, has drowned more that one piped stunt ship.  That turn needs all of the ignition you can get.

[Tim Wescott]

...
The plug manufacturers mark their plugs as hot, medium, or cold.  I assume the greater the area of the element wire in a particular plug, the hotter the plug, or the greater the catalytic action.
...

Hot vs. cold refers to the length of the path that heat has to take to cool the plug element (more properly, I suspect, it refers to how much thermal resistance there is from element to frame).  A hot plug is one that conducts less heat away from the plug element, a cool plug conducts more.

This is the same rule for automotive spark plugs, BTW.

[EricV]

Since there is no electronic ignition in our little 2 cycles, I've always had a belief that the glow plug depth and heat range acted to either advance or retard the ignition timing, just like turning your distributor used to on your old car back in the day. Or if you ever played with a little model external combustion engine, and let the flame get closer and further away, you get the idea.

Compression is the other factor that effects ignition timing, higher compression advances the timing of the boom... so the longer plug not only puts the heat closer to the fuel and compression center, it also takes up a non-insignificant area of the chamber, also raising compression a tad.

In a car, advancing the timing always gave more instant throttle response, retarding the timing killed your low end torque, but gave much better fuel economy, that is why Mallory had the mechanical advance dual point, then vacuum advance came out, then MSD and Electronic ignition, to allow having the best of both worlds with a hot spark and variable timing.

I've always felt you should run the plug that lets you run the fuel you want in order to get the run you want. Oil raises compression too in our motors... but with modern engines, I don't need as much and it kills fuel economy. I don't want to HAVE to run 15% or 20% nitro in my engines, so I run enough compression and mostly synth oil to work with the range I like, 7% to 10% most normal conditions, and 5% for King Orange weather. I can pretty much run 7% year round by switching between an Enya #3 & Enya #4 in cool and hot weather, only needing 10% like at Muncie in July heat or similar days in Florida.

I did some experimenting a while back for a friend and I made a simple tool for measuring glow plug depth, because he was getting flame-outs, and we found we could minimize his particular issue with a particular plug that reached deep into the chamber and protected the element (and Arden hose nose Hot I think? I forget the model number)

But after all that, for me personally, it boiled down to me pretty much running the box stock setup that Randy has recommended from the beginning of time... 5% to 10% nitro range, mostly synth with a bit of castor fuel, Enya #3 or #4, depending on the weather, set the pipe by the chart, pitch the prop until it works, then forget about ever touching it again and go fly.

EricV

[frank williams]

 

But I am not actually sure where this thread is going, or why.   

Anyone have any thoughts on measuring the “hotness” or “coldness” of a glow plug?  I would sure like to see a quantitative assessment of current glow plugs.

Is there some way to quantitatively measure which plug is "hotter" than another, as opposed to just reading the label on the package and believing it, or flying them all and making a personal assessment of how it performed.

[Howard Rush]

This is a cool project. I like the idea of measuring filament temperature by measuring resistance. Then I guess you could determine catalytic effect as a function of filament temperature and area. Would you want to do the measurement in a running engine, rather than in a flagon of methanol vapor? 

If you like, I can probably make you a circuit to measure plug resistance.

I don’t know if filament temperature would suffice to determine plug hotness. Both making the filament more available to the fuel mixture by lowering the plug and making it less available by shielding it (and increasing its temperature) seem to make the plug “hotter “.  Maybe you need to measure ignition advance more directly, as I think Eric suggests. How about putting a pressure sensor in the head and comparing pressure to shaft position on a sillyscope?

Any measurements in a running engine would probably be a strong function of needle valve setting. The upchuck of your experiment could be a thing that enables you to set the needle valve by plug resistance, rather than RPM.

[Tim Wescott]

This is a cool project. I like the idea of measuring filament temperature by measuring resistance. Then I guess you could determine catalytic effect as a function of filament temperature and area. Would you want to do the measurement in a running engine, rather than in a flagon of methanol vapor? 

If you like, I can probably make you a circuit to measure plug resistance.

I don’t know if filament temperature would suffice to determine plug hotness. Both making the filament more available to the fuel mixture by lowering the plug and making it less available by shielding it (and increasing its temperature) seem to make the plug “hotter “.  Maybe you need to measure ignition advance more directly, as I think Eric suggests. How about putting a pressure sensor in the head and comparing pressure to shaft position on a sillyscope?

Any measurements in a running engine would probably be a strong function of needle valve setting. The upchuck of your experiment could be a thing that enables you to set the needle valve by plug resistance, rather than RPM.

Measuring temperature by resistance should be OK-ish, although it presents all sorts of practical difficulties.  You may need to calibrate the resistance vs. temperature curves differently for different plugs -- I'm not sure how much that'll change with different alloys.  Some sort of take on a PTC circuit should work, although you're starting at a much lower resistance.

Rather than a pressure sensor in the head, you may be able to determine the moment of firing with a ping sensor from a car -- assuming that such things aren't larger than one of our engines.  You could correlate that with engine angle using a magnet in the spinner and a hall-effect sensor.

[Istvan Travnik]

Dear Friends,
I do not want to write too much "offtopic" things, but I think the final goal is to better handle the ignition features of our glowplug engines.
Well, not the plug is "everything" in this battle, but many other tiny elements in and around the combustion chamber and cylinder head.
Maybe most of you have  seen "RETRO 60" engine combustion chamber, with that titanium "deflector" or "fender" close to the plug, shading it partially, and glowing dark red during the working time of engine.
Upon this idea I made several inserts into combustion chamber (different material and shape), and I was able to adjust very precisely the ignition features of my engine (MOKI-51, Schneurle, plain piston). I use it for at least 5-6 years. Summarizing, all my glowplug troubles ended forever.
Upon your request I can load up some photos.
Maybe here, or shall I start a different topic about?
Istvan
 

[Dan McEntee]

Dear Friends,
I do not want to write too much "offtopic" things, but I think the final goal is to better handle the ignition features of our glowplug engines.
Well, not the plug is "everything" in this battle, but many other tiny elements in and around the combustion chamber and cylinder head.
Maybe most of you have  seen "RETRO 60" engine combustion chamber, with that titanium "deflector" or "fender" close to the plug, shading it partially, and glowing dark red during the working time of engine.
Upon this idea I made several inserts into combustion chamber (different material and shape), and I was able to adjust very precisely the ignition features of my engine (MOKI-51, Schneurle, plain piston). I use it for at least 5-6 years. Summarizing, all my glowplug troubles ended forever.
Upon your request I can load up some photos.
Maybe here, or shall I start a different topic about?
Istvan

      This would be good to see, and not off topic at all I think. Photos would be most informative, and I don't think I have ever seen what you are referring to. It gets my vote.
   Type at you later,
  Dan McEntee

[frank williams]

Istvan
I would very much like to see your photos.  I had heard that different metals (iron for one) in the combustion chamber could effect engine performance by reacting with the methanol vapors.  This was why I never felt that helicoils in the head were a good thing to be doing.

Howard
This could turn into something that might be Scott Bair worthy  He had the only model engine pressure traces that I have ever seen.  For sure some type of bridge would be needed to measure changes in plug resistance.

[Reptoid]

Hot vs. cold refers to the length of the path that heat has to take to cool the plug element (more properly, I suspect, it refers to how much thermal resistance there is from element to frame).  A hot plug is one that conducts less heat away from the plug element, a cool plug conducts more.

This is the same rule for automotive spark plugs, BTW.

This is accurate for spark plugs and affects the heat range greatly.
The cooling path has a much smaller effect on the heat range of a glow plug in a Methanol fuel based glow engine. There are many factors that are indeed hard to measure that affect this; Wire diameter, # of coils, diameter of coil winding, depth of coils in plug body, diameter of hole in plug body, alloy composition of element wire, total surface area of wire, total volume of wire chamber, alloy composition of glow plug stem, and even the color of the glow plug body.

[RandySmith]

As mentioned  3 things in general affect heat range
Size of the hole the element sits in
The formula of the wire, ie 30% rhodium wire runs hotter than 20% does
the diameter of the wire

Also the  depth as Frank mentioned has many times ,a good effect, sometimes not
Very thick shims will make them normally run cooler, very thin washers and they will run hotter, or cleaner
I have bought and ran almost all plugs over the years, and tried them in stunt runs, most as as labeled and the companies that make them really do know  hot from cold
A list of them , that are hot and work well for stunt is, and in no particular order :
Glow Bee  Rc long
Glow devil #300 rc long
Enya #3  #4
Merlin 2005
Merlin 2004
Thunder Bolt 4 cycle    ( 20% rhodium)
Thunder Bolt BIg Bore  2  and  4 cycle (30% Rhodium)
Thunder bolt #3 good for  wet 2 cycle runs
McCoy MC55
McCoy MC 59
OS A3   #8
OS type F
Rossi RC Hot
Rossi #1
Rossi #2
Thunder Bolt RC Long
SIG  RC long
OS LC 3
OS #8  is  medium and works well for engines running a hotter  wet 2 cycle
Fireball  HOT plugs are  good  IF you can find ones with good seal, They are mostly BAD on sealing plugs, and  most I have tried Still leak


On Engines I setup, I normally machine a  "heat dam" around  the glow plug,  this makes the glow plug  retain much more heat than normal. Works well  to keep the engine running cleaner, and allows still full use of fins  to help cool the head and engine as much as possible. 

Strange looking but in cold winter months I have turned the  loop charge motors head, sideways, so the fins are not as efficent, helps keep heat in the plug too, I do not recommend this  , but it works.

I will add more if I remember them, I did not add  FOX plugs

Randy

[Istvan Travnik]

Dear Dan and Frank, & Friends,
here are some quick photos on the deflectors (one old, used, one new, unused).
Instead of telling a long-long story, finally I found that aluminum piston engines are too cold inside to achieve the proper behaviour (quick and safe change towards-backwards between 4 and 2 cycles).
With these tiny pieces I can keep temperature high enough in the combustion chamber.
I wanted to keep power high enough, too. I fly now with Xoar 13X6 electric. Engine is .51 . I think it is o.k.
Special bonus: one plug lasts at least for 300 flights.

[frank williams]

Istvan

Thanks for sharing the info ....

Are the deflector discs aluminum, titanium, steel or other material? 
Does the disc function to "hold heat" in the combustion chamber as well as blocking the plug element from incoming raw fuel?.  The holes in the disk allow for circulation of the charge and sizing of the thermal area for the disc, I assume.

Frank

[Lauri Malila]

I use a titanium umbrella. I tried stainless steel but iit won't last very long. Next material to try is zirkonium.

Lauri

[frank williams]

Lauri
Beautiful work ...
... can you describe to me the engine run anomaly that the umbrella fixes? 
... how is the umbrella attached to the head material?
Frank

[Garf]

Maybe this will help.

[frank williams]

Garf
Very interesting ..... all a bit different .... Thanks for the pictures ..... how many thumbs did you grind off getting these sectioned?
Frank

The Nelson plug I assume is bigger diameter than the rc car "turbo plugs"  both utilizing a pipe thread seal to improve performance.

At a Nats back in the 80's I got hold of a special head for the Nelson 15 Goodyear motor.  I think it was probably the year before he came out with the plug.  The special head was the same combustion chamber and all dimensions the same except that the drill for the 10-32 tap of the glow plug hole was undersized.  This made for a head that you could not screw the plug in by hand.  It was too tight.  You had to use a plug wrench to get the plug into the head.  That simple change was a 500 rpm max rpm increase.  This took me about 15 minutes to accomplish to r and r the head, so there was no guessing at the experiment.  Obviously ultimate power was being lost through the threads of the head/plug.

Which leads me to .... has anyone in stunt made a head that will accept a "turbo style" plug.  Since the turbo plug is slightly bigger diameter ... could a regular head be retrofitted by drilling and making a seat for the new plug?

The "seat" of the Nelson plug is where the increased performance comes from ... true not a one to one comparison, stunt to speed or racing, but neither want a source of power loss.

[Dave Hull]

Frank,

And before someone starts to say that the 500 rpm was due to different heat flux between the nelson plug and the head, I would note that we have found a similar performance change when changing from a head that loosely fit the liner, vs one that was a very snug---but non-distorting---fit.

Randy,

No need to rotate the head to reduce the convective heat transfer on a cold day. On a profile, just slip O-rings over the cylinder fins. Keep adding until you get the thermal control you are after. On a cowled engine, just partially tape over the air inlet. Blenderm tape works nicely. Leave the engine together and happy....

Dave

[Brett Buck]

Beautiful work ...
... can you describe to me the engine run anomaly that the umbrella fixes? 

  The same one you found and fixed by mounting the ST60 with the cylinder inboard, I think - he fixes it at the business end rather than preventing it from happening at all. The Discovery-Retro has something similar.

   Brett

[Brett Buck]

I use a titanium umbrella. I tried stainless steel but iit won't last very long. Next material to try is zirkonium.

  Stainless steel doesn't last? Why, fatigue? If so, zirconium isn't likely to be any better.


    Brett

[Lauri Malila]

Frank,

I don't know exactly which mechanism is dominant, but the umbrella somehow keeps burning process more stable, by either pre-heating the mixture before full combustion or just shading the plug from cooling fuel mixture.
Whatever it does, it effectively removes the hysteric behaviour from 4-stroke in beginning of maneuvre and especially after it. 4-stroke mode is inherently unstable and pretty sensitive to temperature variations.
My engine does not do much 4-2-4 shift, but rpm changes from 4-stroke to maximum in more linear way. At the moment I'm working on a baffle-piston version that should behave more in a classical 4-2-4 way, so propably I'll get more clear test results between umbrella- and no umbrella heads.
The umbrella is pressed to #2024 aluminium head *very* tightly, with 0,1mm interference fit (2,00mm dia pin to 1,90mm hole, 4mm deep.

Lauri

[Lauri Malila]

Brett,

The stainless steel (316-something) started peeling or corroding after a few dozen flights so I abandoned it.
Zirconium is interesting because when heated in a flame, it forms an extremely hard and slippery oxide layer. If it stays like that in combustion chamber, it may stay cleaner from carbon buildup.
(Zirkonium is also funny because when titanium shavings have a risk of combusting during machining, zirconium does not have a risk. It WILL combust.) L

[Dan McEntee]

     Randy Smith,
    "On Engines I setup, I normally machine a  "heat dam" around  the glow plug,  this makes the glow plug  retain much more heat than normal. Works well  to keep the engine running cleaner, and allows still full use of fins  to help cool the head and engine as much as possible."

     Hi Randy;
  Just to clarify, this is opposite of what it sounds like? You just remove material to reduce the heat sink properties of the aluminum? The words "heat dam" implies that something is added or built up like a literal dam to hold heat in.  I have heard of turning the head a bit or 90 degrees before, just have never felt the need to try it. In cold weather I'm usually just trying to keep it out of the dirt and don't pay real close attention to the engine run! Just get it up and down!
   Type at you later,
    Dan McEntee

[Lauri Malila]

Dan,

Just look at the last photo on my post (#20), that's a heat dam. I just did not mill it all the way around, had to leave some material where to press the umbrella. I usually do it with 2mm milling cutter, leaving 1..1,5mm material between groove bottom and top of combustion chamber. L

[Brett Buck]

The stainless steel (316-something) started peeling or corroding after a few dozen flights so I abandoned it.

   

   That's remarkable! I am stunned that anything going on in the very mild conditions of a model engine, with very mild solvents and relatively low temperatures, would have significant corrosion issues. We use stainless immersed in very strong acids and moderately high temperatures for decades with only mild leaching of ferrous metals from the matrix. Titanium does handle it better, but stainless is OK for at least many months/year. And I would expect 316 to be a good choice.

   Let me ask this - is this happening after a few flying sessions (run, put away for a week, run some more, fail)? Or is it simply due to working (fails or degenerates in a single session)?   What sort of passivation or pickling are you using (if any)?  Where does it fail/peel - on the "struts" or on the "umbrella" end?

     I ask because the only way I can see this happening is that the passive layer that normally forms is getting mechanically damaged somehow (fatigue on the "struts" from the vibration and flexing), and is then prevented from re-forming by the oil. It might be improved by reducing the thickness/mass of the "umbrella", reducing the flex and raising the frequency. If it is there to just block the charge from going straight to the plug,  or some internal ballistics effect, the mass shouldn't matter.

    If it functions by creating a heat reservoir, titanium (and maybe zirconium) might not work the same way. It's not obvious whether the relatively poor thermal conductivity of titanium would hurt or help. I presume neither because I think the action is the blocking action (like a super-duper idle bar). I would remove it and try a "hose-nose" plug, myself.

   Fascinating issue, and not what I would have expected.

     Brett
 

[frank williams]

Just to confuse things a little ..... after watching the platinum wire glow in the video above ... just in the presence of the alcohol vapor ......
..... I hooked an old glow plug with jumpers to a voltmeter ..... I then took a propane torch and briefly heated the glowplog element ... it just took a second to make it glow ......
..... sure enough,   "wait for it" , a voltage was produced (~ a milli volt or so) no battery involved .... some kind of thermoelectric reaction .... interesting, ... very interesting .....
Frank

[Howard Rush]

Just to confuse things a little ..... after watching the platinum wire glow in the video above ... just in the presence of the alcohol vapor ......
..... I hooked an old glow plug with jumpers to a voltmeter ..... I then took a propane torch and briefly heated the glowplog element ... it just took a second to make it glow ......
..... sure enough,   "wait for it" , a voltage was produced (~ a milli volt or so) no battery involved .... some kind of thermoelectric reaction .... interesting, ... very interesting .....
Frank

That would mess up any resistance measurement I could do.

[Istvan Travnik]

Uhh,
I think this deflector-story is more interesting, than I expected.
Well, in the ancient times, some good old (and lazy-to-think) friends of mine made me calm: "Schneurle engines are not for stunt, only baffled pistons are...") .
In my praxis the normal steel deflector had been burn in half, after ca. one hundred flights. (Central part became half thick of that I made it.)
I had no problems with aluminum alloy (former Hungarian coins), and no problems with stainless steel, too.
My basic idea was interchangeability (even on flying site), and playing with the shape, mostly with the width of three "bridges", which are conducting the  heat from the center part to the cylinderhead.
 

[Dan McEntee]

   This is an interesting thread. I had never heard of this before and had no idea anyone was using this technology. It makes me ask one question, though. I have used idle bar plugs, (mainly Glow Devil R/C longs) for quite a while, because they seem to run much better and last a lot longer. No real scientific proof, just from my experience. The idle bar is a spot welded on piece of, I assume, steel? It just seems to turn black with carbon over time. My reasoning for using these also included the idea that the idle bar gave carbon and other junk a place to call home, instead of fouling the element. Is it possible that the idle bar is have the same effect as the umbrella and such? Not to the same extent, certainly, but since it is located where it is during the running cycle, and my experience that my engines just "seem" to run better, could that little improvement be from this effect?
   Type at you later,
    Dan McEntee

[Istvan Travnik]

Dear Dan,
I think, that opinion is right which says that the main destructive effect against the coil is some supersonic shockwave which starts from top of the piston. When we shade the coil, this shockwave cannot destroy it too soon.
Since I have no neutrographic microscope (only nuclear laboratories have that) I cannot say "yes" or "no" to this idea but I near to afford it...

[Brett Buck]

I m well and truly amazed - if the steel "umbrella" wears away, and aluminum does not,  that certainly does suggest some sort of chemical process.

   Another thing I am amazed about - we have been running schnuerle engines with completely conventional squish band heads, no idle bars, or nothing at all in the head for about 20 years now. We have had exactly one minor problem that we could not solve with external (i.e. setup, venturi type, and oil contest) factors, that having been later completely solved, perhaps by accident, by a proprietary method that has *nothing* to do with the glow head end of the system. My engine will grind through 100 patterns of a row with it set to never touch a 2-stroke with no "anomalies* if I set it that way. And I have had that work that way on three individual engines, two of which are identical and the third very close but with a 4 degree difference in the exhaust duration. They run slightly differently but nothing that suggests I need to cover the plug up. 

  So the question becomes ( and I am not saying you guys are wrong, I presume you know what you need to do and have solved the problems) - why is it so different?

   There are at least major three differences:
       We run at generally higher RPM and power levels, and I presume much cooler
      We run at much lower compression ratios (enabled/required by copious amounts of nitro...)
      We have pipe regulation

and one perhaps minor difference - our engines are run with the cylinder down instead of to the side. It runs about the same on it's side, so I discount it.

    Brett

p.s. are you sure there isn't something else in the fuel beyond just methanol and castor oil? Some sort of chlorine-containing chemical, maybe in the oil or other additives?   I have some experience running items (model airplane engines and otherwise) with non-AMA-approved fuel constituents, also with no ill effects, aside from chlorinated solvents which screwed everything up in short order.
     
     

[Istvan Travnik]

Dear Brett,
I cannot tell you anything else:
as I tried first pure normalsteel deflector, after aluminum ones (hoping a little bit higher temperature, by worse heat conducting by "bridges",
at the end of flying season I disassembeld, and started to clean the middle part from residue of oil (I don't use Castor, it was some PAG-based).
And after scratching off that black, carbonized coat, I found typical brown iron oxide - Fe2O3 or Fe3O4...
When it was cleaned too, the steel was half thick than original.
Stainless steel deflector cannot get oxidized (my deflectors are 1.00 millimeter thick exactly.)

About Schneurle story of my engines: this is too long, I fly with normal silencer, no pipe.
Istvan

[Brett Buck]

Dear Brett,
I cannot tell you any thing else:
as I tried first pure normalsteel deflector, after aluminum ones (hoping a little bit higher temperature, by worse heat conducting by "bridges",
at hte end of season I disassembeld, and started to clean the middle part from residue of oil (I don't use Castor, it was some PAG-based).
And after scratching off that black, carbonized coat, I found typical brown iron oxide - Fe2O3 or Fe3O4...
When it was cleaned too, the steel was half thick than original.

  Remarkable! You have to be burning the fuel at much, much higher temperatures that we are. I wonder if you are getting *water* in your fuel, specifically, if there is water from the "oil", since it's either water-soluble or at least has an affinity for water. That and the very high temperatures, maybe that is enough.

    I would be curious if the same thing happens if you use castor, or mineral-based synthetic, instead of glycol-based.

      Brett

[frank williams]

Well .....
... at least one of the elephants in the room is ...
... if platinum is good .... why doesn't just a two plug head solve all problems?
Frank

[Istvan Travnik]

Dear Brett,
I think this question (about possible water appearance) was solved now automatically: I will bind myself to use MOTUL Micro 2T, nothing else. As I know this is Ester -based, and a little bit more heat resistant than PAG oils.
I won't return to castor, since it is a great effort/pain to make silencers by myself, and I am up to throat cleaning them after castor. 

Dear Frank,
In the ancient times Merco (from the UK) made very impressive looking double plugged engines (maybe .35 and .50), without remarkable success in C/L stunt...

[RandySmith]

Frank,

And before someone starts to say that the 500 rpm was due to different heat flux between the nelson plug and the head, I would note that we have found a similar performance change when changing from a head that loosely fit the liner, vs one that was a very snug---but non-distorting---fit.

Randy,

No need to rotate the head to reduce the convective heat transfer on a cold day. On a profile, just slip O-rings over the cylinder fins. Keep adding until you get the thermal control you are after. On a cowled engine, just partially tape over the air inlet. Blenderm tape works nicely. Leave the engine together and happy....

Dave

Hi Dave

I have done that too, however turning the head  was quick and easy, especially if you do not have the right size O rings,  Both work OK , You can also use a slice of beer can  and 2 pieces of copper wire

Regards
Randy

[RandySmith]

     Randy Smith,
    "On Engines I setup, I normally machine a  "heat dam" around  the glow plug,  this makes the glow plug  retain much more heat than normal. Works well  to keep the engine running cleaner, and allows still full use of fins  to help cool the head and engine as much as possible."

     Hi Randy;
  Just to clarify, this is opposite of what it sounds like? You just remove material to reduce the heat sink properties of the aluminum? The words "heat dam" implies that something is added or built up like a literal dam to hold heat in.  I have heard of turning the head a bit or 90 degrees before, just have never felt the need to try it. In cold weather I'm usually just trying to keep it out of the dirt and don't pay real close attention to the engine run! Just get it up and down!
   Type at you later,
    Dan McEntee

Dan

Yes  the  aluminum is  removed from around the outside of the glow plug head area,   so it now  filled with  air, instead  of solid aluminum, which pulls heat from the plug, The  removal of the  metal  makes the plug run hotter.

LOL if you really want a "hot" chamber, machine a head button out of a ceramic material, ..extreme heat increase.

Randy

[Dave Hull]

I didn't have much luck with MACOR ceramic parts. Not sure our machinists had the knack for it. The parts were very fracture sensitive--and thus not usable. But they would have been excellent thermal isolators....

The theoreticians get worked up periodically about building IC engines with a ceramic block and top end. They envision running much, much hotter and benefiting from the thermal efficiency. And yet we still have aluminum and cast iron....

I haven't had to resort to the beer can and wire thermal shield yet. The O-rings are practically de rigueur on F2CN diesels, which suffer greatly from not being cowled, and thus are very difficult to get hot enough to hold a setting. I would note though, that the earlier Nelson 15 diesels with the old metals technologies would hold a setting and perk along perfectly. In contrast, the AAC versions are a battle. For glow, about the coldest weather I've flown in was about 50F, and no real changes were required.

Dave

[Lauri Malila]

Well .....
... at least one of the elephants in the room is ...
... if platinum is good .... why doesn't just a two plug head solve all problems?
Frank

..something like this, Frank..? L

[Chuck_Smith]

I didn't have much luck with MACOR ceramic parts. Not sure our machinists had the knack for it. The parts were very fracture sensitive--and thus not usable. But they would have been excellent thermal isolators....

The theoreticians get worked up periodically about building IC engines with a ceramic block and top end. They envision running much, much hotter and benefiting from the thermal efficiency. And yet we still have aluminum and cast iron....

...

Interesting. We use ceramic coatings and parts on race car engines, but for different reasons. Mostly we're trying to keep the heat from moving from the top to the bottom or radiating to the CF matrix of the surrounding parts and softening them. This of course causes overheating issues on the top end - leading high cooling flows - leading to the use of mechanical seals - leading to -, you get the picture. It's the old trade-off, by the time you add the required extra parts and parasitic losses to the system to make the new parts work it may be a giant step backwards.

One of the Formula 1 teams we worked with tried to use neodymium in place of samarium cobalt in the ERS system for it's higher magnetic strength, but since the neo doesn't hold it's properties to as high a temp as SmCo they encountered crippling issues that made them uncompetitive and unreliable. So a classic case of where the "better" material doesn't always yield superior results.

Chuck

[Istvan Travnik]

Beautiful work, Lauri!
Have you try to mount on this cylinderhead in different positions? If yes, which one was better?
Istvan

[frank williams]

Lauri
I agree ..... beautiful work ....
US stunt flyers would rather "eat worms" than run an engine in any other configuration than cylinder down, although it works better in a sidewinder mode.
Frank

[john e. holliday]

Especially if the head of the cylinder is pointed towards the pilot.

[frank williams]

Doc
Sidewinder is kinda like belly buttons ..... you got your innies and your outties ....