Go Back  PPRuNe Forums > PPRuNe Worldwide > The Pacific: General Aviation & Questions
Reload this Page >

How to thread drift in 720 posts!!!

The Pacific: General Aviation & Questions The place for students, instructors and charter guys in Oz, NZ and the rest of Oceania.

How to thread drift in 720 posts!!!

Old 2nd Apr 2014, 10:23
  #21 (permalink)  
 
Join Date: Aug 2013
Location: AUS
Age: 39
Posts: 39
Likes: 0
Received 0 Likes on 0 Posts
you must hypothetically be getting paid the big bucks for all that
GTang is offline  
Old 2nd Apr 2014, 12:25
  #22 (permalink)  
 
Join Date: Jun 2011
Location: Perth
Posts: 146
Received 0 Likes on 0 Posts
I love a good debate

Jabba,
Champion provide both a tool and a procedure for gapping fine wires see here:
http://www.championaerospace.com/ass...nical/93-2.pdf

There may have been some misunderstanding in my last post, i thought you were advocating for annual only on private aircraft with engine monitors and fine wire plugs hence my comments regarding eyeball inspections and magnetos.

The mention of magnetos at the start of your paragraph on plugs led me to believe that you felt plugs were sum of ignition system maintenance.

I have never had a problem with massive electrode plugs gapped properly every 100 hours, although few do this properly.

Unfortunately you seem to be conducting the tempest resistance check on champion plugs. This test works fine on tempest plugs which have a ceramic resistor (linear resistance). Unfortunately champion use a silicone carbide resistor (not carbon pile as suggested by Tempest - true carbon pile were phased out in the early 90's).

Silicone carbide resistors are generally NON-LINEAR in resistance and optimized for resistance at operating voltages so they would need to be tested at operating voltage/conditions.

Champions advice here is simple if the plug is making a proper spark when tested in a properly calibrated (there is a procedure) plug tester then the resistor is doing its job. Using the tempest procedure on champions is just wasting potentially good plugs.

http://www.championaerospace.com/ass...ical/72-10.pdf (yes this is old)

Incidentally tempest based the resistance value on the spark-plug MIL-SPEC, since the mill spec is a production standard this is hardly appropriate for maintenance. (Like maintaining your aircraft using the original build specs instead of wear limits). The last revision of the MIL-SPEC was 1990 and it does not include iridium plugs as far as I can tell.
Progressive is offline  
Old 2nd Apr 2014, 21:51
  #23 (permalink)  
 
Join Date: Nov 2000
Location: Salt Lake City Utah
Posts: 3,079
Received 0 Likes on 0 Posts
Debate is good.

My personal view is that “silicone [silicon perhaps?] carbide voltage dependent resistors” are comprised mainly of unicorn farts and reptile lubrication, but let’s concentrate on the laws of physics and the results of empirical testing.

The laws of physics dictate that before the spark, the voltage in the ignition secondary circuit is the same up to the plug tip, whether the resistor in the plug is 1 Ohm or 1,000,000 Ohms. It’s an open circuit at the plug tip.

When the voltage in the secondary builds sufficiently to jump the gap, current flows in the secondary circuit. I haven’t the formula at my fingertips, but the laws of physics dictate that the voltage must build to about 2,000 to 2,500 to jump a 0.018 gap. The spark itself has low resistance.

It must be at this point onwards that the resistor in the plug does its high voltage-dependent magic. Before the spark the voltage across the resistor is zero.

The laws of physics dictate that, after the spark starts, the current flowing in the secondary circuit and the voltage at the plug tip are determined by, among other things, the resistance of the resistor in the plug. (The secondary coil has resistance as well.)

The higher the resistance, the lower the current and the greater the voltage drop across the resistor.

And the important bit: The higher the resistance, the weaker the spark and the shorter the duration of the spark.

There is a very strong correlation between Champion plug resistors that measure very high on a ‘standard’ low voltage Ohmmeter and improvement in engine performance when replaced with a plug that doesn’t measure very high. My personal view is that the resistance measured by a ‘standard’ low voltage Ohmmeter is an analogue for what’s happening at higher voltage. Whatever is the actual cause, the change in performance is a fact.

I’ll bet your bench test doesn’t measure strength and duration. And there are lots of plugs that pass bench tests and fail LOP at altitude.

By the way, an expert in high voltage circuits (he has the patent for the Taser technology) did a test on one of his plugs. The spark jumped around the resistor in the plug. Imagine how high the voltage had to get to do that, and imagine what that was doing to the coil in the magneto.

And there ain’t no engineer coming anywhere near my fine wire plugs with gapping tools. (No debate.)

Last edited by Creampuff; 2nd Apr 2014 at 22:01.
Creampuff is offline  
Old 2nd Apr 2014, 23:26
  #24 (permalink)  
 
Join Date: Feb 2006
Location: Melbourne
Posts: 1,693
Received 0 Likes on 0 Posts
The laws of physics dictate that, after the spark starts, the current flowing in the secondary circuit and the voltage at the plug tip are determined by, among other things, the resistance of the resistor in the plug. (The secondary coil has resistance as well.)
The voltage of the secondary circuit is primarily determined by the rate of collapse of the magnetic field of the primary circuit. This might be Faraday's law. I forget. Its part of the reason that point gap & condition is important.

I think spark voltage is around 20,000 volts but might be as high as 40,000 volts. If the primary side draws 10 amps (guess, I'm not sure what the real figure is) then the secondary current will be 0.003 to 0.006 A.

Using V=IR if the plug resistance is 5 k Ohm, then the voltage drop due to the resistor will be 5000 * 0.006 = 30 volts. Hardly significant.

I think plug performance is about the insulator and its integrity. I suspect that plug resistance might just be a metric of insulator condition.

The resistor is there for suppression of radio interference. So, I think its real job is to damp some of the transient voltage spikes that surround the main spark voltage.

Here is a bit of an explanation by NGK

PLUG STUDIO / NGK
Old Akro is offline  
Old 3rd Apr 2014, 00:50
  #25 (permalink)  
 
Join Date: May 2012
Location: Sydney
Posts: 71
Likes: 0
Received 0 Likes on 0 Posts
DO NOT try to gap fine wires, because they do not need it and NO you can't buy tools for it. The ones you buy are for Massive Electrode plugs
Is this what you teach at your pilots courses?

Not enough information here mate. Without further details, this information is not accurate. Disappointing to see you post this.
Aviater is offline  
Old 3rd Apr 2014, 02:29
  #26 (permalink)  
 
Join Date: Nov 2000
Location: Salt Lake City Utah
Posts: 3,079
Received 0 Likes on 0 Posts
Not sure I agree with your numbers or logic there, OA.

The spark event occurs when there is zero current flow in the primary circuit. That’s what causes the collapsing magnetic field in the primary coil and consequential build up of voltage in the secondary coil. The amount of primary current therefore seems irrelevant to how much current flows in the secondary during the spark event.

There is a very useful waveform at this link: Engine Management - Primary versus Secondary Circuits (see figure 1.0).

The red line is the secondary voltage, and the scale for that is on the right hand side.

The primary voltage and secondary voltage build up quickly when the current stops flowing in the primary (on most steam-driven GA engines, that’s when the mechanical points open).

Then the spark happens. The spark event is happening during the approx 1.1 milliseconds during which the measured secondary output voltage is about 2,500 volts. (The ‘ringing’ happens when the spark stops. Current ceases in the secondary circuit and coils do what coils do when current stops flowing through them.)

During the spark event the ‘sparked gap’ has very low resistance. Therefore the amount of current flow depends on the total resistance in the secondary circuit.

If we assume the plug resistance is 2,500 Ohms (to make the numbers simple), the current flowing during the spark event is 1 Amp.

(E = IR; I = E/R; E = 2,500 volts; R = 2,500 Ohms; I = 1 Amp.)

However, it’s not quite that neat. For example the secondary coil has resistance as well. The tech data suggests that a ‘normal’ coil secondary resistances have a broad normal range that varies between brands, but the very rough average is about 10,000 Ohms. Also, inductive circuits do really weird things ...

However, the spark event is for most intents and purposes a (very short) DC event. The voltage necessary to bridge the spark gap will always be the same but, once it sparks, the amount of current flow in the secondary circuit is determined mostly by the voltage and resistance in the secondary circuit. The higher the plug resistance, the lesser the current flow during the spark event. The higher the plug resistance, the ‘weaker’ and ‘shorter’ the spark.

Of course, these aren’t ‘1’ or ‘0’ things. There is so much ‘slop’ in these systems that it’s a slow deterioration.

But you can feel it in your nether regions and see it on the engine monitor, eventually. And there’s lots of real world experience that shows that if you throw away ‘that brand’s’ plug if the internal resistance measures in excess of 5,000 Ohms on a ‘standard’ low voltage multimeter, the problem goes away (even if the plug was squeaky clean and perfectly gapped, and even if it sparks on the test bench).

Aviater: From the first link in Jabba’s post:
For fine wire iridium plugs, setting the gap is rarely an issue. … If you do try to bend the fine wire ground electrode, you’ll probably break it. …
Ain’t no engineer going anywher near...

Last edited by Creampuff; 3rd Apr 2014 at 03:13.
Creampuff is offline  
Old 3rd Apr 2014, 04:39
  #27 (permalink)  
 
Join Date: Jul 2011
Location: nosar
Posts: 1,287
Received 23 Likes on 12 Posts
Is this what you teach at your pilots courses?
No, this is not what he teaches. What he does teach is awesome! Take it from someone who has attended.
Aussie Bob is offline  
Old 3rd Apr 2014, 07:31
  #28 (permalink)  
 
Join Date: Feb 2006
Location: Melbourne
Posts: 1,693
Received 0 Likes on 0 Posts
creampuff. That's pretty technical for a bush lawyer!!

The voltage in the secondary coil is generated by the collapse in the magnetic field of the primary coil and is dependant on the rate of collapse of the magnetic field. Its governed by Faraday's law of Induction. I guess you could say that the magnetic field has collapsed with the current is zero, but its about the magnetic field, not the current.

I used 10 amps in the primary only to make an estimate of the current involved in the spark. But I think I got it wrong. I think energy should be the common parameter not power as I did. It did take me 2 goes to pass my electrical engineering subjects!

The point I was trying to get to was that the amount the spark voltage is diminished by the spark plug resistor is dependant on the current. And the current is bugger all, so the voltage drop from the spark plug resistor is small.

My good friend Google tells me you need a minimum of 12,000 - 25,000 volts for a spark which is consistent with other figures. I think your 2,500 volts might have a decimal point wrong. The Bosch handbook will be the oracle, but its at work. I'll check later.

The point I was trying to make was that I don't think the resister per se is the issue. I think the changes in resistance you measure are indicators of insulation breakdown, not deterioration of the resistor itself.
Old Akro is offline  
Old 3rd Apr 2014, 07:35
  #29 (permalink)  
 
Join Date: Jul 2007
Location: in the classroom of life
Age: 55
Posts: 6,864
Likes: 0
Received 1 Like on 1 Post
Progressive, no worries I figured you had misread.

I have never had a problem with massive electrode plugs gapped properly every 100 hours, although few do this properly.
You might be surprised, usually around 75-80 hours you can tell the difference. I have proven this with many a set, and let them go past 100 and it is dead easy to spot. Most pilots would never know.


Silicone carbide resistors are generally NON-LINEAR in resistance and optimized for resistance at operating voltages so they would need to be tested at operating voltage/conditions.
OK this argument has been made before in the USA, however a few things come to mind. Confuscious say do not tell man something impossible when he is already doing it. Now besides the funny aspect, when you take a set of Champion fine wire plugs that the pilot says is running not as smooth as he thinks they should and you measure them, with the Tempest method, and they are anywhere from 100,000 ohms to 1,000,000+ ohms and you replace them, and yet the gaps were still fine, because they hardly wear at all, with a new set and it runs baby bottom smooth. What does that tell you?
It tells me that the non linear tests even though it is not at 20000 volts it is still detecting a sub optimal plug, so the end result is what matters.

Now I could say I do not have the test equipment here to go testing plugs at very high voltages, although I do have the gear here at work, I am not doing it. But what if i said I know a bloke who has?

Perhaps one of the founders/directors of the TASER company, who has or had a C421, might also have a 441, anyway after being semi stranded due poor plugs on the ground with family etc loaded aboard, he decided to do some research.

I think this guy is somewhat qualified, here is what he had to say; Max Nerheim (edited to remove irrelevant stuff for brevity)
I decided to take the Autolite UHRB32E (same as Tempest?) spark plugs I had from before I put in the Champion Fine Wire plugs, as well all the Champion fine wire plugs and test the continuity in them using a Digital Volt Meter (DVM). The Autolite plugs read from 1115 to 1351 ohms. The Champion plugs read from 1330 ohms (the one new plug) to open/infinity. So not only did the fine wire plugs crack, they also had resistive readings that were seemingly totally random!

I suspected the open readings were due to slight corrosion buildup between the elements of the Champion spark plug: The Champion spark plug is assembled with a resistive “slug” that is held in place by a spring and a screw, which (at least in theory) can both develop some surface corrosion. I thought, if there is just some slight surface corrosion, this would be no big deal as the magneto would “burn” a path through the bad contact areas, and the resulting “high voltage impedance” should be close to nominal. To test this theory I utilized a high voltage source (a TASER X26 stun gun), an oscilloscope, a non-contact current probe, and a 25kV high voltage/high frequency probe. The oscilloscope captured the current and voltage waveforms across the plug from the spark plug wire terminal to the front round electrode (not including the spark plug gap) during the high voltage discharge. The voltage and current readings were captured after all the “bad” circuit elements had been "burned" through. By using the captured voltage and current, the plug resistance during the firing of the plug could be calculated.
I tested all the plugs using this setup. The X26 is capable of generating up to around 50,000 volts, and had no problem jumping across the spark plugs (from the back spark plug wire connection to the round electrode on the front).

Using the High Voltage oscilloscope approach, all of the Autolite plugs measured within 11% of their corresponding DVM readings. Very nice. This demonstrated an acceptable consistency and also validated the approach.

The 16 Champion plugs (4 that were replaced initially, and the remaining 12) measured from 194 to 11,000 ohms using the oscilloscope method. A big surprise was that 6 Champion plugs measuring from 135 to 534 ohms. These plugs had all measured “open” on the DVM. When discharging the TASER across these plugs I noticed there was arcing noise within each spark plug. The arcing noise is caused by the TASER having to arc across an air gap. This caught my attention - why would the TASER have to arc across INSIDE the plug (the spark plug gap was not part of the test).

To investigate I opened up the Champion spark plugs by unscrewing the screw where the spark plug wire is normally inserted. The spring and the resistive element was then removed from the plug. With good access to the element I used a DVM with sharp test clips attached to try and measure the resistance of the element. OPEN!!! Well, it must be "surface corrosion" I still thought. I then attached the TASER X26 to both sides of the resistive element, and discharged the X26, hoping to observe the current going through the resistor, so I could measure the resistance. Instead, the X26 formed an arc on the outside of the resistor: Champion Fine Wire Spark Plug RHB32S resistive element testing - YouTube Each time the X26 discharged, a blue arc of ionized air formed across the surface of the resistor. The resistor element itself was completely OPEN. It did not conduct any electricity at all! Normally in a test setup like this, the current would flow through the body of the resistor, not arc across it. In this case, the resistor element acted as an insulator. Hence, spark plugs with “resistive” elements like this one would present the magneto with roughly a 0.5” extra spark gap in series with the approximately 0.02” spark plug gap! With this much extra gap to jump, there is not much point in arguing if a “proper” spark plug gap should be 0.02” or 0.03”!!! With my limited understanding of how a magneto works, I am also concerned regarding the possibility of the high voltage required to arc across a plug like this, could instead jump from the rotor to the next cylinder contacts (instead of to the current one). The probability of this happening would increase if the adjacent magneto contacts had normally working spark plugs. Hence, if one plug is bad and requires a much higher voltage, it is better if they are all bad!

The arcing across the resistive element also explains the very low resistive oscilloscope readings during my previous experiment: The X26 generates enough voltage to arc and ionize the air across up to around 2 inches through air or even longer across a partially contaminated surface. Once the air has been ionized the resistance of the air (gap) drops from “open” to close to zero (that is how a TASER device can across up to 2 inches of clothing.) The resistive element that was open also read “open” on the DVM TEST. I weighted the resistive element on a laboratory grade scale. It came in at 0.23 grams. The TASER X26 discharging 19 pulses per second for 5 seconds (compared to a magneto at 28 pulses per second continuously) through a working resistor made it too hot to touch. Is it a possibility that the resistor is too small to dissipate the electric energy from the magneto without degrading..? How much energy does a magneto put out? It sure seems like a good idea to have the plug resistor thermally and mechanically coupled to the spark plug body to help dissipate the electric heat (like the Autolite plugs).

Arcing Spark Plug Voltage:
I also measured the peak voltage necessary to arc across the various spark plugs. This was a slightly different test setup, as now the spark plug gap is part of the circuit. The voltage was measured from the spark plug wire attachment point to the body of the plug. In order to fire the plug, the magneto would have to put out this voltage in addition to the extra voltage needed to jump through the compressed air mixture present in the cylinders during compression – more cylinder pressures at higher manifold pressures requires higher magneto voltages. At ambient pressures the old Autolite URHB32E plugs measured somewhat consistent (nothing in High Voltage is entirely consistent) peak voltages from 6200 to 9300 volts. With the Champion RHB32S the voltages measured from 6300 to 17000 volts. With some of these I had intermittent arcing at the back connection of the spark plug – from the screw connection, across the ceramic to the metal body. In this case there would be no arc across the spark plug gap. Operating the spark plugs in a running engine with cylinders compressing the air would require a higher break-down voltage across the spark plug gap, and thus would make this condition more likely to happen.

Summary/discussion:
I think there are two separate problems with the Fine Wire Champions:
-Roughly half the plugs I removed had ceramic missing (1 plug) or cracked ceramic.
-Only one Champion plug read around 1300 ohms (this was the one new plug from Provo). The other 15 plugs, including 3 that were only “slightly used” (installed in Provo) displayed readings on the DVM from 4000 ohms to “open”. 9 of the plugs read “open”. I had only one plug out of 16 that read close to 1300 ohms. I would not use a plug that read higher that 1500 ohms.

FOLLOW-UP April 11

The TASER brand stun guns do have a current limit, which is why the output of these devices do not wary much depending on if they are discharged into a "short" or a high impedance load (fat person). Most of the cheap contact type stun devices use only a capacitor discharge across the front, and hence they are loud, and not current limited. Different technology.

Luckily I have access to equipment to measure high voltage and current at the same time, calculate the resistance of the spark plug resistor WHILE the current is flowing through it, and also measure the peak arcing voltage across the plug and across the resistive element. These measurements raised my concern. The engine will run fine as long as he magneto can jump across the burned out resistor AND the spark plug gap - without the rotor inside the magneto arcing to the next contact point. That scenario is my largest concern. I fly a pressurized twin to 28,000 feet, and am concerned about keeping the ignition system fault-free. As we all know, the lower air pressure at high altitude makes it more likely for an arc-over inside the magneto (to the next cylinder with a "good" spark plug requiring lower arc-over voltage).

I also thought there were inherent low-voltage effects that prevented the fine wire plug resistance from being measured by an ohm meter. I proved myself wrong: What makes the plug read a higher resistance (with an ohm meter) is not surface corrosion or effects from the type of resistor used, but rather that the resistive element is burned out. Notice that the only Champion plug I had that tested close to resistance specification was the ONE new plug I had. All the other ones had various resistances, up to infinity/open. The ones that read "open" were loud when I arced across the plug from back to front electrode. The plugs with low resistance reading, including all the old Autolites were "quiet" when I passed the current through them. After taking them apart, I discovered that the resistive elements were completely open. The loud arcing was the current having to arc across the resistor to make a connection.

I think the parts should work according to specification/theory. I am afraid that if my plugs malfunction at altitude I will be out a new engine.....
The mag check is done at lower manifold (cylinder pressure) and therefore require less spark-over voltage across the plug gap. At altitude I run higher manifold pressure, resulting in higher cylinder compression/pressures and therefore higher spark plug arc-over voltages. In addition, there is less air pressure in the magnetos, making the possibility of an internal magneto arc-over higher....
Jabawocky is offline  
Old 3rd Apr 2014, 07:48
  #30 (permalink)  
 
Join Date: Nov 2000
Location: Salt Lake City Utah
Posts: 3,079
Received 0 Likes on 0 Posts
OA

I’m pretty sure that the rough approximation of the breakdown field for air is 33KV per cm, or 3.3KV for 1mm or about 1.7KV for 0.018 inches. (I realise the conditions in a cylinder are not quite the same as ‘free air’ but let’s not complicate things with that yet.)

But I'll have to confirm.
Creampuff is offline  
Old 3rd Apr 2014, 07:49
  #31 (permalink)  
 
Join Date: Feb 2000
Location: Alaska, PNG, etc.
Age: 60
Posts: 1,550
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by Jabawocky
and NO you can't buy tools for it. The ones you buy are for Massive Electrode plugs

Oh, Reeeeeeeaaaly???

Well, I'll be damned ! Somebody should let Champion Aerospace know. For some odd reason they are printing "fine wire gap tool" on This tool. Not sure what it is, but I have one in my tool kit, and I've mistakenly used it for setting the gap on my fine wire spark plugs.


Oh, disregard, I see Progressive has already addressed your inane twaddle.
A Squared is offline  
Old 3rd Apr 2014, 08:30
  #32 (permalink)  
 
Join Date: Feb 2006
Location: Melbourne
Posts: 1,693
Received 0 Likes on 0 Posts
Creamy, are you sure you chose the right profession?

The Bosch Automotive Handbook (Robert Bosch invented the magneto / spark plug system) says you need about 12,000 volts for a spark, but most ignition systems deliver about 30,000 volts.

It goes into some detail about the energy of the spark (0,2MJ is required) and the voltage profile. It seems modern systems need a sharp defined initial spark for what they call "flashover" followed by a continued lower voltage spark which "helps stabilise combustion".

It reminds us that the spark intensity required varies with A/F mixture, BMEP (ie turbocharging) and spark timing.

The debate on plug gaps also reminds me that a spark initiates more easily from a sharp edge. In the olden days (when we re-gapped automotive plugs rather than throwing them out and replacing them) part of the procedure was to file the centre and outside electrodes to get square edges again. This is impracticable with massive electrode aircraft plugs.
Old Akro is offline  
Old 3rd Apr 2014, 09:19
  #33 (permalink)  
 
Join Date: Jul 2007
Location: in the classroom of life
Age: 55
Posts: 6,864
Likes: 0
Received 1 Like on 1 Post
AxA

Yes I was wrong, despite having seen them in that Champion catalogue filed away.

Tempest do not sell one I should have said. As I was using them as reference material. My humblest apologies. Something about the president from Tempest telling me "do not gap them and we don't sell a tool to do it anyway" might be why And they do not encourage it because of damage to the tips.

Bottom line is they should not need gapping.

Will pay more attention to detail in future. Sorry!
Jabawocky is offline  
Old 3rd Apr 2014, 10:22
  #34 (permalink)  
 
Join Date: Nov 2000
Location: Salt Lake City Utah
Posts: 3,079
Received 0 Likes on 0 Posts
AO: My profession is "goat herder". I love my goats...

Max Nerheim is not a goat herder. He knows what he's talking about, and he's proved that, consistent with the laws of physics, you don't need anywhere near 25,000 volts to get a spark out of a good spark plug.

The secondary coils in a standard steam driven magneto can indeed put out lots of volts. Lots and lots of volts.

It builds up and up and up until it finds a path to earth ....

That's what eventually kills coils.

I prefer to use plugs that put the least stress on the coil for the best spark.

A squared: As a matter of interest, have you ever paid for a set of iridium fine wire spark plugs out of your own pocket, and let someone loose on them with a 'gapping tool'? My guess is you haven't.
Creampuff is offline  
Old 3rd Apr 2014, 23:06
  #35 (permalink)  
 
Join Date: Feb 2006
Location: Melbourne
Posts: 1,693
Received 0 Likes on 0 Posts
Creampuff

We are pretty much in agreement. Except I don't herd goats. Nor do I own a cattle prod. We do have electric fences for my wife's horses, but the main thing I've learned about them is that I'm chicken and prefer to use a fence testing device and not the farmers wet grass method of checking the fence.

Max Nerheim is not a goat herder. He knows what he's talking about, and he's proved that, consistent with the laws of physics, you don't need anywhere near 25,000 volts to get a spark out of a good spark plug.
Bosch, your Pico reference (fig 1.1, point A) and other references are all consistent that you need about 12 kV for a spark. Bosch note that most ignition systems however deliver up to 30 kV.

The spark needs a point to launch from. The better automotive plugs (eg NGK, Bosch) have the centre electrode ground flat and a sharp edge side electrode to promote the spark. I think Champion are better now, but they used to cut the centre electrode with shears. They were truly dreadful plugs. I have never understood why massive electrode plugs are made with electrodes shaped as they are because they do not really have an edge that creates a focal point for spark initiation.

Fine wire plugs, on the other hand do this. And the whole point of using unobtainablium for the wire is so they don't wear and don't need maintenance (ie regapping).

This post from the Vansairforce kind of deals with Jaba's conundrum

Not knowing any better I "sand" blasted mine and have noticed no difference - but I'm considering not doing it again after reading this thread. However, I adjusted the gap and the very brittle platinum electrode broke on one of my $76 (as I recall) plugs. I used the fine wire adjusting tool from ACS to bend the side electrode. I called the company and the tech support specialist said never try to change the gap on them. He said you can get away with one slight adjustment in one direction if they are out of spec but the second tweak back will often break the electrode it as it did in my case.
It seems that the companies who make gapping tools for fine wire plugs don't advocate using them!
Old Akro is offline  
Old 4th Apr 2014, 04:59
  #36 (permalink)  
 
Join Date: Nov 2000
Location: Salt Lake City Utah
Posts: 3,079
Received 0 Likes on 0 Posts
Alas, I remain wifeless. Just me and the goats…

It’s interesting to note where lots of manufacturer R&D time and dollars have been spent, because often that provides some insight into the underlying technical issues and constraints.

The ‘holy grail’ of GA piston engine ignition systems remains, of course, catching up with the 1980s and electronic ignition. (Plus no lead AVGAS…) Some ‘no moving parts’ electronic ignition systems for GA piston engines are making their way through the glacial certification process – a couple have made it through. Meanwhile, for almost all of the piston GA fleet for the near future …

It’s obvious that lots time and money has been spent on trying to get the spark plug to spark at the lowest possible voltage. As you (OA) have noted, one of the variables in the formula that determines the voltage at which a spark will jump a gap relates to the surface area of the conductors at the gap. Hence the manufacturers have gone to the trouble of tooling up to produce “massive dual electrode” plugs, “massive triple electrode” plugs, “massive extended dual electrode” plugs, “single fine wire” plugs and “double fine wire” plugs, as well as use different ‘unobtainium’ materials for the electrodes.

Yes: some of this can be attributed to ‘new toothpaste’ syndrome and the propensity of people to believe that ‘new’ and ‘different’ is always ‘better’. But note that nowhere near the same amount of time and money has been put into the rest of the standard, steam-driven GA ignition system. The innards of magnetos have been the same for half a century or so. So have the distributor caps and plug leads.
Creampuff is offline  
Old 4th Apr 2014, 05:20
  #37 (permalink)  
 
Join Date: Jul 2007
Location: in the classroom of life
Age: 55
Posts: 6,864
Likes: 0
Received 1 Like on 1 Post
OA
It seems that the companies who make gapping tools for fine wire plugs don't advocate using them!
Good research, and yes

I am but a mere piece of Plankton in the aviation food chain, and do get accused of inane twaddle at times, but hey, having learned a thing or two away from the normalised deviation of mainstream monkey see/do, I do expect to cop a bit of flack. A bit like the amazing pasting dished out to John Deakin in another thread yesterday. He thanked me for sending him the link, it was a great source of entertainment.
Jabawocky is offline  
Old 4th Apr 2014, 07:15
  #38 (permalink)  
 
Join Date: Jun 2011
Location: Perth
Posts: 146
Received 0 Likes on 0 Posts
You cannot test champion plugs with an ohm meter!

I was wrong about silicone carbide:

From champions own literature (with emphasis added by me):
SAC-9 Suppressor
Champion developed the SAC-9 suppressor in the early 1980’s. This extremely reliable
resistor/suppressor is formed from strontium carbonate, aluminum oxide and copper
oxide powders. In fact, out of billions made, not a single SAC-9 suppressor has ever been found to fail in service. They are used in Champion “R” type resistor plugs. An
important feature of Champion plugs with the SAC-9 suppressor is that the resistance of
the plug cannot be accurately measured with typical low voltage ohmmeters.

This resistor is a proprietary type (hence why tempest do not use them) and very little info is available except that they are the resistor used in every champion plug with a R designation (aviation plugs).

As for magneto operation the primary coil is 200-300v secondary is 20-30,000V however this is only used for a nano second at the start of spark when ionization of the spark gap occurs. After this the spark voltage decreases exponentially. Thus excessive voltage in the coil is more likely to be created by excess plug gap which increases both the voltage required for ionization and the duration that voltage is required for.

As for gaping fine wires, generally they will need it once in a life. At approximately half wear life they will exceed .019". they can then be delicately re-gapped. I have not broken one yet. But would much rather risk breaking a fine wire than operating with too large a gap (with increased resistance at the point of spark gap ionization and thus excessive voltage and heat.

Your only other option is to throw the plug out when it exceeds .019" gap which is a waste when you can re-gap it with a $10 tool and 5 minutes of patience.

Tempest advocate for resistance testing of all plugs and no re-gapping for two simple reasons: They do not understand how the SAC-9 resistor works (and champion wont tell them) and they would rather sell another $70 plug.

Champion do not tell you NOT to test their resistance for two reasons; You should be doing what they (not their competitor) tell you to maintain their plugs and if you buy another $70 plug because you didn't that is their gain.

Creamy,
Perhaps the inventor of taser doesnt know that most variable resistors are subject to a sustained voltage limit after which the material fuses and goes to infinite resistance and that by putting 50,000V across it he was effectively making it open circuit with greater resistance than the air gap. The tazer then did exactly what it was designed to do and provided a high voltage current at low amps which ionized the air gap (which is easier to ionize than the pressurized fuel air mixture) between he electrodes and bypassed the resistor. Use of a voltage in the 12-30k range would have produced a better result.
Progressive is offline  
Old 4th Apr 2014, 07:21
  #39 (permalink)  
 
Join Date: Jun 2011
Location: Perth
Posts: 146
Received 0 Likes on 0 Posts
It is true that the spark will jump more easily to an edge however having a narrow edge would result in rapid opening of he gap as spark erosion occurred in the soft electrodes. Fine wire plugs can have a smaller electrode size and sharper edge because of the reduced wear rates of the iridium material.
Progressive is offline  
Old 4th Apr 2014, 08:02
  #40 (permalink)  
 
Join Date: Nov 2000
Location: Salt Lake City Utah
Posts: 3,079
Received 0 Likes on 0 Posts
Strontium carbonate, aluminum oxide and copper oxide powders.
Phwoooarrh! That stuff's gotta be more expensive and better than unicorn farts and reptile lubrication.
In fact, out of billions made, not a single SAC-9 suppressor has ever been found to fail in service.
Wow! That's gotta be the mostest reliablest electronic component ever!

Funny thing is, like Mr N, I took one of my ditched Champion plugs and unscrewed the cap holding the 'magic resistor' and removed it.

After an appropriate period of respectful awe as a consequence of being in the presence of 'strontium carbonate, aluminium oxide and copper oxide powders' which, notwithstanding their reputedly deadly awesome high voltage powers and the expectation of an ethereal glow, seemed to look just like a bit of black baked crap, I applied a mulitmeter to it. Imagine my disappointment when no matter what I did to it, I got a big fat 'infinite'.

Imagine my further disappointment when the same multimeter applied to the 'magic resistor' from another Champion plug gave a resistance reading and didn't look like a bit of black baked crap.

And apparently the tests carried out by Mr N were at too high a voltage? Gimme a break...

This is just my personal opinion and I have no insight into what happened, but if I had to guess I'd say that for a short time Champion outsourced its 'magic resistor' manufacturing to the Chinese company that specialises in baby formula.

Last edited by Creampuff; 4th Apr 2014 at 09:38.
Creampuff is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.