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How to thread drift in 720 posts!!!
Howdy. I want to put to you guys a few questions that might hypothetically be happening to someone who isn't me.
1: This person has accepted a job on an aircraft flying privately, yet happens to be doing an insane amount of flying and duty hours that would beach CAO 48 pretty much every day. Considering this is a private operation, legally, is it this persons own responsibility to monitor their own fatigue, performance levels and flying hours or could some unforeseen issues arise with it? Whether it be insurance or otherwise. 2: The owner of this hypothetical Lycoming io540 equipped aircraft has neglected a 50 hourly oil change for in excess of 50 hours. As in, it has done over 100 hours since it's last oil change. The maintenance release does not stipulate any oil change beyond the first which has already taken place, but being a private operation, 100 hourlies are not required. Would you have any input as to the status of a near end of life aircraft engine operating under such conditions? Whether it be physical damage, insurance issues, decreased margin of safety, mandatory manufacturer guidelines or anything else? The hypothetical pilot of the aircraft has serious concerns about the insurance and passenger liability status of the aircraft as well as general failure potential of the engine. |
being a private operation, 100 hourlies are not required |
No. A maintenance release is not required but all maintenance require dMUST be done. This include all ADs if the flying time has exceeded the limits.
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Annual inspection
I believe that, for private ops, an annual inspection is required to renew the maintenance release but there is no hourly limit between inspections i.e you may exceed 100 hours in the year. Also, oil changes at 25 and/or 50 hours are recommended, not compulsory.
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Interesting questions. I think that if it is PVT and the MR does not have inscribed a 50hr oil change then it is not legally required.
For that matter it only requires as a bare minima an annual inspection. The engine manuals do state oil change intervals but they are not a mandatory thing depending on the system of maintenance applicable. I think......but I am not 100% sure and I bet you get lots of opinions. All the legal BS aside, lets examine some reality of engineering. Oil changes are not as necessary when the oil is not old, is regularly topped up(progressive replacement) and the plane is flow a lot. That said, depending on how the engine is operated (read mixture management) the oil deposits could vary significantly. This is why oil change intervals are recommended depending on usage. In particular H2O which helps form acids. Next is spark plugs and magneto's. If they are fine wires, then no big deal. 100 hrs is fine. All they need is a resistance check and checked for cleanliness. If they are Champion, this is far more critical. Air cleaners, this is a 100hrly thing but depending on locations this may be prudent at 50 as well. Is there an engine monitor? Is it downloaded regularly and the data examined. Is it examined by someone who really knows what they are looking at? (only 1% of pilots and LAME's are in that boat) Are the cylinders borescoped each 100 hours. Oil analysis as much as this is a variable test? There are so many variables.....if you wanted to talk in private I would happily help point you in the right direction but here could be a wild ride. Last of all, remember this. Just because it is legal does not mean it is prudent. All maintenance should be viewed with this integrity test. Does it do everything it should and nothing it shouldn't? Feel free to PM.:ok: |
concerns
The requirement for the oil change/filter inspection is clearly set out in AD/ENG/4 requirement A3 for private ops - within the manufacturers recommended period + or - 10%
Although a 100 hourly is not required for private (annual only) AD ENG 4 requirements A1+2 require a compression test and engine test run to be conducted @100hrs + or - 10% in addition to the above oil change and filter inspection which is/was due again at 100 hrs. No amount of Schedule 5 / private ops leniency will allow you to avoid the above AD. If your friend has been flying the aircraft with these items overdue on the MR then he is in breach of the regs!:uhoh: The owner may be relying on the pilot to tell him when maintenance is due. If they are not on the MR the aircraft is on manufacturers maintenance schedule in which case and the inspections are required under that OR the maintenance guys failed to put it on and THEY are in breach of the Regs Since your friend is obviously keen to keep his flying job I suggest he go to the owner (non pilot?) bearing a copy of the AD and the responsibility for the owner to maintain the aircraft IAW the regs for a friendly discussion. This may turn out to be a case of owner and maintainer ignorance combining in the perfect storm. As for the flying hours if there is a good relationship with the owner perhaps your friend could review their flying pattern and suggest alternate schedules which could save them both time. As a single pilot for a private operation your friend may just have to accept the role of maintenance and flight scheduler as well. |
Jaba,
As per my other posts Oil changes and filter inspections ARE a required thing either under the Manufacturers Maintenance schedule or AD/ENG/4 as an engineer you should know that. Fine wire plugs are good for over 100 hours but "champions" are not? Since Champion is a brand that manufactures both fine wire and massive electrode (the other type spark plugs) this make no sense at all. If you are suggesting that fine wires need less maintenance than massive electrode plugs then this is also untrue. Both require cleaning and gapping, both have electrode wear (faster in massive electrode but spread over two electrodes instead of one in the FW) As for the magnetos, type of plug fitted has nothing to do with the rate of wear in points, gears, capacitors and other components so advising that less than normal maintenance is "no big deal" is just plain wrong. I know what I am looking at during oil analysis, engine monitoring, and bore-scope inspections and none of these things will identify a cracked crankcase, cracked cylinder head (not yet separated), holed muffler or any one of 100 other things that can kill you and can only be found by good old MK1 eyeballs. Not to mention the airframe parts that would also be inspected at the 100hr It may be legal to operate a private aircraft over 100 hours without inspection but it is definitely not prudent. Also feel free to PM for advice |
Some slight tweaks to yours, progressive, so that you’re giving the whole picture.
The requirement for the oil change/filter inspection is clearly set out in AD/ENG/4 requirement A3 for private ops - within the manufacturers recommended period + or - 10%. AD/ENG/4 only applies to piston engines fitted to aircraft maintained to Schedule 5. Further … AD/ENG/4 ‘points’ to the engine manufacturer’s data. So… What you meant to say was: (1) if a piston engine is fitted to an aircraft maintained to Schedule 5; and (2) the engine manufacturer’s data specifies oil/filter changes more frequently than e.g. Annually/100 hourly, the outcome is that AD/ENG/4 mandates the more frequent changes, subject to the margin specified in the AD. What those periodicities happen to be change from engine-to-engine type/part number to engine type/part number. Also… It’s possible for the aircraft to be maintained in accordance with a system of maintenance (i.e. neither Schedule 5 nor the manufacturer’s maintenance schedule, although I concede that a system of maintenance would normally reflect the engine manufacturer’s oil/filter change recommendations). Re ignition systems: You obviously think you know lots about ignition systems, but have learnt very little. Do a search on the Champion massive electrode internal resistor problem. You 'gap' fine wire plugs? You’re not going anywhere near my engine. |
If he is paid to fly, it is not a private operation.
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Not accurate.
There are lots of operations during which the pilot may be paid, handsomely, but it's still a private operation. One example of many is the transport of the owner of the aircraft ... Another is agricultural ops on land owned by the owner of the aircraft ... Decades of this classification of operations system, and still ignorance pervades. |
Another spanner in the works here.... Didn't specify what type of operation. Given the hours and skimpy maintenance, one might guess that your friend is parachute dropping? If so there is a requirement for 100 hourlies and oil changes every 50 hours even though it's a private op under the apf's casa instrument.
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It disappoints me that there is often a flavour on pprune that all bosses are exploitative crooks taking advantage of young pilots.
The relationship with your boss should be good enough to ask honest, open, enquiring questions like these. This applies whether you are a pilot or the office girl. If your relationship with the boss is not good enough for this, it would be a signal to look for a new job. Regarding the oil changes, I agree that I would prefer to change oil more frequently. But from the pilots perspective its what's on the MR that counts. It will have a validity date, airframe hours and notes on interim maintenance. If the MR does not require the oil change, then its legal. If the MR requires an oil change that has not been signed off, then its not legal and he shouldn't fly it. If the MR is not requiring an intermediate oil change, then frankly its as much a question for the LAME that signed it as the owner. If there is an accident attributable to lack of oil change (which there won't be) then it will be the LAME in the gun, not the owner. Once again, this would be an entirely reasonable question to ask the signing LAME. The owner will pay the price of lack of oil change in increased engine wear / shorter engine life. Its very unlikely to be a safety issue. Regarding duty times, frankly who cares about CAO 48. Its probably the single worst written CAO. If you want evidence, just look at the huge volume of exemptions granted by CASA. The real question is whether the pilot is happy with the duty hours? This varies hugely with the style of operation. If the aircraft is flying VFR in good weather west of the J-curve and the owner is also a pilot who shares some of the duty (not an uncommon scenario), then I'd suggest you could easily, safely and happily fly twice the duty hours of (say) a single pilot IFR freight run in bad weather (ie across Bass Strait). But, really these are both conversations that an employee should have with his / her employer. |
Why not just change the oil yourself, rather than continuing to worry about it?:confused:
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Yeah it's based out of the middle of no where and there isn't enough oil to change it themselves.
The pay is fantastic and the hours just as good. it is not skydiving ops, just many 1 - 3 hour legs in a day, and it is considered a private op. The pilot is looking to quit because of the abrasive personality of he owner and the fact that he gets yelled at whenever he voices concerns. Thanks for all the replies so far, they have been very enlightening. The maintenance release stipulated the first oil change at a predetermined time, but not any subsequent ones. The engine is a Lycoming 540. And yes, the pilot has no problems with the long days, but was still enquiring in the event of a logbook review or something similar. |
We covered the MR thing a few months back on here.
An annual inspection is an annual inspection, not a 100 hourly, but of course they can be done at the same time. If you have 2 hours on the VDO for the last year, you still get an annual inspection. If you do 300 hours in one year, you are still up for ONE annual inspection, but potentially 6 "services" or oil changes. |
You 'gap' fine wire plugs? You’re not going anywhere near my engine. |
Ain't no engineer going anywhere near my fine wire plugs with any gapping tools.
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If you do 300 hours in one year, you are still up for ONE annual inspection, but potentially 6 "services" or oil changes. The pilot should not need to do anything past reading the MR. If the MR is OK, and the required inspections are completed (including the daily) then the pilot should be able to fly it. If the MR requirements are not complied with, the pilot cannot legally fly it. |
Progressive,
I think you may have confused yourself with what I said Vs what we both know is prudent and generally legal. It is possible that a certain manufacturer does not specify a 50hr oil change. I have never seen one, but there could be, and so if by Sched 5 and AD/Eng/4 it points to the aircraft manual and it does not, then legally it does not. As best I can tell. As for Creamies post, I think that explains it all. Ok spark plugs. I am not sure how you did not follow what I said. If you need to call me please do, happy to chat, but let me try to explain in more detail. Next is spark plugs and magneto's. If they are fine wires, then no big deal. 100 hrs is fine. All they need is a resistance check and checked for cleanliness. If they are Champion, this is far more critical. Fine wires, they rarely need cleaning, unless the operator is a poor mixture knob user. (I have a solution to that) and the gaps stay very reliable even out to 1000+ hours. As Creamie noted.....nobody is touching his fine wires! Champion Vs another major brand. Champions are a great plug and work fine but they have a very short life in the resistor, typically 300 hours is when they start to drift and once at 5k ohms they go in the bin. This is important for other reasons than just good smooth running. As for the magnetos, type of plug fitted has nothing to do with the rate of wear in points, gears, capacitors and other components so advising that less than normal maintenance is "no big deal" is just plain wrong. But I must pull up one point. You suggest that spark plugs have nothing to do with magneto's. Well this seems to be something that even CASA failed to address in a recent AWB on magnetos where they talked about coils suffering from heat stress yet they have no idea where this magical extra heat stress comes from. No it is not the continual heat from years of operation. It is from years and hundreds or thousands of hours of operating on plugs with high resistance. Problem is not many folk know this and it is a long forgotten bit of knowledge. I hope that helps :ok: I know what I am looking at during oil analysis, engine monitoring, and bore-scope inspections and none of these things will identify a cracked crankcase, cracked cylinder head (not yet separated), holed muffler or any one of 100 other things that can kill you and can only be found by good old MK1 eyeballs. Now just a note though, you say that there are things you can't see with an EMS, well holes in exhaust systems can at times be found, broken flame cones too. Maybe you might be surprised what an EMS tells you. By the way I have a suggestion on where that and many more things can be learned. But I will be accused of advertising a course which is run not to make profit, but is a company none the less. ;) It may be legal to operate a private aircraft over 100 hours without inspection but it is definitely not prudent. |
Gapping spark plugs. I have written articles on this, much to the delight of Tempest, who at first I thought were going to sue me for something, until I realised that was not their intent at all and quite the opposite. But rather than blab on here, go to this link.
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 http://www.tempestplus.com/Portals/0...ire%200813.pdf http://www.tempestplus.com/Portals/0...y%20081412.pdf http://www.tempestplus.com/Portals/0...ugs%201012.pdf Enjoy! |
you must hypothetically be getting paid the big bucks for all that
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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. |
Debate is good. :ok:
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.) |
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.) 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 |
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 Not enough information here mate. Without further details, this information is not accurate. Disappointing to see you post this. |
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. … |
Is this what you teach at your pilots courses? |
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. |
Progressive, no worries :ok: 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. 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. 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.... |
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. :ok: |
Originally Posted by Jabawocky
(Post 8414452)
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. |
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. |
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 :ok: 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! :ouch: |
AO: My profession is "goat herder". I love my goats... :ok:
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
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. 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. |
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. |
OA
It seems that the companies who make gapping tools for fine wire plugs don't advocate using them! 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. :} |
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. |
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.
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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. 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. ;) |
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