It's true. I was never aware of this.
Have yall ever heard of "SAG"
Sparkplug attention getter.
Check out this site.
http://www.rotarycopilot.com/observa...oncerning-sag/
It makes sense to me and I will be dissecting some sparkplugs.
if a detonation event has occurred or even misfires---this info is good to know while you trouble shoot.
Damn.
OD

 

um ... yeah.... over time spark plugs fail. if they have been in an environment that is "corrosive" to them- preigniton,heavy lead, bad tuning, run at a high rpm for long periods of time - then they will fail sooner. towards the end of their useful life they will begin to perform less than ideally.

 

SAG is only relevant in aerospace where you have a motor sustaining high rpm's for a long amount of time anyway.

 

moral of the story; don't buy those cheap sparkplugs

 

aint no cheap plugs where I come from lol.
At what rpms do you think airplanes fly at? The load may be a bit heavier, but rpms? Not to much so. Speaking on the average?
Its heat isnt it?
AV gas is better and they have better control over timing, etc etc.
50 hrs of running is not that long.
Anyway just food for thought.

 

do you know what this person is using for timing control?

50 hrs? he states in the article 30 hr life.

 

Those 4 & 6 cylinder Continental engines that are used in small craft, I believe, only cruise at about 2K rpm. They don't go too fast otherwise the propeller tips go supersonic and loose efficiency. There are gear reduction units used for automotive engines that are re-purposed for aviation.

 

no it's not, just the usual misapplied generality scenario ...

that said, I was thinking of buying and installing the dual EGT setup from Pinapple in my manifold over the winter but not for this reason

 

my point is- i guess its nice or cool to understand the failure method. if it can be identified that some make of plug does this over others it might make a difference in your purchasing decision. but really, plugs go bad with use. why exactly doesnt really matter to the end user unless its caused by the tuning. other wise its just an old plug that has served its time in hell and gets replaced.

 

I changed plugs on some 350 Chevy engines years back, and sometimes had hell with misfires.

We sold Spark plugs for most vehicles, so I could obsess about different plugs and heat ranges being swapped around in different engines.

I found the most important thing to do with a bunch of plugs on the table before instalation was to check resistance with ohm meter.

Most modern plugs have about 5k ohms resistance, but about 1 in 8 or 10 would have excess resistance of 15k or more, so when them were run you could have an annoying misfire.

I think I found one once that was completely open ( no fire ) , but I think over the years I've had trouble finding high 5k+ resistance ( not installing many either).

So that aviation rotary application is neat, but I think the rpms are prop which a geared down about 3 times which would give him 4k -5k rpms of sustained output, with 230 water, and lean fuel ratios.

He did say that he was flying denser air so if the same fuel was flowing, it would be leaner.

Bottom line is: I'm not ever running on the track more than 20 minutes and my highest water temp was 229 on a 95 deg f day. Our engines probably never get to those lean conditions unless the fuel surge problem on corners, and that's only a few seconds and a mere annoyance.

The pilot has wonderful logging, but needs to conclude that he needs to lower temp to 210 deg f while climbing or cruising, and he won't BURN up anymore plugs.

 

Are we talking piston/rotary engines or wankel engines? Remember that rotary in the aviation world more closely means the radial engine as opposed to wankel.

Now if we are talking wankel, then those engines operate at roughly 6k-7krpm, and yes, as Al said, most non-turbofan aircraft engines use an PSRU to reduce the propeller shaft to a fraction of the engine rotational output, we are talking roughly 2.4:1 ratio. So yes, albeit your propellers are operating at a 2K rpm cruise, your engine is roughly rotating at double that. Again, this also goes for the radial engine, but if I remember correctly the PSRU ratio is a lot lower.

Pratt & Whitney ftw lol

 

Is this the benefit of the wire time iridium or platinum plugs? Essentially no copper?

I remember when copper in that electrode was a selling point, then it stopped and we got platinum.

 

this is the mazda rotary engine that was being spoken off.
He was running lean a/f's. I didnt get that part? He was getting some varience in egt due to misfires?
Rotary av guys are fanatics (most home build plane guys are fanatics and rightfully so) and a lot of good info is posted concerning their findings.

I thought it would be good info to share here, mainly to those folks that have FI on this car.
FI cars have much higher loads than the NA folks etc etc and if you track the beast, the heat range of the plug is very important. I know of some guys that dont have a dedicated set of track plugs--perhaps they should? I know myself I have gone on track (successfully) with 5K mile plugs. After reading what this fellow has shared--I wont anymore. I never realized that internal breakdown like this was possible. The last thing I want is a glowing sparkplug.

The resistance test is a good one, but there is more to the story? I have always wondered exactly why our plugs go bad so fast and why the only symptom at times is a dyno that shows lost of power up top. I know coils are part of that scenario, but plugs that look good and have good resistance findings, now I have a better idea of what MAY be wrong.

The part about the separation between the cooper core and the ceramic was particulary interesting. And the fact that you cant see it with just an eyeball inspection. The trailing plug seems vulunable here especially?

 

:facepalm:

 

That's a lot of neat technical information and I'm a sucker for tech info, but what I basically get from the entire thing is that when your plugs wear out, they need to be replaced.

 

^^ And if you plan on sustaining high RPM's for an extended period of time, they need to be changed faster lol

 

Lol--true. I am cursed by that omni present " Why" question. I will drag yall through my ramblings/suspisions and what the hell's because a psychitrist friend once told me " Your mind is a dangerous place, dont ever go in there by yourself".

So yea the pragmatic approach to this is change your dang sparkplugs. I get it.

But it is neat to know that an increase in egt's can be an indication that your plugs may need changing even when there are no "misfires" or performance difference. I never knew that. I understand why the egt's go up but I always though that the engine would have some tangiable symptoms before that happened.
Its good for dummy's like me to know that 9 heat range plug you think you have may now be a 7 heat range plug.--oh crap!
To show you how dum I am--i never knew that a proper heat range plug could be a direct cause of detonation just because it has some wear( but no classic symptoms). I never knew that the heat range of a sparkplug could change while it is in the engine. I do now.

I really dont know a lot of stuff.

 

I hear you OD. "Just because" doesn't satisfy some people, and even if we know the end result is the same, we want to follow the path between the two points to understand the entire thing, and aren't comfortable until we do. Hashing it "out loud" becomes natural at that point.

 

OEM or maybe a 2nd colder set, to change to, for when you do go to the track. But, OEM should be ok for a non-modified engine.

 

take a look at the rotary engine coolant flow paths, now look at where the rear leading spark plug is located, which also happens to be one of the hottest spots in the engine for heat transferrence.

piston engines have a more even coolant flow distribution, rotary engines pass coolant through the front rotor then the rear. poor rear rotor... redheaded stepchild.

of course on the return pass the rear rotor gets cooled first but not in as such critical areas.

of course that is just speculation as to why certain things get fatigued more and less.

 

its a good point--i have never understood why they make it a loop system--why not just exit it all in the rear. More expensive design i suppose?

Interesting find for me tonight. I was messing around with my multimeter and 8 Denso sparkplugs ( slightly used ) would not register any resistance at all--it was too low I guess.
Whereas the oem NGK's ( less than 5k on them) the resistance reading just popped up.
Probably not enough to make any difference in anything--but it was interesting.
I just jacked my own thread!!!!!

 

it's worked for years but obviously something has gotta give when you stress the limits and make more power with the engines. i figure they just adapted the iron casting mill to the same principles it was used for over the last 40 years. the iron design hasn't changed much since it's inception by mazda.

but if you look at the racing engines they have bypass ports in various points on the engines to cool more evenly.

mazda isn't notorious for testing things for extreme durations otherwise the iron failures that now plague the 2nd and 3rd generations might not have been overlooked.

but at any rate, i'm not sure if it is a jack as i would tend to believe the additional heat takes it's toll on the rear plugs and that is what that article is seeing.

 

Understand--many race engine (recips) do cooling mods like you are speaking off--i havent seen a street/track rotary engine with this--yet. I am sure they are out there like you say.
The heater supply is a pretty big hose that comes off the rear iron--that supply never even sees the radiator putting more stress on the cooling system due to it having to blend in. That increases the temperature of the coolant as it enters the engine and that doesnt help anything at all--the same with the TB hose on the other side.
The no bar spark plug is the right idea--i think? Its heat range is more stable by design? It just takes a good amount of power to fire the thing and they need replacing often--at least for me they do.
I think race prep has taken on a new meaning for me. A new set of Denso's the 5431's and 27's if i remember right will be put in every 3-4 track w/e no matter how they look or run. Sigh.

 

Continental/Lycoming engines cruise in the 2300-2500 rpm range with max power around 2700 rpm, with a few exceptions. Usual prop diameters are ~70-80". The prop tips never go supersonic or even very close to it. What happens is that the accelerated *airflow* over the "top" part of the propeller goes into a range called trans-sonic, which greatly increases the drag and reduces thrust. Airshow pilots, for purposes of making lots of noise, will push that airflow into the supersonic, but there is no practical reason for doing so. Investigations into true supersonic tip speeds during WWII resulted in blade and crankshaft failures caused by uncontrollable resonances set up by the ss shockwave.

Gear reduction units from the automotive world are seldom suitable for aviation use. The problem is torsional resonance between the crankshaft and prop. The reduction units have to be designed from the start to match the resonant characteristics of the engine/prop combination. Once that is done, changing anything, like going to a lighter prop or flywheel, can (and does) lead to catastrphic failure. This can happen even when the prop is bolted directly to the crankshaft and very slight differences in the particular model of the engine, can result in a safe combination becoming a very dangerous one.

 

"Radial" refers *only* to the arrangement of cylinders. "Rotary" should in a sense only to Wankel, but historically there were piston aircraft engines called 'rotaries'; in that context, it referred to whacko engines where the crankshaft was bolted to the plane and the cylinders rotated with the propellor.

99% of general aviation planes have their props bolted to the engine crankshaft directly. It's simpler, cheaper, and more reliable. Exceptions have come in recently on the low-hp end of the scale, primarily from Rotax, but then the properly engineered reduction unit comes with the engine. The only car to aircraft conversions on sees in any numbers are VW's of ~ 70 hp and very modified Subarus of ~120 hp (which you can buy for $18,500.) http://www.usjabiru.com/images/pdf/p...st10-18-10.pdf