Champion Service Letter: Lean-of-peak ops

Dan Thomas

Dan Thomas

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Dan Thomas
http://www.championaerospace.com/assets/Champion-Fine-Wire-Spark-Plug-Service-Letter.pdf

Excerpt:

"Champion believes the most likely cause of these fine wire core nose cracks to be excessive lean-of-peak operation in which precise control over the engine's performance cannot be maintained to avoid detonation
and/or pre-ignition. Champion recognizes that some limited groups advocate running engines aggressively lean of peak; outside the engine OEM recommended procedures. Champion’s belief is that running the engine
outside the OEM operating guidelines can increase the likelihood of detonation and/or pre-ignition which will potentially cause significant engine damage, including damage to spark plugs."

Dan
 
I hope they realize the hell they just unleashed upon themselves....
 
Running LoP requires an accurate reading from each cylinder ror you're rolling dice.

How many LoP fans also have a full instrumentation package such as a JPI hooked up?

I'm betting lots of burn outs are being caused by extremely lean, max power ops with nothing more than an RPM, oil pressure and temp gauges.
 
I'm not sure what "aggressively lean of peak beyond the manufacturers guidelines." Continental says you can lean all the way into misfiring if you want.
 
dmccormack said:
How many LoP fans also have a full instrumentation package such as a JPI hooked up?.
Click to expand...

I would hope all of them. It takes some serious equipment to do LOP successfully over a long period of time, not to mention a near perfect ignition system.
 
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flyingron said:
I'm not sure what "aggressively lean of peak beyond the manufacturers guidelines." Continental says you can lean all the way into misfiring if you want.
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Sounds aimed right at Tornado Alley to me..they have long advocated 50-100 degrees LOP in TNIO-550's Where as Beech limits the n/a 550 20C rich or lean of peak in the POH.

from tornado alley's operation guide
"Note the maximum value of the TIT. Then, reverse the process, leaning the mixture until the mixture is set at a fuel flow that produces a TIT that is 50 to 100°F lean of the peak TIT."
 
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Yeah, like the vacuum pump letters from whoever-that-was that said "you may die if you use our product, don't say we didn't warn you"
 
taters said:
Sounds aimed right at Tornado Alley to me..they have long advocated 50-100 degrees LOP in TNIO-550's Where as Beech limits the n/a 550 20C rich or lean of peak in the POH.
Click to expand...

The Champion letter is a reply to TATs mandatory service bulletin that blames Champion for all evils in the world. So yes, it is certainly aimed at TAT.

I believe that with 'aggressively operating LOP' they are referring to the concept of running an engine at 85-90% power in cruise under the mantra of 'I can't possibly do any damage because I am operating LOP and LOP operation has never hurt an engine show me the data data datattaat data'.
 
dmccormack said:
Running LoP requires an accurate reading from each cylinder ror you're rolling dice.
Click to expand...

If you would add "at high power settings" I think most would agree with you. Otherwise, I think you are wrong or at best painting with too broad a brush.
 
Looks like CYA to me. Maybe this is why you should buy Tempest fine wire plugs? :rofl:

While Lycoming does not recommend running LOP they have said in the seminars I attended you can run LOP without damage to the engine if you do it correctly, with a properly instrumented and fuel flow calibrated engine. Thank you Don Rivera, Air Flow Performance! http://www.airflowperformance.com/

I run my IO-540, RV-10 LOP anytime I want to conserve fuel and run a cool engine. Oil temps drop 25 F, CHTs drop 50F, fuel consumption drops from 14 to 10 GPH, speed drops 15 MPH. Over 500 hours now (on mogas) and I have not fallen out of the sky. ;)

Most (certainly not all) RV's being built today are equipped to monitor proper LOP operations. The cost of doing so (instrumentation) is minor compared to the fuel savings alone.
 
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Why is no one blaming the plugs?
We have apparently forgotten how to make almost every other aviation component (cylinders, crankshafts, crankcases) in any reasonable quality, so maybe that's what is happening to spark plugs these days too?
 
I would like to know whether TAT took those engines apart to check for piston crown cracks or cylinder head cracking. Such damage is usually a sign of detonation.

TAT is blaming Champ's plugs for causing preignition. Champ is blaming TAT for its advocation of aggressively LOP operation causing detonation. Preignition can indeed cause detonation but the usual cause isn't the plugs; it's hot points of carbon on the cylinder head and piston.

Detonation risk rises with leaner mixtures, lower RPM, larger cylinders, and higher manifold pressures. The pressure wave ahead of the flame front causes heat and a resultant breakdown of the complex fuel molecules into simpler molecules that are prone to spontaneously ignite instead of waiting for the flame front chain reaction to set them off. So instead of a 100 foot-per-second flame front and the nice gradual pressure rise it creates, the detonation of autoignition can reach 5000 FPS and a massive pressure spike that breaks things like pistons, heads, and sparkplug insulators. Anything that allows time for the fuel molecules to break down contributes: the large cylinder takes longer to burn, lean mixtures burn more slowly, low RPM allows more time. High MP raises compression and combustion pressures and temperatures.

Lycoming says you can do anything you like with the mixture on a normally-aspirated engine if at 75% power or less. Turbocharging raises the MP and changes all that. Running above 75% changes it. Lycoming has been around long enough and has probably spent enough cash testing engines to see detonation under various circumstances and have likely run some engines to destruction.

Dan
 
Dan Thomas said:
Detonation risk rises with leaner mixtures, lower RPM, larger cylinders, and higher manifold pressures. The pressure wave ahead of the flame front causes heat and a resultant breakdown of the complex fuel molecules into simpler molecules that are prone to spontaneously ignite instead of waiting for the flame front chain reaction to set them off. So instead of a 100 foot-per-second flame front and the nice gradual pressure rise it creates, the detonation of autoignition can reach 5000 FPS and a massive pressure spike that breaks things like pistons, heads, and sparkplug insulators. Anything that allows time for the fuel molecules to break down contributes: the large cylinder takes longer to burn, lean mixtures burn more slowly, low RPM allows more time. High MP raises compression and combustion pressures and temperatures.
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According to GAMI's data, detonation margins are thinest around 25 ROP and get better as you go richer or leaner from there.
 
We have always had a problem with cracked fine wire plugs on the Mirage (Lyc.) engine, I can count on at least one plug at each annual. Most owners are running them ROP. I really don't see any more plugs cracking on those Mirage owners that are running LOP. The TSIO 520 BE that is in my old Malibu was built for LOP operations and has always been kept there in cruise. I'm cheap, I only use the massive electrode plugs. I do find cracked plugs on some of the TCM engines.

On the Mirage engine it's always common to find the fine wire plugs cracked and many times to find pieces of the ceramic insulator missing. I can't say I have ever seen any damage to a cylinder or turbo that was caused by a failed spark plug insulator.

Kevin
 
Here's an A to one Q posed above...

"Running LoP requires an accurate reading from each cylinder ror you're rolling dice. How many LoP fans also have a full instrumentation package such as a JPI hooked up?"

We all walk the tie-down line, visit open hangars and look a the transient a/c on occasion, right? How many a/c - by far, most of them older Part 23 a/c - do we see that have the kind of instrumentation needed to insure accurate, safe LoP ops? Almost none, IME.

Jack
 
I have the full engine analyzer and it also helps to have the injectors on your engine balanced (GAMIs or in my case the Continental Platinum Series that came really well balanced). However, you can run LOP fine with a single point EGT and frankly, even without an EGT at all.
 
Re: Here's an A to one Q posed above...

Jack in Jax said:
"Running LoP requires an accurate reading from each cylinder ror you're rolling dice. How many LoP fans also have a full instrumentation package such as a JPI hooked up?"

We all walk the tie-down line, visit open hangars and look a the transient a/c on occasion, right? How many a/c - by far, most of them older Part 23 a/c - do we see that have the kind of instrumentation needed to insure accurate, safe LoP ops? Almost none, IME.

Jack
Click to expand...
While having all cylinder EGT/CHT makes it a lot easier to learn what's going on when you go LOP, it can be done without (additional) risk with no EGT or CHT. In fact, it's been shown that running ROP without full instrumentation is far more likely to result in problems than LOP. If an injector's flow is reduced while LOP the result is a cooler cylinder and a rough engine and the roughness is a pretty good clue that's hard to ignore. The same issue when ROP will take the associated cylinder on a trip through the "red box" which can be disastrous at high power settings.

If you can get a 3-4% reduction in airspeed leaning from best power mixture without significant roughness your engine has sufficiently balanced fuel flow and is running LOP.

That said, engine monitors are a great tool to have for engine diagnosis and management.
 
Re: Here's an A to one Q posed above...

gismo said:
That said, engine monitors are a great tool to have for engine diagnosis and management.
Click to expand...


The new stuff available to experimentals and OEM EFIS systems is simply amazing. Makes running LOP simple and safe once the plane is set up properly.

Electronics International put togeather this information about their engine monitors and running LOP if anyone is interested.

http://www.buy-ei.com/Information/Pilots Manual.pdf
 
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alaskaflyer said:
A dollar an hour is a dollar an hour :wink2:

I'm betting that at least half my cylinders are running lean of peak every time I'm in cruise flight. :D
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I suspect that it may be a bit better than that if you you can hit the sweet spots (balanced injectors and good instrumentation). The big advantage comes when you can avoid making a fuel stop.

My favorite feature of my engine analyzer is the miles per gallon meter.
 
gismo said:
According to GAMI's data, detonation margins are thinest around 25 ROP and get better as you go richer or leaner from there.
Click to expand...

That has to do with the timing of the pressure peak. Just rich of peak puts the pressure peak too close to TDC, with the chances of detonation being better in such a scenario. Richer that that slows the burn, and leaner slows the burn, both moving the pressure spike to a later point.

The best answer would be variable ignition timing and knock sensors along with MP, RPM and induction temperature sensors to get the best spark advance. But that would be too expensive for airplanes. Cheap cars all have it, but the FAA has nothing to do with those.

Dan
 
flyingron said:
I suspect that it may be a bit better than that if you you can hit the sweet spots (balanced injectors and good instrumentation). The big advantage comes when you can avoid making a fuel stop.

My favorite feature of my engine analyzer is the miles per gallon meter.
Click to expand...

I guess my point was that the benefits of LoP operation are seen at all power settings, not just high ones, and at typical NA engine cruise settings, risks to your engine are low/nonexistant even at just rich-of-peak or peak EGT.
 
taters said:
I would hope all of them. It takes some serious equipment to do LOP successfully over a long period of time, not to mention a near perfect ignition system.
Click to expand...

That's BS, Cessna operators have been running lean of peak IAW their POHs for years. "pull until it skips and lichen until it runs smooth" will leave you LOP in all engines on both Piper and Cessna. You can not harm any engine by leaning, it will simply quit producing power. Quicker on the lean side than the rich side.
 
Dan Thomas said:
That has to do with the timing of the pressure peak. Just rich of peak puts the pressure peak too close to TDC, with the chances of detonation being better in such a scenario. Richer that that slows the burn, and leaner slows the burn, both moving the pressure spike to a later point.

The best answer would be variable ignition timing and knock sensors along with MP, RPM and induction temperature sensors to get the best spark advance. But that would be too expensive for airplanes. Cheap cars all have it, but the FAA has nothing to do with those.

Dan
Click to expand...

My Warner has variable timing, and you can't cause detonation by retarding the timing, I've tried, it won't work until you advance timing until BMEP occures before TDC.
 
Tom-D said:
That's BS, Cessna operators have been running lean of peak IAW their POHs for years. "pull until it skips and lichen until it runs smooth" will leave you LOP in all engines on both Piper and Cessna. You can not harm any engine by leaning, it will simply quit producing power. Quicker on the lean side than the rich side.
Click to expand...

Interesting...I tried that today in a Cessna 172 and ...wound up ROP at "smooth", Its my understanding running the average carbed engine too lean can have adverse effects over a long period of time.
 
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taters said:
Interesting...I tried that today in a Cessna 172 and ...wound up ROP at "smooth", Its my understanding running the average carbed engine too lean can have adverse effects over a long period of time.
Click to expand...

There is some thing wrong some place. most engines will not go to a lean misfire until you are 100+ LOP. and your engine should not have that big of a spread.
 
dmccormack said:
OK -- "at high power"

But, what's the point of running LoP at low power settings?
Click to expand...

You are ****ing unburned fuel out the exhaust if you are RoP. But, somtimes you have to do that for knock prevention and/or cooling.

For the same actual crankshaft delivered power, you do less pumping work (loss) and have less heat transfer (loss) to the cylinder walls at leaner mixtures (up to a point) (assuming sufficent air is available).

In an ideal world, you would be advancing the spark as the mixture went lean for maximum return on enleanment.
 
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Capt. Geoffrey Thorpe said:
You are ****ing unburned fuel out the exhaust if you are RoP. But, somtimes you have to do that for knock prevention and/or cooling.

For the same actual crankshaft delivered power, you do less pumping work (loss) and have less heat transfer (loss) to the cylinder walls at leaner mixtures (up to a point) (assuming sufficent air is available).

In an ideal world, you would be advancing the spark as the mixture went lean for maximum return on enleanment.
Click to expand...

All you need to know about LOP / ROP is, do you have enough O2 to burn all the fuel, or do you have enough fuel to burn all the O2

when you have the exact amount of both you are at peak EGT, the removal of either will reduce temps.
 
Capt. Geoffrey Thorpe said:
You are ****ing unburned fuel out the exhaust if you are RoP. But, somtimes you have to do that for knock prevention and/or cooling.

For the same actual crankshaft delivered power, you do less pumping work (loss) and have less heat transfer (loss) to the cylinder walls at leaner mixtures (up to a point) (assuming sufficent air is available).

In an ideal world, you would be advancing the spark as the mixture went lean for maximum return on enleanment.
Click to expand...


Right -- which is why we takeoff full rich -- we're wasting some fuel, but it's still cheaper than an overhaul.

My Chief has a mixture control -- on the firewall, safety wired in place. The mixture is set for optimal per book recommendations and that's that.

Then again, I'm burning 3.8 GPH and rarely exceed 3k MSL.
 
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