LOP Noob...where to start?

[Jaybird180]

 

[Geico266]

Assuming the monitoring equipment is accurate. The spread between EGTs should no more than 100f. The spread between CHT's should be no more than 25f.

 

[Ted]

Assuming the monitoring equipment is accurate. The spread between EGTs should no more than 100f. The spread between CHT's should be no more than 25f.

Not entirely true. Yes the EGTs should be pretty close if the instrumentation is correct, but it often isn't. For example, on the left engine of the 310 there's always been a spread of EGTs that's closer to 200F, and the right engine has been pretty much dead on. It's been that way for 500 hours and an engine overhaul, so it's consistent. What matters is the changes and when they occur. So long as they all peak near eachother, you're good.

For CHTs, your spread will mostly have to do with the cooling characteristics. Depending on your aircraft, those can vary wildly. On the Aztec, the spread was close to 100F between hottest and coldest CHT. It was just a really bad cooling setup that provided extremely uneven airflow to the cylinders.

 

[Fearless Tower]

Assuming the monitoring equipment is accurate. The spread between EGTs should no more than 100f. The spread between CHT's should be no more than 25f.

One thing I noticed is that as far as CHTs go, all were generally running within 20F of each other 360-380 except the number 6 cylinder on both engines which ran warmer - on the warmest day of the trip 90F+ at the surface, The number 6s were running around 395 on the left and 405-410 on the right.

On one leg, it seemed like the only way to bring the temp on the right down below 400F was to enrich the mixture. Leaning it further made it noticeably rough.

I did read in the EDM 760 manual, that it is apparently common to have one cylinder that runs 20F warmer that the others due to the installation of the probes using the previously existing factory probe point. I'm wondering if the NR 6 cylinders were where they had the single temp probe installed originally.

Any thoughts or recommendations?

 

[Ted]

Sounds like the Baron has much better cooling than the Aztec. I also think Continentals seem a bit more even than Lycomings usually.

If it gets rough leaning, you might want to clean the injectors. They're Gamis, right? If not you might want to swap out for some. Also check the baffling. I don't know how Barons do - Lance is the expert in your case.

380F or less for hottest cylinder, especially on Continentals. Longevity will be your reward. Keep in mind this is harder in summer.

 

[JHW]

Sounds like the Baron has much better cooling than the Aztec.

depends on the type of baffling installed in the baron. Aztec baffling is pretty universally mediocre. Barons can range from stellar to horrible.

 

[Fearless Tower]

If it gets rough leaning, you might want to clean the injectors. They're Gamis, right? If not you might want to swap out for some. Also check the baffling. I don't know how Barons do - Lance is the expert in your case.

They are Gamis. My A&P IA who did the prebuy asked me if I wanted to have the injectors cleaned, although when he said that while some folks swear by it, others say there is no need to clean them I opted to save the money for some other items I wanted to get ahead on. Sounds like I may want to try having them cleaned now.

Does anyone know if cylinder 6 is where the factory CHT probe was originally installed?

 

[Ted]

They are Gamis. My A&P IA who did the prebuy asked me if I wanted to have the injectors cleaned, although when he said that while some folks swear by it, others say there is no need to clean them I opted to save the money for some other items I wanted to get ahead on. Sounds like I may want to try having them cleaned now.

Here's my perspective, and I probably have a bit more knowledge on it than the average A&P.

Mechanical injectors do get clogged over time. A certain amount of this is due to the poor filtration by the gascolator (I think on the order of 100-250 microns), and some of it is also due to the fuel itself. Typically, the clogging happens slowly such that you won't notice the difference until you have some weird little problem. GAMIjectors that won't lean out very well, weird noises (especially at high power) and the other big clue is when you have a fuel flow gauge (mechanical pressure-driven) that reads way, way high.

When I bought my Aztec, my injectors were so clogged that I got people making comments about the noise the engine was making. It still was smooth overall, but sounded bad on takeoff. My A&P insisted that there was no reason to clean the injectors - after all, he'd maintained that airplane for 8 years and it never did it, and the fact that the fuel flow gauge was reading way off the chart was obviously a faulty gauge. Remember, these gauges read on pressure, and a clogged injector will raise pressure (more pressure = more indicated flow).

Finally I said "Screw this" and cleaned the injectors myself one day (under supervision, of course). The Hoppes #9 turned BLACK within a matter of minutes, and I must have gained 50 HP out of that engine. Sounded better, better power, leaned better. Oh, and the fuel flow gauge now read a bit lower than the left engine. When I cleaned the injectors on the left engine (which were much better off) then they both came right in line with eachother.

When you're running ROP, you probably won't notice these issues. Of course, you also are more likely to end up with a cylinder clogged (leaned out) into a bad zone. It will still probably be smooth. When you're running LOP, you notice it more since now that lean cylinder will cut out and become rough.

While I think that most planes probably don't need the injectors clogged every 100 hours as is recommended, I think that it's a cheap and easy thing to do while you're doing your annual. It ends up being preventative maintenance that helps keep your engines running right. I just have 6 little glass bottles (in my case I use Starbucks Frappuccino bottles - perfect size) and I dump each injector in one. This way I make sure I put the injectors back in the same engine.

The counter point to this is that if you over-torque the injectors you do risk having cracks in the head or cracked/kinked fuel lines. I personally view this as a very small risk.

 

[Fearless Tower]

Here's my perspective, and I probably have a bit more knowledge on it than the average A&P.

Mechanical injectors do get clogged over time. A certain amount of this is due to the poor filtration by the gascolator (I think on the order of 100-250 microns), and some of it is also due to the fuel itself. Typically, the clogging happens slowly such that you won't notice the difference until you have some weird little problem. GAMIjectors that won't lean out very well, weird noises (especially at high power) and the other big clue is when you have a fuel flow gauge (mechanical pressure-driven) that reads way, way high.

When I bought my Aztec, my injectors were so clogged that I got people making comments about the noise the engine was making. It still was smooth overall, but sounded bad on takeoff. My A&P insisted that there was no reason to clean the injectors - after all, he'd maintained that airplane for 8 years and it never did it, and the fact that the fuel flow gauge was reading way off the chart was obviously a faulty gauge. Remember, these gauges read on pressure, and a clogged injector will raise pressure (more pressure = more indicated flow).

Finally I said "Screw this" and cleaned the injectors myself one day (under supervision, of course). The Hoppes #9 turned BLACK within a matter of minutes, and I must have gained 50 HP out of that engine. Sounded better, better power, leaned better. Oh, and the fuel flow gauge now read a bit lower than the left engine. When I cleaned the injectors on the left engine (which were much better off) then they both came right in line with eachother.

When you're running ROP, you probably won't notice these issues. Of course, you also are more likely to end up with a cylinder clogged (leaned out) into a bad zone. It will still probably be smooth. When you're running LOP, you notice it more since now that lean cylinder will cut out and become rough.

While I think that most planes probably don't need the injectors clogged every 100 hours as is recommended, I think that it's a cheap and easy thing to do while you're doing your annual. It ends up being preventative maintenance that helps keep your engines running right. I just have 6 little glass bottles (in my case I use Starbucks Frappuccino bottles - perfect size) and I dump each injector in one. This way I make sure I put the injectors back in the same engine.

The counter point to this is that if you over-torque the injectors you do risk having cracks in the head or cracked/kinked fuel lines. I personally view this as a very small risk.

Thanks Ted.....sounds like a cleaning of the Gamis will be the first thing I'll do.


Sent from my iPad using Tapatalk HD

 

[brywd]

Use the last cylinder to peak as you are leaning as the one you set up with because it will be the one that gets hurt if you have it to close to peak or slightly rich with higher power settings as the cylinders that peaked first are on the LOP side.

Herein lies the problem if your FF's for each cylinder aren't really close. You set the last to peak for 25 degrees or so LOP and the first to peak are now so lean that the cylinders are starving. They will not be damaged, but the engine may be rough running.

In a perfect world all cylinders will peak at the same time and then you can just pull the mixture until you feel the plane slow down and you are LOP. Then a little fiddling with the mixture to get them where you want and you are good to go. After the mixture pull and the slowing of the plane you are safe to slowly come back towards peak to find exact temps to tune with if you are so inclined.

For my plane I just pull till I feel it slow down, and then after a minute or two I set the mixture for 12.4 gph which is about 64 percent power. This is after fiddling around with this for a few years though. I always end up at 12.4 anyhow, so now I just start there.

 

[Ted]

Use the last cylinder to peak as you are leaning as the one you set up with because it will be the one that gets hurt if you have it to close to peak or slightly rich with higher power settings as the cylinders that peaked first are on the LOP side.

Herein lies the problem if your FF's for each cylinder aren't really close. You set the last to peak for 25 degrees or so LOP and the first to peak are now so lean that the cylinders are starving. They will not be damaged, but the engine may be rough running.

In a perfect world all cylinders will peak at the same time and then you can just pull the mixture until you feel the plane slow down and you are LOP. Then a little fiddling with the mixture to get them where you want and you are good to go.

This is why you end up often running a balance between being on the edge of roughness and keeping the CHTs happy.

If the CHTs are always happy, then aim for your 50F LOP. If they aren't, then on many aircraft you'll be trying to thread that needle. It's not hard once you get the hang of it.

 

[azure]

Use the last cylinder to peak as you are leaning as the one you set up with because it will be the one that gets hurt if you have it to close to peak or slightly rich with higher power settings as the cylinders that peaked first are on the LOP side.

Herein lies the problem if your FF's for each cylinder aren't really close. You set the last to peak for 25 degrees or so LOP and the first to peak are now so lean that the cylinders are starving. They will not be damaged, but the engine may be rough running.

This is exactly why I can't run LOP at higher power settings -- to get my richest cylinder (#2) safely LOP, I've got to lean so far that my leanest (#3) isn't making much power at all, and I get noticeable roughness. At low power settings or high altitudes, I just lean to rough and then enrich to smooth, at which setting #2 is about 50 ROP and #3 is about 25 LOP. In spite of what some folks have tried to tell me, I'd be afraid to do that at higher power settings since I'm not convinced that my 200 hp IO360 doesn't have a "red box" danger zone, and at that setting, if it does my #2 is right smack dab in the middle of it. (And if it is, I normally won't learn that by watching CHTs, since I almost never see CHTs above 350F no matter what I do.)

I've asked me A&P to do a careful inspection of my mags and plugs this annual to make 100% certain I don't have an ignition problem that's causing or exacerbating this issue. He is (or should be) doing that right now. If he doesn't find anything then I'm going to spring for GAMIs. With avgas at $6/gal I just can't afford to be wasting fuel like this, when most of my legs are relatively short ones at 4-6kft.

 

[Ted]

This is exactly why I can't run LOP at higher power settings -- to get my richest cylinder (#2) safely LOP, I've got to lean so far that my leanest (#3) isn't making much power at all, and I get noticeable roughness. At low power settings or high altitudes, I just lean to rough and then enrich to smooth, at which setting #2 is about 50 ROP and #3 is about 25 LOP. In spite of what some folks have tried to tell me, I'd be afraid to do that at higher power settings since I'm not convinced that my 200 hp IO360 doesn't have a "red box" danger zone, and at that setting, if it does my #2 is right smack dab in the middle of it. (And if it is, I normally won't learn that by watching CHTs, since I almost never see CHTs above 350F no matter what I do.)

Seeing as I've done fully instrumented detonation tests on your motor and you don't believe me...

 

[Fearless Tower]

I'd be afraid to do that at higher power settings since I'm not convinced that my 200 hp IO360 doesn't have a "red box" danger zone, and at that setting, if it does my #2 is right smack dab in the middle of it. (And if it is, I normally won't learn that by watching CHTs, since I almost never see CHTs above 350F no matter what I do.)

I'm a little confused by this statement. I thought that the whole context of the Red Box was that was the zone with potentially damaging temperatures and pressures.

How can an engine be in the Red Box with CHTs at 350F?

 

[Ted]

I'm a little confused by this statement. I thought that the whole context of the Red Box was that was the zone with potentially damaging temperatures and pressures.

How can an engine be in the Red Box with CHTs at 350F?

CHTs are only part of it. It is possible for an engine with good cooling to be operating with high internal cylinder pressures which are causing extra wear while having low CHTs observed. This isn't saying that the engine is experiencing detonation, but that is possible also.

I've had engines detonate with CHTs of 350 or less. But those were detonation prone engines and I was doing other things to poke them.

 

[Fearless Tower]

CHTs are only part of it. It is possible for an engine with good cooling to be operating with high internal cylinder pressures which are causing extra wear while having low CHTs observed. This isn't saying that the engine is experiencing detonation, but that is possible also.

I've had engines detonate with CHTs of 350 or less. But those were detonation prone engines and I was doing other things to poke them.

Okay, so the Red Box is more of a detonation prone zone than straight temp or pressure?

 

[azure]

Seeing as I've done fully instrumented detonation tests on your motor and you don't believe me...

What don't I believe? I don't remember you saying anything specifically about my engine. You did offer to teach me how to operate it safely. But that was before you moved.

Lots of people have said lots of things about my engine. Lots of things, both ways. You're about the only person whose opinion I would trust, if I heard it first hand from you.

So are you saying that it can't be made to detonate during normal operation? What about accelerated wear due to high ICPs? Or am I misunderstanding you (again?) ?

 

[Clark1961]

CHTs are only part of it. It is possible for an engine with good cooling to be operating with high internal cylinder pressures which are causing extra wear while having low CHTs observed. This isn't saying that the engine is experiencing detonation, but that is possible also.

I've had engines detonate with CHTs of 350 or less. But those were detonation prone engines and I was doing other things to poke them.

Question: Given an engine with 7.5:1 compression ratio and 100LL operating at 30 inches or less manifold pressure, what are the chances of detonation at any mixture setting?

Where I'm going with this is that I have seen high CHTs when running the TSIO-360 above 30 inches with various mixture settings but I have not seen high CHTs when running at any speed in the range of 2,300 to 2,500 and any mixture when 30 or below.

Basically, I'm curious about what you've seen in terms of detonation with low compression engines at various manifold pressures.

 

[gismo]

Seeing as I've done fully instrumented detonation tests on your motor and you don't believe me...

While I have complete faith in your knowledge that an IO-360 won't suffer from detonation or more importantly pre-ignition in cruise with any mixture, that might not account for glowing deposits, hanging helicoil tangs, or overheated spark plug electrodes which can and do occur in the "real world" with no outward indications outside the "red box".

 

[Fearless Tower]

While I have complete faith in your knowledge that an IO-360 won't suffer from detonation or more importantly pre-ignition in cruise with any mixture, that might not account for glowing deposits, hanging helicoil tangs, or overheated spark plug electrodes which can and do occur in the "real world" with no outward indications outside the "red box".

Lance,

Do you have any Baron specific thoughts on what I am seeing with my CHTs?

 

[gismo]

I use this as my reference for LOP ops (Hopefully no issues with posting this):

I believe that is a bit overconservative, at least for a NA engine. For instance I think the APS recommendation these days calls for staying out of the 25-50 ROP range at 65% as long as CHTs are under control.

 

[gismo]

They are Gamis. My A&P IA who did the prebuy asked me if I wanted to have the injectors cleaned, although when he said that while some folks swear by it, others say there is no need to clean them I opted to save the money for some other items I wanted to get ahead on. Sounds like I may want to try having them cleaned now.

Does anyone know if cylinder 6 is where the factory CHT probe was originally installed?

I'm pretty sure the OEM CHT was on #3 but it might be #4. In any case it's easy to spot a spark plug gasket probe, just look for a metal shielded wire about 1/8" diameter coming from the base of one of the plugs. I had one on my Bonanza and never liked it much. JPI offers a much better solution that goes in between the OEM probe and the cylinder with both in the same boss under the cylinders as the rest of the JPI probes. I strongly recommend getting one of those so you don't have ambiguous CHT readings. It is true that the plug gasket probe will read higher but the amount higher varies significantly with airspeed and power along with which plug location (top or bottom) is used.

As to LOP ops, the first thing to do is get a handle on your mixture distribution. IO470s are notoriously difficult to balance well but with some effort it can be done. If your JPI has FF taking a measure of the "GAMI spread" is easy but without that it can require an hour in the air and is best accomplished with an assistant.

I recommend doing the check at 7000 MSL with full throttle and 2300 RPM first. If the engine is set up properly (good ignition system and well balanced mixtures) you should be able to get the richest cylinder at least 30-40 LOP while running smoothly and this should result in a fuel flow between 11 and 11.5 GPH per engine. You might improve things by closing the throttles just enough to drop the MP by a few tenths of an inch of Hg.
CHTs should be in the low to mid 300s with ISA standard OAT. Anything above 350 suggests that you're either running ROP or need to attend to baffling or ignition timing.

If the engine runs OK LOP there try 10,000 MSL (DA actually). At that density they probably won't run smoothly more than 5-10° LOP and even peak EGT is close enough for efficient and cool operation. CHTs here should be in the 300-325 range.

Another good check involves comparing the relative order of the EGT peaks at or above 8000 MSL with what you get at least 4000 ft lower using the same MP and RPM (obviously the throttle must be partially closed then). If the order changes AND there's at least a .1gph Peak EGT FF difference between cylinders the change order you probably have an induction leak.

11.5 GPH is 65% max rated power and you really can't hurt the engine with the red knob at that FF, especially if you keep the CHTs at 380°F or less. When I had IO470s I'd almost always run that power (11.5 Gph) at or below 11,000 MSL (that's about peak EGT at 11) and would see around 175 KTAS at 7 and 180 at 11 with CHTs around 300°F.

I don't generally check how far from peak EGT I'm running unless I'm down low and running hard (rare for me). But at first it's a good idea to check this on almost every flight until you find the "sweet spot" for your engines. I prefer to check by leaning until the engine is either noticeably rough or the power drops enough to feel the plane decelerate (the "Big Pull") then slowly enrichening the mixture looking for the first cylinder to peak. The EDM 760 usually does a decent job of identifying the first cylinder to peak but is pretty lousy at capturing the exact temp at which that peak occurred so you'll want to tweak the FF slowly (.1 gph between EGT checks) while monitoring the first to peak (richest) cylinder.

I especially don't like JPI's "LOP Lean Find mode" as it requires you to start on the ROP side and move the mixtures smoothly but more slowly than I found practical with the levers in a Baron. The results from that for me were inconsistent in terms of the displayed peak and LOP values by 25-30°F and it often identified the wrong cylinder as the richest. I recommend either just using the Normalize mode and watching the bars (10°F resolution) to find the richest cylinder and then selecting that cylinder to show the digital EGT for it but the original "Lean Find" mode does pretty well at finding the richest cylinder if you approach from the LOP side.

One caution when searching for the richest cylinder from the LOP side is that there are often two peaks and you want to use the one with the highest FF so after you think you have the first to peak from the lean side you should continue going richer until that EGT gets at least 25° cooler. If you find a second peak at a higher FF make sure you're working with the richest cylinder as you might have gone past peak EGT on another cylinder on your way to the second peak on the first cylinder to peak (falsely).

If you can't get the engine to run smoothly up high but LOP seems to work OK down low you probably have some ignition system issues. A WOT LOP mag check at or above 8000 MSL might identify a specific cylinder and that could be a spark plug or wire issue. If all are misfiring or (more likely) the leanest 2-4 cylinders are misfiring (EGTs become erratic) it's probably a magneto problem. I use fine wire plugs (Tempest) and I think they help, especially up high but I also have the more powerful and arc-over resistant Bendix 1200 series magnetos.

BTW, Champion has been having issues with their internal resistors breaking down and if your plugs are affected by that this could make it difficult to run LOP especially above 5000 MSL.

One last tidbit: Cylinder 5 is almost always the hottest if the mixtures are well balanced and a 20-30°F cylinder to cylinder CHT difference isn't unusual. Just make sure they are all at or below 380 and they should be less than that in LOP cruise.

 

[NineThreeKilo]

Read the JPI manual. The read it again. And again. Then let's discuss.

Seriously, and the injectors documentation, then ask any question to your engine manufacturer (they will answer questions too lol)

Or pay me $900 and I'll get on Skype and host a webinar where I summarize whats in said manuals.

 

[Ted]

Okay, so the Red Box is more of a detonation prone zone than straight temp or pressure?

Keep in mind that the Red Box is a term that APS coined. So in my world of doing detonation testing and other engine running, we never used it.

But in the range of peak to 100F ROP (or larger, or smaller, depending on the engine) is an area where you will have higher internal cylinder pressures, which will lead to higher cylinder head temperatures (observable) and higher pressures and temperatures within the cylinder (not observable).

All of these contribute to detonation. Whether or not you will have it is dependent on a number of other factors.

What don't I believe? I don't remember you saying anything specifically about my engine. You did offer to teach me how to operate it safely. But that was before you moved.

Lots of people have said lots of things about my engine. Lots of things, both ways. You're about the only person whose opinion I would trust, if I heard it first hand from you.

So are you saying that it can't be made to detonate during normal operation? What about accelerated wear due to high ICPs? Or am I misunderstanding you (again?) ?

On more than one occasion when you've brought this question up, I've said that at 75% power you really don't have to worry about it. So maybe you missed it.

I'm actually probably closer to you in Cincinnati now than I was in Pennsylvania, but I've also pretty much given up on flight instruction because of family commitments.

Maybe I should write a thread that goes into the anatomy of what exactly a detonation test entails.

Question: Given an engine with 7.5:1 compression ratio and 100LL operating at 30 inches or less manifold pressure, what are the chances of detonation at any mixture setting?

Where I'm going with this is that I have seen high CHTs when running the TSIO-360 above 30 inches with various mixture settings but I have not seen high CHTs when running at any speed in the range of 2,300 to 2,500 and any mixture when 30 or below.

Basically, I'm curious about what you've seen in terms of detonation with low compression engines at various manifold pressures.

Keep in mind that your engine is a TSIO-360, which I have never run a detonation test on. I have no idea as to its specific characteristics and how it behaves compared to others. Now with that said, I would think at under 30" with 7.5:1 compression on 100LL you would be pretty unlikely to have any detonation occur.

A casual observation WRT CHTs on turbocharged engines is that I've seen them rise noticeably at power settings above 30". I'm not entirely what sure what makes that the magic number for most engines, but I suspect it probably just has to do with the pressure ratio increasing by that extra few percent once you get above 30" resulting in the turbocharger having more exhaust (heat) going through it, heating the intake air charge more (both from a hotter turbo and higher pressure ratio), and the engine working a bit harder.

While I have complete faith in your knowledge that an IO-360 won't suffer from detonation or more importantly pre-ignition in cruise with any mixture, that might not account for glowing deposits, hanging helicoil tangs, or overheated spark plug electrodes which can and do occur in the "real world" with no outward indications outside the "red box".

What I had told Liz wasn't that her 200 HP IO-360 was detonation-free at any mixture and power setting, but rather that at 75% power she didn't have to worry.

You are, of course, correct about the potential for other issues. If you have glowing deposits or some problem of that nature, that's a whole 'nother kettle of fish. I had a bad plug glowing and causing detonation on the 310 once, and I couldn't get it to stop regardless of mixture until I pulled down to below 20" and right about at full rich. My levers (and gauges) were very uneven that evening.

 

[Skylane81E]

Explain this if ya don't mind...

Sure,

Take a clean (we have one that has only ever been used to check induction and exhaust systems, never as a vaccum) shop vac set to blow and cram the hose into the air inlet, seal it up with rags. Turn on the vacuum and spray the induction system down with soapy water. The vacuum will provide sufficient pressure to make any leaks bubble up, but not enough to hurt anything.

Did I mention to use a clean vacuum? You don't want to be blowing crap up into the induction system:wink2:

Shove it up the tail pipe and you can do exhaust systems the same way.

 

[Clark1961]

Keep in mind that your engine is a TSIO-360, which I have never run a detonation test on. I have no idea as to its specific characteristics and how it behaves compared to others. Now with that said, I would think at under 30" with 7.5:1 compression on 100LL you would be pretty unlikely to have any detonation occur.

A casual observation WRT CHTs on turbocharged engines is that I've seen them rise noticeably at power settings above 30". I'm not entirely what sure what makes that the magic number for most engines, but I suspect it probably just has to do with the pressure ratio increasing by that extra few percent once you get above 30" resulting in the turbocharger having more exhaust (heat) going through it, heating the intake air charge more (both from a hotter turbo and higher pressure ratio), and the engine working a bit harder.

Thanks for sharing your knowledge and observations.

 

[azure]

Ted, thanks for saying it clearly. If you said it before, I must have missed it. I do recall you saying that below 75@ (damm iPad doesn't sem to have a percent symbol), the risk drops off rapidly, or something to that effect, but it sounded fuzzy enough that I didn't feel safe at much above 65. Even so, since the optimum LOP setting puts one of my cylinders right at peak power/ICP, I'm not too comfortable about running it that way. My A&P is still not completely sure that there isn't something screwy with my induction system and wants to try checking for leaks with a shop vac before telling me to go for GAMIs.

 

[Ted]

Ted, thanks for saying it clearly. If you said it before, I must have missed it. I do recall you saying that below 75@ (damm iPad doesn't sem to have a percent symbol), the risk drops off rapidly, or something to that effect, but it sounded fuzzy enough that I didn't feel safe at much above 65. Even so, since the optimum LOP setting puts one of my cylinders right at peak power/ICP, I'm not too comfortable about running it that way. My A&P is still not completely sure that there isn't something screwy with my induction system and wants to try checking for leaks with a shop vac before telling me to go for GAMIs.

Well, if there is something funny going on with your induction system, then that needs to be checked out and see what's going on. Either way, at 75% power on your engine with the low CHTs that you've reported, detonation just isn't something that will happen on your engine unless you've got something really weird going on (like being in 120F ambient temps). And if there is, you'll notice abnormal temperatures (CHTs will go up up up on that cylinder).

I don't think you're planning on making it to Wings, but if you do make it that way, we can go up for a quick demo flight.

 

[gismo]

Maybe I should write a thread that goes into the anatomy of what exactly a detonation test entails.

Yes you should!

A casual observation WRT CHTs on turbocharged engines is that I've seen them rise noticeably at power settings above 30". I'm not entirely what sure what makes that the magic number for most engines, but I suspect it probably just has to do with the pressure ratio increasing by that extra few percent once you get above 30" resulting in the turbocharger having more exhaust (heat) going through it, heating the intake air charge more (both from a hotter turbo and higher pressure ratio), and the engine working a bit harder.

Adiabatic and frictional heating of the intake air, higher ICP, higher exhaust back pressure, and more power. Sounds like worse than a triple whammy.

 

[azure]

Well, if there is something funny going on with your induction system, then that needs to be checked out and see what's going on. Either way, at 75% power on your engine with the low CHTs that you've reported, detonation just isn't something that will happen on your engine unless you've got something really weird going on (like being in 120F ambient temps). And if there is, you'll notice abnormal temperatures (CHTs will go up up up on that cylinder).

The reason he is suspicious is that I have (twice now) seen the #3 EGT (not CHT) shoot up >25F for a half minute or so. The first time it was close to 100 degrees higher, the second time (today) it was about 40 degrees.

I don't think you're planning on making it to Wings, but if you do make it that way, we can go up for a quick demo flight.

I wasn't planning on it because of my annual. The annual is done, but there are some issues to iron out, the most pressing being that my fuel selector valve failed to turn off my fuel flow today when turned to the "off" position. It only happened once, and wiggling it fixed it, but if it gets stuck in one position I wouldn't trust it not to get stuck in a different one...

If by some miracle my A&P solves this by late in the week, I might make a surprise trip over on Saturday and take you up on that demo flight. I have a hike to lead in the morning, though, and an AME appointment on Monday, so my schedule is a little tight this weekend.

 

[Fearless Tower]

I'm pretty sure the OEM CHT was on #3 but it might be #4. In any case it's easy to spot a spark plug gasket probe, just look for a metal shielded wire about 1/8" diameter coming from the base of one of the plugs. I had one on my Bonanza and never liked it much. JPI offers a much better solution that goes in between the OEM probe and the cylinder with both in the same boss under the cylinders as the rest of the JPI probes. I strongly recommend getting one of those so you don't have ambiguous CHT readings. It is true that the plug gasket probe will read higher but the amount higher varies significantly with airspeed and power along with which plug location (top or bottom) is used.

As to LOP ops, the first thing to do is get a handle on your mixture distribution. IO470s are notoriously difficult to balance well but with some effort it can be done. If your JPI has FF taking a measure of the "GAMI spread" is easy but without that it can require an hour in the air and is best accomplished with an assistant.

I recommend doing the check at 7000 MSL with full throttle and 2300 RPM first. If the engine is set up properly (good ignition system and well balanced mixtures) you should be able to get the richest cylinder at least 30-40 LOP while running smoothly and this should result in a fuel flow between 11 and 11.5 GPH per engine. You might improve things by closing the throttles just enough to drop the MP by a few tenths of an inch of Hg.
CHTs should be in the low to mid 300s with ISA standard OAT. Anything above 350 suggests that you're either running ROP or need to attend to baffling or ignition timing.

If the engine runs OK LOP there try 10,000 MSL (DA actually). At that density they probably won't run smoothly more than 5-10° LOP and even peak EGT is close enough for efficient and cool operation. CHTs here should be in the 300-325 range.

Another good check involves comparing the relative order of the EGT peaks at or above 8000 MSL with what you get at least 4000 ft lower using the same MP and RPM (obviously the throttle must be partially closed then). If the order changes AND there's at least a .1gph Peak EGT FF difference between cylinders the change order you probably have an induction leak.

11.5 GPH is 65% max rated power and you really can't hurt the engine with the red knob at that FF, especially if you keep the CHTs at 380°F or less. When I had IO470s I'd almost always run that power (11.5 Gph) at or below 11,000 MSL (that's about peak EGT at 11) and would see around 175 KTAS at 7 and 180 at 11 with CHTs around 300°F.

I don't generally check how far from peak EGT I'm running unless I'm down low and running hard (rare for me). But at first it's a good idea to check this on almost every flight until you find the "sweet spot" for your engines. I prefer to check by leaning until the engine is either noticeably rough or the power drops enough to feel the plane decelerate (the "Big Pull") then slowly enrichening the mixture looking for the first cylinder to peak. The EDM 760 usually does a decent job of identifying the first cylinder to peak but is pretty lousy at capturing the exact temp at which that peak occurred so you'll want to tweak the FF slowly (.1 gph between EGT checks) while monitoring the first to peak (richest) cylinder.

I especially don't like JPI's "LOP Lean Find mode" as it requires you to start on the ROP side and move the mixtures smoothly but more slowly than I found practical with the levers in a Baron. The results from that for me were inconsistent in terms of the displayed peak and LOP values by 25-30°F and it often identified the wrong cylinder as the richest. I recommend either just using the Normalize mode and watching the bars (10°F resolution) to find the richest cylinder and then selecting that cylinder to show the digital EGT for it but the original "Lean Find" mode does pretty well at finding the richest cylinder if you approach from the LOP side.

One caution when searching for the richest cylinder from the LOP side is that there are often two peaks and you want to use the one with the highest FF so after you think you have the first to peak from the lean side you should continue going richer until that EGT gets at least 25° cooler. If you find a second peak at a higher FF make sure you're working with the richest cylinder as you might have gone past peak EGT on another cylinder on your way to the second peak on the first cylinder to peak (falsely).

If you can't get the engine to run smoothly up high but LOP seems to work OK down low you probably have some ignition system issues. A WOT LOP mag check at or above 8000 MSL might identify a specific cylinder and that could be a spark plug or wire issue. If all are misfiring or (more likely) the leanest 2-4 cylinders are misfiring (EGTs become erratic) it's probably a magneto problem. I use fine wire plugs (Tempest) and I think they help, especially up high but I also have the more powerful and arc-over resistant Bendix 1200 series magnetos.

BTW, Champion has been having issues with their internal resistors breaking down and if your plugs are affected by that this could make it difficult to run LOP especially above 5000 MSL.

One last tidbit: Cylinder 5 is almost always the hottest if the mixtures are well balanced and a 20-30°F cylinder to cylinder CHT difference isn't unusual. Just make sure they are all at or below 380 and they should be less than that in LOP cruise.

Thanks Lance!

Sounds like I have some testing/recording to do on my next flight. I do believe that my EDM 760 records FF....I just need to figure out the button sequence to get it to display when I want it.

 

[Ted]

Yes you should!

Adiabatic and frictional heating of the intake air, higher ICP, higher exhaust back pressure, and more power. Sounds like worse than a triple whammy.

I'll put the detonation test explanation on my "to do" list. It'll pop up in Maintenance Bay, maybe we can have another sticky there.

And we pretty much said the same things, you just got more technical.

A number of Twin Cessna folks do operate above 30" in cruise, but I haven't seen their CHTs. My friend's RAM T310R is remarkably cool at something like 33", but as part of the package RAM used a bigger turbo and intercoolers.

The reason he is suspicious is that I have (twice now) seen the #3 EGT (not CHT) shoot up >25F for a half minute or so. The first time it was close to 100 degrees higher, the second time (today) it was about 40 degrees.

I wasn't planning on it because of my annual. The annual is done, but there are some issues to iron out, the most pressing being that my fuel selector valve failed to turn off my fuel flow today when turned to the "off" position. It only happened once, and wiggling it fixed it, but if it gets stuck in one position I wouldn't trust it not to get stuck in a different one...

If by some miracle my A&P solves this by late in the week, I might make a surprise trip over on Saturday and take you up on that demo flight. I have a hike to lead in the morning, though, and an AME appointment on Monday, so my schedule is a little tight this weekend.

It does sound like some investigation is prudent. Could also be some sort of weird clogging in the nozzle or a spark plug that's firing intermittently. When that happened on my Aztec it was an ignition issue - bad plug wire.

We're leaving Wings around 2 or so to get to a wedding in New York, so it probably won't work this trip.