252 peak EGT spread-what's yours? And: too much engine roughness?

[nationwide]

Hello all, I've owned an '86 252 for coming up on two years now that I continue to learn about.

 

I'm learning about LOP ops.  I've researched many articles and also many posts here and elsewhere regarding this topic.  I'm curious what kind of peak EGT spreads (a.k.a. "GAMI spread"; not peak EGT value difference) folks are getting (or got) out of their stock TSIO-360-MBs or SBs.

 

A question that I can't find an answer to is:  How much roughness on the lean side is too much?  I don't want to start a ROP/LOP argument, but hopefully we can all agree that with a fixed MP/RPM power generated decreases quickly as we continue to lean past peak, which can cause power imbalances and roughness when all cylinders are not operating at the same mixture.  A lot of LOP ops articles will say that you cannot run LOP if it is rough, but how do you determine that?

 

I have a spread of ~0.5 gph at a MP the book calls 65% (it's not actually 65% of course unless the mixture is at the book-specified ratio).  I can go about 30 LOP and I wouldn't call it "rough", but it is perceptibly different.  I can't feel any new shaking feeling in the pedals or the yoke.  The whisky compass seems to shake just as badly as it does any other time.  BTW, the prop seems well balanced on this aircraft.

 

During one flight, while operating very LOP, my wife--who doesn't get into the details of my neurotic FE-like fiddling, only recognizes that I am doing "something"--asked "why is it running so rough?"  I'm assuming that's too much!    But I was about 80-100 LOP at that point.

 

I, personally, believe in trying to run LOP (I'm fine with it if you don't) but I definitely don't want to crack anything by doing it.

 

Thanks for your thoughts!

[aviatoreb]

Hi nationwide, I have a different engine, the TSIO520nb, but a turbo engine so a bit of feedback.

 

My spread is roughly 0.4gph.  When I go LOP I get a tiny change in sound and roughness so slight I have a hard time to decide if it is really there but it is.  But within a minute or so it settles out and just disappears.  So have you tried running your LOP setting you describe above a bit letter to see if it settles in smoother?

 

Also, your book MP/rpm setting does not correctly give your power percentage when you are LOP.  It is your fuel flow that does. Your fuel flow (in gph) x 13.7 hp.gph is your horsepower then divide by 210 to get the percentage.  I bet you are a lot lower in % hp than you think, meaning that you can safely run that engine closer to peak on the lop side than perhaps you are right now - I am commenting that you are running very lop and perhaps you do not need to.

That said, how is your TiT when you are LOP?  For my engine TIT is the main active limiting parameter that prevents me from running high power settings when LOP.  But it runs cool enough at lower power settings.

[philipneeper]

Hi nationwide, I have a different engine, the TSIO520nb, but a turbo engine so a bit of feedback.

 

My spread is roughly 0.4gph.  When I go LOP I get a tiny change in sound and roughness so slight I have a hard time to decide if it is really there but it is.  But within a minute or so it settles out and just disappears.  So have you tried running your LOP setting you describe above a bit letter to see if it settles in smoother?

 

Also, your book MP/rpm setting does not correctly give your power percentage when you are LOP.  It is your fuel flow that does. Your fuel flow (in gph) x 13.7 hp.gph is your horsepower then divide by 210 to get the percentage.  I bet you are a lot lower in % hp than you think, meaning that you can safely run that engine closer to peak on the lop side than perhaps you are right now - I am commenting that you are running very lop and perhaps you do not need to.

That said, how is your TiT when you are LOP?  For my engine TIT is the main active limiting parameter that prevents me from running high power settings when LOP.  But it runs cool enough at lower power settings.

I see you have a formula for % power. Where would I find out my formula for my C?

[nationwide]

Hi nationwide, I have a different engine, the TSIO520nb, but a turbo engine so a bit of feedback.

 

 

Thanks for your perspective, Erik.  I usually run about 10-30 LOP and it does not "improve" much over time, assuming any "improvement" is needed (I don't know).  I've never tried fine wire plugs which I learned a lot of people have good luck with.  Really, I'm trying to figure out if my current situation is acceptable or not.

 

I am aware that leaning from book 65% numbers (peak power mixture) is not actually 65%, but thanks for re-affirming--that's a difficult concept at first.  I've done the GAMI spread test at 65% though to avoid harming the engine while going through peak, so that's where my 0.5 gph spread number comes from.  I've not tried LOP with a higher MP yet.  I like to keep TIT as low as I can...targeting the low- to mid-1500's, and with the conservative settings I use, I don't have trouble doing that (this is mostly at 12k and below).

[nationwide]

I see you have a formula for % power. Where would I find out my formula for my C?

 

Philip, see this article:

http://www.avweb.com/news/pelican/182106-1.html

 

It's about forced induction engines but the examples he provides are all normally aspirated:

 

"On the flat, horizontally opposed, air-cooled aircraft engines with 8.5:1 compression ratios (including TCM IO-520/550 and Lycoming IO-540), simply multiply fuel flow in GPH times 14.9. The result is HP. If you insist on percent, divide that by the rated power of the engine. For the same engines with 7.5:1 compression ratio (most factory-installed turbos), the numbers are worse, and the multiplier drops to about 13.7."

 

This only applies when LOP (i.e., you can boost FF way up ROP past the point of productive combustion and you are not making any more HP; less, in fact, once past the best power air-fuel ratio).

[aviatoreb]

I see you have a formula for % power. Where would I find out my formula for my C?

 

See in here where it says "what power setting is that" - http://www.avweb.com/news/pelican/182106-1.html?redirected=1

The formula is this for a turbo engine (compression being 7.5:1)

 

gph * 13.7 hp/ gal = your actual horsepower and this formula only works when lean of peak

 

because rich of peak you are using excess fuel also as a cooling agent (its not all getting burned).

 

If you want percent power then take your max take-off power (210 for the TSIO360) so formula is %=your actual horsepower/210.

 

So getting more power lean of peak efficiently (so therefore more speed) becomes a game of trying to squeeze as much fuel as possible through your engine while still lean of peak and while still within temperature constraints (lean enough to remain out of the red box and lean enough that nothing is getting too hot.  For some engines cylinders start getting hot - not mine mine remain very very cool when LOP.  For my engine it is the turbo TiT that starts getting hotter than I would like if i do not remain enough deep in the LOP).

[aviatoreb]

Philip, see this article:

http://www.avweb.com/news/pelican/182106-1.html

 

It's about forced induction engines but the examples he provides are all normally aspirated:

 

"On the flat, horizontally opposed, air-cooled aircraft engines with 8.5:1 compression ratios (including TCM IO-520/550 and Lycoming IO-540), simply multiply fuel flow in GPH times 14.9. The result is HP. If you insist on percent, divide that by the rated power of the engine. For the same engines with 7.5:1 compression ratio (most factory-installed turbos), the numbers are worse, and the multiplier drops to about 13.7."

 

This only applies when LOP (i.e., you can boost FF way up ROP past the point of productive combustion and you are not making any more HP; less, in fact, once past the best power air-fuel ratio).

 

I have no idea why my engine stabilizes and smooths out when lop, and I have never heard of or read of anyone else having this behavior.  But I will take it.  Even before it smooths out it is already acceptably smooth but it gets smoother as I say within a minute or so.

 

When I first got my airplane it was not as smooth LOP.  I had to do some things.  

-The balance was not good enough - so I was able to achieve better than the magic 0.5gph without buying Gami's but rather by swapping the stock injectors I had around between the cylinders.

 

That helped but it was still not smooth enough and the turbo was still a bit hotter than now.  Your entire ignition system needs to be in tip top shape to work well LOP.

 

-Then I got fine wires and that helped.  Why?  I don't know but perhaps it is because the fuel burns more completely with fine wires?

-Then we searched with a fine tooth comb for any induction leaks and sure enough we found a few pin size holes in the induction tubes, which we therefore replaced with new hoses. I figure therefore LOP is a great way to diagnose and make sure your engine setup is in tip top shape even if you are planning just to run ROP.

-Then when it was time to replace mags, it runs just a tad better still with fresh mags.

[Z W]

I have read a lot on the internet to try to learn about running my TSIO-360-MB in the LOP realm.  I've found it very difficult or impossible to find good information.  Some lean by the TIT gauge, and some by last EGT to peak.  Some swear their engines are always smooth; Some claim a lot of roughness.  I've decided it's probably very subjective.  Also, that engine is very rare.  Most of the things you read are for Continental IO-550's or Lycoming 540's, which really does not apply to us.

 

Myself, I've settled on using the TIT gauge to lean, after some very knowledgeable people on beechtalk.com said that's what you do for a turbo engine.  Our TSIO-360-MB LOP fuel flow is 11.5 GPH for 75% power.  I flew for quite some time at 2500 RPM, 32" MP, and 11.5 GPH, which is right around 20-30 degrees LOP.  I found this gave me about 140 knots of indicated airspeed, which is a good cruise speed.  It kept CHTs at 350 or below, which was good.  However, it always came with a very slight, almost imperceptible, roughness.  That same roughness persists all the way to 100 degrees LOP.  I don't feel it in the pedals or yoke, but I can hear it, and feel it in my knee against the center console.  It's slight enough that I would bet plenty of guys would just fly with it, and passengers would never notice.  Some pilots probably wouldn't notice.

 

I decided I don't like it, so I went back to book power settings, which is 2500 RPM, 28" MP, lean to peak TIT, which is 11.5 GPH very consistently.  I get the same indicated airspeed.  CHT's run about 350-370, which is a little higher, but very acceptable.  And the engine is buttery smooth and happy.  TIT is usually 1600-1615.  Sometimes as high as 1625 if I'm over 15,000 ft.  But everything I've read says turbo's can be run right up to redline TIT (1650 in our case) without damaging them or decreasing their life, so I find that acceptable.

 

I'm also interested to hear anybody else with the TSIO-360-MB engine's perspective, and to compare notes.

[231LV]

Sounds like you have found the "sweet spot" for your engine! I run a TSIO 360 GB ( the infamous hot runner) with nearly the same settings although my FF is closer to 10 gph...CHT for my hottest is typically 380 degrees and my TIT limits me when it hits 1625 ( with inter cooler) to 65 percent power..slightly rough with KTAS at 17 k ft of about 170. I am also at just about 30" mp and 2500 rpm....I use both the " last to peak" and TIT when setting things up LOP...engines love it

[nationwide]

I have read a lot on the internet to try to learn about running my TSIO-360-MB in the LOP realm.  I've found it very difficult or impossible to find good information.  

 

...

 

I'm also interested to hear anybody else with the TSIO-360-MB engine's perspective, and to compare notes.

 

That's been my finding too (lack of information).  Thank you for sharing.  Anyone else willing to weigh in?

[Earl]

I too would love to run LOP with my 86 252 but with no luck.  It just runs too rough.  I have an EDM-730 and sent a spread test to GAMI and they responded that my spread was decent but could be helped by their injectors but have not pulled the trigger as yet.  I usually run at 60% power so I can stay out of the red box and lean to the edge of roughness.  Only gives up 3-5 kts in airspeed at around 9.5gph which works well for me. CHTs on my hottest cylinder is usually around 340-365 degF depending on OAT and cowl flap setting.  TIT's at that setting are usually around 1550 degF.   But if I run above 60% I always lean to 100 degF ROP which at 65% is around 13.5gph.  So the answer may be GAMI injectors but if the engine runs rough at LOP I would not do it.  And I consider rough running as any shaking above what you would get running ROP but maybe that is too cautious.  I just don't think running an engine where the cylinders are not firing at the same time is not a great idea and definitely not very comfortable.

 

Have you taken the Advanced Pilot course yet?  If not, I highly recommend it although it sounds like you already understand the value of LOP operation.   

[Earl]

I have read a lot on the internet to try to learn about running my TSIO-360-MB in the LOP realm.  I've found it very difficult or impossible to find good information.  Some lean by the TIT gauge, and some by last EGT to peak.  Some swear their engines are always smooth; Some claim a lot of roughness.  I've decided it's probably very subjective.  Also, that engine is very rare.  Most of the things you read are for Continental IO-550's or Lycoming 540's, which really does not apply to us.

 

Myself, I've settled on using the TIT gauge to lean, after some very knowledgeable people on beechtalk.com said that's what you do for a turbo engine.  Our TSIO-360-MB LOP fuel flow is 11.5 GPH for 75% power.  I flew for quite some time at 2500 RPM, 32" MP, and 11.5 GPH, which is right around 20-30 degrees LOP.  I found this gave me about 140 knots of indicated airspeed, which is a good cruise speed.  It kept CHTs at 350 or below, which was good.  However, it always came with a very slight, almost imperceptible, roughness.  That same roughness persists all the way to 100 degrees LOP.  I don't feel it in the pedals or yoke, but I can hear it, and feel it in my knee against the center console.  It's slight enough that I would bet plenty of guys would just fly with it, and passengers would never notice.  Some pilots probably wouldn't notice.

 

I decided I don't like it, so I went back to book power settings, which is 2500 RPM, 28" MP, lean to peak TIT, which is 11.5 GPH very consistently.  I get the same indicated airspeed.  CHT's run about 350-370, which is a little higher, but very acceptable.  And the engine is buttery smooth and happy.  TIT is usually 1600-1615.  Sometimes as high as 1625 if I'm over 15,000 ft.  But everything I've read says turbo's can be run right up to redline TIT (1650 in our case) without damaging them or decreasing their life, so I find that acceptable.

 

I'm also interested to hear anybody else with the TSIO-360-MB engine's perspective, and to compare notes.

Zane:  Do you happen to know where you are vis-a-vis ROP at these setting?  My recollection from my 252 is those settings would put me at around 50 degF ROP which results in the highest internal cylinder pressure (ICP) even if CHTs are reasonable.  As I understand from the Advanced Pilot course that is the worst place to run your engine.  As I indicated above to the OP, I now run at 60% power so there is no red box or if I run above there I use my EDM-730 to lean to 100 degF ROP.  Gives me CHTs on my hottest cylinder (always #6) of around 345-365 degF.

[Z W]

Well, if you go by TIT, I am at peak. Using EGT is actually usually almost the same,  within a few degrees. I know everybody who has gone to APS says that is high ICP territory and the worst place to run your engine. None of those guys have our engine in my experience. And our engine has an unusual turbocharger configuration. Using the APS guidelines you describe leads to the roughness I described on my engine. 

 

Peak TIT is where the POH says to run the engine. That's where it's smooth, cool, and efficient.  Some engineer and test pilot got together and figured that out.  So that's where I've been running it. There may be better ways, but there's a lot of bad information on the Internet in my experience. 

 

I find 100+ ROP unacceptable. It's always 13.5 gph like you stated, for the same speed I get at 11.5 gph.  Over a 2000 hour engine life, that's 4000 wasted gallons of fuel. At a conservative $5 per gallon, that's $20,000.00.  Almost half the cost of an overhaul, even before you consider wasted useful load and extra fuel stops. Even if it costs some hours between overhaul, going leaner makes sense. And I'm not at all convinced going leaner is going to cost hours between overhaul. 

 

I also find 60% power unacceptable. Just because I like to go fast. 

 

Thanks for sharing. It's good to compare what others are doing. Did you go to APS, and did they tell you anything specific about the 252 engine? 

[Earl]

Zane:  

 

Lot to think about there.  I've taken the advanced pilot course and the data was pretty convincing that running 50degF ROP is where the highest ICP occurs.  The way you run your engine was exactly how I did until I took the online course.  Since I didn't attend the course in Ada I could not ask questions but I am going to ping George or Walter about the differences in engines as they did not indicate that the results would differ vis-a-vis an IO-550 vs a IO-360 with turbo but maybe there is.  

 

As for the issue of running at 100degF ROP I agree it is a fuel waste compared to running at 11.5 gph at similar speeds and the real question is exactly what does running the engine at the highest ICP do to you in terms of needing a top overhaul before TBO and ultimately TBO.  I suspect that is very dependent on the airplane, how often it is flown, etc. and could not be quantified.  However if you are running the engine that way and reaching TBO without a top overhaul or having to replace cylinders that to me is the only data point you should need.

 

I too like speed but when you compare losing 3-5kts while saving 2 gph it seems like a good trade off to me.  Saves me 5 gallons of $6/gal gas on a 500 nm trip and only adds 6 minutes to the trip (assuming my math is right).  Anyway, I really appreciate your perspective on this and the feedback.

[DonMuncy]

Zane,

Where do you find the recommendation in the POH to run at peak TIT. It may be there, but I don't find it in mine. Mine says do not exceed 1650 degrees, except that you can go to 1725 for a max of 30 seconds (to find peak).

[Z W]

You can see the pages attached.  The first two are from my plane's original POH with the TSIO-360-GB engine.  It says lean to peak TIT for economy cruise, or 125 ROP TIT for best power.

 

The third page is from my POH supplement that came with the 262 conversion, when a TSIO-360-MB engine was bolted on.  It says "Lean to peak" for cruise power settings.

M20K 262 Leaning Instructions.pdf

[DonMuncy]

We have the same information. You can lean to peak so long as you don't exceed 1650 degrees.

[Parker_Woodruff]

I too would love to run LOP with my 86 252 but with no luck. It just runs too rough. I have an EDM-730 and sent a spread test to GAMI and they responded that my spread was decent but could be helped by their injectors but have not pulled the trigger as yet. I usually run at 60% power so I can stay out of the red box and lean to the edge of roughness. Only gives up 3-5 kts in airspeed at around 9.5gph which works well for me. CHTs on my hottest cylinder is usually around 340-365 degF depending on OAT and cowl flap setting. TIT's at that setting are usually around 1550 degF. But if I run above 60% I always lean to 100 degF ROP which at 65% is around 13.5gph. So the answer may be GAMI injectors but if the engine runs rough at LOP I would not do it. And I consider rough running as any shaking above what you would get running ROP but maybe that is too cautious. I just don't think running an engine where the cylinders are not firing at the same time is not a great idea and definitely not very comfortable.

Have you taken the Advanced Pilot course yet? If not, I highly recommend it although it sounds like you already understand the value of LOP operation.

Earl,

Regardless of if you can get your engine to run LOP, GAMIs and Tempest Fine Wire plugs do wonders, especially in the oxygen altitudes and flight levels.

My guess is with no induction leaks, GAMIs, and Tempest Fine Wire plugs, you will get the plane to run LOP.

At a minimum, you should get a modest improvement to your current leaning technique.

As a note, Tempest plugs gave me a slight decrease in TIT

[nationwide]

...None of those guys have our engine in my experience. And our engine has an unusual turbocharger configuration.

 

How is our turbo configuration "unusual"?

 

...Have you taken the Advanced Pilot course yet?  If not, I highly recommend it although it sounds like you already understand the value of LOP operation.   

 

I have not.  One of the things I've been frustrated with is the lack of "small block" information (Zane seems to agree--don't meant to put words in his mouth, though).  The TSIO-360-M/SBx in particular seems to be a real "asterisk" engine with GAMI anyway, perhaps because of the tuned induction (?).  Correct me if I'm mistaken, but I thought the TSIO-360 didn't even have GAMIjectors available for it until fairly recently.

 

Zane, do you open the cowl flap when cruising at the 28"/2500 RPM/11.5 (Peak TIT) power setting?  From memory, I think that's a pretty high power setting (>70%), and if I did that, my hottest (#5 up front--which has always seemed weird to me) would definitely be 400+ without opening cowl flaps at least 1/4.

[aviatoreb]

I am curious - how many of you are running at 1650TiT?

[KSMooniac]

A TSIO-360 is subject to the same physics as the IO-550, and pretty much every other gasoline powered piston engine.    The APS Live Course is a BARGAIN relative to the amount of knowledge conveyed in 2.5 days, and should be at the top of every owner's list of things to do in the aviation department.  It is the most efficient way to learn what happens under the cowl, how to read an engine monitor, and what moving the red knob of death really does.  After you learn it, you get to actually see it live with your own eyes in the test cell.  Very compelling.  A lot more is known today in the realm of engine management compared to when all of the POH sections were written for our Mooneys, and if you really want to learn, going to Ada is the easiest and fastest way to learn.

[DonMuncy]

Not me!

[Earl]

I am curious - how many of you are running at 1650TiT?

I don't.

[aviatoreb]

Me neither - but I have read it is fine by people who should know. Like deakins on pelicans perch. So I am wonder who does?

[Z W]

A TSIO-360 is subject to the same physics as the IO-550, and pretty much every other gasoline powered piston engine.    The APS Live Course is a BARGAIN relative to the amount of knowledge conveyed in 2.5 days, and should be at the top of every owner's list of things to do in the aviation department.  It is the most efficient way to learn what happens under the cowl, how to read an engine monitor, and what moving the red knob of death really does.  After you learn it, you get to actually see it live with your own eyes in the test cell.  Very compelling.  A lot more is known today in the realm of engine management compared to when all of the POH sections were written for our Mooneys, and if you really want to learn, going to Ada is the easiest and fastest way to learn.

 

Scott,

 

No offense intended.  Seriously.  But some version of your post appears in every LOP/ROP thread on the internet.  It adds zero useful information to the discussion, beyond the fact that there is a really good live course available.  It's one of the things that I find frustrating about trying to find good information.  

 

If you attended the course, can you tell us why a lot of our engines are rough at 20-30 degrees LOP TIT?  My EGTs all peak at almost exactly the same time.  My engine has GAMI's.  Can you tell us how many hours we can expect to lose on TBO, on average, if we run our engines at peak TIT, instead of 100+ ROP?  Or how many hours we can expect to lose between overhaul/replacement of cylinders?  Or how many hours we lose, on average, between catastrophic in-flight engine failures?

 

Can you tell us, for certain, if we should base our ROP/LOP measurement off of peak TIT, or the last EGT to peak?  

 

I submit that's the kind of information we need to be able to make an informed decision about where to set the red knob.

 

I don't mean to bash the APS course. I have not been able to attend it, and I would like to.  I've read posts by the guys that put it on, and they seem knowledgeable.  When life slows down a bit (ha ha) I plan to do it.  Right after I've gotten my tailwheel endorsement, seaplane rating, glider rating, aerobatic course, etc. done...

 

For now, I have to settle for what some people will post on internet forums.