Discussion on the Continental engine in the 231

[jetdriven]

That article was written by george braly.  He also operates a TN bonanza at 85% power LOP.  

Ok, then where is the data that a 5 minute cool down while idling after clearing the runway  is beneficial ?   See?  Tradition.  tell you what. I can instrument a thermocouple on a housing and measure it.  I am just short one 231.   I actually think a 5 minute cool down period from cruise temps is good, just that it probably starts when you drop the gear and reduce power for landing.  Your turbo housing is nowhere near 1600 degrees unless you like to enter the pattern at 75% power.   So it takes two minutes to descend and land, a minute for rollout and another minute to taxi directly to your hangar.  Maybe two.    There is your 5 minutes.  See how easy that is?

 

EDIT: that's a bad link. I will find a better one.   It talks about cool down.  

[FlyingAggie]

To answer the OP's question, my 231 has the -MB engine, which is usually found in the 252.  My engine is approaching 800 SMOH, so I am entering that midlife top overhaul zone.

I like the margin of safety the turbo provides operating out the airports in Colorado where density altitudes can be close to 10K' in the summer.  It is nice in the summer to get up above the bumps into smooth cool air.

Regarding making TBO without a TOH, one of the experienced 231 drivers at KBJC has made it to TBO on two different 231's and one of those had the -GB engine.  He treats the engine very gently.

Equiping the a/c with an electronic engine analyzer and learning to use it to manage the engine will greatly improve the chances of making it to TBO.  The panel CHT gauge is only attached to one cyclinder.  I have seen CHT's on the other cylinders over 400 degF with the JPI, while the OEM CHT would lead you to believe the CHT is well within the green.

A friend of mine, bought his 231 a couple of months before I bought mine.  His came without an electronic engine analyzer and he was running it in cruise at the very top of the GREEN on the OEM CHT gauge.  I was alarmed when we flew together for the first time, knowing that on my a/c the other CHT's could be much higher.  He has since added a new JPI to his bird. Also from reading some of the articles published during the late 70's and 80's, it seemed to be accepted practice to run with CHT's between 420-440 degF on the OEM CHT gauge.  No wonder, so many K's needed tops.

Besides making sure the baffling and baffle seals are in good shape, that there are no exhaust header leaks, another very important aspect to cylinder longevity is making sure the fuel injection is set up properly according to TCM's SID97-3. It should be checked or redone at every annual or anytime any changes are made to the fuel system.

I would also be interested in seeing Scott's APS data on turbo temperatures.  I follow the same practice as others have mentioned of waiting at least 5 minutes from the time I reduce power until I shut down.  I also wait until the TiT is below 820 degF before pulling the mixture.  This may be unnecessary, but my transition trainer was a very experienced Mooney 252 and Mooney Rocket owner and this is the way I was taught to shut down.  My 5 minutes starts usually when I reduce power abeam the numbers and has expired by the time I have taxied to the hangar.

Also I do all climbs at full power (36"/24GPH/2700RPM) and 105-110 kntsand have found the CHT's actually stay cooler than at the POH's recommended 33"/2600rpm. 

I have put 150 hrs on my 231 in the last 18 months and have had no problem with cyliners or the turbo system (so far).  The compression readings between the first and second annual were almost identical.  My engine is approaching 800 hrs SMOH----It will be interesting to see at my next annual to see if my instrument training has taken any toll on my cylinders.

Something else that has not been mentioned is the smoothness of a 6 cyl engine turning a three bladed prop.  Besides heat, vibration is the next biggest enemy of rotating equipment's longevity.  Also another lesser factor mitigating cost difference slightly, is there is no muffler to repair or replace on a 231.

One question to the other K drivers: Do you make any adjustment to power setting on takeoff based on OAT?

The POH instructs that the MP should be increased or decreased 1" for every 10 degC above or below standard temperatue when makeing cruise settings.   Howver the POH makes no mention of adjusting MP for OAT on takeoff.  I thought about this morning when I went to the airport and the OAT was -16 degC.  The POH does warn about the possibility of overboosting on cold days, even with the -MB engine, but this is the controller allowing the MP to overshoot, not a consideration of air density at temps different than std.

After 150 hrs, I am very glad I bought the K.  Finally, you can't really quantify it, but I ljust ove the "kick in the ass" feeling when the turbo kicks in during the takeoff roll.

[kortopates]

Jim, Congrats on upgrading to a K. Would love to see it sometime. I think your wise to follow your POH recommendations for cool down. However you most likely do have the instrumentation to be able to judge when you can shutdown earlier and I do believe Scott and Byron's quoting of APS and George Braly is mostly right - but its not the whole story in my opinion.

First off, the issue we're trying to avoid is as you listed above, to 'reduce oil coking in bearings'. Its a bit of a stretch to call them bearings but we'll leave that for another time. The point is oil is pumped through until shutdown, where upon after shutdown a hot turbo can result in coking, which in turn will lead to less than optimal lubrication and cooling and lead to faster wear. If it was totally an OWT, then don't you think the folks that rebuild our turbos would never see coking? But I digress.

I believe TIT is a quite adequate indicator for determining when the turbo has sufficiently cooled. Although I don't have much confidence in my factory TIT gauge I do have full confidence in my JPI TIT readings. My factory TIT probe is almost right at the exhuast inlet of the turbo but always reads over a hundred degrees cooler than than JPI probe which is an inch away from the factory probe.

The big disconnect I believe is the non-turbo pilots who assume the big power reduction for landing, such as reducing power and lowering gear for landing, is when the 5 minute cool down period commences. It could be, but it all depends on how you operate your mixture. If you enrichened the mixture at this point, then yes, I do agree you'd be able to count this time as part of your cool down. But I never do this. Every power reduction is accompanied by leaning the mixture to mainain a TIT of 1400+F till landing is assured on short final. Otherwise I risk not being able to develop full power from an overly cool engine and even shock cooling cylinders if I went full rich (NA pilots will say that just another OWT, but its very possible with a turbo).

Given my TIT is at about 1400 till short final, and thus glowing a cherry red, my coolest TIT is not right after landing but takes a few minutes after mixture enrichment to cool down. I've found it will cool to just under 900F (at idle) and its always cool enough by the time I taxi to my hangar. But if I have a very short taxi then I'll wait for a couple of minutes till TIT cools to the 900F range. I do believe that's adequate, since TIT is the entire source of heat to cause an coking. I'd suggets you collect your own TIT data on cool down, using a good 5 minutes of cool down as a control, and then form your own personal target TIT shutdown temp based accordingly on your own operating style and instrumentation; as it will cause variances.  That should enable you to develop your own shutdown timing procedure with confidence in adequate cooling.

[231BB]

Getting back to the original post, if you live in LA you should seriously consider a turbo. Unless you plan to fly over the Pacific, most of your flights will involve transitions over mountainous terrain. Flying a turbo in the mid to high 'teens will make mole hills out of mountains.

In terms of maintainence, I agree with posters who state the importance of engine management and temperature monitoring for longevity. Power settings, mixture, cooling, and temperatures play a huge role. Several K models on my home field, operated by "enlightened" pilots, have reach TBO's without an intervening TOH.

I also agree with no need to idle 5 mins on a turbo'd airplane prior to shut-down, unless you normally land with a MP >30";) This is car-think transferred to aircraft. The normal descent to landing, especially in a Mooney, requires a sustained period of low power settings. The turbo is not spooled up during this time, as exhaust gets bypassed through the wastegate. Temps begin to increase after landing, enroute to your tie-down.

Learn about your powerplant by performing a few owner assisted annuals if you can. Study turbo systems and internal combustion theory. The engines are a little more complex, but like anything else, if you deal with it everyday it will become second nature.

Needless to say, I'm a very happy 231 owner, and with today's prices on K models, I can't think of a good reason to fly a normally aspirated Mooney out West.

Happy flying!

M20K/KCCR

[jetdriven]

Do you think that at 20% power your turbo housing is at 1400F at that flow rate?   (descending for landing).  My 201 egt is that nearing the airport but that's not to say the exhaust is that temp.  

 

[jetdriven]

for some reason my laptop shows the whole article.  Here you go, John.  edited for length.

 

Top five engine myths: the science of piston aircraft engine operation has been overhauled in recent years, putting to rest many myths. How many of these five do you still believe? Publication: Aviation Safety Publication Date: 01-MAR-07 Format: Online Full Article Title: Top five engine myths: the science of piston aircraft engine operation has been overhauled in recent years, putting to rest many myths. How many of these five do you still believe?(AIRCRAFT SYSTEMS)

Full Article It seems that since Leonardo de Vinci first placed his mental concept of a flying machine on paper we aviators have had a hard time separating fact from fiction. Aviation, not unlike most other human endeavors, has its share of commonly stated "truths" the scientific data doesn't support. Let's call them aviation myths. Why then, do they continue? One reality is that we are all busy in our daily lives and digging through reams of material to verify what someone else says is just too time consuming--not to mention boring. Another issue is that we have learned that those who have gone before us are generally a reliable source of information on how not to get one's name included in an NTSB report--much less looking stupid in that report. It's an understandable shortcoming. Let's take a look at a few of the commonly held aviation concepts related to engine operation for which there is no supporting data, contradicting data or, at the very least, data calling them into question. HIGH RPM INCREASE WEAR HIGH MP STRESSES THE ENGINE TURBO COOL-DOWN No one seems to know for sure where the idea came from that sitting at idle for any period of time cools off a turbocharger after a flight--particularly one housed under a tight cowl. Instead, there is compelling evidence that the coolest a turbo ever gets is after a low-power approach, something that happens about the time the aircraft touches down and turns off the runway. So far, no one has offered any data that suggests otherwise. Measured oil temperature is lower after a long descent and landing and will frequently heat up as one sits on the ramp at idle with no cooling airflow through the oil cooler. This myth just makes no sense but the conventional wisdom on the need for a turbo cool-down period--to allow oil in the turbo to cool down and prevent "coking"--lives on unsupported by any data I've seen. Turbocharged aircraft were flown for many years before this was ever heard of with no ill effects from turning off the runway, taxiing straight to a nearby hangar and immediately shutting down. I have seen no data to suggest that turbo failures were more of a problem then than they are now--which is very low anyway. Based on my watching my own engine, sitting at idle heats things back up after a landing. I've come to call this the "turbo heat-up period" and I don't do it. The biggest reason not to adhere to the conventional wisdom on turbo cool-downs is that you have to wait five extra minutes to go pee. That could be serious! Walter Atkinson holds the ATP, CFII, MEI and A&P certificates and is a co-founder of Advanced Pilot Seminars . He has accumulated more than 3900 hours of flight time.

[jetdriven]

SOME MORE HARD DATA:  

from:    http://www.avweb.com/news/pelican/182107-1.html

 

comments?

Okay, let's tie the ribbons on this series by discussing the right way to manage our turbocharged powerplant at the end of our flight when it's time to get our airplane down from altitude and back on terra firma. (We've been airborne for five months now, and frankly I'm ready to stretch my legs and take a pit stop!)

 

 

Cooldown/Shutdown

I would guess that when you see (and hear!) someone running their engine in the parking spot after landing "to cool the turbo," you are almost always seeing someone who is getting it hotter than it was when he arrived at the spot. If you don't make the high-drag approaches, and you lean brutally after landing, that turbo will be just about as cold as it will ever get, short of a shutdown. On the other hand, if you've made a long, high-drag approach with high power, or you're one of those dreadful types who taxi with cruise power while dragging the brakes to keep the speed down, or you have a long, sharply uphill taxi to the ramp, you may need the cool down. A tip that might do your engine more good is to hop right out after shutdown, and pop the cowling open (or even just the oil access door) if you can. That will let a LOT of heat out of the accessory section, avoiding "cooking" the components, hoses, and seals there. But even that little tip is probably completely unnecessary if there is more than 3-5 knots of wind blowing in the general direction of either the front or the back (cowl flaps open, please) of the engine.

 

George Braly again:

We know of one operator of a turbo twin Cessna. He owned the aircraft for 15 years before the issue of "turbo cool down" ever showed up in the aviation literature. Through three full TBO runs, with almost no premature engine or turbo problems, this operator would routinely land at his uncontrolled airport, turn off at mid-field, taxi about 100 yards, and immediately shut down both engines. The aircraft was then promptly pushed into a T-hangar, where it could not benefit from any natural wind for a further cool down. These would have been ideal conditions to promote problems with turbochargers not being properly allowed to cool down, if there was any truth to this OWT. This operator, in more than 8000 engine hours, never experienced any problems with the issue of "coking" a bearing on a turbocharger.

 

Finally, here's a graph of the type of descent I've just described.

 

Click for a high-resolution version.

 

The chart begins at 11:49:21 PDT, on 10/02/2000, at 10,500 feet. Note that TIT and EGT is read against the left side numbers, while all other parameters are read against the right side. For the first five minutes, I pre-cool the CHTs by beginning a gentle descent, and reducing RPM and fuel flow on the lean side. That CHT drop too fast for you? Fine, you have complete control over how fast you drop the CHTs, take all the time you want.

At about 11:55:00, I simply pulled the throttle back, and dropped the MP from 31.0" to 18.0". In order to demonstrate where the mixture ended up to a passenger, I fiddled with it a bit, and added just a bit of fuel. In fact, it would probably have been better if I'd just left it alone (as I usually do) because that extra tweak actually caused the CHTs and EGTs to RISE! Uhh, what WERE you saying about "shock cooling"? We have just pulled off 12 full inches of MP in one swell foop, and all engine temps go UP! The reason is, of course, we have gone from very LOP (and relatively cool CHTs) at a very high power setting, to just ROP at a very low setting. The linkages in my engine are "just right" for this purpose, yours may vary, but at worst, you'll need to fiddle with the mixture once, to get it just ROP, or wherever you want it.

For the next 10 minutes on the chart, we descend at about 1,000 fpm, at about 140 knots, gear up. If I'd wanted more descent, all I had to do was run the IAS up to the bottom of the yellow arc, or put the gear down, or even pull off more MP. For a couple minutes in the pattern, the CHTs dropped very gently and then they rise a bit while taxiing in. At shutdown, they begin a long, slow cooling process.

Well, we've gone from startup to shutdown, with a "flight time" of five months! I hope I've not led you too far astray, and above all, I hope I've made you think.

I think I'll take a break from engines, for a while!

 

Be careful up there!

[RJBrown]

I have owned a 1980 231. Now own a 1990 J. The 231 had about 1100 hour when bought at 1200 hours major engine work became neccesary and the plane was converted to a Rocket. There are examples of TSIO360 engines making TBO, you have heard a few here. While searching for my second airplane I planned on buying a 231. Over the 6+ years I was without a plane I followed the market quite closely. I found that most 231s had an engine OH around the 1200 hour number or were topped.

On Controller now:

3 appear to be on second engine,

57638 got 1350

1163D got 1150

1172K got 900

These 3 are on 2nd or 3rd you would have to see logs but I would bet they were at least topped.

233JB got 1610

231EU got 1700

231RU got 1900

4 more appear to have a 3rd engine

1041G 2100 average 1150

231PP 2500 average 1250

C-GROV 2640 average 1320

231HN first 2 got 2000? and it now has a runout at 1700.

When I was calling and checking logs for every one that got over 1600 there were 2 that did not make 1000 and most got something about 1200.

Knowing what I know I would consider any GB/LB runout at 1200 for purchase consideration. 

 

[rainman]

I went through this discussion while searching for my Mooney in April of 2011. I read the MAPA article on the comparison of the 201-vs-231, then I focused on how I would be using the airplane.  In my case I would be making frequent trips to Albuquerque all year around, and the DA and surrounding mountains made the turbo a reasonable consideration.  I have met several 201 drivers who do very well based on the mission they fly and you can't argue about the reliability of the Lycoming four cylinder engine.  Right now seems to be a buyer's market, so define your mission and pick the plane that best fits that mission.  I've flown my 231 from San Antonio to Detroit at 13,500 to 15,500 ft and the turbo got me in uncrowded skies and favorable winds .....it was nice to have the option, but not a necessity.

Ray

[NotarPilot]

This is excellent information and I appreciate all the helpful comments.  I think my mission profile leans towards a 201 but I'm fairly certain I can afford the extra cost associated with the 231.  I plan to build up my $ reserve over the subsequent years of aircraft ownership in case of needed unforeseen repairs that might come up.

Can you guys tell me what the costs of replacing a cylinder vs. a top overhaul in a 231 might run?

[231BB]

On the low end of the scale, a TCM Cylinder Kit runs about $1370 and include rings, piston, valves, gaskets

http://www.aeroinstock.com/products/346--thru-360-Series/5843/0/product_cat/index.html

Add labor and a few additional parts. Once the baffling, intake and exhaust pipes and fuel lines are removed, it's not much more time to replace one cylinder vs 3 on side, or 6 all together.

 

[FlyingAggie]

Byron,

That is some good infomation on turbo cool down.  It would be more interesting to see what the body temperature of the turbo is doing after shut down or even more pertinent, the temperature of the oil in the turbo after shutdown.  Isn't a more important consideration what the metal temperatures are doing after shut down than the TiT while the engine is running? After the EGT's goes to zero and the oil circulation ceases, you have a fixed quantity (mass) of oil being the heated from the residual heat stored in the metal body/impleller parts of the turbo?  Seems like that should be the concern about the oil coking is after shut down not when the engine is running and the oil is circulating.

Ron,

I saw the same thing when shopping for my K.  It would be interesting to see how many of the planes you listed have engine analyzers.  Of course, even if an a/c has an engine analyzer, it doesn't mean the operator used it.  Nevertheless, being new to turbos and a first time a/c owner, I included the likelihood of doing mid-tbo cylinder replacements in my purchase decision, so I am prepared.

Maybe this should be in a seperate thread, but I find the biggest limitation of the K over the J is lower useful load and should be factored in the 201 vs 231 purchase decision and is dependent on your mission.   My K's useful load is 892lbs whereas Scott '77J is 1050lbs.  That is another person or 25 more gallons of 100LL.  Although my typical mission is me and my copilot, there have been times when I would have like to be able to bring four people on a flight.

Without the gross weight increase STC for eligble K serial #'s, seems like most 231K's are in the 900 to 950 lbs useful load range and early 252K's are 850 to 950 lbs.  J's are usually more.  The later J's got fat, but are eligble for the 160lbs GW increase STC.

If I fill my K to 106 gallons, it becomes a single place plane, but then who wants to fly 9 to 10 hr legs?

[FlyDave]

Notar,

I'm based at El Monte. If you want to get a feel for 201 performance and discuss my 2 years of ownership, PM me and we can work out a time to go flying and talk.

[rainman]

Guys, Thanks for including the supplemental info on the "five minute cool down". Now I can make a decision about the procedure based on data not dogma.  And Wow, an offer for Notar to go fly in a 201 before deciding, that's what I love about Mooney pilots....always willing to help. 

Ray

[kortopates]

With the discussion on cool downs and material Byron posted from the Avweb George Braly articles I closely monitored my own temperatures on a couple of approaches this past weekend. I re-verified, as I recalled in my earlier post, that leaning the mixture will mainatin the TIT up there at 1400F easily enough although I found myself inching it in such that I was in 1200-1300 range by short final. However, I found as soon as I enrichened the mixture for landing at 200' agl, the TIT was down to the low 800's shortly thereafter as I rolled off the runway where upon it stayed as I taxied to my final destination. Thus my engine's cool down began just before I touched down, given my SOP to keep the engine warm for a potential missed till committed to the landing, and the 3-4 minute taxi time should provide plenty enough time for the turbo housing to stabilize at that temperature eliminating any cooling benefit from further idling time. The IFR approach profile is the worst case scenario for me, whereas during a VFR pattern landing I'll enrichen the mixture with a large MP reduction for landing (about a minute earlier from landing) and those that enrichen at the FAP with the large MP reduction should see temperatures just like Braly's graph that Byron posted. My only point in this is that the cool down doesn't necessarily begin with the MP pull but when the mixture enrichens. Secondly, anyone with an engine analyzer can collect their own data for their own specific techniques. Thanks to Byron for posting the Braly article and data.

[NotarPilot]

Quote: rainman

Guys, Thanks for including the supplemental info on the "five minute cool down". Now I can make a decision about the procedure based on data not dogma.  And Wow, an offer for Notar to go fly in a 201 before deciding, that's what I love about Mooney pilots....always willing to help. 

Ray

[jwilkins]

Turbo Cool Down, continued

Continental recommends a cool down perioid for both normally aspirated and turbo engines,  one reason is to allow stabilization of internal engine component temperatures.

I will continue to follow the cool down period (5 minutes; I just don't have the patience to do 10).  I guess I'm just too much of a conservative engineer to think that the manufacturer with probably 50 years of turbo experience does NOT know what they are doing. The temperature graphs are really interesting, but how do we know that the correct metrics are being monitored?

Everyone is welcome to thier own opinion and to follow thier own operating procedures. but I wanted to post the link to the Continental tutorial. I agree there are WAY too many turbo engines for sale with SMO or STO at half recommended TBO. I ask myself how many times I have seen a pilot do a 5 minute ramp cool down (once or twice) and wonder if the frequent TOHs might be related. Ask me again in 3 or 4 years.

Cheers everyone, and Happy Holidays!

http://tcmlink.com/fiddefault.aspx?cgroup=MATTITUCK&cpagename=GOODHABITS

Jim

 

[Parker_Woodruff]

Jim,

The turbo cool down is probably the farthest thing from being related to top overhauls. When an engine is turning at low power on the ground, it isn't the culprit in baking cylinders or providing huge amounts of pressure. 

[RJBrown]

Quote: Parker_Woodruff

Jim,

The turbo cool down is probably the farthest thing from being related to top overhauls. When an engine is turning at low power on the ground, it isn't the culprit in baking cylinders or providing huge amounts of pressure. 

[jlunseth]

I agree.  The plane I bought, the owner had had a medical issue and loaned the plane out.  You could see from the logs the loanee was heavy handed.  All of a sudden it was needing cylinders at annual.  They need to be operated conservatively.  Especially if intercooled, the intercooler makes a significant difference in power production at a given MP, and because air temp and density is constantly changing as altitude changes, you need to watch the MP and modify it accordingly.  It is not hard to do, but it would definitely be hard to stay on top of with the factory gauges.

[jetdriven]

If you start th cooldown period when the pilot reduces power abeam the numbers or at the FAF (come on, its like 20% power) then you will have your 5 minutes by the time you taxi to the fuel pump or the hangar. I am with Parker and RJ on this one, the reason they need top overhauls is the 440 CHT and high power settings in cruise.

[NotarPilot]

How do you know when it's time for an overhaul on the GB engine?  Is it just based on compression readings and oil analysis?

[RJBrown]

Quote: NotarPilot

How do you know when it's time for an overhaul on the GB engine?  Is it just based on compression readings and oil analysis?

[rainman]

Can you explain the TSIO 520NB and it's advantages?

[rainman]

Are we talking about a Rocket ?  I was told the company no longer does the conversion, but will continue to maintain the ones that are out there? There generally don't seem to be many Rockets for sale at any given moment, but all I've heard from the owner I met (there is one on my home field) is that he loves the speed and performance, and if he sells it, he's getting a small jet!