Myths and Choice of IO-360 Lycomings

[gmcjetpilot]

Originally Posted by David Johnson

OWT. I say that very carefully and with much respect because I know you're a rather helpful and prolific poster hereabouts, but this is a topic I've studied. Respectfully,
Dave

Originally Posted by N395V

Like Dave I am not a big believer in shock cooling being a major cause of cracking of cases or cylinders based upon my experience and watching CHTs during drastic power reductions, descents and when flying through heavy precip.

I guess I stand corrected. This prolific poster is wrong AGAIN! Doha!

Dave, I appreciate your cordiality and you make some good points. Milt good points also. I think overheat is way worse. However "quick cooling" is not without damage. I also agree extensive engine instruments (8 and 12 channels of cylinder temps) helps a lot.

OK, slam the throttle shut and push it over, no problem, right? I concede. It does not sound correct but I'll go with it for the time being. The reason I concede is I never tried it. I was taught don't do it. So I don't. I never questioned it.

I do know when I was flying a C182 jump plane we did this; they replaced cylinders like people change oil? I was under the mistaken idea there was a correlation to pulling the throttle back, quickly descending and shock cooling? I agree slamming the mixture full rich is an even better way to shock cool an engine.

OK, Now this is what the manufacture says, but what do they know?
http://www.lycoming.textron.com/main...enCooling.html

--------------------------------------------------------------------------

QUOTE Lyc:

"Sudden cooling is detrimental to the good health of the piston aircraft
engine. Textron Lycoming Service Instruction 1094D recommends a
maximum temperature change of 50oF per minute to avoid shock
cooling of the cylinders.


Operations that tend to induce rapid engine cool down are often associated
with a fast let down and return to the field after dropping parachutists or a
glider tow. There are occasions when Air Traffic Control also calls for fast
descents that may lead to sudden cooling.

The engine problems that may be expected when pilots consistently make fast letdowns with little or no power include:

1. Excessively worn ring grooves accompanied by broken rings.

2. Cracked cylinder heads.

3. Warped exhaust valves.

4. Bent pushrods.

5. Spark plug fouling.

Generally speaking, pilots hold the key to dodging these problems. They must
avoid fast letdowns with very low power (high cruise RPM and low manifold
pressure), along with rich mixtures that contribute to sudden cooling. It is
recommended that pilots maintain at least 15" MP or higher (I like 19"-20" min)
and set the RPM at the lowest cruise position. This should prevent ring flutter
and the problems associated with it.

Letdown speed should not exceed high cruise speed or approximately 1000
feet per minute of descent. Keeping descent and airspeed within these limits
will help to prevent the sudden cooling that may result in cracked cylinder
heads, warped exhaust valves, and bent pushrods.

The mixture setting also has an effect on engine cooling. To reduce spark
plug fouling and keep the cylinder cooling within the recommended 50o per
minute limit, the mixture should be left at the lean setting used for cruise and
then richened gradually during descent from altitude. The lean mixture,
maintaining some power, and using a sensible airspeed should achieve the
most efficient engine temperatures possible.

The operating techniques recommended in this article are worth consideration
as they will be a positive step toward saving dollars that might be spent on
maintenance. Whatever the circumstances, pilots must plan their flight
operations so that the potential damage caused by sudden engine cooling
can be avoided."

--------------------------------------------------------------------------

I think there is more to it besides temperature, such as ring flutter.

Here is Service Instruction SI-1094D
http://www.lycoming.textron.com/supp...ns/SI1094D.pdf

The bottom line is NOT cooling more than 50F per minute. How its done is up to the pilot. My recommendation is start down early, leave the mixture lean, reduce the throttle only slightly (no more than 1"-2" at time and no less than 19" for me, Lyc says 15" min), trim for a descent airspeed producing say 500 fpm so it does not exceed Vne or Vno (max structural) or less as needed for conditions. When I flew part 135 in turbo piston twins the "airline" gave pilots training in "shock cooling" because they where sensitive to it and affected the bottom line (according to them). I am paying for my cylinders, so am not too cavalier about it, but than each to their own. I will continue to baby my engine.

The point you make Dave about thermal cycle fatigue is a good one. That is why its important to cool the engine down before shut down; however if you do it right this should not be a big shock. The same applies at altitude. Even a little "shock" it adds up. I agree over 400F is worse than an occasional chop and drop.


As far as Avweb article, I think they like to make a splash with their Myth Busted articles. I try to read them but sometimes its not really based on science as much as based on prove me wrong. I already said I concede, I am wrong. However I tend to blindly follow Lycomings recommendations and what I have been taught over the years. May be conservative but that is they way I am.

The article in question does not really address anything and it's main argument there's no info counter to his "hypothesis". With a turbo engine flying hot at altitude, followed with a slam dunk, you can expect increased exhaust, turbo, valve and cylinder maintenance. How do I know, I flew freight in Aerostars, Navajos and Seneca II's. He says "no parts are raining down". Well that is silly. Of course not, the damage is cumulative and small but costly. Also most freight dogs know better or get fired. The writer of the article even says common sense says it's good not to slam the throttle shut, but you can. OK, HE CAN DO IT. I am not.

Any rapid movements of throttle and mixture is bad. Again bottom line is if rate of cooling is less than 50F than you are good to go. Of course as someone pointed out we did not always have 4 and 6 channel engine monitors and computers. So if you are well instrumented, than by all means fly your engine monitor. 50F/min is a max BTW.

Also common wisdom is don't back drive and engine. Always keep it driving the prop, even if it's just a little. I am sure AvWeb has an article that says that's wrong also, but there is "back lash" and my gut feel is keep the chain tight and don't yank on it. Keep letting it go loose and than yank on it, over and over. The chain may not break, but it will make a heck of a noise.

BTW way no chain yanking. Appreciate Dave's and Milts input. Something to think about.

Cheers, respectfully George (prolific poster, ATP/CFI)

[rv8ch]

Originally Posted by gmcjetpilot

...Any rapid movements of throttle and mixture is bad. Again bottom line is if rate of cooling is less than 50F than you are good to go. ... 50F/min is a max BTW.

I think Dave addressed this here:

Originally Posted by David Johnson

The greatest thermal stress your engine will endure is when you pull the mixture to idle cutoff before you back it into the hangar.

Not much avoiding that, and it happens on every flight. It's kind of hard to argue that this will be less brutal than any chop and drop. Shock cooling does seem to be an OWT. I'd like to hear about how the big, old radials were managed.

[David Johnson]

Originally Posted by gmcjetpilot

I guess I stand corrected. This prolific poster is wrong AGAIN! Doha!

OK, slam the throttle shut and push it over, no problem, right. You guys know more than I do, so I concede. It does not sound correct but I'll go with it.

OK, Now this is what the manufacture says, but what do they know?

Well, I had hoped you might respond in a less sarcastic way so we might get at the issues and leave the rhetoric aside. I offered same as a courtesy. I'll do my best to continue to do so. Again, no disrepect is intended.

There have been several instances in the last couple of decades where Lycoming and/or Continental's published recommendations have been in direct conflict with the known physical laws of combustion and thermodynamics. Literature warning against running an engine LOP is another example, but that's a discussion for another day. In the case of the article you posted, Lycoming is offering no hard data to support their recommendation. It would be reasonable to suggest that they don't have any.

Take a look at the analyzer data provided by Milt in a previous post and note the gradual and shallow CHT drop after the engine loses its fuel supply. When we pull the throttle to descend, we still have fuel and combustion continues, so the curve you would see in a crowbar descent would be shallower still. If I can find a data file from one of my recent flights, I'll post it, but suffice it to say that when I pull the mixture to idle cutoff on the ground, the cooling curve is similar, but more importantly, much deeper. That's where the fatigue happens.

Originally Posted by gmcjetpilot

My recommendation is start down early, leave the mixture lean, reduce the throttle only slightly (no more than 1"-2" at time and no less than 19" for me, Lyc says 15" min), trim for a descent airspeed producing say 500 fpm so it does not exceed Vne or Vno (max structural) or less as needed for conditions.

I think that's a good practice also, but probably not for the same reasons you do. All I'm saying here is that pulling the power quickly to descend is not going to hurt the engine. At the same time, unless there is a good reason to do so, proper descent planning is wise, as much for passenger comfort and keeping the pilot on the ball as anything.

Originally Posted by gmcjetpilot

I do know when I was flying a C182 jump plane we did this; they replaced cylinders like people change oil? I was under the mistaken idea there was a correlation to pulling the throttle back, quickly descending and shock cooling? I agree slamming the mixture full rich is an even better way to shock cool an engine.

Did you have an engine monitor in that C182? Were you relying on the factory CHT probe (mounted on a single cylinder)? Is it possible that in the climb at least some of the cylinders were running well into the 400s and you never knew it? I know several people whose experience with maintaining jump aircraft is very different.

As for slamming the mixture full rich, there were cases where turbocharged twin Cessnas coming down from high altitude were experiencing cracks in the intake ports. For a long time it was chalked up to shock cooling at the top of the descent. Turns out the culprit was the cold fuel (chilled at altitude) being injected into the ports when the pilot went full rich in the pattern. They stopped going full rich, and the problem ceased.

As for the 50 deg./min. as the maximum acceptable rate of change, can you explain why it's OK to double that rate when heating the cylinders from idle to takeoff power on the takeoff roll, as we all do? While you're at it, can you explain why flight training aircraft frequently make TBO, even with instructors and students chopping the power from full to zero several times per flight? there's an O-320-H2AD sitting in the hangar at Erie with 4000 hours SMOH, straight from a flight line trainer with nary a jug pulled.

Shock Cooling

Cheers,
Dave

[fodrv7]

Cylinder cracking! Interesting?
Anyway, for those of you who have yet to decide on an engine to drag your RV around the sky, I?ll attempt to drag this post back to where I intended it.
There is only one engine you should use to power your RV.
The one that suits YOUR needs.
But like all decisions along the rewarding journey towards the ?First Flight? it will be based on collected wisdom; and that is the real value of Doug?s forum.
It is a shame that so many of these posts turn into pissing competitions on Tail Wheel v. Nose wheel, Aero engine v. Auto engine or the length of our respective family jewel. You end up having to spend so much time filtering the post replies.
Cylinder head cracking. Interesting subject, but is not going to determine which engine you purchase.
If you need to out climb, out run and do it with less fuel, then maybe Dan is right. Buy an Angle Valve. Although, even with the finest pencil I cannot discern any difference in economy from the Part Throttle Fuel Consumption Charts page 3-22 for the IO-360A and page 3-23 for the IO-360B of my Lycoming Operators Manual.
So, the facts I originally post remain just that and not opinion or anecdotal.
The Straight Valve and Angle Valve IO-360 engines at around 7000? at cruise power are within a BHP of each other for a weight difference of 30lb and a purchase difference $4000. Facts.

So the cleaner breathing Angle Valve produces more power at high revs than the Straight Valve, but ONLY the same at cruise RPM.

You simply need to decide if the higher power available above cruise RPM is worth the expense.
Pete.

[gmcjetpilot]

Originally Posted by David Johnson

Well, I had hoped you might respond in a less sarcastic way so we might get at the issues and leave the rhetoric aside. I offered same as a courtesy. I'll do my best to continue to do so. Again, no disrespect is intended. Cheers,
Dave

Dave you are confusing me, I am just agreeing with you. I think my sense of humor was miss interpreted. Doha!

Your data is irrefutable. Milt's comment, data and referenced article have some great points. I am freely admitting you know more about it than I do, because I never tried it. I was taught not to do it, and that is the way I fly. However I reserve the right to change my mind. To be clear "IT" being big power changes, especially long low power descents.

No sarcasm, in fact I thanked you for being so polite and commented you made good points, several times. What else can I say. I never offended anyone before by saying they where right, well may be except for my ex-wife, but I am sure I was never married to you. (NOW THAT IS sarcasm, bada BOOM bada BANG. ). Lets laugh, OK.

I did point out Lycoming has put a quantitative number to shock cooling and their technical opinion to the subject. However I don't see this countering your conclusion if indeed you do not cooling more than 50F/min. The "ring flutter" is interesting. I take that as don't go below their recommended 15" MAP. I call that don't let the prop push the engine. Another controversy no doubt.

Hey its hard to change years of training, but I respectfully submit you have changed my mind, albeit with some prejudice. I will not change my way of operation but I will look into it further. When I get my plane flying I'll do some experiments myself. However I see no need to stay high and drop in from upon high at "MIN POWER".



The AvWeb article said many things in the start that makes a lot of sense. The math sounds OK and backs Milts data, that CHT does not change much, but the other stuff I don't think makes much impact on the subject.

"To my way of thinking, there is no scientific proof that shock cooling plays a
significant role in cylinder damage in aviation."

It's true and there is no evidence one way or the other. Than it gets into other peripheral or anecdotal evidence that "shock cooling" is a myth and not critical, such as flying in rain (verga). This is kind of weak. Very little water gets to your engine, unless its a typhoon, and wet air is LESS dense and provides less cooling. However if you're in a "verga" the evaporation has occurred and cooled the air. Sure that will help but a very small amount. The author pointed out that its not wise flying into a verga. He is right. (Extreme down drafts occur in verga's and are one sign of possible micro burst.) The RIAN evidence is a non-sequitur.

The cooling at shut down is also weak anecdotal evidence that shock cooling does not exist, in my opinion. The logic is if is OK here it is OK in flight? First the total temp at shut down is much less. Yes there is rapid cooling but from a much lower temp. Cooling from 260F fast is not like going from 400F to 300F fast. Also the engine has to keep running in flight, while going thru this temp transition. The shut down evidence is also non-sequitur, true but logic does not follow conclusion.


So I follow Lycomings recommendations, while still agreeing with you. If you have the full meal deal engine monitor than by all means drop a chop if you maintain Lycs limitations, like:

Minimum in-flight CHT 150F (I like high 200's or 300F. BELOW 300F lead fouling!)
Max CHT rate of change 50F
Min Oil Temp 165-190F
Min Oil Press 55 psi
Min MAP 15" (my personal rule 19" MAP min until final)

No offense. Besides temp there are reasons as you and I agree to keep it hot. Lead fouling, piston ring flutter and carb heat to name a few.

Cheers George

PS as far as jump planes, the name of the game was to get on the ground. There was no CHT gauge. To get down, put it in a 60-70 degree bank spiral right after the climb and passengers "stepped out". The name of the game was to get on the ground. You tried to keep some power and use the drag from the high "g" steep descending spiral. Some just chopped and dropped. There was no worry of cylinders. It was part of the business.

PSS In fact as a CFI and CFI (ME) I chopped power. Students needed to get simulated power loss demos, multi engine pilots single engine work. However I did things to minimize the danger (of really loosing power) and abuse of the engine. I made sure the engine was in low power cruise or descent before the demo. Therefore it was already cool. The NTSB has so many accident from simulated engine failures they, AOPA, FAA have reports on it. That is why your CFI added power on occasion during a simulated engine failure. GOING TO REAL LOW POWER in descents can be bad. The engine may NOT come back when you need it to. Carb ICE is a good reason to "keep it hot". Go to idle and you don't have carb heat. When you are ready for power, push the throttle forward and nothing.

[gmcjetpilot]

Originally Posted by fodrv7

Cylinder cracking! Interesting? It is a shame that so many of these posts turn into pissing competitions. So, the facts I originally post remain just that and not opinion or anecdotal.

It is a shame that so many of these posts turn into pissing competitions on Tail Wheel v. Nose wheel, Aero engine v. Auto engine or the length of our respective family jewel. You end up having to spend so much time filtering the post replies.

Pete.

Sorry Pete I guess I hi-jacked your threat. Sorry there are no pearls of wisdom's, but you answered your own question, get what ever you want.

It really does not matter that much, does it? You have the facts, the rest is opinion. If your hardest decision is to pick a new 180HP or 200HP engine you got it made. Many can only afford a used H2AD or conical O320 150HP, if they can build a RV at all. Its not that serious of a questionis is it? What engine should I get. Who knows.

I would go with 180HP myself (and did) because its enough HP (heck 150HP is enough), cheaper and lighter. I don't think these are in dispute. I rebuilt a used O360 and it awesome, but that does no help you. However the 200HP Lyc is a very nice machine. It has a damper weighted crank and no prop restrictions. It does cost a bunch more. Are you without a budget? On a related note to rapid throttle movements you can "De-Tune" the counter weights of a IO360 (200HP), but this is simple to avoid, don't slap the throttle around. I know a lot of formation guys love to slam the throttle shut, doing 180 or 360 over heads. I would be less comfortable with that on a 200HP IO360 than a 180HP (no damper weight crank) .

I am convinced the better breathing 200HP counter weight engine is able to fly LOP better than the smaller engines. The counter weight keeps it smooth even when running on the ragged edge of roughness. The heads are just better, obviously by the 20HP extra on the same displacement (and 0.20 compression bump).

As far as the shock cooling Pete, that was one comment made about the IO360, someone made, taking the time to answer your question. I am sure they gave their opinion in good faith. I made the comment as Dan C. did we had not heard of this. Than Dave and Milt added good info on this topic which is related. I found it interesting and useful to me at least and sure other's did as well. Like all things on the web its something to look into and add to the mix. It may be true. I just never heard of a spacific problem with the IO360 (200HP). It's the nature of a forum and free discussion. Comparing this to primer debates is not fair. Don't you want to know if 200HP IO360's are more subject to cylinder cracks? (at least get opinions on the matter) Your thread is about "Myths of the IO360". Don't you think this shock cooling is relevant? You did not say, Facts of the IO360, ONLY, no opinions, lol.

However two things: You get what you pay for. Speaking for myself I can say my advice is worth what you pay for it.

Second and last are you really complaining about the advice and opinions you are getting? You sound disgruntled because no one said anything that makes one engine a clear winner? You do know there is no definitive answer, right. You will have to decide. Get what you want and makes you happy. It will still be a RV and fly great, 150HP or 200HP. If you want speed, reduce airframe drag. I think you already know the answer, so good luck on your engine decision to drag you RV and "respective family jewels" around the sky. I am sure it will be the right one.

You are expecting too much from the forum. It is just a bunch of guys shooting the breeze. Sometimes good stuff comes out. I know I learned something. Its all in fun.

Again I am sorry this was of no use to you and you have to filter. I promise I'll never hi-jack your thread ever again. I would suggest that the info Dave, Milt and myself gave is interesting and useful to others, if not to you, so its not a total waste as you imply. It's like any discussion, it may digress. Again you get what you PAY for. I think you got you money's worth. It's all in good fun, no one is serious. I am sure you are decisive and don't need anyone's opinion anyway. No worries mate.

Cheers George

[fodrv7]

Thanks George,
I wouldn?t say the thread was hijacked. Just a little diverted.
But I must say I was surprised when I found from Kevin Horton?s Spreadsheets just how grunty the Straight Valve was and thought it worth passing on. After all, if Flight Test Engineer Kevin Horton hadn?t noticed it, I assume it wasn?t common knowledge and I know that blokes like you a genuinely interested in such matters.

Diverting the thread myself now, before I bought my IO-360 (Straight Valve) I had the good fortune to discuss engines with Brett Turner, Jon Johanson?s brilliant young engineer who clearly knows his stuff; enabling Jon to stay up for 36hrs straight requires some good engineering.
Anyway, he put me on to Bart at Aero Sport Power and said; quote, ? Bart will get you the same power out of a Straight Valve as Factory Angle Valve and save you 30lb out the front.? ( I think Dan has an Angle Valve from Bart, so who knows what it puts out and that probably contributes to Dan?s Machine?s excellent speeds.)

Well, I won?t quote speed and rates of climbs of my RV-7 as I am not a test pilot and they are probably suspect, but last week I took off in my IO-360 Straight Valve and stayed with my mates Angle Valve RV-8 all the way to 7500?. Level at 7500? he was gradually drifting ahead of me until we both reduce to 2500rpm, after which we just stayed wing tip to wing tip. Made for a great photo shoot.

Both aircraft have Lightspeed Ignition and mine has high comp pistons.

Cheers, Pete.

[fodrv7]

Just trying to sort out this image inserting.
"Testing, wun, two, tree!"
http://img148.imageshack.us/img148/6...drivex14ut.jpg

[David Johnson]

Originally Posted by fodrv7

It is a shame that so many of these posts turn into pissing competitions on Tail Wheel v. Nose wheel, Aero engine v. Auto engine or the length of our respective family jewel. You end up having to spend so much time filtering the post replies.
Cylinder head cracking. Interesting subject, but is not going to determine which engine you purchase.

I'm sorry you feel that way, Pete. I'll take the rap for hijacking the thread if you feel a reprimand is in order. George was offering a valid opinion, I just chose to correct what I saw as an error with one small part of it, that's all. As is often the case in open discussion, one person's comments lead another to expand and the hope is that we all get a little more knowledge and hopefully a little richer experience. I've spent a great deal of time on other forums and have learned far more than I ever paid for. Certainly, I had no intention of getting into a pissing contest with George. I have learned a great deal about RVs from many of his other posts, and saw this subject as one opportunity for me to be able to return the favor, as it touches on an area I've looked into quite a bit.

And so it goes- we come to ask questions and learn, and maybe share what we know when we can. Sometimes it gets off the topic originally intended, but that's the price of free advice when you ask for it. Welcome to the www.

Respectfully,
Dave

[Mustang]

George and all,

It just came to mind that our company recommended that the power reduction procedure at the top of descent on the 747/767 was to reduce power slightly for a couple of minutes before making the big pull and starting down. This was on a General Electric CF-6 I believe. So, there might be something to this shock cooling stuff, even on the big iron of today. Something about turbine blades.......
Cheers, Pete