Shock Cooling a myth?

[CpnCrunch]

There’s nothing special about adding full power for a go around compared to adding full power for any other reason.

I think you train to put the mixture rich as a prelude to applying full power, at any time you apply full power. I do that, several times on any flight.

I have no greater concern that I’ll forget to enrichen the mixture(s) on a go around than I do on any other occasion I apply full power.

I also think checking the aircraft is correctly configured for whatever phase of flight you intend, is wise.

If you find you don’t get the go around correct, perhaps practicing it more often is the answer.

I don't really see why I should fly contrary to my initial training, 22 years of flying, and every single POH and checklist just because someone on avcanada says so. That seems like a recipe for disappointment. And yes I do practice go-arounds more often now.

[ahramin]

Let me ask a naïve student question here.

Assume I'm flying a trainer. Assume I have correctly configured to land, with the mixture correctly leaned as per however the PoH tells me is correct. What is the risk inherent in forgetting to go full rich? Is it a loss of power upon applying full throttle, or is it the risk of overheating? Or is it something I have not considered?

There is a risk of loss of power but that's not very realistic. You'd have to be in cruise at a high altitude flight on a hot day, leaned for best range rather than best power, then descend all the way down and do to the circuit without noticing a loss of power, all without ever thinking about the mixture control and then forget it on the go-around as well. In that unlikely scenario yes you could put the throttle in and the engine could die.

The real danger is detonation. From the article mentioned above:

Studying the data of this three-and-a-half-hour flight, it appeared to Joe that the engine was running fine for the first hour of the flight, at which point the pilot made what looked like a touch-and-go landing. When executing the “go” portion of the touch-and-go, it looked like the pilot forgot to set the mixture control to full-rich. This resulted in a rapid rise of all six CHTs on the Lycoming IO-540, with the #5 cylinder going into a serious thermal runaway in what looked almost certainly like a pretty severe detonation event.

So if you never make a mistake and never omit any action in an aircraft, no matter how startled you are from whatever it is that caused the unexpected go-around, photofly's method is definitely the best one. Personally I'm not capable of that level of perfection unless I'm flying every couple days, and my last flight was two weeks ago.

[ahramin]

Another note on "full rich". At full rich our aircraft is flowing about 115% of full rated fuel flow which is fine in the winter at sea level but too much fuel in the summer. The EFIS gives us real time density altitude and we use that information to set the mixture out as much as an inch and a half from the stop as the "full rich" setting in the before takeoff or landing checklists. Full rich can rob you of a significant amount of power, not just for high density altitude takeoffs but go-arounds as well.

[RedAndWhiteBaron]

Let me ask a naïve student question here.

Assume I'm flying a trainer. Assume I have correctly configured to land, with the mixture correctly leaned as per however the PoH tells me is correct. What is the risk inherent in forgetting to go full rich? Is it a loss of power upon applying full throttle, or is it the risk of overheating? Or is it something I have not considered?

There is a risk of loss of power but that's not very realistic. You'd have to be in cruise at a high altitude flight on a hot day, leaned for best range rather than best power, then descend all the way down and do to the circuit without noticing a loss of power, all without ever thinking about the mixture control and then forget it on the go-around as well. In that unlikely scenario yes you could put the throttle in and the engine could die.

The real danger is detonation. From the article mentioned above:

Studying the data of this three-and-a-half-hour flight, it appeared to Joe that the engine was running fine for the first hour of the flight, at which point the pilot made what looked like a touch-and-go landing. When executing the “go” portion of the touch-and-go, it looked like the pilot forgot to set the mixture control to full-rich. This resulted in a rapid rise of all six CHTs on the Lycoming IO-540, with the #5 cylinder going into a serious thermal runaway in what looked almost certainly like a pretty severe detonation event.

So if you never make a mistake and never omit any action in an aircraft, no matter how startled you are from whatever it is that caused the unexpected go-around, photofly's method is definitely the best one. Personally I'm not capable of that level of perfection unless I'm flying every couple days, and my last flight was two weeks ago.

Interesting. My scientific mind will need to look up exactly why, but on its merits this seems to make sense. It's quite extreme I think, that too high a CHT due to a lean mixture could produce detonation that quickly, but not outside the realm of possibility. It seems to me it would take more time - but I've only flown trainers (well, and automobiles to be fair, but the risk factor is quite different, and yes, haha, in my youth I was known to fly one or two automobiles).

You are positing that the real and immediate risk of a full power lean go-around arises only after an expedited descent?

[photofly]

There’s nothing special about adding full power for a go around compared to adding full power for any other reason.

I think you train to put the mixture rich as a prelude to applying full power, at any time you apply full power. I do that, several times on any flight.

I have no greater concern that I’ll forget to enrichen the mixture(s) on a go around than I do on any other occasion I apply full power.

I also think checking the aircraft is correctly configured for whatever phase of flight you intend, is wise.

If you find you don’t get the go around correct, perhaps practicing it more often is the answer.

I don't really see why I should fly contrary to my initial training, 22 years of flying, and every single POH and checklist just because someone on avcanada says so. That seems like a recipe for disappointment. And yes I do practice go-arounds more often now.

I have two planes. Neither POH says mixture rich before landing. One doesn’t mention mixture at all in either pre-landing or balked landing, and the other specifically says mixture rich on balked approach, *after* full throttle. We all fly as we judge best, obviousIy, but many of the things I learned when I got my PPL 31 years ago (see, I can play that game too!) were just wrong. I don't see why I should apply a rich mixture before every landing just because someone on avcanada says so. That does, as you point out, seem like a recipe for disappointment.

So if you never make a mistake and never omit any action in an aircraft, no matter how startled you are from whatever it is that caused the unexpected go-around, photofly's method is definitely the best one. Personally I'm not capable of that level of perfection unless I'm flying every couple days, and my last flight was two weeks ago.

Expext a go around on every landing. An imminent mid air collision is about the only situation I can think of in flying that benefits from a startle response. If a go around stimulates so much adrenalin so that a pilot screws up so badly they forget to check the mixture for six minutes they should definitely practice them more.

More importantly I think good training should associate considering a mixture adjustment with *every* touch of the throttle lever(s). There will be times when an urgent climb is called from from a descent other than on short final, and the mixture will not be rich because the "short final, I might have to go around" checklist has not been run. It's the imminent advancement of the throttle(s) that has to trigger the mixture adjustment, not the landing.

[PilotDAR]

Though shock cooling and detonation conditions are not normally discussed in the same sentence, it seems that they have been drawn together here. Firstly, read the flight manual, and fly the plane the way it describes. Be as gentle as conditions permit, because of your own sense of pride of airmanship, and, follow other good airmanship as you have been taught (generally, being ahead of the plane).

Airplane piston engines are ground and flight tested to establish detonation margins - I have done the testing, and experienced the results first hand. I have never destroyed an engine, but I sent one directly to overhaul when I was finished with it! The point is to establish a "detonation margin" That is a very nebulous thing, as there is no number as a pass/fail criteria. More to the point, the operation procedures developed will assure that while operating IAW the flight manual, the engine is safely away from detonating.

Getting cylinder head temps very hot reduces detonation margins. Fuel cools. Running an engine at a slower RPM reduces detonation margins - it takes "time" for detonation to occur, the less time, the less risk of detonation. Demanding more power reduces detonation margins. As the pilot, it is very unlikely that you will be aware of detonation while it is occurring, you can't hear it - until you melt a piston (which I have seen, but never did). And, once denotation starts, stopping it is not so easy. When I saw it on the instruments I was testing with, my test was complete, I reduced power, and the detonation continued for a few seconds.

The risk of damage from detonation is two major things: preignition, resulting in a downward force on an upward moving piston (like wrong mag timing), and ignition of the fuel/air charge at a place in the combustion chamber other than where is intended. That can result in a "wash" of extremely hot combustion products across the piston top, or cylinder head "ceiling", which subjects the aluminum to much hotter local temperatures than are intended.

So, in the most simple perspective, operate the engine gently, the way the airplane manufacturer tells you to. Consider the engine operation manual too, but the airplane manual prevails (because they put the systems and cowlings around it). When I use to meet with Caesar Gonzalez, Cessna's detonation engineer at the time, he'd tell me stories of detonation testing, and cowling design in the 400 series Cessnas, where they would literally fly home with one engine shut down, 'cause they'd melted it.

[digits_]

Airplane piston engines are ground and flight tested to establish detonation margins - I have done the testing, and experienced the results first hand. I have never destroyed an engine, but I sent one directly to overhaul when I was finished with it! The point is to establish a "detonation margin" That is a very nebulous thing, as there is no number as a pass/fail criteria. More to the point, the operation procedures developed will assure that while operating IAW the flight manual, the engine is safely away from detonating.

Did you manage to cause detonation in small engines as well? Such as O320 or IO360? Is there a difference in lycoming vs continental?

I've only flown one small engine airplane that had CHT gauge, but in that one it was practically impossible to approach the CHT temp limits by going too lean, you'd simply start losing power. Which leads me to think that there are no dangers of damaging anything in a small engine simply by having a too lean mixture. That's only one data point, and it wasn't approached as methodically as you probably do your test, but it does make me wonder.

[CpnCrunch]

I have two planes. Neither POH says mixture rich before landing. One doesn’t mention mixture at all in either pre-landing or balked landing, and the other specifically says mixture rich on balked approach, *after* full throttle.

C150, C172, PA28, PA44, C182 all say mixture rich in pre-landing checklist.

[CpnCrunch]

Another note on "full rich". At full rich our aircraft is flowing about 115% of full rated fuel flow which is fine in the winter at sea level but too much fuel in the summer. The EFIS gives us real time density altitude and we use that information to set the mixture out as much as an inch and a half from the stop as the "full rich" setting in the before takeoff or landing checklists. Full rich can rob you of a significant amount of power, not just for high density altitude takeoffs but go-arounds as well.

What do you mean "too much"? I only really have an issue with cooling in summer, so it seems counterintuitive to actually reduce mixture on takeoff in summer.

[CpnCrunch]

There is a risk of loss of power but that's not very realistic. You'd have to be in cruise at a high altitude flight on a hot day, leaned for best range rather than best power, then descend all the way down and do to the circuit

What data is that based on? The reason I ask is because I once leaned the mixture aggressively on the runway after landing, and the engine then died when I increased the power a bit to taxi off the runway. A bit embarrassing, so now I don't lean the mixture till crossing the hold short lines.

[ahramin]

In that unlikely scenario yes you could put the throttle in and the engine could die.

You are positing that the real and immediate risk of a full power lean go-around arises only after an expedited descent?

No. I never mentioned an expedited descent, I'm just trying to think of an example situation for you that could actually lead to an in flight mixture setting so lean that it causes a power loss when applying full power. This is an unlikely and theoretical situation. The engine will run rough long before it dies, giving the pilot plenty of warning that she would have to ignore. On the aircraft I usually fly, I run lean of peak to very lean of peak in cruise. Even at a very lean of peak setting, it's not lean enough to kill the engine at full power. There won't be 100% power available, but plenty of power for a go-around.

The risk of a full power lean go-around is that it reduces your detonation margin to the point where you might actually get detonation. It's hard to do with an aircraft engine but it can be done. Detonation does a massive amount of wear and tear in a very short period of time, and can easily lead to damage. Left long enough (I've seen as little as 30 seconds), it can destroy a cylinder.

What data is that based on? The reason I ask is because I once leaned the mixture aggressively on the runway after landing, and the engine then died when I increased the power a bit to taxi off the runway. A bit embarrassing, so now I don't lean the mixture till crossing the hold short lines.

No data, but you can lean the engine enough at any power setting that it will die. At idle on the ground, the leaner the mixture, the better it is for the engine. When I'm on the ground I'm always lean enough that an application of power will kill the engine. When this happens I either reduce the throttle or increase the mixture. I can think of a couple times where I wasn't fast enough and the engine died (always with a cold engine) and I had to hit the starter. I don't see anything embarrassing about it.

I have noticed two schools of thought with ground leaning. One school doesn't know about it and doesn't do it. The other school is completely paranoid about being brutally lean every last second on the ground. It's not going to do any harm to to your engine to leave it full rich for the rollout or 30 seconds before the takeoff roll. If you spend 90% of your time idling at a lean setting, you're getting 99.9% of the benefit.

[ahramin]

I think you train to put the mixture rich as a prelude to applying full power, at any time you apply full power.

Agreed.

[ahramin]

I have two planes. Neither POH says mixture rich before landing. One doesn’t mention mixture at all in either pre-landing or balked landing, and the other specifically says mixture rich on balked approach, *after* full throttle.

Interesting. Could you share the types please?

[photofly]

I have two planes. Neither POH says mixture rich before landing. One doesn’t mention mixture at all in either pre-landing or balked landing, and the other specifically says mixture rich on balked approach, *after* full throttle.

C150, C172, PA28, PA44, C182 all say mixture rich in pre-landing checklist.

My C182 POH doesn't:

Screen Shot 2021-03-05 at 1.16.47 PM.png (249.26 KiB) Viewed 2139 times

More to the point, there are airplanes not built by Cessna or Piper.

No. I never mentioned an expedited descent, I'm just trying to think of an example situation for you that could actually lead to an in flight mixture setting so lean that it causes a power loss when applying full power. This is an unlikely and theoretical situation.

It's not theoretical: it's happened to me, levelling off in the downwind, from a long descent. The mixture was too lean to support even a slow cruise power. Mental note to self: think about the mixture as one of the engine controls, to be adjusted whenever the throttle is, not as a "pre-landing" item.

[CpnCrunch]

My C182 POH doesn't:

Yeah, it's kind of odd. I see yours is listed as 1975 in the database, but perhaps it's the 1976 model year? The xx POH includes "mixture rich" in the landing checking, the xx POH doesn't (and has similar wording to yours), and it's back in the 79 POH. 76 was the first year the changed from owner's manual to POH, so my guess is they just forgot that step. It is missing from the balked landing checklist as well. It does say enrichen mixture as required on the descent checklist. Anyway, if you follow your unusual checklist to the letter you could have a bad day.

More to the point, there are airplanes not built by Cessna or Piper.

Yes, of course. I just listed the ones I'm familiar with and I know you fly a 182.

[photofly]

Anyway, if you follow your unusual checklist to the letter you could have a bad day.

I get bored of telling people, a checklist isn't a complete set of instructions for how to fly a plane. I think it should be law that no checklist is allowed to include the step of "start engine", to enforce a bare minimum level of intelligence to be allowed to pilot an aircraft - that step you have to figure out yourself. Checklists and morons go together very badly.

Yeah, it's kind of odd. I see yours is listed as 1975 in the database

It's kind of creepy that you're looking up my airplane registration. Do I need to warn the kids about a weird guy with a beard?

[digits_]

Anyway, if you follow your unusual checklist to the letter you could have a bad day.

I get bored of telling people, a checklist isn't a complete set of instructions for how to fly a plane. I think it should be law that no checklist is allowed to include the step of "start engine", to enforce a bare minimum level of intelligence to be allowed to pilot an aircraft - that step you have to figure out yourself. Checklists and morons go together very badly.

Funny you should say that. If I get in an unfamiliar airplane type, that is probably the only checklist I *really really* want

[photofly]

Didn't we have a thread on "if you get to fly a new type, what information do you want to know?" It's a great dinner table question between pilots.

[CpnCrunch]

It's kind of creepy that you're looking up my airplane registration. Do I need to warn the kids about a weird guy with a beard?

You previously posted the year of your plane and where you're based.

[photofly]

It’s still creepy.

[CpnCrunch]

It’s still creepy.

Sorry. I thought you had given me your name by pm but perhaps not. Happy to delete. No big deal for me...always happy to give my name to anyone who doesnt appear too crazy.

[photofly]

It’s still creepy.

Sorry. I thought you had given me your name by pm but perhaps not. Happy to delete. No big deal for me...always happy to give my name to anyone who doesnt appear too crazy.

Possibly I did, and I don’t object to anyone looking things up, it’s just weird to read about.

[RedAndWhiteBaron]

It’s still creepy.

Sorry. I thought you had given me your name by pm but perhaps not. Happy to delete. No big deal for me...always happy to give my name to anyone who doesnt appear too crazy.

In that case, I would avoid giving your name to PF

[CpnCrunch]

Possibly I did, and I don’t object to anyone looking things up, it’s just weird to read about.

It was actually just quicker downloading the db, grepping for 182s at your airport, and looking through the few results than going through your prior posts here to see which year it was. But if you'd reposted the year in this thread you could have saved me that 30 seconds of effort. No matter, sorry for being weird by posting how I solved a problem that was bugging me.

[PilotDAR]

Did you manage to cause detonation in small engines as well? Such as O320 or IO360? Is there a difference in lycoming vs continental?

I did not test those models. I would expect the O-320 to be fairly detonation resistant, as it has a very low compression ratio. IO-360 Lycomings come in different versions, and some with higher compression ratios would have tighter margins. The HIO-360 is a higher compression, harder working engine, and a part of the detonation margin for that model is that it turns faster than it would in an airplane. A faster turning engine has less time per compression stroke to allow detonation to occur. I was trained to never lean the HIO-360 in the SW300, full rich all the time.