Shock Cooling a myth?

[photofly]

But I doubt that's what you did in primary training. The manufacturers know that this technique would be better for the engine, but they also know that it is not what is being taught.

I see your point, but really we ought to teach best practice, not advocate poor practice just because poor practice is what is taught. Tail wagging the dog, and all that.

[goldeneagle]

And you can’t move the mixtures to rich at the time when you decide to go around because...?
I see the comment above about “regulatory authorities didn’t like it”, but why?

The manufacture checklist in the 'pre landing' section says 'mixture rich'. Regulatory folks these days are pretty adamant, we can add items to various checklists, but, that listed in the POH must still be there. When I initially re-worked checklists for the airplane while we were applying for the 703 certificate, I was forced to move the 'mixtures rich' back to pre-land before the transport inspectors would approve things.

As to whether going mixture rich with the throttle at idle would make any difference to temperature, regardless of how cold the fuel is, there’s hardly any of it flowing. Mixture rich with significant power? Sure. But with the throttles closed? Who would have thought.

Thing is, those throttles will not be at idle when completing the pre-land checklist. Dunno about other airplanes, but I can say with some certainty for the 421, with the gear down and flaps out, you will require 22 inches of manifold pressure to hold the glideslope, possibly a bit more if you have a heavy airplane with seats full. In this day and age of stabilized approaches, those throttles wont come back to idle until the flare. So yes, from pre-land to flare the engine will sit at significant power for at least a minute or two, longer if you are doing an approach in IMC.

[ahramin]

But I doubt that's what you did in primary training. The manufacturers know that this technique would be better for the engine, but they also know that it is not what is being taught.

I see your point, but really we ought to teach best practice, not advocate poor practice just because poor practice is what is taught. Tail wagging the dog, and all that.

I'm not so sure. Not everyone is always going to be current, competent, and confident at all times. When I transition a pilot for the first time to an aircraft with a constant speed prop, one of the first things we go over is that the blue knob can stay all the way in as much as they want. It can stay there all day long if that's what it takes. Basically they are not to touch it unless everything else it done and they have time to think about what they are doing. This lets them get used to everything else new with their aircraft without stressing about a system that they do not yet understand instinctively.

It's not ideal, it's certainly not best practice, it's definitely not efficient. It's safe, and easy. Similarly, training pilots with procedures for the red knob that are easy and reduce the workload during a go around is a skill that may come in useful at some point down the road when they haven't flown in 6 months or are in a new aircraft for the first time. Unless we're going to require every pilot to have 10 hours dual on every aircraft they fly and then 10 hours PIC a month to maintain currency.

Keep in mind some of us are barely hanging on for dear life, we're not all professional pilots.

[photofly]

I just can’t in my head classify a go-around as a difficult and stressful manoeuvre that needs workload-reducing but suboptimal suboptimal hacks to make it accessible to an average pilot.

And if mixture rich on final damages engines, it doesn’t meet the “safe and easy” test, does it?

I’m a lazy pilot, I’m afraid. I don’t touch a lever until it needs to be touched. It reduces wear to the finish on the knobs and handles, and keeps the plane in tip top condition.

Now, if you want to talk about shock cooling a cylinder head by the rapid introduction of lots of very cold fuel, let’s talk about go-arounds themselves.

[PilotDAR]

I've never seen a benefit in using an uncertain outcome to attempt to justify not being easy going on an engine, and airplane, or any machine, for that matter. Plan ahead, and be gentle on the machine. For those [hopefully]rare occasions when things surprise you, do what you have to do to assure a safe flight.

I recently sat right seat to a well experienced pilot while stall testing a turbine airplane. He was rough with the power lever. He'd pull it rapidly from cruise power to idle (and I'd test my shoulder harness), and then open it up again quickly enough the I was seeing 100 RPM propeller exceedances, as the governor tried to keep up. There was zero urgency in the maneuver, nor operational need for haste. I commented a couple of times about this during the flight. In the post flight company debrief, he asked if there had been any safety concerns during the last flight. In the presence of everyone, I said that I had no safety concerns, though I would appreciate a more gentle touch on the power lever. He acknowledged, and the following flights were better.

If you can be gentle to the plane, be gentle to the plane, don't try to argue why you shouldn't have to be....

[CpnCrunch]

The problem with not putting the mixture full rich on final is that if you forget to richen it on a go-around you could destroy the engine. See today's savvy aviation newsletter where a guy did exactly this with an IO-540, and his #5 CHT went up to 600F and was over redline for 6 minutes! Luckily there was only minor damage to the spark plugs, perhaps thanks to Lycoming cylinders being more tolerant of high temperatures.

[photofly]

The problem with not putting the mixture full rich on final is that if you forget to richen it on a go-around you could destroy the engine. See today's savvy aviation newsletter where a guy did exactly this with an IO-540, and his #5 CHT went up to 600F and was over redline for 6 minutes! Luckily there was only minor damage to the spark plugs, perhaps thanks to Lycoming cylinders being more tolerant of high temperatures.

There are a million "if you forget to do X then you'll screw up the plane, crash, die, etc." items involved in flying. Training involves learning to not forget to do any of them.

Leaving the mixture too lean in a full power climb for six whole minutes is a defect in procedure way, way, way beyond simply "forgetting to put the mixture rich on the go around". It involves that, yet, and but way more significantly in involves failing for six minutes (count them, yes all six of them) to check the configuration of the aircraft or the engine indicators.

Frankly, if you can learn to put the mixture rich on short final then you can learn to put the mixture rich at any given time, including when you increase power for a go-around. If you are a pilot who is likely to forget to put the mixture rich on a go-around then you're likely to forget it at any other time, too.

[CpnCrunch]

Frankly, if you can learn to put the mixture rich on short final then you can learn to put the mixture rich at any given time, including when you increase power for a go-around. If you are a pilot who is likely to forget to put the mixture rich on a go-around then you're likely to forget it at any other time, too.

The problem is that if you don't do a go around on every flight, you're not training yourself to do that. I don't think I've done an actual go-around in years, other than practice ones. The last time I did an actual one I forgot to turn the carb heat off. I've also forgotten to put the flaps up after takeoff a few time, so I practice takeoffs with flaps more often now. If you put the mixture rich on every flight at the same point, you are much less likely to forget it than if you only do it once every 5 years when you do a go-around.

[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.

[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?

[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.