Shock cooling

For the THIRD time:

Treat your airplane with TLC, and you'll get more out of it.
 
Tom-D said:
Ron and I both agree these engines will never see operating temps that will harm the cylinders at any rate you can cool them, thus shock cooling is a myth.
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I never said that. Please remove that misquotation from your post. All I said was that quench cracking couldn't occur at any rate at which you could cool your engine. I never said you couldn't create a cooling rate rapid enough to harm your engine, and in fact, said the exact opposite.
 
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Fearless Tower said:
Hmmm.....what's the TBO on a RR Merlin?

I think my wallet would rather take its chances with air cooled...
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Ben's liquid-cooled engine is slightly different than a Merlin. ;)
 
Ron Levy said:
I never said that. Please remove that misquotation from your post. All I said was that quench cracking couldn't occur at any rate at which you could cool your engine. I never said you couldn't create a cooling rate rapid enough to harm your engine, and in fact, said the exact opposite.
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When you say this

"
Quote:
In my mind, as I've understood the term, a shock cooled engine will fail immediately. If it doesn't crack and fail prior to touchdown, then something else is occurring.
If you could cool the engine that fast (1000's of degrees per second), yes, that's what would happen. But you can't, so it's not an issue.

it's a minuscule difference.

Heat causes damage, the rate of cooling does not.

It's a true fact that you can not cool a cylinder in the air to a point the cylinder will choke a piston, specially when the engine is still running and producing heat to the cylinder barrel.
 
Ted DuPuis said:
Tom, you simply do not have the evidence to prove or disprove that.
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Should I quote the Lycoming overhaul manual? It gives the piston to cylinder wall clearances and the ring end gap, dead cold as we assemble the engine.

and if you will remember the piston is aluminum, and the barrel is steel, aluminum has a greater Coefficient of expansion than steel. So the colder the temps the greater the clearance will be, and the hotter the engine temps the lessor the clearance will be, That was figured out long ago, and the clearance set to compensate to never allow the the piston to grow and touch the cylinder bore. If that wasn't true we would have failure on every engine that gets over heated.

Almost every body here knows you are an employee of Lycoming, and that you have all the data, but simple common sense and experience tells us there is no data to support the theory of shock cooling.
 
Inverted said:
Ummm no. I have seen cracked cylinders from shock cooling.
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I've seen cracked cylinders too, but I didn't see the little label that said it was from shock cooling. ;)

My point is - Sure you've seen cracked cylinders - How do you know it was shock cooling that caused it? About the only thing that everyone else in the thread agrees on is that shock cooling cannot possibly cause cracked cylinders, and here you are throwing that out! :crazy:
 
Ted DuPuis said:
The point is that if you fly like you ought to, then it's irrelevant. When I instruct pilots, I teach them gradual power changes, because it's how I think people ought to fly.
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Yet another thing to go on my "list of things that should be taught that aren't on the Private Pilot PTS."

It's hard to argue with the fact that a smooth pilot is typically better appreciated by his or her passengers, and reduces propensity to having the previous meal regurgitated all over the plane.
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And it's not all about pax not barfing - It's about them having a GREAT time so that they may want to become pilots, or at least ride with you again, or at least be on GA's side of things next time a referendum comes up on whether or not to keep the local airport open...

Be nice to your pax and nice to your plane. :yes:
 
Ron Levy said:
You can still do serious damage to your engine with CHT's well below 830F. The 500F redline on most engines is not to be trifled with.
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500F is still too high. 400F is a much saner limit. At 450F or so, aluminum has lost half of it's tensile strength. If you're nudging 500F you're really playing with fire. Get the nose down, the airspeed up, the cowl flaps open, and if you have to, the fuel flow higher (mixture).

And at 500F how hot is your oil and how often do you change it? Anywhere from 30-40% of engine cooling in so-called "air cooled" engines is by oil through the oil cooler. And remember the FAA in their infinite wisdom requires the oil temp gauge sensor be installed at the point in the oil system is at it's COOLEST. Nice of 'em to do that, eh?

Oh and just how much do you trust that cheap factory gauge to be on the hottest cylinder? ;)
 
PittsDriver said:
I may not be remembering correctly but didn't the APS folks prove that heat wasn't as big a factor in engine wear and reliability as head pressures? IOW, peak head pressures were found at 50 - 80 ROP and this was worse than operating at the same temp LOP. I don't have the reference handy and will try to find it.
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It sounds like you're confusing CHT and EGT. Peak pressures were around 50 ROP, but that's rich of peak EGT - They found that CHT directly correlated with internal cylinder pressures, so you could think of that as "peak CHT" but it's probably better to use another term lest others be confused. The "peak" in leaning (LOP, ROP) means peak EGT.

So, to pick apart the quote: They DID find that *EGT* wasn't as important as *internal cylinder pressure*. Peak pressures were in the 50 ROP range, and 50 LOP, while it will be the same *EGT*, will provide lower *CHT*.

One of many references to be found in John Deakin's columns on AvWeb is here: http://www.avweb.com/news/pelican/194452-1.html

BTW, I picked up this gem from the above column - Sounds like a summary of this thread:

We are deeply suspicious of any of the "shock cooling" theories, with an awful lot of data that suggests it's largely an artifact of aviation mythology (another term for OWT). But it certainly makes good sense to be gentle with power changes. We look at Bob Hoover, who would go from full power to instant feather, then right back out of feather to full power again, several times during his Shrike Commander act, several shows a day, and many shows a year. His engines routinely made full TBO without problems. Sky-diving airplanes, flight school airplanes, all routinely go to TBO, given decent treatment otherwise. All of those seem to suffer a LOT of "shock cooling" with complete aplomb.
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flyingcheesehead said:
It sounds like you're confusing CHT and EGT. Peak pressures were around 50 ROP, but that's rich of peak EGT - They found that CHT directly correlated with internal cylinder pressures, so you could think of that as "peak CHT" but it's probably better to use another term lest others be confused. The "peak" in leaning (LOP, ROP) means peak EGT.
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Peak CHT happens well before peak EGT while still ROP, and then is relatively flat until LOP on most engines... if you let them settle out. The problem is, CHT takes longer, so the "lag" can be deceiving. It usually happens somewhere right around "Best Power" which is significantly ROP.
 
Tom-D said:
Should I quote the Lycoming overhaul manual? It gives the piston to cylinder wall clearances and the ring end gap, dead cold as we assemble the engine.

and if you will remember the piston is aluminum, and the barrel is steel, aluminum has a greater Coefficient of expansion than steel. So the colder the temps the greater the clearance will be, and the hotter the engine temps the lessor the clearance will be, That was figured out long ago, and the clearance set to compensate to never allow the the piston to grow and touch the cylinder bore. If that wasn't true we would have failure on every engine that gets over heated.

Almost every body here knows you are an employee of Lycoming, and that you have all the data, but simple common sense and experience tells us there is no data to support the theory of shock cooling.
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Unlike you, Tom, I only bring my knowledge with me to this forum, not my employment, and that is very clear in my posts. So I'd appreciate you keeping out of that. Unlike you, I don't use this place as a means of advertising, which is why I don't talk about what I do, other than what I can share as a result of my experience here. You make a habit of using improper terms, give out advertising as advice, and frequently keep it inconsistent at that.

Common sense? Hardly. Common sense would tell you to be nice to your engines. You just tell people to go to you or your buddy to get work done, and denounce anyone else. :rolleyes2:

I'm done.
 
denverpilot said:
Peak CHT happens well before peak EGT while still ROP, and then is relatively flat until LOP on most engines... if you let them settle out. The problem is, CHT takes longer, so the "lag" can be deceiving. It usually happens somewhere right around "Best Power" which is significantly ROP.
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Peak CHT is around the 50-80 ROP range. Richer than that, it goes down. Leaner than that, it goes down. See:

http://www.lycoming.textron.com/support/publications/service-instructions/pdfs/SI1094D.pdf

Final page.
 
PittsDriver said:
I think that was what I was trying to say but just didn't say it as concisely. I generally live in a state of confusion so thank you for the reference and clearing that up.
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That's what I thought you were trying to say, too.

I understand the state of confusion. After all, it is a Tuesday. I never could get the hang of Tuesdays...
 
denverpilot said:
Peak CHT happens well before peak EGT while still ROP, and then is relatively flat until LOP on most engines... if you let them settle out. The problem is, CHT takes longer, so the "lag" can be deceiving. It usually happens somewhere right around "Best Power" which is significantly ROP.
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Nope - CHT peaks at about 25-50ºF ROP, where Best Power is about 100-160ºF ROP. See either the Lycoming link that Ted provided (last page), or the Deakin link I posted earlier.

What I really laugh about on the Lycoming one is how it says "TEXTRON LYCOMING DOES NOT RECOMMEND OPERATING ON THE LEAN SIDE OF PEAK EGT" but their labeled "Best Economy Range" in the graph immediately above that statement is lean of peak. :rofl:
 
I've always been taught, and follow it carefully, to treat the engines with care. Gently bringing power back seems to be a more reasonable approach than slamming it to idle and pointing the nose at the ground. If you plan far enough in advance, you can easily reduce MP in small increments. If ATC gives you a slam dunk, you start slowing down prior to the letdown and then add drag to descend. If I tried to keep power up until ATC let me down and then chopped power in the Aerostar, I'd be past the airport and close to the next city before I slowed enough to land.

So, I am intrigued a little by the LOP operations you all speak of. Admittedly, I do not have an engine monitor, so it may be a moot point, but I have always been taught to lean toward
~50 ROP for proper leaning. Certainly, it is probably a better power setting for getting the passengers there on time, but it does burn a bit more fuel. What is the danger of overheating? How much loss of power is there and will it shorten the exhaust valve life? Twinkie seems to like to ruin his exhaust valves on a regular basis, and I don't know if it is from my flying, which is generally 50 ROP, or from my partners, which I imagine is somewhat more "frugal."
 
flyingcheesehead said:
Nope - CHT peaks at about 25-50ºF ROP, where Best Power is about 100-160ºF ROP. See either the Lycoming link that Ted provided (last page), or the Deakin link I posted earlier.
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And around there you talkin' about a 25F difference there in the CHT from Best Power on up through 25-50 ROP... on the chart I was using. If it's significantly different from Deakin's or the other one, I'll post it.

If you can read 25F on a normal Cessna CHT gauge, or most of the other standard GA gauges, be my guest. Cheating with a JPI doesn't count. ;)

In fact, even as vehement as I am about my 400F hard-limit... I will pretty much have to guess where it is, on my gauge, unless I get some welding dots and go calibrate the silly thing.

For now it's interpolation down from knowing the range of the gauge on my aircraft, but there's no way that thermocouple and circuit driving that gauge are linear.

"3/4 of the green" is about the right spot until a real calibration can be done, or a JPI installed. And with a normally aspirated O-470-R, the JPI's kinda silly.

Great to slap one on (like you guys did) during engine overhaul, but thousands of O-470 engines make it to TBO and beyond without one.

The O-470 is about the easiest powerplant to "manage" of the over 200 HP crowd.

75% power and up, full rich.

75-65% power, 100 ROP. You're nibbling at the "Red Box" I believe, here... so if you're gonna stay there and not climb up further, maybe give her more gas.

65% and lower, Continental says you can do whatever the heck you want with the mixture control, and so does everybody else. Max EGT is a good spot for it.

LOP barely works on O-470s in Skylanes if at all, and you gotta fart around with partial carb heat and "cocking" the throttle plate and yadda yadda, and those with JPIs still say the CHTs are all over the place. It's just a big fat tractor engine with crappy induction. Give it gas and stop whining.

Finally, keep MP up and RPM low for happy rings and bottom-end. Anything in the chart in the POH is fair game. There is absolutely nothing wrong with "over-square" operating in an O-470. Pick your power setting from the POH chart, set for lowest possible smooth running RPM, and go.

I'm pretty rarely above 75% power at this altitude. I'm also not exactly seeing high MP numbers, ever. :)

In fact, I'd probably have to fly it lower to replace the engine and get the rings to seat properly. I'd also have to revisit my "full-rich" at 75% power or above if I were tooling around at 3500 MSL on any kind of a regular basis.

flyingcheesehead said:
What I really laugh about on the Lycoming one is how it says "TEXTRON LYCOMING DOES NOT RECOMMEND OPERATING ON THE LEAN SIDE OF PEAK EGT" but their labeled "Best Economy Range" in the graph immediately above that statement is lean of peak. :rofl:
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[/QUOTE]

Another good reason not to fly behind Lycomings. ;) Heh... kidding. Lawyers vs. Engineers, right there on the same page for all to see. Embarrassing for them, I suppose.
 
Bryon,

Come fly with me for an hour, I'll teach you about engine management. I might even have cause to come to LNS this weekend.
 
denverpilot said:
If you can read 25F on a normal Cessna CHT gauge, or most of the other standard GA gauges, be my guest. Cheating with a JPI doesn't count. ;)
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Factory gauges on the 182 are freakin' worthless. They basically read

....................500
\-----------------/ /

And the needle doesn't seem to follow any meaningful path, either.

In fact, even as vehement as I am about my 400F hard-limit... I will pretty much have to guess where it is, on my gauge, unless I get some welding dots and go calibrate the silly thing.
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With a factory gauge, you have no 400F hard limit. It's a wild guess.

And with a normally aspirated O-470-R, the JPI's kinda silly.
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No, it's really not. I've discovered a lot of things about operating the 182 since we installed it.

Great to slap one on (like you guys did) during engine overhaul, but thousands of O-470 engines make it to TBO and beyond without one.
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Well, that shouldn't be too hard since TBO is only 1500. FWIW, prior to the JPI we made it 2451 hours between overhauls. Poplar Grove Airmotive earned our repeat business!

In fact, I'd probably have to fly it lower to replace the engine and get the rings to seat properly.
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Or send it to Poplar Grove, where they'll run it for 3 hours in the test cell before they even send it back to you, so the rings are already pretty well seated. After we got it back from them, we burned ONE quart of oil in the first 50 hours!
 
Tom-D said:
http://www.tcmlink.com/pdf2/SIL98-9A.pdf

WE never change any engine until it needs it.

2 0-470s last year at annual both have well over 2500 hours and are running fine.
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Yeah, ours ran great for about 2350 of the 2451 hours we ran it - Then we started having some compression problems, burning oil, and finally the prop governor started "heaving" and we found a pile of metal in the oil filter. It was time.
 
flyingcheesehead said:
Factory gauges on the 182 are freakin' worthless. They basically read

....................500
\-----------------/ /

And the needle doesn't seem to follow any meaningful path, either.

With a factory gauge, you have no 400F hard limit. It's a wild guess.

No, it's really not. I've discovered a lot of things about operating the 182 since we installed it.
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Kent is correct on all of these, and that's pretty common for a lot of factory CHT gauges to be pretty useless. My Aztec's factory readings are probably among the worst I've seen, but the truth is you have no idea what your CHTs are if you're using the factory gauges.

Additionally, there are lots of other things that engine monitors do for you. The most noticable for me is diagnostics. It turns "I have a bad plug" into "The plug on the #2 cylinder connected to the left mag is bad."

While I'd agree that a factory 182 doesn't benefit from one as much as the 310 or the Aztec (or, even better, something like a 421), you still benefit from it.
 
Speaking of unreliable gauges - back in the day, we used to "jet" our motorcycle engines by the exhaust color. We were always looking for a medium tan color to find the proper jetting or in pilot parlance, mixture. I do a lot of full throttle flying right over the airport with the mixture full rich and when I do, I'm getting black exhaust stacks - which is perfect because I'm running full power and RPM at really low airspeeds alot and cool is good. When I land after flying even a 20 minute cruise at 65% power at what my EGT gauge is showing about 50 ROP I get white exhaust stacks. I know I'm ROP (leaning raises temps) so I'm now confused. White exhaust means too lean, right?

Any of you engine gurus have any thoughts? Should I be targeting more like 100 ROP? It's tempting to run as lean as possible since the plane is basically a fuel emergency when I take off but am I running the engine properly? It's an AEIO 540/ 260 hp.
 
PittsDriver said:
Speaking of unreliable gauges - back in the day, we used to "jet" our motorcycle engines by the exhaust color. We were always looking for a medium tan color to find the proper jetting or in pilot parlance, mixture. I do a lot of full throttle flying right over the airport with the mixture full rich and when I do, I'm getting black exhaust stacks - which is perfect because I'm running full power and RPM at really low airspeeds alot and cool is good. When I land after flying even a 20 minute cruise at 65% power at what my EGT gauge is showing about 50 ROP I get white exhaust stacks. I know I'm ROP (leaning raises temps) so I'm now confused. White exhaust means too lean, right?

Any of you engine gurus have any thoughts? Should I be targeting more like 100 ROP? It's tempting to run as lean as possible since the plane is basically a fuel emergency when I take off but am I running the engine properly? It's an AEIO 540/ 260 hp.
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Depends on your power setting. At or below 65% max rated HP you can run any mixture you like without fear of engine damage as long as you keep the CHTs below 380F, and at 65% slightly LOP is probably the best compromise between cruise speed and efficiency. The most stressful mixture (highest peak cyl pressures) is around 25 ROP (which also corresponds to max CHT) and as you increase power above 65% you want to be moving away from the peak to 50 ROP range. Also FWIW, when you are in the peak to 50 LOP (even further LOP at high power) range your actual power in HP will be pretty close to 14.9 times your GPH (i.e. don't use MP & RPM to figure power there).
 
Ted DuPuis said:
Additionally, there are lots of other things that engine monitors do for you. The most noticable for me is diagnostics. It turns "I have a bad plug" into "The plug on the #2 cylinder connected to the left mag is bad."

While I'd agree that a factory 182 doesn't benefit from one as much as the 310 or the Aztec (or, even better, something like a 421), you still benefit from it.
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Yup - TONS of good stuff comes from having an engine monitor. I wouldn't want even a simple airplane without one any more. (Okay, maybe it's overkill on a J-3 - But it'd be useful even on a 172.)

As Ted describes, it's a huge help with diagnostics, which will save you $$$$$$.

It allows you to KNOW your CHT's and keep them in the proper range, which will save you $$$$$$.

It makes the leaning process much more precise, which can save you $$$$$$.

It can alert you to engine problems long before the fan stops turning, which can save your life and some $$$$$$.

Plus, it helps you get to know your airplane even better. Aside from the EDM 700 with fuel flow, we also added a carb temp probe. THAT has been VERY interesting! But it's also been highly educational to see when CHT's hit 400 despite the cowl flaps being open and the mixture rich. Nate, chances are you're regularly putting 1-3 cylinders over 400ºF without even knowing it.
 
It was educational to see the temps on the new monitor in the Frankenkota. Most of the CHTs were around 280 but two were around 305. The monitor also had a faster response than the factory analogue TIT so leaning was quick. Okay, so I didn't lean it the way the EI manual sez to do it (slow procedure), I just did it the way I normally do.

Hope I never have to see that diagnostic stuff folks talk about...
 
flyingcheesehead said:
As Ted describes, it's a huge help with diagnostics, which will save you $$.

It allows you to KNOW your CHT's and keep them in the proper range, which will save you $$$$$$$$$$$.

It makes the leaning process much more precise, which can save you $.

It can alert you to engine problems long before the fan stops turning, which can save your life and some $$$$.

Plus, it helps you get to know your airplane even better. Aside from the EDM 700 with fuel flow, we also added a carb temp probe. THAT has been VERY interesting! But it's also been highly educational to see when CHT's hit 400 despite the cowl flaps being open and the mixture rich. Nate, chances are you're regularly putting 1-3 cylinders over 400ºF without even knowing it.
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I fixed the number of $$$ on those for you. And the "save your life" part, well... if you have life insurance, some of us are worth more dead than alive... if you're only talkin' about $. ;)

I'm sure we're flirting with or exceeding 400F regularly on some cyls on hot days here, or on mountain trips with long slow climbs. Not much way to tell other than to pour the gas to her, keep the cowl flaps open, and hope with that gauge, I know. Not my style, but I'm not sure the other owners/wallets are interested in adding the JPI right now.

Maybe if I suddenly feel rich, I'll just pop for the whole installation someday, or do it with whichever other wallet feels saucy at the time. Probably Cap'n Barry.

I'll "demand" (maybe too strong a word, but close) the JPI when we replace the engine, but if all goes well that's still many many years away. We'll especially want the JPI if we do the P.Ponk, which is what we're leaning towards doing right now (no pun intended).

Things change, but right now we're at least four years if not more, from TBO, let alone flying it beyond, which we'll do. Getting "Looks like a perfect O-470" from Blackstone these days, and the oil filters are looking good so far...

Did you miss the "welding dots" idea? I am definitely meaning to try that out. Cheap/simple way to at least it'll tell us if the gauge is grossly wrong for the time-being. Or so I hear. Haven't done it yet.

Have a long checklist of items I want to look at under the cowl after the CPA course. Some a big deal, others just to see what's up. Getting our bottom cowl off is a huge PITA. Well, off isn't bad... back on is usually elicits a few "WTF?!" moments, and "Almost got it, awwww, crap... it moved!" moments. Also takes two people, minimum. (Anyone got any tricks for the lower C-182 cowl on a P model with the frakkin' landing lights in the cowl?)

I'm ridiculously jealous of the majority of CPA class members who appear to have A&Ps who allow them to work on their aircraft and sign off on things. Almost impossible to find such people around here unless you go out to KFTG I hear, and you probably need to be KFTG-based to be in the in-crowd. I dunno. :dunno:

One guy at the class spoke of his A&P/IA actually having a "wait list" and would only take 12 aircraft a year... but who also did top-notch work... Well, you probably could have seen me turning green with envy just standing there listening to that story.

Another guy who said his A&P/Avionics guy traded him the installation of a Garmin 530 (he'd bought it, but needed it installed) for house wiring a bathroom. Grrr. Bathroom wiring is easy. Sheesh. I'd do that! (Don't forget the GFCI! GRIN!)

Ah well... I'll fly it as best as I can with the data we've got. Oh, and I'll be doing some serious baffle-checking too... baffles goofed up/missing/broken in the 182 really messes with CHT...
 
denverpilot said:
We'll especially want the JPI if we do the P.Ponk, which is what we're leaning towards doing right now (no pun intended).
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Check out the Texas Skyways conversions too. You will need a new 3-blade prop for those, but if you end up needing a new prop anyway like we did it might not be too out of line cost-wise. It also has a 2,500-hour TBO (not that that means anything...)

Did you miss the "welding dots" idea? I am definitely meaning to try that out. Cheap/simple way to at least it'll tell us if the gauge is grossly wrong for the time-being. Or so I hear. Haven't done it yet.
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So, what the heck are welding dots? :dunno:
 
flyingcheesehead said:
Check out the Texas Skyways conversions too. You will need a new 3-blade prop for those, but if you end up needing a new prop anyway like we did it might not be too out of line cost-wise. It also has a 2,500-hour TBO (not that that means anything...)
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They're nice, but the difference in cost is significantly higher than the P.Ponk. HP per dollar, the P.Ponk is probably the way to go. A guy on the CPA Forum just went through it, and posted a very nice spreadsheet in today's $$$$$$$ (ha! lots of $) of six or seven different options on C-182 engine replacements.

He was "fair" and included just floppin' in another bog-standard Continental after a local shop rebuilt it, and a Factory Reman too, if I remember correctly, so you could see the difference between the straight Connie and the upgrades. I have the spreadsheet stashed in the Dropbox (somewhere...) if you want to see it.

Fascinating how much money they get for the Texas Skyways IO-520 and IO-550 upgrades. I think I'll start calling them Texa$ $kyway$, like Micro$oft.

The thing is... who knows how the quality control will go at Continental now that the Chinese own them, and you still need Connie parts for a P.Ponk, and obviously for a Factory Reman or any of the Connie options... so none of this analysis will really matter by the time we need an engine. We'll be doing homework all over again, then. But it at least gives us a "feel" for what to budget for, etc.

flyingcheesehead said:
So, what the heck are welding dots? :dunno:
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Ya stick 'em on metal, and they turn color/black when the metal hits that temperature. Commonly used in welding, I guess. Was an idea that a couple of people from the class had done. You do have to find an appropriate place to stick 'em, somewhere near your factory CHT probe, which isn't super easy, but then you can go fly, note your highest CHT (water marker right on the gauge works fine, or whatever way to mark the gauge that you like) and then pop the cowl and see which ones have changed color.

There are a type that go back to their original color when they cool down... you don't want those. Get the "non-resetting" type.

Welding shops like McMaster-Carr carry them.

http://www.mcmaster.com/#temperature-indicating-dots/=bka7w3

(I'm still figuring out which ones I want to use from their website, so I can't link direct to the "right" ones for ya, but the list doesn't look too bad at first look. You're seeing their list about 10 minutes behind the first time I've ever seen it too. :cornut: :dunno: )

Supposedly they're also a good way to see if your fancy-schmantzy JPI probe is accurate too, I hear. :thumbsup:
 
BTW, if you look carefully at the nose of SpaceShip One, you can see a similar technique used so they could learn what the re-entry temperatures were on the nose cap. They used welding temperature "sticks"/"crayons"... the only stuff melts within 5C of a particular temperature...

http://www.tempil.com/thumbnail.asp?cid=22

A rainbow of colors on the front of the nose. :)
 
denverpilot said:
Ya stick 'em on metal, and they turn color/black when the metal hits that temperature. Commonly used in welding, I guess. Was an idea that a couple of people from the class had done. You do have to find an appropriate place to stick 'em, somewhere near your factory CHT probe, which isn't super easy, but then you can go fly, note your highest CHT (water marker right on the gauge works fine, or whatever way to mark the gauge that you like) and then pop the cowl and see which ones have changed color.

There are a type that go back to their original color when they cool down... you don't want those. Get the "non-resetting" type.

Welding shops like McMaster-Carr carry them.

http://www.mcmaster.com/#temperature-indicating-dots/=bka7w3

(I'm still figuring out which ones I want to use from their website, so I can't link direct to the "right" ones for ya, but the list doesn't look too bad at first look. You're seeing their list about 10 minutes behind the first time I've ever seen it too. :cornut: :dunno: )

Supposedly they're also a good way to see if your fancy-schmantzy JPI probe is accurate too, I hear. :thumbsup:
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Any kind of stick-on indicator is going to give you exterior surface temperature, which is probably not what the engine manufacturer is basing their CHT limits and recommendations on. I would expect the manufacturer to base their numbers on whatever type of probe they've made provisions for. So, I'm not sure that the information you would get from a sticker would really tell you much.
 
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