School me on shock cooling.

rbridges said:
Dave, when ATC tells you to drop 2000 ft, do you just nose over or pull power (or a combination). My CFII taught me to pull power to lose altitude, but this almost always triggers my shock cooling alarm on my UBG17 monitor.
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Well, I don't fly IFR anymore so that scenario doesn't come up often, but I would in that case nose over. If the speed was going to build up to the red, or I was on an approach and near the runway, I would nose over and start power reduction at the same time. If they give you a real crappy slam dunk, I might then choose to chop and drop. Like I said, probably not the end of the world on occasion. If they do that to you all the time at your airport, I would ask them why and then consider getting speed brakes.
 
rbridges said:
Dave, when ATC tells you to drop 2000 ft, do you just nose over or pull power (or a combination). My CFII taught me to pull power to lose altitude, but this almost always triggers my shock cooling alarm on my UBG17 monitor.
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Then don't pull it so much (or check to see that your shock cooling alarm is set to an appropriate level).
 
Dav8or said:
Well, I don't fly IFR anymore so that scenario doesn't come up often, but I would in that case nose over. If the speed was going to build up to the red, or I was on an approach and near the runway, I would nose over and start power reduction at the same time. If they give you a real crappy slam dunk, I might then choose to chop and drop. Like I said, probably not the end of the world on occasion. If they do that to you all the time at your airport, I would ask them why and then consider getting speed brakes.
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I'm at an untowered airport, so it doesn't happen often, but I notice my shock alarm comes on quite a bit when I reduce power to drop altitude. I tend to watch my temps closely and never run the engine higher than 380. I don't think shock cooling is really an issue from what I've read, but I still have things running through the back of my mind.
 
EdFred said:
Why is shock heating never an issue? I see temps rise just as fast as they fall off, but no one ever says to keep your heating delta at 30°(or whatever temp)/minute. Of course if we did, we would need 40,000' runways.
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Actually it is. That's why we preheat, so we don't "choke" cylinders. Also, if excessively cold, the clearance between bearings and crank are reduced and a bearing can spin.

At least that's what "they" say.
 
Chip Sylverne said:
I had a Yamaha RD350. Adding 2 cycle oil was a pleasure. That thing was a rocket.

Wish I still had the bike.
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I had the almost identical machine. I bought a 1972 R5C in 1973. The '73 RD350 replaced it but was basically the same machine. It was fast and I had a lot of fun and adventures with it. Rode it up to the Adirondacks from Long Island and down to Florida. It would do 115 flat-out and saw a lot of time at that speed but it was the 0 - 60 where it shined.
 
denverpilot said:
So what are you flying, OP?
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A PA-28-181 with a Lycoming O-360.

I need to be practicing for an upcoming checkride so I need to be doing stalls. I think later in the week it's supposed to warm up to around 15F... although I'm not sure how much difference another 10-15 degrees will make.
 
alfadog said:
I had the almost identical machine. I bought a 1972 R5C in 1973. The '73 RD350 replaced it but was basically the same machine. It was fast and I had a lot of fun and adventures with it. Rode it up to the Adirondacks from Long Island and down to Florida. It would do 115 flat-out and saw a lot of time at that speed but it was the 0 - 60 where it shined.
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I rode mine all over the Southeast 1977-81. Was going to school in Gainesville, FL at the time. Loved that bike. Man, once you hit 4k rpm, the world turned blurry. There was an RD racer who lived in town who kept it tuned it for me, bored the cyls .030 over. Almost lost it one time, badly, so I got religion and sold it. That kid got he deal of a lifetime.

Tire technology has come a long way since then.
 
cowman said:
A PA-28-181 with a Lycoming O-360.

I need to be practicing for an upcoming checkride so I need to be doing stalls. I think later in the week it's supposed to warm up to around 15F... although I'm not sure how much difference another 10-15 degrees will make.
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I wouldn't worry about doing stalls. In the case of the departure stall, it's done withe engine on anyhow and in the case of the power off stall, just gradually slow down to landing speed then go to idle and stall. In other words, just take a little longer to get down to stall speed.
 
cowman said:
I had an instructor tell me we shouldn't be practicing any stalls or other maneuvers where there would be lots of big changes in power settings because of shock cooling.. this was on a day when surface temps were around 0F.

I also read something on the internet saying there's nothing supporting the idea that shock cooling happens/causes any harm.

I honestly don't know a lot about the subject but it seems suspect to me that such a thing would really be a problem. Can you guys educate me on the subject?
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500 hour TT CFIs will tell you a lot of things, some of which will be accurate.
 
weilke said:
A lot of damage attributed to 'shock cooling' is probably the result of cylinders getting too hot in the first place.
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I'll buy this, only place I know of theta suffered shock cooling issues was a dive operator, strait up to 15 and strait back down as fast as possible. While I have no doubts that the rapid cooling didn't help anything I suspect that they were also overheating the cylinders on the climb.

So maybe it is real, but not something that the typical operator needs to worry about.
 
cowman said:
A PA-28-181 with a Lycoming O-360.

I need to be practicing for an upcoming checkride so I need to be doing stalls. I think later in the week it's supposed to warm up to around 15F... although I'm not sure how much difference another 10-15 degrees will make.
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Good stout engine, don't sweat it
 
weilke said:
It is real in one particular operation, and that is glider-towing. Some big british training operation published a paper on this. When their SOP was to release the glider, pull power to idle and to immediately dive back to the field, they kept buying cylinders by the dozen. Once they changed their SOP to include 1min of level flight with a lower power setting before descending, their cylinder replacement frequency dropped back to baseline.

Skydiving operations dont seem to have a problem, they already include the jump-run with a reduced power setting. It seems to be the first 20degF that make the difference, once the cylinders have cooled down just a little bit from peak temp, it doesn't matter much how fast the further cooling takes place. If you never have hot cylinders to start with, it probably makes no difference either way.
P

(above is my personal opinion based on reading up on this a while ago, ymmv)
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O-540 in tow operations. Full power climbs to 2-4K AGL, tow release, reduce to about 2200-2300RPM, pushover to between 80-100knts, after about 1min reduce to 1800-2000RPM, enter the pattern, still descending on downwind, 1500-1700RPM, reducing to approach speed, 55-65KIAS, power to idle on landing. No shock cooling issues. I have been on the ground in as quick as 40 seconds from a 2K AGL release.

For the original OP. power on stalls not an issue, some reduced cooling airflow in the cowling but power level not changed. Power off stalls, momentary reduction in power to idle for the stall and then back on, should be no issues.

Bigger issue in the cold is exposed cylinders, power to idle and the engine could quit. J-3 cubs in winter, gotta keep the engine warm.
 
TMetzinger said:
Question, does the airplane come with a winterization kit? I don't recall if the PA28s have one or not.
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The ones I have worked with only have oil cooler blocking plates. Never have played with a -181 though.
 
Skylane81E said:
The ones I have worked with only have oil cooler blocking plates. Never have played with a -181 though.
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Mine has a winterization kit also. Otherwise known as duct tape on the oil cooler...FAA approved duct tape...AKA high speed tape.

;)
 
It has the blocking plate for the oil cooler installed, that's it.
 
BillTIZ said:
O-540 in tow operations. Full power climbs to 2-4K AGL, tow release, reduce to about 2200-2300RPM, pushover to between 80-100knts, after about 1min reduce to 1800-2000RPM, enter the pattern, still descending on downwind, 1500-1700RPM, reducing to approach speed, 55-65KIAS, power to idle on landing. No shock cooling issues. I have been on the ground in as quick as 40 seconds from a 2K AGL release.
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The folks who had problems towed with an O360 under full power, released, pulled back to idle and pointed the nose at the runway. I can see how that would go from very hot to very cold in a short time.
 
TMetzinger said:
Question, does the airplane come with a winterization kit? I don't recall if the PA28s have one or not.
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There is indeed a special winterization plate for many PA28's, and there should be both a note in the POH and a placard in the engine compartment to tell you about this.
 
There's nothing really special about it. It's a piece of Al with 3 or 4 tapped holes in it.
 
weilke said:
A lot of damage attributed to 'shock cooling' is probably the result of cylinders getting too hot in the first place.
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Exactly. The best post of the thread.

It amazes me what another 1.5-3.0 gph does in big-bore Continentals. I had problems with CHTs sniffing 400 in the climb. The fuel flow was pretty close red-line, but not at redline. I was pushing 26gph or so (IO520) and having to throttle back to avoid going over 400F -- with nothing over 380F really being ideal. While waiting on getting the fuel flow re-metered, I started going to 27/2700 on the runway, boost on, lean to redline, and head on up. Holding full-power and doing that procedure, I never saw over 350F CHT in the climb. On the climb to altitude, I just keep leaning to hold around 1300F EGT. Then, level off and do Lean of Peak, and CHTS are 300-320F in cruise. On the descent, I just pull back to 20 inches and keep slowly reducing to keep power 18-20" all the way down to approach altitudes -- with the cowl closed. At final, I go ahead and open the cowl to reduce the steps should a go-around be needed. Never have gotten a shock-cooling alarm since keeping the CHTs 350F and below. Before that, I'd get then routinely (from the EDM monitor).

In the end, we added just 2.2 gph flow to our full-rich / full-throttle setting. I just imagine 2 1/2 milk jugs suspended on a string with a small enough hole in them to cause it to take AN ENTIRE HOUR for the fuel to leak out. THAT little amount of fuel dropped the CHTs 50F! Then, after take-off, the leaning gets the flows back into what was previously normal -- so the extra $3-4 of fuel, max, seems well worth it in the long run...

Doing that, I've never seen a shock-cooling alert again.
 
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Martymccasland said:
It amazes me what another 1.5-3.0 gph does in big-bore Continentals. I had problems with CHTs sniffing 400 in the climb. The fuel flow was pretty close red-line, but not at redline. I was pushing 26gph or so (IO520) and having to throttle back to avoid going over 400F -- with nothing over 380F really being ideal.
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Well, according to TCM, 26.1 is the upper limit for most IO520 installations (some are 24.9), so you should have been fine. People smarter than me claim that TCM historically has been low-balling take-off fuel flow settings so they can achieve the specified power output. Those smarter people advocate to give the FF setting another gph or two for good measure to keep the CHTs in check. Some shops will refuse to set the upper limit to anything higher than what the SID specifies, in that case it is probably worth finding someone who will. You do have to be aware that if you push fuel flow beyond factory settings, you give up a couple of % of peak hp, but with that nifty red lever, you can allways recover that power if the trees look taller than advertised.
 
weilke said:
Well, according to TCM, 26.1 is the upper limit for most IO520 installations (some are 24.9), so you should have been fine. People smarter than me claim that TCM historically has been low-balling take-off fuel flow settings so they can achieve the specified power output. Those smarter people advocate to give the FF setting another gph or two for good measure to keep the CHTs in check. Some shops will refuse to set the upper limit to anything higher than what the SID specifies, in that case it is probably worth finding someone who will. You do have to be aware that if you push fuel flow beyond factory settings, you give up a couple of % of peak hp, but with that nifty red lever, you can allways recover that power if the trees look taller than advertised.
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Some of it could be my faulty memory on the exact GPH starting and ending point. Also, there's metered vs unmetered flow -- not sure exactly if we were doing apples to apples on the flows.

All I remember was the visual picture of the couple of milk jugs per hour extra fuel that dropped the CHTs so dramatically. Prior to that we did the D'Shannon baffles, cleaned everything up, and still had to immediately go back to 25/25 or lower to keep the cylinders from exceeding 400F. That extra 2 gph was all that was needed to get it to Mike Busch / John Deakin suggested levels of performance... And, like you said, just lean it a little if you want a little more umph. As it was, our only choices were "hot" and "hotter"... But to the larger point, after keeping the CHTs deep within the suggested ranges, I've never seen another shock cooling alert...
 
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