Cessna 210's and Shock Cooling

[msw]

I've been flying C-210's for awhile and was always taught (and subsequently flew) in such a manner as to avoid shock cooling. (No rapid power reductions; try to "stage cool" i.e. 1" MP power reduction per 1 minute in descents.) I recently attended a 210 training class where the instructor said that Continental had never found an engine damaged by shock cooling in a 210, and it was really a "non-issue", despite popular opinion to the contrary.

What are some of your thoughts on this? I am in the midst of training a guy in a RAM T-210, to the commercial/inst level. So far, I have been reluctant to do power off spot landings in this aircraft with him, due to the worry about shock cooling. How do some of the other C-210 operators out there train in emergency or forced landings ("power off spot landings") in the 210, if they are worried about the shock cooling issue?

 

[bigD]

I'd be interested in hearing some ideas myself. I can't seem to get anywhere near a consistent answer from people.

As a data point, John Deakin from AvWeb seems to think there's not much problem. He points to the jump schools' routinely getting TBO out of their engines without any problems. For the record, the drop zone I flew with for awhile got to TBO easily as well (these were 206's and 182's).

But in reality, I'm a renter, and until I own my own airplane, I'll just operate what I'm renting to the owner's requirements. If he wants me to pull 1" in one minute, fine.

 

[throttlejockey]

It is my opinion that higher utilization rates reduce the chance of damage due to shock cooling than an aircraft that sits in the hangar and flys only once a month. My reasoning is as follows:

When an engine sits for a long period of time, corrosion and pitting of the cylinder walls occurs. If the aircraft is then flown, the corrosion changes the wear patterns inside the cylinder walls. This change could possibly create areas wear a crack could begin to develop. Thus a very abrupt temperature change could exacerbate the problem and lead to cylinder problems.

On the other hand, jump aircraft and commuter operated aircraft (i.e. Cape Air) are flown at very high utilization rates. These aircraft do not sit, and internal cylinder corrosion is not a issue. Thus they do not tend to have shock cooling problems. Back in the old days (Piston Airliners) the big supercharged radial engines could be maintained on wing for several thousand hours before removal for overhaul.

The above is only an opinion - not based on any facts.

Another issue has to do with leaning. I do not enrichen the mixture on the engine until final approach. If I am cruising at 13000 Ft. I will not enrichen the mixture at all in the decent. Only until I am turning final does the mixture go to a rich position. This helps keep the tempertures up inside the engine.

There are some interesting articles at the AvWeb Website regarding this procedure.

tj

 

[GeorgeTG]

Shock Cooling

I think throttlejockey hit the nail on the head.

High utilization makes the shock cooling issue a moot point.

We have almost 30 TCM550 powered A/C in our fleet.

Routinely 25hr students fly them solo.

The students have absolutely no idea what shock cooling is and will set mixture full rich before starting a descent.

The planes fly every day and all engies make TBO and have been for the past 10 years, save for the occasional cracked jug.

No top overhauls ever...

Cheers
George

 

[7B2]

I agree 100% with throttlejockey.
Thanks, that is a very good post.

 

[Cat Driver]

Would you throttle back a large radial such as a Wright 1820 and not consider shock cooling?

 

[moving2vegas]

shock cooling

I agree with the utilization posts, but I would avoid shock cooling whenever possible. I have a little time (200+- hrs) in a ram 210 and you can really cool the $hit out of that plane fast. Regardless of how much you fly, it's not good for the engine and it's not good pilot technique. I understand you need to train emergency procedures and power off landings. How about stage cooling before emergency training? No sense in flying along at 40" MAP and 180 KTS and simply chopping the power and saying "make the runway". Plan ahead, cool the engine as much as possible, slow down and then chop it. Going from 25" to idle will be much less shock. At least you won't be training a pilot that shock cooling is OK.

Someone mentioned "The students have absolutely no idea what shock cooling is and will set mixture full rich before starting a descent." Maybe someone should teach them. They (students) pull that during an employment interview and they'll never get hired. As for an engine making it TBO. Lots do, but with what left? An engine at TBO with cylinder pressures at 74, versus 60? Treat an engine good and at TBO you'll get a heck of alot more back on that core than an abused one.

throttlejockey has some great insight but in a high power plane like a 210, I would use some caution not enriching during the descent. It only takes a split second of detonation to cause severe damage. Mixture has an effect on CHT's, but not nearly as much as power, airspeed and cowl flaps. In the 402 (TSIO-520) I use to fly, before descent, I would richen the mix 1/2 way. The CHT's would only drop about 60 degrees and I'd leave them there until final. It reduced my workload while IFR but didn't cool the engines significantly.

IMHO- better to baby the engine, you'll save $ in the end and maybe it won't dump on you when you really need it.

 

[7B2]

throttlejockey has some great insight but in a high power plane like a 210, I would use some caution not enriching during the descent. It only takes a split second of detonation to cause severe damage.

Is really not a problem, I'd stick to throttlejockey's technique. (and thus my own)

 

[moving2vegas]

leaning

Every circumstance differs, but I routinely flew a RAM 210 at 22-23K to get over weather. If you didn’t enrich the mix during the decent, the engine would be sputtering at 10, 000. Better to train to rich the mix, and let the pilot adjust the procedure as he gains experience. For example, the POH in twin commander I fly now (and most A/C) says turn on boost pumps and full rich for landing. However, the AC50 has huge boost pumps for the size of engine and it just about floods when you do that. I leave the pumps off. When I mentioned that to a fellow pilot, he said I was crazy. I think it’s crazy to try a go around with flooded engines. I didn't say anybody was wrong or criticize, just said use caution. Again, adjust procedures for the situation.

 

[Cat Driver]

While we are on the shock cooling subject, how do instructors teach full feather shut downs in northern states when the temps are way below freezing?

 

[Mmmmmm Burritos]

very quickly

Minimize engine off time, then when restarted, keep at a low power setting until CHT comes up into the green.

 

[Cat Driver]

How low a temperature do you do full feathering?

 

[SDCFI]

Turbo

The way I was taught in the Navajo was to stage cool to 300 degrees CHT (cruise was around 400). Once you get down to 300 you can do what you like with the power. It's the initial shock (pun intended) of going from 400 or higher to 300 in a matter of seconds that you want to avoid. Even if you don't buy into shock cooling, why take the chance with a 50,000 dollar engine (TIO-540 for example)? Detonation is only a problem at high power settings, and usually only if the octane is too low so leaving the mixture lean during descent shouldn't be a problem, just enrichen it for smooth operation.

 

[Dustin H]

For large turbo recips (520/540) I would stage cool inch/min

Same engines without turbos, I wouldn't worry about it.