Cold weather flying

[Al Downs]

Here in Wisconsin we have had a very cold winter with many days and nights of below zero temperatures. Are there any considerations to be aware of for our CT's? Always hangared with a heater plugged in.

[Anticept]

Check drain holes (on all aircraft for that matter). The critical ones are those in the tail. Although rare, It only takes a little bit of ice back there to throw weight and balance off considerably. Ice also is a terrible enemy of composites, so make sure the water can drain out!

[Doug G.]

If your situation is the saw as ours...it it's difficult for any water to accumulate when the temps don't ever get above freezing. (Or even close.)

[Al Downs]

I have heard some people talking about cold schocking there engine in cold temps. Is this a consideration?

[FastEddieB]

People who know seem to feel that shock-cooling the engine is probably a myth.

 

In a water-cooled and oil and air cooled engine like the ROTAX, I would think its no more a factor than when you lift your foot of the gas in your car at 70 mph and decelerate at idle to the next exit. I don't recall VW's or Porsches or Corvairs having issues with that either.

 

Anyway, its touched upon here:

 

http://www.avweb.com/news/pelican/183094-1.html?redirected=1

[Tom Baker]

Cold shocking normally has to do with cylinder heads cracking. It happens because you have a high temperature under power, and a sudden change when you reduce power. This allows for a rapid temperature change, and the chance for cracking. With the liquid cooled heads on the Rotax you won't get the big sudden temperature drop, so shock cooling shouldn't be a problem.

[FastEddieB]

As a data point, I taught aerobatics in two different Citabrias.

 

In a loop, you would throttle back a little and dive to the entry speed. Then go to full throttle as the nose came up through the horizon. Then, at the top of the loop go to idle for the descent down the back side of the loop.

 

A Hammerhead Stall was similar, going from full throttle to idle very quickly.

 

Did those again and again and again and never "cracked a cylinder head". 

 

May be more of a factor with larger engines, but read the linked article for some reasons it may not be, unless mishandled terribly.

[FlyingMonkey]

I did a long descent at idle from 8500ft in cold air temps a few weeks ago. I planned to just come all the way down, but added some power in at 4000ft when my CHT was reading 140...didn't want things to get too cold, though who knows if it's really a concern.

[Anticept]

Note: the following applies to air cooled engines.

 

Shock cooling is something that increases wear over time. Both the cylinder heads and pistons are aluminium, so they have large thermal expansion coefficients than the steel barrels. It takes longer for the pistons to cool than the heads and barrels, and the heads will change temperature the most. So, you end up with big pistons in a small barrel, and the head might warp if it cools too quick.

 

Anyways, it won't suddenly crack the head. That would take a lot of careless cycles to do and other factors in play. It's more of a "be nice to your engine" concern, and it might make the difference between 2,000 hours and 2,100 hours before replacing.

[FastEddieB]

I recall it being proffered that if shock cooling was a big deal, then shock heating would be as well.

 

You know, the kind that's done on every takeoff.

 

I did learn originally learn that shock cooling was a "thing", and only more recently was led to doubt it, based partly on Deakin's columns with no real evidence presented to counter them.

[Tom Baker]

I'm not arguing one side or the other, just saying what the theory is behind the idea, and that the Rotax with the liquid cooled heads wouldn't have the problem.

 

Eddie, some people now teach to keep the power in all the time for aerobatics for less altitude loss. I know the fellow here with the 90hp clipwing Taylorcraft does that, except for spins. He can fly for quite a long time without having to break and climb for altitude.

[Tom Baker]

I will add that some people flying big Continentals have problems with cracked cylinders, and others do not. There must be someting operational that causes cylinder cracking.

[Anticept]

I recall it being proffered that if shock cooling was a big deal, then shock heating would be as well.

 

You know, the kind that's done on every takeoff.

 

I did learn originally learn that shock cooling was a "thing", and only more recently was led to doubt it, based partly on Deakin's columns with no real evidence presented to counter them.

 

Shock heating isn't a concern because the heat originates from within the head and heats uniformly, whereas cooling is not uniform. That is, assuming you haven't gone from start to takeoff in 10 seconds.

 

 

I will add that some people flying big Continentals have problems with cracked cylinders, and others do not. There must be someting operational that causes cylinder cracking.

 

 

Well it is a continental too... . They just aren't what they used to be.

[FastEddieB]

I will add that some people flying big Continentals have problems with cracked cylinders, and others do not. There must be someting operational that causes cylinder cracking.

Not sure that follows.

 

The case could be made that some cylinders, like some cases, are just more prone to cracking.

 

BTW, both my Citabrias had fixed pitch props, so they had to be throttled back in dives to prevent engine overspeed.

[sandpiper]

I will add that some people flying big Continentals have problems with cracked cylinders, and others do not. There must be someting operational that causes cylinder cracking.

I was about to say the same thing. As the owner of an IO-520 for 18 years I was not going to try to debunk the idea of shock cooling on my nickel. I was always gentle with that engine and it served me well - and with little maintenance expense.

 

Also, about half my flying year was a little cold to painfully cold. Reducing power was carefully managed usually with some power held to the ground because you wanted the engine to respond properly if a go around was required due to, perhaps, a moose on the runway.

[Ed Cesnalis]

Turbo charged engines sometimes have cool down procedures like 5 minutes at idle before shut-down.  Automotive turbos used to have similar issues but today they tend to be water jacketed.

 

Turbo charged aircraft fly at higher / colder altitudes and shock-cooling can be more of an issue if you have a rapid 100F drop.

[FastEddieB]

And here's a turbo-related Pelican's Perch:

 

http://www.avweb.com/news/pelican/182107-1.html?redirected=1

[FastEddieB]

I do the same thing, but with 500 fpm as the goal. Just preference and 300 fpm is fine.

 

All things being equal, the lower rate is probably marginally more efficient, since the slightly lower TAS means slightly lower drag.

 

As an aside, I have my 496 set to have me descend at 500 fpm to arrive at 1,500' AGL three miles out from my destination. Clouds permitting, I just follow the faux glideslope on down, then stay at that altitude to overfly the field, if non towered. The increased groundspeed usually results in the need for a little more than 500 fpm at some point in the descent.

 

As an aside to the aside, before GPS we all figured out descent profiles in our heads or with an E6B. Probably still could!

[Tom Baker]

Not sure that follows.

 

The case could be made that some cylinders, like some cases, are just more prone to cracking.

 

BTW, both my Citabrias had fixed pitch props, so they had to be throttled back in dives to prevent engine overspeed.

Over the years I have seen pilots have problems, where others flying the same make and model of aircraft with the same engine have not had issues.

 

BTW, the aerobatic airplane I mentioned also has a fixed pitch propeller.

[FastEddieB]

Over the years I have seen pilots have problems, where others flying the same make and model of aircraft with the same engine have not had issues.

Fair enough. There are certainly detrimental ways to operate certain engines.

 

BTW, the aerobatic airplane I mentioned also has a fixed pitch propeller.

OK. But it sure seemed like my Citabria would exceed redline if kept at full throttle when pitching to aggressive down lines.

 

Maybe mine was pitched finer?

[mocfly]

There have been occasions where the engine has actually cold seized and then was able to be restarted prior to an emergency landing.

[FastEddieB]

There have been occasions where the engine has actually cold seized and then was able to be restarted prior to an emergency landing.

I'd love a source for that - maybe run it by John Deakin and/or Mike Busch for their take.

 

Is the allegation the engine later rewarmed by descending to a lower, warmer altitude? But that the heat of combustion at low power at altitude was not enough?

 

Deakin's observations about a very slow decline in CHT even with a sudden shutdown seem relevant.

 

But, to repeat, likely not an issue for a ROTAX owner.

 

 

Edited to add: just Googled "cold seized" and the references all seem to be to snowmobiles and two stroke engines, at least on the first page. I had not heard the term before applied to planes.

[FlyingMonkey]

There have been occasions where the engine has actually cold seized and then was able to be restarted prior to an emergency landing.

Doesn't "cold seized" imply metal-to-metal contact binding the parts? If that's the case, I don't see how that engine is turning again without a teardown. My suspicion is that these cases are actually something else happening and are misdiagnosed. I'm open to information contradicting my statement, but it just seems like an engine that hard binds due to metal interference is not just going to just start working again...

[Tom Baker]

Doesn't "cold seized" imply metal-to-metal contact binding the parts? If that's the case, I don't see how that engine is turning again without a teardown. My suspicion is that these cases are actually something else happening and are misdiagnosed. I'm open to information contradicting my statement, but it just seems like an engine that hard binds due to metal interference is not just going to just start working again...

 

I didn't look it up, but can understand what is happening. If they are running a close tolerance between the piston and cylinder like we do, I could see it happening to a 2 stroke engine. When the cylinder cools it contracts before the piston has had time to cool closing down the tolerance. Once the piston cools the tolerance comes back and it is free to turn and start. I'm sure there is some scuffing and damage going on with this. Like I said probably more likely for a 2 stroke engine.

[sandpiper]

Isn't there some dissimilar metal with different expansion/contraction rates at play?