FlyboyKC

So whats too cold for the plane

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I thought I had seen this question posted before, but my search came up nil.

So winter flying, is there too cold? I did the Christmas trip of flying in some really cold WX, like -27c at altitude. My coldest cylinder was down to 179 degrees CHT with the others around 236 degrees. EGTs were split around 1260 to 1360. Oil temp range was from 149 to 163. Cabin temp was about 50 degrees with the heat on full blast. (although the defrosters leave a lot to be desired, even with everything shut off, still got weak airflow to the windscreen.)

The engine seemed to run fine but I was just curious at what temperatures could be more on the harmful side of things. Discounting pilot comfort...

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The coldest I flew mine it was -30 C on the ground. The aircraft is parked outside. After ground pre-heat it started OK. On take-off one or two dials went berserk (do not remember which one(s) it was too long ago). It settled after a few minutes. The rest of the flight went well without any events. The kids sitting in the back seat were freezing though. Since then, I avoid going to the airport when it is anything cooler than -20 C.

Yves

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22 minutes ago, FlyboyKC said:

I thought I had seen this question posted before, but my search came up nil.

So winter flying, is there too cold? I did the Christmas trip of flying in some really cold WX, like -27c at altitude. My coldest cylinder was down to 179 degrees CHT with the others around 236 degrees. EGTs were split around 1260 to 1360. Oil temp range was from 149 to 163. Cabin temp was about 50 degrees with the heat on full blast. (although the defrosters leave a lot to be desired, even with everything shut off, still got weak airflow to the windscreen.)

The engine seemed to run fine but I was just curious at what temperatures could be more on the harmful side of things. Discounting pilot comfort...

Good question.

Some thoughts - water crystals suspended in the fuel can block the flow of fuel and cause a problem - I use pure (not the drug store stuff that contains a large fraction of water) isopropyl alcohol in the fuel (there is a specified dose) - it is an allowed substance, and it helps prevent this problem.  I have also used prist-for avgas (a special version of their product instead of the jet A version) - which the Canadian mounties use so I figure it is good enough for me.

Also - I set an arbitrary line in the sand - 0F below which I don't fly for safety reasons - I figure I would not want to be stuck in an off field landing colder than that trying to treck out.  -20F predicted for tonight.  Also make sure you have cloths with you appropriate for 0F (or whatever you do fly in), and I also carry camping like stuff - sleeping back etc.

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3 minutes ago, yvesg said:

The coldest I flew mine it was -30 C on the ground. The aircraft is parked outside. After ground pre-heat it started OK. On take-off one or two dials went berserk (do not remember which one(s) it was too long ago). It settled after a few minutes. The rest of the flight went well without any events. The kids sitting in the back seat were freezing though. Since then, I avoid going to the airport when it is snything cooler than -20 C.

Yves

Yeah  -20C = -4F ...so we have come to the same point.  I have also flown in the past in -30C.

Last winter I flew home from kweepnomore Wilmar, MN - 4hrs at 19,000ft and it was -35F (almost in Fahrenheit the same as that's about the cross over point) and even though normally my heat is pretty good - I was pretty chilly by the time I got home - even with my big coat.

Also - I arctic temps, I limit manifold pressure slightly on take off and climb to prevent over boosting as you are producing more than rated horsepower - and you don't need it anyway since you will climb fantastically anyway.

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With a good preheat (oil runs nicely off the dip) and a decent battery your start should go well. I fired up the other day in CYYN after the plane had been plugged in for 3 days of -32C nights and -26C daytime highs. Starts just fine on a decent battery. Get up into some warmer and thinner air and the temps run nicely with the cowl flaps closed. 10-15 degrees warmer is not uncommon only 4-6K above the ground. Depends on your air mass though. The oil cooler congealing can be a concern. You may need to tape up half of it. A sign of this is usually high oil temp and low oil pressure on those -25C days. Talk to your AME.

For what it’s worth when I flew Navajos up north we had a -35C cutoff for anything piston powered. On a side note I didn’t trust those damn janitrol heaters one bit but hey I was 20 and getting paid to fly!


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I live in Minnesnowta.  The coldest I have been in the aircraft was a trip from Williston ND a few years ago, back to MN.  We were in the low flight levels, I think FL210, and it was in the minus 50’s.  That’s Fahrenheit.  The cabin heater could not keep up, all the windows frosted over, but the plane otherwise was fine, just me and the co-pilot who were suffering.  

I like to keep the CHT’s in the normal operating range, which is set out in my POH at 250 dF and above.  The limit I have to really watch is Oil Temp., which cannot fall below 100. I have a turbo, and there are all kinds of warnings in the POH about allowing the OT to fall under 100.  The oil needs to flow through the turbo bearings to cool and lubricate the bearings, and this function is impaired when the oil is too cold. I use an oil cooler block which is in the engine now.  I will use the mixture to adjust for heat in the engine, the objective in the winter being the opposite of summer, I am trying to keep the engine warm.  However, it is still not a good idea to run dead in the center of the red box, right at 50 ROP.  The engine may be cool, but the Internal Cylinder Pressures are very high if you are in a cruise speed range.

There are other weird things that happen.  I had the air/oil separator freeze up once.  Condensation forms and water collects in the separator, which freezes.  That causes the crankcase to pressurize which in turn causes oil to exit the engine through any available orifice.  I had five foot long, two foot high heavy oil streaks down the sides of the aircraft in just the few minutes it took to take off and immediately return for landing.  What I learned from that was to always give the engine time to warm the engine compartment in the winter, because there are things in there other than the cylinders and engine oil that need to be warm.  How well are your brakes going to work if the fluid is sludge?  The compartment cools off quickly on take-off, so everything in it needs to be warm before you go.  During our cold snaps up here I always taxi with the cowl flaps closed just to keep heat in the engine compartment, and when it is under 20 dF I will use only half cowl flaps on takeoff, and then close them as soon as I can, sometimes even during the climb.  As long as the CHT’s are not too high, it helps to keep everything else in the engine compartment somewhat warm.

One interesting thing you learn if you fly in the flight levels is induction icing.  At high altitudes the clouds are made up of ice crystals, these will clog the air filter and without air the engine will lose power.  The altitude at which this happens is much lower in the winter than in the summer.  Snow has the same effect.  My 231 is fitted with the automatic alternate air door, but I don’t let it get that far, I manually close the door if I am in these conditions and the MP starts to degrade even a little.

I carry a very long extension cord if I am flying somewhere and the plane will be parked.  I have run the cord through the front door of small rural FBOs to get electricity for the engine heater.  I have foam plugs for the cowl openings.

The tail section is going to be quite cold.  Some of the flight control mechanics are back there, like the chain and gears for the trim.  They can be balky in cold weather and your elegant electric trim is not going to work very well, which of course means that your autopilot, which uses that trim, is not going to perform well.

One thing to be aware of is that frost - and generally very heavy frost - can build up very quickly at cold temps in the right (or wrong, depending on your point of view) circumstances.  I mean down around or below 0 dF.  I have had that happen in International Falls among other places.  I keep a car scraper in the plane for such circumstances, a sprayer with TKS fluid would probably work also.  But I stress, this is not your ordinary frost, this is thick heavy stuff, and it builds so fast you can watch it happening.  It will even happen while you are cleaning the plane off, the areas you just did will be frosting over, so work fast.  This is a ground condition, it does not form in the air.  I surmise that there is moisture from the snow pack in the air, and the temp and dew point are close to each other on the ground, triggering this condition.  The frost will sublimate once you are in the air.

I just generally don’t like flying if it is below 20 dF, and you would have to drag me kicking out to the airport if it is below 0 dF, although I am going to go up today just to fly around the practice area.  It is going to be in the single digits below zero dF.

Oh, my plane is hangared but it is unheated.  Lots of us just leave the plane plugged in full time, but with the oil cap cracked open so any moisture can depart.

Edited by jlunseth
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11 hours ago, yvesg said:

The coldest I flew mine it was -30 C on the ground. The aircraft is parked outside. After ground pre-heat it started OK. On take-off one or two dials went berserk (do not remember which one(s) it was too long ago). It settled after a few minutes. The rest of the flight went well without any events. The kids sitting in the back seat were freezing though. Since then, I avoid going to the airport when it is anything cooler than -20 C.

Yves

When I was a kid with my first Mooney, I flew It almost every day for work. It was parked out side and the only time I would preheat it is If i couldn't get it started. It was in Colorado. I would usually start the engine and let it run until all the temps stabilized and the amp meter got close to zero. I would then shut it down an clean the ice and snow off the airframe. This would let the cabin and instruments thaw out from the little bit of heat the heater put out while running.

I discovered early on that preheating the instrument panel is a good idea. I had gyros that would tumble and pneumatic instruments that wouldn't move until they warmed up.

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For me once the temps move south of 40 degrees F or late November I move the airplane to a place with palm trees.  Keep it there all winter and have my mx done and visit it every so often to fly it.  It is just to much of a pain in the ass to fly when cold as well as to hard on the airplane.  In 53 years my plane has never seen a snow flake.

Plus it is fun to fly in different places.

 

 

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My guess is it will be aircraft specific. I’ve flown three different aircraft through 17 Ohio winters. If the engine is decently warm the airplane will fly just fine. I don’t tend to want to go if it’s too dang cold to do a decent preflight. Too dang cold varies with the duration since the last VFR weather.

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1 hour ago, steingar said:

My guess is it will be aircraft specific. I’ve flown three different aircraft through 17 Ohio winters. If the engine is decently warm the airplane will fly just fine. I don’t tend to want to go if it’s too dang cold to do a decent preflight. Too dang cold varies with the duration since the last VFR weather.

Me, too, three planes through 8 Ohio winters. Moving back South again, I sometimes miss the higher performance from supercooled air, but I'm otherwise happy with the move. We're set for almost Ohio-like weather the next few days, with highs barely above freezing, although panic has been restrained by removing the awful S-word from the forecast. 

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18 hours ago, FlyboyKC said:

I thought I had seen this question posted before, but my search came up nil.

So winter flying, is there too cold? I did the Christmas trip of flying in some really cold WX, like -27c at altitude. My coldest cylinder was down to 179 degrees CHT with the others around 236 degrees. EGTs were split around 1260 to 1360. Oil temp range was from 149 to 163. Cabin temp was about 50 degrees with the heat on full blast. (although the defrosters leave a lot to be desired, even with everything shut off, still got weak airflow to the windscreen.)

The engine seemed to run fine but I was just curious at what temperatures could be more on the harmful side of things. Discounting pilot comfort...

Great questions.  I agree mainly with @steingarand @jlunseth, in that there are critical temps you should be aware of.  On the Ovation platform, the CHTs should not drop below 250F either.  If you're a LOP guy, this means running ROP and burning a little extra gas to increase your CHTs to stay in this limit.

To help your oil temp...on my Ovation, I have the "cold weather kit" installed, which is really only a rectangular bracket roughly-equal to the height and length of the oil cooler.  It bolts neatly to the front of the oil cooler, and there's a sheet metal plate that slides down vertically and seats into place to block ram air from entering the cooler.  This helps increase oil temps in weather like you describe.  Not sure if a kit like this is available for the "J" model, but someone here with a "J" should be able to clarify.

Steve

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Check your density altitude...

Max rated power for your power plant is based on standard conditions and SL...

Over boosting a NA engine is pretty easy.

Head cracking is a result from such an occurrence.

For each 1k’ below SL is similar to getting an extra 1” MP...

You might see -2000’ DA.  

The ICPs will be significantly larger than normal.

If nothing else, make sure everything is warmed up and adjust power gently/slowly.

A combination of high pressure and low temperature can cause a DA of -3000’.  Like Adding 3” of MP to the normal 29” some of us get on the ground...  10% more power is a noticeable difference from acceleration to climb... the cold dense air adds to the magic of a strong climbing capability...

Don't crack a cylinder...

It is a great reminder of how DA effects flying... you can feel it.  :)

PP thoughts only, neither a mechanic nor a CFI.

Best regard,

-a-

 

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1 hour ago, carusoam said:

Check your density altitude...

Max rated power for your power plant is based on standard conditions and SL...

Over boosting a NA engine is pretty easy.

Head cracking is a result from such an occurrence.

For each 1k’ below SL is similar to getting an extra 1” MP...

You might see -2000’ DA.  

The ICPs will be significantly larger than normal.

If nothing else, make sure everything is warmed up and adjust power gently/slowly.

A combination of high pressure and low temperature can cause a DA of -3000’.  Like Adding 3” of MP to the normal 29” some of us get on the ground...  10% more power is a noticeable difference from acceleration to climb... the cold dense air adds to the magic of a strong climbing capability...

Don't crack a cylinder...

It is a great reminder of how DA effects flying... you can feel it.  :)

PP thoughts only, neither a mechanic nor a CFI.

Best regard,

-a-

 

-4500ft right here right now and -6000ft this morning

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2 hours ago, StevenL757 said:

Great questions.  I agree mainly with @steingarand @jlunseth, in that there are critical temps you should be aware of.  On the Ovation platform, the CHTs should not drop below 250C either.  If you're a LOP guy, this means running ROP and burning a little extra gas to increase your CHTs to stay in this limit.

I'm pretty sure you mean 250°F!

Otherwise, 250°C = 482°F, which is bad for the aluminum parts in your engine . . . .

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On the isopropyl, Bruce Jaeger used to recommend it.  Ice forming in the fuel was a concern for me for awhile.  Even in the summer it can be quite cold in the flight levels.  However, I have never had an issue with ice forming in the fuel.  The best defense is sumping so you don’t have water in the fuel to begin with.  I haven’t used isopropyl in a few years, I used to just get the 100% isopropyl (red bottle) at Fleet Farm.  There is an optimal mix of. fuel and ispropyl, but it has been so long since I have used it that I don’t remember what it is, maybe someone here will.

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1 hour ago, Hank said:

I'm pretty sure you mean 250°F!

Otherwise, 250°C = 482°F, which is bad for the aluminum parts in your engine . . . .

Yes thanks.  I edited that.  :-j

Jeez...I think my keyboard needs to be suspended or revoked...

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1 hour ago, aviatoreb said:

-4500ft right here right now and -6000ft this morning

I should fly there... mother nature’s free turbo charger without any of those pesky moving parts!

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59 minutes ago, jlunseth said:

On the isopropyl, Bruce Jaeger used to recommend it.  Ice forming in the fuel was a concern for me for awhile.  Even in the summer it can be quite cold in the flight levels.  However, I have never had an issue with ice forming in the fuel.  The best defense is sumping so you don’t have water in the fuel to begin with.  I haven’t used isopropyl in a few years, I used to just get the 100% isopropyl (red bottle) at Fleet Farm.  There is an optimal mix of. fuel and ispropyl, but it has been so long since I have used it that I don’t remember what it is, maybe someone here will.

I had ice crystals build up in my gascolator during a flight in the very cold winter (-15c or so) a few years back.  My power and fuel pressure kept dropping off- motor was stumbling- I had the boost pump on, I had switched tanks a couple times, tried the mixture, and it still wasn’t helping.  Just when I thought I was going to have to execute an off airport landing (I was flying over eastern Oregon), I thought... maybe the gascolator is plugged or something.  I pulled the gascolator ring and let it go, and it flushed out the crystals (or whatever may have been in there) luckily.... and I immediately got full power back.  That was one of the more interesting days in the Mooney.  

After that flight, I disassembled the gascolator and changed the screen out.  No trace of contamination... that’s why I think it was ice crystals.

Edited by M016576
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Interesting thoughts...

1) Storing outside you get some moisture in the tanks.

2) below freezing, you may get solid ice in a couple of locations...

  • bottom of the tanks.
  • bottom of the fuel strainer.
  • Top of the fuel caps. Gets in the way of looking in the tanks.
  • In the spinner. Off balance issue...

3) Always Consider If There is known ice, what happens if the ice melts on the way to your destination...

4) Nice ice crystal warning, Job!  I haven’t experienced ice crystals in the fuel yet...

Best regards,

-a-

 

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17 hours ago, JasonW said:

This is a good read if you haven't seen it.  https://www.lycoming.com/content/operating-cold-weathe

 

A good read, thank you. I found one practice that I have been doing since reading Busch/Deakins. I lean to peak for low power settings to keep the temperature up. This makes particular sense in the winter and I was happy to see it. I unfortunately have a big guppy mouth (my M20E) and I'm cautious about flying when the temperatures up here in Maine get down close to freezing. I worry about over cooling the oil and also about creating a particularly cold spot on one of the mechanical parts of the engine and causing a crack to develop.

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1 hour ago, jlunseth said:

On the isopropyl, Bruce Jaeger used to recommend it.  Ice forming in the fuel was a concern for me for awhile.  Even in the summer it can be quite cold in the flight levels.  However, I have never had an issue with ice forming in the fuel.  The best defense is sumping so you don’t have water in the fuel to begin with.  I haven’t used isopropyl in a few years, I used to just get the 100% isopropyl (red bottle) at Fleet Farm.  There is an optimal mix of. fuel and ispropyl, but it has been so long since I have used it that I don’t remember what it is, maybe someone here will.

While sumping is obviously a good idea, ice crystal formation is possible even if all traces of free water are removed. This can occur if you take on fuel stored in relatively warm conditions and then encounter a very large drop in temperature. The warmer fuel can hold a small amount of water in solution, and very fine ice crystals can form as the water solubility drops with temperature. Isopropyl alcohol will effectively prevent crystal formation by increasing water solubility in that very cold fuel.

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While on my flight I had to use carb heat. The ice crystals in the air were causing an issue over time. Let me tell you applying carb heat really robs the cabin of heat. I might have to look into an oil cooler winterization plate. 

Some other Lessons Learned even though the plane was in a hanger when it's so cold out like say 0 and it's a light snow the snow melts on the warm wing causing the snow tofreeze and then you have ice on the wing. So I had to contend with deicing the wings fresh from the hanger,. Also in 0 degree temperature I have found that it doesn't take long for the engine to cool to where it gets to be a little harder to start. 

Oh the joys of winter flying. 

Edited by FlyboyKC

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What is the difference in Isopropyl alcohol and regular(?) alcohol that is used when precleaning Inside the fuel tank prior to leak repair.  I did notice that the cleaning (?) alcohol softened the old sealant. Would this be a problem with the Isopropyl alcohol?? I hope I get the right answer, or the one I hope to get, as I am a proponent of alcohol in the gas tank in the winter to keep the water(if any) in solution.

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