Starting a plane in the cold

[Stewartb]

Yup. An engine compartment heater can help with that if the battery is located there. I don't know if aviation versions of electric battery blankets are available. Most battery boxes would be too tight anyway. I think Zeldman mentioned having a sump heater on the bottom of the box.

Battery heaters used to be popular but these days, especially with firewall mounted batteries, we’re using AGM batteries and they’re excellent performers in the cold. But even with a flooded battery, they don’t freeze unless they’re dead.

 

[Dan Thomas]

But even with a flooded battery, they don’t freeze unless they’re dead.

Right. But lead-acid batteries suffer decreased performance in the cold. From Concorde's RG Series Aircraft Battery Owner/Operator's Manual:



Like most other chemical reactions, battery chemistry is slowed by low battery temperatures. Concorde claims that their RG batteries are better that way, and I don't doubt it, but the cold still affects it mightily. Winter makes everything ten times harder, and this winter promises to be a nasty piece of work.

Edit: Concorde's RG series are AGM batteries. From their brochure:

 

[WannFly]

I ran concord RG in my archer, plugged in to a battery minder, never had a problem in ND

 

[Dan Thomas]

I ran concord RG in my archer, plugged in to a battery minder, never had a problem in ND

Just maintaining a bit of charge current on it will warm it somewhat.

Some old guys had a trick to getting their vehicles started on a cold day when the engine didn't want to crank much. They'd turn the headlights on for a couple of minutes. The current flow through the battery warmed it enough to start the car.

 

[Sinistar]

Just maintaining a bit of charge current on it will warm it somewhat.

Some old guys had a trick to getting their vehicles started on a cold day when the engine didn't want to crank much. They'd turn the headlights on for a couple of minutes. The current flow through the battery warmed it enough to start the car.

My dad taught me that up her in ND and MN. It does work...but not many attempts.

I found the same with portable jump packs. That first start attempt on a cold jump pack seems like they are trashy gimmic. But turn on the headlights on the car or just crank it that first time - not much. Second attempt or 3rd attempt is like there's a new batter in the car.

I never used to leave the 182 Concord battery on a tender in the cold winters but by the 3rd winter I think the battery wasn't liking it. So I finally caved and bough the Concord specified minder. Wow! Flew with a friend the other day and the first start went in 2 blades or less and he couldn't believe it. Can't wait to have the hangar fully insulated and heated.

 

[Dan Thomas]

Just remember it’s more than just thick oil you are trying to eliminate. Aluminum and steel expand and contract differently. Aluminums “size change” is greater than steel. I’ve read that a cold soaked engine the bearing tolerances can be less than factory new standards to point there is no room for oil… aluminum case around a steel crank and the aluminum is squeezing that bearing. Also our cylinder walls are less diameter at top than bottom so that at operating temps they are the same being the top is hotter than the base. So a piston jammed into the top of an ice cold cylinder could be really tight. I want my entire engine warmed, I’m not a fan of quick blasts of heat, if ya don’t have the fancy stuff slow n steady wins the race over a quick hot blast.

I just have a sump pad, but with an insulated cowl cover and prop covers my cylinders temp out in the 80s when it’s 20 out… I do all I can before taking that cover off, being aluminum bleeds heat quickly to get that time between taking cover off a d firing up to a minimum.

Not to worry much there. The crankcase is aluminum (some are magnesium) and the crank is steel, but the bearing shells are also steel, lined with copper, tin and lead, and those steel shell halves are butted tightly against each other when the engine is assembled and the through-bolts are tightened. The aluminum case simply can't crush them enough to tighten onto the crank itself. Minimum bearing clearances are, in a Lyc, depending on model, run between .0011" to .0025". The smaller clearance is in the thickwall bearing shells.

The cylinders are steel. The pistons are aluminum. In the cold weather the pistons contract MORE than the steel cylinders, and the clearances increase. That's why combustion blowby and subsequent crankcase moisture and corrosion are so much worse in cold climates.

And, contrary to popular myth, those cylinders on many of our little-airplane engines are not intentionally tapered. From Lycoming's Direct Drive Overhaul Manual:



In the Continental O/IO-470 overhaul manual we find an intentional "choke" (taper) specification of .0035". Considering that the minimum clearance for the piston in that cylinder is .009", you're never going to get it tight in any cold weather. The bigger risk is cold-seizure, where the pilot starts that cold engine and takes off, and the piston heats faster than the cold cylinder and starts scuffing. Ultralight two-strokes are famous for that. They can seize solid.

The coefficient of linear thermal expansion for aluminum is, IIRC, around .001255 per degree F. For steel it's around half that, at .00065. A 2" journal on a steel crankshaft will shrink by about .0013" in a 100-degree F temperature drop. The bearing shells would have to contract that much (and they do) plus they'd have to contract almost that much more again to seize the crank, in the tightest engines. They won't.

I'm not defending starting that engine cold. There are far too many other reasons not to do that. That cold oil can be so thick that the oil pump can't suck it fast enough; it just makes vacuum, and no oil goes anywhere. Even if it does manage to move it, it's slow, and some components (oil cooler) can suffer damage from overpressure. Oil coolers are plumbed into the system all the time; they're not disconnected by the thermal controls. Those things just open a bypass, but the pressure on the cooler is still there. That cold, thick oil has a hard time making its way into the small galleries in lifters, pushrods, crankshafts, gear-lubricating nozzles, and so on. They all suffer. Crankshaft main and rod bearings will get the worst of it.

 

[Huckster79]

Not to worry much there. The crankcase is aluminum (some are magnesium) and the crank is steel, but the bearing shells are also steel, lined with copper, tin and lead, and those steel shell halves are butted tightly against each other when the engine is assembled and the through-bolts are tightened. The aluminum case simply can't crush them enough to tighten onto the crank itself. Minimum bearing clearances are, in a Lyc, depending on model, run between .0011" to .0025". The smaller clearance is in the thickwall bearing shells.

The cylinders are steel. The pistons are aluminum. In the cold weather the pistons contract MORE than the steel cylinders, and the clearances increase. That's why combustion blowby and subsequent crankcase moisture and corrosion are so much worse in cold climates.

And, contrary to popular myth, those cylinders on many of our little-airplane engines are not intentionally tapered. From Lycoming's Direct Drive Overhaul Manual:

View attachment 103069

In the Continental O/IO-470 overhaul manual we find an intentional "choke" (taper) specification of .0035". Considering that the minimum clearance for the piston in that cylinder is .009", you're never going to get it tight in any cold weather. The bigger risk is cold-seizure, where the pilot starts that cold engine and takes off, and the piston heats faster than the cold cylinder and starts scuffing. Ultralight two-strokes are famous for that. They can seize solid.

The coefficient of linear thermal expansion for aluminum is, IIRC, around .001255 per degree F. For steel it's around half that, at .00065. A 2" journal on a steel crankshaft will shrink by about .0013" in a 100-degree F temperature drop. The bearing shells would have to contract that much (and they do) plus they'd have to contract almost that much more again to seize the crank, in the tightest engines. They won't.

I'm not defending starting that engine cold. There are far too many other reasons not to do that. That cold oil can be so thick that the oil pump can't suck it fast enough; it just makes vacuum, and no oil goes anywhere. Even if it does manage to move it, it's slow, and some components (oil cooler) can suffer damage from overpressure. Oil coolers are plumbed into the system all the time; they're not disconnected by the thermal controls. Those things just open a bypass, but the pressure on the cooler is still there. That cold, thick oil has a hard time making its way into the small galleries in lifters, pushrods, crankshafts, gear-lubricating nozzles, and so on. They all suffer. Crankshaft main and rod bearings will get the worst of it.

interesting! You always seem to have technically insightful posts- I appreciate that!

so long and short of it- is it’s still best to thoroughly warm the engine but not necessarily for the reasons I believed?

 

[Dan Thomas]

so long and short of it- is it’s still best to thoroughly warm the engine but not necessarily for the reasons I believed?

Still best to warm that engine. It does take time for the heat to penetrate, though.

 

[Dry Creek]

Cars are NOT airplanes. Too many owners have found that out the hard way.

Exactly! Although sometimes they do make an "acceptable" landing.

 

[Huckster79]

Still best to warm that engine. It does take time for the heat to penetrate, though.

yea I like 6-8 hours… or overnight if possible.

do you give any credence to leaving it preheated too long hurts the oil itself? What are your thoughts on sump heater on all the time?

 

[Dan Thomas]

yea I like 6-8 hours… or overnight if possible.

do you give any credence to leaving it preheated too long hurts the oil itself? What are your thoughts on sump heater on all the time?

Sump heaters will tend to vaporize any moisture in the oil if they're just left on all the time. It will rise in the case and condense on the colder surfaces, especially on the cam and lifters, and corrosion happens. Pulling a mag off might find that the gears are rusty.

Best thing for an engine is to fly it until that oil temp comes up, and hold it there for awhile to drive off the moisture that got past the pistons and rings into the case while the engine was warming up. Cars have PCV systems and much tighter clearances; airplane's don't, and the moisture will accumulate there on ground runs or short flights. Pull the dipstick after a shorter flight on a cold day and see the milkiness of the oil; that's water/oil emulsion. If it drips from the breather onto the hangar floor, it sometimes separates into oil and water.

 

[MooneyDriver78]

I always pull the stick and let the water vapor escape after a flight, don’t know how much it helps, but it can’t hurt.

 

[Huckster79]

Sump heaters will tend to vaporize any moisture in the oil if they're just left on all the time. It will rise in the case and condense on the colder surfaces, especially on the cam and lifters, and corrosion happens. Pulling a mag off might find that the gears are rusty.

Best thing for an engine is to fly it until that oil temp comes up, and hold it there for awhile to drive off the moisture that got past the pistons and rings into the case while the engine was warming up. Cars have PCV systems and much tighter clearances; airplane's don't, and the moisture will accumulate there on ground runs or short flights. Pull the dipstick after a shorter flight on a cold day and see the milkiness of the oil; that's water/oil emulsion. If it drips from the breather onto the hangar floor, it sometimes separates into oil and water.

mug I do leave my heater on for a bit, as I try just the night before but life happens at times I always upen the dipstick- idk if that helps.

I always figured I was playing being with the insulated cowl cover the cylinders get to mod 80s… ??

so when I get new cylinders someday you’re saying a heater that hits the cylinders direct is better for keeping corision away from the more even heat ?

 

[RonP]

I have heard the headlight theory to warm a battery before by turning the headlights on. Haven owned two vehicles with 6V systems they were always slow cranking no matter what technique I used. My question is what would heat a battery more; headlight current or a 200A starter draw? Seems to me turning on the headlights depletes the battery charge that would be better saved for the cranking load.

 

[kgruber]

My oil was drained the night before on the woodstove. Then poured back in hot. Then use the oil dilution pump for the prescribed time.............and off into the wild blue yonder.

 

[Dan Thomas]

so when I get new cylinders someday you’re saying a heater that hits the cylinders direct is better for keeping corision away from the more even heat ?

Heating the whole engine might be better than just the sump. I think it would. It more closely imitates an engine sitting in warm weather, with the whole engine at ambient temperature.

 

[Stewartb]

Definitely better. I’ve tried the sump heater route. And the Red Dragon route. A total engine heat system is far more efficient.

 

[Stewartb]

My oil was drained the night before on the woodstove. Then poured back in hot. Then use the oil dilution pump for the prescribed time.............and off into the wild blue yonder.

Is that what you’d do today or are you romanticizing the days of old?

Hot oil and oil dilution? BS. Engines won’t start when the cylinders are cold. Or it wasn’t very cold.

 

[kgruber]

My Cessna 185 had an oil dilution system.

 

[Half Fast]

Wouldn’t it be simpler to hangar the plane in Florida?

 

[Jim K]

Wouldn’t it be simpler to hangar the plane in Florida?

I'll take preheating my engine over Florida corrosion.

Serious question:
How far do you have to get from the ocean before steel stops instantly rusting? I left my plane on the ramp at TFP (10mi from the beach, about 4 from the bay) for 5 days and various screw heads and door hinges were already starting to rust.

 

[Half Fast]

I'll take preheating my engine over Florida corrosion.

Serious question:
How far do you have to get from the ocean before steel stops instantly rusting? I left my plane on the ramp at TFP (10mi from the beach, about 4 from the bay) for 5 days and various screw heads and door hinges were already starting to rust.

I don’t know exactly, but 4 miles from saltwater is certainly not nearly enough. In my experience, 30 miles or more seems to be plenty, but I can’t give you a number between those two.

 

[Stewartb]

Depends on the climate. Lake Hood, Alaska is about a half mile from an ocean inlet and with outdoor parking of hundreds of airplanes we don’t see much corrosion.

 

[Jim K]

I don’t know exactly, but 4 miles from saltwater is certainly not nearly enough. In my experience, 30 miles or more seems to be plenty, but I can’t give you a number between those two.

I picked TFP over RAS as I didn't want to be that close to the beach. I assumed it was the wave action that put the salt in the air, so I was surprised to see rust blooming so fast. Planning a trip to VNC pretty soon. Not looking forward to leaving her sit out there.

Depends on the climate. Lake Hood, Alaska is about a half mile from an ocean inlet and with outdoor parking of hundreds of airplanes we don’t see much corrosion.

Good point. I suppose the heat & humidity is a much a factor as the salt air.

 

[MooneyDriver78]

Depends on the wind I would guess. My car is 200 yds from the ocean and it sometimes gets a salty film on it. I never saw this before when I lived close to the river, but 5 miles from the ocean.
My plane lives in a hangar 4 miles from the ocean and doesn’t get this, neither does my old camshaft that sits out on the floor, only where it’s dirty. Clean surfaces don’t rust.
So the lesson is keep clean oil in your engine and keep the plane clean.

 

[Dan Thomas]

I picked TFP over RAS as I didn't want to be that close to the beach. I assumed it was the wave action that put the salt in the air, so I was surprised to see rust blooming so fast. Planning a trip to VNC pretty soon. Not looking forward to leaving her sit out there.


Good point. I suppose the heat & humidity is a much a factor as the salt air.

Prevailing winds, too.

 

[Half Fast]

I suppose the heat & humidity is a much a factor as the salt air.

Yep. Florida’s humid air may contain some salt near the coast. I know we have salt fogs near the beach.

 

[Justin M]

The last time I started the 1969 Cessna 182 in the cold, I had to pull carb heat once the engine fired. It was running really rough and I was having trouble figuring it out until it dawned on me it might be carb ice. Sure 'nuff, carb heat hot and the engine ran smoother after 15-30 seconds. I think it was about 30 degrees that morning.

 

[Sinistar]

The last time I started the 1969 Cessna 182 in the cold, I had to pull carb heat once the engine fired. It was running really rough and I was having trouble figuring it out until it dawned on me it might be carb ice. Sure 'nuff, carb heat hot and the engine ran smoother after 15-30 seconds. I think it was about 30 degrees that morning.

its hard to believe the carb iced up so quickly.

Isn't another possibility that it just needed a richer mixture while it was cold and warming up? Carb heat on a 182 will eat ice...but the exhaust has to be pretty warm. The other thing carb heat will do is make it run rich which is what it needs when the air is really cold and dense.

 

[Dan Thomas]

its hard to believe the carb iced up so quickly.

Isn't another possibility that it just needed a richer mixture while it was cold and warming up? Carb heat on a 182 will eat ice...but the exhaust has to be pretty warm. The other thing carb heat will do is make it run rich which is what it needs when the air is really cold and dense.

Yup. Richer mix acts like the choke on an old car. Cold engines need more fuel.

But carbs can and do ice up real quick under the right conditions. The thing to remember is that you can get ice on a beautiful summer day if there's enough moisture in the air. Not visible moisture; that's obviously wet air, but higher humidity reflected in the smaller gap between temperature and dewpoint, the lifesaving little numbers on the METAR you should have checked before flying. In some engines ice can form in ambient temps up to 100°F. The idea that it's a winter thing is a good way to suffer an engine failure. You won't be expecting it in warmer weather.