How cold is too cold?

It was 11 below this morning and I'm missing that heated hangar I used to rent space in.

It's awesome to see Dave Hirschmann's video on Facebook (you're following him on Facebook, right?) with his two day journey in a Stearman -- a Stearman!!! -- from Minneapolis to Missouri. Somehow he was able to survive in an open-cockpit airplane.

But it's gotten me thinking: What's too cold to fly for RVers? And what is the area of concern? For me, I think it's the plexi. Oh, and the cold air coming up through the stick boots.

Oh, and the frost that accumulates on the inside of the canopy.

Oh and....

My own take is that so long as engine (CHT, oil) and pilot (body) temps are kept in a decent range then fly as long as you want. I flew for an hour or so in -4?F weather yesterday without issue - the plate over the oil cooler made sure oil temps were up to over 180? for most of the flight and sun + heat muffs kept the cockpit comfortable.

I was pretty careful with opening & closing the canopy; mine is Sika'd on so there are fewer chances for cracks but even Sika'd canopies have cracked before so ...

Great question - I'm really curious to see what others' thoughts and opinions are.

What would be a minimum temp for CHT and oil?

Also, and this harkens back to Mike Busch, would it be OK to lean into the "red cube" area to get there (for CHT's)

For oil temp, my Lycoming operating manual says 165ºF is the lower limit on for an acceptable oil temp. Mike Busch has stated he thinks 170ºF is the lower limit, which is probably close enough.

For CHTs, I like no less than 320ºF, but I cannot state why that number resonates with me or where I first read it. Mr. Busch likes 350ºF, and states that that at least 300ºF is required to avoid lead fouling. For it's part, Lycoming states "For maximum service life of the engine maintain cylinder head temperature between 150°F and 400°F during continuous operation" in the engine manual.

See FAQ item #6 in his AvWeb article for a slightly more in-depth explanation.

I've flown the 10 in -10f, the 8 in -4, and the 12 in -7f. By far the most comfortable was the 12 with the hot water heat and the Bender Baffle. The 10 was a close second with 2 heat muffs, the 8 needs work.

How Bad Do You Want to Fly?

When I was a kid, I'd fly the J-3 on skis in the winter Bob - brutal cold, but hey, the airplane was available! (No one else was dumb enough to fly in that temperature...

I have the same worries as everyone about canopies in the cold. If I can get the airplane warm enough before-hand, I don't mind the cold temps. Al the extra clothing for pre and post-flight survival makes everything more difficult. And think about contingencies - if you go down out in the forest....will you survive?

Ironflight said:

When I was a kid, I'd fly the J-3 on skis in the winter Bob - brutal cold, but hey, the airplane was available! (No one else was dumb enough to fly in that temperature...

I have the same worries as everyone about canopies in the cold. If I can get the airplane warm enough before-hand, I don't mind the cold temps. Al the extra clothing for pre and post-flight survival makes everything more difficult. And think about contingencies - if you go down out in the forest....will you survive?

Click to expand...

Yep, was just out a couple of weeks ago in a rental Cherokee and temperature was around -13F (-25C). I was the only one flying that day. It had an O320 and needed plenty of carb heat but as long as you can get the oil temp up, it's fine. I love winter flying but definitely keep survival gear in the plane.

I suppose the other thing to keep in mind is things start to get a little brittle in extreme cold.

Cheers.

ChiefPilot said:

For oil temp, my Lycoming operating manual says 165?F is the lower limit on for an acceptable oil temp. Mike Busch has stated he thinks 170?F is the lower limit, which is probably close enough.

...

Click to expand...

True but the manual also states the engine oil is warm enough for takeoff anytime you can apply full throttle and the engine doesn't stumble. No number is given.

I usually pre heat with temps below 40 F. Since I have steam gauges, I have a little heater in the cabin to warm the gyros. Last Feb, with temps at ~15F, I got about 5 minutes down the road (headed for warm weather), when there was a humongous BANG. After checking that I hadn't hit anything and the wings were still on, I landed and found my canopy had a 1/4" crack from side to side.

I've decided that my mistake was in over warming the plexi, and in taking off too soon after pulling the plane out of the hangar. BTW the plane was 12 years old at the time, and had lots of cold weather flying, but the cabin warming is rather recent.

It has always been my understanding that the minimum oil temp value of @ 160 -180 degrees had more to do with boiling out any moisture that was in the oil and nothing to do with lubrication qualities (other than at very cold temps where viscosity and flow characteristics come into play.)

Cold Weather Testing In USAF

Back around 1970 I was one of the helicopter mechanics on the H-53 cold weather testing project. We spent the winter in Alaska trying to keep our test helicopter flying. We had to run test missions if it was below -20F (which worked out; the local ski hill closed if it got colder than -20F).

Much of our flying was below -50F and a lot of it around -60F. We all had cold weather survival training and one of the crew was a survival expert - that was his job and official function.

It was so long ago that I might misremember some of it.

1. Tires and windows were just fine. So were the aluminum and composite structure. We didn't have anything akin to an RV canopy, though; the windshield was a thick thing like jets have and the side windows were basically unstressed in their mountings.

2. The helicopter was much more hydraulic than electrical, at least for the major stuff. We had many seal failures.

3. Hydraulic and engine oil would freeze or at least get very thick. We had to heat them up and quickly put it into the system and immediately attempt a start. Since the starter was driven by a hydraulic accumulator, if the start failed, we'd be in for a laborious job of slowly hand-pumping the accumulator back up for a retry. It had to be slow because otherwise the fluid in the pump would separate. Like cavitation, but it probably wasn't.

4. Inside the helicopter, the heat was always insufficient. My feet got so cold - seemed colder than being outside.

5. We had lubrication issues on a number of components. I remember one tach generator that I replaced, I could look right through it because the seals had failed so badly.

6. Fuel was fine, both jet fuel and in the cars, the car gas.

7. The northern lights were incredible. Moving, dancing curtains from horizon to horizon. If you haven't seen that, go north and stay there till you do.

8. Everything was difficult and slow, wearing cold-weather gear and freezing our eyelashes when we blinked. Facial hair would freeze. Forget bare skin, it would freeze.

9. It was our consensus that this was lots better than 'Nam.

10. We dropped the survival guy from the back ramp. He was evaluating parachute jumping in that weather. He reported that the air was so thick that descents were slow and, in the snow, landings were very soft. But on one instance, he got stuck in deep snow. He post-holed in and had to wait for ground support to get him out.

11. The rescue hoist jammed - and that was at around -40F, I think. Whoever was hanging there got stuck. For some operational reason we couldn't land him and we couldn't winch him back up. I was on the ground watching and there wasn't a darn thing I could do. Eventually they got him back aboard and warmed up.

12. White-outs were a frequent phenomenon because of the snow we'd blow up on landing or take off. Of course this was more a helicopter thing than something you'd encounter in an RV. Still - if you're landing or taking off in formation, it could be an issue from the tip vortices.

13. After a snow, we'd make a pass down the runway and blow it clear. Saved the base a lot of effort.

14. I had my camera there. I'd take it in and out of the warm heated hangar to the cold helicopter on the ramp several times a day. It ruined it. Even after three trips to the factory repair center in LA, it would jam unexpectedly.

15. The cars had battery heaters and engine heaters. Plug them in and you could get a restart. Fail to find a plug for them and they wouldn't start. We'd have them towed to a garage where they'd warm up overnight. I think 20 minutes was the time limit for an unplugged car to restart but I might be wrong.

Dave

Keep in mind too that some parts of your plane may not work as they usually do when it's frigid. Last year, I had tip tanks installed on my Bonanza and took it to Buffalo, MN for the installation...on the descent (where it was colder on the ground than at altitude), the pitch trim froze up and I had to land it without pitch trim. It would not move, period. Needless to say my landing wasn't that pretty trying to hold the nose up without the plane being trimmed properly. I had it looked at in Buffalo, and it turned out that a small plate had been installed very slightly incorrectly and the metal being cold soaked had created a clearance issue. Every time I've flown in MN, it's been frigid! I don't know how they do it up there!

LettersFromFlyoverCountry said:

But it's gotten me thinking: What's too cold to fly for RVers? And what is the area of concern? For me, I think it's the plexi. Oh, and the cold air coming up through the stick boots.

Oh, and the frost that accumulates on the inside of the canopy.

Oh and....

Click to expand...

I fly all year around. As soon as I am able to start the engine I am good. The temperature in the cockpit it's the whole another story

I flew in Alaska for about 40 years. Helicopters (National Guard) and various fixed wing. Personal flying cut off for me was -20F. Have gone out as cold as -55F. Although it can be downright unpleasant at these temperatures the main issue, at least for me was "would I be able to survive if I went down?" Especially in remote areas and probably injured. And at least for one night and possibly more.

Rarely did a properly prepared aircraft have problems, other than doors not closing and plastic interior parts cracking. And usually there was an inversion so if it was -40F on the ground it might only be -15F a couple of thousand feet up. But, if things went wrong..........

I couldn't take it any more today; one full month without flying due to crappy weather, primarily very cold temps. Had some sunshine and favourable winds, so I darn well went flying. Temp was -22 C (-8 F). No problems with preflighting in my newly insulated and heated hangar (10 C, 50 F), no starting difficulties or preheat needed for the same reason. Once flying, my not particularly well sealed slider canopy did produce a pretty good draft behind my head, but feet and hands were okay (I have dual heat muffs on my exhaust, thankfully). CHT's were in the 270 range, and oil temps gradually climbed to about 160 (I have a cockpit controllable butterfly that shuts off airflow to the oil cooler; this is the first time I've flown with it when I couldn't get the oil temp above 180). Kept the flight pretty short, primarily because of a cloud layer moving in that was making for a very indistinct horizon with the flat, completely snow covered ground. Pulling the throttle back in the pattern resulted in a major decrease in cabin temperature; as I turned final I suddenly realized I could see my breath, and I was glad that I flew a fairly tight pattern and didn't have to spend much time in those conditions!

All in all, a good day in the air. Probably the coldest conditions I've flown in since I did my flight training in the winter of 1987. Got a little work to do on sealing that slider, though?.back to another review of the ongoing thread on techniques for accomplishing that goal

The company I work for has a cut-off at -35*C (-31*F) for piston aircraft. Of course, the oil coolers all have "screens" that almost completely block off the air flow through the cooler.

The turbine aircraft have a cut-off at -40*C (-40*F), but that's because the steel landing gear, axles, etc. get too brittle and the risk and maintenance cost is too high.

Just a point of interest, a few days ago, it was around -35*F, and I went to add oil to a truck. The 5W20 synthetic automotive oil was thick as molasses. It gobbed out of the bottle until the heat from the motor warmed up the bottle.

David Z said:

The company I work for has a cut-off at -35*C (-31*F) for piston aircraft. Of course, the oil coolers all have "screens" that almost completely block off the air flow through the cooler.

The turbine aircraft have a cut-off at -40*C (-40*F), but that's because the steel landing gear, axles, etc. get too brittle and the risk and maintenance cost is too high.

Just a point of interest, a few days ago, it was around -35*F, and I went to add oil to a truck. The 5W20 synthetic automotive oil was thick as molasses. It gobbed out of the bottle until the heat from the motor warmed up the bottle.

Click to expand...

Which brings up a very important requirement when pre-heating. Get the oil warm. It's easy to get the cylinders warm enough to start and that can be done in a relatively short period of time. The oil will take a lot longer at below zero temperatures. Failure to do so damages the engine over time.

Cold Opps

Flying is a passion / hobby for me. I like warm weather activities. Even though the airplanes can operate in cold WX. I rarely will push out if the temps are below freezing.

Jaypratt said:

Flying is a passion / hobby for me. I like warm weather activities. Even though the airplanes can operate in cold WX. I rarely will push out if the temps are below freezing.

Click to expand...

BELOW FREEZING?!!!! Oh, come on! If I didn't fly when the temp went below freezing, I'd only be flying 6 months of the year! Keep in mind the benefits of flying in colder weather: denser air = improved power from your engine, improved efficiency for your prop, improved lift from your wings, and complete absence of thermal turbulence. When I went flying in -22C (-8F) temps a couple of days ago, I saw 2400 ft/min on climb out. With an 86" pitch FP Sensi prop. At 130 mph indicated and still at a deck angle that precluded forward visibility of any kind. And on landing, your groundspeed at your usual approach IAS makes it seem like everything is happening in slow motion; you'll feel like you can have a coffee on short final.

In all seriousness, there is NOTHING like flying in crisp, cold weather; it makes flying on a hot day feel like you're stuck in mud. Really bumpy mud. It's very much worth a tiny bit of cold. For me, the best flying day is probably about -10C, or about 14F; plenty warm enough to be comfortable, and all the benefits of cold weather aviating. You are missing out on a good thing Jay

gerrychuck said:

BELOW FREEZING?!!!! Oh, come on! If I didn't fly when the temp went below freezing, I'd only be flying 6 months of the year! Keep in mind the benefits of flying in colder weather: denser air = improved power from your engine, improved efficiency for your prop, improved lift from your wings, and complete absence of thermal turbulence. When I went flying in -22C (-8F) temps a couple of days ago, I saw 2400 ft/min on climb out. With an 86" pitch FP Sensi prop. At 130 mph indicated and still at a deck angle that precluded forward visibility of any kind. And on landing, your groundspeed at your usual approach IAS makes it seem like everything is happening in slow motion; you'll feel like you can have a coffee on short final.

Click to expand...

All good, but you missed the single biggest (I mean BIG!) benefit of flying when it's well below freezing out:

NO BUGS!

ChiefPilot said:

All good, but you missed the single biggest (I mean BIG!) benefit of flying when it's well below freezing out:

NO BUGS!

Click to expand...

This isn't a challenge, but rather a serious question. How cold does it have to be for no bugs? Here in Central Virginia we occasionally see day time temps in the 20s F for short periods (usually well under a week). Tonight the low is predicted to be 14 with a high in the mid 40s tomorrow. I don't know that I've ever seen a flight without at least some bug splatters when I return. I am certain I'll have some tomorrow afternoon. I certainly had a lot after my January 1 flight. Air temps ranged for the 40's on the ground to the low 30s at 6,500'.

I don't doubt you, but I just don't know how cold it really has to be. As an ardent fly-fisherman, I've fished caddis hatches in the snow. Scraping bugs off the cowl and wings gets old and there are fewer of them this time of year but I'm always surprised at the number of wintertime bug splats I pick up.

Good question - I too have seen bugs when it was as low as about 20ºF. I don't know an exact answer, but our recent sub-zero days however have resulted in leading edges that are as clean coming back into the hangar as they were leaving. It might also be a question of duration - we go for months at a time below freezing, with the occasional week or two of sub-zero.

Icing

Below approximately 0*F, the risk of airframe icing decreases dramatically. That's also the temperature where snow starts to become really grippy. There's no slush or muck around anymore, everything is clean, clear and crisp. I'd rather fly at 0*F than at 30*F

As long as your dressed and prepared for the weather and have appropriate survival gear, cold weather flying can be great fun.

Too cold is when your instruments and avionics won't run. The engine will usually run just fine at those temps... if you can get it started.

ChiefPilot said:

All good, but you missed the single biggest (I mean BIG!) benefit of flying when it's well below freezing out:

NO BUGS!

Click to expand...

Too true, Brad! Thank you for catching that major omission! I always look forward to that first flight in the late fall when I push the plane back into the hangar, go get my cleaning cloths and spray bottle, walk back to the front of the plane, and discover there is nothing to clean off. Magic

it's only -1F

No bugs and no snow plough!! Airport manager is busy clearing the taxiways.





In 40 minutes I am free







there is an RV8 in the shop down there

Vlad said:

No bugs and no snow plough!! Airport manager is busy clearing the taxiways.

Click to expand...

Same idea and no plow

It was 14 degrees outside when I woke up, and 17 when I left for the airport. I'm not sure what the temperature was at the airport but we had just a dusting of snow (no shoveling)?and I smashed a few bugs as the temps warmed into the upper 30s. Four days into the new year and I'm averaging a bit better than 1.5 hrs/day smashing winter bugs. I sure wish I could maintain that average.

So for me anyway, the teens isn't too cold (and it's rare that it gets colder here)

I routinely fly the Musketeer down to 0F with no concerns. Just before Christmas I took off at -11F. That was a little cool but it was warmer aloft. A Reiff makes the engine happy and I get a ton of heat from the big can muffler hanging under the 200HP angle valve.

The challenge is usually the wind - we tend to get very strong south or northwest winds this time of year.

That said, I'm not flying this weekend. Lows are predicted to be -22F and the high on Monday will be -10F. Wind chills to -50F.

Stay warm all!

Cracked my windscreen

I think I jinxed myself; after bragging about my New Years Day cold weather flight, I went back to the airport today to fly (in much milder temps) and discovered a 2" crack in the windscreen, probably from the cold temps last time out Bummer. The crack is at the bottom of the screen on the passenger side at the "corner" where the screen curves from the frontal plane to longitudinal. It can't be seen from inside the cockpit at all, and there is zero separation; can barely feel it with a fingernail.

I know I should stop drill it; but would appreciate advice re: techniques, bit sizes, etc for doing so. With no separation, I don't know if it needs to be glued as well or if this isn't needed. Again, any advice appreciated.

I apologize for the lack of pictures; for some reason I left my phone behind at the house when I left for the airport today.