I think this has come up before, but maybe not in its own thread. I'm mainly interested in the -20F and colder range, where it seems things have more tendency to become interesting.

I launched in -25F conditions yesterday, and flew about four hours in which it didn't warm up a whole lot. I've managed to avoid flying in that for much of the winter, so it was a good day for remembering how stuff can go a little differently. I just thought I'd share some, and am hoping that others have stuff to add too about cold wx ops.

First off was air density. I'm based at 2,000', and I usually start to lean the mixture to my carb'ed engine at around 3,000'. If my math is right, I think the D.A. at my runway was about -3,700' yesterday. I found I could not begin to lean the fuel until around 7,000' and -10F OAT, and below that the only way I found to smooth the engine was to run full carb heat to lean the air.

Another thing was feedback squeal in my ANR helmet. I checked with the manufacturer today, and apparently in real cold there is an issue with condensation forming on the ANR mic inside the earcups, causing it to be overly sensitive. Even though it was cold out, I evidently got my head and hair steamed up enough under my hat that when I took it off and put on my helmet, instant feedback squeal.

One last item is the breather tube in conjunction with a tight-fitting engine blanket. I found that my new engine cover presses tightly against my breather outlet, causing the breather spooge to back up and freeze in the tube overnight. I've got the extra air hole higher up on the breather tube, but it still took some heat and a long wire to unplug the tube end. In future I won't close the blanket bottom tightly until most of the spooge has had a chance to drip out.

So, those were some of my reminders from yesterday. Any thoughts, stories, or additions from fellow frozen BCPers?

Cheers, -DP

This thread had some good info...

viewtopic.php?f=6&t=3124&p=39075&hilit=makeshift+preheating#p39075

Gump

Stay home by the fire.

I think I remember that carb heat richens the mixture, not leans it. Heat creates less density, which means less oxygen, per "slug" or cubic foot or whatever physical volume you measure. For the same amount of fuel you would get a richer mixture using warm air then you would get with cool air.

Carb heat would of course combat icing, which is many times well worth the slightly rich mixture.

EZFlap wrote:I think I remember that carb heat richens the mixture, not leans it. Heat creates less density, which means less oxygen, per "slug" or cubic foot or whatever physical volume you measure. For the same amount of fuel you would get a richer mixture using warm air then you would get with cool air.

Carb heat would of course combat icing, which is many times well worth the slightly rich mixture.

We're in agreement I think. Carb heat "thins" the air, which is beneficial when your DA is -3,700'

I think this means that a normal carburetor operating range is way too lean FUEL delivery for that super-dense DA, so you "lean out" THE AIR to bring it into the usable range of the carburetor.

Where I live they declare a disaster zone when the temperature plummets below +60 (the actresses' breast implants and collagen injection sites begin to experience high frequency vibration problems).

I'll bet there's a few pilots here who have significant experience with really cold temperatures who can offer "real-world" advice that is better than mine.

I’ve a question for the old pros on cold weather ops. Our engines are capable of producing over 100 percent power at very low density altitude, right? If this is true then I would see the extra power as increased static RPM, right? We’ve been blessed with an extra measure of snow in Southcentral Alaska and a lot of overflow to go with it. I’m operating on skis and at times I’ve needed all the thrust I’ve got just to avoid getting stuck. There is no mention in my Airplane Flight Manual of limiting power in cold weather for the O-300 in my ’52 C170b, and the only criteria that I can see would apply is the maximum static RPM specified in the STC for my DM80 prop. At what point should I be concerned about overstressing the engine or prop and not push the throttle to full open?

What kind of carb temp were you showing, or do you have a carb temp gauge?

I will GUESS that there is a maniforld pressure limit (to control maximum pressure in the combustion chamber, BMEP), as well as an RPM limit?

Glider: Dunno about the carb temp as I don't have a gauge.

EZ: I typically glance at the tach shortly after I firewall the throttle to see if we are in the right range but about then things start happening fast and my attention is needed elsewhere. I do have a manifold pressure gauge but don't pay much attention to it with the fixed pitch prop. In any case my AFM references RPM but doesn't mention manifold pressure. Sometimes a slight change in manifold pressure while in steady cruise at fixed throttle position will clue me in that I am starting to get a bit of carb ice. Otherwise the MP gauge just fills a hole in the panel.

You aren't going to create more horsepower with an O-300 and fixed pitch prop than the engine is rated for. In fact, very few engines with fixed pitch props ever make full rated power static. If they did, they run well over red line once they're in flight. So, you don't make anywhere near max rated power in normal ops, so if the engine makes a LITTLE more power in cold dense air, you can rest assured that the propeller will kill most if not all of that additional power, since the propeller still has the same pitch, and it's now running in VERY dense cold air. So, that very dense air, while it may permit the engine to make a little more power, also limits the amount of drag/resistance the engine experiences from the prop. So, it's generally no problem at all to run fixed pitch props in very cold weather.

Now, constant speed propeller equipped airplanes are a little different. In those, the prop governor changes the blade angle of the prop to change rpm, and to maintain the rpm selected. Since these engines CAN make full rated power in standard conditions, it also is possible to make MORE than rated power when temperatures are very cold. The prop governor changes the blade pitch angles to permit the engine to run up to max rpm, and at that rpm, with very cold induction temps, the engine is capable of making more than rated power.

Cessna, in their 180/185/206/207 series airplanes provided a cold weather winterization kit. One component of that kit (and the only one I used regularly) is a metal plate that blocks off the air induction filter, and that plate is equipped with a small (around 3 inch diameter) hole. This small hole is sufficient to flow enough air to the engine for normal cruise power, and idle. But, as you open the throttle, the vacuum drawn within the induction causes a spring loaded hinged door inside the cowling to open, inducting air from inside the lower portion of the cowling into the engine induction. This air, being on the lower side of the cowling contains air that just cooled the engine, and thus is substantially warmer than the outside air.

Problem fixed...at max power, the engine won't develop more than maximum rated horsepower, because it is inducting warm air from within the cowling.

MTV

I fly a '52 170B and if I talk too much, the windows all frost up.
Did you guys modify the heating system to get some more hot air in the cabin?
Mine is luke warm below 20f, but I'm not sure how much it will improve once I replace the worn engine baffles at annual.
Also are there any tricks to get the doors to fit better? The doors are showing some daylight...

AKclimber,

My '53 170B has a heat box out of a 172 courtesy of the previous owner. He claimed it was more effective than the original one. It's been plumbed to put out heat at the toes on both sides, but only on the pilot's side of the dash. Seems to help keep the frost off the windscreen where it matters most. For the rest I try to breathe to the side, open a window while taxiing, or just blast the air vents in the wing roots. Also, I try hard not to work up too much of a sweat during ground handling, but that's not always so easy with skis and deep snow and warm clothing, as you know.

-DP

DenaliPilot,
Do you just have a different heatbox (the one on the firewall), or are the hoses also routed differently from the engine? I wonder if my IA will easily sign off on this mod, or a 337 will be required...

My '52 170b is sporting a firewall forward off an early 172 so has the 172 carb air box Denali mentioned. I get full cabin heat off the muff on one side and on the otherside heat is either directed to the carb or to the cabin. There is an expensive double cable that controls the flappers on this side. Worth it tho 'cause it makes my wife comfortable and that is priceless.

AKclimber wrote:DenaliPilot,
Do you just have a different heatbox (the one on the firewall), or are the hoses also routed differently from the engine? I wonder if my IA will easily sign off on this mod, or a 337 will be required...

AK-
I just went back to the logs to get my story straight. For the record, the 337 says:

"To increase effectiveness of cabin heating. Removed existing heating system and installed type specified on same model, later serial number aircraft."

It goes on to list about a dozen parts and part numbers. PM me an email and I'll send you a scan of it. Judging by your description, it's an improvement over the original.

-DP

p.s. If you happen to have a copy of "The Cessna 170 Book" by the International Cessna 170 Association, this mod is described on page 117.

More fun shit, and a talk about mixture and below sea level DA's.

viewtopic.php?f=1&t=4625&hilit=below+sea+level+mixture

Gump

GumpAir wrote:More fun shit, and a talk about mixture and below sea level DA's.

viewtopic.php?f=1&t=4625&hilit=below+sea+level+mixture

Gump

GumpAir wrote:Lots of problems with cold below minus 40 degrees F.

Way easy to overboost. Mixture gets way too lean (way I remember it, is you push rich as you descend) but the knob only goes in so far, and I think the accurate DA it those conditions is actually about 4,000 feet below sea level . In a carbureted engine you gotta pull on carb heat to raise the DA by warming the air. Shock cooling is real, MP and RPM stay in cruise down to short final. And, rubber and plastic just explode.

Nosewheels are most at risk. They like to pop off the rim as you make the turn from the runway to the ramp. There's no flex in the tire or tube and the turn puts a load on the sidewall. Make the turn, and flat they go. You either wheelie to get home, or you're stuck in some shithole native village for a few days until you can get a company mechanic out to change the tire for you.

And heaven help you if you crash and get hurt at those temps. You break an arm and you're gonna die. 20 below is a non-event. 50, 60 below and you'd better be scared. Luckily those temps are actually rare on the Arctic coast, but we still flew when it got that cold. Just very, very carefully.

Gump

Thanks Gump. That's the thread.

mtv wrote:You aren't going to create more horsepower with an O-300 and fixed pitch prop than the engine is rated for. In fact, very few engines with fixed pitch props ever make full rated power static. If they did, they run well over red line once they're in flight. So, you don't make anywhere near max rated power in normal ops, so if the engine makes a LITTLE more power in cold dense air, you can rest assured that the propeller will kill most if not all of that additional power, since the propeller still has the same pitch, and it's now running in VERY dense cold air. So, that very dense air, while it may permit the engine to make a little more power, also limits the amount of drag/resistance the engine experiences from the prop. So, it's generally no problem at all to run fixed pitch props in very cold weather.

Now, constant speed propeller equipped airplanes are a little different. In those, the prop governor changes the blade angle of the prop to change rpm, and to maintain the rpm selected. Since these engines CAN make full rated power in standard conditions, it also is possible to make MORE than rated power when temperatures are very cold. The prop governor changes the blade pitch angles to permit the engine to run up to max rpm, and at that rpm, with very cold induction temps, the engine is capable of making more than rated power.

Cessna, in their 180/185/206/207 series airplanes provided a cold weather winterization kit. One component of that kit (and the only one I used regularly) is a metal plate that blocks off the air induction filter, and that plate is equipped with a small (around 3 inch diameter) hole. This small hole is sufficient to flow enough air to the engine for normal cruise power, and idle. But, as you open the throttle, the vacuum drawn within the induction causes a spring loaded hinged door inside the cowling to open, inducting air from inside the lower portion of the cowling into the engine induction. This air, being on the lower side of the cowling contains air that just cooled the engine, and thus is substantially warmer than the outside air.

Problem fixed...at max power, the engine won't develop more than maximum rated horsepower, because it is inducting warm air from within the cowling.

MTV

MTV—where can one find a cold weather winterization kit for a C180? I've been looking diligently over the last few years (have even made my own), but am wondering if I'd be able to purchase an already made [prettier] version. Thanks!

C180Lady wrote:

mtv wrote:You aren't going to create more horsepower with an O-300 and fixed pitch prop than the engine is rated for. In fact, very few engines with fixed pitch props ever make full rated power static. If they did, they run well over red line once they're in flight. So, you don't make anywhere near max rated power in normal ops, so if the engine makes a LITTLE more power in cold dense air, you can rest assured that the propeller will kill most if not all of that additional power, since the propeller still has the same pitch, and it's now running in VERY dense cold air. So, that very dense air, while it may permit the engine to make a little more power, also limits the amount of drag/resistance the engine experiences from the prop. So, it's generally no problem at all to run fixed pitch props in very cold weather.

Now, constant speed propeller equipped airplanes are a little different. In those, the prop governor changes the blade angle of the prop to change rpm, and to maintain the rpm selected. Since these engines CAN make full rated power in standard conditions, it also is possible to make MORE than rated power when temperatures are very cold. The prop governor changes the blade pitch angles to permit the engine to run up to max rpm, and at that rpm, with very cold induction temps, the engine is capable of making more than rated power.

Cessna, in their 180/185/206/207 series airplanes provided a cold weather winterization kit. One component of that kit (and the only one I used regularly) is a metal plate that blocks off the air induction filter, and that plate is equipped with a small (around 3 inch diameter) hole. This small hole is sufficient to flow enough air to the engine for normal cruise power, and idle. But, as you open the throttle, the vacuum drawn within the induction causes a spring loaded hinged door inside the cowling to open, inducting air from inside the lower portion of the cowling into the engine induction. This air, being on the lower side of the cowling contains air that just cooled the engine, and thus is substantially warmer than the outside air.

Problem fixed...at max power, the engine won't develop more than maximum rated horsepower, because it is inducting warm air from within the cowling.

MTV

MTV—where can one find a cold weather winterization kit for a C180? I've been looking diligently over the last few years (have even made my own), but am wondering if I'd be able to purchase an already made [prettier] version. Thanks!

Cessna used to sell the cold weather kits, which consisted of three plates: One plate on each of the upper air inlets of the cowling, and an induction plate, as described above. In my experience, the plates that block off the upper air inlets to the cowl, which have much smaller openings in them, block off way too much air for most operations. The first winter I worked out of Fairbanks, i diligently installed the cold weather kit that came with the 185 that I was assigned. Right away I discovered inversions, as described above. The cold weather kit blocked off too much air to operate in the relatively warm temperatures above the inversion. If it was much above -25 F, the engine started to warm up a bit too much. Might not be a problem with a 180.

But, I then removed the upper plates, left the induction plate in place and simply put duct tape over half or more of the oil cooler. Even in very cold temperatures, that solution seemed to work just fine.

You'll see all kinds of block off plates as home made "winter kits". Personally, I stay away from anything that blocks off air or even disturbs the air flow through the cowling. Covering the oil cooler is no big deal. But, when you start blocking off part of the upper cowl inlets, you really don't know what sort of turbulence you're creating in the flow over and through the cylinders. If you look at the original Cessna plates, the openings are very small, but they are transverse, as in horizontally aligned. That provides some airflow to all parts of the cylinders.

I've seen all kinds of home brewed block off plates, and if that winds your watch, go for it. Me, I just worry about keeping the oil temperatures up. That'll keep your engine healthy. Those cylinders are hotter than, well you know, anyway. It's actually pretty hard to over cool cylinders, at least good cylinders.

For what it's worth. That solution (just covering the oil cooler) worked fine for me on several airplane types for 20 seasons in interior Alaska, and I never saw any sign of harm from doing so.

MTV