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Winter engine temps

Denok

Active Member
Patron
Canadian winters are harsh and very cold so in order to keep my engine in cozy territory, and when temperatures are below -5 C (23*F) I block my oil cooler with aluminum tape which gives me around 180*F oil temp. Satisfying indeed but the cylinders are not so happy with temps that won't go above the 275-300F range. I do block some airflow with duct tape on the cowling air intake (I know...this might set this thread on fire) and results have been satisfying but I find this solution to be a bit sketchy and unorthodox. What temporary (or seasonal) solution do most people use to restrict airflow? Has any carbon/glass fibre guy ever made something that fits that opening.
 
Check out Steve Melton’s 3D printed cowl inlet “air blockers”. Not sure what they are called, but they work. rvplasticparts.com.
 
Ugly but it works

Denis, duct tape is not sexy but it works well.
You probably know this, we had tape on all the trainers back then every winter.
One question is how does it affect the paint in the long term after many removals.
As for a sexier, temporary and reusable airflow restrictor, I'm working on an idea.
I love winter flying, and I hope to try my idea next winter and if it works, I'll be glad to share. :D
 
Block the Exit

There was a thread on here a while ago about blocking the exit. The aerodynamics and discussion was above my understanding. Possibly a better idea from an aerodynamics perspective?

The excess air spills out the front, and remains higher velocity out the exit vs blocking the entrance and having slow moving air out the exit. Maybe I'm completely out to lunch.

On a certified aircraft, I've seen little pits of aluminum made into a "winter kit". There were small holes in the cowl cooling inlets and the aluminum blockers fit in nice and snug. I'm sure it was worth $1000 to basically drill some holes and add a piece of 0.040" alclad that restricts the cooling air intake. I can't find any pictures on the internet, otherwise I'd post a link.
 
Cutlass C72R Winter Inlets

David, I don't know what they are worth as they came with the Cutlass when bought 3 years ago.
I just installed them today, easy to do: 3 screws that are in a Camlock style holder.
And I also have a plate covering the oil cooler. Makes for a warm engine in sub-zero temps.
Ready to fly in the cold air... But not flying much as I'm working hard on the 8 to finish the darn thing !!! ;)
 

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Just a data point . Over the last 25 years I have flown 2 engines in very cold winter temps.
1) O-320 down to -30C on a great many 2 -3 hour XC flights. Oil sump heating pad pre heat always with a cowl blanket . No air restrictors on the cowl for in flight. I do block off the air for the oil cooler, but only if upper air temps are below -10C This engine now has close to 4000 hours since OH.

2) IO -540 in an F1 Rocket down to -23C on a few 1 hour XC flights Oil sump and cylinder base pre heat with cowl plugs for initial , then only cowl plugs at the destination for 2-3 hours before return. Over 10 years on this machine .

Both get flown in very hot summer conditions also.

Even at -20 C on the ground, upper air temps can often be only a few degrees below zero to plus 10C That is normally one of the go decision criteria for me. For that reason I have never restricted the cylinder cooling air. Often times one can be flying into warmer air at the destination as well as warmer air aloft.

Plan ahead carefully and don't cook your cylinders.

I think the perfect solution for inflight control is an exit cowl flap like Dan Horton has on his RV 8 , along with a cockpit operated butterfly valve on the oil cooler duct work, with a failure mode that always opens and allows air flow to the cooler.
 
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The system I was familiar with is over 10 years ago now since I saw and used it. It looked quite similar to the pictures riseric posted, but not a Cessna aircraft. I recall temperature limitations that were relatively generous. I don't think they were ever truly required, but had a minimum recommended temperature, -25*c or so. The maximum limit temperature, I think it was -5*c or -10*c.

Each flight the pilot needed to consider the temperature at departure, temperature at altitude enroute and forecast temperature at destination. They were also very easy to remove and reinstall, 5 minutes, a screwdriver, logbook entry and good to go.
 
Why should cylinders not be happy with 275 - 300 F? These Temps are still above Lycoming's recommendation of 150 - 200 F.
 
i'd like to ask again, maybe someone knows... what's the problem with very cool running cylinders? as long they are above 200 or so it should be ok...?
 
... but the cylinders are not so happy with temps that won't go above the 275-300F range.

What leads you to believe that this temp range is bad for your cylinders? Do you know what bad things are happening at that temp?

Personally, I would do some research before fixing a problem that may not be a problem. Blocking your inlets does not come without some risk.

I have no concerns flying with my CHTs at that temp range. Numerous flight school planes here in Chicago that don't even have CHT instruments and fly all winter long. Seem to routinely make TBO.

Larry
 
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Cylinder Choke

Contrary to some opinions, keep the CHTs in the range the Cylinder OEM recommends. Air cooled jugs, especially aluminum heads, have a significant amount of choke. The design intent being at proper operating temperature, the cylinder walls are then straight. Too cool = smaller than designed cylinder diameter at the top end = excessive wear there and on rings. The typical, ultimate result = "step" in the cyl wall and loss of compression. That said, the majority of similar wear is at start-up. So while on the subject, keep the starts easy and RPMs low until things warm-up. Yes, I know that's not always feasible. Best of luck.
 
min temp of lyc cylinder?

Contrary to some opinions, keep the CHTs in the range the Cylinder OEM recommends. ...
This is the question - all the documentation I've found from Lycoming only shows the max temp, not the min.

Edit: see below, seems Lyc says min temp is 150 degrees F.
 
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i once "heard" from an A&P that the choke is gone (cylinders straight) at 150 to 200 °F and lycoming states 150 F to be the minimum CHT, some others say it's 200. So when your engine is running at 250 or so, everyting's "cool"... i guess.
 
For what it's worth.

@KayS. Not saying your guy is wrong but 250DegF sounds low. There are a lot of different alloys in a jug with very different thermal expansion properties. The thermal strains and resulting stresses cannot exceed their individual limits; all of this while accounting for the range of temperatures each element would experience. If the other metallurgical properties are steering the component to a higher temperature design point, one would assume cylinder choke would follow.

I attached a page from my old Mooney POH (O-360-A1D) for what it's worth. It would only make sense that these numbers came from Lycoming. I have an old (*ancient*) Lycoming Engine Operations handbook somewhere at home if I can find it. Will be interesting if any listed numbers there don't line up with the aforementioned POH. This is for interest only; not starting a debate.
 

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Awesome

I love forum smart guys or in general when when anyone tries to swing above their weight class. I do have an extensive and varied design background from aerospace to Gas Turbines. I gave open, candid reasoning for a position. A gentleman following with a chemistry perspective that was appreciated (We mostly utilize very clean burning natural gas, No lead obviously. There is a lot of de-rating when liquid distillates are involved). That information lined up with the airframe OEM's POH (and many others, BTW). I have the manual that was referenced. If cylinder walls aren't straight, they wear faster, rings wear faster and have been known to have fatigue failures.

"Maximum Service Life" does not infer the components won't have their service life impacted when operated away from their aforementioned design points. The operator isn't exceeding any material limitations while in the green. Run your power plant or car even at redline all the time. It probably won't come apart in normal service life but component/engine life will be affected. Part of the design intent is to find such at inspection intervals, not through component failure.

Elvis is alive and working at a gas station in Iowa. Google it!

edit; That stinks. The previously preceding post that highlighted minimum CH operating temp of 150 telling me to google it was deleted.
 

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@Freemasm: you are wrong! Elvis is alive, but he works at an auto repair shop in slovenia close to the austrian border. i met him once, he fixed my Fiat Tipo.

my CHT's are in the 300 F range when it's cool and i throttle back and lean. but i run 100LL on the left tank for take off and landing, during cruise i switch to the right tank with mogas.

i got the point with the straightened cylinders and guess 300 to 350 F CHT's are ok.
 
No one suggested choking the exit of the cowl to raise temps. Seems to me like that would slow down mass airflow over the cylinder fins without changing airflow patterns on top.
 
Hi Denis
After experimenting with double layer of duct tape I made metal air dams that attach to the cowl joint screw locations blocking off some of the air entering the cowl. They are 1 1/4 inches wide and 6 inches long. They work well keeping cyl head temps at 350 to 360 F at air temps of 0c to -5 C . I haven’t flown below -5C but a wider set of strips could be easily made. The ones I use took about an hour to make. The plates easily come off at temps above +5C . I also blocked off 1/3 of oil cooler with a metal plate and that gives me oil temps in the high 180 range sometimes 190’s depending on ambient air temp. I have electric oil sump heaters that I plug in about an hour before flight.
Send along your email and I’ll forward should some pics. I may post them here if I can figure out how to do that.

Dave C
RV 7
C GCPD
 
If you're burning 100LL, running excessively low CHTs will inhibit the lead scavenging process and cause a buildup of oxybromide (very hard metalic deposits) on the pistons and the exhaust valve stem. CHT sweet spot is 350-400F on Lycoming engines to keep the oxybromides in a gaseous state while leaving the cylinder.

https://www.aopa.org/news-and-media/all-news/2020/july/pilot/savvy-maintance-valves

The heat required for vaporizing lead (around 800-1000F, I recall) is the heat of the combustion gasses themselves and has nothing to do with the temperature of the barrel or the head, generally speaking. Material temp is all about the effectiveness of heat transfer/removal and is not necessarily reflective of specific internal gas temps.
 
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49clipper

I once asked a Lycoming Tech service about running my -320 at about 275f and he said they would last forever don't worry about it. Then said, call me when they get down to 175f and we will talk about it.
 
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