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Good lift in FAI today,, keep it!

scout88305

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Northern Minnesota
[h=2]Fairbanks, Fairbanks International Airport (PAFA)[/h] Lat: 64.8°NLon: 147.88°WElev: 433ft.
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Fog/Mist
-35°F
 
Here's a pic of Fairbanks town looking south: http://old.co.fairbanks.ak.us/airquality/CRCurrentPhoto.jpg It updates periodically. The Fairbanks airport is to the extreme right.

Not too bad here yet. Not much ice fog or wind: http://w1.weather.gov/obhistory/PAFA.html Altimeter setting 30.63 getting close to the max 31.00 for some equipment.

Lots of Pilgrims will be trying to start their vehicles in the cold for the first time. This was my personal temp limit when winter flying frequently. Now it's gotta' be warmer for my Taylorcraft and C-85.

GAP
 
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Lots of things start to fail at those temps, but, the amazing part of cold dense air is, the performance! The ASOS at Tanana the other day said -6500' density altitude! (-28C).
 
Lots of things start to fail at those temps, but, the amazing part of cold dense air is, the performance! The ASOS at Tanana the other day said -6500' density altitude! (-28).

I've never flown a piston that cold, but I've heard you have to be careful to make sure your carb can flow enough fuel for max power settings.
 
Carb heater (or better yet maybe a warmer) can help with extra lean condx due to cold intake air. Practice to learn the engine's cutoff temp before it's needed. It's -10F limit for my small Continental at altitude. It simply doesn't warm up and freezing of the breather is a problem despite insulative covering.

GAP
 
One quickly learns to tape off air inlets as the temps fall, making smaller and smaller openings for cooling.
 
Cowl flaps work better. Bachner's Aircraft in Fairbanks used to offer one for Cubs that closed the side and bottom outlets. Some were adjustable from in the cockpit. I made a copy with fixed sides and bottom, plus an air adjustable oil cooler cover for the old front mounted Piper product.

GAP
 
I've never flown a piston that cold, but I've heard you have to be careful to make sure your carb can flow enough fuel for max power settings.

I've seen more problems with the big Continentals running too lean in the dense air. They will do that when they are not set-up properly for max pump pressure and run at low altitude @1000'
 
Of course, we now have to apply the new cold temp corrections on approach to FAI. As one needs to be consulting a table rather than flying the plane. Sorry, rant and rave style. When it gets pretty cold, weather (not counting ice fog) tends to be pretty good
 
I've seen more problems with the big Continentals running too lean in the dense air. They will do that when they are not set-up properly for max pump pressure and run at low altitude @1000'
nanook, My 185 has an altitude compensated fuel pump. Have you any experience with these in these weather conditions? The advantage to this pump on the IO-550 engine is that you can use full power at any altitude without being concerned with leaning the maximum fuel flow at higher altitudes.
 
The last two IO-550s I've run were set up too lean for negative density altitude and both had the altitude compensating pump. The pump pressure needs to be near redline to have a rich enough mixture in these conditions (Cessna).
 
Might the observed span between full rich and peak EGT tell if the fuel flow is adequate? Like less than normal if lean; more if ok?

GAP
 
nanook, My 185 has an altitude compensated fuel pump. Have you any experience with these in these weather conditions? The advantage to this pump on the IO-550 engine is that you can use full power at any altitude without being concerned with leaning the maximum fuel flow at higher altitudes.

On the 550s We disabled the altitude compensating pump, and cranked the fuel flows up to max, or a little more. Engines loved that setup. Lots of cylinder issues prior to going there. Those engines were originally set up way too lean. I wanted to see the stock Cessna fuel flow(actually a pressure guage) go all the way over into the other side of that dual gauge.

MTV
 
I special ordered the altitude compensating pump as I'd never heard of one being used in this application. It seemed to be a good idea and has proven to be the correct decision. Of course I do not fly in the winter conditions that are prevalent in Alaska. I also have two pressure gauges installed in order to verify both the high and low full power pressures on each take off.

I had heard of the cylinder issues before making my installation. During the installation I noted that the cylinder cooling fins taper in diameter from top to bottom unlike the IO-520 which are all the same diameter. This makes sense in that the cooling is tuned in relation to the heat production areas of the cylinder. Nowhere in the STC instructions is there any mention of altering the baffles. Thus this leaves a large gap on the two forward and two rear cylinders with no cooling. Needless to say I modified these baffles. A friend here just installed an IO-550 in his 185 and the instructions still do not mention this. Mike, which cylinders caused the troubles?
The fuel pressure on the 550 does push the gauge to it's limit.
 
I don't think the altitude compensating pump was designed for below sea-level densities. What you see coming out of the Continental factory & overhaulers who set these up at run-up is 23-24 psi at the pump (unmetered). The Cessna fuel flow gauge which is actually just pressure, red lines @27psi. If you aren't at 27 you are running super lean at TO and lean at cruise until you climb a couple thousand feet. You will see the EGT drop once you get out of that cold/dense air.
 
Mine is set at the high side of the red line 27 psi. I tried to find a replacement gauge that would go a little higher, but was unsuccessful.
 
Mine is set at the high side of the red line 27 psi. I tried to find a replacement gauge that would go a little higher, but was unsuccessful.

Sounds good, there is some cold WX headed your way. High pressure ridge building from north of us on the Arctic Coast all the way to the Gulf of Mexico! Running the length of the N American continent. This is a true Arctic High with notams showing above 31" in the Eastern Interior of Alaska and Yukon Territory. PFYU current WX -44, altimeter 30.78, so it is getting there.
 
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There were a few C 206s converted to 550s when that engine first was STCd for those planes. We had two of those, and cylinder head temps ran high and all the cylinders had to be changed at around 1000 hours. These cylinders were stepped, so no rebuilding was possible with them.

Seems like everyone initially had these problems in the early installations. My 206 was scheduled to be converted next, and I wasn't sure it was such a good idea. I called Continental, and explained my concerns. The tech rep asked me the serial number of the engine going in my plane. I called back with that and he said I shouldn't have a problem. He also strongly recommended carefully reading the operating instructions, particularly on leaning.

Finally, he recommended that we not use the altitude compensating fuel pump, and setting fuel flows higher than recommended in the installation instructions. He said most of the issues we were seeing were likely a result of running the engines too lean.

We followed his recommendations, and that engine was a great running engine. Cylinder head temps were always in the 315 to 330 range, and the engine ran LOP beautifully with GAMI injectors. For about 1300 hours, that is. At that point, one of our other pilots borrowed the plane and put 25 hours on it. It came back due for a 100 hour, and two cylinders were bad. Not stepped, but they'd been subject to heat.

Talked to the guy who used the plane and asked him what kind of power settings he was using. He said "Same as the IO-520, 24 square. He then noted that he'd run it LOP at that power setting. Continental specifically prohibits ANY leaning at that high a power setting. I retired that winter, so don't know if any other cylinders were changed.

Later, I ran into that tech rep at OSH, and asked him what Continental changed in those early engines to cause them to run so much cooler. He responded that they changed the oil control piston rings to allow more oil into the combustion chamber. Who'd a thunk?

It seemed to me that the biggest issue was getting pilots to pay attention to the operating recommendations of these engines. Seems like a lot of pilots want to run them as if they were 520s, and the 550 is a somewhat different engine.

MTV
 
Mike,
You're making me think that the pilots who were overheating the 550s were leaning to a fuel flow gph number rather than EGT differentials. Mine seems to like 15.8 gph which is above the 520 as you know. If it were leaned to the 520 fuel flow it would be smack in the middle of too lean and too hot. 24/24 runs great rich of peak with Continental balanced injectors. Setting lean of peak looses too much power for float flying.
 
Pete,

I ran that 206 LOP on those monster ship-like Wip 4000 floats for hundreds of hours, using ~ 2300/21 or so, running LOP at 13.2 gph. Engine ran cool, and plenty of power, even at 3800 AUW, and warm interior Alaska temps.

You should give that power setting a try....I think a 185 would do well there.

I agree, however that running too lean was likely a factor in those early engines. It's important to note that (at least on the ones I ran) Continental specifically prohibits leaning at power settings greater than 70%.....or is it 75%??

Also, when comparing 520 to 550 power settings, it's important to recognize that the 520 is a 285 hp CONTINUOUS rated engine, where the 550 is a 300 hp continuous rated engine. So, 70% in a 550 is more power than 70% in a 520.

MTV
 
Mike,

The manual says "Do not attempt to adjust mixture by use of EGT at setting above 78% of maximum power".

It also says: "The maximum recommended cruise setting is 235 BHP at 2500 rpm and 25" MAP with the mixture set at 25 degrees rich or lean or (maybe a misspelling?) peak EGT. At cruise settings below 65% engine may be operated at peak EGT".

I'm still nervous about the LOP operation after burning a hole in a cylinder of my 520 operating ROP but with low indicated air speeds. Besides I like seeing well in excess of 120 KIAS when on floats at 24/2400. Gas is cheap when compared to the engine cost and the potential for a remote location failure.

I could find no reference to negative density altitudes. At least in my operation there will be no negative numbers such as you in the north country experience.
 
FWiW the 520 manual prohibits leaning at or above 75% power and there's a note to correct power output (from memory) 1% for every 10* below standard conditions.
 
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