Yup. Swear I had to turn the dial forever to get to 30.57. Tried to get up, but couldn't get the prop to cycle in the cold. Sigh.

Brett

We had some DA below -2000 here this morning. It made for some good performance.

You ought to see it when it gets cold!

The 170 virtually JUMPED out of 14" of powder today!
-DP

Mister701 wrote:You ought to see it when it gets cold!

This is about as cold as it gets here in Rio Vista!

Holy super charging? As in, provided free by the weather Gods....
We had over 30" at BVS the other day. With 30 gallons of fuel and me and nothing on board, the old 180 was impressive (even after all of those holiday meals),

So when the DA goes to -5600' do you guys automatically get free lean of peak operation?

Yeah, we had 30.55" here last week and the weather was severely clear, albeit a bit colder than normal. The plane jumped off the ground once the oil warmed up, but it took forever to get the oil warm, even with the oil cooler 3/4 blocked!

I laid awake all night trying to figure out how it got to 69% humidity at 27 below in Fairbanks. It says severe clear with -31 dew point. I recall days like that but the humidity more in the neighborhood of 15% or so. I must be thinking this through too hard. Spring time in Mississippi.

At the opposite end of the extreme, the day I went to Leadville as a bucket list item in September 2009, when I took off the DA according to the AWOS was 12,100'. I think my climb out was at about 150 fpm, after a take off roll of nearly 4000'. When I leaned on the ground, the mixture control looked like it was just about to idle cut-off!

Cary

Mister701 wrote:I laid awake all night trying to figure out how it got to 69% humidity at 27 below in Fairbanks. It says severe clear with -31 dew point. I recall days like that but the humidity more in the neighborhood of 15% or so. I must be thinking this through too hard. Spring time in Mississippi.

The key word in the Humidty definition is "Relative". It is relative to how much moisture the air can hold at that temperature (-16F). The colder the air the less moisture it can hold. At 69%RH and a temperature of -16F the air is holding very little moisture and that is about average for the low relative humidity of a day in Jan. in Fairbanks.

Now, take that 69% RH air with a -23F Dew Point inside the house and warm it up to say 65 degrees F and the RH will drop to 2%. That's why it is so dry in the house in northern climates in the winter. Think about the carb icing chart. When the temperature is 68F it can hold a lot of moisture to turn to ice in the carb.

Relative Humidity calculator http://www.hpc.ncep.noaa.gov/html/dewrh.shtml

tcj wrote:

Mister701 wrote:I laid awake all night trying to figure out how it got to 69% humidity at 27 below in Fairbanks. It says severe clear with -31 dew point. I recall days like that but the humidity more in the neighborhood of 15% or so. I must be thinking this through too hard. Spring time in Mississippi.

The key word in the Humidty definition is "Relative". It is relative to how much moisture the air can hold at that temperature (-16F). The colder the air the less moisture it can hold. At 69%RH and a temperature of -16F the air is holding very little moisture and that is about average for the low relative humidity of a day in Jan. in Fairbanks.

Now, take that 69% RH air with a -23F Dew Point inside the house and warm it up to say 65 degrees F and the RH will drop to 2%. That's why it is so dry in the house in northern climates in the winter. Think about the carb icing chart. When the temperature is 68F it can hold a lot of moisture to turn to ice in the carb.

Relative Humidity calculator http://www.hpc.ncep.noaa.gov/html/dewrh.shtml

Hey thanks! I should know that but now I do. Very good sir!

So, how much manifold pressure can you pull at 6k below sea level? I don't think my carburated 470 would even run, but if it did, I doubt the jetting would accomodate that air. Maybe with carb heat on

Gettin better yet!

Nosedragger wrote:So, how much manifold pressure can you pull at 6k below sea level? I don't think my carburated 470 would even run, but if it did, I doubt the jetting would accomodate that air. Maybe with carb heat on

My old O-300A responded very well to pulling carb heat in those conditions. Smoothed it out considerably and increased RPMs by 50-100, if memory serves.
-DP

Yeah it was cold out our way today also. I took off from Takotna this afternoon at -27. About 3/4 throttle will get me red line on manifold pressure at those temps. Nothing works well. Flaps are stiff. Grease on the tailwheel is froze. Just roll back some trim and nice easy climb to warm sunny flying. No Idea what the density altitude is at those temps, the map on my seat don't tell me that.

I had -1,000ft today in tx. The old cub was flying before I was ready.

denalipilot wrote:

Nosedragger wrote:So, how much manifold pressure can you pull at 6k below sea level? I don't think my carburated 470 would even run, but if it did, I doubt the jetting would accomodate that air. Maybe with carb heat on

My old O-300A responded very well to pulling carb heat in those conditions. Smoothed it out considerably and increased RPMs by 50-100, if memory serves.
-DP

That was one of the little tricks that I was taught when I was learning to fly at Elmendorf 42 years ago. In really cold weather, we often flew the 150s and 172s with carb heat on--much smoother. "Really cold" was like -20 or so.

Cary

175 magnum wrote:So when the DA goes to -5600' do you guys automatically get free lean of peak operation?

I think the answer would be "no", because the fuel control unit meters the flow in proportion to the air pressure. Denser air will exert more pressure on the diaphragm. So more air pressure just means more fuel to the engine in proportion, so the net result is more horsepower but you should see the same air/fuel mix, roughly speaking. But I haven't thought that through in detail.......