Density Altitude hit 9k ft


Pre-takeoff checklist
Apr 24, 2017
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Density Altitude hit -9k feet here today.

Not that I’ll be trying out the plane, my personal min is -40, but thought it was interesting.
Where is here.??

In Kotz -4000 was fairly common in winter.

Lots of fun to see a contrail behind a 207.!!
Where is here.??

In Kotz -4000 was fairly common in winter.

Lots of fun to see a contrail behind a 207.!!
Supposed to do Fairbanks Tanana Kotz but i went back to bed after I saw the weather. Nearly -60 in Tanana, with the negative density altitude to match. Maybe someone can flap their wings and see what happens. Kotz is pretty warm, -20 today.

Someone else can go blow their struts and tires and get stuck out there at those temps if they dare. I’m happy to be home and warm.
If the air is only 70% as thick at 9,000 feet vs sea level, then would a density altitude of -9,000 be the same as if the air at sea level was 1.4 times thicker?
Operate the engine at 70% of normal manifold pressure, get normal horse power.
70% rated manifold pressure at the air density will near give rated RPM from the engine, and rated HP. The stall speed is reduced since the more dense air produces more lift at a given speed. The cruise speed, as the drag goes up by the density, goes down. With the lower stall speed, the take off roll is decreased.
All the things that get worse with high density altitude get better, and vice versa.

I have many hours in an airplane with a horsepower limitation of 180, but engine capability of 215 HP. At normal sea level density altitude, that limited us to 23 inches of manifold pressure, and as we climbed, the throttle was slowly pushed in to maintain 23 inches. Normally, actual full throttle occurred at 7,000 feet. In the winter, the chart of MP adjusted the MP down for colder air temperature, and in hot weather, higher MP was allowed, as the air density was lower. Winter full throttle might not occur until 10,000 or higher.

At 10,000 feet, I cruised at 140 K, TAS, in that Skyhawk.