In the Kestrel episode, Frank talks about how when temp goes up or down the DA changes. I get the why. What I am curious about is what the reference conditions are. There has to be conditions to that altitude, doesn't there? Is it sea level at 29.92, 68° and 50% humidity?
- Thread starter ShortShooter1908
- Start date
Temperature, pressure and to a very minor degree humidity effect DA.
All three of those variables have to be considered (You could just use temp and pressure).
All three of those variables have to be considered (You could just use temp and pressure).
What I am trying to figure out is when you come up with say a DA of 5000'. That bullet thinks it's at 5000', but what are the conditions of the air at the hypothetical 5000'?
You can get to a 5,000ft DA many ways, temperature and pressure are the main factors. You could have 5,000 DA at a variety of different combinations of temperature and pressure.
Here’s a DA calculator;
https://wahiduddin.net/calc/calc_da.htm
If you play around with it, it may make more sense.
The calculator uses dew point, if the temperature and dew point are the same that’s 100% humidity
https://wahiduddin.net/calc/calc_da.htm
If you play around with it, it may make more sense.
The calculator uses dew point, if the temperature and dew point are the same that’s 100% humidity
I'm sorry for going round and round. I'm a newbie.
Going back to the example I gave, I get that I could be at 3000' and come up to 5000' or be at 6000' and come down. When it's saying 5000' though, what are the conditions it uses to say 5000'? There has to be a baseline that the only thing that changes is the altitude. What are those conditions? Does this make sense or am I not understanding the concept properly?
Going back to the example I gave, I get that I could be at 3000' and come up to 5000' or be at 6000' and come down. When it's saying 5000' though, what are the conditions it uses to say 5000'? There has to be a baseline that the only thing that changes is the altitude. What are those conditions? Does this make sense or am I not understanding the concept properly?
Standard conditions are always based off
29.92 sea level
59 degrees
0% humidity
For every 1000ft of alitude you go up, Station Pressure drops 1” of pressure
In Denver standard conditions are 24.89 as you lose a tiny bit for temp as well. Why it’s not 24.92 it’s .89
Density altitude combines those three factors
29.92 sea level
59 degrees
0% humidity
For every 1000ft of alitude you go up, Station Pressure drops 1” of pressure
In Denver standard conditions are 24.89 as you lose a tiny bit for temp as well. Why it’s not 24.92 it’s .89
Density altitude combines those three factors
]
That's what I was looking for. Thanks.
To add to what Frank said. Every geographic elevation (sea level is the datum we use) has a Standard Day, in Denver with an elevation of 5280ft above sea level, the Standard Day is 24.64 inHg and 40.5 deg F (using standard lapse rate) under those conditions the Density altitude would be the same as the elevation 5280ft. If pressure decreases below 24.64 inHg (temp staying the same) or the temperature increases above 40.5 deg F (pressure staying the same) the Density Altitude will increase.
++++ Frank's post
It's called ISA (International Standard Atmosphere) ...if you wanted something to Google search or research.
It's called ISA (International Standard Atmosphere) ...if you wanted something to Google search or research.
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