Altitude vs. Barometric pressure

[TXTrained]

I am Talking about the word "high" and "low" density altitude, I'm a pilot. "High Density altitude" means thin air opposite of what it sounds like.

Are you talking about how the plane flys or how the engine runs in that thin air? Thanks

 

[Mikecr]

This statement here: "Gravity is proportional to your elevation. It is decreasing as you move away from the center of the earth. The force of gravity is reduced by 1/R^2 where R represents your distance from the center of the earth" is a generalization, which does not hold true for us.
Earth is not uniform in density but changes in density with topography. With this, gravity is a local affect, with center of gravity changing from position to position. So if you reached 5000'ASL by standing on a rocky mountain, gravity would likely be a little higher there, due to higher density of the mountain, even while further from Earth's center.
A gyro stabilized platform, which normally points to near center of Earth, will tilt toward a mountain as you pass by it.

Since it's tiny and we have no way to practically measure it while hunting, we dismiss the variance.

 

[RTK]

Are you talking about how the plane flys or how the engine runs in that thin air? Thanks

It affects both, Less molecules in the air to interact with in "High Density altitude".
You would think something with a High Density is more dense than something with low density, not true in this case.

 

[Mikecr]

It's not high density, but high altitude density (per standard conditions for altitude). Or another way to see it: (High) Density-Altitude.
Again, all of the confusion with it validates my assertion that DA holds little to no value in ballistics.
That's one matter

The other bigger matter is that DA is based on standard conditions per altitude, and it would be extremely rare for conditions (wherever you stand) to actually be at standard conditions. This means your conditions must be measured to know your DA (as calculated). But if you're measuring, it's logical to just enter what you measure in ballistic software (without extraneous calcs).
After all, if you don't understand this stuff, you will screw it up.

 

[RTK]

DA in aviation is pressure altitude corrected for "non standard conditions".

For our needs just use pressure, temp and if wanted humidity. Use a chart or some other electronic means to figure out.
Most newer electronic range finders will figure all that out along with shooting angle.

 

[parshal]

DA in aviation is pressure altitude corrected for "non standard conditions".

And that's important! Some of the mountain airports here in Colorado have density altitudes over 11K which makes it quite difficult for a little Cessna to get enough lift without a very long runway.

 

[cantfixstupid]

And that's important! Some of the mountain airports here in Colorado have density altitudes over 11K which makes it quite difficult for a little Cessna to get enough lift without a very long runway.

That situation can be pretty hairy, I got the tee shirt

 

[RTK]

Us sea level dwellers don't have that problem Although I am very conscious of it when flying to Tahoe.

 

[Mikecr]

DA in aviation is pressure altitude corrected for "non standard conditions".

Yes DA and PA are equal under standard conditions for altitude. And since standard conditions couldn't ever be relied on, the separate parameters must be measured -> for ballistics.

Those measured parameters can be used to calculate DA, but inside ballistic software, the individual parameters are better taken for their separate contributions to drag calcs & lookups. This, rather than forcing the software to rely solely on air density as a general term.
For instance, temperature and relative humidity affect Mach, and every lookup on a drag table is w/resp to Mach#. This individual attribute is independent of air density itself. So if you force software to set temperature based on DA, the Mach#s/Drag will be wrong all the way.
It won't affect a local G7 BC much, but it is another inaccuracy added.

 

[TXTrained]

This statement here: "Gravity is proportional to your elevation. It is decreasing as you move away from the center of the earth. The force of gravity is reduced by 1/R^2 where R represents your distance from the center of the earth" is a generalization, which does not hold true for us.
Earth is not uniform in density but changes in density with topography. With this, gravity is a local affect, with center of gravity changing from position to position. So if you reached 5000'ASL by standing on a rocky mountain, gravity would likely be a little higher there, due to higher density of the mountain, even while further from Earth's center.
A gyro stabilized platform, which normally points to near center of Earth, will tilt toward a mountain as you pass by it.

Since it's tiny and we have no way to practically measure it while hunting, we dismiss the variance.

Well said and explained.Thanks

 

[TXTrained]

It's not high density, but high altitude density (per standard conditions for altitude). Or another way to see it: (High) Density-Altitude.
Again, all of the confusion with it validates my assertion that DA holds little to no value in ballistics.
That's one matter

The other bigger matter is that DA is based on standard conditions per altitude, and it would be extremely rare for conditions (wherever you stand) to actually be at standard conditions. This means your conditions must be measured to know your DA (as calculated). But if you're measuring, it's logical to just enter what you measure in ballistic software (without extraneous calcs).
After all, if you don't understand this stuff, you will screw it up.

This stuff is confusing and way over my pay grade...lol

 

[VICTORNTN]

Has anyone figured "air density" like pilots use?

 

[Mikecr]

You want to reference an industry that actually loses their most hi-tech commercial planes. They lose them!
Hey OnStar, where is MH370?

 

[VICTORNTN]

Because they lost a few planes doesn't mean the science that keeps them up there is bad or flawed.