Thread: Effects of cartridge temp on velocity

Originally Posted by R93

Dont forget air pressure lapses with altitude as well at a given rate per 100ft.

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Yeah. That's what I am thinking. As the altitude increases the pressure decreases (because of reducing air density) but the temperature also decreases (increasing air density) but not necessarily at the same rate.
Please let a scientist clarify this before I talk myself into a hole.
In the example given, air will cool between 1.5 and 3 degrees /1000' of altitude (depending on it's saturation level), so a rise of 4000" altitude will equate to a temperature drop of between 6 and 12 degrees Celsius.

Originally Posted by Shearer

Yeah. That's what I am thinking. As the altitude increases the pressure decreases (because of reducing air density) but the temperature also decreases (increasing air density) but not necessarily at the same rate.
Please let a scientist clarify this before I talk myself into a hole.
In the example given, air will cool between 1.5 and 3 degrees /1000' of altitude, so a rise of 4000" altitude will equate to a temperature drop of between 6 and 12 degrees Celsius.

Ha Ha you did alright. I passed my met exam that was full of all that stuff a while ago. I can't remember we the formula as I just went off QNH or dialed my know altitude on the altimeter

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Originally Posted by Shearer

Yeah. That's what I am thinking. As the altitude increases the pressure decreases (because of reducing air density) but the temperature also decreases (increasing air density) but not necessarily at the same rate.
Please let a scientist clarify this before I talk myself into a hole.
In the example given, air will cool between 1.5 and 3 degrees /1000' of altitude, so a rise of 4000" altitude will equate to a temperature drop of between 6 and 12 degrees Celsius.

The main thing, I think, is that the lower temperature reduces MV. This largely offsets the lower pressure/air density so the trajectory is much the same.