# Density altitude and applied ballistics

1. Mar 17, 2011

### RS2G

Hello, I am struggling with understanding air temperatures effect on density altitude and it's effect on the flight of a bullet. I understand that as temp goes up air resistance/density goes down but in looking at a chart I have I can’t seem to make out a pattern in relation to temp.

It appears that at some points on the chart a 10deg change in temp makes a 500’ shift in elevation one way but 10deg shift in the opposite direction can be 1000’ shift.

How do altitude/barometric pressure relate with temp in overall air density? Is this shift I am seeing in the chart, is it related to how water vapor/humidity is acting in those temp/baro conditions?

Thanks in advance for helping an ex-army grunt understand…..

2. Mar 18, 2011

### nucleus

I don’t know what chart you are looking at, but density altitude depends on the air pressure, temperature and humidity. Decreased air pressure, increased temperatures and increased moisture reduce the density of the air. You can usually ignore moisture,

There are rules of thumb to determine density altitude, but the easiest way is to use an online calculator. You need to know you altitude and obtain the weather. For the calculator below you need air temperature, dew point temperature (for moisture), your pressure and elevation. Note: The calculator uses mb for pressure and your pressure may given in kPa.. To convert simply drop the decimal ie 102.0 kPa is 1020 mb.

http://www.pilotoutlook.com/calculators/density-altitude-calculator