Abdullah

iTrader: (2)

can any one explain DA to me? and what is a positive DA and negative DA? i want some one to give me a feeling of the meaning of the DA.

thanks.

Mr. Luos

iTrader: (9)

DA = Density altitude.

Basicly it is a number that equates weather and altitude together to give you an idea of the conditions you are running in.
Last time I was out at Bandimere the DA was 7200 early in the day and even higher in the afternoon. The actual altitude of the track is 5800 feet.
But it was like being at 7200.
If that makes any sense.

cenTX-LS1

iTrader: (1)

Its a way of leveling the playing field and giving us a way to talk about track conditions in a comparable way. Given a fixed set of weather conditions the density of air is much higher at sea level that at higher altitudes. You can literally think of it as a column of air with the weight of all mollecules above it compacting those at the bottom. More o2 mollecules at sea level give you more power and better combustion. The fact that weather conditions aren't the same at all locations makes this a bit trickier. Higher temps cause mollecules to spread out making the DA actually higher than it is. Take HRP in Houston for example. It sits at about sea level so guys run amazing times there. On a hot humid day the DA at HRP can become higher than its actual elevation causing you to run worse because you are getting a "weaker" charge of air. This is why the DA was worse in the afternoon in the earlier post. On a cool morning with lower humidity in the fall the DA can actually dip into the negative range meaning that the conditions are very favorable for good times due to the low altitude of the track and fact that colder air is more dense. Hopefully this helped to explain the basics of DA. To find DA you need to know the current altitude, barometric pressure, and dewpoint. A calculator can be found here.

http://www.csgnetwork.com/densaltcalc.html

Lower is better.

Abdullah

iTrader: (2)

as i know as we go higher the density of the air becomes less and less and this is not good for horspower. so does that mean i have denser air at 1200 DA than at 5700 DA?

what about the negative DA does it mean it is below sea level and the air is denser than even at sea level? is that correct? or the densest air is at 0 DA.

thanks.

Abdullah

iTrader: (2)

thanks for the informative info. i was typing the 4th post while you post yours and didn't see your post except after i post mine. so i'm correct in my guessing. so even in negative DA you have denser air than in 0 DA?.

so the DA is like a mix of altitude, temp, pressure, humidity....etc measurments compacted in one number that gives idea of how dense the air is.

ratboy

Basically it's pressure altitude (combination of actual altitude and baro pressure)
corrected for temperature........

RaNsOm

iTrader: (2)

correct. 0 DA is the density of the air at Sea Level. a negative DA is air that is denser than sea level, hence why negative DA days like early spring and later fall are the best to race in.