Density Altitude Discussion

[BurnTire]

I had a discussion today about Density Altitude with a person who will remain unnamed, but he does referrer to me as a bush diver I mean bus driver.

Being I have a little knowledge of the subject due my career I will share some of my knowledge.

Lets Define the Subject.

Density altitude is the altitude in the International Standard Atmosphere at which the air density would be equal to the actual air density at the place of observation. "Density Altitude" is the pressure altitude adjusted for non-standard temperature.
Well I am sure that makes no sense to most.
Put into simple terms.
Phoenix has a 1200 MSL altitude (1200 feet above sea level)
Standard atmosphere is 59 degrees F and 29.92 inches or ( 15 C and 1013 MB) This is at sea level.
So basically DA well tell you what your altitude performance gain or loss is based on atmospheric conditions.
If it is really hot and humid with low pressure a car in Phoenix may have a 5000 ft DA. (reduced performance)
If it is really cold, dry, and high pressure you may have a 0 DA (sea level performance)

DA Calc.
http://wahiduddin.net/calc/calc_da.htm

Engines Tuner Calculator
http://wahiduddin.net/calc/calc_hp_dp.htm

Below is some results using the DA Calculator.

Change Air temp, Alt, Dew point one at a time to see how each affect DA.

Dew Point is the temperature the air must be cooled to to become 100% saturated. When the temperature and dew point are the same number the humidity is 100%.

High pressure is usually in the 30.10-30.20 range.
I have seen lows in the 29.60-29.70 range.

Take a sea level track 0 feet elevation on a humid low pressure day
90 Degrees
29.70 alt
85 dew point humid
DA is 2744


Take Phoenix at 1200 ft elevation on a dry high pressure day.
90 degrees
30.20
0 dew point
DA 3138
That is real close to the sea level track DA wise with the same temperature.
Say it was a little cooler like 80 in PHX the DA would be 2523 which beats the sea level track.

Take phoenix on a 45 degree winter night.
30.20 altimeter
10 dew point
DA is -45 (Nice if the damn track would hook)


But all being relative the sea level track is the best place to race with a good atmosphere, but in the winter in PHX we have some good conditions also.


Hope This Helps.

Jeff

[fazm]

the lowest DA ive ever raced at here in phoenix was 900DA. ive seen DA about -1200 before (when we hit 17 degrees this past winter) but never when itd be time to hit the track. average DA is closer to 3000 when im racing.

ive seen a couple of calculators online that convert DA to sealevel DA for a timeslip correction, as well as autolooking up what your DA was at a certain time and track.

[Lucafu1]

bush driver, LMAO!

[MinGry03]

Holly Crap.....After reading that, I need to go back to school just to understand....

[Indy]

BurnTire, you mean to tell me that you two actually had a civilized conversation.


Anyway thats some good info.

[BurnTire]

the lowest DA ive ever raced at here in phoenix was 900DA. ive seen DA about -1200 before (when we hit 17 degrees this past winter) but never when itd be time to hit the track. average DA is closer to 3000 when im racing.

ive seen a couple of calculators online that convert DA to sealevel DA for a timeslip correction, as well as autolooking up what your DA was at a certain time and track.

17 Degrees. I missed that day. LOL
-1200 that is some damn good air for the phoenix.

[BurnTire]

BurnTire, you mean to tell me that you two actually had a civilized conversation.


Anyway thats some good info.

I didn't list who I talked to. Oh the bus driver must have gave it away.

[fazm]

17 Degrees. I missed that day. LOL
-1200 that is some damn good air for the phoenix.

january 12th? 21st? somin like that, we got snow in maricopa lol

[The Nunn's]

I didn't list who I talked to. Oh the bus driver must have gave it away.

My crystal ball told me who you talked to. (posted by Indy, f'n shop computer I didn't check to see who it logged in under.)

[BurnTire]

My crystal ball told me who you talked to. (posted by Indy, f'n shop computer I didn't check to see who it logged in under.)

LOL. I never know who is behind the screen name.