Corrected Times / Density Altitude

[red]

Can we add fields that can be used to calculate the density altitude? For example: either 1) separate elevation, temperature, humidity, pressure, and dew point fields, or 2) track (already there), date, and time, which can be used to lookup the weather information. Concerning the latter, I know there was talk of requiring timeslips, but some tracks do not print the dates, sometimes the dates are incorrect, and other times the track info gets cut out. The point is to determine where we stand using times corrected according to sealevel--the NHRA standard. So, would it also be possible to have a calculated field that computes the corrected time and speed using this information?

[red]

If you're interested in how DA is calculated, you can read this:

http://wahiduddin.net/calc/density_altitude.htm

Or, simply use one of these calculators:

http://wahiduddin.net/calc/calc_da.htm
http://wahiduddin.net/calc/calc_da_rh.htm
http://wahiduddin.net/calc/calc_da_em.htm

You can lookup your weather data here:
http://data.nssl.noaa.gov/
http://www.wunderground.com/

And you can use the correction factors here:
http://www.smokemup.com/auto_math/nhra_correction_factors.php

And, here is information from the NHRA (NOTE: turbo/super-charged cars use half factors):
http://www.nhra.com/tech_specs/altitude.html

Alternatively, using the weather data and your timeslip, you can use the calculator here:
http://www.modulardepot.com/density.php

[red]

I used the following parameters (SELV;TMPF;ALTI;DWPF;RELH) to get the weather numbers for my current best run of 13.551@99.85:
Elevation = 9 feet
Temp = 71.96° Fahrenheit
Altimeter = 29.87 inches Hg
Dew Point = 64.94° Fahrenheit
Relative Humidity = 78.57% The results:
Density Altitude: 1178 feet
Absolute Pressure: 29.86 inches Hg
Relative Density: 96.6%
Using the correction factors for an altitude of ~1200 feet (.9874 ET and 1.0129 MPH):
ET: 13.551 * .9874 = 13.380
MPH: 99.85 * 1.0129 = 101.14

[sailsmen]

Threads contain 411;
http://www.mercurymarauder.net/forums/showthread.php?t=36816

http://www.mercurymarauder.net/forums/showthread.php?t=39502

http://www.mercurymarauder.net/forums/showthread.php?t=6409&highlight=density+altitude

[red]

Thanks, Sailsmen. Using the Modular Depot calculator (http://www.modulardepot.com/density.php), the corrected is 13.38@101.11, only a slight change in MPH from the table method.

[red]

Mary, any chance of getting an automatically-calculated, corrected ET/MPH field added to the timeslips page? I can provide the formula.

[MM03MOK]

Mary, any chance of getting an automatically-calculated, corrected ET/MPH field added to the timeslips page? I can provide the formula.
Honestly? We have trouble getting people to add their timeslips and there's are software issues with linking timeslips. The hack is no longer supported by the author.

[red]

Honestly?
Yes. I wouldn't have asked otherwise.

We have trouble getting people to add their timeslips and there's are software issues with linking timeslips. The hack is no longer supported by the author.
As I'm not a licensed vBulletin member, I do not have access to the vB Timeslip Database hack (i.e., plugin). If there's interest and I can get access to the source, I can see how much would be involved in calculating this on the fly--not ideal, but doesn't require database modifications. If there's no interest, I won't bother and people can just use the links in this thread to do it themselves.

[ctrlraven]

I'd be curious to see what my corrected numbers are but all those formulas just confuse me lol.

[red]

I'd be curious to see what my corrected numbers are but all those formulas just confuse me lol.
If you give me the time of day for each of your runs, I can do the calculations for you. If there's a lot of interest, I might write a calculator.

[red]

I'd be curious to see what my corrected numbers are but all those formulas just confuse me lol.
I'm going to assume that your run was around 3:00pm. From Weather Underground (http://www.wunderground.com/) site and using the observations from Crofton, MD for March 30th (http://wundersearch.com/weatherstation/WXDailyHistory.asp?ID=MC7344&month=3&day=30&year=2008), the following readings were obtained:
Temp = 51.0 degrees Fahrenheit
Altimeter = 30.63 inches Hg
Dew Point = 28.0 degrees Fahrenheit
Relative Humidity = 41%
The track elevation for Capitol Raceway is 41 feet.

The results using the DA calculator (http://wahiduddin.net/calc/calc_da.htm):
Density Altitude: -1221 feet
Absolute Pressure: 30.585 inches Hg
Relative Density: 103.62%
This means your conditions were better than NHRA standard of sea level, and your corrected ET/MPH according to the Modular Depot calculator (http://www.modulardepot.com/density.php) is:
13.88 @ 98.63

[ctrlraven]

Boooo I like my 13.72 a lot better lol.

Thanks for doing that.

[chader]

so is this saying a s/c'd car is affected the same way a n/a car is at lower elavation and v/v??

[Glenn]

Unreal - it looks like I should jump 2-3 positions on the Timeslips page. I'm right behind Mark at 11.80. Let me calculate it again. If I include the dry air I could deduct another -0.05 sec. Hmmmm - !!! Mary - we need to look into this!!

Glenn :burnout:

[chader]

an elavation corrected time slip page would be awsome

[red]

so is this saying a s/c'd car is affected the same way a n/a car is at lower elavation and v/v??

No, the NHRA uses half factors for forced induction cars (i.e., super/turbo-charged). See here (http://www.nhra.com/tech_specs/altitude.html). I'll add this clarification above.