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Weather math…

 
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Rascal
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Location: VA
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PostPosted: Mon May 03, 2004 5:26 pm    Post subject: Weather math… Reply with quote

Anybody have something in the way of math to “convert” weather conditions to an altitude…?…to then factor against sea level? Thanks…Rascal
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SMOKEmUP
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1979 Chevrolet Camaro

PostPosted: Mon May 03, 2004 6:02 pm    Post subject: Reply with quote

Check the automath. Timeslip corrections pages.

Link 1

Link 2
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bill jones
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PostPosted: Wed May 05, 2004 9:44 pm    Post subject: Reply with quote

-Rascal,,,Did you have something specific in mind?
-I lived at altitude all my life and I deal with it on a regular basis so I have several different ways of running the numbers.
-I checked the two links and I don't see answers to what I would be looking for but I have some empirical data that I could pass along if I knew a couple of examples of what you are up against.
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Rascal
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PostPosted: Wed May 05, 2004 10:06 pm    Post subject: Reply with quote

I've got a buddy I'm working with who's early passes were laid down in some wicked fast air this spring...and every improvement I have him make is hard to see as the air gets worse the closer we get to summer...to date he's "gone" 4-5 tenths faster but still hasn't bested his "slowest" ET...lol...if you know what I mean...
I don't have all the numbers with me here...so I'll have to post em some time tomorrow...but I believe I do have enough info since my original post to use Smoke's calculators...
Anyway my thought was to translate our early air to an altitude for a baseline and use the NHRA factors...then do the same each time he tests...
I'm pretty comfortable with what the car has done so far as I've been this stuff for a long time...but he's getting frustrated and I'd like to use some science to get an accurate view of what we've been doing...

Thanks!

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SMOKEmUP
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PostPosted: Wed May 05, 2004 10:22 pm    Post subject: Reply with quote

bill jones wrote:
I checked the two links and I don't see answers to what I would be looking for.

What are you looking for? Maybe I can cook one up.
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bill jones
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PostPosted: Wed May 05, 2004 11:51 pm    Post subject: Reply with quote

-I have studied air quite a bit diifferent than NHRA and the way most racers chase the numbers.
-I first leaned that a cubic foot of air weighed .0763694 pounds from a Holley book where that is based on 59.9 degrees F and zero percent humidity and 29.92 icnches of mercury.
-But I live at 4200 base elevation in Salt Lake City Utah where the humidity is seldom ever over 50% during the summer, and a lot of people live in high humiditys of 60 to 90% at low altitudes so they could care less.
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-The absolute air pressure is what I deal with and I see 25.80 inches of mercury as our normal so on a 59.9 degree day with zero perent humidity the weight of a single cubic foot of air is .0658533 pounds
-The formula is:
-example #1 is: 29.92" x 1.326, divided by, 59.9 degrees F plus 459.6, equals .0763694
-example #2 is: 25.80" x 1.326, divided by, 59.9 plus 459.6, equals .0658533 pounds per cubic foot of air.
------------------------------------------
-I deal with temperatures racing at Bonneville where we see at least 100 degrees f and 15% humidity (where I have to subtract .2895 inches of vapor pressure) and 26.00 inches of mercury at the starting line and 1.74 inches of ram air pressure at 220mph.
-so this example #3 goes like: 26.00 minus the vapor pressure of .2895 equals 25.71 inches of mercury, add the ram air pressure of 1.74 equals 27.45 inches of mercury at 220mph times 1.326, divided by, 100 degrees F + 459.6 equals .0650441 pounds per cubic foot of air that we have in the air box or hoodscoop to work with at 220MPH.
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-Now I know this has nothing to do with corrected altitude like you'd see on some weather station but weather stations don't usually measure the air pressure/temperature and humidity of the air inside the air box at speed.
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-I don't see any weather stations that measure in absolute pressures to altitudes much higher than about 4000 feet, and I've never seen one yet that gives you the weight of air per cubic foot (but then I haven't looked at very many either) and the vapor pressure loss from the humidity needs to be shown and factored in.
------------------------------------------------
-so if you take the answer from example #3 which is .0650441 and divide
it by .0763694 you get an answer that you have 85.17% less air to work with at 220 MPH than you have at sea level in perfectly still, cool, dry air.
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-If I wanted to enter the weight of one cubic foot of air then there should be a way to make it print out the altitude that would correspond with that and the % loss of density from a standard at sea level.
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-I doubt that very many racers have a clue as to what absolute air pressures really are unless they are turbocharger/EFI guys.

-This doesn't answer Rascals questions but the complexity of the entire deal is pretty overwhelming and the computer programs I have seen all miss several key points that are needed to get the EXACT answers.
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SMOKEmUP
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PostPosted: Thu May 06, 2004 12:10 pm    Post subject: Reply with quote

So if I understand you correctly.

You looking for temp, press, and humidity as inputs. Outputs would be air density and density as a percentage of std correction.
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bill jones
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PostPosted: Thu May 06, 2004 10:59 pm    Post subject: Reply with quote

-would anybody else be able to use it tho because how many people have a REAL barometer that measures in absolute pressure.
-Personally I'm only concerned the weight of a cubic foot of air and it's relationship back to the .073694 pounds per cubic foot of air that Holley and myself use.
-But along with that I am also concerned about the ram air pressures and higher altitudes than 4200, like we have active oval race tracks in Elko Nevada and in Rock Spring Wyoming that are 6500 elevation and dynos in similar elevations.
-I'd like to see a chart or a program that showed for example if the corrected elevation of a weather station showed the elevation to be 1920ft or 5544ft or whatever that the program or chart would include and show what the weight of a cubic foot of air is at that elevation and maybe even show the vapor pressure of the humidity if you entered the humidity.
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-When we run at Bonneville we get into wondering and try to figure out what is happening on the 400 mph cars as well so the ram air is a big deal.
-Another thing that I don't think most of these programs even consider is the frontal area or coefficient of drag of a car has a lot to do with the speed but then not many people even have an inking of a clue as to what their frontal area is or what the CF of drag is.
-An example is running at Bonneville with a slick transam body and a 370ci small block vs an old 49 Mercury flathead and each car having the choice of running at 40 degrees F in the morning vs 106 dgrees F in the afternoon, will both cars run faster in the cool morning or in the hot afternoon?
-I can speak from experience that the 49 Merc will ALWAYS run faster in the hot afternoon than in the cool morning but most small frontal area cars will always run faster in the cool air.
-------------------------------------------
-If anybody cares to speculate as to why and get a discussion going on it, I'll explain why the old Merc doesn't like the cold air.
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63IIPost
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Joined: 16 May 2006
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PostPosted: Wed May 17, 2006 10:48 am    Post subject: Reply with quote

Interesting topic. So the frontal area of that car is so much that denser (cold) air creates more drag, therby slowing it down?

I hear mixed opinions on DA calculators/et predictors. Im just learning about them now after a weekend of bad air, and after talking with some index class drag racers there seems to be some method to the madness, just trying to determine what works.
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mchat
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Joined: 02 Dec 2003
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PostPosted: Wed May 17, 2006 5:52 pm    Post subject: Reply with quote

smokemup wrote:
So if I understand you correctly.

You looking for temp, press, and humidity as inputs. Outputs would be air density and density as a percentage of std correction.


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

Question

Edit: Actually this one is better:

http://wahiduddin.net/calc/calc_hp_dp.htm
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63IIPost
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1963 Chevrolet Chevy II

PostPosted: Wed May 17, 2006 6:08 pm    Post subject: Reply with quote

has anyone yet to find all these handy formulas in an excel file someplace? I started making a log using excel, and I have recently added the DA calcs in to give me DA for each run.. Would be handy to have it show HCF and sea level corrected et for each run to just to track consistency as well. I know im outside the box a bit lol
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63IIPost
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1963 Chevrolet Chevy II

PostPosted: Wed May 17, 2006 11:16 pm    Post subject: Reply with quote

Also is there any way to analyse the air weight, to predict et changes as the air changes? Probably a loaded question but I dont see anyone else even considering air weight, only air density (dry pressure minus the vapor press), so many ways to skin one cat.
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