Weather station graph

[WRIGHTWAY]

IM trying to clear out some of the inconsistent runs from my tag
And create a graph based on E/T and density altitude
The manual from my tag showed how to do this but I lost it
Is there set increments for the d/a that work best
Any help appreciated



joe

[Warpspeed]

Pilots do this all the time Joe:

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

[David Redszus]

There is absolutely no reason to measure density altitude.

Air density alone, computed from temperature and barometric pressure is all that is needed. In some cases, relative humidity can also be factored in but its effects are typically very small.

If you would like a simple spreadsheet to calculate air density, viscosity, fuel correction, power correcton and water vapor content, send me your email address.

[Doug Schriefer]

David,

In some Drag Race applications (usually Methanol cars) the engine tune-ups and performance are linked very closely to the relative humidity in the air.

[David Redszus]

In some Drag Race applications (usually Methanol cars) the engine tune-ups and performance are linked very closely to the relative humidity in the air.

Agreed. In extreme humidity conditions (desert racing or winter racing vs racing in the tropics) the water vapor content of the air does indeed have a tuning effect. But it does not usually affect the mixture tuning; it does greatly affect the ignition timing that should be used.

Unprotected methanol is very subject to sucking up all available moisture. Now we have an azotrope for a fuel. Who the hell knows how to tune an azotrope?

[maxracesoftware]

Patrick Hale has just finished a Book

" Motorsports Standard Atmosphere and Weather Correction Methods "

its jammed pack full of equations and explanations

its around $40-45 dollars USD

here's my Saturation/Vapor Pressure Formula
i developed around 1990's , old QuickBASIC source code.

a few Companies are using it in their Weather Station
source code

its free for Public use , but i retain the Copyrights


This formula "mirrors" Smithsonian Meteorlogical Tables from -65 F to 212 F deg

which to me is more accurate Weather Data than ASHRAE org.




http://www.aprweather.com/pages/calc.htm

Meaux Saturation Pressure Curve Formula

dryr = (dry bulb temperature deg.F) + 459.67 <--conversion to Rankine

Psat = 29.9213 / (EXP((671.67 - dryr) * 35.913 * (dryr ^ -1.152437)))

[Dave Koehler]

Patricks book is good as Larry said. If it's of any help I have a few on hand.
http://www.koehlerinjection.com/Koehler ... eather.htm

[David Redszus]

A very brilliant engine builder made an observation recently that stuck in my craw.

He said, '"There is no such thing as corrected power, at the track or on the dyno, except for very, very small changes in operating enviornments."

His explanation is interesting.
When inlet temperature changes, along with inlet pressure, air density is not the only resulting change that is produced. Air viscosity also changes which will then change the Reynolds number, Mach number and flow co-efficients. In addition, changes in inlet temperature will necessitate a change in ignition timing. Fuel evaporation will also change with temperature. The net result is that neither air nor fuel will be the same, regardless of air density, and they will affect the combustion process.

Perhaps his explanation might help us understand why major engine programs use dyno cells that have the ability to fully condition the air in the cell; pressure, temperature and humidity. They don't use correction factors, they correct the air that the engine actually ingests.

[Doug Schriefer]

Perhaps his explanation might help us understand why major engine programs use dyno cells that have the ability to fully condition the air in the cell; pressure, temperature and humidity. They don't use correction factors, they correct the air that the engine actually ingests.

There are two main reasons for adjusting the air while testing (rather than use a correction).

1) For consistency. If you're testing in the same conditions you won't have to worry about how certain variables affect your specific combination when trying to do specific A/B/A testing.

2) And probably more important is that you can duplicate the air where you're racing to get more accurate feedback for the type of racing, and location of racing...

[maxracesoftware]

how are you controlling Barometric Pressure in the Dyno Room ?

[Doug Schriefer]

how are you controlling Barometric Pressure in the Dyno Room ?

Most of the Cup and some of the Top Pro-Stock teams are using DynoAir Systems right now.

They can control Temperature within .25°F, Humidity within +/- 1%, and pressure within .5 kpa according to their information.

[David Redszus]

Doug
Have you obtained any dyno data that compare measured engine performance in a conditioned cell, to corrected performance in a non-conditioned cell?

We know the errors are quite substantial but don't know exactly how far off the correction factors really are.

[Doug Schriefer]

Doug
Have you obtained any dyno data that compare measured engine performance in a conditioned cell, to corrected performance in a non-conditioned cell?

We know the errors are quite substantial but don't know exactly how far off the correction factors really are.

Yes, there are some big changes. The other thing is once you get to that level most of them are not using standard correction factors. Most dyno programs figure in frictional losses which are way more than what top of the line engines are producing today, so these guys will run their own programing at that point after running motoring dyno.

We've got to remember a dyno like any tool is only as good as the people using it. So just having everything weather wise be the same doesn't solve all of the problems that most people have with running an engine on them. I laugh when I get dyno sheets from customers that not only are running the engine in the same temperature range (oil, water, etc) as they race, but don't have the same temps from run to run. I know when I've done testing I've spent more time stabilizing before runs to eliminate variables, and analyzing data after the fact than the tests themselves.