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Interactive ET & MPH Correction Program

ET and MPH Environmental Correction By Bowling

The purpose of this program is to correct quarter-mile Elapsed Time (ET) and Miles-per-Hour (MPH) to Standard Conditions. This is useful in comparing ET/MPH values obtained at different environmental conditions, and for predicting what a car will run at a given environment. The inputs are temperature in degrees F, barometric pressure in inches of mercury, and percent relative humidity, as well as the measured ET and MPH.

To use this program as a predictor for dial-in times at the track, simply correct a run to standard conditions, using the "Correct To Standard" option, and record these values. Next, enter these new values into the ET/MPH inputs, set the environmental variables to the new "environment", choose the "Correct To Environment" option, and hit compute.


Input the 1/4 Mile Elapsed Time (ET) in seconds:

Input the 1/4 Mile Miles-Per-Hour (MPH):

Environmental Conditions:

Carburetor Air Temperature in degrees F:

Test Condition Barometric Pressure (Inches Hg):

Test Condition Percent Relative Humidity:

Want to Compute:

Press this button to submit a computation: .

To reset the form input: .


Algorithm:

The general equations for this calculation are the following:
cfet = 0.9986 + 0.0095 * (CorrBaro - 29.1) - 0.0002556*(Temp - 35.0)
cfmph = 1.0003525 - 0.00975 * (CorrBaro - 29.1) + 0.0002667*(Temp - 35.0)

For Correction TO Standard:
    Et = EtOld * cfet
    Mph = MphOld * cfmph

For Correction FROM Standard:
    Et = EtOld / cfet
    Mph = MphOld / cfmph

These equations were obtained from a empirically-derived correction chart, which was fitted to the above form (least-squares).

Special "thanks" to Eric Thaxton (thaxton@ksccdun6.ksc.nasa.gov) for straighteni ng out the nomenclature errors on this page!

More special "thanks to Eric Thaxton (again) for finding a sign error in the MPH correction.


Bruce Bowling
bowling@cebaf.gov
Bowling Superior