Weather Stations 101

Welcome to Weather Stations 101.
Have you ever wondered what a drag racing weather station does, how it works and how it can help you go more rounds? Well, read on...

So how can a Weather Station help me?
We all want to go a few rounds right? Maybe even take out a final at a bracket meeting? What about a gold Christmas tree, how cool would that be!

In order to achieve any of these goals you need to know what you will run as the weather changes. And that's exactly what a weather station will help you do…

Every drag racing weather station basically works like this:

1. It samples and displays the current weather conditions.
2. It allows you to record your runs from your time slip along with the weather conditions at the time of the run.
3. It predicts your ET based upon the current weather conditions and your previously recorded runs.

For this article we will be using the Altronics PerformAIRE Eclipse Weather Station to illustrate examples.

Sampling and Displaying the Current Weather Conditions
The most common weather conditions sampled are:

• Temperature - in degrees Fahrenheit.
• Barometric Pressure - in inches of mercury, inHg.
• Relative Humidity - as a percentage.

These three values are combined to calculate density altitude, or DA (the actual calculation is complicated and beyond the scope of this article). Density altitude is a theoretical figure, calculated in feet, and used to illustrate changes in the weather conditions. For example, a temperature of 73.5ºF, relative humidity of 68.9% and a barometric pressure of 29.97" equates to a density altitude of approximately 1693 FT.

As a general rule, the higher the DA the slower your ET:

• Temperature increase = DA increase
• Barometric pressure decrease = DA increase
• Humidity increase = DA increase

To sample the current weather conditions on the Eclipse you press the '1' button from the main menu. The internal fan draws air across the sensors and displays the information as seen in this screen shot. The figures are 1 - temperature, 2 - barometric pressure and 3 - relative humidity.

Recording Your Runs
Now that you can see how the current weather conditions are sampled and displayed, the next step is to enter your runs into the weather station.

Each weather station can be configured to store runs from different tracks and for different vehicles, often referred to as databases. For example, the Eclipse weather station can have up to 10 databases and store 400 runs in total. Databases should be created using the following guidelines:

• A different database for each track you run at.
• A different database for each vehicle that you run.

For example, if you run two cars and race at WISD and Willowbank you would create 4 databases:

• WSID -Car 1
• WISD - Car 2
• Willowbank - Car 1
• Willowbank - Car 2

Most weather stations have the ability to hold the current weather conditions for use when entering a run. This is very important so you can get an accurate reading as close as possible to the time of your run. Often you will see crew members on the start line pressing buttons on a weather station - they are most likely holding the current conditions for entry once they get back to the pits.

Once you are back in the pits it is time to enter the run into the weather station. For the Eclipse, the values entered consist of the following:

• DA - current, held or manual. Here you enter the DA, either based on a current reading, a held reading (e.g. from the start line) or you can enter the figure manually.
• 1000' ET - Your 1000' ET from the time slip. This figure is normally entered for run completion analysis and will be discussed in a future article.
• ET - Your ET from the time slip.
• Wind Speed and Direction - Many weather stations can account for wind factors and their affect on your ET. This will be discussed in a future article.

This screen shot is of an entered run and includes the run number, date and time, ET, DA and the wind speed and direction (which were not entered for this example).

Garbage In = Garbage Out
When entering runs into the weather station it is important that they all make sense given the following guidelines:

• When DA goes up your ET should be slower.
• When DA goes down your ET should be faster.
  

So looking at these three runs, which one does not make sense?

• Run 1 - ET = 10.00, DA = 2000 FT
• Run 2 - ET = 10.05, DA = 3000 FT
• Run 3 - ET = 10.06, DA = 2800 FT

If you picked run 3 you would be correct. With a lower DA of 2800 FT, the run should have been quicker than run 2 with a DA of 3000. Leaving these 'bad' runs in the weather station will affect its ability to accurately predict your ET. In this instance you need to investigate why run 3 is slower. Did you turn the tyres off the start line, did the wind pickup or did you back-off before the finish line? Whatever the case may be, the run should be removed. Many weather stations provide a function to locate these 'bad' runs.

Predicting Your ET
Once you have entered a minimum number of runs (usually 3) the weather station will be ready to start predicting your ET. When you sample the current weather conditions, the weather station will now display an ET prediction.

This screen shot highlights 1 - the current DA, and 2 - the predicted ET. The predicted ET is what you base your dialin on.

With DA, ET predictions are based upon the runs you have already entered into the weather station and the current weather conditions. For example, you have entered the following 5 good runs into your WSID database:

• Run 1 - ET = 10.01, DA = 1010
• Run 2 - ET = 10.06, DA = 2237
• Run 3 - ET = 10.11, DA = 2567
• Run 4 - ET = 10.12, DA = 2870
• Run 5 - ET = 10.15, DA = 3602

With these values plotted on a graph you can see how as DA changes, ET changes in a predictable manner. Refer to the graph below.

Looking at the graph, the weather station will now be able to accurately predict what your ET will be as the DA changes. For example, if you were going out for first round of eliminations and the weather station displayed a DA of 2000 FT, the predicted ET would be approximately 10.064. So now, with this accurate prediction, you can go into eliminations confident you can run your number.

Golden Rules for Going Rounds
Here are some golden rules to make the most of your drag racing weather station:

• Make sure your vehicle is running consistently. For a weather station to be accurate your vehicle must run similar times at similar DAs.
• Once your vehicle is running consistently, STOP changing things. I know this is hard for some, but as the saying goes…"if it ain't broke don't fix it".
• Track conditions change from meeting to meeting, day to day and lane to lane. Be flexible and make allowances for these changes.
• Remove bad runs from your weather station. They will have a major effect on the accuracy of the predictions.
• Analyse your runs before you enter them into your weather station. Are they representative of the vehicles usual performance?
• Use different databases for each track and each vehicle.
• Do not leave your weather station in the blazing sun or on the wet grass. These environmental factors will influence the weather station readings.
• Use a log book to record data, whether it is pencil and paper or a lap top. This will help you learn more about your vehicle and how it responds to changing conditions. You will then be able to use the weather station combined with your own knowledge to make predictions.

Future Articles
In future articles we will be looking into the following:

• Different types of ET prediction methods including Oxygen Altitude (OA) and horsepower correction factor (HCF).
• Advanced topics - how wind speed and direction affect ET, run completion analysis and bad run analysis.