In a message dated 12/29/2001 8:32:01 AM Pacific Standard Time,
speedtimer@charter.net writes:
> Henry & list
> SCTA has been using the Davis weather station for several years but the
> primary use has been for wind speed and direction. We have been discussing a
> new system to add to the computer base and would be included in the run
> print out for each vehicle.
>
> All of us feel this would be an asset to the racer. I will be talking to the
> computer engineers after the first of the year to get this moving and
> hopefully on line by the first lakes meet in May 2002.
>
Glen,
That would be a great help. Even though ERC has their weather board
updated a couple of times during the day and we tow past it on every run,
having the density altitude (commonly called the equivalent altitude or
corrected altitude) printed on the timing tag would really help.
I've found that there are basically two density altitudes that are
revelant to our operation, a. the early morning figure during record runs,
and b. the "high-noon" figure when most of the qualifying is done.
Given the injector correction constant of .003" pill size for every 1000
ft. variation in density altitude, our morning to mid-day correction was
usually between .010" and .005". This year at Speed Week I believe that the
AM density altitude was somewhere between 5000' and 6000' while the mid-day
reading was somewhere 7500' and 8500'. Don't hold me to those figures however.
We use a Jeb's hand-held performance calculator (no longer in business),
an old aircrafter altimeter that flunked FAA specs, a common household
thermometer, and a hardware store relative-humidity gauge. The calculator
also gives recommended pill or jet changes, giving us something to compare to
the figure I mentioned above.
The Jeb's calculator says that until the humidity gets above 80% it has
little effect on the tuneup. Maybe someone on the list could share their
experience on that one. The relative humidity I observed on my hardware store
gauge at Bonneville and El Mirage ran about 35% in the early morning to 15%
at mid-day.
If the Davis setup will give density altitude it would be a good
investment for the racer.
Unless a crew has a person to do the paperwork like calculate the density
altitude, log the tuneup specifics for a run, file the timing tag, etc. it's
quite often an hour after the run before all that gets written in the book.
With the density altitude on the timing slip the "ledger-person" could do it
at their leisure............Ardun Doug King
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