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THE PREZ SEZ
Hi
everyone
August is here and finally the
monsoons have arrived. The swimming hole at the end of my drive is full
again and the mud flaps on my truck finally have something to do. Of
course along with the rain, the weeds out at the field will be in full
bloom so expect a field work day soon. Hopefully we can get a little
help from the city.
For those of you who missed the
July meeting here's a quick recap of events
Runway resurfacing has been
postponed until after monsoon season, Yes this is an old story but the
product they are going to use is put down wet and has to dry so it makes
some sense to me.
Tom Fenn (Treasurer) gave a
presentation concerning the state of our finances and gave the opinion
that we should be saving for the future. After lengthy discussion it was
decided to put a lump some of money into a separate savings account and
add to it each year from the general funds. Along with this plan it was
also decided that the club would not pay for this years Christmas party
and we are looking into alternative ideas for funding it.
We will be holding another fun fly
this fall. It will be an unsanctioned event due to the lack of time
needed for AMA paperwork. The event is tentatively scheduled for
October. Bill Hermes will be running things and we should have a firm
date at the next meeting.
This months article comes from the
Pine Barren Modelers, Barnegat, New Jersey but I think it also applies
to the Mesquite Modelers, Sierra Vista, Arizona.
Mick
Water Can Be Dangerous
By Bill Bowne
Water is wonderful stuff. Without it,
we wouldn’t have life as we know it. But, water can be dangerous too.
Oh, I’m not talking about drowning in it, I’m talking about what happens
when water evaporates and recondenses in midair. I’m talking about what
can lead to thunderstorms and lightning.
You see, water is great at absorbing
heat. That’s why it takes so long to boil water. Water stores a lot of
heat in it when it is evaporated. When water evaporates, it turns into a
gas, making the parcel of air it’s in moister. To turn it back into
water, all you need to do is cool that parcel of air, either by
expanding it or by moving it to where the temperature is less. The
easiest way to do both is by lifting the parcel of air to a higher
altitude, where the temperature and pressure are lower.
There are several ways to start the
moist air on its upward trek. It can be forced upwards by an advancing
cold front, by being blown against a hill (like the hill our site is on)
or by being heated by the sun until it expands and rises like a balloon.
The first is more common in spring and fall, whilst the latter two are
more common in the summertime.
When some of the water in the air cools
enough return to a liquid state, it releases the heat that had
evaporated it, warming the air around it. If the air surrounding that
parcel of air is cooler than the parcel, the parcel will keep rising,
expanding, and cooling, and water will keep condensing and warming the
air. Eventually, the parcel will either run out of water vapor or else
it’ll reach a level where it’s no longer warmer than the surrounding
air. If the parcel tops out shortly after condensation starts, then we
get some nice, puffy cumulus clouds. Those are the little cotton balls
that often show up in the middle of a summer’s day. But, if the parcel
keeps growing and is joined by other parcels, eventually the moisture
that has condensed will grow until droplets form.
Those droplets can then combine and
grow until they become too heavy for the rising air to keep them up. So,
they fall as raindrops.
That’s still not too bad. We need rain.
Without it, balsa wouldn’t grow, and where would the hobby be without
balsa (You foamy fliers, just be quiet!)? It isn’t much fun to fly in
rain, but we can put up with some light showers. The problems start when
the rising parcels get high enough to form ice crystals. You can tell
that’s happening when the puffy cloud starts to spread out and form a
classic anvil shape. When the ice crystals form, the cloud starts to
develop areas of different electrical charge (Exactly how is still a
mystery argued over by a multitude of meteorologists and their grad
students). This is when we start seeing flashes within the clouds, as
charges try to equalize each other within the cloud.
Meanwhile, as the electrical charges
grow in the cloud, a similar (but opposite) charge starts to form in
sort of a “shadow” on the ground below. That “shadow” will follow the
cloud as the cloud drifts along.
The big problems start when the charges
in the cloud and the “shadow” on the ground start reaching feelers
towards each other. You see, air is a wonderful insulator, so it takes a
strong charge difference between the cloud and the ground before the air
separating the two charges can be bridged. So, when the bridge is made,
the spark is a big, powerful flood of electricity, not a little seepage.
That’s the big spark of cloud to ground lightning. The lightning stroke
can travel miles through the air to find an opposite charge. It can
strike, literally, miles away from the nearest storm and can hit in
areas where the rain hasn’t even started or has already ended.
Now it gets personal. Lightning isn’t
malicious, it just wants to seek ground; the source of the opposite
charge. If something like a guy flying a model airplane just happens to
be in the way, that’s just too bad for the guy. Hey, when you drive down
the Turnpike, do you seek out the butterfly that innocently passes in
front of you? Heck, no, but it’s still kind of fatal for the butterfly
to be in your way.
To make it worse, the “shadow” charge
will try to climb the tallest conductor it can find, so it can get
closer to the bottom of the cloud charge. And, if the tallest object is
a person holding an R/C transmitter with a 3-foot whip antenna, oh well.
So, what can we do to be safe during
thunderstorm season?
1) If you can hear thunder, land
immediately and take cover, even if the cloud is no longer overhead.
People have been hit by lightning from clouds that were over 5 miles
away. So, just because the storm seems to have passed, don’t consider it
to be time to go back up. Wait until you’re sure it’s over.
2) Remember, our particular field is on
a hilltop, so it’s closer to the cloud base and will attract more
lightning strikes than the surrounding lowlands. Remember, too, that the
trees at our site are not very tall, so anyone standing on the field is
a much more attractive target.
3) Lightning is not like a laser-guided
bomb. It’s more of area weapon. If it were to strike our flagpole, for
example, the “bloom” from it would still have the ability to kill or
injure everyone within several dozen yards of the pole. So, don’t expect
the flagpole to protect you.
4) What if you see showers, but haven’t
heard any thunder? There does have to be a first rumble, and others
could be hearing it as you are being hit. So, if you feel your hair
standing on end or you feel a “prickly” sensation, you are feeling that
charge “shadow” move over you. You may be within seconds of being hit!
Either hit the ground or dive into your car immediately. Don’t take the
time to clean off your plane, etc., as you may not have that much time
left.
5) The speed of light is so fast as to
be almost instantaneous for us. But, the speed of sound is about 1100
feet per second at sea level. So, if you see a flash and hear the rumble
about 5 seconds later, you can assume the stroke was about a mile away.
What you have to ask yourself is “Am I sure that rumble was the sound
from that flash?” and “Was the rumble from the near end of the flash or
from the far end?” If in doubt, err on the side of caution – No model
airplane is worth dying for!
MEETING
The next meeting of the
MMRCC is scheduled for August 2, 2007 at 7:00 P.M. The meeting will be
held at the Northrop Grumman facility. Personnel are required to sign-in
and sign out for security purposes.
See you at
the meeting……………….Will
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