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ZL3AI > APRDIG 21.02.04 17:39l 253 Lines 9931 Bytes #999 (0) @ WW
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From: ZL3AI@ZL3VML.#80.NZL.OC
To : APRDIG@WW
Subject: Re: Tetroon construction?
From: "Robert Bruninga" <bruninga@usna.edu>
Date: Thu, 19 Feb 2004 09:25:49 -0500
X-Message-Number: 7
I was suprised by the photos that the balloon was clear. Wasnt this a
solar-thermal balloon? I asumed that there would be some "black" somewhere
inside to absorb the solar heat? Maybe black smoke?
Bob
>>>Jeff King <jeff@aerodata.net> 2/18/04 8:12:03 PM >>>
I'm trying to figure out how to build one of these, and this is what I have
found so far:
http://tetroon.hypermart.net/
http://tetroon.hypermart.net/TOM.html
http://www.deering.org/balloon/tetroon.xls
And from these I can see the tetroon is 4 equilateral triangles.
Now, these can be placed together to form a parallelogram.
And then by dividing the parallelogram back into 4 equilateral triangles,
it can be folded to make a tetroon, and only three sides need to be joined.
The rest are continuous material.
Looking at the hardware store, I see something call "painter's plastic"
which comes in 12' x 400' rolls:
http://paint-and-supplies.aubuchonhardware.com/tape_and_drop_cloths/drop_cloth
s/high-density_painter's_plastic-788669.asp
So, one $19 roll would make ~11 11.2' high tetroon's.
Anyone have any thoughts on a lightweight tape that could be used to join
this thin plastic and any other thoughts?
--
Jeff King, jeff@aerodata.net on 02/18/2004
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Subject: Re: Tetroon construction?
From: "Rochte, Robert" <rrochte@gpacademy.org>
Date: Thu, 19 Feb 2004 09:46:19 -0500
X-Message-Number: 8
>I was suprised by the photos that the balloon was clear.
>Wasnt this a solar-thermal balloon?
As long as the heat lost through convection and radiation is less than what
is gained by insolation, the interior will heat up. At altitude, convective
losses are minimized, so radiative losses are the biggest concern. Thus, a
metallized film will actually work best - no matter how counter-intuitive
this may seem!
-R
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Subject: Re: Tetroon construction?
From: "Robert Bruninga" <bruninga@usna.edu>
Date: Thu, 19 Feb 2004 09:57:48 -0500
X-Message-Number: 9
Wow, so it is only clear plastic and warm air... Hummh... Has anyone
considered using black smoke inside to improve the solar heat gain?
Bob
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Subject: Re: Tetroon construction?
From: "Rochte, Robert" <rrochte@gpacademy.org>
Date: Thu, 19 Feb 2004 09:59:13 -0500
X-Message-Number: 10
>Wow, so it is only clear plastic and warm air... Hummh...
>Has anyone considered using black smoke inside
>to improve the solar heat gain?
>
>Bob
Just remember that black is also a good emitter - that's why a translucent
solar Montgolfier will outperform a black one (note that my earliest SMs,
like the Spirit of Piccard, were black)... And why an aluminized one will
outperform the translucent variety...
-R
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Subject: Re: Tetroon construction?
From: David VanHorn <dvanhorn@cedar.net>
Date: Thu, 19 Feb 2004 10:06:49 -0500
X-Message-Number: 11
At 09:25 AM 2/19/2004 -0500, Robert Bruninga wrote:
>I was suprised by the photos that the balloon was clear.
>Wasnt this a solar-thermal balloon? I asumed that
>there would be some "black" somewhere inside to
>absorb the solar heat? Maybe black smoke?
It doesn't take much.
I suspect the material is pretty much opaque in the 10 micron band, which
is where the heat is. Visible light pours in, and heats up the air, and
the skin. The energy is re-radiated inside the envelope, but can't escape
easily.
As long as you have more input than output, you heat up, till the losses
equal the input.
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Subject: Re: Tetroon construction?
From: David VanHorn <dvanhorn@cedar.net>
Date: Thu, 19 Feb 2004 10:10:40 -0500
X-Message-Number: 12
At 09:57 AM 2/19/2004 -0500, Robert Bruninga wrote:
>Wow, so it is only clear plastic and warm air... Hummh...
>Has anyone considered using black smoke inside
>to improve the solar heat gain?
If you could keep the black stuff suspended in the active part of the
balloon, then it would probably work. Making the envelope itself black,
would increase the loss. Heat sinks are black for a reason.
Wether you'd get enough gain to make a profit, I don't know. On this scale,
electrostatics are powerful forces. I think you'd end up with your smoke
stuck to the inside of the envelope.
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Subject: Re: Tetroon construction?
From: "Rochte, Robert" <rrochte@gpacademy.org>
Date: Thu, 19 Feb 2004 10:07:42 -0500
X-Message-Number: 13
>I recall reading that aluminum is very reflective at a wide
>range of wavelengths, but cannot emit much infrared. Supposedly,
>this is why we wrap potatoes in aluminum foil before tossing them
>into the oven.
>
>I guess this is what Robert is referring to?
>
>Paul
Basically, yes. It is simply a matter of the balance between emissivity and
absorptivity of the material.
Take three pieces of aluminum stock and paint one white, one black and leave
the third bare but bring it to a high polish. Put all three in the sun and
see which one gets hottest.
And again, keep in mind that convective losses are minimized at altitude
(forced convection on the way up is another issue, but doesn't figure into
this simple explanation)...
-R
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Subject: Re: Amperage rating of cigarette ligher plug
From: Adi Linden <adil@adis.on.ca>
Date: Thu, 19 Feb 2004 10:30:20 -0600 (CST)
X-Message-Number: 14
>I thought at that time, the idea was to put another battery at the back
>-in this case it could be charged from the cigarette lighter connection
>-7amps ought to be more than enough.
Putting a small gel cell in the back might work. It could be run off a
charging/isolating circuit. Since the charging circuit limits current off
the vehicle this could safely run from the cigarette lighter plug.
My voice FT-1500 has been installed properly. Wiring through the firewall
directly to the battery. Works like a charm. Finding a hole to get to the
engine compartment was a challenge. I didn;t want to add my own holes and
what I found comfortable fit the two 12 gauge power wires and the RG-58
antenna lead, no room for anything else.
This new radio is for APRS only. So transmit will be low duty cycle and of
short duration. I think the gel cell solution might just work and it is a
good way to automatically disconnect the radio from the vehicle battery
without running a relay from the ignition. Now I just need to dream up a
circuit to do this...
BTW, the vehicle is a lease. Not sure if I am buying it or if it is going
back the deal in Oct 2005. For the little time left I'd much rather have
scratches on the roof then holes to explain.
Adi
--
Adi Linden | va3adi | va3adi@adis.ca | http://adis.ca
+-----------------------------------------------------------------+
IRLP Node 2590 in Sioux Lookout, Ontario
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Subject: Re: Amperage rating of cigarette lighter plug
From: blitz <blitz@macronet.net>
Date: Thu, 19 Feb 2004 11:54:48 -0500
X-Message-Number: 15
I might caution users about gell cells as Ive done before. Gell cells are
for long term low current draws, and any attempt at drawing a large amount
of current, even for a short period of time is futile. Due to their gelatin
electrolyte, they charge slow and discharge show, this is due to an
electron mobility problem caused by the gelatin electrolyte. (The price we
pay to be spill-proof) They are designed for burglar alarms and standby
power sources where current draws are fairly constant. Utilizing them for
high current applications like PTT high power will result in excessive
terminal voltage drop, mimicking a bad cell when the cell is perfectly
fine. Connecting one in parallel with a car's charging system without
adequate fusing and isolation is asking for a fire or possible explosion if
the gel cell shorts out. Be advised, they will. Having used both gel packs
and motorcycle batteries extensively for backup power for electronic
devices in cars, you also want to limit charging current to a motorcycle
battery to around 1-5 amps depending on the battery rating. Overcharging
will result in sulphation, stink, expulsion of electrolyte (acid) from
vents and the possibility of warping the plates and causing damage ranging
from a bad battery to an explosion. Use care, read manufacturers ratings
and always fuse. A shorted battery of any type from gell cell to motorcycle
can produce sufficient current to start fires, especially in small gauge wire.
In the setup you describe, do you see any strange resets of the TNC?
Especially during starting?
I would imagine you would, without any isolation of the smaller cell from
the car's electrical system.
Be cautioned that small voltage drop in that smaller wire feeding is quite
capable of starting a fire under certain circumstances. I dont want to
sound too alarmist, but Ive seen a $100,000 motor home go up in flames from
stupid stuff like this. For any standby power like you describe, I'd use a
DC to DC converter to keep the secondary battery charged. They have the
added advantage of having a small voltage boost, so the charge output can
be a little higher voltage so battery maximum capacity can be achieved.
When you use a diode in series, you automatically loose that advantage, as
charge voltage will always be .7v lower than alternator output.
Marc
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