[CRAPRS] Balloon

[Jerry Pasker]

I should clarify what I'm up to a little better.  A video is here: 
http://www.youtube.com/watch?v=6sb0_3MlNxc

I found only a few solar balloons that were combined with APRS payloads.

   http://www.arrl.org/news/stories/2004/03/03/103/?nc=1

I've done small ones with no payloads, and to see a half dozen 
garbage bags and a few dozen yards of scotch tape rise in to the sky 
under their own power is pretty damn sweet.  I can't explain it any 
other way.  McGyver would be proud.  Just unfold, let the wind 
inflate, and after about 5 minutes the sun heats it enough that it 
just lifts off.  As long as the bottom stays open, and there's enough 
weight attached to keep it from inverting when it ascends through 
wind sheers, cool air keeps entering the bottom and compensating for 
any leakage.  It's a self regulating, sustainable system.

It only gets lift from the sun heating the air inside the black 
plastic envelope.  No other lift gases are used. For inflating larger 
balloons, a blower is used, but by no means is any artificial heat 
(from a hairdryer) needed.  As a matter of fact, if any artificial 
heat is used, it can melt the plastic, or make the tape adhesive 
release.  I've done that.

The envelope gets surprisingly hot with just sunlight hitting it. 
Enough so that leaving it in the sun without inflating it on a calm 
day can actually melt the plastic.

It's also been my experience that it's hard to get static (tethered) 
lift out of solar balloons.  I'm under the assumption that it's 
because of the airflow around the outside of the balloon.  It has too 
much of a cooling effect on the plastic, and doesn't let it heat up 
as much.   But once its released and gets in to static air mass and 
it's "indicated airspeed" drops to zero meaning that it's moving with 
the wind, the lift really kicks in.

In many cases, I've inflated, released, and watched it bounce along 
the ground for 30-40 feet until it got up to speed.  As soon as it's 
moving with the wind, it lifts off very quickly.  They get so much 
vertical speed that they deform.  That of course pushes out hot air 
and slows their ascent.  I marvel at the self-regulating nature.

Since it is only heated by the sun, there is a 100% chance that it 
will land before night.

That's good.

There is also a high degree of certainty that it will land when the 
sun is near the horizon making visibility difficult if one is east of 
the balloon, and looking in to a setting sun.

That's bad.

Because it's powered by hot air, rather than lift gases, the lift 
will decrease as the altitude increases faster than it would if it 
were using helium. This will limit the max altitude to a MUCH lower 
level than helium latex balloons. That means it will probably spend 
nearly it's whole flight inside controlled airspace.

That's bad.

Because the lift will decrease as the sun gets lower in the sky, the 
altitude of the balloon will decrease slowly. So it won't come 
crashing to the ground.

That's good.

However, the problem is that I fear it could just hover along the 
ground, bouncing and dragging until it crashes in to a tree, power 
line, house, building, roadway, fence, etc.  I don't care if the 
balloon gets damaged, it's just garbage bags and tape.  The problem 
is collateral ground damage.

That's bad.  Really really bad.

-Jerry