Jos=E9 and the list,
I stand corrected. (That's what happens when you spout off with the
keyboard before engaging the gray matter :-)
The lift that you get with a balloon (ignoring the weight of the balloon) is
equal to the weight of air that the balloon displaces minus the weight of
whatever gas you use to inflate it. (Just like the bouyancy of an object in
water is equal to the water it displaces.)
Air at 0=BAC weighs 1.30 kg/cubic meter. So the maximum possible lift (if=
you
could "fill" your ballon with a vacuum) is 1.30 kg/cubic meter of volume.
Since it is kind of hard to fill out a balloon with a vacuum, we usually use
some other gas, such as helium or hydrogen. Helium weighs 0.18 kg/cubic
meter at 0=BAC, and Hydrogen weighs 0.09 kg/cubic meter at 0=BAC.
Therefore at 0=BAC, the lift you can expect from He is (1.30 - 0.18) =3D=
1.12
kg/cubic meter. For H2, you can expect (1.30 - 0.09) =3D 1.21 kg/cubic=
meter.
Note that the hydrogen lift is 8% higher than the helium lift, just as Jos=
=E9
explained. You must subtract the weight of the balloon in all cases, of
course, to get your net useful (i.e., antenna) lift.
Air at 100=BAC has a density of 0.95 kg/cu meter. I don't have the density=
of
He or H2 at this temperature. I believe (here I go, guessing again!) that
at higher temperatures the increase in volume of the balloon due to the
expansion of the helium more than compensates for the decrease in air
density, so you actually get more lift at higher temperatures. Do you
agree, Jos=E9?=20
For all of us here in the land of the unit challenged, 1 cubic meter =3D=
35.3
cubic ft, and 1 kg =3D 2.21 lb =3D 35.36 oz. So for He, you get 1.12 oz/cu=
ft.
For H2, you get 1.21 oz/cu ft. (Pretty weird how the number of cu feet in a
cu meter is nearly the same as the number of oz in a kg!)
So where does all this lead us? It just re-inforces my desire to stay away
from hydrogen, since the lift advantage over helium is only 8%. Thinking
back to the day I purchased my gas cylinder, the thing that really pushed me
toward helium was its availability. I can go down to the welding shop and
exchange my empty helium cylinder for a full one; they keep them in stock.
If I want hydrogen, however, I must leave my cylinder - they send it
downtown, fill it and return THE SAME CYLINDER to me. It takes at least 3
working days, maybe longer. Now maybe I should have tried other suppliers,
but I didn't.
Oh well, it works for me! (Now if I could only HEAR :-(=20
My apologies if I have expounded in too much detail, I just wanted to
clarify details and admit the error of my calculations :-)
73, DX es happy new year
Scotty WA2DFI
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