fotoobscura wrote:

I am wondering if there is a formula or way to determine:

a) how much helium in volume is in a balloon after filling it.

Depends on the shape of the balloon.

b) how high the balloon can rise before it begins to deflate due to
slow leaking and altitude
c) how long it would take for the balloon to return to the ground
deflated (roughly).

My goal? To determine if I launch a helium balloon in the air with a
certain mass attached to it how long will it take to return to the
ground.

This will depend, in a fairly complicated and difficult to
calculate fashion, on the details of the material of the
balloon. Diffferent materials leak Helium at different rates,
and differently at different temperature and pressure.

It will also depend to some extent on the details of size
and shape of your balloon, and possibly on the amount of
weight hanging from the balloon. A larger balloon has
more volume to surface area, so will leak differently
from a smaller balloon.

You should probably do some simple tests. Get a cheapo
transmitter and let go a few balloons while you monitor.
If you have some extra sophistication you can get some
kind of altitude monitoring, either through barometric
pressure or a GPS. Or both. You might be able to get some
data simply by watching the balloon rise, by using a
telescope. Or maybe two scopes to triangulate.

Also, you could try it with tethered balloons at various
heights. Reel out, say, 1000 feet of string and see how
long it keeps tension on the string. If you have a handy
mountain, you could try it at the base of the mountain,
then go up the mountain and retry.
Socks

tot Volume push the balloon under water(Archimedes) You would think
helium would have half the lifting power than hydrogen but reality is it
has more than that. Uncle Al knows why. Beert