Thanks for looking. I assume the data was consistent with the data you shared.
Dennis
Correct. I also did a test during a flight but couldn't find the data.
Jerry On Tue, Jul 21, 2020 at 6:31 PM, Dennis Klipa - N8ERF Jerry,
Thanks for the data. Pretty small differential. I assume that the graph shows the differential pressure vs time during which you added gas to the balloon at a more or less constant rate. Is that correct?
Best Regards, Dennis, N8ERF I did some experiments on the differential pressure on a balloon This was a ground test on a fairly small latex balloon (100 Grams I believe) but larger ones would be similar. As you approach burst the diff. pressure rises.
A good analogy is a rubber band. There is a high force for the initial stretch of a new band then it drops off. The pressure increases as you reach the breaking point.
The pressure doesn't change much on a balloon so you have to be pretty accurate if you want to obtain float wit a latex balloon. It has been done with a very low amount of lift gas.
I suspect a Mylar balloon would have a sharper curve since they don't stretch but I haven't done any burst experiments with those.
On Tuesday, July 21, 2020, 6:05:54 PM MST, Joe WB9SBD < nss@...> wrote:
I did have these numbers, But
it was a long time ago.
The numbers I got I did it by testing a piece of the envelope
it's tensile strength, and doing the tons of math to learn what
the pressure differential would be.
What was interesting was someone ( do not remember who) actually
did flight(s) with a pressure sensor.
The neat part was my measured of material and the math
calculations, the number I got was within like 5% of what they
measured.
Joe WB9SBD
On 7/21/2020 7:39 PM, Dennis Klipa -
N8ERF wrote:
I am curious. Many of us have measured the
atmospheric pressure versus altitude. I have wanted to, but
haven't, measured the pressure inside the latex balloon as it
rises. Has anyone measured the pressure differential (inside vs
outside) of the latex balloon as a function of altitude? How
much difference are we talking about trying to control with this
valve. If the balloon were a fixed volume you could do the
calculation, but the latex balloons are not.
Best Regards,
Dennis Klipa, N8ERF
On Tue, Jul 21, 2020, 8:23 PM
Joe WB9SBD < nss@...> wrote:
It was a 1500
Kaymont balloon.
Knowing the pressure differential is extremely low. When
I tested the ping pong ball, I know it leaked badly. The
texture of the ball just would not give a good seal.
I went with the silicone on both the "O" ring and the
ball.
I also went with a pressure of the spring, Actually a
spring I just could not find a spring suitable. So I
used a left over strip of balloon latex, attached to the
ball and to a acrylic shaft.
The shaft was rotated to tighten the tension on the ball
and seal.
I made it as loose as possible,, just enough to make the
seal, and I mean barely!
I was worried that motion would even break the seal. It
was that slight.
Even as light as that was, it was not light enough, the
flight still had a standard flight profile with rise to
burst altitude, and did still pop.
Joe WB9SBD
On 7/21/2020 3:41 PM, Hank Riley via groups.io wrote:
Joe,
please tell us more.
Latex
or other envelope? How did it work out for you?
Any special reason for trying this valve method
out? What altitude was reached? How long did it
remain in the air?
___________________________________________________________
On
Sunday, July 19, 2020, 09:06:33 AM EDT, Joe
wrote:
I did
that once. But the ping pong ball
surface is too textured and does not
make a bubble tight seal. I did a
silicone ball and o ring.
|
